8/3/2019 Anubhav Report
1/23
CHAPTER 1
INTRODUCTION TO VRD
Typical displays feature a screen composed of a reflective or transparent material to present
images, but VRD technologies use a video source, typically a laser or LED, to describe
a raster (a pixilated image similar to those on computer or television monitors) on the eye itself.
The image is only viewable to the user, and appears to them as a small, floating, semi-transparent
picture. Many VRD systems are designed for virtual reality experiences, and present the viewer
with a wide, more encompassing image. Other VRDs are intended to aide job functions, and
present the viewer with a standard square image similar to that of a computer that appears to be
about one yard in front of them. The VRD creates images by scanning low power laser light
directly onto the retina.
This special method results in images that are bright, high contrast and high resolution.
The technologies of virtual reality (VR) and augmented reality (AR) are the new paradigm
for visual interaction with graphical environments. The VRD has features that can beoptimized for the human computer interfaces.
8/3/2019 Anubhav Report
2/23
8/3/2019 Anubhav Report
3/23
1.1 Evolution
Paul Gottlieb Nipkow - Mechanical Television History
German, Paul Nipkow developed a rotating-disc technology to transmit pictures over wire in1884 called the Nipkow disk. Paul Nipkow was the first person to discover television's scanning
principle, in which the light intensities of small portions of an image are successively analyzed
and transmitted.
Cathode Ray Tube - Electronic Television History
Electronic television is based on the development of the cathode ray tube, which is the picture
tube found in modern TV sets. German scientist, Karl Braun invented the cathode ray tube
oscilloscope (CRT) in 1897.
Color Television
Color TV was by no means a new idea, a German patent in 1904 contained the earliest proposal,
while in 1925 Zworykin filed a patent disclosure for an all-electronic color television system. A
successful color television system began commercial broadcasting, first authorized by the FCC
on December 17, 1953 based on a system invented by RCA.
Plasma TV
The very first prototype for a plasma display monitor was invented in 1964 by Donald Bitzer,
Gene Slottow, and Robert Willson.
BUT..Current display technologies require compromises that prevent full implementation of VR
and AR. A new display technology called the Virtual Retinal Display (VRD) has been created.
The development of this device has been driven by the need for a ubiquitious display that is
lightweight, full color and high resolution. In particular, the demands for displays for virtual
environments and augmented vision are most pressing. In the past, virtual environments displays
have been very heavy, low resolution and have a small field of view. To create compelling
virtual environments, the opposite is needed. The demands of displays for augmented reality,
where the computer graphics image is superimposed on the real world, include a bright, high
contrast image, and color that is appropriate.
http://inventors.about.com/library/inventors/blnipkov.htmhttp://inventors.about.com/library/inventors/blcathoderaytube.htmhttp://inventors.about.com/library/inventors/blcolortelevision.htmhttp://inventors.about.com/od/pstartinventions/a/plasmaTV.htmhttp://inventors.about.com/library/inventors/blcathoderaytube.htmhttp://inventors.about.com/library/inventors/blcolortelevision.htmhttp://inventors.about.com/od/pstartinventions/a/plasmaTV.htmhttp://inventors.about.com/library/inventors/blnipkov.htm8/3/2019 Anubhav Report
4/23
8/3/2019 Anubhav Report
5/23
CHAPTER 2
2.1 VRD Overview
The following sections describe the operational concepts and features of the VRD.
The Basic System
In a conventional display a real image is produced. The real image is either viewed directly or, as
in the case with most head-mounted displays, projected through an optical system and the
resulting virtual image is viewed. The projection moves the virtual image to a distance that
allows the eye to focus comfortably. No real image is ever produced with the VRD. Rather, an
image is formed directly on the retina of the user's eye. A block diagram of the VRD is shown in
Figure 1.
Figure.1
To create an image with the VRD a photon source (or three sources in the case of a color
display) is used to generate a coherent beam of light. The use of a coherent source (such as a
8/3/2019 Anubhav Report
6/23
laser diode) allows the system to draw a diffraction limited spot on the retina. The light beam is
intensity modulated to match the intensity of the image being rendered. The modulation can be
accomplished after the beam is generated. If the source has enough modulation bandwidth, as in
the case of a laser diode, the source can be modulated directly.
