Optical problems in creating effective displays

RESEARCH

Optical problems in creating effective displaysYu. A. Cherkasov* ) and E. L. Aleksandrova

S. I. Vavilov State Optical Institute, St. Petersburg, Russia~Submitted January 18, 1999!Opticheski� Zhurnal67, 19–29~February 2000!

The optical problems in the visualization of information, including optical informationtechnologies and their optical element base, are analyzed. The main areas analyzed are: opticalinformation technologies, optical information carriers, optically controlled transparenciesor spatial light modulators, deflectors, optical screens, and the optics of projection systems.Promising optical methods and displays are singled out. ©2000 The Optical Societyof America.@S1070-9762~00!00302-X#

ulinnainusonp

thrcr,emc

co

as-

drd

s-

gh

ec

rs

p

-

loy-oto-tem

allTI,

gh-600

laysnum.

oningand

ionntsthe

ee

ityby

1. INTRODUCTION

Projection displays are promising for application in atomated control systems for various purposes: for controlmilitary forces and complex technical systems in the natioeconomy, as well as in transportation, power engineerincluding nuclear power engineering, the advertizing indtry, the situational control of simulation, managementcredit and financial institutions and systems, and natioeducation. All industrially developed countries are develoing and producing projection displays. As for Russia,work of the ARTI company, the Platan Scientific-ReseaInstitute, MNITI AO, etc. should be mentioned. In particulathe work at ARTI, which is based on unique domestic devopments, has led to the production of projection systewith significantly improved quality and better output charateristics compared with the non-Russian counterparts atsiderably lower prices.

The purpose of this paper is to examine the opticalpects of visualizing information, including optical information technologies and their optical element base, in regarthe priority areas for developing optical methods and haware ~optical materials, elements, and systems! for projec-tion displays.

2. PRINCIPAL AREAS OF DEVELOPMENT OF DISPLAYSFOR INFORMATION-CONTROL SYSTEMS

The following principal areas of development of diplays can be singled out:

• rear-projection monitors for group use based on hibrightness kinescopes,

• video walls for collective use,• projection systems employing quantoscopes for coll

tive use,• projection systems employing spatial light modulato

~SLM’s!,• laser projection systems with intracavity SLM’s,• 3D laser monitors in virtual-reality systems for grou

use,• volume holographic screens for visualizing static im

ages in virtual-reality systems,

103 J. Opt. Technol. 67 (2), February 2000 1070-9762/2000/02

-gl

g,-fal-eh

l-s

-n-

-

to-

-

-

• projection systems for individual use~head-worn dis-plays! for virtual-reality and aircraft control systems,

• intensifying optical projection screens,• optical processors for information-control systems.

One distinguishing feature of these areas for the empment of optical elements, as opposed to, for example, phgraphic optics and eyeglasses, where millions of each iare manufactured, is that they are manufactured in smnumbers. For example, according to the estimates of ARthe demand for rear-projection monitors based on hibrightness kinescopes and video walls does not exceedpieces per annum, and the demand for projection dispbased on quantoscopes does not exceed 40 pieces per an

As for the principal areas of development of projectidisplays, the priority areas for creating and manufacturtheir principal optical elements have been determined,the optical schemes have been designed.

3. PRIORITY AREAS FOR CREATING ANDMANUFACTURING OPTICAL ELEMENTS FOR PROJECTIONDISPLAYS

The configurations of the optical schemes of projectdisplays are presented in Fig. 1. The current requiremeplaced on the objectives can be illustrated in the case ofprojection monitor shown in Fig. 1a.

The illuminanceE8 at the center of the screen equals

E85pB sin2 u8t.

HereB is the brightness of the cathode-ray tube~CRT!,u8 is the aperture angle in the image space~the half-anglewithin which the exit pupil is seen from the center of thscreen!, and t is the transmission of the objective. Thbrightness of a Lambert scatterer is

B5~1/p!E,

where E is the illuminance on the scatterer. The quantcharacterizing the efficiency of the objective is expressedthe formula

R5E8/E5t sin2 u8.

1030103-09$18.00 © 2000 The Optical Society of America

thn

e

onhtr

emigvn

foageal

eni

lor

ed

tes

esergtive

e-aticcialain

all

he

e-e,

es

justith

rsionjec-

areanngifi-d in

isex-wnadi-f ac-

cent

h-

le-h--ics

.

Since the aperture angle in object space

u5u8M ,

whereM is the magnification of the objective, we have

R5t sin2 ~u/M !.

For the entire fieldRf5R cos4 W8, whereW8 is the half-angle within which the screen is seen from the center ofexit pupil. This formula specifies the drop in illuminance othe edge of the field.

To obtain high illumination characteristics, it would bdesirable to have an aperture angleu ~Fig. 1a! at the 45– 50°level ~or a corresponding cone angle in the rangeu580– 90°; this parameter, which is often used in the nRussian literature, is defined as the angle between rays wemerge from edges of the subject and go to the axial pointhe aperture diaphragm! at a relative aperture of 1:1.5 omore.

