Have you ever felt that the very title, Progress in Optics, conjured an image in your mind? Don’t you see a row of handsomely printed books, bearing the editorial stamp of one of the most brilliant members of the optics community, and chronicling the field of optics since the invention of the laser? If so, you are certain to move the bookend to make room for Volume 16, the latest of this series. It contains seven chapters on widely diverging topics, written by well-known authorities in their fields. These are: 1) Laser Selective Photophysics and Photochemistry by V. S. Letokhov, 2) Recent Advances in Phase Profiles (sic) Generation by J. J. Clair and C. I. Abitbol, 3 ) Computer-Generated Holograms: Techniques and Applications by W.-H. Lee, 4) Speckle Interferometry by A. E. Ennos, 5 ) Deformation  Invariant, Space-Variant Optical  Pattern Recognition by D. Casasent and D. Psaltis, 6) Light Emission from High-Current Surface-Spark Discharges by R. E. Beverly, and 7) Semiclassical Radiation  Theory within a  QuantumMechanical Framework by I. R. Senitzkt. The  breadth of topic  matter  spanned  by  these  chapters makes it impossible, for this reviewer at least, to pass judgement on the comprehensiveness, relevance, and completeness of every chapter. With an editorial board as prominent as that of Progress in Optics, however, it seems hardly likely that such comments should be necessary. It should certainly be possible to take the authority of each author as credible. The only remaining judgment to be  made on these chapters is their readability. In short, what are they like to read? The first sentence of the first chapter greets the eye with an obvious typographical error: “The creation of coherent laser light source, that have tunable radiation, opened the . . . .” Two pages later we find: “When two types of atoms or molecules of different isotopic composition ( A and B ) have even one spectral line that does not overlap with others, it is pos-

Progress in optics

An Interferometric Modulator (IMod) is a microelectromechanical device for modulating light using interference. The colors of these devices may be determined in a spatial fashion, and their inherent color shift may be compensated for using several optical compensation mechanisms. Brightness, addressing, and driving of IMods may be accomplished in a variety of ways with appropriate packaging, and peripheral electronics which can be attached and/or fabricated using one of many techniques. The devices may be used in both embedded and directly perceived applications, the latter providing multiple viewing modes as well as a multitude of product concepts ranging in size from microscopic to architectural in scope.

Interferometric modulation of radiation

An interference modulator (Imod) incorporates anti-reflection coatings and/or micro-fabricated supplemental lighting sources. An efficient drive scheme is provided for matrix addressed arrays of IMods or other micromechanical devices. An improved color scheme provides greater flexibility. Electronic hardware can be field reconfigured to accommodate different display formats and/or application functions. An IMod's electromechanical behavior can be decoupled from its optical behavior. An improved actuation means is provided, some one of which may be hidden from view. An IMod or IMod array is fabricated and used in conjunction with a MEMS switch or switch array. An IMod can be used for optical switching and modulation. Some IMods incorporate 2-D and 3-D photonic structures. A variety of applications for the modulation of light are discussed. A MEMS manufacturing and packaging approach is provided based on a continuous web fed process. IMods can be used as test structures for the evaluation of residual stress in deposited materials.

Photonic mems and structures

A modulator for modulating an incident beam of light, the modulator comprising a plurality of equally spaced-apart elements, each of which includes a light-reflective planar surface. The elements are arranged parallel to each other with their light-reflective surfaces parallel to each other. The modulator includes means for supporting the elements in relation to one another and means for moving particular ones of the elements relative to others so that the moved elements transit between a first configuration wherein the modulator acts to reflect the incident beam of light as a plane mirror, and a second configuration wherein the modulator diffracts the light reflected therefrom. In operation the light-reflective surfaces of the elements remain parallel to each other in both the first and second configurations. The perpendicular spacing between the reflective surfaces of the respective elements is equal to m/4 × the wavelength of the incident beam of light, wherein m equals an even whole number or zero when the elements are in the first configuration and m equals an odd whole number when the elements are in the second configuration.