The resulting modulated beam is then scanned to place each image point, or pixel, at the proper
position on the retina. A variety of scan patterns are possible. The scanner could be used in a
calligraphic mode, in which the lines that form the image are drawn directly, or in a raster mode,
much like standard computer monitors or television. Our development focuses on the raster
method of image scanning and allows the VRD to be driven by standard video sources. To draw
the raster, a horizontal scanner moves the beam to draw a row of pixels. The vertical scanner
then moves the beam to the next line where another row of pixels is drawn.
After scanning, the optical beam must be properly projected into the eye. The goal is for the exit
pupil of the VRD to be coplanar with the entrance pupil of the eye. The lens and cornea of the
eye will then focus the beam on the retina, forming a spot. The position on the retina where the
eye focuses the spot is determined by the angle at which light enters the eye. This angle is
determined by the scanners and is continually varying in a raster pattern. The brightness of the
focused spot is determined by the intensity modulation of the light beam. The intensity
modulated moving spot, focused through the eye, draws an image on the retina. The eye's
persistence allows the image to appear continuous and stable.
Finally, the drive electronics synchronize the scanners and intensity modulator with the incoming
video signal in such a manner that a stable image is formed.
A good understanding of different methods of scanning a light source on the retina can be found
in the papers of Webb, et al [2,3,4]. In his scanning laser ophthalmoscope development, Webb
scanned a laser into the eye forming an NTSC resolution raster on the retina. The reflection of
the light off the retina was then captured. Using this technique an image of the retina could be
formed.
2.2. How the VRD Works
The Eye
A brief review of how the eye forms an image will aid in understanding the VRD.
8/3/2019 Anubhav Report
7/23
A point source emits waves of light which radiate in ever-expanding circles about the point. The
pupil of an eye, looking at the source, will see a small portion of the wavefront. The curvature of
the wavefront as it enters the pupil is determined by the distance of the eye from the source. As
the source moves farther away, less curvature is exhibited by the wavefronts. It is the wavefront
curvature which determines where the eye must focus in order to create a sharp image (see
Figure 1).
If the eye is an infinite distance from the source, plane waves enter the pupil. The lens of the eye
images the plane waves to a spot on the retina. The spot size is limited by the aberrations in the
lens of the eye and by the diffraction of the light through the pupil. It is the angle at which the
plane wave enters the eye that determines where on the retina the spot is formed. Two points
focus to different spots on the retina because the wavefronts from the points are intersecting the
pupil at different angles (see Figure 2).
Neglecting the aberrations in the lens of the eye, one can determine the limit of the eye's
resolution based on diffraction through the pupil. Using Rayleigh's criteria [1] the minimum
angular resolution is computed as follows:
angular resolution = 1.22 lambda / D
where:
lambda = wavelength of light
D = diameter of the pupil
If we assume a 2 mm pupil diameter (the size in a bright light situation) and light near the center
of the visible spectrum at 550 nm, the minimum angular separation required to resolve two
8/3/2019 Anubhav Report
8/23
points is 1.15 arc minutes. Thus, to approach the resolution of the eye, the VRD must be capable
of scanning with angular resolution of less than 2 arc minutes.
Using the VRD technology it is possible to build a display with the following characteristics:
Very small and lightweight, glasses mountable
Large field of view, greater than 120 degrees
High resolution, approaching that of human vision
Full color with better color resolution than standard displays
Brightness sufficient for outdoor use
Very low power consumption
True stereo display with depth modulation
Capable of fully inclusive or see through display modes
In a conventional display a real image is produced. The real image is either viewed directly or
projected through an optical system and the resulting virtual image is viewed. With the VRD no
real image is ever produced. Instead, an image is formed directly on the retina of the user's eye.