The development of color television raised the problof obtaining a color image on screens with good color, hresolution, and small dimensions. We are now using telesion picture tubes with a number of lines equal to 625, aprojection objectives that were previously developedother purposes and therefore do not provide a high imquality are used for projecting on screens. The developmof television picture tubes which provide a high image quity ~tubes with a number of lines above 2000! calls for cre-ating special high-power projection systems. The currstate of the methods for designing optical systems permthe development of a new generation of high-power co

FIG. 1. Configurations of the optical schemes of projection displays

104 J. Opt. Technol. 67 (2), February 2000

e

-ichof

hi-drent-

tts-

image projection objectives. A color image can be producon a screen from three television tubes~red, blue, and green!in two fundamentally different ways:

1! by three projection objectives, each of which operain its own spectral range@red (R), blue (B), and green (G)],

2! by a single objective in a broad spectral range~fromgreen to blue! with a color-separating unit.

The development of high-power projection objectivhaving a high image quality and a uniform resolving powwithin the entire field of view should lean toward creatincompound objectives, i.e., astigmats. Increasing the relaaperture~to 1:1.5! and the field of view~to 65°) while main-taining a fairly high image contrast over the entire field rquires good correction of the monochromatic and chromaberrations of the rays in wide oblique beams. The sperequirements placed on projection objectives and the mproblems in developing them are as follows:

• maintenance of image contrast and resolution ofdetails in the picture,

• preservation of the geometric similarity between tprojected picture and its image on the tube,

• a distribution of the illuminance on the screen corrsponding to the distribution of the illuminance on the tubi.e., minimal vignetting of the objective,

• correct color reproduction of the image, which requirgood correction of chromatic aberrations.

Objectives with the characteristics and requirementscited are unavoidably compound multiple-lens systems waspherical surfaces. Special glasses with a special dispepath and a low specific gravity must be used in such obtives.

3.1. Optical glass

The main problems facing modern materials scienceassociated with obtaining and investigating materials withassigned set of properties or with a unique, nearly limitivalue of one of the parameters, which is of decisive signcance for practical use. These problems were examineRef. 1. Depending on the area of application, the problemeither to preserve the properties of the material undertreme service conditions or to alter them according to knolaws in response to various external effects. The most trtional use of optical glass is to alter the geometric path olight flux for the purpose of transmitting it in assigned diretions to form an optical image of an object.2 Numerous col-orless glasses were developed and introduced in reyears.3,4

3.2. Optical elements of rear-projection monitors for groupuse based on kinescopes

Color-image projection systems employing higresolution ~from 1250 to 2000 lines! television tubes arewidely produced outside of Russia at the present time~bySony, Philips, etc.!. The Russian projection systems use tevision tubes with a resolution of about 625 lines. Higdefinition ~2000 lines! rear-projection monitors are being developed, in particular, for use as the principal color graph

104Yu. A. Cherkasov and E. L. Aleksandrova

tioor

dsenrorsT

7

e

on

reobe

0d

00

t

rerly-

00

gh-

d

0

m-t

a-ter-d athe

andheontohavee

’sble,

n-bylys-ro-

display in the work stations of air-traffic controllers.5 Theservice characteristics can be improved for a rear-projecmonitor in comparison to the Trinitron television system fsimilar purposes~Japan!, and the cost can be reduced.

A rear-projection system actually has a dual use andual purpose. A high-definition rear-projection televisioncan be obtained on its basis by adding a tuner, and wheR,G, andB signals are supplied, it can serve as a video pjector. Projection CRT’s for the primary luminescent colohave been created on the basis of existing PT2171 CRand have the following characteristics:

CRT screen diagonal, cm 1Image size, mm 76376Number of lines 2000Type of luminescence monochrom

The optical unit conveying the image from the projectiCRT’s to the translucent screen~Fig. 1a! includes three ob-jectives, two tilting mirrors, and a translucent screen. Itquires the use of high-resolution wide-angle high-powerjectives with short working distances. The expectcharacteristics of the optical elements are:

Objectives

Relative aperture 1:1.2Cone angle, deg up to 8Spectral range blue, green, reResolution 200032000Magnification 7–10Size of linear field in subject

space~diagonal!, mm120

Size of linear field in image space, mm 700–12Distance from subject plane to image

plane, mm1100–1300

Objective length, mm 250Vignetting, % no more than 50Distortion, % less than 2

Tilting mirrors

Maximum size, mm 450Thickness, mm 100Number of rings 1

3.3. Optical elements of video walls

Video walls combinen2 ~for example, 333) projectiontelevisions in a single image. The requirements placed onoptical elements are somewhat lower than in the casehigh-resolution rear-projection systems. However, theyquire the use of wide-angle high-power objectives with faishort working distances~Fig. 1b!. The expected characteristics of the optical elements of video walls are:

Objectives

Relative aperture 1:1.5Cone angle, deg up to 9Spectral range, nm 400–70Resolution up to 116831728Magnification 6–10


n

at

-

’s

--

d

heof-

Size of linear field in subjectspace~diagonal!, mm

165

Size of linear field in imagespace, mm

1200–1800

Distance from subject planeto screen, mm

800–1300

Vignetting, % no more than 50Mirrors

Maximum size, mm up to 8003600350Reflectivity, % up to 90Mass, kg up to 6

Screen

Diagonal, mm 1170–1680

3.4. Optical elements of projection systems employingquantoscopes for collective use

These systems require the use of wide-angle hiresolution high-power objectives~Fig. 1c!. The expectedcharacteristics of the objectives of such systems are:

Spectral range blue, green, reRelative aperture 1:1.5Cone angle, deg up to 80Resolution 10 000310 000Magnification 70–120Size of linear field in subject

space~diagonal!, mm165

Size of linear field in imagespace~diagonal!, m

12–20

Distance to screen, m 5–1

3.5. Optical elements of projection systems employingspatial light modulators for collective use

These systems, which are also called light valves, eploy modulation of the light flux by a spatiotemporal lighmodulator. The modulator@spatial light modulator~SLM!,which is an optically controlled transparency# is controlledby an image projected onto it from a kinescope~see Fig. 1d!.

