Seminar Report of Vrd

8/3/2019 Seminar Report of Vrd

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VISVESVARAYA TECHNOLOGICAL UNIVERSITY

BELGAUM

SEMINAR REPORT

ON

VIRTUAL RETINAL DISPLAY

Submitted in the partial fulfillment of requirements for the award of

BACHELOR OF ENGINNEERING

in

ELECTRONICS & COMMUNICATON

Submitted by

SUHAS.D.N

1DA07EC109

DEPARTMENT OF ELECTRONICS & COMMUNICATON

DR.AMBEDKAR INSTITUTE OF TECHNOLOGY

BANGALORE-56

2010-11

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DR.AMBEDKAR INSTITUTE OF TECHNOLOGY

BANGALORE-56

Department of Electronics & Communication

CERTIFICATE

Certified that the seminar report entitled VIRTUAL RETINAL DISPLAY is submitted by

SUHAS.D.N having the USN 1DA07EC109 in partial fulfillment for the award of the Degree

of Bachelor of Engineering in Electronics & Communication of the Visvesvaraya Technological

University, Belgaum, during the year 2010-11.

The seminar report has been approved as it satisfies the academic requirements in respect of the

seminar on current topicsprescribed for the Bachelor of Engineering Degree.

Signature of Examiners Signature of HOD

(1)

(2)

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ACKNOWLEDGEMENT

With great pleasure and gratefulness, I extend my deep sense of gratitude to Mrs. USHARANI

& Mrs. GIRIJA.S. for giving me an opportunity to accomplish my seminar under their

guidance and to increase my knowledge.

I also like to thanks Dr G.V.Jayaramaiah (HEAD, Electronics & communication

Engineering, Dr. Ambedkar Institute of Technology, Bangalore) for giving his precious time &

guidance for the successful completion of my seminar.

I would express my sincere gratitude towards Electronics & communication

Department, Dr. Ambedkar Institute of Technology for providing me required facilities and

state-of-the-art technology.

I am indebted to all our elders, lecturers and friends for inspiring me to do my seminar

with immense dedication. Lastly I wish to thank each and every person involved in making my

seminar successful.

Thank You.

Dr.AIT, E & C, 2010-11

Suhas.D.N

VIII Sem.

ECE


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PREFACE

Seminar is an important constituent of any curriculum and the B.E course is no

exception to this general rule. A seminar helps a student in increasing his

knowledge and confidence.

Seminar switches process of learning to process of presenting knowledge.

This provision offers a very good opportunity to the students to supplement their

knowledge and skills by giving presentation. This opportunity should be utilized

for developing and enhancing our skills.

This report describes in detail my seminar in B.E 4th year, on topic

VIRTUAL RETINAL DISPLAY.

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INDEX

1. Abstract.....6

2. Introduction ......7

3. How we perceive Image........8

4. The Virtual Retinal Display ..10

5. System Description ...13

6. Safety Analysis...........16

7. Advantages ......22

8. Disadvantages.......24

9. Application.......25

10.Comparison with other systems.......29

11. Future Scope.30

12. Conclusion........33

13. References & Bibliography.. 34

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ABSTRACT

The technologies of virtual reality (VR) and augmented reality (AR) are the new paradigm for

visual interaction with graphical environments. The features of VR are interactivity and

immersion. To achieve these features, a visual display that is high resolution and wide field of

view is necessary. For AR a visual display that allows ready viewing of the real world, with

superimposition of the computer graphics is necessary. 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 VRD has features that can be

optimized for the human computer interfaces.

As one stares at a computer monitor, light is focused into a dime-sized image on the

retina at the back of our eyeball. The retina converts the light into signals that enters our brain

via the optic nerve. To eliminate the bulky, power-hungry monitor by painting the images

themselves directly onto your retina. To do so, use tiny semiconductor lasers or special light-

emitting diodes, one each for the three primary colors-red, green, and blue-and scan their light

onto the retina, mixing the colors to produce the entire palette of human vision. Short of tapping

into the optic nerve, there is no more efficient way to get an image into your brain. And they call

it the Virtual Retinal Display, or generally a retinal scanning imaging system.

VRD readily creates images that can be easily seen in the ambient room light and it can

create images that can be seen in ambient day light. All subjects are readily able to match the

VRD brightness.

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INTRODUCTION

The Virtual Retinal Display (VRD) is a new technology for creating visual images. It was

developed at the Human Interface Technology Laboratory (HIT Lab) by Dr. Thomas A. Furness

III. 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. Current

prototypes of the system produce full color images at a true 640 by 480 resolution. The

technologies of virtual reality (VR) and augmented reality (AR) are the new paradigm for visual

interaction with graphical environments. The features of VR are interactivity and immersion. To

achieve these features, a visual display that is high resolution and wide field of view is

necessary. For AR a visual display that allows ready viewing of the real world, with

superimposition of the computer graphics is necessary. 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 VRD has features that can be

optimized for the human computer interfaces.

