U.S. patent application number 10/119570 was filed with the patent office on 2004-11-04 for depolarizer.
Invention is credited to Guo, Qingdong, Li, Wei-Zhong.
Application Number | 20040218845 10/119570 |
Document ID | / |
Family ID | 28789942 |
Filed Date | 2004-11-04 |
United States Patent
Application |
20040218845 |
Kind Code |
A1 |
Li, Wei-Zhong ; et
al. |
November 4, 2004 |
DEPOLARIZER
Abstract
An optical depolarizer includes a non-reciprocal
combination-device, a birefringent block, and a reflector. The
non-reciprocal combination-device has a principal direction and
includes a first birefringent wedge, a second birefringent wedge,
and a non-reciprocal rotating element. The non-reciprocal rotating
element can be a Faraday rotator. The birefringent block is
optically coupled to the second birefringent wedge. The reflector
is optically coupled to the birefringent block. The optical
depolarizer can include a lens that is optically coupled to the
first wedge. The optical depolarizer can include a capillary for
holding at least a PM optical fiber and an output optical
fiber.
Inventors: |
Li, Wei-Zhong; (San Jose,
CA) ; Guo, Qingdong; (Sunnyvale, CA) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
3300 DAIN RAUSCHER PLAZA
MINNEAPOLIS
MN
55402
US
|
Family ID: |
28789942 |
Appl. No.: |
10/119570 |
Filed: |
April 9, 2002 |
Current U.S.
Class: |
385/11 |
Current CPC
Class: |
G02B 6/2746
20130101 |
Class at
Publication: |
385/011 |
International
Class: |
G02B 006/00 |
Claims
What is claimed is:
1. An optical depolarizer comprising: a non-reciprocal
combination-device having a principal direction including (a) a
first birefringent wedge having a first optical axis perpendicular
to the principal direction, (b) a second birefringent wedge having
a second optical axis perpendicular to the principal direction, the
second optical axis forming a first angle with respect to the first
optical axis, and (c) a non-reciprocal rotating element optically
coupled between the first and the second birefringent wedge and
adapted to rotate a polarization of light passing therethrough by a
second angle; a birefringent block optically coupled to the second
birefringent wedge, the birefringent block having a third optical
axis perpendicular to the principal direction, the third optical
axis forming a third angle with respect to the second optical axis;
and a reflector optically coupled to the birefringent block.
2. The optical depolarizer of claim 1 further comprising a lens
optically coupled to the first wedge.
3. The optical depolarizer of claim 2 further comprising a
capillary for holding at least a PM optical fiber and an output
optical fiber proximate to the lens such that, light exiting from
the PM optical fiber passes through the lens and enters the
non-reciprocal combination-device in an input direction with a
first polarization, and light exiting from the non-reciprocal
combination-device in the reverse principal direction passes
through the lens and enters the output optical fiber.
4. The optical depolarizer of claim 2 further comprising a
capillary for holding at least a first and a second PM optical
fiber, and an output optical fiber proximate to the lens such that,
light exiting from the first PM optical fiber passes through the
lens and enters the non-reciprocal combination-device in a first
input direction with a first polarization, and light exiting from
the second PM optical fiber passes through the lens and enters the
non-reciprocal combination-device in a second input direction with
a second polarization, and light exiting from the non-reciprocal
combination-device in the reverse principal direction passes
through the lens and enters the output optical fiber.
5. The optical depolarizer of claim 1 wherein the first angle is
substantially 45 degrees and the second angle is substantially 45
degrees.
6. The optical depolarizer of claim 1 wherein the third angle is
substantially 45 degrees.
7. The optical depolarizer of claim 1 wherein the non-reciprocal
rotating element is a Faraday rotator.
8. An optical depolarizer comprising: a non-reciprocal
combination-device having a principal direction including a first
birefringent wedge having a first optical axis, a second
birefringent wedge having a second optical axis, and a
non-reciprocal rotating element, the non-reciprocal
combination-device configured at least for enabling (1) light
entering the first birefringent wedge as an e-ray in a first input
direction to exit from the second birefringent wedge as an o-ray in
the principal direction, (2) light entering the first birefringent
wedge as an o-ray in a second input direction to exit from the
second birefringent wedge as an e-ray in the principal direction
(3) light entering the second birefringent wedge as an e-ray in a
reverse principal direction to exit from the first birefringent
wedge as an e-ray in the reverse principal direction, and (4) light
entering the second birefringent wedge as an o-ray in the reverse
principal direction to exit from the first birefringent wedge as an
o-ray in the reverse principal direction; a birefringent block
having a third optical axis forming an angle with the second
optical axis, the birefringent block being optically coupled to the
second birefringent wedge; and a reflector optically coupled to the
birefringent block.
9. The optical depolarizer of claim 8 further comprising a lens
optically coupled to the first wedge.
10. The optical depolarizer of claim 9 further comprising a
capillary for holding at least a PM optical fiber and an output
optical fiber proximate to the lens such that, light exiting from
the PM optical fiber passes through the lens and enters the
non-reciprocal combination-device in the first input direction as
an e-ray, and light exiting from the non-reciprocal
combination-device in the reverse principal direction passes
through the lens and enters the output optical fiber.
11. The optical depolarizer of claim 9 further comprising a
capillary for holding at least a PM optical fiber and an output
optical fiber proximate to the lens such that, light exiting from
the PM optical fiber passes through the lens and enters the
non-reciprocal combination-device in the second input direction as
an o-ray, and light exiting from the non-reciprocal
combination-device in the reverse principal direction passes
through the lens and enters the output optical fiber.