A block diagram of the VRD is shown below. To create an image with the VRD a photon source
(or three sources in the case of a color display) is used to generate a coherent beam of light. The
use of a coherent source (such as a laser diode) allows the system to draw a diffraction limited
spot on the retina. The light beam is intensity modulated to match the intensity of the image
being rendered. The modulation can be accomplished after the beam is generated or, if the source
has enough modulation bandwidth as is the case with a laser diode, the source can be modulated
directly.
The resulting modulated beam is then scanned to place each image point, or pixel, at the proper
position on the retina. A variety of scan patterns are possible. The scanner could be used in a
calligraphic mode, in which the lines that form the image are drawn directly, or in a raster mode,
much like standard computer monitors or television. Our development focuses on the raster
method of scanning an image and allows the VRD to be driven by standard video sources. To
draw the raster, a horizontal scanner moves the beam to draw a row of pixels. The vertical
scanner then moves the beam to the next line where another row of pixels is drawn.
8/3/2019 Anubhav Report
9/23
In the original prototype the faster horizontal scanning is accomplished with an acousto-optical
modulator and the vertical scanning with a galvanometer to produce a 1280 pixel by 1024 line
raster that is updated at 72 Hertz. The use of the acousto-optical modulator does, however, come
with a number of drawbacks. First, it requires optics to shape the input beam for deflection and
then additional optics to reform the output beam to the desired shape. Second, it requires
complex drive electronics that operate at a very high frequency. Next, it has a very limited scan
angle (4 degrees in our current prototype) such that additional optics are needed to increase the
angle to the desired field-of-view. Due to the optical invariant, this optical increase in angle
comes with the penalty of decreased beam diameter which leads to a small exit pupil. The small
exit pupil necessitates precise alignment with the eye for an image to be visible. Finally, the
acousto-optical modulator is expensive and will not, in the foreseeable future, allow us to reach
our cost goals for a complete VRD system.
To overcome the limitations of the acousto-optical modulator HITL engineers have developed a
proprietary mechanical resonant scanner. This scanner provides both horizontal and vertical
scanning, with large scan angles, in a miniaturized package. The estimated recurring cost of this
scanner will allow the VRD system to be priced competitively with other displays. A prototype
VRD using the new mechanical resonant scanner has been developed and is currently being
refined.
After scanning, the optical beam must be properly projected into the eye. The goal is for the exit
pupil of the VRD to be coplanar with the entrance pupil of the eye. The lens of the eye will then
focus this collimated light beam on the retina to form a spot. The position on the retina where the
eye focuses a spot is determined by the angle at which light enters the eye. This angle is
determined by the scanners and is constantly varying in a raster pattern. The intensity of the
focused spot is determined by the intensity modulation of the light beam. The intensity
modulated moving spot focused on the retina forms an image.
The final portion of the system is the drive electronics which must synchronize the scanners with
the intensity modulators to form a stable image.
For 3-D viewing an image will be projected into both of the user's eyes. Each image will be
created from a slightly different view point to create a stereo pair. With the VRD, it is also
possible to vary the focus of each pixel in the image such that a true 3-D image is created. Thus,
8/3/2019 Anubhav Report
10/23
the VRD has the ability to generate an inclusive, high resolution 3-D visual environment in a
device the size of conventional eyeglasses.
2.3. CONTRUCTION
Figure 2 is a block diagram of the VRD. Laser sources are introduced into a fiber optic
strand which brings light to the Mechanical Resonance Scanner (MRS) (patent pending). The
MRS is the heart of the system. It is a lightweight device approximately 2 cm X 1 cm X 1cm in
size and consists of a polished mirror on a mount. The mirror oscillates in response to pulsed
magnetic fields produced by coils on the system mounting. It oscillates at 15 KHz and rotates
through an angle of 12 degrees. The high frequency of scanning allows the fine resolution in
the images produced. As the MRS mirror moves, the light is scanned in the horizontal direction.
Because the mirror of the MRS oscillates sinusoidally, the scanning in the horizontal direction
has been arranged for both the forward and reverse direction of the oscillation. The scanned
light is then passed to a mirror galvanometer or second MRS which then scans the light in the
vertica direction.The horizontally and vertically scanned light is then introduced to the eye. The
light can be sent through a mirror/combiner to allow the user to view the scanned image
superimposed on the real world.
