AFFIDAVIT OF Pamela Stansbury
`
`STATE OF NEW YORK
`
`COUNTY OF TOMPKINS
`
`)
`) ss.
`)
`
`Pamela Stansbury being of full age and duly sworn, deposes and says as follows:
`
`1. I am an employee of the Cornell University Library, and specifically Library Technical
`Services, located at Cornell University, Ithaca, New York 14853. I have personal
`knowledge of the facts set forth below.
`
`2. I am the Administrative Supervisor in Library Technical Services, which maintains
`bibliographical and processing information for many historical documents. I have held
`such position since 1996.
`
`3. Included in the Library's historical collection are various publications. As part of that
`collection, the Library maintains custody of an original issue of Applied optics, Volume
`10, Number 1, January 1971, which includes the paper Photoluminescent conversion
`of laser light for black and white and multicolor displays. 2: Systems I by D.A.
`Pinnow, L.G. Van Uitert, and M. Feldman.
`
`4. Mr. Richard F. Moncrief requested information about Applied optics, Volume 10,
`Number 1, January 1971 - specifically when this item was first made publicly available
`by the Library. As best I can determine, the publication was publicly available at the
`Cornell University Library as January 5, 1971.
`
`~ ANDREA DENISE SMITH COLON
`I NOTARY PUBUC-STATE OF NEW YORK
`Tompkins County
`Registration #01 SM6276256
`Commission Exp. 02/11/201.1.
`
`VIZIO 1023
`
`

`
`plied
`Optics
`
`January
`1971
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`VIZIO 1023
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`

`
`Applied
`Optics
`
`VOLUME 10
`NUMBER 1
`JANUARY
`1971
`
`A monthly publication of the
`Optical Society of America
`
`J. H. Howud Editor
`P. R. Wakellng Managing Editor
`
`eo.,.r. See page 153.
`
`Published monthly by the Optical Society ol
`America at 20th and 'Northampton Streets,
`Easton, Pa. 18042. Olllee of the Editor:
`AFCRL; Bedford, Mass. 01730: 617-861 ·
`4211. Off'oc:e of the Managing Editor:
`:~~~lnJ~~~ ~-'C~1"~: '$trl~'-la/!Ji3:
`Advwti&l~ offlca: American Institute of
`r,~;n~·m-M5· ~:~tre~·tS:,i' T:~·.Z11s
`!>'!'year. Included in members~•P dues to
`OSA members; nonmembers and libraries
`. Second Class post.ge paid at Easton,
`. 0 Copyrtl(ht 1970 by the Optical
`Soctety or Amer1ca, Inc.
`
`E. Sin(lle copies $4; comple te volumes
`
`1
`
`• 14
`
`1t
`
`2A
`2t
`
`31
`
`-.....,.cz
`
`46
`51
`
`74
`
`11
`
`17
`
`" lOS
`
`lot
`
`-.......114
`Ut
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`112
`U6
`141
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`144
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`150
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`154
`
`~Ul
`
`lil
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`174
`
`.......... 112
`
`117
`
`ltJ
`
`Ge~e,.s;~~rot':::!~l:!!?b~'L.•:;a~~~mon Varlanm of Color Matching by 14
`A Visual Trlstlmulus Projection Colorimeter-A. Valbera
`Adjustment of the Munsell· Value and W'"-Scalea to Uniform Lightness Steps
`for Various Background Reflectance-c. C. Semmelroth
`Internal Reflection Spectroscopy: Validity of Effective Thickness Equations
`- N. J . Harrlck and A. I. Carlson
`Hadamard-TrartsfOrm Exhaust-Analysis Spec:trometer-J. A. Deeker, Jr.
`A Gt<azlnt Incidence Monochromator for Satellite Studies of the Solar Hell
`Lyman .... Line at JGJ.I A-P: J. Bowen, J . A. Bowles, W. M. Glencross, R. J .
`Speer. A. F. Timothy , J. G. Timothy, a n d A. P. Willmore
`A Convonlont Technique for Determining the Relative Quantum Effklanq of
`a Monochromator and Detector Syste m-J . L Kohl, L. J . Curtis, D. A.