12. The optical depolarizer of claim 9 further comprising a
capillary for holding at least a first and a second PM optical
fiber, and an output optical fiber proximate to the lens such that,
light exiting from the first PM optical fiber passes through the
lens and enters the non-reciprocal combination-device in the first
input direction as an e-ray, light exiting from the second PM
optical fiber passes through the lens and enters the non-reciprocal
combination-device in the second input direction as an o-ray, and
light exiting from the non-reciprocal combination-device in the
reverse principal direction passes through the lens and enters the
output optical fiber.
13. The optical depolarizer of claim 8 wherein the angle is
substantially 45 degrees.
14. The optical depolarizer of claim 8 wherein the non-reciprocal
rotating element is a Faraday rotator.
15. A method of combing first and second polarized light to form
depolarized light in an output port comprising the steps of:
providing a birefringent block and a non-reciprocal
combination-device having a principal direction and a reverse
principal direction; directing the first polarized light to enter
the non-reciprocal combination-device in a first input direction
and to exit from the non-reciprocal combination-device in the
principal direction as first intermediate light; directing the
second polarized light to enter the non-reciprocal
combination-device in a second input direction and to exit from the
non-reciprocal combination-device in the principal direction as
second intermediate light; passing the first and the second
intermediate light through the birefringent block in the principal
direction; reflecting the first and the second intermediate light
back through the birefringent block in the reverse principal
direction; and directing the first and the second intermediate
light to pass through the non-reciprocal combination-device in the
reverse principal direction and enter the output port as
depolarized light.
16. The method of claim 15 wherein the non-reciprocal
combination-device includes a first birefringent wedge, a second
birefringent wedge, and a non-reciprocal rotating element.
17. The method of claim 16 wherein the non-reciprocal rotating
element is a Faraday rotator
18. The method of claim 15 wherein the non-reciprocal
combination-device includes (a) a first birefringent wedge having a
first optical axis perpendicular to the principal direction; (b) a
second birefringent wedge having a second optical axis
perpendicular to the principal direction, the second optical axis
forming a first angle with respect to the first optical axis; and
(c) a non-reciprocal rotating element optically coupled between the
first and the second birefringent wedge and adapted to rotate a
polarization of light passing therethrough by a second angle.
19. The method of claim 18 wherein the first angle is substantially
45 degrees and the second angle is substantially 45 degrees.
20. A method of depolarizing a polarized light to form depolarized
light in an output port comprising the steps of: providing a
birefringent block and a non-reciprocal combination-device having a
principal direction and a reverse principal direction; directing
the polarized light to enter the non-reciprocal combination-device
in an input direction and to exit from the non-reciprocal
combination-device in the principal direction as intermediate
light; passing the intermediate light through the birefringent
block in the principal direction; reflecting the intermediate light
back through the birefringent block in the reverse principal
direction; and directing the intermediate light to pass through the
non-reciprocal combination-device in the reverse principal
direction and enter the output port as depolarized light.
21. The method of claim 20 wherein the non-reciprocal
combination-device includes a first birefringent wedge, a second
birefringent wedge, and a non-reciprocal rotating element.
22. The method of claim 21 wherein the non-reciprocal rotating
element is a Faraday rotator
23. The method of claim 20 wherein the non-reciprocal
combination-device includes (a) a first birefringent wedge having a
first optical axis perpendicular to the principal direction; (b) a
second birefringent wedge having a second optical axis
perpendicular to the principal direction, the second optical axis
forming a first angle with respect to the first optical axis; and
(c) a non-reciprocal rotating element optically coupled between the
first and the second birefringent wedge and adapted to rotate a
polarization of light passing therethrough by a second angle.
24. The method of claim 23 wherein the first angle is substantially
45 degrees and the second angle is substantially 45 degrees.
25. The method of claim 20 wherein the step of directing the
polarized light includes directing the polarized light to enter the
non-reciprocal combination-device in the input direction as an
e-ray and to exit from the non-reciprocal combination-device in the
principal direction as an o-ray.
26. The method of claim 20 wherein the step of directing the
polarized light includes directing the polarized light to enter the
non-reciprocal combination-device in the input direction as an
o-ray and to exit from the non-reciprocal combination-device in the
principal direction as an e-ray.
Description
[0001] The present invention relates generally to optical
technology.
BACKGROUND OF THE INVENTION
[0002] Optical depolarizers, optical combiners, and optical
isolators are commonly used in optical communication systems and
optical measurement systems. An optical depolarizer is generally
designed to change a beam of completely polarized light or a beam
of partially polarized light into a beam of depolarized light. An
optical combiner is a device generally designed to combine two
beams of light into one beam of light. An optical isolator is a
device generally designed to allow a beam of light to pass through
the device in a chosen direction and to prevent the beam of light
from passing through the device in the opposite of that chosen
direction.
SUMMARY OF THE INVENTION
[0003] In one aspect, the invention provides an optical
depolarizer. The optical depolarizer includes a non-reciprocal
combination-device, a birefringent block, and a reflector. The
non-reciprocal combination-device has a principal direction and
includes a first birefringent wedge, a second birefringent wedge,
and a non-reciprocal rotating element. The first birefringent wedge
has a first optical axis perpendicular to the principal direction.
The second birefringent wedge has a second optical axis
perpendicular to the principal direction, and the second optical
axis forms a first angle with respect to the first optical axis.
The non-reciprocal rotating element is optically coupled between
the first and the second birefringent wedge. The non-reciprocal
rotating element is designed to rotate the polarization of light
passing through the non-reciprocal rotating element by a second
angle. The non-reciprocal rotating element can be a Faraday
rotator. The birefringent block is optically coupled to the second
birefringent wedge. The birefringent block has a third optical axis
perpendicular to the principal direction, and the third optical
axis forms a third angle with respect to the second optical axis.