8/3/2019 Anubhav Report
11/23
.
Figure-2 Block Diagram of VRD
The mode of illumination of the retina by the VRD is quite different from conventional
8/3/2019 Anubhav Report
12/23
screens. The scanning mechanism rapidly sweeps a spot of light over the retina. The spot passes
over the retinel (an area analogous to the retinal area where a pixel is focused ). Thus the retinel
is not illuminated uniformly in time. Further, the actual time of illumination is extremely brief
(40 nanoseconds). There is only a brief spike of illumination of a portion of the retina for each
refresh cycle of the display. The light from the VRD is coherent and very narrow band in
wavelength. The VRD can be configured such that the spot actually overlaps retinels or is
smaller than a retinal area
2.4 VRD Features
The following sections detail some of the advantages of using the VRD as a personal display.
Size and Weight
The VRD does not require an intermediate image on a screen as do systems using LCD or CRT
technology. The only required components are the photon source (preferably one that is directly
modulatable), the scanners, and the optical projection system. Small photon sources such as a
laser diode can be used. As described below the scanning can be accomplished with a small
mechanical resonant device developed in the HITL. The projection optics could be incorporated
as the front, reflecting, surface of a pair of glasses in a head mount configuration or as a simple
lens in a hand held configuration. HITL engineers have experimented with single piece Fresnel
lenses with encouraging results. The small number of components and lack of an intermediate
screen will yield a system that can be comfortably head mounted or hand held.
Resolution
Resolution of the current generation of head mounted and hand held display devices is limited by
the physical parameters associated with manufacturing the LCDs or CRTs used to create the
image. No such limit exists in the VRD. The limiting factors in the VRD are diffraction and
optical aberrations from the optical components of the system, limits in scanning frequency, and
the modulation bandwidth of the photon source.
A photon source such as a laser diode has a sufficient modulation bandwidth to handle displays
with well over a million pixels. If greater resolution is required multiple sources can be used.
8/3/2019 Anubhav Report
13/23
Currently developed scanners will allow displays over 1000 lines allowing for the HDTV
resolution systems. If higher resolutions are desired multiple sources, each striking the scanning
surface at a different angle, can be used.
If care is taken in the optical system design then the primary cause of diffraction will be the
primary scanning aperture. The aperture with the current scanner, developed in the HITL, is a
mirror. The scan angle from the mirror must be magnified for large field of view systems
yielding a smaller effective aperture. The current mirror size of 3 millimeters will limit
resolution in a 50 degree field of view system to better than two arc minutes. Further refinement
in scanner design should improve this figure.
Field of View
The field of view of the VRD is controlled by the scan angle of the primary scanner and the
power of the optical system. Initial inclusive systems with greater than 60 degree horizontal
fields of view have been demonstrated. Inclusive systems with 100 degree fields of view are
feasible. See through systems will have somewhat smaller fields of view. Current see through
systems with over 40 degree horizontal fields of view have been demonstrated.
Color and Intensity Resolution
Color will be generated in a VRD by using three photon sources, a red, a green, and a blue. The
three colors will be combined such that they overlap in space. This will yield a single spot color
pixel, as compared to the traditional method of closely spacing a triad, improving spatial
resolution.
The intensity seen by the viewer of the VRD is directly related to the intensity emitted by the
photon source. Intensity of a photon source such as a laser diode is controlled by the current
driving the device. Proper control of the current will allow greater than ten bits of intensity
resolution per color.
Brightness
Brightness may be the biggest advantage of the VRD concept. The current generation of personal
displays do not perform well in high illumination environments. This can cause significant
problems when the system is to be used by a soldier outdoors or by a doctor in a well lit
operating room. The common solution is to block out as much ambient light as possible.
Unfortunately, this does not work well when a see through mode is required.
