U.S. patent application number 10/386242 was filed with the patent office on 2003-09-04 for optical system for miniature personal displays using reflective light valves.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Doany, Fuad Elias, Singh, Rama Nand.
Application Number | 20030165013 10/386242 |
Document ID | / |
Family ID | 25267234 |
Filed Date | 2003-09-04 |
United States Patent
Application |
20030165013 |
Kind Code |
A1 |
Doany, Fuad Elias ; et
al. |
September 4, 2003 |
Optical system for miniature personal displays using reflective
light valves
Abstract
An illumination system and display are disclosed that include a
light for providing light, a polarizing beam splitter (PBS) having
a first surface that receives the light from the backlight. The PBS
passes a first polarization of the received light to a curved
mirror located at a second PBS face, which second PBS face is
opposite the first PBS face. The curvature of the mirror provides
the optical power necessary for proper imaging, while limiting the
reflecting area of the mirror provides an aperture stop that
determines the numerical aperture of the optical system. The
display also includes a quarter wave plate and a spatial light
modulator (SLM). The quarter wave plate is located between the PBS
and mirror and changes the first polarization of light, directed
from the PBS to the mirror, to a second polarization which is
reflected from the mirror back to the PBS. The SLM receives this
second polarization of light after reflection thereof by the PBS,
and selectively rotates the second polarization of light to form an
image forming light having the first polarization, which is
reflected back to the PBS. Through an exit face, the PBS provides
the rotated image forming light to a viewer. Between the viewer and
the PBS exit surface, an imaging lens system is provided that
includes at least one folding mirror.
Inventors: |
Doany, Fuad Elias; (Katonah,
NY) ; Singh, Rama Nand; (Bethel, CT) |
Correspondence
Address: |
SCULLY SCOTT MURPHY & PRESSER, PC
400 GARDEN CITY PLAZA
GARDEN CITY
NY
11530
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
25267234 |
Appl. No.: |
10/386242 |
Filed: |
March 11, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10386242 |
Mar 11, 2003 |
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09876403 |
Jun 7, 2001 |
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09876403 |
Jun 7, 2001 |
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08834570 |
Apr 7, 1997 |
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6310713 |
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Current U.S.
Class: |
359/489.07 ;
353/20; 359/489.08; 359/489.18 |
Current CPC
Class: |
G02B 27/0172 20130101;
G02B 5/30 20130101 |
Class at
Publication: |
359/485 ;
359/494; 353/20 |
International
Class: |
G03B 021/14; G02B
005/30; G02B 027/28 |
Claims
Having thus described our invention, what we claim as new, and
desire to secure by Letters Patent is:
1. An illumination system for a display comprising: a light source
for providing a light; a polarizing beam splitter for splitting
said light into first and second polarizations; and a reflective
device for reflecting light received from said polarizing beam
splitter back to said polarizing beam splitter.
2. The illumination system of claim 1, wherein said reflective
device is an aperture stop that determines a numerical aperture of
the illumination system.
3. The illumination system of claim 2, wherein said reflective
device reflects light within said numerical aperture back to said
polarizing beam splitter, and rejects light falling outside said
numerical aperture onto a light absorbing substrate.
4. The illumination system of claim 1, wherein a reflective surface
of said reflective device provides an aperture stop.
5. The illumination system of claim 1, wherein said reflective
device is a mirror.
6. The illumination system of claim 1, wherein said reflective
device is curved to provide a predetermined optical power.
7. The illumination system of claim 1 further comprising a spatial
light modulator for rotating a polarization of said light reflected
back to said polarizing beam splitter from said reflective device,
and reflecting said rotated light back to said polarizing beam
splitter.
8. The illumination system of claim 1 further comprising a quarter
wave plate located between said polarizing beam splitter and said
reflective device.
9. The illumination system of claim 1 further comprising a lens
located between said light source and said polarizing beam
splitter, said lens directing said light from said light source to
said polarizing beam splitter.
10. The illumination system of claim 1 further comprising a
collimating film located between said light source and said
polarizing beam splitter, wherein said collimating film collimates
said light from said light source.