The reflector is optically coupled to the birefringent block. The
optical depolarizer can include a lens that is optically coupled to
the first wedge. The optical depolarizer can include a capillary
for holding at least a PM optical fiber and an output optical
fiber.
[0004] In another aspect, the invention provides an optical
depolarizer. The optical depolarizer includes a non-reciprocal
combination-device, a birefringent block, and a reflector. The
non-reciprocal combination-device has a principal direction and
includes a first birefringent wedge having a first optical axis, a
second birefringent wedge having a second optical axis, and a
non-reciprocal rotating element. The non-reciprocal rotating
element can be a Faraday rotator. The birefringent block is
optically coupled to the second birefringent wedge. The
birefringent block has a third optical axis perpendicular to the
principal direction, and the third optical axis forms an angle with
respect to the second optical axis. The reflector is optically
coupled to the birefringent block. The optical depolarizer can
include a lens that is optically coupled to the first wedge. The
optical depolarizer can include a capillary for holding at least a
PM optical fiber and an output optical fiber. The non-reciprocal
combination-device is configured for enabling at least the
following functions: (1) light entering the second birefringent
wedge as an e-ray in a first input direction exits from the second
birefringent wedge as an o-ray in the principal direction; (2)
light entering the first birefringent wedge as an o-ray in a second
input direction exits from the second birefringent wedge as an
e-ray in the principal direction; (3) light entering the second
birefringent wedge as an e-ray in a reverse principal direction
exits from the first birefringent wedge as an e-ray in the reverse
principal direction; and (4) light entering the second birefringent
wedge as an o-ray in the reverse principal direction exits from the
first birefringent wedge as an o-ray in the reverse principal
direction.
[0005] In another aspect, the invention provides a method of
combing first and second polarized light to form depolarized light
in an output port. The method includes the step of providing a
birefringent block and a non-reciprocal combination-device having a
principal direction and a reverse principal direction. The method
includes the step of directing the first polarized light to enter
the non-reciprocal combination-device in a first input direction
and to exit from the non-reciprocal combination-device in the
principal direction as first intermediate light. The method
includes the step of directing the second polarized light to enter
the non-reciprocal combination-device in a second input direction
and to exit from the non-reciprocal combination-device in the
principal direction as second intermediate light. The method
includes the step of passing the first and the second intermediate
light through the birefringent block in the principal direction.
The method includes the step of reflecting the first and the second
intermediate light back through the birefringent block in the
reverse principal direction. The method includes the step of
directing the first and the second intermediate light to pass
through the non-reciprocal combination-device in the reverse
principal direction and enter the output port as depolarized
light.
[0006] In another aspect, the invention provides a method of
depolarizing a polarized light to form depolarized light in an
output port. The method includes the step of providing a
birefringent block and a non-reciprocal combination-device having a
principal direction and a reverse principal direction. The method
includes the step of directing the polarized light to enter the
non-reciprocal combination-device in an input direction and to exit
from the non-reciprocal combination-device in the principal
direction as intermediate light. The method includes the step of
passing the intermediate light through the birefringent block in
the principal direction. The method includes the step of reflecting
the intermediate light back through the birefringent block in the
reverse principal direction. The method includes the step of
directing the intermediate light to pass through the non-reciprocal
combination-device in the reverse principal direction and enter the
output port as depolarized light.
[0007] Aspects of the invention can include one or more of the
following advantages. Implementations of the invention provide an
optical depolarizer and an optical depolarizing combiner that may
also function as an optical isolator. Implementations of the
invention provides an optical depolarizer and an optical
depolarizing combiner that may have small insertion loss, compact
size, and reduced manufacturing cost. Other advantages will be
readily apparent from the attached figures and the description
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1a illustrates an implementation of a non-reciprocal
combination-device.
[0009] FIG. 1b illustrates a specific configuration of birefringent
wedges and a Faraday rotator of FIG. 1a.
[0010] FIGS. 1c-1e illustrate alternative configurations of the
birefringent wedges and the Faraday rotator of FIG. 1a.
[0011] FIG. 2a illustrates the paths traveled by light that enters
the non-reciprocal combination-device of FIG. 1a in the principal
direction.
[0012] FIG. 2b illustrates that light entering the first
birefringent wedge as an e-ray in the principal direction exits
from the second birefringent wedge as an o-ray in the first output
direction.
[0013] FIG. 2c illustrates that light entering the first
birefringent wedge as an o-ray in the principal direction exits
from the second birefringent wedge as an e-ray in the second output
direction.
[0014] FIG. 3a illustrates the paths traveled by light that enters
the non-reciprocal combination-device of FIG. 1a in the first and
the second input direction.
[0015] FIG. 3b illustrates that light entering the second
birefringent wedge as an e-ray in the first input direction exits
from the second birefringent wedge as an o-ray in the principal
direction.
[0016] FIG. 3c illustrates that light entering the first
birefringent wedge as an o-ray in the second input direction exits
from the second birefringent wedge as an e-ray in the principal
direction.
[0017] FIG. 4a illustrates the paths traveled by the light that
enters the non-reciprocal combination-device of FIG. 1a in the
reverse principal direction.
[0018] FIG. 4b illustrates that light entering the second
birefringent wedge as an e-ray in the reverse principal direction
exits from the first birefringent wedge as an e-ray in the reverse
principal direction.
[0019] FIG. 4c illustrates that light entering the second
birefringent wedge as an o-ray in the reverse principal direction
exits from the first birefringent wedge as an o-ray in the reverse
principal direction.
