U.S. patent application number 10/298697 was filed with the patent office on 2003-05-22 for display with variably transmissive element.
This patent application is currently assigned to University of Washington. Invention is credited to Furness, Thomas Adrian III, Kollin, Joel S..
Application Number | 20030095081 10/298697 |
Document ID | / |
Family ID | 27048427 |
Filed Date | 2003-05-22 |
United States Patent
Application |
20030095081 |
Kind Code |
A1 |
Furness, Thomas Adrian III ;
et al. |
May 22, 2003 |
Display with variably transmissive element
Abstract
A display includes an image source for generating light and a
lensing system. The lensing system defines an optical path from an
input to an output, receiving the generated light at the input and
transmitting light at the output. The lensing system includes a
variably transmissive element which maintains contrast between the
transmitted light and an ambient light.
Inventors: |
Furness, Thomas Adrian III;
(Seattle, WA) ; Kollin, Joel S.; (Seattle,
WA) |
Correspondence
Address: |
Steven P. Koda, Esq.
KODA LAW OFFICE
P.O. Box 10057
Bainbridge Island
WA
98110
US
|
Assignee: |
University of Washington
Seattle
WA
98195
|
Family ID: |
27048427 |
Appl. No.: |
10/298697 |
Filed: |
November 18, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10298697 |
Nov 18, 2002 |
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09918329 |
Jul 30, 2001 |
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09918329 |
Jul 30, 2001 |
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09312932 |
May 17, 1999 |
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6317103 |
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09312932 |
May 17, 1999 |
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08911989 |
Aug 13, 1997 |
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6008781 |
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08911989 |
Aug 13, 1997 |
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08485630 |
Jun 7, 1995 |
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5659327 |
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08485630 |
Jun 7, 1995 |
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07965070 |
Oct 22, 1992 |
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5467104 |
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Current U.S.
Class: |
345/32 ;
348/E9.026 |
Current CPC
Class: |
G02B 27/0172 20130101;
G02B 2027/0118 20130101; G02B 2027/0132 20130101; G02B 2027/0187
20130101; G02B 2027/0138 20130101; G02B 2027/0198 20130101; G09G
3/003 20130101; G02B 27/017 20130101; H04N 9/3129 20130101; G09G
3/02 20130101; G02B 2027/0116 20130101; G09G 3/025 20130101 |
Class at
Publication: |
345/32 |
International
Class: |
G09G 003/00 |
Claims
What is claimed is:
1. A display apparatus, comprising: an image source for generating
light; a lensing system defining an optical path from an input to
an output, the lensing system receiving the generated light at the
input and transmitting light at the output, the lensing system
comprising a variably transmissive element which maintains contrast
between the transmitted light and an ambient light.
2. A display apparatus according to claim 1, in which the variably
transmissive element comprises a photochromic material which alters
transmissiveness of the variably transmissive element as a function
of the ambient light.
3. A display system comprising: an image generator responsive to an
image signal to generate image light; a variably transmissive
element which changes transmissiveness as a function of ambient
light to attenuate light passing through the variable transmissive
element, wherein light including the image light and the attenated
light is presented for viewing.
4. A display system according to claim 3, in which the variably
transmissive element is a passively variable transmissive element
light which changes transmissiveness as a function of ambient
light.
5. A display system according to claim 3, in which the optical
element is an actively variable transmissive element light which
receives a control signal to actively vary the transmissiveness of
the optical element.
6. A display system according to claim 5, further comprising a
photosensor responsive to the ambient light, the photosensor
generating the control signal.
7. A display system according to claim 3, in which the variably
transmissive element comprises a liquid crystal device.
8. A method of display, comprising: generating image light in
response to an image signal; receiving the image light at a lensing
system, the lensing system including a variably transmissive
element; varying transmissiveness of the variably transmissive
element as a function of ambient light received at the variably
transmissive element to maintain contrast between the image light
and the ambient light.
9. A method of display according to claim 8, in which said variably
transmissive lement comprises photochromic material and said
varying comprises: passively varying transmissiveness of the
variably transmissive element as a function of the ambient
light.