The VRD is a visual display device that uses scanned light beams. Instead of

viewing a screen, the user has the image scanned directly into the eye. A very small spot is

focused onto the retina and is swept over it in a raster pattern. The VRD uses very low power

and yet can be very bright. The technology has been developed such that the scanning element

will cost only a few dollars in mass production. Low cost light sources, optics and controllers

will make up the rest of the system. Ultimately, the overall device should be very inexpensive

yet it will be small enough to mount on a spectacle frame. The development of this device has

been driven by the need for a ubiquitous 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. The special characteristics of images from the VRD may make it very

useful for people with partial loss of vision.

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How we perceive Image.

A brief overview of human visual system is presented here in order to better understand how

VRD works.

2.1 Retina

A multi-layered sheet of nerve cells at the back of each eye which converts light signals to

electrical signals by performing a chemical reaction. The electric signals are transmitted to brain

through the optic nerves.

2.2 Photoreceptor

Photoreceptors are the nerve cells in the retina which emit electrical signals when activated by

light of particular wavelength. There are two types of photoreceptors cells. Rods which are

responsible for low light perception and Cones which are used to perceive colour and bright

light.

2.3 Macula

The macula is located roughly in the center of the retina. It is a small and highly sensitive part of

the retina responsible for detailed central vision. The fovea is the very center of the macula. The

macula allows us to appreciate detail and perform tasks that require central vision such reading.

Fig. 1 _ Macula view in eye

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2.4 Fovea

The fovea is the center most part of the macula and contains very large number of densely

packed cones. This tiny area is responsible for our central, sharpest vision. A healthy fovea is

key for reading, watching television, driving, and other activities that require the ability to seedetail. It is because of very high concentration of the cones (photoreceptors responsible for color

vision) which allow us to appreciate color.

Fig. 2 _ Fovea view in Macula

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The Virtual Retinal Display

The VRD scans modulated, low-power laser light to form bright, high-contrast, and high-

resolution images directly onto the retina. This technology is related to the technology

underlying the scanning laser ophthalmoscope (SLO) (4) but with the sole intent of imagedisplay, not acquisition. The VRD accepts the standard (RGB color or monochrome) output of a

computer and generates a raster-scanned image similar to the CRT monitor (Figure 1). The

portable VRD used in this study converts the VGA(red only) video output of a computer into a

signal that modulates the laser diode light source. The modulated beam of light (636 nm) is

scanned horizontally (15.75 kHz) and vertically (60 Hz) by two mirrors. A lens system

converges the raster-scanned beam to a 0.8-mm exit pupil. When the viewer aligns his or her

eye at the exit pupil, the collimated beams of scanning light create a virtual image that appears

in the distance. A detailed explanation of the VRD during early development at the University

of Washington is found in Johnston and Willey (5).

Figure 1.

Schematic diagram of the portable VRD used in this study. The directly modulated laser diode

produced a monochrome red (636 nm) output. The video input was standard VGA (6403480)

color video from a PC laptop computer.

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History

In the past similar systems have been made by projecting a defocused image

directly in front of the user's eye on a small "screen", normally in the form of large

glasses. The user focused their eyes on the background, where the screen appeared to be

floating. The disadvantage of these systems was the limited area covered by the "screen",

the high weight of the small televisions used to project the display, and the fact that the

image would appear focused only if the user was focusing at a particular "depth".

Limited brightness made them useful only in indoor settings as well.

Only recently a number of developments have made a true VRD system

practical. In particular the development of high-brightness LEDs have made the displaysbright enough to be used during the day and adaptive optics have allowed systems to

dynamically correct for irregularities in the eye (although this is not always needed). The

result is a high-resolution screenless display with excellent color gamut and brightness,

far better than the best television technologies.

The VRD was invented by Kazuo Yoshinaka of Nippon Electric Co. in 1986.

Later work at the University of Washington in the Human Interface Technology Lab

resulted in a similar system in 1991. Most of the research into VRDs to date has been in

combination with various virtual reality systems. In this role VRDs have the potential

advantage of being much smaller than existing television-based systems. They share

some of the same disadvantages however, requiring some sort of optics to send the

image into the eye, typically similar to the sunglasses system used with previous

technologies. It also can be used as part of a wearable computersystem.

More recently, there has been some interest in VRDs as a display system for

portable devices such as cell phones, PDAs and various media players. In this role the

device would be placed in front of the user, perhaps on a desk, and aimed in the general

direction of the eyes. The system would then detect the eye using facial scanning

techniques and keep the image in place using motion compensation. In this role the VRD

offers unique advantages, being able to replicate a full-sized monitor on a small device.

