U.S. patent application number 10/963946 was filed with the patent office on 2005-12-08 for liquid crystal waveguide having refractive shapes for dynamically controlling light.
Invention is credited to Anderson, Michael H., Davis, Scott R., Rommel, Scott D..
Application Number | 20050271325 10/963946 |
Document ID | / |
Family ID | 34811360 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050271325 |
Kind Code |
A1 |
Anderson, Michael H. ; et
al. |
December 8, 2005 |
Liquid crystal waveguide having refractive shapes for dynamically
controlling light
Abstract
Liquid crystal waveguides for dynamically controlling the
refraction of light. Generally, liquid crystal materials may be
disposed within a waveguide in a cladding proximate or adjacent to
a core layer of the waveguide. In one example, portions of the
liquid crystal material can be induced to form refractive or lens
shapes in the cladding that interact with a portion (e.g.
evanescent) of light in the waveguide so as to permit electronic
control of the refraction/bending, focusing, or defocusing of light
as it travels through the waveguide. In one example, a waveguide
may be formed using one or more patterned or shaped electrodes that
induce formation of such refractive or lens shapes of liquid
crystal material, or alternatively, an alignment layer may have one
or more regions that define such refractive or lens shapes to
induce formation of refractive or lens shapes of the liquid crystal
material. In another example, such refractive or lens shapes of
liquid crystal material may be formed by patterning or shaping a
cladding to define a region or cavity to contain liquid crystal
material in which the liquid crystal materials may interact with
the evanescent light.
Inventors: |
Anderson, Michael H.;
(Lyons, CO) ; Rommel, Scott D.; (Lakewood, CO)
; Davis, Scott R.; (Denver, CO) |
Correspondence
Address: |
DORSEY & WHITNEY, LLP
INTELLECTUAL PROPERTY DEPARTMENT
370 SEVENTEENTH STREET
SUITE 4700
DENVER
CO
80202-5647
US
|
Family ID: |
34811360 |
Appl. No.: |
10/963946 |
Filed: |
October 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60539030 |
Jan 22, 2004 |
|
|
|
Current U.S.
Class: |
385/40 ; 385/129;
385/141; 385/144; 385/39; 385/4; 385/8 |
Current CPC
Class: |
G02F 1/295 20130101;
G02F 1/133757 20210101 |
Class at
Publication: |
385/040 ;
385/004; 385/008; 385/039; 385/129; 385/141; 385/144 |
International
Class: |
G02B 006/26; G02B
006/42 |
Goverment Interests
[0002] This invention was made with Government support under
contract No. 0319386 awarded by the National Science Foundation.
The Government has certain rights in the invention.
Claims
1. A waveguide for controllably refracting a light beam,
comprising: a core for guiding the light beam through the
waveguide; at least one cladding having a liquid crystal material
therein; and at least one electrode for receiving at least one
voltage; wherein the light beam is refracted at an interface by an
amount that is controlled by the voltage.
2. The waveguide of claim 1, wherein the light beam has an
evanescent portion, and wherein the liquid crystal material in the
cladding interacts with the evanescent portion of the light beam to
control refraction of the light beam.
3. The waveguide of claim 1, wherein the at least one cladding
includes an upper cladding and a lower cladding, the upper cladding
having the liquid crystal material disposed therein.
4. The waveguide of claim 1, wherein the at least one cladding
includes an upper cladding and a lower cladding, the lower cladding
having the liquid crystal material disposed therein.
5. The waveguide of claim 1, wherein at least a portion of the
liquid crystal material in said at least one cladding defines at
least one refractive shape, said one refractive shape having an
index of refraction controlled by the at least one voltage applied
to the at least one electrode.
6. The waveguide of claim 1, wherein at least a portion of the
liquid crystal material in said at least one cladding defines a
first refractive shape and a second refractive shape in series
controlled by the at least one voltage applied to the at least one
electrode.
7. The waveguide of claim 1, wherein at least a portion of the
liquid crystal material in said at least one cladding defines at
least a first refractive shape and at least a second refractive
shape in series controlled by the voltage applied to the at least
one electrode, the first refractive shape being different from the
second refractive shape.
8. The waveguide of claim 1, wherein at least a portion of the
liquid crystal material in said at least one cladding defines a
lens shape controlled by the voltage applied to the at least one
electrode.
9. The waveguide of claim 1, wherein the core includes a silicon
oxynitride material.
10. The waveguide of claim 1, wherein the liquid crystal material
is a nemetic material.
11. The waveguide of claim 1, wherein the voltage is an AC
voltage.
12. The waveguide of claim 1, wherein the at least one electrode
includes a conductive film layer.
13. The waveguide of claim 1, wherein the at least one electrode
includes a p-doped silicon substrate.
14. The waveguide of claim 1, wherein the light beam is a TM
polarized light beam and travels through the waveguide along a
propagation axis; and wherein the liquid crystal material is
orientated with its long axis substantially parallel to the
propagation axis when the voltage is approximately zero, and the
liquid crystal material is oriented with its long axis titled
relative to the propagation axis when the voltage is non-zero such
that the TM polarized light beam is controllably refracted in the
waveguide based on the voltage.
15. The waveguide of claim 1, wherein the light beam is a TE
polarized light beam and travels through the waveguide along a
propagation axis; and wherein the liquid crystal material is
orientated with its long axis titled at a first angle relative to
the propagation axis when the voltage is approximately zero, and
the liquid crystal material is oriented with its long axis titled
at a second angle relative to the propagation axis when the voltage
is non-zero such that the TE polarized light beam is controllably
refracted in the waveguide based on the voltage.
16. The waveguide of claim 1, wherein the light beam is a TM
polarized light beam and travels through the waveguide along a
propagation axis; and wherein the liquid crystal material is
orientated with its long axis titled at a first angle relative to
the propagation axis when the voltage is approximately zero, and
the liquid crystal material is oriented with its long axis titled
at a second angle relative to the propagation axis when the voltage
is non-zero such that the TM polarized light beam is controllably
refracted in the waveguide based on the voltage.
17. The waveguide of claim 1, wherein the at least one electrode
defines at least one refractive shape.
18. The waveguide of claim 1, wherein the voltage includes a first
voltage and a second voltage; and wherein the at least one
electrode includes a first electrode for receiving the first
voltage and a second electrode for receiving the second
voltage.
19. The waveguide of claim 18, wherein the first electrode defines
a first refractive shape and the second electrode defines a second
refractive shape, and wherein the first and second voltages are
independent.
20. The waveguide of claim 1, wherein the at least one electrode
includes an upper electrode and a lower electrode.
21. The waveguide of claim 20, wherein the upper electrode includes
at least one refractive shape.
22. The waveguide of claim 20, wherein the upper electrode includes
a lens shape.
23. The waveguide of claim 20, wherein the upper electrode includes
a wedge shape.
24. The waveguide of claim 20, wherein the lower electrode includes
a p-doped silicon substrate.
25. The waveguide of claim 20, wherein the lower electrode includes
a refractive shape.
26. The waveguide of claim 1, wherein the at least one cladding has
an upper surface and a lower surface, and the waveguide further
comprising: an upper alignment layer adjacent the upper surface of
the at least one cladding; and a lower alignment layer adjacent the
lower surface of the at least one cladding.
27. The waveguide of claim 26, wherein the upper and lower
alignment layers initially bias an orientation of said liquid
crystal material.
28. The waveguide of claim 1, wherein the at least one cladding
includes an upper cladding and a lower cladding, the upper cladding
having the liquid crystal material disposed therein, the upper
cladding having an upper and lower surface; wherein the at least
one electrode includes an upper electrode and a lower electrode,
the upper electrode including a refractive shape and the lower
electrode defining a plane; and the waveguide further comprising:
an upper alignment layer adjacent the upper surface of the upper
cladding; and a lower alignment layer adjacent the lower surface of
upper cladding.
29. The waveguide of claim 28, wherein the lower cladding is
positioned below the core, the lower alignment layer is positioned
above the core and below the lower surface of the upper cladding,
the upper alignment layer is positioned above the upper surface of
the upper cladding and below the upper electrode.
30. The waveguide of claim 1, wherein the at least one cladding
includes an upper cladding and a lower cladding, the upper cladding
having the liquid crystal material disposed therein, the upper
cladding having an upper and lower surface; wherein the at least
one electrode includes an upper electrode and a lower electrode,
the lower electrode including a refractive shape and the upper
electrode defining a plane; the waveguide further comprising: an
upper alignment layer adjacent the upper surface of the upper
cladding; and a lower alignment layer adjacent the lower surface of
upper cladding.
31. The waveguide of claim 30, wherein the lower electrode is
positioned below the lower cladding, the lower cladding is
positioned below the core, the lower alignment layer is positioned
above the core and below the lower surface of the upper cladding,
the upper alignment layer is positioned above the upper surface of
the upper cladding and below the upper electrode.
32. The waveguide of claim 1, further comprising: at least one
alignment layer adjacent the at least one cladding, the alignment
layer having at least a first region biasing said liquid crystal
material in a first orientation, and the alignment layer having a
second region biasing said liquid crystal material in a second
orientation, said second region defining at least one refractive
shape.
33. The waveguide of claim 32, wherein when the voltage is applied
to the at least one electrode, the first orientation of the liquid
crystal material in the first region changes, and the second
orientation of the liquid crystal material in the second region
changes, thereby altering an amount of refraction of the light beam
in the waveguide.
34. The waveguide of claim 32, wherein the light beam travels
through the waveguide along a propagation axis, and wherein the
first orientation is substantially perpendicular to the propagation
axis, and the second orientation is substantially parallel to the
propagation axis.
35. The waveguide of claim 32, wherein the second region includes
at least one wedge shape defined therein.
36. The waveguide of claim 32, wherein the second region includes
at least one lens shape defined therein.
37. The waveguide of claim 32, wherein the at least one cladding
includes an upper and lower cladding, the lower cladding is
positioned below the core, the alignment layer is positioned above
the core and below the upper cladding, and the upper electrode is
positioned above the upper cladding.
38. The waveguide of claim 1, wherein the at least one cladding
includes a cavity defined therein, said cavity containing the
liquid crystal material disposed therein, said cavity defining at
least one refractive shape.
39. The waveguide of claim 38, wherein the cavity includes at least
one wedge shape defined therein.
40. The waveguide of claim 38, wherein the cavity includes at least
one lens shape defined therein.
41. The waveguide of claim 1, wherein the at least one cladding
includes an upper cladding and a lower cladding, the upper cladding
having an upper surface and a lower surface, the upper cladding
having a cavity defined therein, said cavity containing the liquid
crystal material, the cavity includes at least one refractive shape
defined therein; wherein the at least one electrode includes an
upper electrode and a lower electrode; the waveguide further
comprising: an upper alignment layer adjacent the upper surface of
the upper cladding; and a lower alignment layer adjacent the lower
surface of upper cladding.
42. The waveguide of claim 41, wherein the liquid crystal material
in the cavity has an index of refraction, and when the voltage is
applied to the at least one electrode, the index of refraction of
the liquid crystal material in the cavity changes, thereby altering
an amount of refraction of the light beam in the waveguide.
43. The waveguide of claim 41, wherein the lower cladding is
positioned below the core, the lower alignment layer is positioned
above the core, and the upper alignment layer is positioned above
the upper surface of the upper cladding and below the upper
electrode.
44. A waveguide, comprising: a core for guiding a light beam; at
least one cladding having a liquid crystal material within at least
a portion of said cladding wherein at least a portion of the liquid
crystal material forms one or more refractive shapes having an
index of refraction; and at least one electrode; wherein as a
voltage is applied to said electrode, the index of refraction of
the one or more refractive shapes is altered to controllably
refract the light beam as it travels through the waveguide.
45. The waveguide of claim 44, wherein the light beam has an
evanescent portion, and wherein the liquid crystal material in the
at least one cladding interacts with the evanescent portion of the
light beam to control refraction of the light beam.
46. The waveguide of claim 44, wherein at least a portion of the
liquid crystal material in said at least one cladding defines at
least one or more refractive shape, said at least one or more
refractive shape having an index of refraction controlled by the
voltage applied to the at least one electrode.
47. The waveguide of claim 44, wherein the at least one electrode
defines at least one refractive shape.
48. The waveguide of claim 44, wherein the at least one voltage
includes a first voltage and a second voltage; and wherein the at
least one electrode includes a first electrode for receiving the
first voltage and a second electrode for receiving the second
voltage.
49. The waveguide of claim 48, wherein the first electrode defines
a first refractive shape and the second electrode defines a second
refractive shape, and wherein the first and second voltages are
independent.
50. The waveguide of claim 44, further comprising: at least one
alignment layer adjacent the at least one cladding, the alignment
layer having at least a first region biasing said liquid crystal
material in a first orientation, and the alignment layer having a
second region biasing said liquid crystal material in a second
orientation, said second region defining at least one or more
refractive shapes.
51. The waveguide of claim 44, wherein the at least one cladding
includes a cavity defined therein, said cavity containing the
liquid crystal material disposed therein, said cavity defining at
least one or more refractive shapes.
52. A waveguide for steering a light beam, comprising: a core for
guiding the light beam through the waveguide; at least one cladding
having a liquid crystal material disposed therein, said cladding
having a first region characterized by a first index of refraction
and a second region characterized by a second index of refraction;
and at least one electrode; wherein at least the second index of
refraction is controlled by a voltage applied to the electrode.
53. The waveguide of claim 52, wherein the light beam has an
evanescent portion, and wherein the liquid crystal material in the
at least one cladding interacts with the evanescent portion of the
light beam to control an amount of steering of the light beam.
54. The waveguide of claim 52, wherein at least a portion of the
liquid crystal material in said at least one cladding defines at
least one refractive shape, said refractive shape having an index
of refraction controlled by the voltage applied to the at least one
electrode.
55. The waveguide of claim 52, wherein the at least one electrode
defines at least one refractive shape.
56. The waveguide of claim 52, wherein the at least one voltage
includes a first voltage and a second voltage; and wherein the at
least one electrode includes a first electrode for receiving the
first voltage and a second electrode for receiving the second
voltage.
57. The waveguide of claim 56, wherein the first electrode defines
a first refractive shape and the second electrode defines a second
refractive shape, and wherein the first and second voltages are
independent.
58. The waveguide of claim 52, further comprising: at least one
alignment layer adjacent the at least one cladding, the alignment
layer having at least a first region biasing said liquid crystal
material in a first orientation, and the alignment layer having a
second region biasing said liquid crystal material in a second
orientation, said second region defining at least one refractive
shape.
59. The waveguide of claim 52, wherein the at least one cladding
includes a cavity defined therein, said cavity containing the
liquid crystal material disposed therein, said cavity defining at
least one refractive shape.
60. A waveguide for refracting a light beam, comprising: a core; at
least one cladding having a liquid crystal material disposed
therein, said cladding having at least a first region that includes
at least a portion of the liquid crystal material having a first
orientation; and at least one electrode; wherein the first
orientation of the first portion of the liquid crystal material in
the at least first region selectively changes from a first state to
a second state based on a voltage applied to said electrode.
61. The waveguide of claim 60, wherein the light beam has an
evanescent portion, and wherein at least a portion of the liquid
crystal material in the at least one cladding interacts with the
evanescent portion of the light beam to control refraction of the
light beam.
62. The waveguide of claim 60, wherein at least a portion of the
liquid crystal material in said at least one cladding defines at
least one refractive shape, said refractive shape having an index
of refraction controlled by the voltage applied to the at least one
electrode.
63. The waveguide of claim 60, wherein the at least one electrode
defines at least one refractive shape.
64. The waveguide of claim 60, wherein the voltage includes a first
voltage and a second voltage; and wherein the at least one
electrode includes a first electrode for receiving the first
voltage and a second electrode for receiving the second
voltage.
65. The waveguide of claim 64, wherein the first electrode defines
a first refractive shape and the second electrode defines a second
refractive shape, and wherein the first and second voltages are
independent.
66. The waveguide of claim 60, further comprising: at least one
alignment layer adjacent the at least one cladding, the alignment
layer having at least a first region biasing said liquid crystal
material in a first orientation, and the alignment layer having a
second region biasing said liquid crystal material in a second
orientation, said second region defining at least one refractive
shape.
67. The waveguide of claim 60, wherein the at least one cladding
includes a cavity defined therein, said cavity containing the
liquid crystal material disposed therein, said cavity defining at
least one refractive shape.
68. A method for dynamically controlling refraction of light
through a waveguide having a core and at least one cladding,
comprising: providing a liquid crystal material within said at
least one cladding; providing for forming at least one refractive
shape from said liquid crystal material in said at least one
cladding; and providing for passing an evanescent portion of said
light through said at least one refractive shape, thereby
refracting the light.
69. The method of claim 68, wherein the at least one cladding
includes an upper and lower cladding, and wherein the operation of
providing a liquid crystal material further comprises: providing
the liquid crystal material in said upper cladding.
70. The method of claim 68, wherein the at least one cladding
includes an upper and lower cladding, and wherein the operation of
providing a liquid crystal material further comprises: providing
the liquid crystal material in said lower cladding.
71. The method of claim 68, wherein the operation of providing for
forming at least one refractive shape further comprises: providing
for applying an electric field to at least a portion of the liquid
crystal material, thereby inducing said portion of the liquid
crystal material to form at least one refractive shape.
72. The method of claim 71, wherein the at least one refractive
shape has a variable index of refraction, the method further
comprising: providing for varying the electric field, thereby
adjusting the variable index of refraction of the at least one
refractive shape.
73. The method of claim 68, wherein the operation of providing for
forming at least one refractive shape further comprises: providing
at least one electrode for receiving at least one voltage; forming
said electrode to include at least one refractive shape; and
providing for applying a voltage to said electrode thereby inducing
said portion of the liquid crystal material to form at least one
refractive shape.
74. The method of claim 73, further comprising: providing for
varying the voltage applied to said electrode in order to adjust an
index of refraction of the at least one refractive shape.
