Introduction to the featureon spatial light modulators and their applications

Anthony L. Lentine, John N. Lee, Sing H. Lee, and Uzi Efron

The special issue of Applied Optics on spatial light modulators presents a collection of papers that describeimprovements in basic devices, smart pixels, and system applications.

Spatial light modulators (SLM's) are key componentsfor many optical and optoelectronic systems, such asoptical processing, optical interconnections, imageprocessing, and displays. SLM's are generally anarray of optical modulators that can be used tomodulate an array of beams or a continuous imagespatially. SLM's modulate light in response to ei-ther electrical or optical inputs. In many cases,SLM's comprise individual elements or pixels, al-though they can be unpixelated as well. Examples ofunpixelated SLM's are those that are optically ad-dressed by a photosensitive layer on top of themodulating material and those that are addressed bya scanned photoelectron beam. The applications forSLM's can be both digital and analog. Spatial lightsources, which use vertical-cavity surface-emittinglasers, can, in some cases, provide functionality thatis similar to that of SLM's, although spatial lightsources are not as well developed.

SLM's are made with a variety of technologies. Byfar the most common are those made from ferroelec-tric liquid crystals. Ferroelectric liquid crystals in-clude the smectic-C (binary or ternary modulationonly), the smectic-A (with gray-scale capability), andthe twisted and supertwisted nematic types. Indeed,most of the papers in this feature describe liquid-crystal SLM's and their applications. Work in thisarea ranges from new materials, improving the perfor-

A. L. Lentine is with AT&T Bell Laboratories, Room 2F229, 263Shuman Boulevard, Naperville, Illinois 60566; J. N. Lee is with theNaval Research Laboratory, Code 5623, Washington, D.C. 20375-5338; S. H. Lee is with the Department of Electrical and ComputerEngineering, University of California, San Diego, La Jolla, Califor-nia 92093-0407; and U. Efron is with Hughes Research Labora-tory, 3011 Malibu Canyon Road, Malibu, California 90265.

Received 24 January 1994.0003-6935/94/142767-01$06.00/0.3 1994 Optical Society of America.

mance of present materials, and increasing the inte-gration of liquid-crystal and Si very-large-scale-integrated (VLSI) circuits. The field of SLM's thatare integrated with electronics (which are known assmart SLM's or, more commonly, smart pixels) is anarea of growing interest in optoelectronic processingand optical interconnections within electronic systems.Besides the work on liquid-crystal-on-silicon VLSIcircuits, there has been significant progress in othersmart-pixel technologies as well.

Two technologies represented in this issue are theintegration of PLZT (lead lanthanum zirconate titan-ate) with Si electronics and GaAs/AlGaAs multiple-quantum-well (MQW) devices with GaAs electronics(field-effect-transistor self-electro-optic-effect devices).Work still continues on improving the performanceand utility of MQW devices, with a significant effortinvolved in providing high-contrast-ratio devices.Progress has also been made on digital mirror de-vices, integrating micromirrors with Si static random-access memories, and the epitaxial lift-off and hybridbump bonding of optical MQW modulators onto Sicircuits, although these are not represented in thisissue. The monolithic integration of MQW modula-tors on Si VLSI circuits remains promising, but stillelusive, to date.

As expected, systems that use liquid-crystal SLM'soutnumber those that use other technologies.Progress is being made in systems that use MQWdevices, as several institutions are now buildingdemonstration systems because this technology ismore readily available than it has been in the past.Further improvements in the technology of many ofthe other SLM's are needed before system demonstra-tions will appear.

The next few years promise to be exciting, asprogress in materials, devices, and systems is ex-pected to continue at a rapid rate.

10 May 1994 / Vol. 33, No. 14 / APPLIED OPTICS 2767