Dr.AIT, E & C, 2010-11
http://en.wikipedia.org/wiki/LEDhttp://en.wikipedia.org/wiki/Adaptive_opticshttp://en.wikipedia.org/wiki/Screenlesshttp://en.wikipedia.org/wiki/Color_gamuthttp://en.wikipedia.org/wiki/University_of_Washingtonhttp://en.wikipedia.org/w/index.php?title=Human_Interface_Technology_Lab&action=edit&redlink=1http://en.wikipedia.org/wiki/Virtual_realityhttp://en.wikipedia.org/wiki/Wearable_computerhttp://en.wikipedia.org/wiki/Cell_phonehttp://en.wikipedia.org/wiki/Personal_digital_assistanthttp://en.wikipedia.org/wiki/Motion_compensationhttp://en.wikipedia.org/wiki/LEDhttp://en.wikipedia.org/wiki/Adaptive_opticshttp://en.wikipedia.org/wiki/Screenlesshttp://en.wikipedia.org/wiki/Color_gamuthttp://en.wikipedia.org/wiki/University_of_Washingtonhttp://en.wikipedia.org/w/index.php?title=Human_Interface_Technology_Lab&action=edit&redlink=1http://en.wikipedia.org/wiki/Virtual_realityhttp://en.wikipedia.org/wiki/Wearable_computerhttp://en.wikipedia.org/wiki/Cell_phonehttp://en.wikipedia.org/wiki/Personal_digital_assistanthttp://en.wikipedia.org/wiki/Motion_compensation


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Retinal Scanning Technology in Low Vision

Scanned laser light for use in low-vision research and rehabilitation has previously

been considered advantageous by several authors (69). Laser sources, as used within the VRD,can produce images beyond the brightness and contrast of conventional displays, such as the

CRT and liquid crystal display (LCD). For example, miniature LCD displays used for the

purpose of a wearable low-vision aid, project inferior images in terms of contrast and brightness

compared to the CRT (10). Since a scanned laser beam is capable of intensity beyond what is

safe for the human eye, the VRD has been designed and shown (11) to produce images at safe

levels, well below maximum permissible exposure levels as defined by ANSI- and FDA-

regulated standards. The capacity of a display to produce bright images is important for low-

vision use. Cornelissenetal. (12) tested partially sighted individuals with a wide range of

maladies and found significant visual acuity improvement at higher illuminance levels.

Specifically, higher illuminations have been suggested to improve reading speed for patients

with macular degeneration (MD)(13).

Previous research with low-vision individuals viewing retinal scanned images has

shown promising results in the clinic. Webb and Hughes (6) reported dramatic improvement in

visual acuity (up to 20/70) for several patients who previously could only distinguish light from

dark. Culhametal (14) used a SLO in low-vision reading performance testing to both locate and

display virtual images onto optimal retinal locations for reading. These authors suggest that their

methods could be used to teach low-vision patients (e.g., with MD) how to more effectively

use the remaining functional areas of their retina. In addition, visual acuity and survey data from

eight lowvision subjects comparing VRD and CRT images with the use of full-color display

systems have been reported by Viirre, et al. (15). In all of these studies, the unique capabilities

of retinal light scanning benefited individuals with low vision.

However, these studies used large, sophisticated lab systems, impractical for use as

low-vision aids. Also, in the Viirre et al. (15) investigation, display brightness was optimized for

each individual and was not matched in a controlled comparison. In study, a portable,

monochrome red version of the VRD is used to better simulate a low-vision aid. It also offer the

first study to match luminance and field of view (FOV) between the VRD and the CRT.

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System Description

The VRD is comprised of six basic parts: video source, control and drive electronics, photon

sources, modulation devices, horizontal and vertical beam scanning, and delivery optics as

shown in the Figure 3.

Fig. 3 _ Block Diagram of VRD

Video Source

Input source for the VRD is like all other display is either from VGA card of a PC or from

Video camera.

Control and Drive Electronics

The control and drive electronics for the VRD store the incoming video signals and controls the

acousto-optic modulators that encode the image data into the pulse stream. The color combiner

multiplexes the individually modulated red, green, and blue beams to produce a serial stream of

pixels, which is launched into a single mode optical fiber to propagate to the scanner assembly.

The drive electronics receive and process an incoming video signal, provide image

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compensation, and control image display. For VGA projection, the electronics process over 18

Mpix/s. The virtual retinal display is capable of providing UXGA resolution of 1600 x 1200 or

115 Mpix/s. reorder alternating lines of the video stream. In addition, the drive and control

electronics control the phasing of the image, and overall system timing.