Most applications of SLM’s are based on their fundmental capability to transform optical images and to altheir brightness and contrast.6 In this case an image is projected from a CRT screen onto a photoconductor layer, anreadout beam is focused at the point where the focus ofprojection lens is located. This lens collimates the beamdirects it onto the SLM. A blocking aperture isolates tscattered beam, and the intensified image is projectedthe screen. Many Russian and non-Russian companiesdevoted their attention to developing SLM’s of thphotoconductor/liquid-crystal~PC/LC! type for display sys-tems. Compared to other light-valve systems, PC/LC SLMhave high sensitivity and speed, are technologically feasisimple to use, and operate at low voltages.7–13 The use ofsuch light-valve devices in displays allows significant icreases in the light fluxes. The real projection CRT madeBarco permits the production of light fluxes equal to on100–200 lm, which are plainly insufficient for modern diplays. Projection systems employing SLM’s promise to p


the

r

nnpoc. Incey,

totatroil

ese

th

l-er-yu-res-thehein-

sia.torstor

te ines

thasicthe

ro-d

on

ou-ri-

de-0el-

ticsnr

st

tor

duce light fluxes up to 1000 lm. In addition, the danger ofeffects of CRT radiation on the operator is reduced whlight-valve systems are used.

An optically controlled transparent film is a multilayestructure enclosed between two glass substrates~Fig. 2!.Transparent conducting coatings are deposited on the isurfaces of the substrates. A photoconductor layer is deited on one of the substrates. Between the photocondulayer and the other substrate there is a liquid-crystal layerthickness is assigned by insulating spacers, and its orietion is assigned by orienting layers deposited on the surfaconfining the liquid-crystal layer. A voltage is applied to thtransparent conducting surfaces. The resistance of the lais chosen so that in the absence of the writing radiationlarge part of the voltage would fall on the photoconduclayer and the part of the voltage falling on the liquid-cryslayer would be less than the threshold value of the elecoptic effect employed. When the photoconductor layer isluminated by the writing radiation, its conductivity increaslocally, and the voltage on the liquid-crystal layer increasto the threshold value. A potential relief corresponding to

FIG. 2. Structure of a photoconductor/liquid-crystal spatial light modula1—glass substrates, 2—transparent electrodes,3—photoconductor,4—mirror, 5—liquid crystal,6—insulating spacer,7—orienting layers.


en

ers-

tortsta-es

ersarl-

-

se

recorded image is formed in the liquid-crystal layer. Moecules of the liquid crystal undergo local reorientation, alting its optical properties. When an SLM is illuminated blight to which the photoconductor is insensitive, it is modlated in accordance with the recorded image. There is pently a fairly good understanding of the physical basis forformation of an image in a PC/LC structure and of how tparameters of the photoconductor and the liquid crystalfluence the characteristics of an SLM.

Several types of SLM’s have been developed in RusThe devices in which chalcogenide glassy semiconduc~GGS’s! and bismuth silicate serve as the photoconducshould be mentioned first. The devices developed operaboth transmission and reflection regimes, including regimwith a glass-fiber output, which provides for coupling wiscreens of cathode-ray or image-converter tubes. The bcharacteristics of these liquid-crystal transparencies inreflection regime are listed in Table I.

The SLM’s based on amorphous silicon and the ferelectric liquid-crystalline material SZhK-392 for high-speeelectro-optic modulators are most promising.14 Their charac-teristics are: working range, from 14 to 51 °C; deflectiangle of the optical axis~director!, 610° at an electric fieldintensity of 10 V/mm; response time at the 10% level, ngreater than 10ms; frequency range without a drop in modlation, up to 30 Hz. The material is stable and easily oented. SLM’s with high uniformity, but restricted speed~10Hz! were previously fabricated on the basis ofp2 i2n a-Si:H with a nematic liquid crystal. Similar SLM’sbased on silicon and nematic liquid crystals, which wereveloped by Hamamatsu~USA!, have a speed equal to 25–3Hz. A Russian SLM based on the amorphous silicon devoped with nematic liquid crystals has the characterislisted in the Table I. The sensitivity of this SLM working ithe TV standard is 102621027 W/cm2 at a resolution greatethan 100 mm21. The limiting sensitivity equals 531027 W/cm2 at a contrast ratio equal to 2:1; a total contraof 30:1 is achieved at 1025 W/cm2. The cost of the Russian

:

TABLE I. Basic characteristics of liquid-crystal transparencies based on chalcogenide photoconductors~CGP/LC!, bismuth silicate~BSO/LC!, amorphoussilicon ~a-Si:H/LC!, zinc selenide~ZnSe/LC!, and polyimide~PI/LC! in the reflection regime.