[0020] FIGS. 5a-5d illustrate an implementation of an optical
depolarizer 500.
[0021] FIGS. 6a-6d illustrate an implementation of an optical
depolarizing combiner 600.
[0022] FIGS. 7a-7c shows that an optical depolarizing combiner 600
can also function as an optical isolator.
[0023] FIGS. 8a and 8b illustrate an implementation of an optical
combiner 800.
[0024] FIGS. 9a and 9b illustrate an implementation of a PM
isolator 900.
[0025] FIG. 10a illustrates an implementation of non-reciprocal
combination-device 10 constructed using birefringent crystal
materials with indexes n.sub.e larger than n.sub.o.
[0026] FIG. 10b illustrates an implementation of non-reciprocal
combination-device 10 constructed using birefringent crystal
materials with indexes n.sub.e smaller than n.sub.o.
DETAILED DESCRIPTION OF THE INVENTION
[0027] The present invention relates to an improvement in optical
technology. The following description is presented to enable one of
ordinary skill in the art to make and use the invention and is
provided in the context of a patent application and its
requirements. Various modifications to the invention will be
readily apparent to those skilled in the art and the generic
principals herein may be applied to other embodiments. Thus, the
present invention is not intended to be limited to the embodiments
shown, but is to be accorded the widest scope consistent with the
principals and features described herein.
[0028] The present invention will be described in terms of a
non-reciprocal combination-device, an optical depolarizer, an
optical depolarizing combiner, an optical combiner, and a
Polarization Maintenance ("PM") isolator each having specific
components having specific configurations. Similarly, the present
invention will be described in terms of components having specific
relationships, such as distances or angles between components.
However, one of ordinary skill in the art will readily recognize
that the devices and systems described can include other components
having similar properties, other configurations, and other
relationships between components.
[0029] In the instant application, implementations of optical
depolarizers, optical depolarizing combiners, optical combiners,
and PM isolators using non-reciprocal combination-devices are
described. The configuration and operation of the non-reciprocal
combination device is described in greater detail below. The
non-reciprocal combination-device generally includes two
birefringent wedges and a non-reciprocal rotating element such as a
Faraday rotator.
[0030] FIGS. 1a and 1b illustrate an implementation of a
non-reciprocal combination-device 10 that includes a birefringent
wedge 15, a birefringent wedge 17, and a non-reciprocal rotating
element such as Faraday rotator 16. Birefringent wedges 15 and 17
are in the form of tapered plates. Surface 11 of birefringent wedge
15 faces surface 12 of birefringent wedge 17. In one implementation
of non-reciprocal combination-device 10, surface 11 of birefringent
wedge 15 substantially parallels surface 12 of birefringent wedge
17.
[0031] A coordinate system is illustrated including the
x-direction, the y-direction and the z-direction. The optical axis
of birefringent wedge 15 is in the x-direction. The optical axis of
birefringent wedge 17 is in the x-y direction. Faraday rotator 16
is designed in such a way that, when light passes through the
Faraday rotator 16 either in the positive or the negative
z-direction, the polarization of the light will be rotated 45
degrees with respect to the positive z-axis. Non-reciprocal
combination-device 10 has a principal direction that is in the
positive z-direction. Non-reciprocal combination-device 10 also has
a first input direction that is in the z-.alpha.y direction, a
second input direction that is in the z+.beta.y direction, a first
output direction that is in the z+.gamma.y direction, and a second
output direction that is in the z-.delta.y direction. Where
.alpha., .beta., .gamma. and .delta. are positive numbers.
[0032] In general, non-reciprocal combination-device 10, including
a first and a second birefringent wedge, is constructed to perform
one or more of the following six functions:
[0033] (1) light entering the first birefringent wedge as an e-ray
in the principal direction exits from the second birefringent wedge
as an o-ray in the first output direction;
[0034] (2) light entering the first birefringent wedge as an o-ray
in the principal direction exits from the second birefringent wedge
as an e-ray in the second output direction;
[0035] (3) light entering the first birefringent wedge as an e-ray
in the first input direction exits from the second birefringent
wedge as an o-ray in the principal direction;
[0036] (4) light entering the first birefringent wedge as an o-ray
in the second input direction exits from the second birefringent
wedge as an e-ray in the principal direction;
[0037] (5) light entering the second birefringent wedge as an e-ray
in the reverse principal direction exits from the first
birefringent wedge as an e-ray in the reverse principal direction;
and
[0038] (6) light entering the second birefringent wedge as an o-ray
in the reverse principal direction exits from the first
birefringent wedge as an o-ray in the reverse principal
direction.
[0039] FIGS. 2a and 2b illustrate the first function in detail.
FIGS. 2a and 2c illustrate the second function in detail. FIGS. 3a
and 3b illustrate the third function in detail. FIGS. 3a and 3c
illustrate the fourth function in detail. FIGS. 4a and 4b
illustrate the fifth function in detail. FIGS. 4a and 4c illustrate
the sixth function in detail.
[0040] As shown in FIGS. 2a and 2b, light 220(e) traveling in the
principal direction (i.e., the positive z-direction) enters
birefringent wedge 15 as an e-ray with the x polarization. Light
220(e) is refracted at surface 11. After passing through Faraday
rotator 16, the polarization of light 220(e) is rotated positive 45
degrees with respect to the positive z-axis, and light 220(e)
becomes light 221(o) with the x+y polarization. Light 221(o) is
refracted again at surface 12 and enters birefringent wedge 17 as
an o-ray. Light 221(o) exits from birefringent wedge 17 traveling
generally in the first output direction (i.e., the z+.gamma.y
direction).