75. The method of claim 68, wherein the operation of providing for
forming at least one refractive shape further comprises: providing
at least one alignment layer adjacent at least one cladding;
forming the alignment layer to have at least a first region biasing
said liquid crystal material in a first orientation, and the
alignment layer having a second region biasing said liquid crystal
material in a second orientation, said second region defining at
least one refractive shape; providing at least one electrode for
receiving at least one voltage, said electrode defining a plane;
and providing for applying a voltage to said electrode, thereby
re-orienting the liquid crystal material in the at least one
cladding.
76. The method of claim 75, wherein the first region has a first
index of refraction and the second region has a second index of
refraction, the method further comprising: providing for varying
the voltage applied to said at least one electrode in order to
adjust a difference between the first and second index of
refraction.
77. The method of claim 68, wherein the operation of providing for
forming at least one refractive shape further comprises: forming a
cavity in the at least one cladding, the cavity defining at least
one refractive shape; placing the liquid crystal material in said
cavity; providing for applying an electric field to said cavity,
thereby re-orienting the liquid crystal material in the cavity.
78. The method of claim 77, wherein the liquid crystal material in
the cavity has an index of refraction, and when the electric field
is applied to the cavity, the index of refraction of the liquid
crystal material in the cavity changes, thereby altering an amount
of refraction of the light in the waveguide.
79. The method of claim 77, wherein the operation of providing for
applying an electric field further comprises: providing at least
one electrode for receiving at least one voltage, said electrode
defining a plane; and providing for applying a voltage to said
electrode.
80. The method of claim 77, wherein the operation of forming a
cavity further comprises: shaping the cavity to include at least
one wedge shape.
81. The method of claim 77, wherein the operation of forming a
cavity further comprises: shaping the cavity to include at least
one lens shape.
82. A method for dynamically controlling refraction of light
through a waveguide having a core and at least one cladding,
comprising: providing a liquid crystal material disposed within
said at least one cladding; providing at least one electrode; and
providing for applying a voltage to said electrode to refract the
light in the waveguide.
83. The method of claim 82, wherein the at least one cladding
includes an upper and lower cladding, and wherein the operation of
providing a liquid crystal material further comprises: providing
the liquid crystal material in said upper cladding.
84. The method of claim 82, wherein the at least one cladding
includes an upper and lower cladding, and wherein the operation of
providing a liquid crystal material further comprises: providing
the liquid crystal material in said lower cladding.
85. The method of claim 82, wherein the operation of providing for
forming at least one refractive shape further comprises: providing
for applying an electric field to at least a portion of the liquid
crystal material, thereby inducing said portion of the liquid
crystal material to form at least one refractive shape.
86. The method of claim 85, wherein the at least one refractive
shape has a variable index of refraction, the method further
comprising: providing for varying the electric field, thereby
adjusting the variable index of refraction of the at least one
refractive shape.
87. The method of claim 82, wherein the operation of providing for
forming at least one refractive shape further comprises: providing
at least one electrode for receiving at least one voltage; forming
said electrode to include at least one refractive shape; and
providing for applying a voltage to said electrode thereby inducing
said portion of the liquid crystal material to form at least one
refractive shape.
88. The method of claim 87, further comprising: providing for
varying the voltage applied to said electrode in order to adjust an
index of refraction of the at least one refractive shape.
89. The method of claim 82, wherein the operation of providing for
forming at least one refractive shape further comprises: providing
at least one alignment layer adjacent at least one cladding;
forming the alignment layer to have at least a first region biasing
said liquid crystal material in a first orientation, and the
alignment layer having a second region biasing said liquid crystal
material in a second orientation, said second region defining at
least one refractive shape; providing at least one electrode for
receiving at least one voltage, said electrode defining a plane;
and providing for applying a voltage to said electrode, thereby
re-orienting the liquid crystal material in the at least one
cladding.
90. The method of claim 89, wherein the first region has a first
index of refraction and the second region has a second index of
refraction, the method further comprising: providing for varying
the voltage applied to said electrode in order to adjust a
difference between the first and second index of refraction.
91. The method of claim 82, wherein the operation of providing for
forming at least one refractive shape further comprises: forming a
cavity in the at least one cladding, the cavity defining at least
one refractive shape; placing the liquid crystal material in said
cavity; providing for applying an electric field to said cavity,
thereby re-orienting the liquid crystal material in the cavity.
92. The method of claim 91, wherein the liquid crystal material in
the cavity has an index of refraction, and when the electric field
is applied to the cavity, the index of refraction of the liquid
crystal material in the cavity changes, thereby altering an amount
of refraction of the light in the waveguide.
93. The method of claim 91, wherein the operation of providing for
applying an electric field further comprises: providing at least
one electrode for receiving at least one voltage, said electrode
defining a plane; and providing for applying a voltage to said
electrode.
94. The method of claim 91, wherein the operation of forming a
cavity further comprises: shaping the cavity to include at least
one wedge shape.
95. The method of claim 91, wherein the operation of forming a
cavity further comprises: shaping the cavity to include at least
one lens shape.
96. A method for controlling refraction of a light beam through a
waveguide having a core and at least one cladding, comprising:
providing a liquid crystal material within said at least one
cladding; providing for forming at least one refractive shape from
said liquid crystal material in said at least one cladding; and
providing at least one alignment layer adjacent the core, said
alignment layer inducing a substantially uniform arrangement of the
liquid crystal material of the at least one refractive shape; and
providing for passing the light beam through the waveguide, wherein
an evanescent portion of the light beam interacts with the at least
one refractive shape having the substantially uniform arrangement
of the liquid crystal material, thereby reducing attenuation of the
light beam as it travels through the waveguide.
97. The method of claim 96, wherein the at least one cladding
includes an upper and lower cladding, and wherein the operation of
providing a liquid crystal material further comprises: providing
the liquid crystal material in said upper cladding.
98. The method of claim 96, wherein the at least one cladding
includes an upper and lower cladding, and wherein the operation of
providing a liquid crystal material further comprises: providing
the liquid crystal material in said lower cladding.
99. The method of claim 96, wherein the operation of providing for
forming at least one refractive shape further comprises: providing
for applying an electric field to a portion of the liquid crystal
material, thereby inducing said portion of the liquid crystal
material to form at least one refractive shape.
100. The method of claim 99, wherein the at least one refractive
shape has a variable index of refraction, the method further
comprising: providing for varying the electric field, thereby
adjusting the variable index of refraction of the at least one
refractive shape.
101. The method of claim 96, wherein the operation of providing for
forming at least one refractive shape further comprises: providing
at least one electrode for receiving at least one voltage; forming
said electrode to include at least one refractive shape; and
providing for applying a voltage to said electrode thereby inducing
said portion of the liquid crystal material to form at least one
refractive shape.
102. The method of claim 101, further comprising: providing for
varying the voltage applied to said electrode in order to adjust an
index of refraction of the at least one refractive shape.
103. The method of claim 96, wherein the operation of providing for
forming at least one refractive shape further comprises: providing
at least one alignment layer adjacent at least one cladding;
forming the alignment layer to have at least a first region biasing
said liquid crystal material in a first orientation, and the
alignment layer having a second region biasing said liquid crystal
material in a second orientation, said second region defining at
least one refractive shape; providing at least one electrode for
receiving at least one voltage, said electrode defining a plane;
and providing for applying a voltage to said electrode, thereby
re-orienting the liquid crystal material in the at least one
cladding.
104. The method of claim 103, wherein the first region has a first
index of refraction and the second region has a second index of
refraction, the method further comprising: providing for varying
the voltage applied to said electrode in order to adjust a
difference between the first and second index of refraction.
105. The method of claim 96, wherein the operation of providing for
forming at least one refractive shape further comprises: forming a
cavity in the at least one cladding, the cavity defining at least
one refractive shape; placing the liquid crystal material in said
cavity; providing for applying an electric field to said cavity,
thereby re-orienting the liquid crystal material in the cavity.
106. The method of claim 105, wherein the liquid crystal material
in the cavity has an index of refraction, and when the electric
field is applied to the cavity, the index of refraction of the
liquid crystal material in the cavity changes, thereby altering an
amount of refraction of the light beam in the waveguide.
107. The method of claim 105, wherein the operation of providing
for applying an electric field further comprises: providing at
least one electrode for receiving at least one voltage, said
electrode defining a plane; and providing for applying a voltage to
said electrode.
108. The method of claim 105, wherein the operation of forming a
cavity further comprises: shaping the cavity to include at least
one wedge shape.
109. The method of claim 105, wherein the operation of forming a
cavity further comprises: shaping the cavity to include at least
one lens shape.
110. A waveguide, comprising: a core for guiding a light beam
through the waveguide; means for controllably refracting the light
beam as it travels through the waveguide.
111. The waveguide of claim 110, wherein the means for controllably
refracting includes: at least one cladding having a liquid crystal
material therein; and at least one electrode for receiving at least
one voltage, said electrode defines at least one refractive shape;
wherein the light beam is refracted by an amount that is controlled
by the at least one voltage.
112. The waveguide of claim 110, wherein the means for controllably
refracting includes: at least one cladding having a liquid crystal
material within at least a portion of said cladding wherein at
least a portion of the liquid crystal material forms one or more
refractive shapes having an index of refraction; and at least one
electrode; wherein as a voltage is applied to said electrode, the
index of refraction of the one or more refractive shapes is altered
to controllably refract the light beam as it travels through the
waveguide.
113. The waveguide of claim 110, wherein the means for controllably
refracting includes: at least one cladding having a liquid crystal
material disposed therein, said cladding having a first region
characterized by a first index of refraction and a second region
characterized by a second index of refraction; and at least one
electrode; wherein at least the second index of refraction is
controlled by a voltage applied to the electrode.
114. The waveguide of claim 110, wherein the means for controllably
refracting includes: at least one cladding having a liquid crystal
material disposed therein, said cladding having at least a first
region that includes at least a portion of the liquid crystal
material having a first orientation; and at least one electrode;
wherein the first orientation of the first portion of the liquid
crystal material in the at least first region selectively changes
from a first state to a second state based on a voltage applied to
said electrode.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. 119(e) to
U.S. Provisional patent application No. 60/539,030 entitled "LIQUID
CRYSTAL WAVEGUIDE HAVING REFRACTIVE SHAPES FOR DYNAMICALLY
CONTROLLING LIGHT AND TUNABLE LASER INCLUDING SAME" filed Jan. 22,
2004, the disclosure of which is hereby incorporated by reference
in its entirety.
FIELD OF THE INVENTION
[0003] This invention relates, in general, to waveguides, and more
particularly, to waveguides having liquid crystal materials
therein.
BACKGROUND OF THE INVENTION
[0004] Various devices such as barcode scanners, compact disk
players, DVD players, and others use light to perform various
functions, such as read data from or write data to optical media.
Beams of light are also used in communication devices, sample
analyzing devices, distance measurement devices, and time
measurement devices.
[0005] Light can be controlled using standard lenses and mirrors.
These passive methods can be made active via mechanical motion. For
example, mirrors can be placed on galvo-motors to move the mirror
to control the direction of light propagation. This technique is
used in barcode scanners, or optical read/write heads in CD/DVD
players. However, mechanical control over light is problematic for
several reasons, as recognized by the present inventors. First, it
is difficult to make such mechanical devices compact. Second, the
mechanical nature of such moving devices have limited lifetimes due
to mechanical wear and failure issues. Third, mechanical devices
are inherently vibration sensitive, which limits the type of
environment in which they can be used. Finally, mechanical devices
necessitate a level of design complexity including gears, bearings,
and other mechanical components which add cost, expense, and
maintenance issues to such designs.
[0006] Rather than move a lens or a mirror with a motor or
actuator, light can be controlled through the use of waveguides.
For instance, U.S. Pat. No. 5,347,377 entitled "Planar Waveguide
Liquid Crystal Variable Retarder" relates generally to providing an
improved waveguide liquid crystal optical device, and discloses in
Table I the use of alternating current voltages between 2 and 50
volts rms for retardation of the polarized light by controlling
only the optical phase delay.
[0007] With conventional waveguides, electro-optic materials such
as lithium niobate are generally employed in the core whereby a
voltage applied across the core material changes the index of
refraction, n. However, with conventional techniques using
materials such as lithium niobate, the index of refraction can only
be changed a very small amount so that the retardation of a half
wave may require thousands of volts. This limitation makes this
type of light control extremely limited, and to date not a viable
alternative to mechanical control of light.
[0008] In non-waveguide devices, liquid crystal materials have
become widespread in display applications where light is attenuated
but not steered nor refocused. However, in order to use
conventional display techniques for liquid crystal materials to
attempt continuous steering of light, prohibitively thick layers of
liquid crystal materials (greater than 100 microns) would be
needed, which would render the device highly opaque and slow. The
thick layers of liquid crystal can take seconds or even minutes to
change, and can be difficult to control. Although non-waveguide,
electro-optic beam-steerers have been made with standard thin
liquid crystal cells, such devices have only realized minimal
steering, in the range of 10.sup.-6 degrees of steering).
[0009] U.S. Pat. No. 3,963,310 entitled "Liquid Crystal Waveguide"
teaches of utilizing liquid crystal-within the core of a waveguide.
However, as recognized by the present inventors, such a waveguide
would be problematic in that there would be substantial losses or
attenuation of light traveling through such a waveguide.
[0010] Accordingly, as recognized by the present inventors, what is
needed is a liquid crystal waveguide for controlling light that
permits active control of the propagation or refraction of light
through the waveguide in a manner that provides for low loss
operation.
[0011] It is against this background that various embodiments of
the present invention were developed.
SUMMARY
[0012] In light of the above and according to one broad aspect of
one embodiment of the invention, disclosed herein is a liquid
crystal waveguide for dynamically controlling the refraction of
light passing through the waveguide. Generally, liquid crystal
materials may be disposed within a waveguide in a cladding
proximate or adjacent to a core layer of the waveguide. According
to an embodiment of the present invention, portions of the liquid
crystal material can be induced to form refractive or lens shapes
in the cladding that interact with a portion (e.g. evanescent) of
light in the waveguide so as to permit electronic control of the
refraction/bending, focusing, or defocusing of light as it travels
through the waveguide. In one example, a waveguide may be formed
using one or more patterned or shaped electrodes that induce
formation of such refractive or lens shapes of liquid crystal
material, or alternatively, an alignment layer may have one or more
regions that define such refractive or lens shapes to induce
formation of refractive or lens shapes of the liquid crystal
material. In another example of the invention, such refractive or
lens shapes of liquid crystal material may be formed by patterning
or shaping a cladding to define a region or cavity to contain
liquid crystal material in which the liquid crystal materials may
interact with the evanescent light.
[0013] According to one broad aspect of one embodiment of the
present invention, a waveguide may include a core, a pair of
claddings surrounding the core wherein one of the claddings (e.g.,
the upper cladding) contains liquid crystal material therein. In
one example, one or more electrodes or an electrode layer is
positioned above the upper cladding that has the liquid crystal
material therein, and a lower electrode or electrode layer or plane
is positioned below the lower cladding and acts as a ground
plane.
[0014] The one or more upper electrodes define one or more shapes
having at least one edge or interface which is non-normal to the
direction of light propagation through the waveguide, or may define
curved or lens shaped interfaces. The one or more shapes defined by
the upper electrode(s) may be used to controllably refract, bend,
focus or defocus light as light passes through the core and upper
and lower claddings of the waveguide. The upper electrodes, also
referred to herein as patterned electrodes, may be shaped or
patterned in various manners, including generally triangular or
wedge shaped for steering light, or the shapes may include various
lens shapes for focusing or defocusing light that passes through
the waveguide.
[0015] When a voltage or range of voltages are applied between the
upper patterned electrode and the lower electrode, at least two
indices of refraction can be realized within a waveguide. As
voltage is applied and increased between the upper patterned
electrode(s) and the lower electrode plane, the index of refraction
n2 of the liquid crystal material under the upper patterned
electrode(s) is controllably and dynamically changed as a function
of the voltage applied.
[0016] The index of refraction n1 of the liquid crystal material
that is not under the electrode is generally not changed. In this
way, the difference between n1 and n2 can be dynamically controlled
by the voltage.
[0017] According to another broad aspect of one embodiment of the
present invention, a waveguide may include a lower electrode plane,
a lower cladding, a core layer, an alignment layer having the one
or more regions defining various shapes, an upper cladding with
liquid crystal material therein, an upper electrode plane, and a
glass cover.
[0018] In one example on the alignment layer, one or more areas or
regions define various shapes in order to induce the liquid crystal
material in the adjacent upper cladding to form various shapes when
no voltage is applied, such as shapes having non-normal interfaces
or shapes having curves or lens shapes. For instance, the alignment
layer of the waveguide may include a first region and a second
region. In this example, the first region aligns the liquid crystal
materials in the upper cladding in a first orientation (e.g., with
their long axis perpendicularly orientated relative to the
propagation direction of light traveling through the waveguide);
while the second region defines a refractive shape (e.g., wedge or
prism shape) or lens shape, wherein within the second region, the
liquid crystal materials in the upper cladding are aligned in a
second orientation (e.g., with their long axis orientated in
parallel relative to the propagation direction of light traveling
through the waveguide).
[0019] In this example, when no voltage is applied between the
upper electrode and the lower electrode/substrate, the index of
refraction n1 of the first region is greater than the index of
refraction n2 of the second region for TE polarized light traveling
through the waveguide. As a voltage is applied between the upper
electrode and the lower electrode/substrate, the electric field of
the applied voltage induces the liquid crystals within the upper
cladding to orient vertically, and therefore for TE polarized light
traveling through the waveguide, the index of refraction n1 of the
first region is approximately equal to the index of refraction n2
of the second region, and no refraction or light bending
occurs.
[0020] According to another broad aspect of one embodiment of the
present invention, a waveguide may include a lower electrode plane,
a lower cladding, a core layer, an alignment layer, an upper
cladding and an upper electrode plane. In the upper cladding,
regions or areas or portions have been removed to form a cavity
defining one or more refractive shapes. In one example, the cavity
is filled with liquid crystal material.
[0021] In one example, one or more cavities, areas or regions of
the upper cladding have been removed or reduced and filled with
liquid crystal material such that the evanescent wave of the guided
light may penetrate into these areas or regions. Liquid crystal
material may be placed in these cavities or areas, such that the
shape or region in which a portion of the guided light may interact
with the liquid crystal defines refractive shapes having non-normal
interfaces or refractive shapes having curves or lens shapes. For
instance, the upper cladding of the waveguide may include a first
region and a second region, wherein the first region may include a
non-electro-optic upper cladding material; and while the second
region defines a refractive shape (e.g., wedge or prism shape) or
lens shape, wherein within the second region, there is liquid
crystal material therein such that the evanescent wave may interact
with the liquid crystal material in this second region.