8/3/2019 Anubhav Report
14/23
The VRD creates an image by scanning a light source directly on the retina. The perceived
brightness is only limited by the power of the light source. Through experimentation it has been
determined that a bright image can be created with under one microwatt of laser light. Laser
diodes in the several milliwatt range are common. As a result, systems created with laser diode
sources will operate at low laser output levels or with significant beam attenuation.
Power Consumption
The VRD delivers light to the retina efficiently. The exit pupil of the system can be made
relatively small allowing most of the generated light to enter the eye. In addition, the scanning is
done with a resonant device which is operating with a high figure of merit, or Q, and is also very
efficient. The result is a system that needs very little power to operate.
A True Stereoscopic Display
The traditional head-mounted display used for creating three dimensional views projects
different images into each of the viewer's eyes. Each image is created from a slightly different
view point creating a stereo pair. This method allows one important depth cue to be used, but
also creates a conflict. The human uses many different cues to perceive depth. In addition to
stereo vision, accommodation is an important element in judging depth. Accommodation refers
to the distance at which the eye is focused to see a clear image. The virtual imaging optics used
in current head-mounted displays place the image at a comfortable, and fixed, focal distance. As
the image originates from a flat screen, everything in the virtual image, in terms of
accommodation, is located at the same focal distance. Therefore, while the stereo cues tell the
viewer an object is positioned at one distance, the accommodation cue indicates it is positioned
at a different distance.
With the VRD it is theoretically (this is currently in the development stage) possible to generate
a more natural three dimensional image. The VRD has an individual wavefront generated for
each pixel. It is possible to vary the curvature of the wavefronts. Note that it is the wavefront
curvature which determines the focus depth. This variation of the image focus distance on a pixel
by pixel basis, combined with the projection of stereo images, allows for the creation of a more
natural three-dimensional environment.
8/3/2019 Anubhav Report
15/23
2.5 Current VRD Development
Using seed funds from the Washington Technology Center the first VRD prototype was
developed in the HITL by Dr. Tom Furness, Joel Kollin, and Bob Burstein . The project's initial
goal was to prove the viability of forming an image on the retina using a scanned laser. As a
result of the work, a patent application was filed and the technology licensed to a Seattle based
start up company, Micro Vision, Inc. Under terms of the agreement, Micro Vision is funding a
four-year effort in the HITL to develop the technologies that will lead to a commercially viable
VRD product. This development work began in November 1993.
Prototype #1
The original prototype had very low effective resolution, a small field of view, limited gray
scale, and was difficult to align with the eye. One objective of the current development effort
was to quickly produce a bench-mounted system with improved performance.
Prototype #1 uses a directly modulated red laser diode at a wave length of 635 nanometers as the
light source. The required horizontal scanning rate of 73,728 Hertz could not be accomplished
with a simple galvanometer or similar commercially available moving mirror scanner. The use of
a rotating polygon was deemed impractical because of the polygon size and rotational velocity
required. It was thus decided to perform the horizontal scan with an acousto-optical scanner. The
vertical scanning rate of 72 Hertz is within the range of commercially available moving mirrors
and is accomplished with a galvanometer.
8/3/2019 Anubhav Report
16/23
The use of the acousto-optical scanner comes with a number of drawbacks:
* It requires optics to shape the input beam for deflection and then additional optics to reform the
output beam to the desired shape. Figure 4 is a schematic of the optical path for Prototype #1.
Total optical path length for this system is 45 centimeters.
* It requires complex drive electronics that operate at frequencies between 1.2 GHz and 1.8 GHz.
* Its total scan angle is 4 degrees. Thus, additional optics are needed to increase the angle to the
desired field-of-view. Due to the optical invariant, this optical increase in angle comes with the
penalty of decreased beam diameter which leads to a small exit pupil. The small exit pupil
necessitates precise alignment with the eye for an image to be visible.
* It is expensive and will not, in the foreseeable future, allow us to reach our cost goals for a
complete VRD system.
