U.S. patent application number 11/086188 was filed with the patent office on 2009-02-26 for electrically controlled optical elements and method.
Invention is credited to Mark Bolas, Ian McDowall.
Application Number | 20090052838 11/086188 |
Document ID | / |
Family ID | 40382248 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090052838 |
Kind Code |
A1 |
McDowall; Ian ; et
al. |
February 26, 2009 |
Electrically controlled optical elements and method
Abstract
The configuration of an optical system can be electronically
controlled using switchable wave plates in conjunction with
polarized light.
Inventors: |
McDowall; Ian; (Woodside,
CA) ; Bolas; Mark; (Mountain View, CA) |
Correspondence
Address: |
IAN McDOWALL;FAKESPACE LABS
241 POLARIS AVE
MOUNTIAN VIEW
CA
94043
US
|
Family ID: |
40382248 |
Appl. No.: |
11/086188 |
Filed: |
March 21, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60554870 |
Mar 22, 2004 |
|
|
|
Current U.S.
Class: |
385/18 |
Current CPC
Class: |
G02B 27/141 20130101;
G02B 15/00 20130101; G02F 2203/07 20130101; G02B 15/14 20130101;
G02B 27/40 20130101; G02B 27/144 20130101; G02B 27/28 20130101;
G02B 5/3083 20130101; G02B 15/143 20190801; G02B 27/286 20130101;
G02F 1/0136 20130101; G02F 1/29 20130101; G03B 13/02 20130101; G02F
1/09 20130101; G02F 1/294 20210101; G02B 5/30 20130101; G02B 27/283
20130101 |
Class at
Publication: |
385/18 |
International
Class: |
G02B 6/27 20060101
G02B006/27 |
Claims
1) an optical system with at least one switchable wave plate,
polarization dependent mirror, and one or more optical elements.
Description
[0001] This application claims priority to U.S. Provisional
Application 60/554,870, filed Mar. 22, 2004.
BACKGROUND
[0002] It is desirable in many optical systems to be able to
dynamically change the focal length of or effective airspaces in an
optical layout. For example, in a camera, it is often advantageous
to have a zoom lens that is capable of altering its focal length in
order to change the magnification of an image. In other optical
systems, such as viewfinders for near-to-eye virtual reality
displays, it is beneficial to have a viewfinder that can quickly
switch from creating a wide-angle, immersive image to displaying a
narrow angle, high resolution image. Implementation of zoom, angle
adjustment, and other focal-length dependent dynamic optical
alterations typically require mechanical adjustment--an element or
optics group is moved in relation to others and the overall focal
length of the system is adjusted.
[0003] The mechanical adjustment of such systems requires the
motion of an element and can thus be adjusted only as quickly as
the elements can be moved. The mechanism for such adjustment
requires some sort of motor if a computer is to control the
adjustment. The attendant size of the adjustment mechanism can be
difficult to incorporate into small cameras such as those in mobile
telephones or virtual reality displays where weight is often an
important factor. Mechanical adjusters are prone to breakage and
must be kept clean in order to function well, necessitating the
delicate treatment of zoom camera lenses, microscopes, and other
equipment optical equipment with mechanically adjusted focal
lengths.
[0004] Accordingly, it is desirable to provide electrically
controlled optical elements and an associated method. The
electrically controlled optical elements afford a method for
altering an optical system's configuration without physically
moving any of the optics, allowing a compact, durable, quickly
adjustable optical package.
DESCRIPTION OF FIGURES
[0005] FIG. 1 schematically illustrates in side plan view an
application of electrically controlled optical elements in
accordance with an embodiment of the invention;
[0006] FIG. 2 schematically illustrates in perspective view an
application of electrically controlled optical elements in
accordance with an embodiment of the invention;
[0007] FIG. 3 schematically illustrates in plan view the operation
of electrically controlled optical elements in accordance with an
embodiment of the inventions;
[0008] FIG. 4 schematically illustrates in plan view the operation
of electrically controlled optical elements in accordance with an
embodiment of the invention;
[0009] FIGS. 5a and 5b schematically illustrate in cross sectional
view a prior art zoom lens in a first and second zoom state,
respectively;
[0010] FIGS. 6a and 6b schematically illustrate in cross sectional
view a zoom lens that employs electrically controlled optical
elements in a first and second zoom state, respectively.