Characteristic CGP/LC BSO/LC a-Si:H/LC ZnSe/LC PI/LC

Sensitivity, W/cm2 1027– 1028 1025 1026– 1027 1027 1025– 1026

Speed, Hz 10–25 30 10–30 5–10Resolving power

at the 10% FCC level, mm21 100–250 30–40 120 150 .100at the 50% FCC level, mm21 70–80 15–20 50

Contrast ratio 100:1 30:1 30:1 20:1 40:1Number of brightness gradations 8 8 8 8 8Spectral range, nm

writing 400–500 400–500 400–650 400–530 380–630reading 400–700 500–700 400–700 600–700 400–700

Working area, cm2 .6 .6 .6 .6 .10Light-blocking coefficient .103 .103 .103 .103 .103

Reading radiation power 0.1–1.0 0.1–1.0 .0.1 0.1–1.0density, W/cm2

Power-supply voltage, V 5–20 30–100Switch-on time, ms 1–10 150 5–20Switch-off time, ms 50–100 500 30–100


ifim

c-olis

eage

alo

ac

op

itge

als

n-ain

n

noson

,

aiesin3

-olie

a

, if atyn

on

ig

torsparttto

theirichms,n-of

n-ion

bydehectedtion

onnd. The

forcyfuloffor

iallytion

thendingnotri-m-

on-naltheis-ingel-c-

d35

0

0

silicon-based SLM’s developed is $3000, which is signcantly lower than the cost of the analogous SLM’s froHamamatsu~$15 000!.15

Another promising group of SLM’s consists of strutures based on a liquid crystal and a photoconductive pmer, viz., polyimide.12,16 The advantage of these devicestheir high resolving power~more than 1000 mm21), which isunattainable by other devices, and their distinguishing ftures are the possibility of producing modulators with lardimensions~more than 10 cm2) and the lower cost of thetechnology.

Apart from the types of SLM’s based on a liquid crystconsidered above, many teams are actively workingSLM’s based on ferroelectric smectics. Their typical charteristics are: sensitivity, 1024 W/cm2; resolving power,90 mm21; speed, 5000 Hz.15

In addition, numerous new devices are in the develment stage. They include:

• SLM’s for enhancing image contrast, which perm8–10-fold enhancement of the contrast of the input ima~when the contrast of the input images is 0.05–0.08!,

• high-speed SLM’s based on ferroelectric liquid cryst~their switching times are of the order of 1 ms!,

• SLM’s for selecting moving objects,• SLM’s for the recording and long-term storage of i

formation with the following characteristics: storage time,least 3 years; recording time, 200 ms; information erastime, 2 ms; resolving power, 50 mm21. One of the promisingareas for employing such SLM’s is in projection systems amemory systems of optical processors.

A projection system with an SLM based on a photocoductor and a smectic liquid crystal, which combines the psibilities of recording and storing the recorded informatifor a long time~up to 3 years!, is of great interest for dis-plays. The sensitivity of such an SLM is 1025 W/cm2, itsresolving power is 50 mm21, its recording time is 200 msand its erasing time is 2 ms.8 A system which employs anSLM with memory and which can project an image onscreen from either transparent or opaque information carrhas also been proposed and realized. The SLM served aintermediate information carrier and permitted the use oftense light fluxes to read it out~the screen measured35 m).

Apart from the LC-based SLM’s, SLM’s in which polymer materials serve as the liquid crystal and the photocductor have been developed. One of them exhibits a reelectro-optic effect and is capable of altering the phaselight transmitted or reflected by it. The structure of suchSLM based on a relief-electro-optic medium17,18 is similar tothe structure of a photoconductor/liquid-crystal modulatorwhich the liquid crystal has been replaced by a thin film opolymer gel. In such SLM’s the light-modulating capacican reach 90%, and the photosensitivity in the spectral ra400–700 nm is 102621027 J/cm2 when SeTeAs or CdSeserves as the photoconductor.19 When polyimide orfullerene-sensitized polyimide is employed as the photocductor, the sensitivity reaches 1025 and 1026 J/cm2,respectively.20 The speed of a gel modulator can be as h


-

y-

-

n-

-

s

tg

d

--

rsan-

n-f-

ofn

n

ge

-

h

as 25 Hz over a broad temperature range~from 280 to1160° C), and the resolving power can reach 300 mm21.Besides the high characteristics just cited, gel modulahave several advantages, which favorably set them afrom other known types of SLM’s. One is their efficienoperation in unpolarized light, which eliminates the needuse polarizers and analyzers. A second advantage isability to operate over a broad temperature range, wheliminates the need for temperature-stabilization systepermitting reduction of the power consumption and dimesions of the system. A third advantage is the possibilityfabricating gel modulators of any size.

Apart from SLM’s, energetically controlled transparecies based on a liquid crystal are of interest for projectdisplays. Transparencies of such a type are producedBNO ~USA!21 and make it possible to use standard sliprojectors for viewing TV images. For this purpose, ttransparency is inserted in the place for a slide and conneto a TV receiver or a video cassette recorder. The resoluis 124031240 elements, and the area is 131 cm2.