`Chotnackl, and R. M. Schectman
`Motion Blurrlnt with Docayint Detector Respon-L Levi
`£1e'1~~:L!'.r'8':~":.fo;;r the Amplitude and Phau Fluctuations of a Wno
`
`A Simple Doubl.e Beam Acc:eosory for Absorption Spec:troscopy-K. Leutweln
`Spectral Absorption Characteristics of the Major Components of Dust Clouds
`- D. F. flanlgan and H. P. DeLong
`Effects of Arton Atoms on the Self-Absorption and the Intensity of Hg 2517-A
`Radiation in He + Ar Dlschargo-T. J . Hammond a nd C. F'. Gallo
`stat~~i~~~:;11.lM,.'1~1n::r:r.:A~ vaar:::,:~:.~~~:::'m1.:'~~~i~~~:r:. ~h,ed 5F~s:
`Bonomo
`Radlanca artd Polarization of Light Reflected from Optically Thick Cloud(cid:173)
`G. W. Kettawar and G. N. Plass
`Rad[atlon·lrtduced ChanJJ•• in Rohactlve Index and Absorption Coefficient
`for Several Optical Material-D. R. Olson , H. D. Oiese.lman, and J. 8 .
`Schroeder
`Damping ol La«ice Vlbratioas in Solid-J. N . Plendl
`The Correction of Optical Aberrations by Nautron lrndiatlon-P . Sinai
`Images of Truncated One-Dimensional Periodic Bar Tar .. ts In Aberration•
`Limited Optical Systems.-.!. W. foreman, Jr., G. H. Hunt, and E. K. Lawson
`lnflue~~c:e of Scattered Radiation on Narrow Field of View Communication
`Link-D. E. Setzer
`Small-Anti• Sc:aHarlng of Lltht by Ocean Water-H. T. Yura
`Bldi[:'_!!;~~ ~~t'!?. ~~:;:~ri;~~~~~R~fA~~a~:;r~raen Soybean and Corn
`Clneholomlc¥osc:opy of Small Animal Mlcroc:lrculation-M. E. Cox. R. G.
`Suckles, and D. Whitlow
`Calorimeter for Laser Energy Measuremen'-M. M. Birky
`The CO, Laser Signature Problom-P. C. Cia spy and Yoh· Han P ao
`CO, laserwith Simultaneous Active and Passive O-Swltc:h ing-0. M. Stafsudd,
`0 . Ersoy, and S . Pin:Jca
`A Precision Variable, Double Prism Attenuator for co, Laser-T. Osekl and
`S. Saito
`Photoluminescent Conversion of Laser Lltht for Black and White a nd Multi·
`color Displays . 1: Matarlai-L. G. Van Uitert, D. A. Pinno w, and J. C.
`WlllilmS
`Photoluminescent Conversion of Laser lltht for Black and White a ltd Multi(cid:173)
`color Displays. Z; System-D. A. Pinnow, L. G. Van Ultert, and M.
`Feldman
`Moesuremont of the Beam Parameters of a Laser ham and Ita Diffraction
`Field. Using a Hologra-T. Miyamoto a n d K. Yasuura
`A C..ntrlbutlon to the Comparison of Single Exposure and Multiple Expoaure
`Storate Hologram-M, Lang, G. Goldmann, and P. Graf
`Hol~~~~0~ubtrac:.tlon-K. Bromley. M. A. Monahan, J . F. Bryant, a nd B. J.
`A Hololraphlc: Interferometer for Measurint Radiation Eae r1y Deposition
`PrOfiles In Transparent Liquid-E. K . Hussmann
`A Ge-rallzad Tecflnlque of Two-WavelenJth, Hond iftuu Holoaraphk
`Interferometry-F. Weigl
`A Techaique for Rec:overl"' Doppler Line Profllas from Fabry-Perot Inter·
`ferometer Fringes of Vary Low Densit)'-P. B. Hays and R. G. Roble
`Schllerea VIsualization Device Allowhtg an Arbitrary Orientation of the Li(cid:173)
`wltlt Respect to tbe Sc:annlnt Dlrect"'-R. Grossln. M. J annot. and S.
