R. Mark Boysel

Integration of deformable mirror devices with optical fibers and waveguides

Deformable Mirror Devices (DMDs) have been under development at Texas Instruments for several years, primarily as spatial light modulators for free-space optical applications such as analog phase modulation and digital projection imaging. A DMD consists of one or more electrostatically deflectable micromechanical aluminum mirror elements, including both micromirrors suspended from thin flexible hinges and membranes. These devices are fabricated using low temperature silicon-compatible semiconductor processing techniques, and thus can be monolithically fabricated over any addressing circuitry. In the last few years DMDs have been integrated into optical fiber switching systems, and efforts are underway to integrate them as routing switches onto optical waveguides. The DMDs used for optical fiber switching are torsion-hinged devices similar to those used for projection imaging. These devices have been integrated with multimode fibers to construct a 4 X 4 multimode optical fiber cross-bar switch with a 19 dB optical (80:1) extinction ratio for all 16 channels. Extinction ratios of 73 dB optical (20 X 106) have been achieved for single point single mode switches. The waveguide switches currently under development are deformable membranes which are monolithically fabricated on silicon wafers with phosphosilicate glass (PSG) waveguide directional couplers to form optical time delay path selection switches. In this paper we describe the fabrication of deformable mirrors, their integration with optical fibers and waveguides, and the resulting system performance.

Deformable Mirror Light Modulators For Image Processing

The operational characteristics of deformable mirror device (DMD) spatial light modulators for image processing applications are presented. The two DMD pixel structures of primary interest are the torsion hinged pixel for amplitude modulation and the flexure hinged or piston element pixel for phase modulation. The optical response characteristics of these structures are described. Experimental results detailing the performance of the pixel structures and addressing architectures are presented and are compared with the analytical results. Special emphasis is placed on the specification, from the experimental data, of the basic device performance parameters of the different modulator types. These parameters include modulation range (contrast ratio and phase modulation depth), individual pixel response time, and full array address time. The performance characteristics are listed for comparison with those of other light modulators (LCLV, LCTV, and MOSLM) for applications in the input plane and Fourier plane of a conventional coherent optical image processing system. The strengths and weaknesses of the existing DMD modulators are assessed and the potential for performance improvements is outlined.

A 128 X 128 frame-addressed deformable mirror spatial light modulator

We describe the design, fabrication, and performance of the frame-addressed spatial light modulator (FASLM), a frame-updated 128 x 128 deformable mirror device (DMD) spatial light modulator(SLM). This new DMD consists of a 128 x 128 array of mirror elements addressed by an underlying virtual phase CCD array. Each mirror element consists of four cantilever beam mirrors attached to a central pillar, allowing contiguous placement of the elements. The FASLM operates at higher speed (up to 4-kHz frame rate with 100% pixel addressing) and with a higher optical duty cycle (96%) than previous DMD SLMs.

Characterization of a micromechanical spatial light modulator

The optical‐beam‐control dynamics of torsion‐beam deformable‐mirror‐device spatial light modulators has been characterized to determine properties important to their operation. The responses of individual picture elements to steady‐state, transient, and harmonic excitation were measured using optical‐beam‐deflection sensors. The steady‐state angular deflection is characterized by a stable, reversible regime for applied voltages less than a critical value, Vc (∼16 VDC), an unstable transition to stable maximal deflection at Vc, and hysteresis as the applied voltage is reduced to zero. Representative devices with 50 μm×50 μm pixels exhibit full‐deflection rise times of tens of microseconds and small‐deflection resonant frequencies of the order of 10 kHz.

Optical time delay network for phased arrays

An optical time delay network (OTDN) for time delay steering of arrays of various sizes is being developed which features passive waveguides and micromechanical switches monolithically fabricated on silicon. Separately packaged directly modulated lasers and optical envelope detectors perform the RF and optical conversions. Recent developments in the areas of phosphosilicate glass (PSG) waveguides and micromechanical switches are presented. Broadband reactive matching circuits for commercially available directly modulated lasers and optical detectors are described which demonstrate VSWRs of less than 1.5:1 and improvement of 16 dB in overall RF/optical/RF conversion efficiency for an octave bandwidth. Finally, plans for demonstrating the operation of the time delay network in a 4 by 16 element phased array with an operating band of 2 to 4 GHz are presented.

Folded spectrum analysis using a frame-addressed deformable mirror device

A folded optical rf spectrum analyzer is described which is built around the 128 x 128 Frame- Addressed Spatial Light Modulator (FASLM). The input waveform is sampled at 32 MHz and displayed on the FASLM at a 2 KHz frame rate. A time-bandwidth product of approximately 8000 is achieved. A brief description of the device operation and optical performance is included.

Deformable mirror device based 4x4 fiber optic crossbar switch

The deformable mirror device (DMD) is a spatial light modulator . that offers both amplitude and phase modulation. The DMD is built on a silicon substrate and consists of small mirror elements (pixels) suspended above addressing electrodes via one or more small hinge. The pixels are deflected by electrostatic attraction created by applying a potential difference between the mirror element and addressing electrode.1 Both area array and linear DMDs have been built and been used in several areas.2-4