anubhav report

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.


2/23


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.htm


4/23


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


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.


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


8/23

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.


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,


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.


11/23

.

Figure-2 Block Diagram of VRD

The mode of illumination of the retina by the VRD is quite different from conventional


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.


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.


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.


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.


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.


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


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.


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.


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_tomography


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.


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


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.

anubhav report

Documents