`Viannay
`
`January 1971 I Vol. 10, No.1 / APPLIED OPTICS A5
`
`VIZIO 1023
`
`

`
`Photolu_minescent ~onversion of Laser Light for Black
`and Wh1te and Mult1color Displays. 2: Systems
`
`D. A. Pinnow, L. G. Van Uitert, and M. Feldman
`
`ltcoont .tecnnul!lgical developments permit the mod\dation and scanning or laser beams at rates c:ompa(cid:173)
`rable ~1th ~bo;e oC ~lcclrou beams in television rcceiverd. Tltis accounts for mncb or the current iotere>;t in
`laser 1~ummated d~:~play ~yatcm~ wbich are not coo.,trained in size, as is the cathode my tube, by the
`ne~t-<~::>tty of a vacuum enclo3llre. The purpose of the pre.ent work is to show how photoluminescent ma(cid:173)
`len~ls ~ be II~ in conj~rlion with rereutly drveloped aro\tStooptic deflectors and modulators to
`ach1evc hrgh qualrty lll,er dl:!play system,. The principal frmction of the photoluminescent materials is
`~hfl~ of ~lor ll<ntv~~ion. when Mated oot.o a viewing screen. This allows an additioual degree of freedom
`10 ~~~~cr d~p!ay eugm~rng by removing Lhe spectral constraint~ imposed by the limited number or practical
`laser em~S.•tons.. Yano~, schemei for both black Blld white and multicolor displays are explored.
`So~te or the eor~cepl.!!. wh1rh evolvt..>d have been PxpcrimenlaUy verified by the operation of a sy~tem which
`proJected the v1deo Mtgllru frorn li PICTUH EPHON E Ret. The source was an argon ion la~er which emit(cid:173)
`ted a ~onochrornatio blue (48.'30-A) beam. After acou,ilooplic modulntion and defiertion, the blue beam
`w:a.~ directed t.n a pho•phor screen where it was r.o11verted into o. brighter and peckle-free black and wrute
`d!!lplay.
`
`I.
`
`Introduction
`In Pttrt 11 wo discussed tho characteristics of o.
`' number of photoluminescent materials that can effi(cid:173)
`cio~tl1 convert ultru.violet and visible light into light of
`a !llmllnr or longer wavelength spectral content. Here
`we will consider the application of these materials to
`white light t\nd multicolor displays that use laser
`sources. A cunt~idcrable effort in tho field of la11er
`scanned uispluys hns been prompted bv potential
`appl~cat.ions for whi~h the ca.thode ray tube (CRT) is
`unsUited. One pnrt•culurly lmportant application of
`laser systems ill U1itt of lt~rgo Screen multicolor display.
`Such sysloms have been successfully developed in a
`n\Lmber of l!lbomtories' including Zenith, Tex!Ui Instru(cid:173)
`ment , General Telephone and Electronics, and Hitachi.
`In general, they :tre complicated, expensive, and re(cid:173)
`qui~f'd o substantial and careful engincedng effort. A
`maJor source of engineering compllcation bas been the
`necessity of using three sopa.mtcly modula.ted la~er
`beams of diffen'ul colors to achieve the de ·ired color
`gamut and the use in many cases of mechanical scanning
`motion. We have found that a greater freedom of
`ac~ion ns well as possibll! simplifications could result by
`usmg pltotolummesccnt scroens to provide some
`switching action between colors. In this paper we will
`describe some !SCheme
`for color switching and the
`
`The authors are with DeU Telephone Laboratories, lnc., Mur(cid:173)
`ray Hill, New Jersey 07974.
`Received Hi March 1970.
`
`154 APPLIED OPTICS / Vo1.10, No. 1 I J a nua ry 1971
`
`systems they make possible. We will also report
`experimentru results of a particularly simple lnr~e
`screen black and white system which is speckle-free
`and provides PICTUREPHONE resolution.
`In discussing laser display systems it is instructive to
`compare them with the conventional CRT ystems.
`Recent
`technological advances
`in acoustooptics*·4
`and electrooptics6 permit efficient and inertialess modu(cid:173)
`lation nnd scanning of laser beams at rates approaching
`or compl'lta.ble with those of electron beams in television
`CRT's. The principal difference bot,weeu luser a.nd
`CRT ~ystcms is not in resolution but in screen shape
`and SLZe. Laser systems are inherently projectiou
`systems which can use flat screens; while the conven(cid:173)
`tional CR.T, which is most often directlv viewed has
`con iderable volume. Generally, the si~e of a CR'f
`screen is limited by mechanical con iderations to at
`roo t 76 em in diameter.6 Even if the CRT ima(l'e i
`projected, the viewing area is constrained by the Light
`intensity that can be developed at the CRT screen.