Method and apparatus for modulating a light beam

A period of rapid growth and change in the display industry has recently given rise to many new display technologies. One such technology, the Digital Micromirror Device/sup TM/ (DMD), developed at Texas Instruments, represents a unique application of microelectromechanical systems to the area of projection displays. In this paper, we describe a representative example of a DMD-based projection display engine, the digital display engine (DDE). The DDE is based on a single-DMD device having array dimensions of 800/spl times/600 elements, illuminated by a metal halide arc lamp through a compact optics train. The engine is designed for portable and fixed conference-room graphics and video display applications, and many design decisions were made to tailor the engine for its intended venue. The design of the projection engine optics and electronics is discussed, along with the basic operation, manufacture, and reliability of the DMD itself.

A MEMS-based projection display

A method for controlling a digital micromirror device resulting in decreased mechanical stress, longer device lifetimes, decreased incidence of spontaneous bit reset, and increased pulse-width modulation accuracy. To reduce the device stress, the bias voltage applied to the mirror may be reduced after the mirror has been latched. To prevent premature mirror changes, the address electrode bias voltage may be reduced after the mirror is driven to the desired position. To ensure that the mirror returns to the neutral position during reset, the mirror bias voltage may be raised from ground potential to approximately halfway between the two addressing voltages during the reset period. To reduce the effects of hinge memory and to ensure that the mirror rotates toward the proper address electrode, the mirror bias voltage may be gradually increased to allow the mirror time to rotate towards the proper address electrode.

Optimized electronic operation of digital micromirror devices

A DMD spatial light modulator (20) having an improved reset waveform (80) that improves the electrostatic control over the DMD mirrors (30) during switching states (T3). An intermediate bias level is provided to the yoke (32) and mirror (30) during the mirror reset cycle (T3) which is sufficient to maintain a voltage differential between the mirror/yoke and the address electrodes (26,28,50,52) to dynamically park the mirror during a same-state transition, but which voltage differential is insufficient to overcome the hinge restoration forces during an opposite-state transition such that the mirror releases toward the neutral position and can be captured in the other state upon reapplication of the bias voltage. The transition bias level is maintained for a sufficient time period (T3) to allow the mirror/yoke to release from the landing pads (82) a sufficient distance toward the neutral position. The operating reliability of the device is improved by preventing incident light during same-state mirror transitions from escaping into the display aperture, without impeding the crossover of the mirror during opposite-state mirror transitions. Greater mirror-to-mirror variations can be tolerated without falling outside the mirror arrays acceptable timing operating parameters.

Multiple bias level reset waveform for enhanced DMD control

Methods are disclosed by which the effects of a defective electromechanical pixel 20 having a beam 30 and a hinge 32,34 are mitigated. These methods may damage the hinge 32,34 or the beam 30 and comprise the step of applying a voltage sufficient to damage the hinge 32,34 or beam 30 of said electromechanical pixel 20 by mechanical overstress, thermal overstress, electrochemical reaction, or thermally induced chemical reaction. Other methods are also disclosed.

Method of repairing defective pixels

A preferred embodiment of the present invention provides a method of addressing a digital micromirror device (DMD) having an array of electromechanical pixels (20) comprising deflectable beams (30) wherein each of the pixels (20) assume one of two or more selected stable states according to a set of selective address voltages. A first step of the preferred method is electromechanically latching, by applying a bias voltage with an AC and a DC component to the array of pixels (20), each of the pixels (20) in one of the selected stable states. A second step is applying a new set of selective address voltages to all the pixels (20) in the array. A third step is electromechanically unlatching, by removing the bias voltage from the array, the pixels (20) from their previously addressed state. A fourth step is allowing the array of pixels (20) to assume a new state in accordance with the new set of selective address voltages. A fifth step is electromechanically latching, by reestablishing the bias voltage with the AC component and the DC component, each of the pixels (20 ). Other devices, systems and methods are also disclosed.

Bistable DMD addressing method

A memory circuit for use with a spatial light modulator having an array of electrically addressable, micro-mechanical, modulating elements, whose address electrodes determine how that element will affect incident light. The memory circuit has at least one static memory cell in communication with the address electrodes of each modulating element. Each memory cell receives data for determining its micro-mechanical movement via a bit-line down each column of memory cells. A row select signal determines whether the data will be written to that row. A two-level voltage line supplies power to each memory cell, with one level being used for writing to the cell and another level being used for operating the modulating element.

Richard O. Gale

Papers

Optimized electronic operation of digital micromirror devices

Multiple bias level reset waveform for enhanced DMD control

Method of repairing defective pixels

Bistable DMD addressing method

Memory circuit for spatial light modulator