Prototype #2
To overcome the limitations of the acousto-optical scanner, HITL engineers have developed a
miniature mechanical resonant scanner. This scanner, in conjunction with a conventional
galvanometer, provides both horizontal and vertical scanning with large scan angles, in a
compact package. The estimated recurring cost of this scanner will allow the VRD system to be
priced competitively with other displays. Prototype #2 of the VRD uses the mechanical resonant
scanner. Achieved performance specifications for this system are given in Table 2. The system
was built and demonstrated during the summer of 1994. The VGA resolution images produced
are sharp and spatially stable. A schematic of the optical path of Prototype #2 is shown in Figure
5. The total optical path length for this system is 8 centimeters.
8/3/2019 Anubhav Report
17/23
Mechanical Resonant Scanner
The mechanical resonant scanner has many unique features. Foremost among these is the fact
that the device has neither a moving magnet nor a moving coil. Instead, it uses a flux circuit
whose only moving part is the torsional spring/mirror combination. Eliminating moving coils or
magnets greatly lowers the rotational inertia of the device, thus raising the potential operating
frequency. Figure 6 shows a drawing of the current version of the mechanical resonant scanner.
Dimensions of the scanner are .9 centimeters high by 1.3 centimeters wide by 2.8 centimeters
long.
The mechanical resonant scanner is used in conjunction with a conventional galvanometer in a
combination which allows for an increase in the optical scan angle. When the mirrors of the two
scanners are arranged in such a manner that a light beam undergoes multiple reflections off the
mirrors, then the optical scan is multiplied by the number of reflections off that mirror. Optical
scan multiplication factors of 2X, 3X and 4X have been realized. Prototype #2 uses a system
with 2X scan multiplication in the horizontal axis.
Prototype #3
The third prototype system developed uses the same scanning hardware as Prototype #2 but uses
three light sources to produce a full color image. In addition the eyepiece optics have been
modified to allow for see through operation. In the see through mode the image produced by the
VRD is overlaid on the external world. Performance specifications for this system are shown in
Table 3.
Future Prototypes
Our plan calls for a new VRD prototype every six months. Each prototype will incrementally add
features to the system. Future prototype work will concentrate on improving image resolution,
increasing image field of view, expanding the exit pupil, generating full color images, and
shrinking the system to head-mounted size.
Color System Development
In order to produce full color images three sources must be used. The blue and green color
sources used in Prototype #3 are gas lasers that are larger than desired for a portable system.
Laser diodes can now be purchased for the red source, however, green and blue laser diodes are
not currently available. A significant industrial effort is under way to develop these shorter
8/3/2019 Anubhav Report
18/23
wavelength devices[6], however, the devices are not likely to be available for a number of years.
As an alternative, small green lasers are now being produced which use a crystal to frequency
double a neodymium YAG laser. These devices are larger than desired and are not directly
modulatable at the required frequency. They do however, offer a short term solution.
In the HITL we are investigating a number of alternatives to blue and green laser diodes. One
frequency doubling technique being researched uses rare earth doped fibers as the doubling
medium. A second technique uses wave guides placed in a lithium niobate substrate for the
doubling.
The above methods all utilize a laser as the light source. Additional work is directed at using
non-lazing, light-emitting diodes (LEDs) as the light source. In order for this to be successful
two primary issues are being addressed. The first issue is how to focus the LED output to the
desired spot size. The second issue is the development of fabrication techniques that will allow
us to directly modulate the LEDs at the desired frequency.
Exit Pupil
The exit pupil in the current prototypes is still quite small. The exit pupil for Prototype #2, for
example, is approximately 1.5 millimeters. Thus, the eye must be aligned with the exit pupil to
view the image. This will not present an issue in a hand held unit but is not optimal for a head
mounted unit. Methods of enlarging the exit pupil are therefore being developed.
Holographic Optical Elements
To minimize the weight of optical components in the system holographic optical elements are
being developed. A complete holographic laboratory has been set up. Results to date include the
development of an off-axis reflective lens that can be used in a see through system to combine
the video image with the outside world view.
Advanced Scanning Methods
The mechanical resonant scanner has been demonstrated to work for displays up to 800 lines.