`In
`order to provide a black and white picture with bright(cid:173)
`ness comparable with that of a typical motion picture
`display the projection CRT screen size is limited to
`approximately 2 m! even with anode voltages on the
`order of 75,000 V, where x-ray radiation and heat
`In contrast,
`dissipation become serious problems.8
`screen hea.t dissipation is not a problem in IMer displays
`since the beam is directly projected to as large n.u ar~a
`a can be comfortably viewed with the available laser
`intensity. A rough estimate of the relation between
`light intensity and viewing area is lhat 1 W to 2 W of
`
`VIZIO 1023
`
`

`
`available laser light are required for each square meter
`or a diffusing screen to achieve typical television bright(cid:173)
`ness levels/ while a factor of 3 less in intensity is satis(cid:173)
`factory for theater viewing. For certain applications,
`directional screens can be used which reduce the re(cid:173)
`quired laser power by factors of up to several hw1dred.
`The laser source is a limiting factor in many display
`system designs. By taking advantage of photolumines(cid:173)
`cent color conversion we can remove spectral con(cid:173)
`straints imposed by the limited number of practical
`laser emission wavelengths. Of the presently known
`laser types, the argon ion la er bas already proven
`satisfactory for long term stable operation at a level of
`several watts,8 and experimental units have demon(cid:173)
`strated output. up to 100 W.9 Although this laser is
`satisfactory for a display system source in almost all
`respects, its efficiency is typically only on the order of
`several hundredths of 1%.10 Thus an argon laser
`source adequate to illuminate a 1 m2 screen would re(cid:173)
`quire several killowatts of electrical power.
`In com(cid:173)
`parison, only a few watts of electrical power are needed
`for modulation and scanning of the laser beam. 3 Be(cid:173)
`cause of this laser inefficiency the operating expense fo;:
`a display system using an argon laser source will tend
`to limit its applications either to commercial uses
`involving large audiences or uses where very low light
`intensities are acceptable. However, it should be
`pointed out that low efficiency is certainly not fw1da(cid:173)
`mental to laser operation. For example, operation of
`an infrared (10600 A) Nd:YAG laser at Z.4% effi(cid:173)
`ciency has already been demonstrated, u and efficiencies
`of approximately 10% appear to be po ible. 12
`For the present, however, the argon ion laser is the
`most suitable prototype for a display system source.
`It has prominent emission lines in the blue (4&'i0 A)
`11nd green (5145 A) . . Because photoluminescent con- .
`version can only produce light of a simihu or louger
`wavelength, it is essential that the source have at least
`one blue or ultraviolet emi ion. The additional
`emission of a second color, such n.s the green line of the
`argon laser, can be used to advantage in certain systems
`that will be discussed in , cc. ITI. By using phosphors
`described in Part 1, 1 it is possible to convc1·t a portion of
`the blue-green beam into red, which is the remaining
`componeut necessary for a multicolor display. This
`technique is substantially simpler than the alternate
`approach taken by othen;2 of adding an additionnl red
`laser source to the display system and avoids the
`problem that presently available red lasers are even
`Jess suitable for a display system than the argon laser.
`The two principal choices are the H e-Ne laser (632 A),
`which is inherently limited to low power operation for
`reasonable sizes by the low $ain per unit length, 13 and
`the krypton ion laser (6471 A), which is nearly an order
`of magnitude less efficient than the argon laser. 14 An
`additional advantage of photoluminescence is that the
`converted light is incoherent so that tho unpleasant
`granular or speckled te.xture generally associated with
`viewing diffusely scattered cohet·ent light is elimi(cid:173)
`nated.15
`The recently developed Cd- He laser which emits in
`
`the blue (44i6 A) should also serve as a useful prototype
`ource, although its intensity is limited like that of the
`He-Ne laser. 10 In addit.ion to the above lasers, it. is
`possible to make multicolor laser hybrids by combining
`two or more gases into a single laser tubc. 17 Experi(cid:173)
`ments with mixed gas lasers which combine argon and
`krypton or He- 1c-Cd to achieve multicolor emission
`indicate that the over-all efficiency of the mi..xed systems
`are considerably less than optimized lasers having
`single components. For example, the red emission
`from a He-Ne-Cd laser has beeu observed to be only
`about one-fourth of that from an optimized H e-Ne
`laser. 17 Thus, the present hybrids have a serious
`problem because of their inefficiency.