The configuration of the optical scheme of a projectisystem employing SLM’s is shown in Fig. 1d. Objective acondenser triads have been developed for such systemsmost important requirements placed on the condensersprojection systems employing SLM’s are: energy efficienin converting the diffuse light flux of the source into a useflux, uniform illumination of the screen or transmissionthe source image, and minimization of image aberrations,example, chromatic and spherical aberrations. In especcomplex cases, the creation of a weakly divergent radiaflux of small diameter~less than 50 mm! is required whenhigh-power radiation sources are used. An analysis ofexisting state of affairs in the optical industry, science, atechnology reveals that a solution to the problem of creathigh-power thermostable condensers must be soughtwithin traditional spherical optics, but in the use of asphecal surfaces, which require unique machine tools and coplicated control methods, and in the employment of uncventional processing methods. One of these nontraditiomethods is based on the sintering and hot molding ofinternal interface of two glasses with different charactertics, which was first used to fabricate amplitude apodizdiaphragms.22 The expected characteristics of the opticalements of projection systems employing SLM’s for colletive use are:

Objectives

Aperture ratio 1:1.5Spectral range blue, green, reSize of linear field in object space, cm 1–Size of linear field in image space, m 2–Magnification 70–100Distance to screen, m 3–1

Condensers

Cone angle, deg more than 11


s s

la

ssu

ti

wdn

nys0

arob

-ceo

th-thpanourere

r

othsel

otrd

ann

e-io

rrees

gu-in

thesingi-

n of

aceinto

re-arly-me

sys-s,

he

be

alofin-

forvi-

is

s

ses

e

hic

3.6. Optical elements of laser projection systems withintracavity SLM’s

In these systems transparencies based on amorphoucon serve as intracavity SLM’s.14 Such an SLM is insertedwithin the cavity of a semiconductor-pumped solid-stateser, for example, a neodymium laser~second harmonic!. TheSLM is coupled to the CRT of a TV system through a glafiber faceplate. This system permits achievement of a gainto 5000 and an image size up to 232 m with a mass below20 kg.

3.7. Optical elements of laser monitors for virtual-realitysystems

Intensive research has recently been conducted inarea of creating systems for real-time image visualizationthree-dimensional space and replacing conventional tdimensional screens by them. Such three-dimensionalplays can provide significant gains in information conteand clarity in television systems.

According to a prediction ~based on non-Russiadata23–25! three-dimensional laser room television displawith a 360° field of view will be created during the next 2years. The main areas of application for such displaystelevision displays, medicine, the computer simulation ofjects, designing, air-traffic observation stations~including ra-dar scanning and charting!, and meteorology~maps ofweather conditions, etc.!. The advantages of threedimensional displays include an increase in clarity and aceration of the simulation of objects and the processingsignals from three-dimensional sensors.

The realization of such displays is possible only onbasis of laser technologies.23–26 Four principal areas for research and development have been formed in this field:formation of dynamic holographic images, autostereoscomonitors, scanning of nonlinear media by laser beams,visualization systems based on moving bodies of varishape and laser beams scanning them. These areas weamined in Ref. 27, in which it was also shown that thesearch efforts in the fourth area have yielded acceptablesults. The method proposed by Asniset al.,27 which belongsto the fourth area, is free of the deficiencies due to tracingthe contour of the outputted image along its perimeter, rathan over its volume, and electronic scanning by a labeam using anXY acousto-optic deflector. The principafunctional elements of a 3D display are:

• a visualizer, which consists of two or more platescomplex form, which are rotated by a contactless elecmotor with automatic adjustment of the rotation rate ansystem of electromagnetic synchronization sensors;

• a laser with collimating and focusing optics andelectronic scanning system for the laser beam based oXY acousto-optic deflector;

• a two-channel radio-electronic unit for exciting the dflector, in which the amplitude and frequency of the radsignal are controlled by digital codes;

• digital units, which include a video buffer memory fothe coordinates of the points and the brightness of the thdimensional image, a generator of controlling digital cod


ili-

-

-p

heno-is-t

e:-

l-f

e

eicdsex-

-e-

ferr

fica

an

e-,

and an interface for connecting to a computer. The confiration of the optical scheme of such a system is shownFig. 1e. To obtain a three-dimensional image of a subject,contours of the cross sections of the subject in planes pasthrough the rotating plates of the visualizer must be illumnated by the scanning laser beam in each angular positiothese plates.

3.8. Optical elements of volume holographic screens forvisualizing static images in virtual-reality systems

Reports of the use of true real-time 3D images in spin medical practice, particularly in surgery, appeared1993. However, the principles and recording media usedobtain such an image were not reported. The scientificsearch performed on erasable recording media, particulphotothermoplastic~PTP! media, and the calculation of digital holograms permit the creation of systems for the real-tiformation of a true 3D image in space.28 Photothermoplasticmedia were chosen as the recording medium in such atem owing to their unique combination of characteristicsuch as a high photosensitivity in the visible region of tspectrum at the level of 102521027 J/cm2, a resolvingpower as high as 1000 mm21, a diffraction efficiency equalto 30%, and a cyclicity up to 103, in dry and fast processingon the real time scale.29

Holographic screens for visualizing static images canmade on the basis of a large-format (89) real-time PTPcamera.28 Visualization is based on the recording of digitholograms followed by their reconstruction in the formthree-dimensional images. It is possible, in principle, tocrease the size of the camera to 149, the photosensitivity ofthe medium, and the speed to 25 Hz. The optical schemerecording holograms in a volume holographic screen forsualizing static images is shown in Fig. 3. The laser beamdivided into object and reference~not shown in Fig. 3!beams. The object beam passes through cylindrical len1,diffuse screen2, liquid-crystal modulator3, and objective4.It then interferes with the reference beam, which pasthrough splitting diaphragm5, on the surface of the PTPcarrier 6 ~the screen!. The principal characteristics of thscreen are:

FIG. 3. Optical scheme for recording a hologram in a volume holograpscreen for visualizing static images in virtual-reality systems:1—cylindricallens, 2—diffuse screen, 3—liquid-crystal modulator, 4—objective,5—splitting diaphragm,6—surface of the PTP material of the screen.