Light source

The light sources in the VRD are typically lasers though it is possible to use LEDs in limited

applications [1]. A single red laser diode having wavelength of 65O(nm)is used to provide a

monochrome display. A blue argon laser(488nm), which produces blue lines and a helium-neon

green laser (488nm) [1, 4], are used for the creation of a full color display. Systems de-

signed for indoor use can incorporate LEDs red, blue, and green devices currently under

development for such systems are being tested. Generally, the energy levels are on the order of

nanowatts to milliwatts, depending on display requirements. Each color light must be

individually modulated such that its intensity matches that of the image pixel being drawn. The

Control and Drive electronics directly modulate the laser diode. The argon gas laser

cannot be directly modulated at video rates. Therefore, an external acoustooptic modulator

(AOM) performs the modulation for each of the argon's colors. For the full color system the

modulated light from all lasers is combined into a single beam and injected into an optical ber,

which runs to the scanner assembly. The safety issue regarding using the VRD is discussed in

the section 4.

Scanner assembly

The modulated beam received from optical fiber is then scanned to place each image pixel at the

proper position on the retina. To draw the raster, a horizontal scanner moves the beam to draw a

row of pixels. A vertical scanner then moves the beam to the next line where another row of

pixels is drawn. The scan rate can be determined by multiplying the number of lines in the

display by the refresh rate of the display. For example a interlaced video which contains 525

lines that are refreshed 30 times per second resulting in a horizontal scanning frequency of

15,750 Hertz. The field-of-view or image size seen by the user is directly related to the angle

through which the optical beam is scanned. The scan angle for the faster horizontal scan is not

likely to match the total angular field-of-view desired for the display. An optical system must

therefore be used to magnify the scan angle. The most important part of research in VRD was to

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send a scanner which can scan at high frequencies to provide high resolution and also having the

property of wider view of angle. The result of this research was Mechanical resonant scanner [2]

which is used for horizontal scanning and have the operating frequency in the range of

15.75KHz to 18.9KHz .The MRS 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(mirror size= 3mm x 6mm)

[1], [4].

Eliminating moving coils or magnets greatly lowers the rotational inertia of the device, thus

raising the potential operating frequency. Currently MRS are available which can support

display up to 800 display lines at a 60 Hz refresh rate. The vertical scanning is accomplished

using a galvanometer with a second mirror. The galvanometer frequency is controlled by the

control and

drive electronics to match the 60Hz video frame rate. The galvanometer and horizontal scanner

are arranged in what is believed to be a novel conguration such that the horizontal scan is

multiplied because of increase in the optical scan angle. The scanners are arranged, such that the

beam entering the scanner assembly strikes the horizontal scanner then strikes the vertical

scanner and then leaves the scanner assembly and enters into pupil expander Figure 4.

In order to achieve high resolution images by generating high scan rates. These days research is

directed towards developing a MEMS(micro electromechanical system)-based full imagescanner capable of bi-directional scanning using just one millimeter-sized mirror. By using

MEMS researcher will be also able to eliminate the potential for "dead" pixels due to

inoperative mirror elements.

Pupil expander

Nominally the entire image would be contained in an area of 22mm [6]. The exit-pupil

expander (not shown in Figure 3) is an optical device that increases the natural output angle of

the image and enlarges it up to 18 mm on a side for ease of viewing. The raster image created by

the horizontal and vertical scanners passes through the pupil expander and on to the viewer

optics.

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Viewer optics

The viewing optics or the optics through which the user sees the intended image. It contains an

exit-pupil with which viewer align his eye in order to see the generated image. One important

property of VRD is to generate images with the ability to see through i-e image is superimposed

on the physical world view thus giving an augmented vision. This property is achieved by

controlling the intensity of output image by using a beamsplitter in the viewer optics. The

convergent tri-color beams emanating from the scanner pass (partially) through a beamsplitter.

The beam splitter is a 2mm thick parallel plate beam splitter which on one side is coated such

that 40% of any light striking it is reflected and 60% is transmitted while on the other side

beam-

splitter contain anti-rejection coating to avoid double reflections. On first pass, 60% of the

energy in the scan is transmitted through the beam splitter to a concave spherical mirror. The

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mirror also collimates the individual ray bundles which are focused at the focal point of the

mirror. The ray bundles now reflect off the mirror onto the beam splitter and finally reflected to

viewer's eye by passing through exit pupil as shown in Figure 5.

VRD with Eye Tracking

A viewer wearing a head-mounted virtual retinal display typically moves their eye as

they look at images being displayed. In VRD with eye tracking, the direction the viewer looks is

tracked with the display. Prior to tracking, a map of the viewer's eye is generated by the display.