[0022] In one example, when no voltage is applied between the upper
electrode and the lower electrode, the index of refraction n1 of
the first region is different than the index of refraction n2 of
the second region for light traveling through the waveguide. As a
voltage is applied between the upper electrode and the lower
electrode, the electric field of the applied voltage induces the
liquid crystals, which are confined within the regions or cavities
of the upper cladding, to reorient, and therefore for light
traveling through the waveguide, the difference between the index
of refraction n1 of the first region and the index of refraction n2
of the second region will change, and therefore the degree of
refraction or light bending will also change.
[0023] According to another broad aspect of an embodiment of the
present invention, disclosed herein is a method for dynamically
controlling refraction of a light beam through a waveguide having a
core and at least one cladding. In one example, the method may
include providing a liquid crystal material within the at least one
cladding; providing for forming at least one refractive shape from
the liquid crystal material in the at least one cladding; providing
at least one alignment layer adjacent the core, the alignment layer
inducing a substantially uniform arrangement of the liquid crystal
material of the at least one refractive shape; and providing for
passing the light beam through the waveguide, wherein an evanescent
portion of the light beam interacts with the at least one
refractive shape having the substantially uniform arrangement of
the liquid crystal material, thereby reducing attenuation of the
light beam as it travels through the waveguide.
[0024] In one example, the at least one cladding may include an
upper and lower cladding, and the operation of providing a liquid
crystal material may comprise providing the liquid crystal material
in the upper cladding or in the lower cladding.
[0025] In another example, the operation of providing for forming
at least one refractive shape may comprise providing for applying
an electric field to a portion of the liquid crystal material,
thereby inducing the portion of the liquid crystal material to form
at least one refractive shape; providing at least one electrode for
receiving at least one voltage; forming the electrode to include at
least one refractive shape; and providing for applying a voltage to
the electrode thereby inducing the portion of the liquid crystal
material to form at least one refractive shape.
[0026] In one example, the at least one refractive shape may have a
variable index of refraction, and the method may comprise providing
for varying the electric field, thereby adjusting the variable
index of refraction of the at least one refractive shape; and
providing for varying the voltage applied to the electrode in order
to adjust an index of refraction of the at least one refractive
shape.
[0027] In another example, the operation of providing for forming
at least one refractive shape may comprise providing at least one
alignment layer adjacent at least one cladding; forming the
alignment layer to have at least a first region biasing the liquid
crystal material in a first orientation, and the alignment layer
may have a second region biasing the liquid crystal material in a
second orientation, the second region may define at least one
refractive shape; providing at least one electrode for receiving at
least one voltage, the electrode may define a plane; and providing
for applying a voltage to the electrode, thereby re-orienting the
liquid crystal material in the at least one cladding.
[0028] In one example, the first region may have a first index of
refraction and the second region may have a second index of
refraction, and the method may comprise providing for varying the
voltage applied to the electrode in order to adjust a difference
between the first and second index of refraction.
[0029] In one example, the operation of providing for forming at
least one refractive shape may comprise forming a cavity in the at
least one cladding, the cavity may define at least one refractive
shape; placing the liquid crystal material in the cavity; and
providing for applying an electric field to the cavity, thereby
re-orienting the liquid crystal material in the cavity. In another
example the liquid crystal material in the cavity may have an index
of refraction, and when the electric field is applied to the
cavity, the index of refraction of the liquid crystal material in
the cavity may change, thereby altering an amount of refraction of
the light beam in the waveguide.
[0030] In one example, the operation of providing for applying an
electric field may comprise providing at least one electrode for
receiving at least one voltage, the electrode may define a plane;
and providing for applying a voltage to the electrode. In another
example, the operation of forming a cavity may comprise shaping the
cavity to include at least one wedge shape or at least one lens
shape.
[0031] According to another broad aspect of an embodiment of the
present invention, disclosed herein is a waveguide for controllably
refracting a light beam. In one example, the waveguide may comprise
a core for guiding a light beam through the waveguide, and a means
for controllably refracting the light beam as it travels through
the waveguide.
[0032] In another example, the means for controllably refracting
may include at least one cladding having a liquid crystal material
therein; at least one electrode for receiving at least one voltage,
the electrode may define at least one refractive shape, wherein the
light beam is refracted by an amount that is controlled by the at
least one voltage.
[0033] In one example, the means for controllably refracting may
include at least one cladding having a liquid crystal material
within at least a portion of the cladding wherein at least a
portion of the liquid crystal material forms one or more refractive
shapes having an index of refraction; and at least one electrode,
wherein as a voltage is applied to the electrode, the index of
refraction of the one or more refractive shapes is altered to
controllably refract the light beam as it travels through the
waveguide.
[0034] In another example, the means for controllably refracting
may include at least one cladding having a liquid crystal material
disposed therein, the cladding may have a first region
characterized by a first index of refraction and a second region
characterized by a second index of refraction; and at least one
electrode, wherein at least the second index of refraction is
controlled by a voltage applied to the electrode.
[0035] In another example, the means for controllably refracting
may include at least one cladding may have a liquid crystal
material disposed therein, the cladding may have at least a first
region that includes at least a portion of the liquid crystal
material having a first orientation; and at least one electrode,
wherein the first orientation of the first portion of the liquid
crystal material in the at least first region selectively changes
from a first state to a second state based on a voltage applied to
the electrode.
[0036] Other features, utilities and advantages of the various
embodiments of the invention will be apparent from the following
more particular description of embodiments of the invention as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 illustrates an example of a waveguide having a
patterned electrode for providing active control of light
propagation, in accordance with an embodiment of the present
invention.
[0038] FIG. 2 illustrates a sectional view taken along section
lines 2-2 of FIG. 1, illustrating an example of an embodiment of
the present invention.
[0039] FIG. 3 illustrates an example of operations for forming a
waveguide having patterned electrodes for controlling light, in
accordance with an embodiment of the present invention.
[0040] FIG. 4 illustrates a sectional view of the waveguide along
section lines 4-4 of FIG. 1 where no voltage is applied to the
patterned electrode, in accordance with one embodiment of the
invention.
[0041] FIG. 5 illustrates a top view of the liquid crystals as
oriented in the upper cladding of FIG. 4 where no voltage is
applied to the patterned electrode, in accordance with one
embodiment of the present invention.
[0042] FIG. 6 illustrates a sectional view of the waveguide along
section lines 4-4 of FIG. 1, wherein a voltage is applied to the
patterned electrode so as to alter the orientation of the liquid
crystal material under the patterned electrode, in accordance with
one embodiment of the present invention.
[0043] FIG. 7 illustrates a top view of the liquid crystal material
in the upper cladding of FIG. 6, when a voltage is applied to the
patterned electrode, in accordance with one embodiment of the
present invention.
[0044] FIG. 8 illustrates a sectional view of the waveguide along
section lines 4-4 of FIG. 1 where no voltage is applied to the
patterned electrode, in accordance with one embodiment of the
present invention.
[0045] FIG. 9 illustrates a top view of the liquid crystal material
within the upper cladding of the waveguide of FIG. 8 where no
voltage is applied to the upper electrode, in accordance with one
embodiment of the present invention.
[0046] FIG. 10 illustrates a sectional view of the waveguide of
FIG. 1 taken along section lines 4-4, when a voltage is applied to
the patterned electrode so as to change the orientation of the
liquid crystal material under the patterned electrode, in
accordance with one embodiment of the present invention.
[0047] FIG. 11 illustrates a top view of the liquid crystal
material within the upper cladding of FIG. 10 when a voltage is
applied to the patterned electrode, in accordance with one
embodiment of the present invention.
[0048] FIG. 12 illustrates an alternative embodiment of the present
invention wherein a patterned electrode is positioned between the
substrate and the lower cladding of a waveguide, in accordance with
one embodiment of the present invention.
[0049] FIG. 13 is a sectional view of a waveguide taken along
section 13-13 of FIG. 12, in accordance with one embodiment of the
present invention.
[0050] FIG. 14 illustrates an example of operations for forming a
waveguide having one or more patterned electrodes for controlling
the propagation of light through the waveguide, in accordance with
one embodiment of the present invention.
[0051] FIG. 15 illustrates an example of a patterned electrode for
controlling light propagating through a waveguide, in accordance
with an embodiment of the present invention.
[0052] FIG. 16 illustrates another example of a patterned electrode
for controlling light propagating through a waveguide, in
accordance with an embodiment of the present invention.
[0053] FIG. 17 illustrates an example of a pair of patterned
electrodes for controlling light propagating through a waveguide,
in accordance with an embodiment of the present invention.
[0054] FIG. 18 illustrates another example of a pair of patterned
shaped electrodes for controlling light propagating through a
waveguide, in accordance with an embodiment of the present
invention.
[0055] FIG. 19 illustrates another example of a patterned electrode
for controlling light propagating through a waveguide, in
accordance with an embodiment of the present invention.
[0056] FIG. 20 illustrates an example of operations for forming a
waveguide having one or more electrodes with curved or lens shaped
interfaces for controlling the propagation of light through the
waveguide, in accordance with one embodiment of the present
invention.
[0057] FIG. 21 illustrates an example of an electrode formed in the
shape of a simple positive lens for controlling light propagating
through a waveguide, in accordance with one embodiment of the
present invention.
[0058] FIG. 22 illustrates an example of an electrode formed in the
shape of a negative lens for controlling light propagating through
a waveguide, in accordance with one embodiment of the present
invention.
[0059] FIG. 23 illustrates an example of an electrode formed in the
shape of a convex-convex lens for controlling light propagating
through a waveguide, in accordance with one embodiment of the
present invention.
[0060] FIG. 24 illustrates an example of an electrode formed in the
shape of a concave-concave lens for controlling light propagating
through a waveguide, in accordance with one embodiment of the
present invention.
[0061] FIG. 25 illustrates an example of an electrode formed in the
shape of a convex-concave lens for controlling light propagating
through a waveguide, in accordance with one embodiment of the
present invention.
[0062] FIG. 26 illustrates an example of an electrode formed in the
shape of a concave-concave asphere lens for controlling light
propagating through a waveguide, in accordance with one embodiment
of the present invention.
[0063] FIG. 27 illustrates another example of an electrode for
controlling light propagating through the waveguide, in accordance
with one embodiment of the present invention.
[0064] FIG. 28 illustrates an alternative embodiment wherein the
waveguide utilizes an alignment layer having two or more areas or
regions having different orientations that align the liquid crystal
material in the adjacent cladding so as to form refractive shapes
within the liquid crystal material in the cladding for controlling
light propagating through a waveguide, in accordance with one
embodiment of the present invention.
[0065] FIG. 29 illustrates a sectional view of the waveguide of
FIG. 28 taken along section lines 29-29 with no voltage applied, in
accordance with one embodiment of the present invention.
[0066] FIG. 30 illustrates a sectional view of the waveguide of
FIG. 28 taken along section lines 29-29 with a voltage applied, in
accordance with one embodiment of the present invention.
[0067] FIG. 31 illustrates a top view of the liquid crystals within
the upper cladding of the waveguide of FIG. 28 when no voltage is
applied, in accordance with one embodiment of the present
invention.
[0068] FIG. 32 is a top view of the liquid crystal material within
the upper cladding of the waveguide of FIG. 28 when a high voltage
is applied so as to re-orient the liquid crystal material therein,
in accordance with one embodiment of the present invention.
[0069] FIG. 33 illustrates an example of operations for forming a
waveguide having two or more areas or regions having different
orientations that align the liquid crystal material in the adjacent
cladding so as to form refractive shapes within the liquid crystal
material for controlling light propagating through a waveguide, in
accordance with one embodiment of the present invention.
[0070] FIG. 34 illustrates an alternative embodiment wherein the
waveguide utilizes an upper cladding layer having a first region
and a second region, the second region including a cavity having
liquid crystal material therein, the cavity defining one or more
refractive shapes for controlling light propagating through a
waveguide, in accordance with one embodiment of the present
invention.
[0071] FIG. 35 illustrates a sectional view of the waveguide of
FIG. 34 taken along section lines 35-35 with no voltage applied, in
accordance with one embodiment of the present invention.
[0072] FIG. 36 illustrates a sectional view of the waveguide of
FIG. 34 taken along section lines 35-35 with a voltage applied, in
accordance with one embodiment of the present invention.
[0073] FIG. 37 illustrates a top section view of the upper
waveguide cladding of the waveguide of FIG. 34, which contains a
first region without liquid crystals and a second region with
liquid crystals, when no voltage is applied, in accordance with one
embodiment of the present invention.
[0074] FIG. 38 illustrates a top section view of the upper
waveguide cladding of the waveguide of FIG. 34, which contains a
first region without liquid crystals and a second region with
liquid crystals, when a high voltage is applied, in accordance with
one embodiment of the present invention.
[0075] FIG. 39 illustrates an example of operations for forming a
waveguide having a cladding with at least a first and second
region, the second region having a cavity with liquid crystal
material therein, the cavity defining one or more refractive shapes
within the upper cladding for controlling light propagating through
a waveguide, in accordance with one embodiment of the present
invention.
[0076] FIG. 40 illustrates an example of a barcode scanner
utilizing a waveguide having a plurality of patterned electrodes
for controlling light, in accordance with an embodiment of the
present invention.
[0077] FIG. 41 illustrates an example of an electrode formed in the
shape of bus bars with multiple connection points, wherein
application of voltages at the three connection points enables
control of voltage gradients across the electrode in accordance
with one embodiment of the present invention.
[0078] FIG. 42 illustrates a sectional view of the waveguide with
the electrode of FIG. 41, when no voltage is applied to the
electrode, in accordance with one embodiment of the present
invention.
[0079] FIG. 43 illustrates a sectional view of the waveguide with
the electrode of FIG. 41, when a voltage is applied to the
electrode so as to change the orientation of the liquid crystal
material under the electrode, in accordance with one embodiment of
the present invention.
[0080] FIG. 44 illustrates a sectional view of the waveguide with
the electrode of FIG. 41, when a plurality of differing voltages
are applied to the different connection points of the electrode so
as to change the orientation of the liquid crystal material under
the electrode, in accordance with one embodiment of the present
invention.
[0081] FIG. 45 illustrates a perspective view of an optical
read/write head for a CD/DVD player including a waveguide having a
plurality of patterned electrodes for controlling light, in
accordance with an embodiment of the present invention.
[0082] FIG. 46 illustrates a top view of the optical read/write
head of FIG. 41 with related circuitry, in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION
[0083] Disclosed herein are various embodiments of a waveguide for
dynamically controlling the refraction of light passing through the
waveguide. Generally and in accordance with an embodiment of the
present invention, liquid crystal materials may be disposed within
a waveguide in a cladding proximate or adjacent to a core layer of
the waveguide. Portions of the liquid crystal material in the
cladding can be induced to form refractive shapes or lens shapes in
the cladding so as to permit electronic control of the
refraction/bending, focusing, or defocusing of light as it travels
through the waveguide. As disclosed herein, a waveguide may be
formed using one or more patterned or shaped electrodes that induce
the liquid crystal material in the cladding to form such refractive
or lens shapes (see FIGS. 1-27); an alignment layer may have one or
more regions that define such refractive or lens shapes and induce
the liquid crystal material in the cladding to form (see FIGS.
28-33); or a cladding may have a cavity, region or area defining a
refractive or lens shape with liquid crystal material therein in
which the liquid crystal material interacts with the guided light
may be (see FIGS. 34-39). Various embodiments of the present
invention are described herein.
[0084] As shown in FIG. 1, in one example, a waveguide 50 may
include a core 52, a pair of claddings 54, 56 surrounding the core
52 wherein one of the claddings (e.g., the upper cladding 54)
contains liquid crystal material 58 therein. In one example, one or
more electrodes or an electrode layer 60 is positioned above the
upper cladding 54 that has the liquid crystal material 58 therein,
and a lower electrode or electrode layer or plane 62 is positioned
below the lower cladding 56 and acts as a ground plane.
[0085] The one or more upper electrodes 60 define one or more
shapes having at least one edge or interface 64 that is non-normal
to the direction of light propagation 66 through the waveguide 50.
As discussed below, the one or more shapes defined by the upper
electrode(s) 60 may be used to controllably refract or bend light
as light passes through the core 52 and upper and lower claddings
54, 56 of the waveguide. The upper electrodes 60, also referred to
herein as patterned electrodes, may be shaped or patterned in
various manners, including generally triangular or wedge shaped for
steering light, or the shapes may include various lens shapes for
focusing or defocusing light that passes through the waveguide
50.
[0086] In general and as discussed below, at least two indices of
refraction can be realized within a waveguide made according to
embodiments of the present invention. The liquid crystal material
58 which is not beneath the patterned electrodes(s) 60 may be
characterized as having a first index of refraction n1, and n1 is
generally unaffected by the application of a voltage 68 to the
patterned electrodes 60.
[0087] The liquid crystal material 58 beneath the patterned
electrode(s) 60 can be characterized as having a tunable and
dynamic index of refraction n2. In one example, when no voltage 68
is applied to the upper electrode 60, n2 equals n1 and no
refraction occurs. As voltage 68 is applied and increased between
the upper patterned electrode(s) 60 and the lower electrode plane
62, the index of refraction n2 of the liquid crystal material under
the upper patterned electrode(s) 60 is controllably changed as a
function of the applied voltage 68. Depending upon the
implementation, the applied voltage 68 can be a DC voltage, or an
AC voltage, for instance, at low frequencies to high frequencies
such as 50 KHz or higher.
[0088] Hence, as the difference between n2 and n1 increases, the
amount of refraction or bending of light passing through the
waveguide 50 can be increased as well. Hence, the amount of bending
or refraction of light as it passes through the waveguide 50 can be
controlled electronically and without any moving parts to perform
numerous useful functions, such as for use in a barcode scanner, a
CD/DVD read/write head, a tunable laser, or other applications. In
FIG. 1, the input light beam is shown as 66, and the output light
beam is shown as 70, with the amount output angle of 70 a function
of the applied voltage 68, among other things.