0

in0

t

inrnthadree.

aI

insT

5

4

ssian

tral,

om

rpTldedneiaine

reloaru

urehe

5

opti-of

tohes-

velyingicsitylo-olo-tc.

a-re-

ore,ho-g ofalre-h-

m-

ticsted;

hasthengingsig-

yial

the-m

Spectral range, nm 400–70Photosensitivity, cm2/J 23105

Diffraction efficiency~DE!, % up to 20Cyclicity, cycles 300DE stability temperature range, °C 0–35Information revision rate 1 frame per 5 mInformation formation time in a line, ms 2Number of resolved elements

in a line, ms 3000in a frame, ms 4000

Number of brightness gradations at leasScreen size, cm2 7.5310

3.9. Optical elements of projection systems for individualuse „head-worn displays … for virtual-reality andaircraft control systems

Projection systems for individual use are widely usedvarious fields of human activity. In particular, head-wodisplays are successfully and efficiently used in aviation,automobile industry, and simulators. The perfection of heworn displays will permit increases in the efficiency andliability of the operator’s work and a reduction in his fatigu

A head-worn display includes an image generator~CRT,liquid-crystal array, etc.!, an optical projection system~Fig.1f!, and a combining element. The output screen ofimage-converter tube, on which the image obtained by ansystem is formed, can serve as the image generator. Shead-worn displays sit on the operator’s head, rigid masize and ergonomic requirements are placed on them.principal characteristics of head-worn displays are:30

Total field of view unrestrictedField of view of the indication channel, deg 40360Transmittance of the indication channel, % at leastFocal distance, mm 25IR and TV channels yesTransmittance of the direct channel, % at least

Similar developments have been made outside of Ruby Marconi Avionics, Hughes, Pilington PE, etc. The radtion sources in these systems are CRT’s with a fundameemission line at a wavelength of 543 nm with a specwidth of 4 nm at the 0.1 level. Sources for liquid-crystalaser, and LED displays are being developed by several cpanies, but no information is available on them.

3.10. Intensifying optical projection screens

One of the main elements which provides for the shaness, contrast, and brightness of images in projectionsystems is the special screen. For this reason, directionatensifying translucent lens-raster lens have been producevarious countries~Japan, the Netherlands, and the UnitStates!. There are three technologies for fabricating Freslens with the required characteristics, but the approprequipment and optimized technologies are presently lackin Russia, although work is being carried out to find othvariants for creating intensifying screens with the requicharacteristics. One of these variants is to use the technoof polymer film composites to create screen units. This vant requires virtually no expenditures to set up mass prod


8

e-

-

nRces-he

0

0

ia-tall

-

-Vin-in

ltegrdgyi-c-

tion and, according to estimates, will permit the manufactof screen units with the following characteristics over tcourse of 1 year:

Translucent intensifying screens:

Screen size~diagonal!, cm 70, 110, 180Intensification factor 2.5–5Radiation pattern:

in the horizontal plane, deg 34in the vertical plane, deg 34

Resolution at least 200032000Contrast for scattered light no more than 0.0

Reflective intensifying screens:

Screen size~diagonal!, m 2–6Intensification factor 2–15Radiation pattern:

in the horizontal plane, deg 34–24in the vertical plane, deg 34–24

Resolution at least 200032000

3.11. Optical processors for information-control systems

Such processors can be created using a high-speedcal disk drive with a high recording density and rewritingthe information on the basis of the holographic approachartificial intelligence. In this report we shall adhere to topinion that studies in the field of promising memory sytems should include the results in two areas that are actibeing developed at the present time: holographic recordand artificial intelligence. The fact is that holographmemory, even with increased speed and recording den~for example, as a result of the recording of volume hograms, superimposed holograms, and polarization hgrams, as well as recording in multilayer structures, e!does not permit a fundamental advance to ultrafast informtion processing with the computational approach used orduction of the amount of computational resources. Therefattempts were made in Refs. 31 and 32 to combine thelographic approach to the recording, storage, and readininformation with the holographic implementation of artificiintelligence methods, which most fully meets the mainquirements for solving the problems of connectivity, teacability, and parallelism of calculations. The novel accoplishments of the approach are as follows:

• a novel PTP recording medium, whose characterishave been confirmed by laboratory testing, has been crea

• a mode theory of superimposed volume hologramsbeen devised, which provides analytical expressions forcalculation of numerical values, determination of recordiconditions that ensure a maximum information recorddensity, and assignment of the relative intensities of thenal and interference waves in the reconstructed image;

• the possibility of a holographic realization of fuzzalgebra as applied to information processing using artificintelligence methods has been substantiated.