11. The illumination system of claim 1 further comprising a
polarizing plate located between said light source and said
polarizing beam splitter, wherein said polarizing plate provides
polarization control of said light from said light source.
12. The illumination system of claim 7 further comprising a lens
located between said polarizing beam splitter and said spatial
light modulator, wherein said lens provides said light to said
spatial light modulator in a substantially normal direction to said
spatial light modulator.
13. The illumination system of claim 7 further comprising a
polarizing plate disposed on an exit surface of said polarizing
beam splitter, said exit surface being opposite a polarizing beam
splitter surface facing said spatial light modulator.
14. The illumination system of claim 7 further comprising an
imaging lens system located between a viewer and an exit surface of
said polarizing beam splitter, said exit surface being opposite a
polarizing beam splitter surface facing said light modulator.
15. The illumination system of claim 14, wherein said imaging lens
system includes at least one folding mirror.
16. A display for projecting an image comprising: a backlight
source for providing a light; a polarizing beam splitter having a
first surface that receives the light from the backlight source,
said polarizing beam splitter passing a first polarization and
reflecting a second polarization of the received light; a reflector
that receives said first polarization of light from said polarizing
beam splitter and reflects it back to the polarizing beam splitter;
a quarter wave plate disposed between said polarizing beam splitter
and said reflector, said quarter wave plate changing said first
polarization of light from said polarizing beam splitter to said
second polarization of light received by said polarizing beam
splitter from said reflector; a spatial light modulator that
receives from said polarizing beam splitter said second
polarization of light received by said polarizing beam splitter
from said reflector, said spatial light modulator selectively
rotating said received second polarization of light to form an
image forming light of said first polarization, and reflecting said
image forming light toward a viewer through said polarizing beam
splitter.
17. The display of claim 16, wherein said reflector is an aperture
stop that determines a numerical aperture of the illumination
system.
18. The display of claim 17, wherein said reflector reflects light
within said numerical aperture back to said polarizing beam
splitter, and reflects light falling outside said numerical
aperture to a light absorbing substrate.
19. The display of claim 16, wherein a reflective surface of said
reflector provides an aperture stop.
20. The display of claim 16, wherein said reflector is curved to
provide a predetermined optical power.
21. The display of claim 16 further comprising a lens located
between said backlight source and said polarizing beam splitter,
said lens directing said light from said backlight source to said
polarizing beam splitter.
22. The display of claim 16 further comprising a collimating film
located between said backlight source and said polarizing beam
splitter, wherein said collimating film collimates said light from
said backlight source.
23. The display of claim 16 further comprising a polarizing plate
located between said backlight source and said polarizing beam
splitter, wherein said polarizing plate provides polarization
control of said light from said backlight source.
24. The display of claim 16 further comprising a lens located
between said polarizing beam splitter and said spatial light
modulator, wherein said lens provides said light to said spatial
light modulator in a substantially normal direction to said spatial
light modulator.
25. The display of claim 16 further comprising a polarizing plate
disposed on an exit surface of said polarizing beam splitter, said
exit surface being opposite a polarizing beam splitter surface
facing said spatial light modulator.
26. The display of claim 16 further comprising an imaging lens
system located between the viewer and an exit surface of said
polarizing beam splitter, said exit surface being opposite a
polarizing beam splitter surface facing said light modulator.
27. The illumination system of claim 26, wherein said imaging lens
system includes at least one folding mirror.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is directed to an optical system for
illuminating and imaging a reflective light valve, and more
particularly, to systems using compact lightweight, and foldable
optics for personal miniature displays using reflective light
valves.
[0003] 1. Discussion of the Prior Art
[0004] Typically, conventional miniature displays, such as head
mounted displays (HMDs), are based on miniature cathode ray tube
(CRT) or transmission-based liquid crystal light valve technology.
The CRT-based systems are bulky, expensive, and heavy, and
primarily used for military helmet-mounted applications. This
technology is not suitable for lightweight, compact personal
displays.