[0089] As shown in FIG. 1, the waveguide 50 may be generally
rectangular in shape and may include a core 52 having a generally
rectangular cross-section or defining a parallel piped between
walls 72. On the front end 74 of the waveguide 50, light 66 is
introduced into the waveguide core 54 and propagates along the
length of the waveguide 50 to the distal end 76 of the waveguide
50. As shown in FIG. 1, the direction of propagation of light 66
through the waveguide 50 is generally along the length of the
waveguide 50, and use of embodiments of the present invention
permit the output propagation direction or angle 70 to be
controllably altered depending, in part, on the shapes of the upper
electrodes 60 and the voltages 68 applied between the upper
electrodes 60 and the lower electrode or plane 62. Although the
waveguide 50 in FIG. 1 is shown as generally rectangular, it is
understood that a waveguide made according to one or more
embodiments of the present invention could have other shapes such
as square, trapezoid, parallelogram, any polygon, or even be diced
or scribed so as to have rounded edges producing elliptical,
circular, or any curved shape.
[0090] In one example, the patterned electrode(s) 60 may include a
tab or extension therefrom 78 which permits the patterned
electrode(s) to be electrically connected to other electrical
elements, such as a voltage source 68 coupled between the patterned
electrode 60 and the lower electrode or plane 62. Alternatively,
electrical traces, conductors, vias or other conventional
connection types may be utilized instead of or with tab 78 to
electrically couple a patterned electrode 60 to other electrical
elements.
[0091] FIG. 2 illustrates a sectional view of a waveguide 50 in
accordance with one embodiment of the present invention. As shown
in FIG. 2, in one example, a waveguide 50 may include a substrate
80 such as a P-doped silicon substrate or any other conductive
material, which provides structural support for the waveguide 50
and also acts as a lower electrode or ground plane 62 to which a
voltage 68 may be applied. The substrate 80 may also be formed from
any metal, such as silver, copper, aluminum, gold, titanium, etc.
Alternatively, the substrate 80 can be nonconductive, such as a
glass or crystal, and a conductive coating or electrical ground
plane can be applied to the top of the substrate surface, between
the substrate 80 and lower cladding 56. This conductive coating can
be ITO, Au, Ag, Al, Cu, or any other of a number of conductive
coatings. If the substrate 80 is constructed from Si, then
circuitry can be directly integrated into the substrate 80 if
desired. The conductive substrate 80 is also referred to herein as
the lower electrode 62.
[0092] A lower cladding layer 56 is provided on the substrate 80
and is preferably made of any dielectric materials with low
absorptions whose index of refraction is less than the index of
refraction of the core. Suitable materials include Silicon
OxyNitride, Silicon-Rich Nitride, Silicon Nitride, Tantalum
Pentoxide, Polymers, Pure Silicon, Ion exchange glass on substances
such as Lithium Niobate, Sol-Gel, thermally oxidized silicon,
glass. In one example, the interface between the lower cladding 56
and the core layer 52 is transparent so that light can penetrate
the lower cladding 56 as it propagates through the core 52.
[0093] On top of the lower cladding 56, a waveguide core or core
material 52 is provided. In one embodiment, the core 52 does not
include any liquid crystal material 58 therein. The core 52 may be
made of materials such as any dielectric materials with low
absorptions whose index of refraction is greater than the index of
refraction of the upper and lower claddings 54, 56. Suitable
materials include, but are not limited to, Silicon OxyNitride,
Silicon Rich Nitride, Silicon Nitride, Tantalum Pentoxide,
Polymers, Pure Silicon, Ion exchange glass on substances such as
Lithium Niobate, Sol-Gel, thermally oxidized silicon, glass. In one
example, the core 54 has a thickness that is tapered or includes a
channel. Furthermore, a core 54 may have a constant index of
refraction along the length of the waveguide 50, or alternatively
have an index of refraction that varies across or along the
device.
[0094] On top of the core layer 52, an alignment layer 82 (shown as
the lower alignment layer 82 in this example) is provided which is
used to initially align or bias the orientation of liquid crystal
material 58 that is proximate to or adjacent to the alignment layer
82 and the core 52. Alignment can be achieved, for example, by
buffed polyimide, nylon, or other polymer coating applied to the
core 52 and or the cover plate 84, photo-aligned polyimide, polymer
or other photo-aligned material, angle deposited SiO, SiO2 or other
angle deposited material, microgrooves etched or directly e-beam
written into the core 52 and or cover plate 84, ion-buffed surfaces
on the core or lower cladding, a dispersed polymer matrix that is
photoaligned, or direct buffing of either surface. In one example
the alignment layer 82 may be a coating or layer that induces a
homeotropic alignment in the liquid crystal 58. In one example, the
lower alignment layer 82 is generally transparent.
[0095] On top of the lower alignment layer 82, the upper cladding
54 is provided having liquid crystal material therein 58. In one
example, the interface between the lower alignment layer 82 and the
upper cladding 54 is transparent. The liquid crystal material 58
may include, but is not limited to, any nematic liquid crystal,
with either a positive dielectric constant or a negative dielectric
constant or a mixture of each, polymer dispersed liquid crystal
material, Smectic A* and C* liquid crystal material, cholesteric
liquid crystal material such as ferroelectrics and surface
stabilized ferroelectrics, or dual-frequency liquid crystal
material, for example. While the various figures herein show the
liquid crystal material 58 as being nematic liquid crystal, it is
understood that embodiments of the present invention may utilize
other types of liquid crystal material.
[0096] In one example, the upper cladding 54 is formed using spacer
material to define a region or volume wherein liquid crystal
material 58 may be contained therein, and optically transparent
glue such as Norland 68 may be used to create transparent boundary
walls 72 to contain the liquid crystal 58.
[0097] On top of the upper cladding 54, an upper alignment layer 86
may be provided to initially align or bias the orientation of
liquid crystal material 58 that is adjacent to or proximate to the
upper alignment layer 86. As with the lower alignment layer 82,
alignment can be achieved, for example, by buffed polyimide
coating, photo-aligned polyimide, angle deposited SiO and or SiO2,
microgrooves etched or otherwise formed, ion-buffed surfaces, a
dispersed polymer matrix that is photoaligned, or direct buffing.
In one example, the upper alignment layer 86 is generally
transparent.
[0098] The alignment of the liquid crystal 58 between the lower and
upper alignment layers 82, 86 can be anti-parallel, parallel,
twisted, or hybrid between twisted and parallel or anti-parallel.
The direction of liquid crystal alignment can be at any angle with
respect to the direction of light propagation 66. Described below
are examples of where the alignment of the liquid crystal materials
58 is adapted to provide for refraction of TE or TM modulated light
as it passes through a waveguide made according to embodiments of
the present invention.
[0099] On top of the upper alignment layer 86 and below the glass
cover 84, a patterned electrode layer 60 or portions of the
patterned electrode layer 60 are present. In one embodiment, the
patterned electrode layer 60 includes one or more electrodes having
non-normal interfaces 64 relative to the orientation of light 66
traveling through the waveguide 50, or includes one or more curved
or lens shaped interfaces 64. In one example, the patterned
electrode layer 60 is a conductive coating applied to the bottom
surface of the glass cover 84. The conductive coating can include,
but is not limited to, ITO, Au, Ag, Al, Cu, or any other conductive
coating. In another example, the patterned electrode 60 can be
p-doped silicon or any metal, such as silver, copper, aluminum,
gold, titanium, alloys, or other conductive material, etc. In one
example, the glass cover 84 may be made of materials such as, but
not limited to, standard float glass such as Corning 1737, fused
silica, or any flat surface. Since the evanescent portion of the
light preferably does not pass through the cover plate 84, the
cover plate 84 can be made from non-transparent materials such as
silicon wafers, ceramics, or polished metal surfaces. In another
embodiment, the cover plate 84 may be a metal or any other
conductive material and serve as the upper electrode.
[0100] Using the structure of FIGS. 1-2 or variations thereof,
various different waveguides 50 can be formed to selectively and
controllably refract, bend, or focus light 66 as it passes through
the waveguide 50. When a voltage 68 is applied between the
patterned electrode(s) 60 and the substrate 80, an electric field
is formed between the patterned electrode 60 and the substrate 80
which induces movement of the liquid crystals 58 in the upper
cladding 54 that are subject to the applied electric field. As the
liquid crystals 58 move or change their orientation based on the
applied voltage, the index of refraction of the affected portion of
the upper cladding 54 is changed relative to the index of
refraction of the non-affected portions of the liquid crystal
material 58 in the upper cladding 54. As shown in FIG. 1, the
portion of the waveguide 50 which is not affected by the electric
field created between the patterned electrode 60 and the substrate
80 can be characterized as having a first index of refraction
(shown as n1), while the portion of the waveguide 50 affected by
the electric field created between the patterned electrode 60 and
the substrate 80 may be characterized as having a second index of
refraction (shown as n2). Under Snell's Law, light refracts when
crossing an interface 64 between two different indices of
refraction if the interface 64 is oriented in a non-normal relation
to the direction of propagation of light 66. In FIG. 1, the
patterned electrode 60 has a non-normal interface 64 on its distal
trailing edge, so that as light 66 propagates through the waveguide
50 from the front end 74 to the distal end 76 of the waveguide 50,
light 66 is refracted or steered (shown as 70) in a controlled
manner depending upon the amount of voltage 68 applied between the
patterned electrode 60 and the substrate 80.
[0101] Preferably, the core layer 52 is surrounded by an upper and
lower cladding 54, 56, wherein the interfaces between the lower
cladding 56 and the core layer 52 and between the upper cladding 54
and the core layer 52 are transparent. As light 66 enters the core
layer 52 and propagates through the core 52 along the length of the
waveguide 50, the evanescent portion of the propagating light 66
waves penetrates into both the upper and lower cladding 54, 56.
Preferably, the core layer 52 has a fixed index of refraction, and
the lower cladding also has a fixed index of refraction. By
providing liquid crystal material 58 within the upper cladding 54,
a portion of which is controllably subjected to an electric field
between the patterned electrode 60 and the substrate 80, the index
of refraction (n2) of the upper cladding layer 54 can be
controllably altered. Stated differently, the average index of
refraction (also referred to herein as the effective index of
refraction, or index of refraction) of the upper cladding 54, core
52, and lower cladding 56 as experienced by a single TM or TE mode
of light in the waveguides can be controllably altered by altering
the index of refraction (n2) of the upper cladding 54. Hence, as
light 66 passes through the waveguide core 52 and upper and lower
cladding 54, 56, the light 66 can be controllably refracted,
steered, or focused (70) through the use of the upper electrode 60
having a non-normal interface 64 therein. Because the liquid
crystal material 58 is disposed within the upper cladding 54 and
interacts primarily with the evanescent portion of the light wave
66 and the fundamental portion of the light wave 66 passes through
the core material 52, there is no significant attenuation of the
intensity of the light 66 as the light 66 passes through the
waveguide 50. This permits the length of the waveguide 50 to be
beneficially long so that numerous electrodes 60 can be utilized in
a cascade or series arrangement if desired, for example as in FIGS.
16-18.
[0102] Furthermore, in one example, the evanescent portion of the
light 66 is only interacting with the liquid crystal molecules 58
that are close to the alignment layer 82. These molecules 58 are
more highly ordered than liquid crystal molecules 58 further away
from the alignment layer 82 and therefore scatter less light. In
one example, the losses are sufficiently low (e.g., less than 0.5
dB/cm) that the waveguide 50 length can be lengthy (e.g., 4 inches
or greater).
[0103] In one embodiment of the invention, a waveguide 50 may be
formed having a first and second assembly 90, 92, wherein the first
and second assemblies 90, 92 are attached to one another in order
to form the overall waveguide 50. As shown in FIG. 2, the first
assembly 90 may include the substrate 80, the lower cladding 56,
the core 52, and the lower alignment layer 82; and the second
assembly 92 may include the glass cover 84, the patterned
electrode(s) 60, the upper alignment layer 96 and upper cladding 54
with liquid crystal material 58 therein. One method for forming a
waveguide is illustrated below in FIGS. 3 and 14.
[0104] While FIGS. 1-2 show a particular arrangement of layers of a
waveguide according to one embodiment of the present invention, it
is understood that the present invention contemplates variations of
this arrangement. For instance, the patterned electrode(s) 60 may
be positioned in a different layer than as shown in FIG. 1-2, such
as proximate the lower portion of the waveguide 50 (see FIG. 12 as
an example). The conductive lower electrode 62 may also be
positioned at different layers within the waveguide if desired.
Further, while two alignment layers 82, 86 are shown, the invention
may include a single alignment layer. While the liquid crystal
material 58 is shown as disposed within the upper cladding 54, it
is understood that the liquid crystal material 58 may be disposed
in the lower cladding 56 if desired.
[0105] FIG. 3 illustrates an example of operations 100 for
controlling the refraction of light through a waveguide, in
accordance with one embodiment of the present invention. At
operation 102, the waveguide is provided with a core, an upper
cladding, and a lower cladding where in one example the upper
cladding has liquid crystal material disposed therein.
Alternatively, liquid crystal material may be disposed within the
lower cladding if desired. At operation 104, one or more electrodes
are provided for controlling the orientation of the liquid crystal
material proximate the one or more electrodes, wherein the one or
more electrodes have at least one non-normal interface relative to
the direction of propagation of light through the waveguide. As
discussed above, the non-normal interface results in refraction,
steering, or bending of light as light exits the non-normal
interface. At operation 106, a second electrode or ground plane is
provided. In one example, a substrate material of the waveguide is
electrically conductive and acts as a lower electrode or ground
plane so that a controlled voltage can be applied between the
patterned electrode and the substrate to create an electric field
therebetween.
[0106] At operation 108, at least one alignment layer is provided
to align the liquid crystal material proximate the core. For
instance, a lower alignment layer (such as 82 in FIG. 2) can be
provided to initially align or bias the liquid crystals within the
upper cladding and adjacent to the lower alignment layer. By
providing the alignment layer, the liquid crystal material responds
to an applied voltage in a faster and more orderly and predictable
manner. Further, when no voltage is applied to the liquid crystal
material, the alignment layer provides sufficient liquid crystal
ordering to minimize scattering of the light propagating through
the waveguide because the evanescent portion of the light interacts
primarily with the highly ordered liquid crystal molecules along
the alignment layer.
[0107] At operation 110, the introduction of light is provided into
the waveguide core such that as the primary or fundamental portion
of the light input into the waveguide travels through the core, and
the evanescent portion of the light passes through the upper and
lower claddings of the waveguide. In one example, operation 110 is
achieved by prism coupling, grating coupling, end-fire coupling or
other conventional coupling techniques. In another embodiment,
polarized light (such as TE or TM polarized light) is introduced
into the waveguide and operation 108 provides a liquid crystal
orientation that is adapted to controllably refract, steer, or
focus the polarized light.
[0108] At operation 112, a voltage is applied between the one or
more electrodes and the lower electrode in order to change the
effective index of refraction of the materials between the one or
more electrodes and the lower electrode. By altering the refraction
of the liquid crystal material under the patterned electrodes
(e.g., shown as n2 in FIG. 1), a modulation index or change in the
index of refraction (referred to as .DELTA.N) is achieved. As the
modulation index .DELTA.N increases, the amount of light beam
refraction also increases, which permits active, solid state
control of the amount of refraction of light passing through the
waveguide. At operation 114, the amount of applied voltage may be
altered to controllably refract or bend the light traveling through
the waveguide.
[0109] In one example of waveguides formed in accordance with
embodiments of the present invention, various degrees of modulation
index through waveguides were achieved, and are summarized in Table
1 and Table 3. Hence, it can be seen that by the operations of FIG.
3, light can be controllably refracted or steered as it passes
through a waveguide.
[0110] Embodiments of the present invention can be used to
selectively control the index of refraction for particular types of
polarized light, such as TM polarized light and TE polarized light.
Generally, TM (Transverse Magnetic) polarized light means that the
magnetic field of the light wave is traversing the plane of the
waveguide, while the electric field is substantially perpendicular
to the plane of the waveguide. TE (Transverse Electric) polarized
light is characterized by the electric field of the light
traversing the plane of the waveguide, while the magnetic field of
the light is substantially perpendicular to the plane of the
waveguide.
[0111] FIGS. 4-7 and 8-11 illustrate various examples of how
embodiments of the present invention may be used to refract, steer,
or focus light that has been polarized either as TE or TM
polarization. Referring to FIGS. 4-7, if the liquid crystals 58
disposed within the upper cladding 54 are initially aligned (e.g.,
through the use of the lower and upper alignment layers 82, 86) in
such a way that the long axis of the liquid crystals 58 are aligned
in parallel with the direction of light propagation 66 through the
waveguide 50 (FIGS. 4-5 show this situation when no voltage 68 is
applied to the electrodes 60, 62), then when voltage 68 is applied
to the electrodes 60, 62, the liquid crystals 120 beneath the
patterned electrode 60 respond by rotating upwardly in a plane
containing the applied electric field vector and the propagation
vector of the light 66. The liquid crystals 122 that are not
beneath the electrode 60 generally maintain their orientation. When
the long axis of the affected liquid crystals 120 are perpendicular
to the direction of propagation of light 66 through the waveguide
50, or the long axis of the affected liquid crystals 120 are at
intermediate stages such that they are not parallel to the
propagation vector 66 (see FIGS. 6-7), then light 66 which is TM
polarized experiences a higher index of refraction within the
volume of liquid crystals 120 beneath the patterned electrode 60.
This is because the E field of the propagating light 66 interacts
more strongly with the LC molecules 120 when the LC molecules 120
are perpendicular to the direction of propagation of TM polarized
light. Accordingly, as seen in FIGS. 4-7, a waveguide 50 can be
formed that can controllably refract, steer, or focus light which
is TM polarized. In one example, the light 66 is TM polarized
before it enters into the waveguide (FIG. 7).
[0112] In FIGS. 4-7, light 66 which enters the waveguide 50 with a
TE polarization would not be affected, refracted, or steered by the
movement of the affected liquid crystals 120 into the second state
because the electric field of TE polarized light experiences the
same interaction with the liquid crystals 120 in both the first
state and the second state. In other words, in one example, the
electric field of the TE polarized light is perpendicular to the
long axis of the molecules.