INNOVATION
[0011] Electrically controlled optical elements manipulate the
polarization of light in order to vary the effective focal length
of an optical instrument. This invention utilizes an element, such
as a switchable ferro-electric half wave plate mirror, that is
capable of variably switching between the polarizations of light it
passes through the optical assembly. When the switchable element
passes light of one kind of polarization, the light travels through
the optical elements normally. When the switchable element passes
light of a different polarization, however, the light is reflected
twice within the assembly, resulting in a longer effective focal
length than before. By using polarization to control the path of
light within the optical elements and folding the light path, it is
possible to create a compact zoom lens or a near to eye display
with multiple fields of view without any moving parts.
PHYSICAL DESCRIPTION
[0012] FIGS. 1 and 2 schematically illustrate electrically
controlled optical elements as applied in a near-to-eye
application, such as one found in a virtual reality head-mounted
display or viewfinder. Viewfinder 10 consists of electrically
controlled optical elements 12 as well as diffusion screen 14 and
viewing optics 16. The components of viewfinder 10 are contained
within an enclosure, such as an aluminum housing (not illustrated).
As illustrated, light rays 18 exit a display, such as an LCD (not
illustrated), enter viewfinder 10 from the right, and exit the
viewfinder from the left into a viewer's eyeball 20.
[0013] Electrically controlled optical elements 12 consist of
linear polarizer 22, quarter wave plate 24, ferro-electric
switchable half wave plate 26, control electronics 27, half
silvered mirror 28, lens 30, quarter wave plate 32, reflective
polarizer 34, and linear polarizer 36. The elements of viewfinder
10 are positioned so that they are substantially parallel to one
another. The distances shown in FIGS. 1 and 2 are purely for
illustrative purposes; those of skill in the art will recognize
that the individual components of the system could be separated by
different distances illustrated in FIGS. 1 and 2 without departing
from the spirit of the invention and optics 16 and 30 would be
composed of one or more lenses and/or air spaces.
[0014] Linear polarizer 22 may be oriented as an "S" or a "P"
linear polarizer; in this illustrative embodiment, polarizer 22 is
an "S" polarizer and passes light with "S" polarization. Quarter
wave plate 24 circularly polarizes the linearly polarized light
that passes through linear polarizer 22. The linearly polarized
light that transmits through linear polarizer 22 is thus circularly
polarized with an "L" handedness.
[0015] Ferro-electric switchable half wave plate 26 may be, for
example, a switchable half wave plate made by Displaytech or
others. The ferro-electric switchable half wave plate is oriented
to pass the circularly polarized light that exits quarter wave
plate 24. The light transmitted can be controlled to be a left or
right handed by switching the switchable wave plate. The wave plate
and switchable element could be a single switchable plate with
suitable switchable retardation performance, such that the
handedness of the light's circular polarization, is controlled by
the state of the electrical signals received from control
electronics 27. For the purposes of illustration, if ferro-electric
switchable half wave plate 26 is "on", it reverses the handedness
of the light's polarization that passes through it, and if the
ferro-electric switchable half wave plate is "off", it does not
change the handedness of the light's circular polarization that
passes through it. Note that the terms "on" and "off" as applied to
the ferro-electric switchable half wave plate are generic terms, as
switching between the "on" and "off" states on the ferro-electric
switchable half wave plate may involve reversing a voltage applied
to the ferro-electric switchable half wave plate or the like.
[0016] Those of skill in the art will recognize that ferro-electric
switchable half wave plate may be replaced by an LCD or the like
that can similarly perform the task of selectably altering the
circular polarization of light without departing from the spirit of
the invention, and that this could be done in an array, not just in
a single large shutter.