[0041] As shown in FIGS. 2a and 2c, light 210(o) traveling in the
principal direction (i.e., the positive z-direction) enters
birefringent wedge 15 as an o-ray with the y polarization. Light
210(o) is refracted at surface 11. After passing through Faraday
rotator 16, the polarization of light 210(o) is rotated positive 45
degrees with respect to the positive z-axis, and light 210(o)
becomes light 211(e) with the x-y polarization. Light 211(e) is
refracted again at surface 12 and enters birefringent wedge 17 as
an e-ray. Light 211(e) exits from birefringent wedge 17 traveling
generally in the second output direction (i.e., the z-.delta.y
direction).
[0042] As shown in FIGS. 3a and 3b, light 320(e) traveling in the
first input direction (i.e., the z-.alpha.y direction) enters
birefringent wedge 15 as an e-ray with the x polarization. Light
320(e) is refracted at surface 11. After passing through Faraday
rotator 16, the polarization of light 320(e) is rotated 45 positive
degrees with respect to the positive z-axis, and light 320(e)
becomes light 321(o) with the x+y polarization. Light 321(o) is
refracted again at surface 12 and enters birefringent wedge 17 as
an o-ray. Light 321(o) exits from birefringent wedge 17 traveling
in the principal direction (i.e., the positive z-direction).
[0043] As shown in FIGS. 3a and 3c, light 310(o) traveling in the
second input direction (i.e., the z+.beta.y direction) enters
birefringent wedge 15 as an o-ray with the y polarization. Light
310(o) is refracted at surface 11. After passing through Faraday
rotator 16, the polarization of light 310(o) is rotated positive 45
degrees with respect to the positive z-axis, and light 310(o)
becomes light 311(e) with the x-y polarization. Light 311(e) is
refracted again at surface 12 and enters birefringent wedge 17 as
an e-ray. Light 311(e) exits from birefringent wedge 17 traveling
in the principal direction (i.e., the positive z-direction).
[0044] As shown in FIGS. 4a and 4b, light 420(e) traveling in the
reverse principal direction (i.e., the negative z-direction) enters
birefringent wedge 17 as an e-ray with the x-y polarization. Light
420(e) is refracted at surface 12. After passing through Faraday
rotator 16, the polarization of light 420(e) is rotated positive 45
degrees with respect to the positive z-axis, and light 420(e)
becomes light 421(e) with the x polarization. Light 421(e) is
refracted again at surface 11 and enters birefringent wedge 15 as
an e-ray. Light 421(e) exits from birefringent wedge 15 traveling
in the reverse principal direction (i.e., the negative
z-direction).
[0045] As shown in FIGS. 4a and 4c, light 410(o) traveling in the
reverse principal direction (i.e., the negative z-direction) enters
birefringent wedge 17 as an o-ray with the x+y polarization. Light
410(o) is refracted at surface 12. After passing through Faraday
rotator 16, the polarization of light 410(o) is rotated positive 45
degrees with respect to the positive z-axis, and light 410(o)
becomes light 411(o) with the y polarization. Light 410(o) is
refracted again at surface 11 and enters birefringent wedge 15 as
an o-ray. Light 411(o) exits from birefringent wedge 15 traveling
in the reverse principal direction (i.e., the negative
z-direction).
[0046] Due to the differences in the refractive index between the
o-ray and the e-ray, light 421(e) and 411(o) can exit from
birefringent wedge 15 with different paths. However, when the paths
of 421(e) and 411(o) are substantially parallel, light 421(e) and
411(o) can be coupled to an optical fiber using a collimator.
[0047] In the implementation of non-reciprocal combination-device
10 shown in FIG. 1b, the optical axes of birefringent wedges 15 and
17 are, respectively, in the x direction and the x-y direction.
Faraday rotator 16 is designed in such a way that the polarization
of light passing through the Faraday rotator 16 will be rotated a
positive 45 degrees with respect to the positive z-axis.
[0048] In another implementation of non-reciprocal
combination-device 10, as shown FIG. 1c, the optical axes of
birefringent wedges 15 and 17 are, respectively, in the x direction
and the x+y direction. Faraday rotator 16 is designed in such a way
that the polarization of light passing through the Faraday rotator
16 will be rotated a negative 45 degrees with respect to the
positive z-axis.
[0049] In a third implementation of non-reciprocal
combination-device 10, as shown in FIG. 1d, the optical axes of
birefringent wedges 15 and 17 are, respectively, in the y direction
and the x+y direction. Faraday rotator 16 is designed in such a way
that the polarization of light passing through the Faraday rotator
16 will be rotated a positive 45 degrees with respect to the
positive z-axis.
[0050] In a fourth implementation of non-reciprocal
combination-device 10, as shown in FIG. 1e, the optical axes of
birefringent wedges 15 and 17 are, respectively, in the
cos(.phi.)x+sin(.phi.)y direction and the
cos(.phi.-45)x+sin(.phi.-45)y direction. Faraday rotator 16 is
designed in such a way that the polarization of light passing
through the Faraday rotator 16 will be rotated positive 45 degrees
with respect to the positive z-axis.
[0051] In the implementation of non-reciprocal combination-device
10, as shown in FIG. 1a, birefringent wedges 15 and 17 are
essentially in contact with Faraday rotator 16. In other
implementations, other optical media (including air) can be
inserted between birefringent wedge 15 and Faraday rotator 16, and
between birefringent wedge 17 and Faraday rotator 16.
[0052] FIG. 5a illustrates an implementation of an optical
depolarizer 500 that includes a non-reciprocal combination-device
10. Depolarizer 500 also includes a lens 540, a birefringent block
580, and a reflector 590. A single mode fiber 510 and a
Polarization Maintenance ("PM") fiber 520 are coupled to lens 540.