10. A method of display according to claim 8, further comprising:
sensing ambient light with a photosensor, wherein the variably
transmissive element is actively variable in response to the sensed
ambient light.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/918,329 filed Jul. 30, 2001 of Furness for
"Retinal Display Scanning," which is a continuation of U.S. patent
application Ser. No. 08/312,932 filed May 17, 1999 of Furness et
al. for "Virtual Retinal Display and Method for Tracking Eye
Position,.infin. which is a continuation of U.S. patent application
Ser. No. 08/911,989 filed Aug. 13, 1997 of Furness et al. for
"Virtual Retinal Display" and issued as U.S. Pat. No. 6,008,781 on
Dec. 28, 1999, which is a continuation of U.S. patent application
Ser. No. 08/485,630 filed Jun. 7, 1995 and issued as U.S. Pat. No.
5,659,327 on Aug. 19, 1997, which in turn is a continuation of U.S.
patent application Ser. No. 07/965,070 filed Oct. 22, 1992 of
Furness et al. and issued as U.S. Pat. No. 5,467,104 on Nov. 14,
1995 for .cent.Virtual Retinal Display..infin.
BACKGROUND OF THE INVENTION
[0002] The present invention is directed to a virtual image display
system and more particularly to a virtual retinal display wherein
photons modulated with video information are projected directly
onto the eye to produce a virtual image without a perceivable
aerial image outside of the user's eye.
[0003] With known virtual image displays, a user does not view
directly a physical display screen such as with real image
displays. Typically, the virtual display creates only a small
physical image using a liquid crystal array, light emitting diodes
or a miniature cathode ray tube, CRT, the image being projected by
optical lenses and mirrors so that the image appears to be a large
picture suspended in the world.
[0004] A miniature cathode ray tube can produce a medium resolution
monochrome picture. However, these devices are heavy and bulky. For
example, a typical weight of a miniature CRT with cables is greater
than four ounces, the CRT having a one inch diameter and a four
inch length. Further, these devices have high voltage acceleration
potential, typically 7-13 kilovolts which is undesirably high for a
display that is mounted on a user's head. Creating color using a
single miniature CRT is difficult and usually causes significant
compromises in image resolution and luminance. Although the CRT
image may be relayed via a coherent fiber-optics bundle to allow
the CRT to be located away from head mounted optics, the hardware
to accomplish this is also heavy and causes significant light loss.
Field sequential color using a multiplexed color filter and CRT
with white phosphor is able to create good color hue saturation but
also at a significantly reduced resolution. For example, three
color fields must be produced during the same period as a normal 60
Hz field, thereby dividing the video bandwidth for each color by
three.
[0005] A liquid crystal array can produce a color image using a low
operating voltage, but it can provide only a marginal picture
element (pixel) density, i.e. less than 800 by 800 elements. One
commercial device is known that uses a linear array of light
emitting diodes viewed via a vibrating mirror and a simple
magnifier. Although this is a low cost and low power alternative,
the display is monochrome and limited in line resolution to the
number of elements which can be incorporated into the linear
array.
[0006] Both the CRT and liquid crystal display generate real images
which are relayed to the eyes through an infinity optical system.
The simplest optical system allows a user to view the image source
through a simple magnifier lens. For fields of view greater than 30
degree., this approach leads to a number of problems including
light loss and chromatic aberrations. Further, these optics are
bulky and heavy.
[0007] Virtual projection optical designs create an aerial image
somewhere in the optical path at an image plane which is then
viewed as an erect virtual image via an eye piece or objective
lens. This approach increases the flexibility by which the image
from the image source can be folded around the user's head for a
head mounted display system, but large fields of view require large
and bulky reflective and refractive optical elements.
[0008] In addition to resolution limitations, current systems also
have bandwidth deficiencies. Bandwidth is a measure of how fast the
display system can address, modulate or change the light emissions
of the display elements of the image source. The bandwidth of the
display image source is computed on the basis of the number of
elements which must be addressed over a given period of time.
Addressing elements temporally is needed to refresh or maintain a
perceived luminance of each element taking into account the light
integration dynamics of retinal receptors and the rate at which
information is likely to change. The minimum refresh rate is a
function of the light adaptive state of the eye, display luminance,
and pixel persistence, i.e. the length of time the picture element
produces light after it has been addressed. Minimum refresh rates
of 50 to 60 times a second are typically needed for television type
displays. Further, an update rate of at least 30 Hz is needed to
perceive continuous movement in a dynamic display or in a
presentation in which the display image is stabilized as a result
of head movement. Refreshing sequentially, i.e. one element at a
time, 40 million picture elements at a 60 Mhz rate would require a
video bandwidth of 2.4 GHz. Bandwidth requirements can be reduced
by interlacing which tricks the eye in its perception of flicker
but still requires that all of the elements of the image source be
addressed to achieve a minimum update rate of 30 Hz or 1.2 GHz
bandwidth. Typical television broadcast quality bandwidths are
approximately 8 MHz, or two orders of magnitude less than the 1.2
GHz. High resolution computer terminals have 1400 by 1100 picture
elements which are addressed at a 70 Hz non-interlaced rate which
is the equivalent to a bandwidth of approximately 100 MHz.