[0017] Control electronics 27 are configured to electrically govern
whether ferro-electric switchable half waveplate is in an "on" or
"off" state by applying signals to the ferro-electric switchable
half wave plate. The control electronics may include, for example,
a microchip, a central processing unit, or the like. Signals to the
ferro-electric switchable half wave plate may include an applied
voltage, an alternating current, or the like.
[0018] Half silvered mirror 28 is designed to reflect a percentage
of light that passes through ferro-electric switchable half wave
plate 26 and transmit the remainder of the light. The percentage of
light that the half silvered mirror reflects versus transmits may
be tailored to meet particular design specifications by altering
the coatings on the half silvered mirror or the like. For the
purposes of illustration, half silvered mirror 28 is designed to
reflect fifty percent of the light that passes through
ferro-electric switchable half wave plate 26 and transmit the other
fifty percent of the light. Surface 29 and/or surface 31 maybe
coated in order to reflect fifty percent of the light and transmit
fifty percent of the light (losses would alter this a bit).
[0019] Lens 30 is a lens and refracts the light transmitted through
half silvered mirror 28. In the preferred embodiment of the
invention lens 30 is a glass lens that does not affect the
polarization of the light that passes through it. While the
illustrated lens in FIGS. 1 and 2 is a circular, double-convex
lens, those of skill in the art will recognize that other possible
lens types, such as a fresnel lens, a lens group, or the like, also
find application in the present invention.
[0020] Quarter wave plate 32 linearly polarizes the circularly
polarized light that passes through lens 30. Thus, light that is
circularly polarized with an "L" handedness becomes "S" linearly
polarized and light that is circularly polarized with an "R"
handedness becomes "P" linearly polarized when passing through
quarter wave plate 32.
[0021] Reflective polarizer 34 reflects linear polarization of one
type and transmits the linear polarization of the other type.
Reflective polarizer 32 may be oriented as either an "S" or a "P"
polarizer, however, as configured in the illustrated embodiments,
reflective polarizer 32 reflects linear polarizations of the same
type that linear polarizer 22 passes. Thus, for the purposes of
illustration, reflective polarizer 32 is a "P" polarizer that
reflects "S" polarized light and transmits "P" polarized light.
Those of skill in the art will recognize that quarter wave plate 32
and reflective polarizer need not be a separate elements but made
be made integrally, either by bonding the two together or
manufacturing them together as one element, without departing from
the spirit of the invention.
[0022] Linear polarizer 36 may be oriented as either an "S" or a
"P" polarizer. Those of skill in the art will recognize that it is
possible to build the present invention without linear polarizer
36; however, in the preferred embodiment of the invention linear
polarizer 36 is included.
[0023] Diffuser 14 of viewfinder 10 acts as a diffuse screen on to
which images from the display are projected by electrically
controlled optical elements 12. The angles at which diffuser 14
disperses light may be selected depending on the optical
requirements of the system. Those of skill in the art will
recognize that it is possible to build a viewfinder without
diffuser 14 without departing from the spirit of the invention.
[0024] Lens 16 is a lens and refracts the light that passes through
diffuser 14 and focuses the light rays for eyeball 20. While the
illustrated lens in FIGS. 1 and 2 is a circular, double-convex
lens, those of skill in the art will recognize that other possible
lens types, such as a fresnel lens, a lens group, or the like, also
find application in the present invention.
[0025] In an additional embodiment of the invention (not
illustrated), lens 30 is removed from electrically controlled
optical elements 12 and only air occupies the space between half
silvered mirror 28 and quarter wave plate 32. Certain applications,
like inexpensive zoom lenses, may not require the additional
expense of a lens or may necessitate the removal of the lens due to
packaging concerns. Those of skill in the art will recognize that
it is possible to fill the volume of space between the half
silvered mirror and the quarter wave plate with a material that
possesses an index of refraction different than air, such as water,
without departing from the spirit of the invention.
[0026] In an additional embodiment of the invention (not
illustrated), quarter wave plate 32 is located between lens 30 and
half silvered mirror 28. It may also be bonded to the half silvered
mirror to make the two a single, integral element.