Development of an even faster mechanical resonant scanner is underway. Based on this work it
appears practical to build mechanical resonant scanners that operate at greater than 1000 lines at
72 Hertz.
8/3/2019 Anubhav Report
19/23
Theoretically the VRD can produce images that approach the resolution of the eye. This will
require scanners that can operate with over 3000 resolution lines. Methods including parallel
scanning and ultra high speed scanners are being investigated to meet this requirement.
CHAPTER 3
3.1Advantages
Apart from the advantages mentioned before, the VRD system scanning light into only one of
our eyes allows images to be laid over our view of real objects, and could give us an animated,
X-ray like image of a car's engine or human body, for example.
VRD system also can show an image in each eye with a very little angle difference for
simulating three-dimensional scenes with high fidelity spectral colours. If applied to video
games, for instance, gamers could have an enhanced sense of reality that liquid-crystal-display
glasses could never provide, because the VRD can refocus dynamically to simulate near and
distant objects with a far superior level of realism.
This system only generates essentially needed photons, and as such it is more efficient for mobile
devices that are only designed to serve a single user. A VRD could potentially use tens or
hundreds of times less power for Mobile Telephone and Netbook based applications.
3.2Safety
It is believed that VRD based Laser or LED displays are not harmful to the human eye, as they
are of a far lower intensity than those that are deemed hazardous to vision, the beam is spread
over a greater surface area, and does not rest on a single point for an extended period of time.
To ensure that VRD device is safe, rigorous safety standards from the American NationalStandards Institute and the International Electrotechnical Commission were applied to the
development of such systems. Optical damage caused by lasers comes from its tendency to
concentrate its power in a very narrow area. This problem is overcome in VRD systems as they
are scanned, constantly shifting from point to point with the beams focus.
8/3/2019 Anubhav Report
20/23
3.3Utilities
Military utilities
VRDs have been investigated for military use as an alternative display system forHelmet
Mounted Displays. However no VRD-based system has yet reached operational use and current
military HMD development now appears focused on other technologies such as holographic
waveguide optics.
Medical utilities
A system similar to car repair procedures can be used by doctors for complex operations. While
a surgeon is operating, he or she can keep track of vital patient data, such as blood pressure or
heart rate, on a VRD. For procedures such as the placement of a catheter stent, overlaid images
prepared from previously obtainedmagnetic resonance imagingorcomputed tomography scans
assist in surgical navigation.
Cameras
In the mass-market of digital cameras, scanned-beam displays provide better image quality at
lower power and cost than liquid-crystal-on-silicon and organic LED displays.
Scanned-beam technology is capable of displaying images, the data channel through a digital-to-
analog converter controlling the light source to paint a picture on a blank canvas in a display.
When an image is captured, the light source is turned on, and the data channel looks at the
reflections from the object through an analog-to-digital converter connected to a photodiode. The
light source, beam optics, and scanner are essentially the same in both applications.
Radiology
One examination performed by radiologists is the fluoroscopic examination. During a
fluoroscopic examination, the radiologist observes the patient with real-time video x-rays. The
radiologist must continually adjust the patient and the examination table until the patient is in a
desired position. When the patient is in a desired position, the radiologist takes a film copy of the
x-ray image. The positioning process can be difficult and cumbersome because the radiologist
must visually keep track of a patient, a video monitor, and an examination table simultaneously.
Because the VRD can operate in a see-through mode at high luminance levels, it is an ideal
http://www.enotes.com/topic/Helmet_mounted_displayhttp://www.enotes.com/topic/Helmet_mounted_displayhttp://www.enotes.com/topic/Magnetic_resonance_imaginghttp://www.enotes.com/topic/Magnetic_resonance_imaginghttp://www.enotes.com/topic/Magnetic_resonance_imaginghttp://www.enotes.com/topic/Computed_tomographyhttp://www.enotes.com/topic/Helmet_mounted_displayhttp://www.enotes.com/topic/Helmet_mounted_displayhttp://www.enotes.com/topic/Magnetic_resonance_imaginghttp://www.enotes.com/topic/Computed_tomography8/3/2019 Anubhav Report
21/23
display to replace the bulky video monitor in a fluoroscopic examining room. The radiologist
could see through the x-ray display and see the patient as well. Other features such as a display
luminance control or on/off switch could easily be included for this application.