[0113] With regard to FIGS. 8-11, these figures illustrate an
embodiment of the present invention wherein the liquid crystals 58
disposed within the upper cladding 54 are aligned with their long
axis perpendicular to the direction of propagation 66 of light
through the waveguide 50. Again, the alignment of the liquid
crystals 58 can be biased or initially aligned through the use of
the upper and lower alignment layers 86, 82. In this embodiment,
light which is TE polarized can be refracted, steered, or focused
as it travels through the waveguide 50, and further, light which is
TM polarized that enters the waveguide 50 can also be refracted,
steered, or focused as it travels through the waveguide 50. FIGS.
8-9 show the liquid crystals 58 in their initial, first, or zero
voltage state, where the liquid crystals 58 have been aligned with
their long axis perpendicular to the propagation 66 of light
traveling through the waveguide 50. For light that is TE polarized
prior to entry into the waveguide 50, the orientation of the liquid
crystals 58 in the initial or first state provides a larger index
of refraction than when the liquid crystals 58 are oriented
vertically upward in the second state (FIGS. 10-11). Accordingly,
TE polarized light can be refracted, steered, or focused through
the use of this embodiment of the present invention. Likewise, TM
polarized light can be refracted as well. For TE polarized light,
in the second state where the voltage is on, n1 is greater than n2.
For TM polarized light, in the second state where voltage is on, n2
is greater than n1.
[0114] While FIGS. 1-11 illustrate one example of the present
invention, it is understood that the principles of the present
invention could be employed in other arrangements of liquid crystal
waveguides, and one such example is illustrated in FIG. 12. In FIG.
12, an alternative embodiment of a waveguide 130 is illustrated in
accordance with the present invention. In this example, the
ordering of the layers of the waveguide 130 are changed when
compared with FIGS. 1-2. In FIG. 12, a substrate 132 defines the
lower portion of the waveguide 130 and a patterned electrode 134 is
placed on top of the substrate 132 (see also FIG. 13). As shown in
FIG. 13, a lower cladding 136 made of non-electro optic material
may be placed on top of the electrode layer 134. The core 138 layer
may be placed on top of the lower cladding 136, and a lower
alignment 140 layer may be placed on top of the core layer 138. An
upper cladding 142 having walls 144 with liquid crystal materials
146 therein may be placed on top of the lower alignment layer 140,
and an upper alignment layer 148 may be placed on top of the upper
cladding 142. A conductive layer or plane 150 may be placed on top
of the upper alignment layer 148, and a cover plate 152 may be
placed on top of the conductive layer 150. In this embodiment, the
liquid crystals 146 are disposed within the upper cladding 142. It
is understood that the liquid crystals 146 could be disposed within
the lower cladding 136 if desired, and the alignment layers 140,
148 could be placed on the upper and lower surfaces of the lower
cladding 136 having the liquid crystal material 146 therein.
[0115] FIG. 14 illustrates an example of operations that may be
used for making one example of a waveguide in accordance with one
embodiment of the present invention. In making a waveguide, the
materials described with reference to FIGS. 1-2 or as described
otherwise herein may be used and conventional materials may be
used. At operation 160 of FIG. 14, a substrate wafer is obtained
for forming the base of the waveguide. In one example, the
substrate wafer is a P-doped, polished silicon substrate wafer such
that the substrate can act as the lower electrode, for example as
in the embodiment of FIGS. 1-2. At operation 162, a lower cladding
material is applied onto the substrate wafer. At operation 164, the
core layer is formed on top of the lower cladding material, in one
example. At operation 166, in one example, the wafer is diced into
desired pieces, wherein each piece will form a separate waveguide,
and cleaned if desired. A conventional dicing saw for semiconductor
substrates may be used. Cleaning may include cleaning in an
ultrasonic cleaner with a mild soap or solvent, or cleaning with
methanol wipes. Also, stresses from the coating process under which
the waveguides are made may induce warp and bow, which can be
removed via optically contacting the waveguide to an optical flat
or stiffener plate. In another example, using wafers polished on
both sides and applying thermally grown SiO2 on both sides, to a
thickness of about 2 microns, can reduce the warp and bow. This
thermally grown SiO2 layer may serve as the lower waveguide
cladding.
[0116] At operation 168, for each piece, an alignment layer is
applied adjacent to the core layer, and this combination may form a
first assembly. There are several methods of applying the alignment
layer, most of which are standard for liquid crystal cells. These
include: i) spin coat a polyimide layer, which is then buffed with
a cloth (to provide directionality); ii) buff the waveguide
directly; iii) oblique deposition of an SiO or SiO2 layer; iv)
photo-align a spin-coated polyimide or other polymer layer via
exposure to polarized light (see FIGS. 28-32 below); v)
microgrooves (see FIGS. 28-32 below); and vi) angled ion
buffing.
[0117] A second assembly may be formed by operations 170, 172, 174.
At operation 170, a piece of glass cover plate material is
obtained, and at operation 172, one or more electrodes are formed
on a first side of the glass cover plate material, wherein at least
one of said one or more electrodes has a non-normal edge or
interface relative to the axis or direction that light will
propagate relative to the cover plate. Operation 172 may be
implemented by applying a coating such as an indium tin oxide (ITO)
layer or any conductive layer, e.g., gold, aluminum. After this
coating is applied it can be patterned via standard
photo-lithographic processes.
[0118] At operation 174, an alignment layer may be applied to the
first side of the cover plate on top of the electrodes, thereby
forming a second assembly. This can be achieved in the same manner
as operation 168. At operation 176 the first and second assemblies
are joined together, preferably using optical glue to define a cell
having three walls and an opening along the fourth wall. At
operation 178, the cell is filled with liquid crystal material, and
this filled structure may form the upper cladding in the example of
FIGS. 1-2. Operation 178 may be implemented by establishing the
cell thickness by mixing spacer balls (typically 3-10 microns) into
the glue that attaches the cover plate to the waveguide. The cover
plate is glued around the edges, but not in the middle, leaving a
cavity. A small hole is left in the glue seal, which is used to
fill the cavity with liquid crystal material. The cell created by
the waveguide and cover plate is then filled with liquid crystal. A
small drop of liquid crystal material, placed at the opening or
hole in the glue seal, will wick into the cell. This can be done
with only one opening or hole under vacuum, or with two holes at
standard air pressure. After the cell is filled, the opening/hole
in the glue seal is covered with more glue.
[0119] It is understood that FIG. 14 is provided for illustrative
purposes only, and that these operations could be interchanged,
subdivided, regrouped, or reordered depending upon the particular
implementation and the particular waveguide being made. For
instance, the operations could be re-ordered so as to form the
waveguide 130 of FIGS. 12-13, or other waveguide structures.
[0120] In accordance with embodiments of the present invention, a
patterned electrode 60, 134 may take various shapes depending upon
the particular application. FIGS. 15-19 illustrate various examples
of shapes for electrodes, such as electrodes 60, 134. If it is
desired to refract or steer light over a small angle, then a simple
wedge shape 180 as shown in FIG. 15 may be used for an electrode.
If a larger amount of refraction is desired, then an electrode can
include multiple wedge shapes 182 cascaded together and
electrically coupled together so that each successive wedge 182
provides a greater amount of refraction of the light received from
the preceding wedge, as shown in FIG. 16. In FIG. 17, an electrode
can include a first and second electrode 184, 186 wherein the first
and second electrode 184, 186 are electrically isolated. The first
electrode 184 may provide a plurality of wedge shapes 188 in series
for refracting or steering light in a downward direction, while the
second electrode 186 provides a series of cascaded wedges 190 that
refracts light upwardly. Hence, the embodiment of FIG. 17 can
provide refraction over large angles. In use, a first voltage 192
could be applied to the first electrode 184 and as the first
voltage 192 increases, the amount of deflection downwardly
increases. As the amount of the first voltage 192 decreases, the
amount of deflection decreases until the point where no voltage is
applied to either the first or second electrode and the light
propagates through the waveguide in a straight line. When a second
voltage 194 is applied to the second electrode 186 (but not the
first electrode), then the light passing through the waveguide
begins to refract upwardly as the voltage 194 increases, and as the
voltage 194 decreases, the amount of refraction decreases until the
point where the light passes through the waveguide is a straight
line.
[0121] The angular tuning range of beamsteerer electrodes such as
184, 186 shown in FIG. 17 can be limited because with successive
refraction at each prism/wedge 188, 190, the beam can be deflected
sufficiently so as to exit the electrodes, and therefore no longer
be steered by the remaining prisms/wedges 188, 190. In other words,
the output aperture eclipses the beam, thus unnecessarily limiting
the angular range. This can be alleviated by: i) forming the prism
array into a horn shape so that the output aperture encompasses the
full deflection range of the beamsteerers, and ii) forming the
input aperture to match to the size of the beam being deflected.
This can increase the steering range and is generally discussed in:
Y. Chiu, K. J. Zou, D. D. Stancil, T. E. Schelsigner,
Shape-Optimized Electrooptic Beam Scanners: Analysis, Design, and
Simulation, J. of Lightwave Tech., Vol. 17, p 108 (1999); and D. A.
Scrymgeour, Y. Barad, V. Gopalan, K T. Gahagan, Q. Jia, T. E.
Mitchell, and J. M. Robinson, Large-Angle Electro-Optic Laser
Scanner on LiTaO3 Fabricated by in Situ Monitoring of
Ferrorelectric-Domain Micropatterning, App. Opt. Vol. 40, p. 6236
(2001), the disclosures of which are incorporated by reference in
their entirety. As applied to embodiments of the present invention,
the outer envelope of a prism array, which defines the maximally
refracted or steered beam, may be characterized by 1 2 x z 2 = n n
1 W ( z ) , where W ( z ) = x ( z ) + 0 { 1 + [ z n 0 2 ] 2 } , Eq
. 1
[0122] and .DELTA.n is the maximum modulation index of the
waveguide, n is the average effective index of the guided mode,
.lambda. is the wavelength of light, and .omega. is the Gaussian
beam waist of the input beam. In one example as shown in FIG. 18,
within this envelope, electrodes 200, 202 can be formed with prisms
204, 206 formed by dividing the length of each electrode 200, 202
into N prisms 204, 206 of equal base length. The differential
equation describing the envelope may be solved using numerical
methods, and an electrode pattern may be constructed. An example of
such an electrode pattern is shown in FIG. 18, wherein a first
electrode 200 defines a plurality of successive prisms 204, and a
second electrode 202 defines a second plurality of prisms 206
opposing the first set of prisms 204.
[0123] In a manner analogous to the two electrode beamsteerer of
FIG. 17, selective application of voltage to one or the other
electrode 200, 202 of FIG. 18 can be used to selectively steer the
beam either to one side or the other.
[0124] Combinations of electrodes such as 180, 182, 184, 186, 200,
202 can be utilized to form optical switches wherein a first
waveguide with one or more electrodes acts as a transmitter and a
second waveguide with one or more electrodes can be positioned to
receive the light transmitted by the first waveguide.
[0125] In another example, a waveguide using the electrodes of FIG.
18 may selectively control light (e.g. a laser beam) through an
aperture, so that a laser beam may be refracted either through the
aperture or refracted so as to not pass through the aperture, so as
to be used as a shutter. This can be advantageous for construction
of shutters with light in the blue or near-UV spectral region, in
part because polarization based shutters suffer from poor contrast
ratios. In other words, in conventional shutters that rotate the
polarization of the light to be either blocked or not blocked by a
polarizer, the off state is typically limited by the quality of the
polarizer. For example, Gallium-Nitride (GaN) diode lasers, with
wavelengths around 400 nm, have utility in optical data storage and
other applications, yet high quality polarizers at these
wavelengths are expensive, and therefore a polarization based
shutter is also expensive. Using embodiments of the present
invention, a shutter can be provided based on steering a GaN diode
beam either through or not through an aperture, and can be both
high contrast and inexpensive.
[0126] Furthermore, horn shaped electrodes 200, 202 can be utilized
as receiving elements. A detector element, such as a photodiode,
can be placed at the narrow end of the horn-shaped prism electrodes
200, 202 (left side of FIG. 18). Depending on the amount of applied
voltage to either electrode 200, 202, the electrode pattern shown
in FIG. 18 can selectively detect portions or regions of light that
are entering the large end of the electrodes 200, 202 (the right
side of FIG. 18). In other words, for a specific applied voltage to
the electrodes 200, 202, only light that enters at a specific angle
and region of the electrode pattern 200, 202 (on the right side of
FIG. 18) will be directed to the detector (on the left side of FIG.
18), and therefore only that light will be detected. By changing
the voltage applied to the electrodes 200, 202, different regions
and angles can be selected. In this way, electrode patterns 200,
202 such as shown in FIG. 18, can not only serve as beam steerers,
but also serve as voltage controllable scanners or imagers.
Combinations of these electrode patterns 200, 202 or others can
serve multiple optical cross-connect and switching functions.
[0127] FIG. 19 shows an example with an electrode 210 having a
parallelogram shape wherein two parallel surfaces 212, 214 are both
non-normal to the propagation direction 216 of the light input 218.
In this embodiment, as the voltage applied to electrode 216
increases, the light beam output 220 passing through the waveguide
can be moved to one side or another. As the voltage increases, the
distance between the input beam 218 and the active output beam 220
grows, while as the voltage decreases, the distance between the
input beam 218 and the active output beam 220 decreases.
[0128] In addition to electrode shapes that can be used for beam
steering as described with reference to the examples above,
electrode shapes may also be provided which focus light as it
passes through the waveguide. FIG. 20 illustrates an example of
operations for forming a waveguide having one or more electrodes
with curved or lens shaped interfaces for controlling the
propagation of light through the waveguide, in accordance with one
embodiment of the present invention. FIGS. 21-28 illustrate some
examples of electrodes having lens shapes that may be utilized in
waveguides according to embodiments of the present invention.
[0129] In FIG. 20 at operation 230, a waveguide is provided with a
core, upper cladding, and lower cladding, wherein liquid crystal
material is disposed within one of the claddings. As described
above, the liquid crystal material may be disposed within the upper
or lower cladding, and for purposes of this example, the liquid
crystal material will be described as being disposed within the
upper cladding. At operation 232, one or more electrodes, also
referred to herein as patterned electrodes, are provided having at
least one curved or lens shaped interface or edge for controlling
the orientation of the liquid crystal material adjacent (i.e.,
above or below) the electrode. The curved or lens shape of the one
or more electrodes induces the liquid crystal material adjacent the
electrode to form a lens shape wherein the index of refraction of
the lens shape is controllable dependent upon the amount of voltage
applied to the electrode. The electrodes can be made in various
such lens or curved shapes, including conventional lens shapes, and
some examples of such shapes are illustrated in FIGS. 21-28. At
operation 234, a lower electrode or plane is provided within the
waveguide so that an electric field can be formed between the one
or more electrodes of operation 232 and the lower electrode or
plane of operation 234 in order to control the orientation of the
liquid crystal material therebetween. In one example, a conductive
substrate layer is provided in the waveguide to act as the lower
electrode or ground plane.
[0130] At operation 236, at least one alignment layer is provided
to align the liquid crystal material proximate the core. In one
example, an upper alignment layer and a lower alignment layer may
be provided as shown in FIG. 2 so that the liquid crystal material
adjacent the alignment layer is biased or oriented in a desired
orientation when no voltage is applied between the upper patterned
electrode and the lower electrode or conductive substrate; or other
arrangements of alignment layers can be used. At operation 238, in
one example, it is provided that light may be introduced into the
waveguide core such that the evanescent portion of the light wave
passes through the cladding, which contains the liquid crystal
material (i.e., the upper cladding, in one example). In one
embodiment, for instance, a prism coupler or endfire coupler or
other conventional coupler may be used to introduce light into the
waveguide.
[0131] At operation 240, a voltage applied between the one or more
electrodes of operation 232 and the lower electrode, plane, or
conductive substrate of operation 234, in order to change the index
of refraction of the cladding, which contains the liquid crystal
material. In operation 240, the liquid crystal material between the
electrode having the curved or lens shaped interface and the lower
electrode/conductive substrate is controllably reoriented depending
upon the amount of voltage applied, and such application of voltage
alters the index of refraction of such liquid crystal material
relative to light propagating through the waveguide. As such,
through the application of voltage between the patterned electrodes
and the lower electrode/conductive substrate, one or more shapes
can be formed within the liquid crystal material which in effect
operate as lenses to focus or direct light under the control of the
applied voltage. At operation 242, the applied voltage may be
varied so as to controllably focus or defocus light as it travels
through the waveguide and the evanescent portion of the light
passes through the liquid crystal material experiencing the
influence of the electric field of the applied voltage.
[0132] FIGS. 21-27 illustrate some examples of electrodes having
lens shapes that may be utilized in waveguides according to
embodiments of the present invention. It is understood that these
figures are provided as examples only, and that the present
invention contemplates any patterned electrode forming any type of
lens shape used for focusing or defocusing light, including
conventional lens shapes, or other shapes for instance as described
with reference to FIGS. 1-19. For purposes of this description, it
is assumed that as voltage is applied to the electrode, the index
of refraction n2 of the liquid crystal material proximate the
electrode is greater than the index of refraction n1 of the liquid
crystal material outside of the electrode.
[0133] In FIG. 21, an electrode 250 is formed in the shape of a
simple positive lens or plano-convex lens, wherein as the voltage
applied to the electrode 250 increases, the index of refraction n2
increases relative to n1, and the focal length 252 is relatively
short. As the voltage applied to the electrode 250 decreases, the
index of refraction n2 approaches the index of refraction n1 and
the focal point 254 moves outward towards infinity. As such, the
electrode 250 of FIG. 21 can be used to selectively focus light 256
along different points (e.g., between 252 and 254) within a
waveguide, and can be used for spectroscopic applications, lab on a
chip, examining micro-fluidic channels, collimation, or the
like.