The map includes `landmarks` such as the viewer's optic nerve, fovea (see Section :2), and

blood

vessels. Thereafter, the relative position of one or more landmarks is used to track the viewing

direction usually it is fovea whose relative position is measured to track the eye position. To

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generate a map, and thereafter to monitor viewing direction, light reflected of the viewer's retina

is monitored. The light reflected from the viewer's eye travels back into exit pupil and by

passing through pupil expander it reaches to beam splitter within the retinal display device. The

beam splitter reflects the incoming light from the pupil expander towards a photodectere which

samples the incoming light. Thus, the beam splitter passes light which is incident in one

direction (e.g., light from the light source) and detects light which is incident in the opposite

direction (e.g., reflected light from the viewer's eye).

The content of the reflected light will vary depending upon the image light projected

and the features of the viewer's retina. During the initial mapping stage, the content of the image

light(light scanner scans) can be fixed at a constant intensity, so that the content of the reflected

light is related only to the feature's (i.e. landmarks) of the retina. The changing content of the

reflected light is sampled at a sampling rate and stored. The scanner position at the time of each

sample is used to correlate a position of the sample. The relative position and the content

represent a map of the viewer's retina,

According to another specification of this system, a specific feature of the retina (e.g.,

fovea position) is monitored over time to track where the viewer is looking (i.e., the viewer's

center of vision). The landmarks in the retina which correspond to such feature will cause the

reflected light to exhibit an expected pattern. The relative position of such pattern in the

reflectedlight will vary according to the viewing direction. By identifying the pattern and correlating the

relative orientation of the pattern to the orientation of the corresponding feature in the map, the

change in viewing direction is determined. In various applications, such position indication is

used as a pointing device or is used to determine image content. For example, as a pointing

device the fovea position indicates pointer position. A blink of the eye for example, corresponds

to actuating a pointing device (e.g., "clicking" a computer mouse.)

Also the map of the viewer's retina can be stored and used for purposes of viewer

identification. In a security application for example, a viewer is denied access to information or

denied operation of a computer or display when the viewer's retina does not correlate to a

previously stored map of an authorized user. Here the whole process of tracking viewer's eye in

VRD has been summarized in a systematic manner.

Tracking a Viewer's Eye Position

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In order to track viewer' eye the following methodology is adopted.

1. The map of viewer retina is obtained by asking from the user to see in a particular

direction generally straight direction is taken, and than by capturing the reflected light from the

viewer's retina. The scan light used for obtaining map of retina can be non-modulated or

modulated. In modulated case some post processing is performed to obtain the map of retina.

2. Once the map of retina is obtained, than it is used to track viewer's eye position. The

location of the viewer's fovea within a map at a given point in time is taken as the direction in

which the viewer is looking. The amount the fovea has moved left of center and upward of

center

determines the degree that the viewer is looking right of center and upward, respectively.

Precise angles can be achieved for the viewing angle based upon the location of the fovea. In an

other technique rather than monitoring relative change in orientation of the fovea, the location of

the fovea within the current scanning pattern is identified. The processor (which takes input

from the photodetector) uses the position of the fovea to identify a group of pixels that the

viewer is focusing on. The identification of the group of pixels determines a viewing orientation

within the current field of view. By correlating the viewing orientation to workspace or external

environment large number of applications can be realized [8].

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Safety Analyses

In order to make the VRD a safer industrial product its safety analysis was performed

[5] Maximum Permissible Exposures (MPE) was calculated for the VRD in both normal

viewing and possible failure modes. The MPE is a level of exposure or irradiance of laser light

which can be thought of as the theoretical border between safe and potentially harmful. The

MPE power

levels were compared to the measured power that enters the eye while viewing images with the

VRD. For calculation of MPE different laser sources were assume and after that most

conservative values were chosen. The authors done the analysis for color VGA system with 640

X 480 configuration, by considering the following parameters of systems , sweep time for each

pixel was considered 40 nsec and system scanning frequency was considered equal to 60Hz. An

8 hour exposure was assumed based on a working day for a user who would be wearing and

viewing the display continuously. Authors used ANSI Z136.1 standard for there worst case

analysis for laser exposure in visible range with in the range of 400-550 nanometer wavelength

while for calculation of range 500 to 700 nanometer the calculation done for the 400-

550nanometer was multiplied with an correction factor CB having value greater than one.

The MPE values calculated for different sources are summarized in Table:1 all values

listed are in watt. The output power of the traditional VRD is in range of 100-300 n watt.