[0027] In an additional embodiment of the invention (not
illustrated), ferro-electric switchable half wave plate 26 and
quarter wave plate 24 are combined into a single electro-optic
shutter.
[0028] In an additional embodiment of the invention (not
illustrated), a ferro-electric switchable quarter wave plate is
used in combination with a static half wave plate in place of
quarter wave plate 24 and ferro-electric switchable half wave plate
26. Alternatively, 24 and 26 could be a single electro-optical
element.
Illustrative Operation of Viewfinder Utilizing Electrically
Controlled Optical Elements
[0029] FIG. 3 shows in plan view the operation of viewfinder 10
with ferro-electric switchable half wave plate "on". With
continuing reference to FIGS. 1 and 2, unpolarized light rays 18
exit the display (not illustrated) and enter viewfinder 10. Light
rays 18 pass through linear filter 22 and become "S" polarized (as
represented by light rays 18(a)) before passing through quarter
wave plate 24 where the "S" polarized light rays become circularly
polarized with an "L" handedness. Light rays 18(b) then transmit
through ferro-electric switchable half wave plate 26. Because the
ferro-electric switchable half wave plate is turned "on" by control
electronics 27, the handedness of the circular polarization the
light rays is reversed so that light rays 18(c) exiting
ferro-electric switchable half wave plate have an "R" handedness.
Next, "R" circularly polarized light rays 18(c) transmit to half
silvered mirror 28 where half the light rays (light rays 18(d))
reflect off the half silvered mirror and half the light rays (light
rays 18(e)) transmit through the half silvered mirror. Light rays
18(e) enter lens 30, which refracts the light rays on to quarter
wave plate 32. When light rays 18(f) exit the quarter wave plat,
their polarization state has been switched from circular "R" to
linear "P". Light rays 18(f) next intersect reflective polarizer
34. Because light rays 18(f) are "P" polarized and reflective
polarizer 34 is a "P" polarizer, the light rays pass through the
reflective polarizer unchanged before passing through linear
polarizer 36, which also does not change the light rays'
polarization. Light rays 18(f) form an image on diffuser 14; this
image has a height a (for example, 4 inches). Lens 16 collects
light rays 18(g) and focuses them on eyeball 20. Based on the
distance b between eyeball 20 and lens 16 (for example, one inch),
the focal length of lens 16, and the height a of the image formed
by diffuser 14, viewfinder 10 in the present configuration has a
viewing angle .theta..
[0030] FIG. 4 shows in plan view the operation of viewfinder 10
with ferro electric switchable half wave plate "off". With
continuing reference to FIGS. 1 and 2, unpolarized light rays 18
exit the display (not illustrated) and enter viewfinder 10. Light
rays 18 pass through linear filter 22 and become "S" polarized (as
represented by light rays 18(i)) before passing through quarter
wave plate 24 where the "S" polarized light rays are circularly
polarized with an "L" handedness. Light rays 18(j) then transmit
through ferro-electric switchable half wave plate 26. Because the
ferro-electric switchable half wave plate is "off", the "L"
handedness of the circular polarization of light rays 18(j) remains
unchanged. Next, light rays 18(j) transmit to half silvered mirror
28 where half the light rays (light rays 18(k)) reflect off the
half silvered mirror and half the light rays (light rays 18(l))
transmit through the half silvered mirror. Light rays 18(l) enter
lens 30, which refracts the light rays on to quarter wave plate 32.
The quarter wave plate changes the polarization state of the light
rays from circular "L" to linear "S", so light rays 18(n) that exit
the quarter wave plate are "S" polarized. Light rays 18(n) next
intersect reflective polarizer 34. Because light rays 18(n) are "S"
polarized and reflective polarizer 34 is a "P" polarizer, light
rays 18(n) do not transit through the reflective polarizer but
rather reflect off it. The light rays are still "S" polarized.