[0005] Transmission-based liquid crystal (LC) technology is the
preferred technology for these portable miniature displays today.
Although appropriate for the low resolution displays currently
available, such as sub-VGA to VGA (64O.times.480 pixels), this
transmission-based LC technology is not adequate for high
resolution miniature portable displays. VGA refers to video
graphics adapter.
[0006] A transmission technology based display requires a clear
aperture for transmission of light through the display. A
transparent substrate is also required which incorporates all the
display driving circuitry (such as active matrix circuitry).
[0007] Typically, the driving circuitry uses amorphous silicon on
glass technology or poly-silicon on quartz technology. The
requirements of transparent substrate, clear aperture, and display
control circuitry limit the minimum size of the display panel, thus
preventing further display size reductions. To achieve smaller size
display panels, reflective liquid crystal (LC) light valves are
used.
[0008] Reflective liquid crystal light valves do not have the size
limitation of transmission-based LC light valves. For reflective LC
light valves, using crystalline silicon CMOS technology, the active
matrix driving circuitry can be fabricated on 10 micron pixel
dimensions or smaller. Furthermore, by using reflection liquid
crystal devices, the requirement for a clear aperture in the
display panel, needed for transmissive LC devices, is dispensed
with. Instead, the reflective device incorporates a mirror array
that is fabricated over the underlying CMOS circuitry. In this
case, the entire surface of the device is available for display
aperture. Thus, the pixel size is only limited by the CMOS
technology required to fabricate the drive circuitry, which today
is less than 10 microns per pixel. The functioning reflective
display panel is completed when the liquid crystal and top glass
are assembled over the mirror array.
[0009] Thus, miniature high resolution (>VGA) displays can be
fabricated using silicon-based reflection liquid crystal devices.
However, reflection-based light valves, such as liquid crystal (LC)
spatial light modulators (SLMs) have complex illumination
requirements. In reflection mode, the SLM must be illuminated and
imaged from the same side. A simple backlight structure typically
used in transmission-based displays is not directly applicable for
reflective SLMs.
[0010] In order to illuminate the reflective SLM with polarized
light, and image the SLM using a perpendicular polarization,
typical optical systems incorporate a polarizing beam splitter cube
(PBS) over the SLM.
[0011] FIG. 1 shows a conventional optical system 10. A light
source 12 illuminates a reflective SLM 14 through a PBS 16. Image
forming light, which is reflected from the SLM 14, passes through
the PBS 16 and is viewed through an optical imaging system 20. The
optical imaging system 20 has several lens elements, such as lens
elements 22, 24.
[0012] The PBS 16 receives polarized light from the light source
12, passes one polarization, e.g., p-polarization, and reflects the
other polarization, e.g. s-polarization. The p-polarized light beam
26 passing through the PBS 16 is incident onto the SLM 14 at
largely normal incidence to the SLM 14.
[0013] The liquid crystal SLM 14 functions by selectively rotating
the p-polarized light beam 26 to s-polarized light beam 28 at the
individual pixel level to form an image in the SLM 14. The
p-polarization of light (not shown) reflected from the SLM 14
passes through the PBS 16 and is discarded. The s-polarized light
beam 28 reflected from the SLM 14, which is the image forming light
resulting from selective polarization rotation by the SLM 14, is
reflected by the inner surface 30 of the PBS 16 and directed toward
the optical imaging system 20. Next, the image forming light 28 is
imaged by the optical imaging system 20 to provide the proper
imaging of the SLM 14 to a viewer 32. The illumination is thus
incident onto the SLM 14 through the PBS 16.
[0014] A typical light source for miniature liquid crystal displays
(LCDs) uses cold cathode fluorescent light sources (CCFL). One
example is a linear CCFL tube coupled to a flat backlight
structure. This example is a miniature version of the backlight
that is typically used for conventional LCD laptop computer
displays. Another example is using a CCFL source that is itself
flat and rectangular. Both examples produce a compact flat surface
emitting light source. The light source 12 depicted in FIG. 1 is a
typical CCFL-based backlight (either flat CCFL or backlight panel
incorporating a linear CCFL tube).