Source Used MPE in watts

MPE for Pulsed Lasers 0.13watt

MPE for Continuous Wave Sources 0.16watt

MPE for extended Sources 1.05 103wattTab. 1-MPE for Different Sources

As it can be clearly seen that all MPE's values calculated for different laser sources are well

above the range of power values calculated for the VRD light source , which makes VRD a safe

device to use. The most worst case considered is that when both the horizontal and vertical

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beam controllers got failed, than one spot of the retina will be exposed to the whole output of

the

laser system. For this case only laser having the continuous wave output was considered. The

power calculated for this case is 0.98103watts. The MPE's values shown in the Table :2 are

calculated when viewer's retina is exposed to laser with continuous wave for 2.78 hours after the

scanner assembly failure. Once again the power value calculated for VRD is well above those

(MPE's) values which are presented in the Table:2 as a function of wavelength.

Wavelength(nm) MPE microwatts

400-550 0.385

600 2.17

640 8.62

670 24.29

700 68.47Tab. 2-MPE Values as a Function of Wavelength in case of Scanner Failure

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Advantages of the VRD

The VRD is able to provide several major advantages over current display technologies : color

range, resolution, luminance and viewing modes, contrast ratio, power consumption and cost

[1].

1. Color Range:

The range of hues that can be produced by the VRD is significantly greater as compared to those

which can be produced by CRTs and FPDs (Flat Panel Displays).CRTs and miniature FPDs are

able to reflect only a portion of the total palette of colors visible to the human eye, and are

limited in the degree of saturation they can achieve. Because red (645 nm), green (513 nm) and

blue(457 nm) light sources used in VRD technology emit highly saturated, pure color, the VRD

can produce a range of possible colors and color fidelity superior to other available electronic

display technologies.

2. Resolution:

The current VRD can produces 800X600 SVGA resolution (monochrome) images [7].Its

resolution is limited only by diffraction and optical aberrations in the light source. It is notconstrained as in the case of FPDs by how physically small one can make an individual pixel

element.

3. Luminance and Viewing Modes:

The amount of energy incident at the corneal surface can be varied in the range of 60nW to 300

nW. This flexibility in the range of intensity allows to produce images in varying environments

as compared to conventional electronic displays which do not emit (or transmit) substantial

amounts of light energy. As a result, they are primarily used in controlled lighting environments,

and it is difficult to see them under bright ambient light conditions such as exist outdoors.

Generally, the VRD can be used in two viewing modes, occluded or augmented. In the occluded

mode, the outside environment is not visible and only images generated by the VRD can be

seen. In the augmented mode, the VRD can overlay an image on the real world allowing both to

be seen at the same time. In the augmented mode, the VRD luminance can be controlled to

allow the user to see an image even under outside ambient light conditions.

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4. Contrast Ratio:

The brightness of the VRD can be increased to very high levels or decreased to minimal levels

as already explained. As a result, its contrast ratio is inherently high and far greater than that of

standard _at panel displays or even conventional CRT monitors. As a result of this greaterrange, the VRD's contrast ratio is inherently higher.

5. Power Consumption:

Conventional displays do not efficiently convert electrical energy into light energy. Both backlit

FPDs and CRTs draw substantial power to produce radiant energy. As a result because most of

their energy input is wasted their brightness is relatively low. In addition, they are among

the biggest battery consumers in portable devices that use them. VRD technology, by contrast,

conveys virtually all of its generated light onto the retina, allowing a brighter display with

minimum power requirements (based on laser emitting diode).

6. Cost:

As already described the basic design of the VRD consists of subsystems that are very simple in

their design and largely make use of established optical and electronic technologies, so the VRD

devices will be able to mass-produced at very low cost as compared to the other available

display technologies of today.

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Disadvantages

Well as we all know, nothing in this world is perfect. And especially the new technologies. Even

though the Virtual Retinal Display Technology is already used in military and medical

industries (since those are the only ones that can afford to use it), it is still at a stage of

development and is still very costly.

Already, there aspects of the VRD technology that can be somewhat disadvantageous in the

future:

1. Since the image is sent directly to the retina, there is no protection against radiation

because the distance between the source and the eye is very short. This may cause some

damage to the retina and later result into blindness.

2. As much as it can assist to the military industry, it will still be a technology used byhumans against humanity and therefore may do more harm then good.

3. The image sent into the eye will surely interfere with the reality objects and can be

distract the user when his attention is most needed.

Unfortunately the VRD technology is still not known and used enough to evaluate more

accurately all the possible disadvantages, so instead let's try to concentrate on the positive side

of it.

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Applications

The range of applications which can be addressed by the VRD are of diversified nature. Among

a large number of application few has been described in this part.

1. Head Mounted Displays (HMDs):

Currently the retinal based displays are manufactured by the MicroVision and marketed with the

name of NOMAD. Two types of HMDs are being made one for being used in the industrial

applications while other is manufactured for the usage of army. The two types have their own

specifications and requirements but both HMDs have some common characteristics which are

listed in Table:3

Resolution SVGA 800 x 600 pixels

Field of View 23 degrees x 17.25 degrees (equivalent to 17-inch monitor at arms length)

Display Color Monochrome red

Grey Levels 32 shades of gray

Refresh Rate 60 Hz

User Controls 4-button keypad

Tab. 3 -Some Common Characteristics of VRD based HMDs

Both systems utilize the same see-through display and control functionality. The system will

project the images in a "see through" fashion the user will still be able to see the background

scene, but has the option of focusing in on the presented information as in Figure :6 .