Light rays 18(n) pass through quarter wave plate 32 again and light
rays 18(p) that exit the quarter wave plate have circular
polarization with "L" handedness. Lens 30 collects light rays 18(p)
and refracts the light rays on to half silvered mirror 28. Half of
light rays 18(p) reflect off half silvered mirror 28 (light rays
18(r)) and half the light rays transmit through the half silvered
mirror (light rays 18(s)). Reflecting off half silvered mirror 28
causes the handedness of the light rays' circular polarization to
reverse; light rays 18(r) now are circularly polarized with an "R"
handedness. Lens 30 collects light rays 18(r) and refracts the
light rays on to quarter wave plate 32. The quarter wave plate
changes the polarization of the light rays from circular "R" to
linear "P". Light rays 18(u) next intersect reflective polarizer
34. Because light rays 18(u) are now "P" polarized and reflective
polarizer 34 is a "P" polarizer, the light rays pass through the
reflective polarizer unchanged before passing through linear
polarizer 36, which also does not change the light rays'
polarization. Light rays 18(u) form an image on diffuser 14; this
image has a height c (for example, 7 inches). Lens 16 collects
light rays 18(v) and focuses them on eyeball 20. Based on the
distance b between eyeball 20 and lens 16 (for example, one inch),
the focal length of lens 16, and the height c of the image formed
by diffuser 14, viewfinder 10 in the present configuration has a
viewing angle .beta..
[0031] As it is configured in FIG. 1-4, the electrically controlled
optical elements in viewfinder 10 produce a larger image, and thus
a more highly magnified image, when the ferro-electric switchable
half wave plate is turned "off". The viewing angle, .beta., when
the ferro-electric switchable half wave plate is "off" is also
larger than the viewing angle, .theta., when the ferro-electric
switchable half wave plate is "on". Note that the effective focal
length of the electrically controlled optical elements increases
when the ferro-electric switchable half wave plate is "on" because
light rays must traverse the distance between the reflective
polarizer and the half silvered mirror three times instead of just
once. The image projected by the electrically controlled optical
elements is only half as bright when the ferro-electric switchable
half wave plate is "off" versus "on", however, because light rays
encounter the half silvered mirror twice when the ferro-electric
switchable half wave plate is "off" instead of just once when it is
"on".
[0032] It is easy to appreciate how it is possible to stack
together several individual electrically controlled optical
elements to create an optical device with multiple possible
effective focal lengths and viewing angles. The ferro-electric
switchable half wave plate in each electrically controlled optical
element stack can be individually turned "on" and "off"; therefore,
an effective focal length for the design can range from a short
distance, when all the ferro-electric switchable half wave plates
are "on", to a long distance, when the ferro-electric switchable
half wave plates are "off." In-between effective focal lengths are
possible by turning some of the ferro-electric switchable half wave
plates "on" and some "off". The distance between the half silvered
mirror and the reflective polarizer could be tailored in each
electrically controlled optical element stack in order to meet
design criteria. The polarizers in each individual electrically
controlled optical stack must be designed to transmit the polarized
light that exits the previous electrically controlled optical
element stack.
[0033] Those of skill in the art will recognize that it is possible
to fabricate electrically controlled optical elements that project
a smaller image or create an image with a smaller field of view
when the ferro-electric switchable half wave plate is "on" without
departing from the spirit of the invention. This can be done, for
example, by replacing lens 30 with a diverging lens. The rest of
the components of a such a system would operate in the same manner
as described in the preceding paragraphs.
Application to Zoom Lenses
[0034] It is also advantageous to use electrically controlled
optical elements in applications such as zoom lenses. FIGS. 5a and
5b schematically illustrate in cross sectional view the optical
elements of a prior art zoom lens in a first and second zoom state,
respectively. The operation of zoom lens 50 is familiar to those of
skill in the art. In FIGS. 5a and 5b, light rays 60 from an object
62 are focused by the zoom lens on to an internal surface 64.