[0015] The angular distribution of light emitted from backlights is
typically larger than the acceptance angle of the LCD. The addition
of light brightness enhancing polymer films improves the
directionality of the light, but cannot produce a collimated light
source. In FIG. 1, a collimating film 35 and an optional lens 40
are shown located between the backlight 12 and PBS 16,
respectively. The collimating film 35 and optional lens 40
collimate light from the backlight 12, and direct the collimated
light to the SLM 14 through the PBS 16. The collimating film 35 is
disposed on the backlight surface that faces the lens 40. The lens
40 is used for focusing and directing the light from the
collimating film 35 to the PBS 16.
[0016] Although the conventional optical system 10 provides useful
illumination to the SLM 14, the optical system 10 is not optimal
and suffers from a number of disadvantages. First, light coupling
to the SLM 14 is inefficient. Second, there is no control for the
numerical aperture (NA) of the illumination.
[0017] Even when used with the collimating film 35 and the focusing
lens 40, the angular distribution of the light entering the PBS 16
from the backlight 12 is larger than the acceptance angles of the
PBS 16 and SLM 14. The polarization of the light beyond the
acceptance angles is not adequately controlled by the collimating
film 35 and/or focusing lens 40. This produces poor contrast in the
resulting image. Furthermore, light at the extreme angles will
scatter off the numerous optical surfaces producing additional
depolarized background stray light and ghost images that will
further degrade the image contrast.
[0018] In order to provide an efficient well-controlled
illumination to the SLM, relay optics and an illumination aperture
stop are included. FIG. 2 shows such a conventional illumination
system 50. The illumination system 50 includes a multi-element
relay optics 52 to couple light from the light source 12 to the SLM
14. In addition, the illumination system 50 includes an
illumination aperture stop 54 in order to control or limit the
numerical aperture or angular distribution of light.
[0019] As in the conventional illumination system 10 of FIG. 1, in
the conventional illumination system 50 of FIG. 2, the illumination
is incident onto the reflective SLM 14 through the PBS 16. The
light source 12 is imaged onto the SLM 14 by the multi-element
relay lens 52, which has several optical elements, such as lenses
56, 58, 60, 62. The aperture stop 54 is within the multi-element
relay lens 52, and is used to limit the numerical aperture of the
illuminating light. The light source 12 itself incorporates the
collimating film in order to enhance throughput. FIG. 2 shows the
collimating film 35 located on a surface of the backlight 12 that
faces the multi-element relay lens 52.
[0020] Although the conventional illumination optical system 50 is
adequate for illuminating the reflective SLM 14, the optical system
50 is large and bulky. In addition, the optical system 50 is not
suitable for portable personal displays, particularly compact,
lightweight, head mounted displays.
SUMMARY OF THE INVENTION
[0021] The object of the present invention is to provide an optical
system that eliminates the problems of conventional optical
systems.
[0022] Another object of the present invention is to provide an
optical system which is compact, efficient, has reduced background
stray light and ghost images, and has enhanced contrast and
brightness.
[0023] Yet another object of the present invention is to provide an
optical system that has high optical performance and accommodates
folding mirrors suitable for compact portable displays and head
mounted displays (HMDs).
[0024] A further object of the present invention is to provide an
optical system that provides the imaging and light controlling
optics, including providing a desired numerical aperture, in a
compact and folded optical package.
[0025] These and other objects of the present invention are
achieved by an illumination system and display comprising a light
source for providing light, and a polarizing beam splitter (PBS)
for splitting the light into first and second polarizations. The
PBS passes the first polarization and reflects the second
polarization of light.
[0026] A reflective device is provided for reflecting light
received from the PBS back to it. The reflective device is an
aperture stop that determines the numerical aperture of the
illumination system/display, and reflects light within the
numerical aperture back to PBS. Light outside the numerical
aperture falls on a light absorbing substrate. Illustratively, the
reflector is a mirror and is curved to provide a predetermined
optical power.