2. Interactive VRD:

Currently the research work is aimed at designing and developing of an interactive VRD for

army pilots. As mentioned VRD is the only display technology that has sufficient luminance to

be used as an augmented display over the pilot's real world view in bright sunlight. The goal is

to

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develop the augmented image as interactive display(Figure :7). Goals of the IVRD project are as

follows :

-Superimpose high luminance color images over the pilot's real world view,

-Measure instantaneous location of the augmented image in the real world view,

-Measure gaze direction, eye, and possibly hand position within the augmented image,

-Display sensor data from 360 degrees within a limited field-or-view, augmented image,

-Allow the viewer to prompt t he display for more detailed information.

Fig. 6 - Augmented image over the real world view

3. Medical applications

VRD as Low Vision Aid:

Possibly the most exciting result has been the identification of the VRD as a potential

low vision aid [3]. Initially it was noticed that people working on the development of the VRD,

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who had myopia (nearsightedness) did not need their glasses to see the images being produced.

This initial discovery was followed by the analysis of improvements brought by using VRD by

persons having low vision (Low vision is defined as ). Usually these individuals are only

correctable to 20/100 to 20/200(higher digit shows greater visual acuity). But with the VRD

and their correction removed, researchers were able to improve their vision to approximately

20/60. Two prototypes (Figure:8) have already been developed to used VRD as wearable low

vision aid. In both the prototypes VGA camera is used to get input from the environment,

after that some machine vision algorithms are applied to identify potential obstacles and than nal

images with enhanced information are scanned on viewer's eye and in this way the person is

warned about different obstacles present in his environment. There are also other large number

of potential applications of VRD which includes image guided surgery, head mounted display

for the vehicles, consumer products etc.

Fig. 7- Interactive VRD and its components

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Fig. 8- Prototype of Wearable Low Vision Aid

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COMPARISON WITH OTHER SYSTEMS

The below table give comparison with other systems. In that VRD is most

advantage than any other systems.

Display

Source

Resolution

(Pixel

Size)

Luminance Color Weight Power

Consumption

CRT 25

Microns

Good -

13,000ft

Only with

sequential

High (with

cabling)

Medium

LCD 12

Microns

Poor- backlit

dependent

With 1/2

monochrome

resolution

Low High with

backlight

Thin Film

Electro-

Luminescent

12

Microns

Poor- 400ft 2-color only with

1/2 resolution

Low High

LED Array 300

Microns

Poor - 100ft With 1/3 resolution Low Low

Monolithic

LED

3 Microns Poor - 5000ft No Low Low

VRD 0.5 Micron Unlimited

Brightness

Full color with no

loss in resolution

Low Low

FUTURE SCOPE

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While development work to date has been very encouraging a number of issues

must be addressed before a complete line of VRD based products is commercially

available. These issues include continued development related to the mechanical

resonant scanner, exit pupil size, methods of generating color in small packages,

increased resolution, and safety testing.

Two issues are currently being addressed relating to the design of the

mechanical resonant scanner. The first is the fact that the scanned beam moves in a

sinusoidal fashion. The beam moves faster at the center of the scan than near the edges.

If uncorrected, this will lead to pixels that are wider in the center of the display and

compressed near the edges and to a display that is brighter at the edges than in the center.

The simplest method of correction is to vary the pixel display time 7 and the pixelintensity as the beam scans across the image. For example, in a 60 Hertz VGA resolution

display the line display time is 31.75 microseconds and each pixel is active for 39.7

nanoseconds (800 effective pixel periods of which 640, or 80 percent, of the pixels are

visible). In the VRD the display would be blanked for 3.17 microseconds at each end of

the scan to remove the highly non-linear portion of the sweep. Pixel durations would

then range from 95.8 nanoseconds at the screen edges to 30.0 nanoseconds at the center

of the image. Intensities would also be varied such that the intensity is increased where

the beam is moving faster and decreased where the beam is moving slower.

The second mechanical resonant scanner issue is the variation of the

phase delay between scanner drive signal and actual scanner position with temperature

variations. As the temperature change the resonant frequency changes slightly. This

change in resonant frequency will change both the scanner deflection and the phase

delay. The resonant frequency changes are small over anticipated operating temperatures

and the change in deflection will result in only a few percent change in image field-of-view. Moreover, this change will be slow and is not noticeable in most applications. The

phase change is, however, much greater and will result in a significant alteration of the

image. To compensate for these changes a feedback mechanism is being developed that

measures the phase difference and compensates for it.