SUMMARY OF THE INVENTION
[0009] A display includes an image source for generating light and
a lensing system. The lensing system defines an optical path from
an input to an output, receiving the generated light at the input
and transmitting light at the output. The lensing system includes a
variably transmissive element which maintains contrast between the
transmitted light and an ambient light.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a block diagram of the virtual retinal display of
the present invention;
[0011] FIG. 2 is a block diagram illustrating one embodiment of the
virtual retinal display depicted in FIG. 1;
[0012] FIG. 3 is a second embodiment of the virtual retinal display
of FIG. 1 utilizing color;
[0013] FIG. 4 is a block diagram illustrating another embodiment of
a color virtual retinal display in accordance with the present
invention;
[0014] FIG. 5 is a diagram of an LED array utilized in a further
embodiment of the virtual retinal display of the present invention
employing parallel photon generation and modulation;
[0015] FIG. 6 is an illustration of a laser phased array;
[0016] FIG. 7 is an illustration of a microscanner utilized in
accordance with the present invention; and
[0017] FIG. 8 is an illustration of another microscanner that may
be utilized in accordance with the present invention.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0018] The virtual retinal display 10 of the present invention as
shown in FIG. 1 utilizes photon generation and manipulation capable
of creating a panoramic, high resolution, color image that is
projected directly onto the eye of a user, there being no aerial
image or image plane outside of the eye that is viewed by the user.
The virtual retinal display does not use a display that generates a
real image such as a CRT, LCD or LED array as in prior virtual
image displays. Nor does the virtual retinal display 10 need the
mirrors or optics necessary in prior virtual image displays to
generate an aerial image. Instead, photons modulated with video
information are scanned directly onto the retina 22 of a user's eye
20 to produce the perception of an erect virtual image. Because the
virtual retinal display 10 does not utilize a real image display or
the mirrors or optics necessary to generate an aerial image, the
virtual retinal display 10 is small in size and weight and is
therefore suitable to be easily mounted on the user's head as a
head mounted display.
[0019] More particularly, as shown in FIG. 1, photons from a photon
generator 12 are modulated with video information by a modulator
14. The modulated photons are scanned in a first direction and in a
second direction generally perpendicular to the first direction by
a scanner 16 to create a raster of photons that is projected
directly onto the retina 22 of the eye 20 of the user by projection
optics 18 to produce the perception of an erect virtual image
without an aerial image or image plane outside of the eye that is
viewed or perceived by the user. Although not necessary, it is
desirable to employ an eye tracking system 24 to reposition the
scanned raster of light as the pupil 26 of the eye 20 moves so that
the light ray bundles are coincident with the entrance pupil of the
eye. The eye tracking system 24 can also be used as feedback to
change the image or the focus of the image scanned onto the retina
as the eye moves so that the user perceives that he is focusing on
a different portion of a panoramic scene as he shifts his eye. It
is noted that the dotted lines shown entering the eye 20 in FIG. 1
as well as in subsequent figures represents the range of scanning
and not the instantaneous ray bundle.
[0020] The photon generator 12 may generate coherent light such as
a laser or it may generate noncoherent light such as by utilizing
one or more LEDs. Further, beams of red, green and yellow or blue
light may be modulated by RGY or RGB video signals to scan colored
photons directly onto the user's eye. In order to reduce the
bandwidth of the virtual retinal display, multiple monochromatic
beams or multiple groups of colored beams can be modulated and
scanned in parallel onto the retina where the video information
used to modulate the photons is divided into different sectors or
regions and each beam or group of colored beams is associated with
a different sector of video information as described below. It is
further noted that the functions performed by one or more of the
photon generator 12, modulator 14, scanner 16 and projection optics
18 can be combined to be performed by fewer elements depending upon
the actual components used in the system. For example, an
acousto-optic deflector may be used to both modulate the light from
the photon generator 12 and to scan the modulated light in at least
one direction. Further, a laser phased array may be utilized to
perform the functions of the photon generator, modulator and one or
possibly two scanners as discussed below.