Surgery
Surgery to remove a cancerous growth requires knowledge of the growth's location. Computed
tomographic or magnetic resonant images can locate a tumor inside a patient. A high luminance
see-through display, such as the VRD, in conjunction with head tracking, could indicate visually
where a tumor lies in the body cavity. In the case that a tumor lies hidden behind, say, an organ,
the tumor location and a depth indicator could be visually laid over the obstructing organ. An
application in surgery for any display would clearly require accurate and reliable head tracking.
Manufacturing
The same characteristics that make the VRD suitable for medical applications, high luminance
and high resolution, make it also very suitable for a manufacturing environment. In similar
fashion to a surgery, a factory worker can use a high luminance display, in conjunction with head
tracking, to obtain visual information on part or placement locations. Drawings and blueprints
could also be more easily brought to a factory floor if done electronically to a Virtual Retinal
Display (with the option of see-through mode). Operator interface terminals on factory floors
relay information about machines and processes to workers and engineers. Thermocouple
temperatures, alarms, and valve positions are just a few examples of the kind of information
displayed on operator interface terminals. Eyeglass type see-through Virtual Retinal Displays
could replace operator interface terminals. A high luminance eyeglass display would make the
factory workers and engineers more mobile on the factory floor as they could be independent of
the interface terminal location.
Communications
The compact and light weight nature of the mechanical resonant scanner (MRS) make an MRS
based VRD an excellent display for personal communication. A hand held monochrome VRDcould serve as a personal video pager or as a video FAX device. The display could potentially
couple to a telephone. The combination of telephone services and video capability would
constitute a full service personal communication device.
8/3/2019 Anubhav Report
22/23
Virtual Reality
The traditional helmet display is an integral part of virtual reality today. The VRD will be
adapted for this application. It can then be used for educational and architectural applications in
virtual reality as well as long distance virtual conference communications. Indeed it can be
utilized in all applications of virtual reality. The theoretical limits of the display, which are
essentially the limits of the eye, make it a promising technology for the future in virtual reality
HMD's.
CHAPTER 5
ConclusionThe ongoing VRD development project at the HITL has proven the viability of building displays
which scan images directly on the viewer's retina. Such displays offer performance
improvements when compared to currently available head-mounted displays in the following
areas:
* Size and weight
8/3/2019 Anubhav Report
23/23
* Cost
* Resolution
* Field-of-view
* Brightness
* Power consumption
To date, three prototype systems have been constructed. The current prototype uses a proprietary
mechanical resonant scanner to generate VGA resolution color images. The system's simple
optical design yields a device that is small and easy to adjust when compared to earlier
prototypes utilizing acousto-optic scanners for horizontal deflection.
Many challenges remain before the VRD reaches it's full potential. Chief among these is the
development of the low cost blue and green light sources needed for a full color display.
Finally, the VRD is applicable to a wide variety of applications in a number of fields including
medicine, manufacturing, communications, and virtual reality.
References
[1] E. Hecht and A. Zajac, Optics, 1979, Addison-Wesley, pp. 353-354.
[2] R. H. Webb, G. W. Hughes,, and O. Pomerantzeff, "Flying spot TV ophthalmoscope",Applied Optics, Vol. 19, pp. 2991, 1980.
[3] R. H. Webb, "Optics for laser rasters", Applied Optics, Vol. 23, pp. 3680, 1984.
[4] R. H. Webb, G. W. Hughes, F. C. Delori, "Confocal scanning laser ophthalmoscope",Applied Optics, Vol. 26, pp. 1492, 1987.
[5] J. Kollin, "A Retinal Display for Virtual-Environment Applications", Proceedings of theSociety for Information Display, Vol. 24, pp. 827, 1993.
[6] G. F. Neumark, R. M. Park, and J. M. DePuydt, "Blue-Green Diode Lasers", Physics Today,June 1994, pp. 26.