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The system exit pupil is still quite small. While this small exit pupil

has allowed some individuals with lens and cornea damage to see images clearly, it is

not desirable in most applications. Work is being performed to solve this problem in a

number of ways. The best solution is to enlarge the exit pupil. As described above, a

larger the scanning aperture will result in a larger exit pupil. Thus it is important to have

the largest possible scanning aperture. Methods of duplicating the exit pupil are also

being investigated. Finally, methods of tracking the eyes movement and moving the exit

pupil such that it lines up with the eye's pupil are being analyzed.

As described above, a full color VRD has been demonstrated. The

disadvantages of this system are its size and cost. The blue and green sources are not

small or inexpensive. Unfortunately neither blue nor green laser diodes are currentlyavailable 8 as they are in the red. As laser alternatives, HITL staffs are working on two

frequency doubling methods, waveguide doubling and fiber doubling. The use of non

lasing sources, particularly light emitting diodes, is also being researched. In fact, when

the system is operated with the red laser diode below the lasing threshold an image is

visible.

Moving the system to higher resolutions should present no

significant problems. The current mechanical resonant scanner design should scale up to

allow for a 1000 line display. Measured performance of the optical system will allow

better than 2 arc minute resolution. If more than 1000 lines are desired a system

consisting of the mechanical resonant scanner and a single light source will not be

adequate. Other solutions being researched involve the use of very fast electro-optical

scanning methods.

A second issue investigated is the minimum time the light source

must illuminate a rod or cone for an image to be perceived. As the spot will be moving

faster for higher resolutions this could present a limiting factor. With the current VGA

resolution system and an earlier acousto-optical scanner based system displaying 1024

lines of data, this does not present a problem. Images are clearly visible and the viewer

perceives high intensity resolution. Flicker frequencies have also been measured and

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match closely those found with other displays. As the eye's response to light occurs in

under 200 femtoseconds 9, we believe this issue will not be a problem.

As with any display device the issue of user safety must be addressed.

The use of coherent light sources in the VRD has highlighted this issue. Because of the

low power levels required in the VRD we believe it does not present a safety hazard 5.

Measured power levels into the eye typically are iunder 300 nanowatts. During the

second half of 1995 we will begin an extensive series of safety tests on the VRD. These

tests will be performed under the supervision of Dr. Eric Viirre, an ophthalmologist with

a joint appointment to the HITL and the University of Washington School of

Ophthalmology.

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CONCLUSION

The VRD offers solutions to many of the problems that have plagued personal

display devices. It will allow a display that is small, low cost, low power, high

resolution, bright enough to operate in an outdoor environment, and functional in either

an inclusive or see-through mode.

Development work at the HITL has centered around making the VRD

technology commercially viable. The creation of the mechanical resonant scanner solves

one of the toughest problem of commercializing the VRD, developing a low cost, high

frequency, large deflection angle horizontal scanning device. Based on this scanner a full

color, VGA resolution VRD prototype has been demonstrated. Future development will

include refinement of the mechanical resonant scanner, enlarging the system's exit pupil,

utilizing small blue and green color sources, increasing system resolution, and system

safety testing.

The VRD appears to be an ideal display for a large number of

commercial, industrial, consumer, and military applications. Micro Vision, Inc. will be

matching product needs to VRD performance parameters.

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REFERENCES/BIBLIOGRAPHY

[1] Homer Pryor, Thomas A.Funress III and Erik Viirre,The virtual Reti-nal Display : A New Display Technology Using Scanned Laser Light,In

Proceedings of Human Factors and Ergonomics Society, 42nd Annual

Meeting,1570-1574,1998.

[2] Richard S.Johnston, Stephen R.Willey, Development of a Commercial

Virtual Retinal Display, Proceedings of Helmet- and Head-Mounted Dis-

plays and Symbology Design,2-13,1995.

[3] Lin, S-K. V., Seibel, E.J. and Furness, T.A.III, Virtual Retinal Display

as a Wearable Low Vision Aid,International Journal of Human-Computer

Interaction,15(2),245-263,2003.

[4] Tidwell.M,A Virtual Retinal Display for Augmenting Ambient Visual En-

vironments,Master's Thesis University of Washington,1995.

[5] Erik Viiree, Richard Johnston, Homer Pryor et.al,Laser Safety Analysis of a Retinal

Scanning Display System , Journal of Laser Applications

,9,253-260,1997.

[6] Virtual Retinal Display (VRD)Technology, WebPage

[7] Head-up Display,http ://www.microvision.com/hud.html

[8] US patent EP1053499, Virtual retinal display with eye tracking

Documents

Seminar Report of Vrd