The positions of single mode fiber 510 and PM fiber 520 can be
fixed with a capillary 530. The optical axis of birefringent block
580 can be in the y-direction. Birefringent block 580 includes
surface 585 of facing wedge 17.
[0053] As shown in FIGS. 5a and 5b, light with the x-polarization
exiting from PM fiber 520 is coupled to non-reciprocal
combination-device 10 through lens 540, and enters non-reciprocal
combination-device 10 in the first input direction (i.e., the
z-.alpha.y direction) as e-ray 320(e). After passing through
non-reciprocal combination-device 10, e-ray 320(e) becomes o-ray
321(o) traveling in the principal direction (i.e., the positive
z-direction) with the x+y polarization. O-ray 321(o) enters surface
585 of birefringent block 580 as light 381.
[0054] Light 381 can be decomposed as light 381(x) with the
x-polarization and 381(y) with the y-polarization. Because the
optical axis of birefringent block 580 is in the y-direction, light
381(x) and 381(y) are, respectively, the o-ray and the e-ray in
birefringent block 580. Light 381(x) travels in the positive
z-direction with the phase velocity of an o-ray. Light 381(y)
travels in the positive z-direction with the phase velocity of an
e-ray. Light 381(x) and 381(y) are reflected by reflector 590, and
become, respectively, light 382(x) and 382(y). Light 381(x) travels
in the negative z-direction with the phase velocity of an o-ray.
Light 381(y) travels in the negative z-direction with the phase
velocity of an e-ray. Light 382(x) and 382(y) are recombined at
surface 585 as light 382.
[0055] When light 381 traveling in the positive z-direction enters
surface 585, the phase difference between the decomposed light
381(x) and 381(y) is zero. The polarization of light 381 is
x+exp(j.theta..sub.i)y, with .theta..sub.i=0. When light 382(x) and
382(y) are recombined at surface 585 as light 382 traveling in the
negative z-direction, the phase difference between the decomposed
light 382(x) and 382(y) is .theta..sub.f. Phase difference
.theta..sub.f is given by
.theta..sub.f=4.pi.(n.sub.e-n.sub.o)L/.lambda., where L is the
length of the birefringent block 580, .lambda. is the wavelength of
light 382 (and light 381), n.sub.e and n.sub.o are respectively the
refractive indexes of the e-ray and the o-ray. The polarization of
light 382 is x+exp(j.theta..sub.f)y.
[0056] For a selected wavelength .lambda..sub.1, the phase
difference .theta..sub.f can be zero, and the polarization of light
382 can be in the x+y direction. For another selected wavelength
.lambda..sub.2, the phase difference .theta..sub.f can be equal to
.pi., and the polarization of light 382 can be in the x-y
direction. For a third selected wavelength .lambda..sub.3, the
phase difference .theta..sub.f can be equal to .pi./2, and the
polarization of light 382 can be in the x+jy direction (i.e., light
382 is circularly polarized).
[0057] When light 382 enters non-reciprocal combination-device 10
with the x+exp(j.theta..sub.f)y polarization, light 382 can be
decomposed as light 420(e) with the x-y polarization and light
410(o) with the x+y polarization and given by equation
[x+exp(j.theta..sub.f)y]2.sup.1/2=[cos(.theta..sub.f/2)o-j
sin(.theta..sub.f/2)e]exp(j.theta..sub.f/2),
[0058] where o=[x+y]/2.sup.1/2 and e=[x-y]/2.sup.1/2. The intensity
of light 410(o) is proportional to [sin(.theta..sub.f/2)].sup.2.
The intensity of light 410(o) is proportional to
[cos(.theta..sub.f/2)].sup.2- .
[0059] As shown in FIG. 5a and FIG. 5c, light 420(e) passes through
non-reciprocal combination-device 10 as light 421(e) with the
x-polarization. Light 421(e) passes through lens 540, and enters
single mode fiber 510 with the x-polarization.
[0060] As shown in FIG. 5a and FIG. 5d, light 410(o) passes through
non-reciprocal combination-device 10 as light 411(o) with the
y-polarization. Light 411(o) passes through lens 540, and enters
single mode fiber 510 with the y-polarization.
[0061] Therefore, light 320(e) with the x-polarization exiting from
PM fiber 520 can be directed into single mode fiber 510 as light
511 that in general has both the x-polarization component and the
y-polarization component. If light 320(e) has wavelength
.lambda..sub.1 and .theta..sub.f=0, then, light 511 has mostly the
y-polarization component. If light 320(e) has wavelength
.lambda..sub.2, and .theta..sub.f=.pi., then, light 511 has mostly
the x-polarization component. If light 320(e) has wavelength
between .lambda..sub.2 and .lambda..sub.1, then, light 511 in
general has both the x-polarization component and the
y-polarization component.
[0062] When light 320(e) has a certain bandwidth, with wavelengths
ranging from .lambda..sub.2 to .lambda..sub.1, light 511 entering
single mode fiber 510 can become depolarized.
[0063] FIG. 6a illustrates an implementation of an optical
depolarizing combiner 600 that includes non-reciprocal
combination-device 10. Depolarizing combiner 600 also includes a
lens 540, a birefringent block 580, and a reflector 590. A single
mode fiber 510, a first PM fiber 520, and a second PM fiber 520'
are coupled to lens 540. The positions of single mode fiber 510,
the first PM fiber 520, and the second PM fiber 520' can be fixed
with a capillary 530. The optical axis of birefringent block 580
can be in the y-direction. Surface 585 of birefringent block 580
faces wedge 17.