[0021] The components of the virtual retinal display 10 can be made
small, compact and lightweight so that the virtual retinal display
10 can easily be mounted on the head of a user without requiring a
helmet or an elaborate head mounting for structural support.
Further, the photon generator 12 and modulator 14 can be separated
from the scanner 16 and projection optics 18 so that only the
scanner 16 and optics 18 need be mounted on the head of a user, the
modulated photons being coupled to the scanner via one or more
monofilament optical fibers. In a preferred embodiment,
microscanners are utilized to scan the photons, such microscanners
being small, thin and deflected to scan the photons in response-to
an electrical drive or deflection signal. The photon generator,
modulator and scanner can therefore be made very small such as
{fraction (11/2)} inch high by {fraction (11/2)} inch wide by 1/4
inch thick or less with a weight of less than an ounce so as to
facilitate a head mounting for the virtual retinal display 10.
[0022] In accordance with one embodiment of the present invention
as shown in FIG. 2, high resolution scanners are used to deflect a
beam of light both horizontally and vertically in a two dimensional
raster pattern. No lens is used to focus the beam to form a real
image in front of the eye. Instead, the lens 29 of the eye focuses
the beam to a point on the back of the retina, the position of the
beam point scanning the retina as the scanner 16 scans the
modulated photons. The angle of deflection of the collimated light
beams corresponds to the position of the focused spot on the retina
for any given eye position just as if an image were scanned at an
infinite distance away from the viewer. The intensity of the light
is modulated by the video signal in order to create an image of
desired contrast. Therefore, when the user's eye moves, the user
will perceive a stationary image while he looks at different parts
of the scene. The lateral extent of the image is proportional to
the angle of the scan. Anamorphic optics are used as necessary to
align the scanned photons and to scale the perceived image. By
forming a reduced image of the scanner aperture, a proportionately
larger scanning angle is yielded. Other than this, the size of the
scanner image is irrelevant as long as the light enters the
eye.
[0023] More particularly, as shown in FIG. 2, light or photons from
a photon generator 12 is projected through a cylindrical lens 30
and a spherical lens 32 to an acousto-optical deflector 34 that
scans the photons in a first or horizontal direction. The
cylindrical lens spreads the light beam from the photon generator
12 horizontally so that it fills the aperture of the
acousto-optical deflector 34. The spherical lens 32 horizontally
collimates the light which impinges onto the acousto-optical
deflector 34.
[0024] The acousto-optical deflector 34 is responsive to a video
signal on a line 36 that is applied as a drive signal to a
transducer of the acousto-optic deflector 34 to modulate the
intensity of the photons or light from the photon generator 12 and
to scan the modulated light from the photon generator 12 in a first
direction or horizontally. The video signal on line 36 is provided
by a video drive system generally designated 38 that includes a
video controller 42. The video controller 42 may include a video
generator such as a frame buffer 40 that provides video signals on
a line 56 and respective horizontal sync and vertical sync signals.
The video controller 42 may also include a microprocessor that
operates in accordance with software stored in a ROM 46 or the like
and utilizes a RAM 48 for scratch pad memory. The horizontal sync
signal from the video generator 40 is converted to a ramp wave form
by a ramp generator 50, the horizontal sync ramp waveform is
applied to a voltage controlled oscillator 52 that provides a
signal in response to the ramp input having a frequency that varies
such that it chirps. The output from the voltage controlled
oscillator 52 is applied to an amplifier 54 the gain of which is
varied by the video data signal 56 output from the video generator
40 so that the video signal 36 output from the amplifier 54 has an
amplitude that varies in accordance with the video information on
line 56 and that has a frequency that varies in a chirped manner.
The video signal on line 36 is applied to a drive transducer of the
acousto-optical deflector 34. Varying the amplitude of the drive
signal on line 36 with the video information causes the
acousto-optical deflector 34 to modulate the intensity of the light
from the photon generator 12 with the video information. Varying
the frequency of the drive signal on line 36 in a chirped manner
causes the acousto-optical deflector to vary the angle at which the
light is deflected thereby so as to scan the light in a first or
horizontal direction.