[0027] The illumination system and display further comprises a
quarter wave plate and a spatial light modulator (SLM). The quarter
wave plate, which is located between the PBS and reflector, changes
the first polarization of light, directed from the PBS to the
reflector, to the second polarization, which is received by the PBS
from the reflector.
[0028] The SLM receives this second polarization of light after
reflection thereof by the PBS, and selectively rotates the second
polarization of light to form an image forming light having the
first polarization. The image forming light is reflected back to
the PBS. Through an exit face, the PBS provides the image forming
light to a viewer. Between the viewer and the PBS exit surface, an
imaging lens system that includes at least one folding mirror is
provided.
[0029] The illumination system and display also includes a first
lens, located between the light source and PBS, for directing light
from the light source to the PBS. A collimating film, located
between the light source and the polarizing beam splitter,
collimates light from the light source. A first polarizing film is
also located between the light source and PBS, and provides
polarization control of the light from the light source.
[0030] A second lens, located between the PBS and SLM, provides
light to the SLM in a substantially normal direction thereto. In
addition, a second polarizing film is disposed on an exit surface
of the PBS, where the exit surface is opposite a PBS surface that
faces the SLM.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Further features and advantages of the invention will become
more readily apparent from a consideration of the following
detailed description set forth with reference to the accompanying
drawings, which specify and show preferred embodiments of the
invention, wherein like elements are designated by identical
references throughout the drawings; and in which:
[0032] FIG. 1 shows a conventional optical system using reflective
light valves;
[0033] FIG. 2 shows another conventional optical system that
includes relay optics and an illumination aperture stop;
[0034] FIG. 3 shows an optical system using reflective light valves
according to one embodiment of the present invention;
[0035] FIG. 4 shows light beam paths of the optical system shown in
FIG. 3 according to the present invention;
[0036] FIG. 5 shows an optical system using reflective light valves
together with a viewing system according to the present
invention;
[0037] FIG. 6 shows an optical system using reflective light valves
together with a viewing system according to another embodiment of
the present invention; and
[0038] FIG. 7 shows an optical system using reflective light valves
according to a further embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] FIG. 3 shows one embodiment of an illumination system 100
suitable for compact portable displays having a reflective SLM 14.
The illumination optics of the system 100 are compact but provide
the full function as the conventional system 50 shown in FIG. 2.
That is, the optics of the system 100 relay light from a light
source, such as the backlight source 12, onto the SLM 14. In
addition, the optics of the system 100 provide an aperture stop to
limit the numerical aperture of the system 100. The compact nature
of the illumination system 100 is derived from folding the optical
path almost entirely within the PBS 16. The individual optical
elements are placed on three surfaces of the PBS 16.
[0040] The illumination optical relay system 100 comprises a light
source, such as the backlight 12 for providing light, and a PBS 16
having a first surface 105, which is an input surface that receives
light from the backlight 12. The first PBS surface 105 is referred
to as an input surface. Illustratively, the light source 12 is a
cold cathode fluorescent light sources (CCFL), such as: a linear
CCFL tube coupled to a flat backlight structure, or a CCFL source
that is itself flat and rectangular.
[0041] The PBS 16 provides one polarization of the received light
to a reflective device 110. Illustratively, the reflector 110 is a
mirror and is curved. The reflector 110 is located at a second PBS
face 115, which second PBS surface 115 is opposite the first PBS
surface or input surface 105. Illustratively, to minimize the size
of the optical system 100, the curved mirror 110 is directly
attached to the second surface 115 of the PBS 16.
[0042] The optical system 100 further comprises first and second
lens elements 120, 130. The first lens element 120 is located
between the backlight 12 and the PBS input surface 105. The second
lens element 130 is located between a third PBS face 135 and the
SLM 14.
[0043] The reflector or mirror 110 provides a dual function: (1) it
provides the optical power required for proper imaging; and (2) it
is the aperture stop that determines the numerical aperture of the
optical system 100.