Surface 64 may be, for example, the surface of a charge coupled
device, light sensitive film, or the like. In order to change the
magnification of the image of object 62 on surface 64, the
effective focal length of the lens is changed. This is executed by
moving lens group 54 relative to lens 52 and lens group 56. A first
zoom state is illustrated in FIG. 5a, with lens group 54 is located
a distance g from lens 52 (for example, 2.6 inches) and a distance
h from lens group 56 (for example, 1.5 inches), resulting in an
effective focal length of, for example, two inches. A second zoom
state is illustrated in FIG. 5b; lens group 54 is moved to a
distance i from lens 52 (for example, 2.9 inches) and a distance j
from lens 56 (for example, 1.2 inches) resulting in an effective
focal length of, for example, 5.9 inches. In typical zoom lenses,
the manipulation of lens group 54 is performed using mechanical
adjusters or a motor. These adjusters take up space, which is often
undesirable. Also, while the overall length of zoom lens 50,
represented by distance k (for example, 12.5 inches), does not
change when moving lens group 54, in many zoom lenses the overall
length does not remain fixed while altering the lens' focal length.
This can be problematic if a static overall lens length is
desired.
[0035] Alternately, electrically controlled optical elements may be
used instead of mechanical adjusters to alter the effective
distances between the lenses and lens groups. FIGS. 6a and 6b
schematically illustrate in cross sectional view a zoom lens that
employs electrically controlled optical elements in a first and
second zoom state, respectively. The optical elements of zoom lens
70 remain unchanged from zoom lens 50 except for the addition of
electrically controlled optical element groups 72 and 74.
Electrically controlled optical element group 72 is located between
lens 52 and lens group 54, and electrically controlled optical
element group 74 is located between lens group 54 and lens group
56. Lens 52 and lens group 54 are physically separated by distance
1 (for example, 2.6 inches), and lens group 54 and lens group 56
are physically separated by distance m (for example, 1.2 inches).
The length of the lens 70 stays the same constant distance k (for
example, 12.5 inches). Unlike with zoom lens 50, these physical
distances do not change as the focal length of lens 70 changes. In
this particular example, the ferro-electric switchable half wave
plates always operate in opposite states; i.e., the ferro-electric
switchable half wave plate in electrically controlled optical
element group 72 is on when the ferro-electric switchable half wave
plate in electrically controlled optical element group 74 is off,
and vice versa. A first zoom state is illustrated in FIG. 6a; the
ferro-electric switchable half wave plate in electrically
controlled optical element group 72 is "on", while the
ferro-electric switchable half wave plate in electrically
controlled optical elements 74 is "off." Therefore, the light path
between lens 52 and lens group 54 is unaffected, and light
traveling from lens 52 to lens group 54 must travel a distance l.
The light traveling between lens group 54 and lens group 56 travels
three times between the half silvered mirror and the reflective
polarizer in electrically controlled optical element group 74. This
results in an effective light path length that is longer than
distance m (for example, the effective light path length between
lens group 54 and lens group 56 may be 1.5 inches). The second zoom
state is illustrated in FIG. 6b; the ferro-electric switchable half
wave plate in electrically controlled optical element group 72 is
"off", while the ferro-electric switchable half wave plate in
electrically controlled optical elements 74 is "on." The light
traveling between lens 52 and lens group 54 travels three times
between the half silvered mirror and the reflective polarizer in
electrically controlled optical element group 72. This results in
an effective light path length that is longer than distance l (for
example, the effective light path length between lens 52 and lens
group 54 may be 2.9 inches). The light path between lens group 54
and lens group 56 is unaffected, and light traveling from lens
group 54 to lens group 56 must travel a distance m.
[0036] Those of skill in the art will recognize that it is possible
to use more or less electrically controlled optical element groups
in a zoom lens to achieve a similar result without departing from
the spirit of the invention.
[0037] Those of skill in the art will recognize that different
configurations also exist, such as ones that do not require each
electrically controlled optical element group to operate in
opposite states.
[0038] While the foregoing invention is described for use in
applications such as viewfinders and zoom lenses, the invention
finds relevance without limitation in a wide range of applications.
Electrically controlled optical elements may be used, for example,
to create diffuser elements with variable diffuser angles,
variable-magnification compact microscopes, and the like.
* * * * *