These optical processors are of interest primarily forrapid processing of large files of information~aerospace photographs! and the creation of an artificial intelligence syste


refose

e

io

ic

rp

ioanid

niose

errdvtif termdisan

s--u

inge

osan

in-of

op-f the

ac-tsms

tionro-s-

al

-

ni-

-

tics

-tors

,

-

htus-

truc-ci-

as-

nsan-

nd’’

for

v,-

mss

capable of functioning autonomously in a complex unpdictable situation that is not subject to formal description,example, for autonomous robots or for controlling proceswith many parameters.

The basic characteristics of the proposed optical procsor, i.e., its high reliability, large amount of memory~morethan 10 Gbyte!, possibility of rewriting, stability toward theeffects of external magnetic fields, contactless informatexchange, and long service life of the carrier~more than 10years!, match the properties of non-Russian erasable optmemory devices~from Philips and Sony!. At the same time,the use of a holographic recording and reading methodduces the requirements placed on the mechanical comnents of the device and the technology of the informatcarrier, making it competitive in price with the non-Russicounterparts~the cost of the non-Russian counterparts$4500–7500, and the expected cost of the system beingveloped is $1000!. As in the case of the non-Russian couterparts, the device can be connected to computers of vartypes ~IBM PC, VAX, etc.! as an external drive, and itparameters are well suited to distributed information nworks.

A laboratory model of a holographic information carriof novel design for optical memory systems that recostore, read, rewrite, and process information has been deoped experimentally. The preliminary experimental invesgations that have been performed on the characteristics ocarrier with respect to its photosensitivity, resolving powand capability of recording superimposed microholograhave shown that they ensure the realization of an opticaldrive ~Fig. 4! based on the holographic approach withincreased capacity~2–40 Gbyte on a disk!, input and outputspeeds up to 43109 bits/s or more, an information procesing speed up to 1011bits/s, and elements of artificial intelligence, which provide for a reduction of the required comping resources by 2–3 orders of magnitude.

4. CONCLUSION

The conception of the development of optics underlythe present study, i.e., the realization of fundamentally nideas in priority areas for developing displays for the purpof creating devices that are competitive in the Russian

FIG. 4. Diagram of an optical processor for information-control syste1—coder; 2—laser; 3—multichannel optical modulator, which includeacousto-optic modulator4 and liquid-crystal array5; 6—recording head,which contains dynamic focusing system7 and microobjective 8;9—holographic PTP memory disk;10—multichannel photodetector;11—decoder.


-rs

s-

n

al

e-o-

n

se-

-us

t-

,el--he,sk

t-

wed

world markets, enables the formulation of proposals pertaing to the following principal areas for the developmentdisplays:

• maintenance and development of the production oftical glass and crystals as areas where Russia is one ofew countries in the world with something to offer;

• preparation for mass production and actual manufture of optical elements~objectives, mirrors, spatial lighmodulators, intensifying screens! and systems for display~rear-projection monitors, video walls, projection systeemploying quantoscopes, and light-valve systems!, as well asdevelopment of promising areas associated with the creaof 3D laser displays, volume holographic screens, laser pjection systems with intracavity control, and optical procesors for information-control systems.

* !Deceased.

1G. T. Petrovski� and A. V. Dotsenko, ‘‘Glassy and glass-ceramic opticmaterials,’’ Opt. Zh.11, 69 ~1993! @J. Opt. Technol.11, 796 ~1993!#.

2G. T. Petrovski�, ‘‘Optical materials. Capabilities of optical materials technology today and in the future,’’ Opt.-Mekh. Prom-st’55, 61 ~1988! @Sov.J. Opt. Technol.55, 758 ~1988!#.

3Catalog of Colorless Optical Glasses@in Russian#, Moscow ~1990!, 132pp.

4Catalog of Colored Optical Glasses and Special Glasses@in Russian#,Moscow ~1990!, 228 pp.

5A. V. Sadchikhin and Yu. A. Cherkasov, ‘‘Certification of high-definitioCRT-based rear-projection displays,’’ inAbstracts of Reports to the Semnar ‘‘Certification and Standardization of Displays’’@in Russian#, St. Pe-tersburg~1966!.

6A. A. Vasil’ev, D. Kasasentet al., Spatial Light Modulators@in Russian#,Radio i Svyaz,’ Moscow~1987!.

7F. L. Vladimirov and J. C. Buchholz, ‘‘High resolution optically addressed spatial light modulators using photoconductors,’’ inLiquid Crys-tal Structures for Real-Time Optical Data Processing Applications. Opand Information, 6th Topical Meeting of EOS, ESSAIM, Mulhouse,France, 22–26 Oct. 1995.

8F. L. Vladimirov, I. E. Morichev, and N. I. Pletneva, ‘‘Influence of photoconductor parameters on characteristics of the spatial light modulabased on photoconductors liquid-crystal structures,’’ in2nd InternationalConference on Optical Information Processing, St. Petersburg, RussiaJune 17–20, 1996, p. 73.

9N. V. Kamanina and N. A. Vasilenko, ‘‘High-speed SLM with a photosensitive polymer,’’ Electron. Lett.31, 394 ~1995!.

10K. Akiyama, A. Takimoto, and H. Ogawa, ‘‘Photoaddressed spatial ligmodulator using transmissive and highly photosensitive amorphosilicon carbide film,’’ Appl. Opt.32, 6493~1995!.

11F. L. Vladimirov, N. I. Pletneva, L. N. Somset al., ‘‘Spatial light modu-lators based on chalcogenide glass photoconductor–liquid crystal stures,’’ in Abstracts of the European Conference on Liquid Crystal Sence and Technology, Zakopane, Poland~1977!, pp. 303–304.