[0044] The optical power is provided by the curvature of the mirror
110. The aperture stop is controlled by providing a desired
reflecting area of the mirror 110. Limiting the reflecting area of
the mirror 110 limits the numerical aperture of the optical system
100. This provides a reflective aperture stop within the complete
optical system 100.
[0045] Thus, the optical system 100 of FIG. 3 is functionally
equivalent to the conventional illumination system 50 of FIG. 2.
However, unlike the conventional system 50, the optical system 100
is very compact. The majority of the optical path is contained
within the PBS 16. The PBS 16 is used in double-pass to provide an
optical path equivalent to the length of two PBSs.
[0046] Light beams emitted by the backlight 12 are collected by the
lens 120 and directed to the PBS 16. The backlight 12 itself may
incorporate a collimating film 35 to enhance throughput. To further
reduce the size of the illumination system 100, the light source
12, collimating film 35, and lens 120 are respectively attached to
each other. In addition, a polarizing film 140 may be placed at the
PBS input surface 105, between the PBS 16 and the backlight 12, to
improve polarization control.
[0047] FIG. 4 shows the light path from the light source 12 to a
viewer 32. Light beam 145 from the light source 12 enters the first
or entry face 105 of the PBS 16. The PBS 16 passes one polarization
of light, e.g., the p-polarization shown as numeral 150, and
reflects the other polarization, e.g., the s-polarization (not
shown), as is well known for a PBS.
[0048] Splitting light into two polarizations by the PBS 16 is due
to a polarization separating surface 155 internal to the PBS 16.
Illustratively, the polarization separating surface 155 is formed
by two solid glass prisms 160, 165 that form the PBS 16.
[0049] The p-polarized light beam 150 then passes through the PBS
16 and impinges onto the reflective aperture stop or mirror 110
located at the PBS surface 115, which is opposite to the PBS input
surface 105 that receives light 145 from the backlight 12.
[0050] As shown in FIGS. 3 and 4, the optical system 100 also
comprises a quarter-wave film or plate 170. Prior to reaching the
reflecting surface 110, the p-polarized light beam 150 first passes
through the quarter-wave plate 170. The quarter-wave plate 170
produces a rotation of polarization of 45 degrees each time a light
passes therethrough. In double-pass, where the light passes through
the quarter-wave film 170, a 90 degrees rotation results.
[0051] As shown in FIG. 4, the p-polarized light beam 150 passing
through the quarter-wave plate 170 toward the mirror 110, passes
through the quarter-wave plate 170 a second time upon being
reflected from the mirror or aperture stop 110. The light passing
twice through the quarter-wave film 170 rotates by 90 degrees. This
converts the p-polarized light beam 150 from the PBS 16 to the
mirror 110 to an s-polarized light beam 175 from the mirror 110 to
the PBS 16.
[0052] The reflecting area of the mirror 110 is limited to provide
a desired aperture stop for the optical system 100. Thus, only
light within a specified numerical aperture is reflected back into
the PBS 16. Light falling outside the specified numerical aperture
is rejected, since this light will "spill over" outside the
reflective stop 110 and will be directed to a black absorbing
substrate (not shown).
[0053] The s-polarized light beam 175, which is reflected from the
mirror 110, is then reflected by the PBS 16, at the interface 155
of the two prisms 160, 165 that form the PBS 16. This PBS reflected
s-polarized light is directed to the SLM 14 and is shown as numeral
180 in FIG. 4.
[0054] The second lens element 130 is placed at the SLM 14 to
collect the s-polarized light beam 180 from the PBS 16 and direct
it to the SLM 14 in a predominantly telecentric or normal
direction. The SLM 14 selectively rotates the s-polarization 180 of
the illuminating light to form a p-polarized image-forming light
185. Only the p-polarized image-forming light beam 185 is passed by
the PBS 16 and directed to the viewer 32. Any s-polarized light
(not shown) reflected from the SLM 14 is reflected away from the
viewer 32 by the PBS 16.