`
`II. Color Control
`There are many analogies between display systems
`that use electron beam sources and those that use laser
`beams. For example, both types of bc.am can be used
`to illuminate a phosphor which in turn produces a
`visible color. In the standard color CRT display three
`spatially separated electron guns are used to illuminate,
`respectively, three different colored phosphors through
`a shadow mask. A similar technique i also practical
`with laser displays. Thus, one method for acl1ieving
`multicolor is by illumin!lting from different spatial
`directions.
`An alternate method for achieving a multicolor effect
`with a CRT is the use oi a single electron gun ,vhich
`e.xcites a white phosphor screen located behind a ro(cid:173)
`tating multicolor wheel. 18 Transparent red, blue, and
`green segments of the wheel sequentially appear in
`front of lhe CRT resulting in a repeating sequence of
`di crete color frames. The wheel rotates sufficieutly
`fast so that an observer cannot distingui8h the separate
`color frames but instead sees only t he total effect.
`V ariatiom; on this approach can all be categorized as
`active (i.e., moving) screen methods.
`, imilar methods
`arc also possible with a loser. system, although the
`scr'een may be substantially dillerent from that used in
`the CR'T system.
`In addition to these well-h."Down methods, which are
`applicable to both electron beam and itl.Ser beam illu(cid:173)
`mination, there are several unique features of laser
`beams which can be used to advantage in achieving a
`multicolor system. First, the la er beam itself may
`provide at least one color, and in the important case of
`!\ext,
`the argon ion laser there are two cill;tinct colors.
`a laser beam, or for that matter any light beam, has
`two orthogonal polarization states which can be used
`to transmit separate color information. And, finally,
`light beams can be brought to a focus in very short
`distances by passive elements such as plastic lenslets
`which can be made an integral part of a viewing screen.
`Tho internationally accepted CIE chromaticity dia(cid:173)
`gram ' 9 shown in I"ig. 1 can be used as a guide in assessing
`In this diagram
`the color quality of a display system.
`the saturated (monochromatic) colors are located on the
`perimeter of the horseshoe shaped plot, while colors of
`decreasing saturation approach illuminnnt C which is
`
`January 1971 I Vol. 10, No.1 I APPLIED OPTICS 155
`
`VIZIO 1023
`
`

`
`converted light from either Rhodumiue dye phosphors,
`type 34 3 or 3484, can produce a white appearance
`since a straight line connecting these primaries on the
`chromaticity diagram passes very near illumhlaot C .
`imilarly the combination of 4880-A light and converted
`light from a YAC :Ce phosphor wiU produce a somewhat
`yellowisb-wltite appearance since the line connecting
`these primaries passes above iUuminant C. T o achieve
`a t ruer white with this phosphor requires a. shorter lnser
`wavelength such as the less intense 4fi79-A line of t he
`argon laser or the 44L6-A line of the Cd- Hc laser.
`A combination of more than two primaries can nl o
`be used t o produce white. Af!t an e.xample, a Cd- He
`laser beam which illuminates a correctly proportioned
`mixture of :\IgO and dye phosphors 348a and 34 5 can
`be used lo achieve a white appearance. Alternately,
`the .:\[gO could be replaced by pyrelene (a blue to blue
`converting phosphor) to eliminate speckle completely.
`R egardless of how many pho~phors are used, it is
`apparent from the chromaticity diagmm that a nec(cid:173)
`essary condition for achieving a true white is that the
`illuminating laser beam have a wavelength of approxi(cid:173)
`mately 4Hfl0 A or shorter. Otherwise it would be
`impossible to include illuminant C within a polygon
`whose primaries arc the source and any combination of
`longer wuvcleugths that can be achieved by coover!:lion.
`Fortun:t1ely, the argon ion laser can satisfy this nec(cid:173)
`essary condition.
`A factor which must be considered in the choice of
`photoluminescent materials is the relative sensitivity of
`the eye. 20 Figure 2 clearly demonstrates that there is
`an incrensingly steep falloff in the eye's sensitivity as
`wavelength varies from the yellow-green portion of
`the spectrum at about 5550 A. Thus, for a fixed laser
`power and a fixed phosphor conversion efficiency, the
`brightness of the screen depends critically upon the
`emission spectrum of the phosphor.