[0064] FIG. 6a illustrates that light 320(e) with the
x-polarization exiting from PM fiber 520 can be directed into
single mode fiber 510 as light 511 that in general has both the
x-polarization component and the y-polarization component.
[0065] FIG. 6a also illustrates that light 310(o) with the
y-polarization exiting from PM fiber 520' can be directed into
single mode fiber 510 as light 511' that in general has both the
x-polarization component and the y-polarization component. FIGS.
6b-6d show in detail the processing of light 310(o).
[0066] As shown FIGS. 6a and 6b, light 310(o) with the
y-polarization exiting from PM fiber 520' is coupled to
non-reciprocal combination-device 10 through lens 540. Light 310(o)
enters non-reciprocal combination-device 10 in the second input
direction (i.e., the z+.beta.y direction) as an o-ray. After
passing through non-reciprocal combination-device 10, o-ray 310(o)
becomes e-ray 311(e) in the principal direction (i.e., the positive
z-direction) with the x-y polarization. E-ray 311(e) enters surface
585 of birefringent block 580 as light 381'.
[0067] Light 381' can be decomposed as light 381'(x) with the
x-polarization and 381'(y) with the y-polarization. Light 381'(x)
and 381'(y) travels in the positive z-direction with the phase
velocity of the o-ray and the e-ray respectively. Light 381'(x) and
381'(y) are reflected by reflector 590, and become, respectively,
Light 382'(x) and 382'(y). Light 382'(x) and 382'(y) travel in the
negative z-direction with the phase velocity of the o-ray and the
e-ray respectively. Light 382'(x) and 382'(y) are recombined at
surface 585 as light 382'.
[0068] As shown FIG. 6c and FIG. 6d, light 382' entering
non-reciprocal combination-device 10 can be decomposed as light
410'(o) with x+y polarization and as light ray 420'(e) with x-y
polarization. Light 410'(o) and 420'(e) exit from non-reciprocal
combination-device 10, respectively, as light 411'(o) with the
y-polarization and as light 421'(e) with the x-polarization. Light
411'(o) and 421'(e) are combined and enter polarization single mode
fiber 510 as light 511'. Light 511' in general has both the
x-polarization component and the y-polarization component.
[0069] When light 310(o) has a certain bandwidth, with wavelengths
ranging from .lambda..sub.2 to .lambda..sub.1, light 511' entering
single mode fiber 510 can become depolarized.
[0070] FIG. 6a illustrates that optical depolarizing combiner 600
functions as both a depolarizer and a combiner. Light exiting from
PM fiber 520 with the x-polarization and light exiting from PM
fiber 520' with the y-polarization are directed into single mode
fiber 510, and combined as depolarized light.
[0071] FIG. 7a illustrates that optical depolarizing combiner 600
can also function as an optical isolator. Light exiting from single
mode fiber 510 can be decomposed as light 220(e) with the
x-polarization and light 210(o) with the y-polarization.
[0072] As shown in FIG. 7b, light 220(e) passes through
non-reciprocal combination-device 10 as light 221(o) traveling in
the first output direction (i.e., the z+.gamma.y direction) with
the x+y polarization. Light 221(o) travels though birefringent
block 580 and is deflected by reflector 590. After deflected by
reflector 590, light 221(o) does not travel back to single mode
fiber 510, first PM fiber 520, or second PM fiber 520'.
[0073] As shown in FIG. 7c, light 210(o) passes through
non-reciprocal combination-device 10 as light 211(e) traveling in
the second output direction (i.e., the z-.delta.y direction) with
the x-y polarization. Light 211(e) travels though birefringent
block 580 and is deflected by reflector 590. After being deflected
by reflector 590, light 211(e) does not travel back to single mode
fiber 510, first PM fiber 520, or second PM fiber 520'.
[0074] FIGS. 8a and 8b illustrate an implementation of an optical
combiner 800 that includes non-reciprocal combination-device 10.
Optical combiner 800 also includes a lens 540, and a reflector 590.
A single mode fiber 510, a first PM fiber 520, and a second PM
fiber 520' are coupled to lens 540. The positions of single mode
fiber 510, first PM fiber 520, and second PM fiber 520' can be
fixed with a capillary 530.
[0075] FIG. 8a illustrates that light 320(e) with the
x-polarization exiting from first PM fiber 520 and light 310(o)
with the y-polarization exiting from second PM fiber 520' are
coupled to non-reciprocal combination-device 10. Light 320(e) and
light 310(o) pass through non-reciprocal combination-device 10 as
light 321(o) and light 311(e) respectively. Light 321(o) and light
311(e) are reflected by reflector 590, and enter non-reciprocal
combination-device 10 as light 410(o) and light 420(e)
respectively. Light 410(o) and light 420(e) pass back through
non-reciprocal combination-device 10 as light 411(o) and light
421(e) respectively. Light 411(o) and light 421(e) are directed
into single mode fiber 510, and are combined.
[0076] FIG. 8b illustrates that light exiting from single mode
fiber 510 can be decomposed as light 220(e) and 210(o). Light
220(e) passes through non-reciprocal combination-device 10 as light
221(o) traveling in the first output direction (i.e., z+.gamma.y).
Light 210(o) passes through non-reciprocal combination-device 10 as
light 211(e) traveling in the second output direction (i.e.,
z-.delta.y). Light 221(o) and light 211(e) are deflected by
reflector 590. After being deflected by reflector 590, light 211(e)
and light 221(o) do not travel back to single mode fiber 510, first
PM fiber 520, or second PM fiber 520'.
