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.
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.
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.
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.