`In pa.rticular, the
`brightest creen will favor the yellow-green emitting
`
`·~000
`
`6000
`8000
`WINE lEfiGTH !AI
`
`1000
`
`Fig. 2. The relal ivc sensitivity of n. standJlrd normal eye to light
`of varying wavelength.
`
`Fig. 1. The CIE chromaticity diagrl\m. The dotted lines en(cid:173)
`close lhe color gamut of a shudow m~•k C'olor C'alhodc my Lube.
`
`a white color equivalent to u.vPmge daylight illumi(cid:173)
`nation. Every real color, regardless of its spectral
`oomplexily, can be represented by 11 single p11i1lf on or
`within this plot. A straight line coon~>ctiug any two
`points (prima ries) represents the locus of possible
`colors that Cll.n be ach ieved by blending tltc t>rimaries
`in varying proportions.
`imilady, f he ganntl of colors
`po!lsible by I he combination of more than two primaries
`nro those thnt fall within the polygon determined by
`straight lines which connect adjacent primaricl:l. As an
`e:<ample, tho dotted tria11gle in Fig. 1 encloses the color
`gamut oft\ shadow mask color CRT.
`Ji'or compMison
`we have also !!hown the major cadmium and argon laser
`' "lines at 4416 A, 4 80 A, nnd 5145 A, as well as the
`emissions of the YAG:Ce phosphor nnd the three
`organic dye phosphors (type 34 3, 34.84, and 34$5)
`which are discussed in Sec. III of Pa rt 1.1 The arrow
`on the type 3485 dye cmis ion shows the effect of adding
`phthalocyanine, which is also discussed in Prtrt 1. It
`can be seen that the combina-tion of blue light. (4416 A
`or 4880 A) from either or these laser sources and emis(cid:173)
`sion from the 34 3 and 3485 phosphors results in a
`color gamut similar tot hat of tho CR'f.
`Ill. Exploratory Systems
`V a.rious laser display systems are proposed and
`evaluated in this section. They are presented in such
`an order that tho relative advantages and disadvantages
`bucome apparent. The first and simplest system con(cid:173)
`cerns the conversion of a monochromatic display int.o
`black and white. The remaining systems are for
`multi.color displays.
`A. Black and White
`A black and white display can be achieved by scan(cid:173)
`ning a monochromatic laser beam on a viewing screen
`that is coated with an appropriate blend of phosphors
`and direct scattering materials such as powdered MgO.
`!?or example, a combination of scattered light from a
`blue argon ion laser beam (4880 A) and blue to red
`
`156 APPLIED OPTICS / Vol.lO, No.1 I January 1971
`
`VIZIO 1023
`
`

`
`respectively, in the horizontal nud vertical deflectors
`since the :;ound velocity in the cry talline lead molyb(cid:173)
`date acoustooptic medium i approximately 3.5 mm
`~ec-•. The thcoreticnl t-esoluliou of a deflector in
`terms of standard TV lines is simply the product of the
`bandwidth and the filling time. 1·:1 Thus, the 75-.MH:ll
`bandwidth of the deflectors allowed a theoretical reso(cid:173)
`lution of 75 line horizou.talJy and 150 lines vertically .
`.\t the time of I he experiment this resolution was deter(cid:173)
`mined by the si.zo of the available lead molybdate
`crystals which set au upper limit ou the filling times.
`Larger crystals aro now available which would allow
`525-linc t·esolution. The i\fod l PICTUREPHONE
`set bas a rcsolut ion of about, 50 horizontal lines by 275
`vertical line.."l. Thus the frequency response of the
`PICTUREPHONE ·ct limited the horizontal resolu(cid:173)
`tion of the laser display to 50 lines while tho vertical
`r~olution was consistent with that theoretically cal(cid:173)
`culat<.'<i. Once aligned, the ystem wa.-: stable and tbe
`
`(A)
`
`MOO I PICTUAEPHONE CRT DISPLAY
`
`(B)
`
`1100 I PICTUREPMOIE LAIER DIM.AY
`
`Fig. 4. A ~rod I PlCTUREPITONE display (A) as soon on a
`CRT monitor and (B) M projected onto a YAG:Ce screen using
`th~ laser system described in the text.
`
`January 1971 / Vol. 10, No.1 / APPLIED OPTICS 157
`
`Fig. 3. Scbematit of the cxpcrimeut41l IIIScr vrojcctiun system.