[0025] A spherical lens pair 64 and 68 images the horizontally
scanned light or photons onto a vertical scanner 62 wherein a
cylindrical lens 68 spreads the light vertically to fill the
aperture of the vertical scanner 62. The vertical scanner 62 may
for example be a galvanometer. The vertical sync signal output from
the video generator 40 is converted to a ramp waveform by a ramp
generator 58 and amplified by an amplifier 60 to drive the vertical
scanner 62. The speed of scanning of the vertical scanner 62 is
slower than the scanning of the horizontal scanner 34 so that the
output of the vertical scanner 62 is a raster of photons. This
raster of photons is projected directly onto the eye 20 of the user
by projection optics taking the form of a toroidal or spherical
optical element 72 such as a refractive lens, mirror, holographic
element, etc.
[0026] The toroidal or spherical optical element 72 provides the
final imaging and reduction of the scanned photons. More
particularly, the toroidal or spherical optical element relays the
scanned photons so that they are coincident near the entrance pupil
26 of the eye 20. Because a reduced image of the scanner aperture
is formed, the deflection angles are multiplied in accordance with
the Lagrange invariant wherein the field of view and image size are
inversely proportional. As the size of the scanned photons, i.e.
the exit aperture of the virtual retinal display are reduced, the
field of view of the image perceived by the eye increases.
[0027] The optical element 72 can be an occluding element that does
not transmit light from outside of the display system.
Alternatively the optical element 72 can be made light transmissive
to allow the user to view the real world through the element 72
wherein the user perceives the scanned virtual image generated by
the display 10 superimposed on the real world. Further, the optical
element 72 can be made variably transmissive to maintain the
contrast between the outside world and the displayed virtual image.
A passively variable light transmissive element 72 may be formed by
sandwiching therein a photochromic material that is sensitive to
light to change the light transmissiveness of the element as a
function of the ambient light. An actively variable light
transmissive element 72 may include a liquid crystal material. A
photosensor can be used with such an element to detect the amount
of ambient light wherein a bias voltage across the liquid crystal
material is varied in accordance with the detected light to
actively vary the light transmissiveness of the element 72.
[0028] The system described thus far with respect to FIG. 2 is
monocular. In order to provide a stereoscopic system a second
virtual retinal display 10' may be utilized in parallel with the
first retinal display 10, the second virtual retinal display 10'
projecting scanned photons modulated with the appropriate video
information directly on the second eye 20' of the user. This
provides a medium for binocular depth information so that displayed
objects appear at different depths. Each pixel of the object,
however, appears at the same distance from the user which can
create a possible conflict between the stereoscopic cue and the
monocular cue where the stereoscopic cue deals with the positioning
of the object with respect to each eye and the monocular cue deals
with the focus of the light of the object being imaged on the
retina. More particularly, in prior virtual image display systems,
each monocular image plane was typically focused at optical
infinity causing each of the pixels within the virtual image to
appear at one distance. However, the combination of two prior
monocular systems to form the binocular view created a possible
conflict between the distance cues and the focus or accommodation
cue.
[0029] The virtual retinal display of the present invention
overcomes this problem by utilizing an accommodation cue 70 either
in the monocular display system 10 or in the binocular display
system formed of displays 10 and 10'. The accommodation cue 70 is a
focusing or depth cue that is controlled to vary the focus or
convergence or divergence of the scanned photons rapidly to control
the depth perceived for each picture element of the virtual image.
Therefore in accordance with the present invention true depth
perception is obtained by modulating each pixel for depth
individually such as by controlling the focus, i.e. the convergence
or divergence, of the individual pixel. The accommodation cue 70
includes a reflective surface that changes shape rapidly. For
example, a miniature mirror having a deformable membrane whose
shape is altered as the membrane is charged and discharged may be
used to form the accommodation cue. The deformation of the membrane
is thus varied by an electrical drive signal to control the
convergence or divergence of each pixel for depth. The drive of the
accommodation cue 70 is provided by the video controller 42 which
may, for example, store a Z axis video information buffer in the
memory 48 or in the video generator 40 in addition to the two
dimensional video information in a typical frame buffer.
[0030] A further embodiment of the virtual retinal display 10 of
the present invention is depicted in FIG. 3 for scanning colored
photons directly onto the retina of a user's eye. As shown in FIG.
