0018-9162/98/$10.00 © 1998 IEEE36 Computer

Optical computing has come a long way since theinvention of laser sources in the 1960s.Research has produced numerous architecturesand applications, covering almost every aspectof computing. Some of these were feasible and

became successful—such as analog correlators and opti-cal memories—while others remained too esoteric or elu-sive to be widely adopted.

ADVANTAGES OF LIGHTCurrent trends in optical computing emphasize the use

of free-space optical interconnects as a potential solutionto alleviate bottlenecks experienced in electronic archi-tectures. Light beams can propagate very close to eachother, and even intersect, without any observable or mea-surable cross talk (the generation of unwanted signals).Therefore, dense arrays of interconnects can be builtusing optical systems. In addition, light is immune to elec-tromagnetic interference, which reduces the risk of noiseeven further.

Finally, light travels fast—faster than anything. And ithas extremely high bandwidth. Light, therefore, is anideal medium for information transport, as the wide-spread use of fiber optics in communications attests. Lightcan be harnessed even further for data processing.

OPTICS AND ELECTRONICSThis issue leads off with John Caulfield’s essay on opti-

cal computing. Caulfield argues that it is foolish to defineoptical computing as the attempt to supplant electron-ics. Needless to say, we fully agree with his thesis. Figure1 compares electronics and optics in four domains, whichrepresent the four major computing engines.

• Memory. Optical memories are quickly catching upto more conventional storage techniques.

• Data transport. Optical communications havetaken the lead over the past few years and showpromise, especially in the long haul.

• Data processing. Here digital optical computingtrails electronic computing significantly, even though

analog optical computing can easily outperformelectronic machines.

• Devices. Despite the impressive characteristics ofcertain optoelectronic device prototypes, the enor-mous investment in electronics has given it a com-fortable lead.

As Caulfield emphasizes in his essay, we should useoptics in computing only where they can serve electron-ics better.

IN THIS ISSUEThe feature articles in this issue highlight applica-

tions that exploit light to enhance computing. Weasked our reviewers to evaluate the submissions notonly for technical and scientific soundness but also fortheir tutorial value. We believe we have achieved a setthat is balanced, both geographically and betweenindustry and academia.

We invited two articles about research that is veryhighly regarded: Demetri Psaltis and Geoffrey Burr out-line the importance of optical storage and describe thevery successful experiments that led to a commercialproduct. And Peter Guilfoyle, John Hessenbruch, andRichard Stone chronicle how they developed a realisticoptoelectronic computer, and they explain the philosophyof their very successful research group.

We were also fortunate to receive articles from theEuropean Union and Japan, where good research in opti-cal computing is being done. James Gourlay, Tsung-YiYang, Julian Dines, John Snowdon, and Andrew Walkerdescribe an extremely interesting application of opto-electronic computing. A prototype system for a similarapplication has been already demonstrated by an inde-pendent research effort in the US,1 and the work by thisgroup at Heriot-Watt University will take this system to a more realistic performance level. From Japan,Masatoshi Ishikawa and Neil McArdle introduce theirresearch and provide a brief review of optical comput-ing research by other groups in that country.

Finally, along with George Betzos, we describe our

Optics: A MaturingTechnology forBetter ComputingThis issue presents a tutorial introduction to the field of optical informationprocessing, in particular, digital optical computing. We present current trendsin optical computing research, in the hopes of a closer interaction with thebroader computer science and engineering community.

Leo J. IrakliotisMCI TelecommunicationsCorporation

Pericles A.MitkasColoradoState University

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research, which focuses on implementing special algo-rithms and novel optoelectronic architectures that com-plement conventional computing systems.

W hat will a Computer issue on optical computinglook like in five or 10 years? We hope that it willinclude reports on the commercial success of free-

space interconnect-based sytems, on the widespread adop-tion of optical memories for massive storage in supportof multimedia applications (including video-on-demand),and advances made in micro-optomechanical systems.

In anticipation of such progress, we invite the broadercomputer science and engineering community to inter-act more closely with optical computing researchers. Wehope the work presented in this special issue will createsome interest for further collaboration, out of which bet-ter computer systems will emerge. ❖

Reference1. F.R. Beyette, Jr. et al., “Bitonic Sorting Using an Opto-

electronic Recirculating,” Applied Optics, Dec. 10, 1994,p. 8,164.

February 1998 37

Optical Computing ResourcesHere is a brief guide to optical comput-

ing resources, for those interested inexploring this topic further.

PeriodicalsWe consider Applied Optics, published

by the Optical Society of America, andOptical Engineering, published by SPIE(International Society for Optical Eng-ineering), to be the leading journals for cur-rent research on optical computing.

Many research groups opt to publishtheir work in the Journal of LightwaveTechnology, Optics Letters, Journal of theOptical Society of America, Journal ofParallel and Distributed Computing, andthe International Journal of OpticalMemory and Neural Networks. Thesepublications also run special issues onoptical computing every few years. Specialissues on optical computing have alsoappeared in Proceedings of the IEEE, andScientific American has also published arti-cles on the subject.

Look for these special issues in particular:

• Special issues on optical computing:Applied Optics, Mar. 10, 1994; Mar.

10, 1996; and Mar. 10, 1998.• Special issue on optical memory,

Applied Optics, May 10, 1996.• Special issue on optical computing

systems, Proc. IEEE, Nov. 1994.• Special issue on optical interconnec-

tions for information processing, J.Lightwave Technology, June 1995.

Conferences and proceedingsWe believe that the Optical Society of

America’s biannual meeting on opticalcomputing and SPIE’s Annual Symposium(which includes sessions on optical com-puting) are the two premium forums, andtheir proceedings are an interesting guideto the most recent accomplishments of sev-eral research groups.

Look for these proceedings in particular:

• Proc. Ann. Int’l Workshop on Mas-sively Parallel Processing usingOptical Interconnections, IEEE CSPress, Los Alamitos, Calif., 1994through 1997.

• Proc. OSA Topical Meeting on OpticalComputing, 1993, 1995, 1997.

• SPIE Proceedings, Vol. 2,754: Ad-vances in Optical InformationProcessing VII, Int’l Soc. for Optical

Eng., Bellingham, Wash., 1996.• SPIE Proceedings, Vol. 2,848: Mat-

erials, Devices, and Systems for Opto-electronic Processing, Int’l Soc. forOptical Eng., Bellingham, Wash., 1996.

• SPIE Proceedings, Vol. 3,159: Algo-rithms, Devices, and Systems forOptical Information Processing, Int’lSoc. for Optical Eng., Bellingham,Wash., 1997.

BooksFinally, we recommend these five books:

• Photonics in Switching, Vols. I andII, J.E. Midwinter, ed., AcademicPress, San Diego, Calif., 1993.

• M.A. Karim and A.A.S. Awwal,Optical Computing: An Intro-duction, John Wiley & Sons, NewYork, 1992.

• A.D. McAulay, Optical ComputerArchitectures, John Wiley & Sons,New York, 1991.

• B.E.A. Saleh and M.C. Teich, Fun-damentals of Photonics, John Wiley& Sons, New York, 1991.

• J.W. Goodman, Introduction toFourier Optics, 2nd Ed., McGraw-Hill, New York, 1996.

Figure 1. Comparative view of the use of digital optical computing, electronics, andanalog optical computing in four principal domains.

Memory

Data transport

Data processing

Devices

Digital optical Electronics Analog optical

Leo J. Irakliotis and Pericles A. Mitkas are coauthors of an article in thisissue. Their biographies appear on p. 51.

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