`
`phosphor , while the requirement for 1\ true white will
`result in a tradeoff in brightness. Clearly, a compro(cid:173)
`mise i · nece$~ary in a laser display whos<' ::;cr en &ze is
`limited by brightness.
`In order to lest some of Lhe above couccpts, u. display
`screen was fabricated by dusting YA(i :C'c powder over
`n white cardboard sheet that IH\d been corl.l cd with a.
`transparent glue. This screen was USl'd in conjunction
`with a real time test dis~ lay sy. tcm which used an nrgon
`ion lu:-;er source (4 0 A) and solid state, ncoustooptic
`deflectors. 3 These acou ·tooptic devices deflect the
`light beam by an angle directly proportional to the
`frcttucncy of tho applied electrical sign~tl, while the
`intensity oft he deflected beam is approximately propor(cid:173)
`tional to t.he drive power. 21 •21 The vicl<'o signal for this
`system was supplied by a .1\lod I PI T REPHONE
`unit, which also served a a monitor when operated in
`the self-view mode. The system schcmat ic is shown in
`Fig. 3. Lt bhould be noted that the large bandwidth
`(7•) ~1Hz) of these recently developed acoustooplic
`deflector:; allowed unusual simplicity in that the ame
`device was u ·ed for both horizontal deflection and for
`video modulation. The deflectors were driven by
`varactor oscillators which had swept frequency outputs
`that were synchronized with the horizontal and vertical
`deflections in the PICTUREPHONE d . At the
`same time the video signal wa u ed to amplitude
`modulute the horizontal frequency drive 1111<.1 hence lhe
`deflected light. The t·esuliing image rcsolut ion on the
`YAG:Ce phosphor screen was nearly as good ru; that on
`the CRT monitor. A direct comparison C'Un be seen in
`L•'ig. 4. The phoRphor screen dispersed I he light in a
`lnmbertian manner with a quantum efficiency of approx(cid:173)
`imately 70%. Visually the picture appc11rcd speckle(cid:173)
`free aod con. iderably brighter than ~~ white sheet of
`p11per illuminated by the same blue liJ,!;ht. The some(cid:173)
`what yellowish appe.arance of the crccn cot~ld be cor(cid:173)
`rected by tw1ing the laser to the weaker 4579-A emission
`line.
`Certain details of t,bi system will now be dU;cw. ed
`$Lnce they arc generally relevant to the de ·ign of oper(cid:173)
`ating systems. The ll\Scr beam cnh'ring tho adjacent
`deflectors waa collimntcd with a ·imple t ele.~cope and
`shaped with a prism to an elliptical cross section luwing
`principal axes of 3 . .5 mm and 7.0 mm. This corresponds
`to filling_ times of approximately 1 ~£!iCC and 2 ~tSec,
`
`VIZIO 1023
`
`

`
`B• BLUE
`G• GREEN
`R• RED
`
`(o)
`
`(a) A rotating color wheel screen which is coated with red
`Fig. 5.
`(b) Rotating prisms
`(R), blue (B), and green (G) phosphors.
`which perform the same function as the oolor wheel but occupy
`less space.
`
`picture remained in focus for hours without readjust(cid:173)
`ment.
`Screen brightness, in addition to resolution, is an
`important measure of the performance of a projection
`system. In our experiment-al system the laser source
`intensity was 0.5 W; however, only 20 mW of light
`reached the screen (open aperture), representing a.
`,
`' 14-dB optical loss. Of this, 10 dB of Joss can be attrib(cid:173)
`uted to ref:l.ections from uncoated optical surfaces
`which could for the most part be recovered by applying
`antireflection coatings. Another 3 dB were lost in the
`vertical deflector which could not be operated at a
`higher electrical power level (0. 5 W) without causing
`noticeable optical distortion due to ohmic heating of
`the tranJ:~ducer electrodes. This heating problem has
`been corrected in subsequent deflectors; however, one
`should still anticipate :t 1-dR to 2-dB optical loss in a
`well designed deflector due to a practical limitation
`which forces a tradeoff between deflection efficiency and
`bandwidth. The remaining 1-dB loss in the experi(cid:173)
`mental system was due to the horizontal deflector which
`could operate at a higher peak power than the vertical
`deflector because the video signal modulated the drive
`level such that the average power remained Jess than
`0.5 W. The picture contrast ratio was limited only by
`the extent to which the drive to the horizontal deflector
`could be amplitude modulated.
