A Three-Color, Solid-State, Three-Dimensional Display

ensional

reeElizabeth

A

-Sate,

Downing,* Lambertus Hesselink, John Ralston, Roger Macfarlane

three-color, solid-state, volumetric display based

version in

rare

earth-doped

heavy

metal fluoride

infrared laser beams that intersect inside to address

Ds pla

a

on

two-step, two-frequency upcon-

glass

is described. The device

uses

transparent volume of active optical material

red, green, and blue voxels by sequential two-step resonant absorption.

images, surface areas, and solids are drawn by scanning point of intersection of the lasers around inside of the material. The prototype device

Three-dimensional wire-frame the

is driven with laser diodes, and is

bright enough

uses

to be

conventional

seen

in ambient

s'suaire real-tim L IlCVoLuMetiItv t VP tic daitain rII-ic Ii1-rce-d imensioniat (313) fomhas been1 a1 gAl if dispLav deivelo)pmenIt efots-.)- forI 1mans, sea~rs. .eCvcrald Clever tech-IIuchaveIC been11C devel pecd, bult noneII has prvde Co niple'te .1IrIti n tor thei neied to ,IC\\, dyna'inlic VOi LunetTic dataI In al real7117 e abi)

istic

initeractivc torntWe present

nieItrie

dII'ispave

a

VoLI-

that is capable of dispLaingm i1) objects Inl rea-l rtime and In trueIC 313 spatial f tin. The device can be VieWed from any~m perspee)Ct vc, throt_igh1 all1 sdes o)f the displas volume, aInd doe)s not requ~jLire spciLglsses (it heaidgear. Thec deViCe fett.~iresunc o111Ciinhe,red viewing" acce'ss to mul,1tipleA uIsers, siiiiul,tan1eOUSIVs' an1d is. ca-_ h

p"ible of dispLaing ,Inf,irmal11.tion USIng the threec ~iddit ve priiiiIrv color's red, g,reen, and1o bI tie (FPig.

Backg,round. Three-dimensional-i pereeptiiin is al Comple\1C C gnulive process inVAvling the eyes an11d the bra-in ais a1 VISual stei.I listiotic a s1 ~iLII InsT to displayingy 3D) mt( riait ion ire' di Verse11 anId varied and hi~1Ve often1 reiedIC in t1iCking1 theC hu1-1man VISMal Sy'StCeIliinto thinking that it Is seeing( aIDscen inthree dimensions. Alhough01 specC If ics5stC1iircjiriie vatsv for- differenit applicatins, asuccessful1 3D) display Shoul,1d poideM-,1 the VIe'Wer, to thec necessary extenit, with a nu1,mniber1 i)tif intrinsic VISoiLKi:_atiii pa)"ranierrs. These parameterS inICIlude the field i vIewv, which is defined by thle solid agesutenided] byv thle obje)ct and thus dectermineo.s thc. appa'~rent Size oft an

E. Dovir iig isin tINe Mc(is ilcil F-ri nearing DepartmTent, Stari Crd Un Ivers It y F-Jart3Ii,CA91405 an d at 3D TeGh icr logy Hdnoratorre-e. Pc" (Cffr a Box 1 14. 200 Blossomi F-via, Mountain Vicw, CA 1)404',2 USA. L. Hesselink is in thea Electrical Encj mar iig DopCI iO at, Stanford University, Stairforid. CA 14 t5USr A. J. Ralstorn is ai SDL

Corrporatioii, 9t Bcs a (J~rda Way. San Jose, CA it IBM Alniiaden Besearch 51St34, BSA. B. M iisIi

Ceiiter, 050 Harr B oidi. &in Josa, CA 35120, USA. 'Towvhom corri ycoii ri1c s A headciraesaed. E-mail:

focusing optics room

lighting

and mechanical scanners,

conditions.

object its seen- by the viewver, and the viewinig :one, which is definedl as th-e range over wh'Iich the ulser ot