[0134] In FIG. 22, an electrode 260 is formed in the shape of a
negative lens or plano-concave lens wherein as the voltage applied
to the electrode 260 increases, the index of refraction N2
increases which defocuses the light 262. As the voltage applied to
the electrode decreases, the index of refraction N2 approaches N1,
and the light rays travel substantially along the same orientation
as on the front side of the lens. As such, the electrode 260 of
FIG. 22 can be used to selectively spread out or diffuse light, or
to collimate a converging beam of light.
[0135] Conventionally, aspherical glass lenses are difficult to
make due to grinding and polishing techniques involved with making
conventional glass lenses. In contrast, aspherical curved surfaces
are easily constructed using embodiments of the present invention.
For example, embodiments of the present invention can use
photolithography techniques to form or etch one or more aspherical
lens shapes in the patterned electrode. In another example,
elliptical or hyperbolic lens shapes can be made in the patterned
electrode according to the present invention, without the negative
affects of spherical aberrations.
[0136] FIG. 23 illustrates an example of an electrode 270 formed in
the shape of a convex-convex lens for controlling light propagating
through a waveguide, in accordance with one embodiment of the
present invention. This type of lens shape may be used to focus a
collimated beam of light or to collimate a divergent beam of light.
Due to the curvature of both sides 272, 274, back reflections may
be reduced. Furthermore, since both sides 272, 274 act as focusing
elements, the curvature of each side 272, 274 may be reduced to
achieve the same focal length as the lens of FIG. 21.
[0137] FIG. 24 illustrates an example of an electrode 280 formed in
the shape of a concave-concave lens for controlling light
propagating through a waveguide, in accordance with one embodiment
of the present invention. This type of lens shape may be used to
focus a collimated beam of light or to collimate a divergent beam
of light. Due to the curvature of both sides 282, 284, back
reflections may be reduced. Furthermore, since both sides 282, 284
act as defocusing elements, the curvature of each side 282, 284 may
be reduced to achieve the same negative focal length as the lens of
FIG. 22.
[0138] FIG. 25 illustrates an example of an electrode 290 formed in
the shape of a convex-concave lens for controlling light
propagating through a waveguide, in accordance with one embodiment
of the present invention. In this example, the radius of curvature
of the front side 292 of the lens shape is greater than the radius
of curvature of the back side 294. This can be useful, for
instance, where it is desired to match the front side's 292 radius
of curvature with a radius of curvature of a preceding lens shape
in the waveguide, or to match the back side's 294 radius of
curvature with a radius of curvature of a subsequent lens shape in
the waveguide. As another example (not shown), Fresnel type lens
patterns may be used. Fresnel type lenses can be useful to limit
the thickness of the lens, and such patterns can be made and
applied in the present invention.
[0139] FIG. 26 illustrates an example of an electrode 300 formed in
the shape of a concave-concave asphere lens for controlling light
propagating through a waveguide, in accordance with one embodiment
of the present invention. In this example, the radius of curvature
of the front side 302 of the lens shape is smaller and oppositely
orientated than the radius of curvature of the back side 304. This
can be useful, for instance, where it is desired to match the front
side's 302 radius of curvature with a radius of curvature of a
preceding lens shape in the waveguide, or to match the back side's
304 radius of curvature with a radius of curvature of a subsequent
lens shape in the waveguide. Furthermore, aspherical shapes can be
utilized to reduce aberrations.
[0140] In another example, two of more lens shaped electrodes may
be placed in series or cascaded or otherwise arranged to achieve
various light beam manipulations, such as beam expansion, beam
compression, telescoping. Since the focusing and defocusing of
light through the waveguide can be controlled electronically
through the application of voltage to the electrodes (without any
mechanically moving parts), embodiments of the present invention
can be used to replace mechanical focusing devices. For instance, a
zoom function can be implemented by combining a focusing and
defocusing lens in series (i.e., combining the electrode shapes of
FIG. 21 with FIG. 22; or combining the electrode shapes of FIG. 23
with FIG. 24). Further, one or more lens shaped electrodes may be
placed in series or cascaded or otherwise arranged with one or more
electrodes having wedge/prism shapes or other non-normal interfaces
such as those shown in FIGS. 1-2 and 15-19.
[0141] FIG. 27 illustrates another example of an electrode 310 for
controlling the propagation of light through the waveguide, in
accordance with one embodiment of the present invention. In this
embodiment, the electrode 310 includes an opening or hole region
312 that defines at least one non-normal interface or curved or
lens shaped edge 314 relative to the direction 316 of propagation
of light 318 traveling through the waveguide. While in this example
the opening 312 defines a single wedge/prism shape, it is
understood that other shapes could be used as well, such as shapes
having non-normal interfaces or curves or lens shapes, for
instance, as shown in FIGS. 15-19 or 21-26, and that the electrode
may include multiple openings in series or cascaded. In this case,
when no voltage is applied to electrode 310, the index of
refraction n2 of the region adjacent the opening 312 is
approximately equal to the index of refraction of the region
adjacent the electrode; and as voltage is applied to the electrode
310, the index of refraction n1 of the region adjacent or proximate
the electrode 310 changes.
[0142] FIG. 28 illustrates an alternative embodiment wherein a
waveguide 320 utilizes an alignment layer 322 having two or more
areas or regions 324, 326 having different orientations that align
the liquid crystal material 328 in the adjacent cladding 330 so as
to form refractive shapes 332 within the liquid crystal material
328 for controlling light propagating through a waveguide 320, in
accordance with one embodiment of the present invention. In one
example and referring to FIGS. 28-30, the waveguide 320 can be
constructed in a manner similar to the embodiments described above
except that in place of one or more patterned electrodes, the
embodiments of FIGS. 28-30 have an alignment layer 322 with regions
324, 326 of patterned alignments and a pair of electrode layers
334, 336 or planes. Hence, the waveguide 320 of the example of FIG.
28-30 may include a substrate 338 acting as a lower electrode plane
336, a lower cladding 340, a core layer 342, an alignment layer 322
having the one or more regions 324, 326 defining various shapes, an
upper cladding 330 with liquid crystal material 328 therein, an
upper electrode plane 334, and a glass cover 344. The substrate
338, lower cladding 340, core 342, upper cladding 330 with liquid
crystal material 328 therein, and the glass cover 344 can all be
made as described above with reference to FIGS. 1-14. The upper
electrode 334 can be implemented as a conductive coating or
conductive layer as described above with reference to FIGS.
1-14.
[0143] On the alignment layer 322, the one or more areas or regions
324, 326 can define various shapes 332 in order to induce the
liquid crystal material 328 in the adjacent upper cladding 330 to
form various shapes when no voltage 346 is applied, such as shapes
332 having non-normal interfaces (such as one or more of the shapes
shown in FIGS. 1-2 and 15-19 or shapes having curves or lens shapes
such as one or more of the shapes shown in FIGS. 21-26).
[0144] In the example of FIG. 28, the alignment layer 322 of the
waveguide includes a first region 324 and a second region 326. In
this example, the second region 326 aligns the liquid crystal
materials 328 in the upper cladding with their long axis
perpendicularly orientated relative to the propagation direction
348 of light 350 traveling through the waveguide 320; and the first
region 324 defines a wedge or prism shape 332, wherein within the
first region 324, the liquid crystal materials 328 in the upper
cladding 330 are aligned with their long axis orientated in
parallel relative to the propagation direction 348 of light 350
traveling through the waveguide 320 (see FIGS. 29, 31).
[0145] In operation, when no voltage 346 is applied between the
upper electrode 334 and the lower electrode/substrate 336, the
index of refraction n1 of the second region 326 is greater than the
index of refraction n2 of the first region 324 for TE polarized
light traveling through the waveguide 320 (see FIGS. 29, 31). As a
voltage 346 is applied between the upper electrode 334 and the
lower electrode/substrate 336, the electric field of the applied
voltage 346 induces the liquid crystals 320 within the upper
cladding 330 to orient vertically (see FIGS. 30, 32), and therefore
for TE polarized light traveling through the waveguide 320, the
index of refraction n1 of the second region 326 is approximately
equal to the index of refraction n2 of the first region 324, and no
refraction or light bending occurs.
[0146] As with the other embodiments disclosed herein that use
patterned electrodes to induce portions of the liquid crystal
materials to form various refractive or lens shapes, the
embodiments of FIGS. 28-32 can be made using different
arrangements, liquid crystal alignments, or orders of layers as
desired.
[0147] FIG. 33 illustrates an example of operations for forming a
waveguide having an alignment layer with two or more areas or
regions having different orientations that induce or align the
liquid crystal material in the adjacent cladding to form refractive
shapes within the liquid crystal material for controlling light
propagating through a waveguide, in accordance with one embodiment
of the present invention. The shapes of the regions can include
shapes with non-normal interfaces, or curved or lens shaped
interfaces.
[0148] In FIG. 33 at operation 360, a waveguide is provided with a
core, upper cladding, and lower cladding, wherein liquid crystal
material is disposed within one of the claddings. As described
above, the liquid crystal material may be disposed within the upper
or lower cladding, and for purposes of this example, the liquid
crystal material will be described as being disposed within the
upper cladding. At operation 362, an upper electrode or plane is
provided, and at operation 364, a lower electrode or plane is
provided within the waveguide. In one example, the upper electrode
is formed as a conductive coating on the glass cover or as a layer
of conductive material. In one example, a conductive substrate
layer or other conductive layer is provided in the waveguide to act
as the lower electrode or ground plane.
[0149] At operation 366, at least one alignment layer is provided
to align the liquid crystal material in the upper cladding
proximate the core. In one example, the alignment layer has two or
more regions with differing alignments so that the liquid crystal
material adjacent the alignment layer is biased or oriented in a
desired orientation when no voltage is applied between the upper
electrode and the lower electrode. The shapes of the regions can
include, for instance, shapes with non-normal interfaces,
refractive shapes, prisms, wedges, curved or lens shapes such as
those described above.
[0150] As with the above described embodiments, the non-normal
interfaces, refractive shapes, curved or lens shapes of regions of
the alignment layer induce the liquid crystal material in the
adjacent cladding to form a corresponding shape wherein the index
of refraction of the formed shape is controllably dependent upon
the amount of voltage applied to the electrodes.
[0151] As to operation 366, one example of how a region or area of
the alignment layer can be patterned or made is by utilizing
regions of photo-aligned polyimide, such as by companies such as
Elsicon Inc., or other photo-aligned polymers or other general
photoalignable materials. Liquid crystal molecules in the adjacent
cladding will generally align according to the orientation of these
regions of polymer.
[0152] Specifically, the polymer may be spin-coated directly onto
the surface of the waveguide core, and such application may occur
in the same manner as how normal polymer would be applied to the
core. Polarized ultraviolet light may be applied to selected
regions of the polymer to create alignments within such regions.
The direction of polarization of the ultraviolet light determines
the director, or liquid crystal orientation or direction, i.e., the
alignment.
[0153] In order to create regions of patterned alignment, a first
mask can be created which would be placed directly above the
polymer to cover the polymer during exposure to ultraviolet light.
Patterns of opaque regions on the mask would cast shadows onto the
polymer, and therefore these dark regions would not be aligned. The
ultraviolet light source would then be turned off and the mask
removed.
[0154] A second mask that is a negative or inverse of the first
mask could then be placed directly above the polymer to cover the
polymer during a second exposure to ultraviolet light. For the
second exposure, the direction of polarization of the ultraviolet
light, with respect to the waveguide, is then rotated ninety
degrees. When the ultraviolet light is turned on during the second
exposure, the regions that were previously not exposed (and
therefore not aligned) are now aligned. Since the direction of
polarization of the ultraviolet light (with respect to the
waveguide) has been rotated ninety degrees, the alignment in these
regions will be rotated ninety degrees with respect to the
alignment outside of these regions. Using this method, various
regions on the alignment layer can be formed having different
alignments so that the polymer induces the liquid crystal material
in the adjacent cladding to align according to the polymer patterns
of the alignment layer.
[0155] Alternatively, in another example, a polymer can be applied
and uniformly buffed. A photoresist can then be applied and exposed
in the desired pattern. The photoresist is then removed in the area
of the pattern and the polyimide is buffed in a different or
orthogonal direction. The remaining photoresist is then
removed.
[0156] Another example of operation 366 to form a patterned or
aligned region or area is via etching microgrooves directly into
the top of the waveguide core. The width and distance between
adjacent microgrooves is chosen to be sufficiently small so that it
does not effect the propagation of the light in the core. Liquid
crystal molecules in the adjacent cladding will generally align
according to the orientation of these microgrooves.
[0157] To create microgrooves, in one example photo-resist may be
applied to the core and then cured using an interference pattern
between two short-wavelength beams. This creates a pattern of
closely spaced lines of photo-resist on the core. Standard etching
techniques are then used to remove a small amount of the core in
the regions that are not covered by the lines of photo-resist. The
photo-resist is removed, and a microgrooved pattern is left on the
core.
[0158] Two or more regions of microgrooves can be formed on the
alignment layer (or on the surface of the core), wherein each
region has a set of aligned microgrooves, and the alignment of a
first region differs from the alignment of a second region. This
can be done by masking techniques. Specifically, a patterned mask
can be inserted prior to exposing the photo-resist to the short
wavelength interference pattern. The photoresist will not be cured
in the regions that are shadowed by the mask. The short wavelength
light is turned off and the mask is removed. A negative of the
first mask is then inserted. The interference pattern created by
the short wavelength light is then rotated ninety degrees with
respect to the waveguide. The short wavelength light is then turned
on, and the exposed regions of the photo-resist are cured in
closely spaced lines, but these lines are now rotated ninety
degrees with respect to the previously cured lines. The waveguide
is then etched using standard techniques. The net result is two
regions, both with microgrooves, but the directions of the
microgrooves in one region is rotated ninety degrees with respect
to the direction of the microgrooves in the other region. Using
this technique, various regions on the alignment layer can be
formed having different alignments so that the microgrooves induce
the liquid crystal material in the adjacent cladding to align
according to the regions of microgroove patterns of the alignment
layer.
[0159] As another example, nano-imprint lithography techniques can
be used to create regions of patterned alignment. In this
technique, a pattern, such as the microgroove pattern described
above, can be used to imprint the pattern onto a softer
substrate.
[0160] At operation 368, in one example, it is provided that light
may be introduced into the waveguide core such that the evanescent
portion of the light wave passes through the cladding, which
contains the liquid crystal material (e.g., the upper cladding, in
one example). In one embodiment, for instance, a prism coupler or
butt-coupling or end-fire coupling technique or other conventional
method or device may be used to introduce light into the
waveguide.
[0161] At operation 370, a voltage is applied between the upper and
lower electrodes of operations 362-364 in order to change the index
of refraction of the upper cladding, which in this example contains
the liquid crystal material. As voltage is applied between the
upper and lower electrodes, an electric field is formed between the
upper and lower electrodes in order to control the orientation of
the liquid crystal material therebetween.
[0162] In operation 370, the liquid crystal material between the
upper electrode and the lower electrode is controllably reoriented
depending upon the amount of voltage applied, and such application
of voltage alters the index of refraction of such liquid crystal
material relative to light propagating through the waveguide. As
such, through the application of voltage between the upper and
lower electrodes, one or more shapes can be formed within the
liquid crystal material which in effect operate as prisms,
refractive elements, or lenses to bend, focus, defocus, or direct
light under the control of the applied voltage. At operation 372,
the applied voltage may be varied so as to controllably
refract/bend, focus or defocus light as it travels through the
waveguide and the evanescent portion of the light passes through
the liquid crystal material experiencing the influence of the
electric field of the applied voltage.
[0163] FIG. 34 illustrates an alternative embodiment wherein a
waveguide 380 utilizes a cladding 382 that includes at least two
regions 384, 386: a region 384 without liquid crystal material 388
and a region 386 with liquid crystal material 388. In one example,
the first region 384 may include a non-liquid crystal material,
such as but not limited to any of the materials that can be used to
create the lower cladding as discussed previously with respect to
FIGS. 1-14. In one example, this first region 384 is generally not
electro-optic, i.e., the index of refraction does not change with
respect to an applied electric field. The second region 386 may
comprise areas or refractive shapes or cavities 390 where the
non-liquid crystal material of the first region is not present or
is reduced in thickness so as to create cavities or chambers 390
into which liquid crystal material 388 is placed and the evanescent
wave of the guided light 389 will penetrate. In this manner,
dynamically voltage tunable refractive shapes 392 are constructed
by controlling the shape or area 390 in which the liquid crystal
388 may interact with the guided light 389 via the evanescent wave.
Of course, the cladding 382 with the cavity 390 with liquid crystal
material 388 therein could be the upper cladding 382 or the lower
cladding 394, depending on the implementation.
[0164] In one example and referring to FIGS. 34-36, a waveguide 380
can be constructed in a manner similar to the embodiments described
above except that in place of one or more patterned electrodes, the
embodiments of FIGS. 34-36 have an upper cladding 382 in which only
regions or areas 386 contain liquid crystal material. Hence, the
waveguide 380 of the example of FIG. 34-36 may include a substrate
396 acting as a lower electrode plane, a lower cladding 394, a core
layer 398, an alignment layer 400, an upper cladding 382 with a
region or area 386 with liquid crystal material 388 therein and a
region 384 with non-liquid crystal material therein, and an upper
electrode plane 402. A second alignment layer 404 may be provided
between the upper electrode 402 and the upper cladding 382, if
desired. A glass cover 406 may also be used if desired. The
substrate 396, lower cladding 394, core 398, upper cladding region
386 with liquid crystal material 388 therein, and the glass cover
406 can all be made as described above with reference to FIGS.
1-14. The upper electrode or plane 402 can be implemented as a
conductive coating or conductive layer as described above with
reference to FIGS. 1-14.
[0165] On the upper cladding 382, the one or more areas or regions
386 in which liquid crystal material 388 interacts with the guided
light 389 can define various shapes 392, such as refractive shapes
having non-normal interfaces (such as one or more of the shapes
shown in FIGS. 1-2 and 15-19 or shapes having curves or lens shapes
such as one or more of the shapes shown in FIGS. 21-26).