[0077] FIGS. 9a and 9b illustrate an implementation of a PM
isolator 900 that includes non-reciprocal combination-device 10. PM
isolator 900 also includes a lens 540, and a reflector 590. An
output PM fiber 910, and an input PM fiber 920 are coupled to lens
540. The positions of output PM fiber 910, and input PM fiber 920
can be fixed with a capillary 530. FIG. 9a illustrates that light
320(e) with the x-polarization exiting from input PM fiber 920 is
coupled to non-reciprocal combination-device 10 as e-ray. Light
320(e) passes through non-reciprocal combination-device 10 as light
321(o). Light 321(o) is reflected by reflector 590, and enters
non-reciprocal combination-device 10 as light 410(o). Light 410(o)
pass back through non-reciprocal combination-device 10 as light
411(o) and is directed into output PM fiber 910. FIG. 9b
illustrates that light 210(o) exiting from input PM fiber 920
enters non-reciprocal combination-device 10 as o-ray. Light 210(o)
passes through non-reciprocal combination-device 10 as light 211(e)
traveling in the second output direction (i.e., z-.delta.y). Light
211(e) is deflected by reflector 590. After being deflected by
reflector 590, light 211(e) does not travel back to output PM fiber
910 or input PM fiber 920.
[0078] In the implementation of FIGS. 9a and 9b, output PM fiber
910 and input PM fiber 920 are aligned in such a way that light
exits from input PM fiber 920 as an e-ray and enters output PM
fiber 910 from non-reciprocal combination-device 10 as an o-ray. In
an alternative implementation, output PM fiber 910 and input PM
fiber 920 can be aligned in such a way that light exits from input
PM fiber 920 as an o-ray and enters output PM fiber 910 from
non-reciprocal combination-device 10 as an e-ray.
[0079] The optical depolarizer of FIG. 5a-5d and the optical
depolarizing combiner of FIGS. 6a-6e include birefringent block 580
with an optical axis in the y-direction that forms a 45 degree
angle with the optical axis of birefringent wedge 17. In
alternative implementations, other angles between the optical axis
of birefringent block 580 and the optical axis of birefringent
wedge 17 can be selected.
[0080] In the implementations of FIGS. 5a, 6a and 7a, reflector 590
can be a mirror. In alternative implementations, reflective
materials can be coated at the end of birefringent block 580 to
function as reflector 590.
[0081] In the implementations of FIGS. 8a and 9a, reflector 590 can
be a mirror. In alternative implementations, reflective materials
can be coated on surface 19 of birefringent wedge 17 to function as
reflector 590.
[0082] Birefringent block 580, birefringent wedge 15, and
birefringent wedge 17 can be constructed from birefringent crystal
materials, such as, calcite, rutile, lithium niobate or yttrium
orthvanadate.
[0083] A birefringent crystal material in general has refractive
indexes n.sub.e for e-ray and n.sub.o for o-ray. Non-reciprocal
combination-device 10 can be constructed using birefringent crystal
materials with indexes n.sub.e larger than n.sub.o, or birefringent
crystal materials with indexes n.sub.e smaller than n.sub.o
[0084] FIGS. 10a and 10b illustrate implementations of
non-reciprocal combination-device 10 including birefringent wedges
15 and 17 in the form of tapered plate. Surface 11 of birefringent
wedge 15 substantially parallels surface 12 of birefringent wedge
17. The tapering angle of birefringent wedges 15 and 17 is
.chi..
[0085] FIG. 10a illustrates an implementation of non-reciprocal
combination-device 10 constructed using birefringent crystal
materials with indexes n.sub.e larger than n.sub.o. FIG. 10a also
illustrates the paths traveled by e-ray 320(e) and o-ray 310(o).
E-ray 320(e) is incident upon surface 11 of birefringent wedge 15
in the cos(.theta..sub.e)z-sin(.- theta..sub.e)y direction and
exits from birefringent wedge 17 in the positive z-direction. Here
.theta..sub.e satisfies equation n.sub.e
sin(.chi.-.theta..sub.e)=n.sub.o sin(.chi.). O-ray 310(o) is
incident upon surface 11 of birefringent wedge 15 in the
cos(.theta..sub.o)z+sin(.- theta..sub.o)y direction and exits from
birefringent wedge 17 in the positive z-direction. Here
.theta..sub.o satisfies equation n.sub.o
sin(.chi.+.theta..sub.o)=n.sub.e sin(.chi.).
[0086] FIG. 10b illustrates an implementation of non-reciprocal
combination-device 10 constructed using birefringent crystal
materials with indexes n.sub.e smaller than n.sub.o. FIG. 10b also
illustrates the paths traveled by e-ray 320(e) and o-ray 310(o).
E-ray 320(e) is incident upon surface 11 of birefringent wedge 15
in the cos(.theta..sub.e)z-sin(.- theta..sub.e)y direction and
exits from birefringent wedge 17 in the positive z-direction. Here
.theta..sub.e satisfies equation n.sub.e
sin(.chi.+.theta..sub.e)=n.sub.o sin(.chi.). O-ray 310(o) is
incident upon surface 11 of birefringent wedge 15 in the
cos(.theta..sub.o)z+sin(.- theta..sub.o)y direction and exits from
birefringent wedge 17 in the positive z-direction. Here
.theta..sub.o satisfies equation n.sub.o
sin(.chi.-.theta..sub.o)=n.sub.e sin(.chi.).
[0087] A method and system has been disclosed for providing optical
depolarizers, optical depolarizing combiners, optical combiners,
and PM isolators. Although the present invention has been described
in accordance with the embodiments shown, one of ordinary skill in
the art will readily recognize that there could be variations to
the embodiments and those variations would be within the spirit and
scope of the present invention. Accordingly, many modifications may
be made by one of ordinary skill in the art without departing from
the spirit and scope of the appended claims.
* * * * *