`
`B. Multicolor
`In the spirit of the rotnting color wheel in front of a
`CRT which is used to produce a repeating sequence of
`discrete red, blue, and green color frames, one can make
`a similar screen for a laser display which is coated with
`red, blue, and green fluorescing materials. It is ap-
`
`158 APPLIED OPTICS I Vol. 10, No.1 I January 1971
`
`parent from Fig. 5(a) that such a wheel would have a
`diameter more than twice the height of the screen. The
`wheel size would become excessive for most large screen
`applications. An interesting alternative to overcome
`this difficulty is the use of a series of parallel rotating
`prisms as shown in Fig. 5(b). Each facet of the prism
`can be coated with either a phosphor or a light scattering
`material.
`In this case the rotating elements require an
`area no greater than that of the viewing screen itself.
`In order to avoid flicker, the framing rate must be at
`least 40 per sec 18• za corresponding to a prism rotation
`speed of 2400 rpm (three color fields per frame).
`The advantage of this system is that it uses the
`simplest possible projection system consisting of a
`laser and beam modulator-deflector of no greater com(cid:173)
`plexity than the one which was already demonstrated
`to be satisfactory for the black and white display. The
`disadvantage is that the burden of performance rests
`upon the screen whose moderately high speed mechan(cid:173)
`ical components would generate some associated noise
`and would require maintenance. It is felt that this
`disadvantage is sufficiently serious to preclude use of
`active screen systems for general applications. Atten(cid:173)
`tion will therefore be turned to passive screens.
`In any system which uses a passive viewing screen,
`the multicolor information must be projected through
`three distinct routes, which we will call cclor channels.
`A color channel can take on several different forms such
`as spatially or angularly separated beams of the same
`color, orthogonal polarization states of a single beam,
`or different laser wavelengths which have collinear
`propagation.
`The simplest example of a passive yet multicolor
`viewing screen is one that is repetitively striped with
`one or more different phosphors. The stripe period
`must be small enough so that an observer cannot detect
`the separate lines, yet the deflection system must have
`sufficient resolution so that each set of lines coated with
`a similar phosphor (i.e., each spatially resolved color
`channel) can be individually illuminated. The advan(cid:173)
`tage of this system is its relative simplicity, requiring
`only a single laser source and scanner as well as a passive
`viewing screen. However, there are two serious
`problems which render the system impractical. First,
`the projection system must be critically aligned with
`respect to the screen to ensure satisfactory color regis(cid:173)
`tration; and second, a factor of 2 (in the case of a
`bichromatic laser) or 3 (in the case of a monochromatic
`laser} in vertical resolution of the projection system is
`sacrificed in order to establish the necessary color
`channels. Fortunately, these disadvantages can be
`overcome with minor modifications.
`The problems of critical alignment and loss of vertical
`resolution discussed above can be eliminated by the
`use of a shadow mask similar to those in present color
`cathode ray tubes. 18 Consider, for example, a system
`in which a monochromatic laser beam is first modulated
`and scanned as in the simple black and white display.
`Immediately after the scanner the beam is deflected
`into three angularly separated channels in accordance
`with the desired color information. This can easily be
`
`VIZIO 1023
`
`

`
`SHO.OOW
`MASK ----,
`
`8• 8LUE
`G•GREEN
`A AED
`
`Fig. 6. A shadow mask and pbospior screen. Monocbroma.tic
`light is incident upon the screeD from the three 811gularly resolved
`color clulnnels.
`
`accomplished with ::m acoust oopt ic device. These three
`channels are then directed so that they arc recombined
`at the screen a.fter passing through n. shadow mask as
`shown in Fig. 6. The function of the mask is to ensure
`that light from each channel illuminates only the o.ppro(cid:173)
`priate colored phosphor. J n practice, the mask and
`phosphor screen could be made as a single unit so that
`the critical alignment tolerances are built into the
`screen assembly. Then the alignment of the projector
`with respect to the screen asRembly could have consider(cid:173)
`able additional tolerance. Furthermore, there is no
`loss in the over-aU !!ystcm resolution, provided that the
`holes in the shadow mask are made closer than a screen
`resolution element. However, this type of screen. can
`be viewed onlr wbetl it