Users can

miovec and

stitll

cleairly see th-e ob)jects displayed in the field of v Iecw. AuItostereo)scopic viewing is the ability for the displayed ob)jects to be conItAinuosly viewvable fromi all reg,ions within the viewing :one, and accomimodaitioni is thec ability f-or theC riser to focrIS on selected depth planes within the o)bject. Dynamic anrd reCal-rime capabilities allo)w mov(ing ob-) jects to be displayed at a refresh rare Suiffiicint to avid flicker (30 to 60 Hz), mcd interactive capability allows thei riser to mo1dify the objects being displayed, that is, :oom, transLate, rotate, CLit, andI paSte. Clolor refers to the ability to address thiree primatteCS suICh aIs the additive ted, gyreeni, and bAlue (RUB), fromi which a wvide spectrum11 of colo)rs, including white, can be produCedi by atppropriate mnixingy. Many o)f the systems that have been deCVeloped toi date, SLich as holographic and stereo)scopic displays (1), have limiited V IeWing :ones and risrUally present staltic himages tir im1-ages wvith very low resoIlution. Othiers, like virtrial reality displays (2), rec(_loire the riser to wear special headgear that initerferes wvith normal ViSLrial processes. DispLay approaches in which 2t) reflecrisec (3) otr emt-issive (4) SLirfaces are swept throrighori0Lt a th-ird dimeiinsion have been demon01strated, brLIt they too) have restricted viewing zones anid recqirtir large srirf aces to be cdeflected o)r rotated at high speeds. The traditional 2 D cathodle-ray tribe (CRT) and 1luicdic-crystal displays (L-CDs), in which dynamic 3D scenes can be tendered With theC rISe of appropriate graphic construicts SLich as shading, shadowing, and perspective, haVe thrIis fr ecIve h higohest deg,ree o)f implementation for th-e VISrIA 7lztio(n of many types of 3D) data. Thecse systems h-owever, display 3D in-formationi fromi on(ly o)ne viewer perspective, S(I EN(E * VOL. 2713 *

30 AUGUST 1996

ouLt intrinisic limitations to visuIalization. Thei display conicepr described in this article has been demonstrated in a smiall-

scale proof-of-principle pro)totype and provides aslto inWh1Ich all1 Of theISe VISuIaization paraimeters hlave an1- attractive ranlge Of VALues. A previOuIs alttemIpt to demonstrate thils techn(ique, ma1,de by Lewis et ali. of Battelle Labo)ratories in the early 1 970s (5), Suicceedied in genera,tinig two) faiunt spots of light inside a crystal o)f erbiuml-do(Iped calcium fluo)ride withi the uise of filtered xenion lamps as excitatiOn Souirces. The pioneering wovrk- of th-is grouIp Of reseairchers pointed] out th-e potential advanitages Of SuICh a display and indicated that thei shortcomigswre rimailyassociated with the lack Of SUitable eXCitation1 souirces and mnaterials with SuIffiCient infraired-to-visible conversion efficiency. We haiVe uIsed- highpower laser diodes (6) and imiproved uipconversion nmaterials to lay the critical fouLndation for thils 31) display technology. Of particrilar importance to the techniqueIL are th-e

absorption ctoss sections an1d initermiediatelevel lifetlimeis o)f thei active rios and the spectral distribUtion Of theI flUOrescence. Here we describe the faibricationi and o)ptimatOn f Up)on_VerSIo)n Maiterias and the inteoyration of these miaterials with laser cdi-

odies andi scanning~systems

to creaite a thiree-

color, solid-state, 3D) display.

Fig. 1. Taken in ambient room light, this photograph shows a red Lissajous figure and blue and green surface areas that have been drawn, by using lR pump lasers, in our small-scale, prototype solid-state, 3D display. 18 1185

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Th~ree-Color,

which p~revents the uSCer fromi emnplo)yIng natLural huIm-an depth- CueCs SuICh as stereo) vision and m-iotioni parallax. M riltipleIXing miethowds thai(t acttemipt to) introduLce stereoscopic viewing capabilities in-to) URT dilsplays have reSuL ted in reduICed viewing zones andl the need for theC user to wear1 glasses otr tracking headgear. None o)f the approaches that havle been presented thuis far has prov-ided a comiplete mnethod fot displaying dynamiic VOluMeCtric data with-

A

B

E2I

IIR 2

Lissajous figures were created in a stack of three individual glass layers that were laminated together with index-matching optical adhesive to form a composite structure. Each layer was doped with a different ion and was pumped with the wavelength combination appropriate for that dopant. All of the wavelengths required to resonantly pump each of the necessary dipole transitions in these rare earth ions are commercially available as laser diodes at power levels greater than 100 mW (7) (Table 1). Simple mechanical scanners, driven by function generators at rates of 30 to 100 Hz, were used to deflect the laser beams into the 1.5 cm by 1.5 cm by 1.5 cm composite sample. Resolution and voxel size in this display are determined by the diameters of the intersecting laser beams, which when focused to 100-p.m spot sizes produce roughly 300 voxels along the perimeter of a 1.0-cm-diameter circle. The transparent host materials used for this display are heavy metal fluoride glasses (HMFG) (8) doped with rare earth lanthanides: praseodymium (red), erbium (green), and thulium (blue) (9). These glasses, the most common of which is ZBLAN (10), have been developed for fiber laser and optical amplifier applications (I 1) and are characterized by low (