12N. V. Kamanina and N. A. Vasilenko, ‘‘Dynamic characteristics ofpolyimide–liquid-crystal structure for optical information-processing sytems,’’ Zh. Tekh. Fiz.67~1!, 95 ~1997! @Tech. Phys.42, 82 ~1997!#.

13N. V. Kamanina and N. A. Vasilenko, ‘‘Influence of operating conditioand interface properties on dynamic characteristics of SLM,’’ Opt. Qutum Electron.28, 1 ~1998!.

14A. P. Onokhov, ‘‘Liquid-crystal light modulators as elements of lasers alaser optics,’’ inAbstracts of Reports to the Conference ‘‘Laser Optics@in Russian#, St. Petersburg, June 22–25, 1998.

15Catalog & Handbook 95/96: Liquid Crystal Modulators, ComponentsOptoelectronic Systems, Jena Optic Group Company.

16Yu. A. Cherkasov, N. V. Kamanina, E. L. Alexandrova, V. I. BerendyaeN. A. Vasilenko, and B. V. Kotov, ‘‘Polyimides: new properties of xerographic, thermoplastic, and liquid-crystal structures,’’ Proc. SPIE3471,254 ~1998!.

:


–Op

r-on

V.geord

or-pt

r’

ta

er

se

,

V.sisIE

.ft-ng.

e,pti-

,r-u-Zh.

17Yu. A. Cherkasov, E. L. Aleksandrova, and M. V. Smirnov, ‘‘Reliefelectrooptical transparent films based on the compression effect,’’Spektrosk.73, 817 ~1992! @Opt. Spectrosc.~USSR! 73, 490 ~1992!#.

18Yu. A. Cherkasov, E. L. Alexandrova, M. V. Smirnov, and E. A. Sidoovich, ‘‘Relief-electro-optical transparent medium for optical informatiprocessing,’’ Proc. SPIE2051, 331 ~1995!.

19Yu. A. Cherkasov, E. L. Aleksandrova, A. I. Rumyantsev, and M.Smirnov, ‘‘Formation kinetics of photothermoplastic relief–phase imaand an analysis of the possibility of implementing adaptive data recing,’’ Opt. Zh. 63~4!, 77 ~1996! @J. Opt. Technol.63, 308 ~1996!#.

20E. L. Aleksandrova, N. V. Kamanina, Yu. A. Cherkasov, and L. N. Kapski, ‘‘Fullerenes as sensitizers of the photoelectric effect in solids,’’ OZh. 65~8!, 87 ~1998! @J. Opt. Technol.65, 676 ~1998!#.

21BNO Brochure~1998!.22A. D. Tsvetkov, V. M. Sedov, and O. S. Shchavelev, USSR Invento

Certificate No. 842062, Byull. Izobret., No. 24~1981!.23J. Shandle, ‘‘It’s here! Real 3-D!’’ Elektronics63~9!, 29 ~1990!.24D. Campbell, ‘‘Formation of real three-dimensional images using a ro

ing disk,’’ Elektronika63~19!, 3 ~1990!.25C. Chinnock, ‘‘Volumetric imaging provides a walk-around view,’’ Las

Focus World29~9!, 20 ~1994!.26S. Bains, ‘‘Radial scanning produces 3-D image on flat screen,’’ La

Focus World29~1!, 41 ~1993!.


t.

s-

.

s

t-

r

27L. N. Asnis, A. V. Voronov, A. A. Golovkov, and S. V. Kuznetsov‘‘Volume laser display with acoustooptic deflectors,’’ Opt. Zh.63~12!, 66~1996! @J. Opt. Technol.63, 927 ~1996!#.

28Yu. A. Cherkasov, E. L. Alexandrova, A. G. Rumjantsev, and M.Smirnov, ‘‘Real-time photothermoplastic 8-inch camera with an emphaon the visualization of digital data by holographic means,’’ Proc. SP2408, 220 ~1994!.

29Yu. A. Cherkasov, ‘‘Photothermoplastic processes,’’ inNonsilver Photo-graphic Processes@in Russian#, A. L. Kartuzhanski� ~Ed.!, Khimiya, Len-ingrad ~1984!, pp. 45–103.

30M. A. Gan, D. D. Zhdanov, V. V. Novoselskiy, S. I. Ustinov, A. OFedorov, and I. S. Potyemin, ‘‘DEMOS: state-of-the-art application soware for design, evaluation, and modeling of optical systems,’’ Opt. E31, 696 ~1992!.

31Yu. A. Cherkasov, L. A. Mirzoeva, and E. L. Aleksandrova, ‘‘Storagprocessing, and visualization of information using devices based on ocal holographic memory,’’ Sredstva Otobr. Inf., No. 1, 46~1993!.

32Yu. A. Cherkasov, A. N. Cha�ka, E. L. Aleksandrova, A. I. RumyantsevM. V. Smirnov, and V. B. Konstantinov, ‘‘Optical memory with a supehigh information-input rate and maximum capacity with recording of sperimposed microholograms on a photothermoplastic medium,’’ Opt.64~4!, 12 ~1997! @J. Opt. Technol.64, 287 ~1997!#.


Documents

Optical problems in creating effective displays