[0166] In the example of FIG. 34, the second region 386 may
comprise a wedge shape where the non-electro optic material of the
upper cladding 382 is absent and the core layer 398 is therefore
exposed. In this second area 386, an alignment layer 400 and liquid
crystal material 388 are disposed therein and may operate in a
fashion analogous to that previously discussed in reference to
FIGS. 1-15. In this particular example, the long axes of the liquid
crystal molecules 388 in the second region 386 are aligned so that
at low or zero voltage 408 their alignment direction is
predominantly parallel to the direction 410 of light 389
propagating through the waveguide 380 (see FIG. 35), although other
orientations are possible.
[0167] In operation and referring to FIGS. 34-38, when no voltage
408 is applied between the upper electrode 402 and the lower
electrode/substrate 396, the index of refraction n1 of the first
region 384 is different than the index of refraction n2 of the
second region 386 for TM polarized light traveling through the
waveguide (see FIGS. 35, 37). As a voltage 408 is applied between
the upper electrode 402 and the lower electrode/substrate 396, the
electric field of the applied voltage 408 induces the liquid
crystals 388 within the second region 386 of the upper cladding 382
to orient vertically (see FIGS. 36, 38), and therefore for TM
polarized light traveling through the waveguide 380, the difference
between the index of refraction n1 of the first region 384 and the
index of refraction n2 of the second region 386 is changed.
Depending on the index of refraction of the first region 384 (which
in this example is constant and not voltage tunable, but can be
chosen from a range of values), the degree or amount of refraction
of the waveguide 380 will change. In other words, since the
difference between n1 and n2 can be voltage tuned, the degree of
refraction can also therefore be voltage tuned. However, unlike the
embodiments using shaped electrodes, the refraction at zero voltage
will not generally be zero, unless the fixed index of region 384 is
deliberately chosen to equal the index of the liquid crystal 388 at
zero volts.
[0168] As with the other embodiments disclosed herein that use
patterned electrodes to induce portions of the liquid crystal
materials to form various refractive or lens shapes, the
embodiments of FIGS. 34-38 can be made using different arrangements
of layers, different liquid crystal alignments, or different orders
of layers as desired. Depending on the implementation, refraction
of TE or TM polarized light (or both) can be achieved.
[0169] FIG. 39 illustrates an example of operations for forming a
waveguide having a cladding layer with two or more areas or
regions, the first region having non-liquid crystal material and
the second region having liquid crystal material to form refractive
shapes within the cladding for controlling light propagating
through a waveguide, in accordance with one embodiment of the
present invention. The shapes of the regions can include refractive
shapes with non-normal interfaces, for example wedge or prism
shapes or curved or lens shaped interfaces. In the example of FIG.
39, a cavity or region with liquid crystal material is provided in
the upper cladding, although it could be provided in the lower
cladding.
[0170] In FIG. 39 at operation 420, a waveguide is provided with a
core, an upper cladding, and a lower cladding.
[0171] At operation 422, in one example, regions or areas of the
upper cladding are removed thereby forming shapes or areas in which
the core layer may be exposed. This may be achieved with standard
photolithographic techniques. For example, a photomask may be used
to cure a patterned photoresist on top of the upper cladding layer.
Etching techniques are then used to remove portions of the upper
cladding in regions where the photoresist has not been cured. The
upper cladding may be etched with a chemical process that only
removes the upper cladding material and not the core, which will
prevent the core from being etched into or etched through (etching
through the core would destroy the waveguide). Alternatively, the
upper cladding can be etched for a sufficient time to significantly
reduce the thickness of that region of upper cladding, but not
completely remove the non-liquid crystal cladding. Such a technique
can create regions into which the evanescent wave will penetrate.
As another alternative, a chemical stop layer may be applied
between the core and upper cladding layer. This chemical stop layer
will prevent etching into the core, and can be made sufficiently
thin so as to not adversely affect the optical properties of the
waveguide. Finally, the etched cavity region can be constructed so
as to provide an opening at the edge of the waveguide. This can
facilitate filling the chamber or cavity of the cladding with
liquid crystal material.
[0172] At operation 424, an alignment layer is provided for biasing
the liquid crystal material that will be disposed within the etched
cavity regions of the upper cladding. This can be accomplished by
the alignment techniques previously mentioned. However, since the
upper surface is no longer of uniform height (regions have been
etched away), application of an alignment layer can become more
challenging. For example, spin coating techniques (for application
of a polyimide or polymer layer) will tend to planarize the surface
and therefore be undesirably thick in the etched regions. One
technique to avoid this problem is to create the etched regions or
cavities such that they extend to the edge of the waveguide. The
waveguide can then be placed on a spin coater off-center, and
oriented so that excess material will have a path to be removed via
centrifugal forces of the spin coat process. Alternatively, oblique
deposition of SiO and/or SiO2 can provide an alignment layer, with
only minimal shadows created by the edges of the etched regions. As
another alternative, prior to applying the non-liquid crystal upper
cladding material, a microgroove alignment layer may be created
along the entire waveguide core via holographic lithography or
nano-imprint techniques. The non-liquid crystal upper cladding
would then be applied, and after etching away regions or cavity
areas to expose the core, the alignment layer would already be
present there.
[0173] At operation 426, an upper electrode or plane is provided.
This upper electrode or plane may also form the ceiling of the
chamber or cavity to be filled with liquid crystal. In one example,
the upper electrode is formed as a conductive coating on the glass
cover or as a layer of conductive material.
[0174] At operation 428, the chamber or cavity in the upper
cladding may be filled with liquid crystal material. With only one
opening, as depicted in the example of FIG. 34, this process may be
conducted under a vacuum. A drop of liquid crystal material placed
adjacent to the opening will wick into the chamber or cavity. This
chamber may be plugged with a standard glue after filling.
[0175] At operation 430, a lower electrode or plane is provided. In
one example, a conductive substrate layer or other conductive layer
is provided in the waveguide to act as the lower electrode or
ground plane.
[0176] At operation 432, in one example, light may be introduced
into the waveguide core such that the evanescent portion of the
light wave passes through the cladding that contains both the
regions with and without the liquid crystal material (e.g., the
upper cladding, in one example). In one embodiment, for instance, a
prism coupler or butt-coupling or endfire coupling technique or
other conventional method or device may be used to introduce light
into the waveguide.
[0177] At operation 434, a voltage is applied between the upper and
lower electrodes of operations 426-430 in order to change the index
of refraction of the sections or cavity areas of the upper cladding
which contain the liquid crystal material. As voltage is applied
between the upper and lower electrodes, an electric field is formed
between the upper and lower electrodes in order to control the
orientation of the liquid crystal material therebetween.
[0178] In operation 436, the liquid crystal material in the shaped
cavities between the upper electrode and the lower electrode is
controllably reoriented depending upon the amount of voltage
applied, and such application of voltage alters the index of
refraction of such refractive shapes of liquid crystal material
relative to light propagating through the waveguide. Such shapes
that contain the liquid crystal material in effect operate as
prisms, refractive elements, or lenses to bend, focus, defocus, or
direct light under the control of the applied voltage. At operation
436, the applied voltage may be varied so as to controllably
refract/bend, focus or defocus light as it travels through the
waveguide and the evanescent portion of the light passes through
the liquid crystal material experiencing the influence of the
electric field of the applied voltage.
[0179] As explained above, embodiments of the present invention may
be used in various applications. FIGS. 40-42 illustrate two
examples of such applications. In FIG. 40, a barcode scanner or
laser print head 440 is formed utilizing a waveguide 442 having a
lens shaped electrode 444 and a plurality of prism shaped
electrodes 446. In this example, a laser light source 448 passes a
laser beam 450 through a lens 452, which directs the laser beam 450
into the waveguide 442, and within the waveguide 442, depending
upon the voltages 455 applied to the patterned electrodes 444, 446
therein, the angle at which the light beam 450 exits the waveguide
442 is controlled. Hence, the output beam 454 of light can be
dynamically steered to scan or read a barcode 456, and the
reflected light can be read by optical receiving devices such as
photodiodes (not shown). In this example, the optical portion 458
of the barcode scanner 440 does not use any moving parts. Instead,
the direction of the output light beam 454 is controlled by the
voltages 455 applied to the patterned electrodes 444, 446.
[0180] FIG. 41 illustrates another example of an electrode for
controlling the propagation of light through a waveguide, in
accordance with one embodiment of the present invention. In this
embodiment, the electrode 460 includes multiple slits, gaps, or
slots, 462 in the electrode 460. In one example, the electrode 460
includes multiple fingers or rectangles 464, or a comb structure,
where each rectangle 464 is separated from the adjacent rectangle
by a small space or slit 462. The rectangles 464 are electrically
connected along one end 466; for example, in FIG. 41 the rectangles
464 are connected along the bottom edge 468 of the electrode 460.
Furthermore, multiple points 470, 472, 474 are provided for
connection of multiple voltages 476, 478, 480 to this electrode
460. If the voltages 476-480 applied to all of the connection
points 470-474 are the same, then this electrode 460 acts as a
uniform plane, which can be used to change the index of refraction
of liquid crystal material under, proximate, or otherwise adjacent
to this electrode 460. Alternatively, the voltages 476-480 applied
to the different connection points 470-474 may be chosen to be
different from one another. In this case, a voltage gradient will
exist from one electrode connection point 470, 472, or 474 to
another. The magnitude of this voltage gradient will be dependent
on the magnitude of the differences in the voltages 476-480 applied
to the different connection points 470-474. The electrode 460 can
be designed to have a sufficiently high resistance, such that a
voltage gradient or difference can be maintained with only limited
current flowing through the electrode 460. This voltage gradient,
which exists between the connection points 470-472-474, will be
extended, via the rectangular shapes 464, to cover a region of a
waveguide over which this electrode pattern extends. In this way, a
gradient in the index of refraction of a waveguide can be created
and dynamically controlled, by controlling the different voltages
476-480 at the different connection points 470-474. Although FIG.
41 shows an electrode 460 with three connection points 470-474, it
is understood that any number of connection points can be
utilized.
[0181] A waveguide may be formed utilizing any of the structures
previously discussed, wherein an out-coupling grating is included
in the waveguide out-coupling gratings can be constructed by
deliberately creating a periodic variation in the index of
refraction within a waveguide. This may be done, for example, by
providing a core layer with periodic variations in its thickness,
as is shown in FIGS. 42-44. Alternatively, either the core or one
of the claddings may be constructed so as to have a periodically
varying index of refraction (e.g., the core layer may be doped with
materials having different indexes of refraction. The spacing or
pitch between index variations may be chosen so that light will be
directed out of the waveguide. In one example, the angle at which
the light is out-coupled, (e.g., the angle of propagation of the
light that leaves the waveguide) is dependent in part on the pitch
or spacing of the out-coupling grating. As recognized by the
present inventors, by dynamically changing this pitch, a waveguide
can be formed so that the angle at which the light leaves the
waveguide can be dynamically changed.
[0182] In one example, an out-coupling grating can be combined with
a patterned electrode of FIG. 41 to control the angle at which
light leaves a waveguide. For example, in FIGS. 42-44, a waveguide
500 may include an out-coupling grating 501 formed by a core 502
having a periodically varying thickness. A cladding 504 having
liquid crystal material and an electrode 508 with slots 510 (e.g.,
FIG. 41) may be placed on top of the cladding 504. A lower
substrate 512 provides both structural support for the waveguide
500 and the electrical ground for all voltages applied between the
connection points and the substrate 512. The sub-cladding 514
(e.g., lower cladding), core 502, liquid crystal upper cladding
504, and alignment layers 516 can be constructed as discussed
previously.
[0183] In order to construct an out-coupling grating 501, in one
example a pattern of grooves 520 can be created in the lower
cladding 514 prior to application or formation of the core layer
502. This groove pattern 520 may be constructed with
photo-lithographic techniques. After the core layer 502 is applied,
a chemical-mechanical polishing step can be used to smooth out the
top surface of the core layer 502. Also, the depth and spacing of
the out-coupling grating can be tapered from one side (e.g.,
entrance) to the other (e.g., distal) of the waveguide 500. Such
tapering techniques can be utilized to alter or condition the shape
of the out-coupled light beam.
[0184] Light 522 is input into the waveguide 500, and the light
output 524 leaves the waveguide 500 due to the out-coupling grating
501. The angle at which output light 524 leaves the waveguide 500
depends in part on the voltages 530-534 V3, V4, V5 applied to the
electrode 508.
[0185] As with FIG. 41, the electrode 508 of FIGS. 42-44 may have
various points at which different voltages may be applied. In the
example shown in FIG. 41, three voltages (530, 532, 534) are
represented as V3, V4, and V5.
[0186] It is understood depending upon the implementation, a
waveguide can be formed with an out-coupling grating 501 or
variation thereof in combination with one or more different
electrodes, including but not limited to a comb-type electrode
(such as 460 or 508), a prism or wedge shape electrode, a lens
shaped electrode, or an electrode which has a plane or shape.
Conversely, an electrode such as electrode 460 can be used in a
waveguide that has a core layer as described with reference to
FIGS. 1-30 or a waveguide or core layer having an out-coupling
grating such as grating 501 of FIGS. 42-44.
[0187] Referring to FIG. 42, if no voltage is applied to the
patterned electrode 508 (e.g., V3=V4=V5=0), then the index of
refraction for the liquid crystal material 506 underneath the
electrode 508 will be uniform. The out-coupling grating 501 formed
by the core 502 will then direct the light 524 out of the waveguide
500 at an angle that is determined by the pitch of the out-coupling
grating 501. As shown in FIG. 42, this angle will be constant along
the length of the grating 501. When light 522 first enters the core
502 with out-coupling region 501, it will begin to leave the
waveguide 500 at an angle that is determined by the pitch of the
grating 501. As the light 522 propagates along the length of the
out-coupling grating 501, the light beam 524 will exit the
waveguide 500 until all of the light 524 has been out-coupled or
the out-coupling grating 501 ends.
[0188] Shown in FIG. 43 is the case where a high-voltage has been
applied to all of the connection points (e.g., V3, V4, V5) of
electrode 500. In this case, the index of retraction of the liquid
crystal material 506 in cladding 504 will be uniform, but different
than the index of refraction that corresponds to zero voltage in
FIG. 42. The change in the index of refraction of the upper
cladding 504 will alter the index of refraction for the guided
light, as has been discussed previously, and changes in the
effective pitch of the out-coupling grating 501. Since this pitch
is effectively different, the angle at which light 524 exits or is
out-coupled from the waveguide 500 will therefore also be
different. In this way the angle at which light 524 exits the
waveguide 500 may be controlled by controlling the voltage V3, V4,
V5 applied to the patterned electrode 508. In the example of FIGS.
42-43, the light 522 is assumed to be TM polarized, in which case
higher voltage will direct the light 524 out of the waveguide 500
at a steeper angle relative to the waveguide normal. For lower
voltage and TM polarized light, the output angle of light 524 with
respect to the waveguide normal will be smaller. In this way, one
may dynamically control the angle of light 524 leaving the
waveguide 500 by controlling the magnitude of applied voltage
(e.g., V3, V4, V5).
[0189] Shown in FIG. 44 is the case where the voltages (e.g., V3,
V4, V5) applied to different connection points of electrode 500 are
not the same. Specifically, shown in FIG. 44 is the case where the
voltage V3 is zero, the voltage V4 is intermediate, and the voltage
V5 is higher than V4. In this case, the index of refraction of the
liquid crystal material 506 underneath the electrode 508 is
varying. This varying index of refraction will result in a varying
out-coupling angle of light 524, as is shown in FIG. 44 for TM
polarized light 522. By controlling the magnitude of the
differences between the voltages V3, V4, V5, the angle at which the
light 524 leaves the waveguide 500 can be controlled as well as the
focusing of the out-coupled light 524. Shown in FIG. 44 is an
example where the voltage differences between V3, V4, V5 are chosen
so that the out-coupled light 524 is coming to a focus. Therefore,
not only can the angle of the out-coupled light 524 be dynamically
controlled with the voltages (e.g., V3, V4, V5), but also the
focusing properties of the light 524.
[0190] In FIGS. 45-46, an optical read/write head 550 for a CD/DVD
player includes a waveguide 552 having a plurality of patterned
electrodes 554, 556, 558 for controlling light, in accordance with
an embodiment of the present invention. FIGS. 45-46 are an
adaptation of a figure in S. Ura, T. Suhara, H. Nishihara, and J.
Koyama, An Integrated-Optic Disk Pickup Device, IEEE J. Lightwave
Technology, LT-4, Vol. 7, pages 913-918, (1986), the disclosure of
which is incorporated by reference in its entirety. In the example
of FIGS. 45-46, the device 550 is dynamic due to the liquid crystal
waveguide 550 and its electrode elements 554-558. In this example,
three patterned electrodes 554, 556, 558 are provided for dynamic
steering and focusing. Application of voltages V1 and V2 steers and
focuses the beam 560 in the dimension of the waveguide plane. The
electrodes 554, 556 are a focusing or lens shape (554) and a
steering or prism shape (556). The voltages V3, V4, and V5 are
applied to a patterned electrode 558, similar to as shown in FIG.
41. In FIGS. 45-46, this electrode 558 is placed above an
out-coupling grating (562). As discussed above, the ratios and
magnitude of voltages V3, V4, and V5, give both steering and
focusing of light 564 out of the waveguide 552. In this example,
the out-coupling grating 562 also serves as an in-coupling grating.
Light that is directed out of the waveguide will hit an optical
storage medium (such as a compact disc), and the light that is
reflected off of that medium will be re-coupled back into the
waveguide. This is the return beam. Shown in FIGS. 45-46 is an
integrated optical lens 566, which serves to both collimate the
light from the laser diode 568 and also to focus the return light
onto detection photodiodes 570. The detection photodiodes 570 are
actually photodiode pairs. Shown in FIG. 46 is a beamsplitting
grating 572, which splits the return beam into two parts that focus
the returned light onto the photodiodes 570. If the surface of the
optical storage medium is too close, the beams fall towards the
outer photodiodes of pairs 570. A tracking error 574 shifts
intensity between the upper and lower photodiode pairs 570. The
circuitry 576 of FIG. 46 shows an example of how the focusing,
tracking, and signal from the CD or other optical storage media can
be amplified and measured.