3, the photon generator 12 includes colored lasers or LEDs such as
a red photon generator 80, a green photon generator 82 and a blue
photon generator 84. If a blue photon generator is unavailable, a
yellow photon generator may be utilized. The colored photons from
the generators 80, 82 and 84 are modulated with respective RGB
video information from the video generator 40 and then combined by
a beam combiner/dispersion precompensator 86. The output of the
beam combiner/dispersion precompensator 86 is projected onto the
horizontal scanner 34 by the cylindrical lens 30 and the spherical
lens 32. It is noted tht the horizontal scanner may be other than
the acousto-optic scanner shown in FIG. 2. For example, a resonant
mechanical scanner or various types of microscanners as discussed
below may be used for the horizontal scanner. The horizontally
scanned color modulated photons output from the scanner 34 are
projected onto a dispersion compensator 88 the output of which is
projected onto a prism before being projected onto the vertical
scanner 62 by the spherical lens pair 64 and 68.
[0031] The colored photon raster as scanned from the output of the
vertical scanner 62 is projected by a spherical lens 92 onto an
offset mirror 96 which is moved by the eye tracker 106 so as to
position the raster of photons directly onto the entrance pupil 26
of the eye 20 as the pupil moves. In one embodiment, a beam
splitter 100 directs an image reflected off of the cornea of the
eye 20 to a lens 102 and a position sensing diode 104 that is
coupled to the eye tracker 106 to detect the position of the pupil
26. In response to the detected position of the pupil, the eye
tracker correctly positions the offset mirror(s) 96 so that the
exit pupil or aperture of the virtual retinal display is
approximately aligned with the entrance pupil of the eye and/or to
adjust the scan angle to reflect changed video information as
described below.
[0032] The instantaneous position of the pupil 26 as determined by
the eye tracker 106 is also communicated to the video controller 42
so that the microprocessor 44 can direct video information to
modulate the colored light where the video information reflects a
change in the direction of the user's view. More particularly, the
detected pupil position is used by the microprocessor 44 to
position a "visible window" on the video information stored in the
frame buffer 40. The frame buffer 40 may for example store video
information representing a panoramic view and the position of the
visible window determines which part of the view the user is to
perceive, the video information falling within the visible window
being used to modulate the light from the photon generator 12.
[0033] It is noted that because the acousto-optical deflector 34
diffracts red light more than green light and diffracts green light
more than blue light, this variation in the diffraction must be
compensated for. In accordance with the present invention, this
variation in diffraction may be compensated for by appropriately
delaying via delays 108, 110 and 112 the RGB video signals that are
coupled to the respective red, green and blue photon generators 80,
82 and 84 to modulate the red, green and blue photons with the
appropriate red, green and blue video information.
[0034] In another embodiment of the virtual retinal display of the
present invention as shown in FIG. 4, composite video or RGB video
signals are received by a digital video scan converter 120 and
separated into multiple compartments that represent sectors or
regions of an image to be scanned. Multiple video drive signals
output from the video amplifiers 124 representing each sector are
used to modulate the light from the photon generator 12 in
parallel. The photon generator may consist of either arrays of
laser diodes or arrays of high luminance light emitting diodes.
Multiple beams of red, green and yellow or blue light are modulated
with the video signals in parallel for each of the divided sectors
or regions and then relayed directly or by monofilament optical
fibers 131 to a microscanner 16. The microscanner 16 essentially
performs two functions. First, the microscanner scans the multiple
color beams associated with each sector or region in two axes to
create a raster of light on the retina and not an aerial image,
there being no image plane between the photon generator 12 and the
eye 20. Second, the microscanner 16 functions to position the
scanned light relative to the instantaneous entrance pupil 26 of
the eye as sensed by the eye tracker 24.
[0035] More particularly, the scanner 16 includes a first
microscanner 132 that is responsive to an X axis deflection signal
output from a deflection amplifier 136 to scan the color beams in a
horizontal direction where the amplifier 136 is driven by the
horizontal sync signal from a scan generator 122. A second
microscanner 134 is responsive to a Y deflection signal from the
deflection amplifiers 136 as driven by the vertical sync or
deflection drive from the scan generator 122 to scan the
horizontally scanned color photons in the vertical direction. A
scan collimation lens 140 receives a two dimensionally modulated
light field that is projected onto a tri-color combiner 142. The
combiner 142 in turn projects the scanned light onto a
Maxwellian-view optical system 148. The optical system 148 projects
the scanned colored photons onto a raster position deflector which
may include two axis galvo mirrors that in turn project the scanned
light onto a toroidal optical element such as a combiner 152 having
a trichoric coating, the toroidal combiner 152 projecting the
scanned color photons directly onto the eye 20.