[0055] Optionally, another collimating film 190 is located between
the SLM 14 and lens 130. The SLM 14, collimating film 190, and lens
130 are respectively attached to each other to further reduce the
size of the illumination system 100.
[0056] FIG. 5 shows an embodiment of the illumination optical
system 100 together with an imaging optics 200 placed between the
PBS 16 and the viewer 32. FIG. 5 shows schematically how the
compact illumination optical system 100 is used with the imaging
optical system 200. In this embodiment, the imaging system 200
comprises a lens 220. The image forming p-polarized light 185 (FIG.
4), that exits the PBS 16 from an exit surface 210 thereof, is
collected by the lens 220 and is imaged to the viewer 32. The PBS
exit surface 210 is opposite the PBS surface 135 nearest the SLM
14.
[0057] The imaging system 200 also comprises an optional polarizing
film or plate 230 located between the exit surface 210 of the PBS
16 and the imaging lens 220. The polarizing plate 230 absorbs
s-polarized light and passes p-polarized light. This polarizing
film 230 absorbs any s-polarized background light and improves the
contrast of the image. The optional polarizing plates 140, 230,
shown in FIGS. 4 and 5, respectively, where one polarizing plate
140 is located at the input (between backlight 12 and PBS 16), and
the other polarizing plate 230 is located at the exit (between PBS
16 and imaging lens 220) surfaces 105, 210 of the PBS, improve
image contrast by providing better polarization purity in the
illumination and imaging optics.
[0058] FIG. 6 shows another embodiment of a complete optical system
250 which uses the illumination optical system 100 described in
connection with FIG. 3. An imaging system 260 is located between
the viewer 32 and the illumination optical system 100. The imaging
system 260 works in conjunction with the illumination optics 100 to
image the SLM 14 to the viewer 32. As shown in FIG. 6, the imaging
system 260 comprises four elements 280, 285, 290, 295 in two
groups. The first and second elements 280, 285 form the first
group, while the third and fourth elements 290, 295 form the second
group. The elements of the imaging system 260 provides desired
relaying, directing, focussing and magnifying of the image from the
PBS exit surface 210 to the viewer 32.
[0059] The complete optical system 250 of FIG. 6 provides a longer
optical path, thus allowing folding thereof to result in compact
displays. In conventional loupes or viewers used with transmissive
and/or emissive displays, the pupil of the eye at location 270
serves as the aperture stop of the lens. In the inventive optical
system, since the aperture stop or mirror 110 (FIG. 3) resides near
the PBS 16 for illumination purposes, it is necessary to make the
pupil of the eye conjugate to this aperture stop 110. This forms an
intermediate image where the field stop 110 is placed near one of
the PBS's sides 115. This additional optical relaying of the image
(between the PBS exit surface 210 and the viewer 32), together with
the pupil of the eye, results in a longer optical system providing
much needed foldability and compactness in head mounted display
(HMD) applications.
[0060] An additional advantage of the embodiment shown in FIG. 6 is
compatibility with folding optics. Foldability is desired to
produce a compact complete system for miniature personal displays,
such as head mounted displays.
[0061] FIG. 7 shows an optical system 300 which is similar to the
optical system 250 of FIG. 6, except the optical system 300 has two
folds incorporated in the optical path between the exit face 210 of
the PBS 16 and the viewer 32. Two folding mirrors 310, 320 are
positioned at convenient locations to produce a compact head
mounted display. FIG. 7 also shows a schematic representation of a
human head viewed from the top and the orientation of the fold
system.
[0062] As shown in FIG. 7, an imaging system 330 comprises six
elements 340, 345, 350, 360, 365, 370 in three groups. The first,
second and third elements 340, 345, 350 form the first group; the
fourth element 360 forms the second group; and the fifth and sixth
elements 365, 370 form the third group.
[0063] While the invention has been particularly shown and
described with respect to illustrative and preformed embodiments
thereof, it will be understood by those skilled in the art that the
foregoing and other changes in form and details may be made therein
without departing from the spirit and scope of the invention which
should be linked only by the scope of the appended claims.
* * * * *