ELECTRODE EXAMPLE ONE
[0191] Described below is one example of a liquid crystal waveguide
in which the waveguide provides for an increased modulation index,
and this is described as an example only. It is understood that
this example is provided for illustrative purposes only, and does
not limit the scope of embodiments of the present invention. In
this example, a waveguide device may be formed utilizing a heavily
p-doped silicon wafer, with both sides polished, as the lower
electrode. Upon the p-doped silicon wafer, a thermally oxidized
lower cladding can be grown with a thickness of 2.+-.0.05 microns.
The lower cladding refractive index at a wavelength of 1550
nanometers was 1.445.+-.0.001 as measured by a broadband
ellipsometer. A SiOxNy guide layer or core was applied over the
lower cladding by plasma enhanced chemical vapor deposition to a
thickness of 800.3.+-.7 nanometers. The ratio of Ox to Ny in SiOxNy
was adjusted during the deposition process to create a core with a
refractive index of 1.811.+-.0.005 at a wavelength of 633
nanometers and a refractive index of 1.793.+-.0.005 at a wavelength
of 1550 nanometers. Identical coatings were applied to both sides
of the wafer in order to balance stresses, and therefore mitigate
warping or bending of the wafer. These stresses are a result of the
plasma enhanced chemical vapor deposition process. A
rectangle/parallelogram was created as the upper electrode using
standard photolithographic techniques, specifically, standard
masking and chemical etching pattern the ITO on the glass cover
plate.
[0192] Once complete, the wafer was diced into smaller 10
millimeter by 25 millimeter parts. Each diced part was then coated
with an alignment film approximately 120 angstroms in thickness.
The alignment film was used to create the homeotropic orientation
of the liquid crystal upper cladding. The film was produced by spin
coating an 8:1 mixture of Nissan polyimide varnish solvent # 26 to
Nissan polyimide type 1211 filtered at 0.2 microns at 2500 rpm. The
same spin coating process was performed on the cover plate, which
was made of 0.7 millimeter thick 1737 corning float glass coated on
one side with an indium tin oxide (ITO) film to produce the 100
ohms/square conductive layer used for the upper electrode.
[0193] Once both the wafer and the cover glass were coated, the
polyimide was imidized by baking in an oven at 200 degrees celsius
for approximately 1 hour. The polyimide coatings were mechanically
buffed with a dense piled cloth to induce preferential alignment
along the light wave propagation direction of the waveguide. The
liquid crystal upper cladding layer was formed by spacing the
ground plane 1737 glass window from the diced wafer parts with
5-micron borosilicate glass spacers immersed in an ultra-violet
curing adhesive Norland 68. Approximately 1-millimeter dots of the
spacing mixture were placed at the four corners that created the
cell gap for the liquid crystal to be disposed therein. The cover
plate was attached to the rest of the waveguide so as to create an
anti-parallel alignment layer on the waveguide core. The cell gap
was then exposed to 365 nanometer light until fully cured. Straight
Norland 68 was used to backfill via capillary action the remaining
exposed edges making up the cell gap. Two 1-millimeter openings
were left, one on each opposite side on the edges 90 degrees to the
buff direction. MBBA liquid crystal, obtained from Aldrich Chemical
Co., was then introduced to one of the two edge openings and
allowed to fill the cell gap via capillary force. Once filled, the
holes were plugged by using Norland UVS-91 visible-uv curing
adhesive. Wires were then attached to the upper electrode and lower
electrode using conductive epoxy.
[0194] In this example, operation of the waveguide included
coupling light into and out of the waveguide by means of gadolinium
gallium garnet GGG 30-60-90 prisms. Equal amounts of TE and TM
light were introduced into the TE0 and TM0 modes of the waveguide.
Amplitude modulated 15 KHz square-wave drive voltages were applied
to change the TM phase relationship to TE. To measure this change
in phase relationship, a 45-degree polarizer prism was used to
interfere the TE and TM light.
[0195] Table 1 shows hypothetical calculations of Beam Deflection
(in degrees) as a function of applied voltage. The modulation
index, which is the difference between n2 and n1, is experimental
data as different voltages are applied to a waveguide made
according to this example, with a wavelength of light of 1320 nm.
Using this experimental modulation index data, a theoretical beam
deflection can be calculated using Snell's law with the assumption
that light is passed through a prism or wedge or triangular shaped
electrode having a right angle and a small angle of 8.44
degrees.
1TABLE I Theoretical Beam Deflection Theoretical Volts Modulation
Beam Deflection (RMS) Index Change (.DELTA.n) (degrees) 3.7 0.00015
-0.01521 7.9 0.001353 0.248549 9.7 0.001954 0.38367 12.2 0.002706
0.555834 14 0.003308 0.696327 15.9 0.003909 0.839424 17.8 0.00451
0.985276 19.5 0.004961 1.096573 22.7 0.005713 1.28593 26 0.006615
1.520026 28.5 0.007216 1.680617 32 0.007968 1.886918 37.4 0.009321
2.275752 45.7 0.010374 2.596174 50 0.010825 2.739055 59.3 0.011877
3.087396 72.5 0.01308 3.515909 90 0.014282 3.985982 92.5 0.014433
4.048325 110 0.015335 4.443064 125 0.015936 4.729873 129 0.016086
4.805172 160 0.016989 5.295375 181 0.01744 5.572446 212.5 0.018041
5.991477 246 0.018492 6.362253 326 0.019244 7.220316 358 0.019394
7.48663
ELECTRODE EXAMPLE TWO
[0196] Described below is one example of a liquid crystal waveguide
in which the waveguide was designed to provide for approximately
28.7 degrees in beam steering, and this is described as an example
only. It is understood that this example is provided for
illustrative purposes only, and does not limit the scope of
embodiments of the present invention. In one example, a waveguide
beam steering device may be formed utilizing a heavily p-doped
silicon wafer, with both sides polished, as the lower electrode.
Upon the p-doped silicon wafer, a thermally oxidized lower cladding
can be grown with a thickness of 2.16.+-.0.05 microns. The lower
cladding refractive index at a wavelength of 633 nanometers was
1.458.+-.0.001 as measured by a broadband ellipsometer. A
stoichiometeric Si3N4 guide layer or core was applied over the
lower cladding by low-pressure chemical vapor deposition to a
thickness of 314.+-.1 nanometers. The Si3N4 was deposited to create
a core with a refractive index of 2.010.+-.0.005 at a wavelength of
633 nanometers. The p-doped silicon wafer with the applied coating
was then chemically and mechanically polished to create an average
surface roughness of 4.+-.0.8 angstroms while creating a final core
thickness of 286.+-.1 nanometers. Identical coatings were applied
to both sides of the wafer in order to balance stresses, and
therefore mitigate warping or bending of the wafer. These stresses
are a result of the low-pressure chemical vapor deposition
process.
[0197] In this example, a pair of upper electrodes were formed
wherein each electrode had a plurality of refractive prism-like
shapes in series, such as shown in FIG. 18. In particular for each
electrode, ten (10) triangle elements were designed using an index
modulation of 0.02, 125-micron beam waist, and a constant triangle
base size. Each electrode was etched into the cover plate by
standard photolithographic techniques. Specifically, standard
masking and chemical etching techniques were used to pattern the
ITO on the glass cover plate.
[0198] Table 2 below shows the coordinates of a 20-micron wide line
of demarcation defining the space between the triangular shaped
electrodes for this example (see also FIG. 18).
2TABLE 2 Dimensions of 2 Electrodes X Dimension Y Dimension Microns
Microns 0 250 1000 -261 2000 294 3000 -350 4000 428 5000 -528 6000
650 7000 -794 8000 961 9000 -1150 10000 1361 11000 -1594 12000 1849
13000 -2127 14000 2426 15000 -2748 16000 3092 17000 -3458 18000
3847 19000 -4257 20000 4690
[0199] The wafer (having a conductive substrate, lower cladding,
and core) was diced into smaller 20 millimeter by 40 millimeter
parts. Each diced part was then coated with an alignment film
approximately 120 angstroms in thickness. The alignment film was
used to create the homeogeneous orientation of the liquid crystal
upper cladding. The film was produced by spin coating an 8:1
mixture of Nissan polyimide varnish solvent # 21 to Nissan
polyimide type 2170 filtered at 0.2 microns at 3000 revolutions per
minute.
[0200] The same spin coating process was performed on the cover
plate (having the two upper electrodes). The glass cover was made
of 1.1 millimeter thick 1737 corning glass coated on one side with
an indium tin oxide (ITO) film to produce the 100 ohms/square
conductive layer used for the upper electrodes.
[0201] Once both the wafer (with the lower cladding and core) and
the cover glass (with the two upper electrodes) were coated, the
polyimide coatings were imidized by baking in an oven at 200
degrees Celsius for approximately 1 hour. The polyimide coatings
were mechanically buffed with a dense piled cloth to induce
preferential alignment along the light wave propagation direction
of the waveguide.
[0202] The cell, into which the liquid crystal upper cladding may
be contained, was formed by spacing the cover plate (e.g., 1737
glass window) from the diced wafer parts with 5-micron borosilicate
glass spacers immersed in a ultra-violet curing adhesive Norland
68. On the bottom side of the coverplate is the patterned
electrode, in this example. Approximately 500-micron dots of the
spacing mixture were placed at the four corners of the wafer
(having the lower cladding and core) to create the cell gap for the
liquid crystal to be disposed therein. The cover plate was attached
to the wafer so as to create an anti-parallel alignment layer on
the waveguide core and positioned such that the cover plate distal
edge corresponding to the beam steerer output was aligned over the
distal output edge of the waveguide. The cell gap was then exposed
to 365 nanometer light until fully cured. Straight Norland 68 was
used to backfill, via capillary action, the remaining exposed edges
making up the cell gap. Two 3-millimeter openings were left, one on
each opposite side on the edges 90 degrees to the buff direction.
MLC-6621 liquid crystal, obtained from EMD Chemicals, Inc., was
then introduced to one of the two edge openings and allowed to fill
the cell gap via capillary force. Once filled, the holes were
plugged by using Norland UVS-91 visible-uv curing adhesive. Once
fully cured the output edge of the assembled device was polished
utilizing diamond impregnated polishing pads supplied by Ultratec
Manufacturing, and the final polish was performed using 0.2 micron
diamond. Braided wires of AWG were then attached to the two upper
electrodes and one lower electrode using conductive epoxy.
[0203] Operation of the waveguide included coupling 780 nanometer
light into the waveguide by means of a gadolinium gallium garnet
GGG 30-60-90 prism. TM light was introduced into the TM0 mode of
the waveguide.
[0204] A simple switching circuit was used to selectively apply a
voltage to electrode 1 or electrode 2, (see FIG. 18 and Table 3).
Amplitude modulated 6 KHz square-wave drive voltages were applied
to the selected electrode to change the index of refraction of the
region of the waveguide under the selected electrode. To measure
the beam deflection change as a function of applied voltage, a
silicon CCD video camera was used to visually map the scattered
propagation streak within the waveguide. The experimental results
are shown in Table 3.
3TABLE 3 Voltage Voltage Electrode #1 Electrode #2 Deviation Angle
(RMS Volts) (RMS Volts) (Deg) 0 0 0 22 0 3.8 26 0 4.7 46 0 7 93 0
9.2 139 0 11.6 190 0 13 230 0 13.5 274 0 13.5 363 0 13.7 0 0 0 0 22
-3.4 0 26 -6.4 0 46 -6.9 0 93 -9.1 0 139 -10 0 190 -14.1 0 230
-14.8 0 274 -14.8 0 363 -15
[0205] As shown in Table 3, approximately 28.7 total degrees of
steering was achieved in this example with an applied voltage of
363 volts RMS. For a voltage of 22 volts RMS, 7.2 total degrees of
steering were realized.
[0206] Embodiments of the present invention may experience swapping
of energy between the fundamental TE and TM waveguide modes at a
particular value of applied voltage. As stated previously, for
liquid-crystal molecular alignment parallel to the propagation
direction of light, the effective index for TM polarized light
decreases as a voltage is applied and the effective index of TE
polarized light is unchanged. It is possible, for certain waveguide
designs, that at a particular value of the voltage the effective
indices of TM and TE polarized light will become equal. In this
case the two modes are phase matched and energy can swap from the
TM mode into the TE mode and visa versa. For devices with molecules
orthogonal to the light propagation vector, the TE index increases
as the TM index decreases and phase matching at a particular
voltage can also occur. In many applications it may be desired to
avoid such TE and TM mode crossings.
[0207] In one example, TM/TE crossings may be avoided by increasing
the index of the guide layer. For planar optical waveguides with
isotropic claddings, the index for TE polarized light is preferably
greater than the index for TM polarized light. Furthermore, an
increase of the index of the guide layer increases the separation
between the indices for TE and TM polarized light. When the
separation between the indices for TE and TM polarized light
becomes substantially large compared to index modulation of the LC
waveguide .DELTA.n, then TE and TM crossings are avoided.
[0208] An example of an LC waveguide without TE and TM crossings is
an LC waveguide with the guide layer replaced with a 0.58 micron
layer of silicon nitride prepared by plasma-enhanced chemical vapor
deposition. The refractive index of silicon nitride at a wavelength
of 1.32 microns is about 2.0. Other suitable guide layers include
stoichiometric silicon nitride prepared by low-pressure chemical
vapor deposition and titianium pentoxide. A device of this design,
with the LC molecules aligned perpendicular to the propagation
vector, was shown to exhibit a tunable birefringence (the
difference between the TE index and the TM index) of 0.035 at a
wavelength of 1.32 microns, with no evidence of TE and TM
crossings. The modulation indices of TM and TE polarized light were
approximately 0.02 and 0.015, respectively.
[0209] In some examples, nematic liquid crystals may be driven with
a voltage source with a very low DC component, such as an AC square
wave. The fast response of the liquid-crystal molecules in
proximity to the guide layer can lead to temporal transients in the
modulation index of the LC waveguide during the finite transition
times of the square wave. In some examples transients in the
modulation index may not be desired. Since the fastest response
times for the LC molecules can be associated with strong molecular
restoring forces and high operational voltages, one example of how
to reduce the transients is to reduce the operational voltage. In
Table 2, the transients operate in time scales of several 10 s of
microseconds for operational voltages above 50 Vrms. For many
applications it is also desirable to reduce the operational
voltages in order to simplify the driving electronics.
[0210] One example that may reduce the operational voltage is to
reduce the polar anchoring energy of the liquid-crystal molecules
to the alignment layer. Alignment layers that produce homeotropic
alignment have lower polar anchoring energies than for buffed
polyimides that produce planar alignment. In the electrode example
given above, approximately 70% of the total device stroke occurred
below 50 Vrms. Other LC alignment methods known to have lower polar
anchoring energies than buffed polyimide include photo-aligned
polyimides and polymers, angle-deposited SiO and SiO2, non-polar
polymers, and the use of surfactant-modified liquid crystals.
[0211] A second method to reduce transients in the modulation index
may be to increase the frequency of the voltage source. The use of
driving frequencies above 20 kHz at 50 Vrms often is aided by the
use of liquid crystal materials with very low conductivity or a
large voltage-holding ratio. The liquid crystal MBBA exhibits a low
conductivity as do superfluorinated liquid-crystal materials.
[0212] By combining the effects of reduced polar anchoring energy
with a high drive frequency, transients in the modulation index can
generally be reduced to a desired or negligible level.
[0213] A way of achieving pure TE modulation is to use smectic A*
liquid-crystal materials exhibiting the electroclinic effect. These
materials rotate about an axis containing the electric field vector
giving pure TE modulation and leaving TM polarized light
unaffected. This configuration has the benefits of low DC voltages,
and completely eliminates any possibility of transients in the
modulation index. However, the modulation index may be less because
the directors typically switch less than 90.degree.. Smectic A
materials also tend to have more restricted temperature ranges than
nematic materials and their development is less mature.
[0214] Accordingly, it can be seen that embodiments of the present
invention provide for dynamic electronic control of light as it
propagates through the waveguide. Embodiments of the present
invention could be replacements for widespread applications such as
retail store barcode scanners, CD/DVD optical read/write heads,
optical/holographic datastorage, telecommuncations optical
switches, bio-sensing (i.e., lab-on-a-chip) applications, optical
computer backplanes, for example. In addition to the beam steerer
applications, the tunable lens designs could permit electro-optic
zoom lenses, selective detection for lab-on-a-chip biosensors,
tunable collimation lenses for fiber to waveguide couplers, for
example.
[0215] Embodiments of the present invention may be used in
conjunction with conventional digital and analog circuitry, either
separately or integrated on a single integrated circuit. For
instance, the voltage applied to one or more patterned electrodes
may be controlled by a microprocessor or other logic or
programmable logic devices, and such logic may be included on the
same integrated circuit with the waveguide.
[0216] While the methods disclosed herein have been described and
shown with reference to particular operations performed in a
particular order, it will be understood that these operations may
be combined, sub-divided, or re-ordered to form equivalent methods
without departing from the teachings of the present invention.
Accordingly, unless specifically indicated herein, the order and
grouping of the operations is not a limitation of the present
invention.
[0217] It should be appreciated that reference throughout this
specification to "one embodiment" or "an embodiment" or "one
example" or "an example" means that a particular feature, structure
or characteristic described in connection with the embodiment may
be included, if desired, in at least one embodiment of the present
invention. Therefore, it should be appreciated that two or more
references to "an embodiment" or "one embodiment" or "an
alternative embodiment" or "one example" or "an example" in various
portions of this specification are not necessarily all referring to
the same embodiment. Furthermore, the particular features,
structures or characteristics may be combined as desired in one or
more embodiments of the invention.
[0218] Similarly, it should be appreciated that in the foregoing
description of exemplary embodiments of the invention, various
features of the invention are sometimes grouped together in a
single embodiment, figure, or description thereof for the purpose
of streamlining the disclosure and aiding in the understanding of
one or more of the various inventive aspects. This method of
disclosure, however, is not to be interpreted as reflecting an
intention that the claimed inventions require more features than
are expressly recited in each claim. Rather, as the following
claims reflect, inventive aspects lie in less than all features of
a single foregoing disclosed embodiment, and each embodiment
described herein may contain more than one inventive feature.
[0219] While the invention has been particularly shown and
described with reference to various embodiments thereof, it will be
understood by those skilled in the art that various other changes
in the form and details may be made without departing from the
spirit and scope of the invention.
* * * * *