[0036] For eye tracking, the eye tracker 24 includes an infrared
light source which illuminates the surface of the eye with low
intensity-infrared light either directly or indirectly as shown.
The surface of the eye is viewed through the raster position
deflector 150 via the combiner 142, a lens 140 and a charge coupled
device, CCD, array 146. The signals from the CCD sensor 146 are
processed by a pupil position processor 154 to generate null
signals, .DELTA.H and .DELTA.V, that are coupled to respective
color deflection amplifiers 158 and to the raster positioning
mirrors 150 so as to cause the scanned photons to follow the pupil
of the user's eye 20.
[0037] An example of a light emitting diode array suitable for use
in the present invention is illustrated in FIG. 5. If an X-Y visual
field is considered to be composed of an array of 2,000.times.2,000
resolvable spots or pixels, the spots must be refreshed 50 times
per second so as to have an information bandwidth of approximately
200 MHz. High brightness LEDs typically have a power bandwidth
curve that starts to roll off above 2 MHz. This result is
essentially an R-C product limitation related to the diffusion
capacitance of a heavily forward-biased p-n junction. In order to
meet the bandwidth requirements of the system, a linear array of 50
to 100 LED pixels per color are utilized. Using a red, green and
blue LED scheme would require 50-100 LEDs of each of these three
colors. As shown in FIG. 5, an array 200 includes LED chips 201,
202, 203-N wherein each LED chip includes an LED active area 205.
The LED active area may include a GaAsP alloys and a Si.sub.3
N.sub.4 dielectric overlayer.
[0038] A laser phased array as illustrated in FIG. 6 functions to
perform photon generation, video modulation and scanning in at
least one direction. The laser phased array includes a thin film
wave guide 210, phase modulator electrodes 212, a cleaned coupled
cavity 214 and laser cavities 216, the array emitting a coherent
beam of about 10 mW power.
[0039] When two closely spaced lasers are fabricated in the same
chip of material, their optical fields become coupled so that the
processes of optical emission in the two devices are correlated and
coherent. The result is a well defined phase front emitted from the
laser pair. In the laser phased array 220 having a number of laser
cavities 216, the optical beam is phase coherent if the lasers are
spaced within 10 microns of each other. This resolution can be
achieved by photolithographic techniques. The electro-optic
modulator works by modifying the index of refraction of the wave
guide medium 210 through which the optical beam must travel before
being launched into free space. By separating the electrical
contacts 212 for each modulator, the relative phase of each
individual laser in the array can be modified by the modulator. For
an appropriate series of modulation voltages, the phase front of
the laser array coupled beam can be modified so that the emitted
beam is launched at an angle to the normal exit direction. With the
appropriate series of modulation voltages the laser beam can be
scanned in a given direction. It is possible to construct a two
axis laser phased array so that an additional scanner is not needed
to scan the laser in a perpendicular direction.
[0040] An example of a microscanner 132, 134 for scanning photons
is illustrated in FIG. 7. The microscanner includes an actuator
230. The actuator 230 is a piezoelectric bimorph cantilever that is
capable of three dimensional motion in response to an electrical
drive signal. By controlling the deflection of the cantilevered
actuator with the appropriate drive signals, the actuator 230
deflects the photons incident thereto to scan the photons.
[0041] Another example of a microscanner that can be made extremely
small is shown in FIG. 8, the microscanner having a curved
reflective surface that translates to scan light impinging thereon
in one direction. More particularly, the microscanner 240 includes
a base or actuator 242 formed of a piezoelectric material with a
substrate 244 formed on the actuator 242 wherein the substrate 244
has a curved reflective surface 246. In response to a varying drive
signal the piezoelectric actuator and the substrate 244 translate
in the direction of the arrows 248 so as to scan the light
impinging on the surface 246 of the substrate in a first direction
generally perpendicular to the direction 248 of translation. A
second microscanner 250 scans the light impinging thereon in a
second direction perpendicular to the first direction so as to scan
a raster image directly onto the retina of a user's eye.
[0042] Many modifications and variations of the present invention
are possible in light of the above teachings. Thus, it is to be
understood that, within the scope of the appended claims, the
invention may be practiced otherwise than as described
hereinabove.
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