Authi A. Narayanan

High-precision detector-switched monolithic GaAs time-delay network for the optical control of phased arrays

We report the fabrication and characterization of the two-bit monolithic optical time-delay network on GaAs. GaAs rib-waveguides and InGaAs waveguide-coupled MSM detectors serve respectively as delay-lines and optoelectronic switches on the photonic integrated circuit. From the linear RF differential phase observed between 1 and 11 GHz, we estimate that the measured time-delays are within 4 psec of their designed values.<<ETX>>

GaAs and silica-based integrated optical time-shift network for phased arrays

We compare the GaAs and Silica-based approaches for realizing integrated time-shift networks. The performance of a fully functional 2-cm X 2-cm monolithic GaAs circuit is reviewed in detail. In addition, we describe the design of an optoelectronic- switched network that uses Silica-based star-couplers and waveguide arrays.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High-efficiency waveguide-coupled lambda =1.3 mu m In/sub x/Ga/sub 1-x/As/GaAs MSM detector exhibiting large extinction ratios at L and X band

The design and fabrication of a 1.3- mu m waveguide-coupled strained-layer In/sub x/Ga/sub 1-x/As/GaAs MSM detector with an optimized active layer thickness is reported. For 100- mu m-long devices, a responsivity of 0.58 mA/mW is observed. Using the detector as an optoelectronic switch, on/off ratios better than 40 dB were achieved at L and X band.<<ETX>>

GaAs optical time-shift network for steering a dual-band microwave phased-array antenna

A monolithic optical time-shift network is described which is designed to steer a dual-band microwave phased array antenna at 2 and 10 GHz. The advantages of using cascade type network architectures to achieve the desired resolution are demonstrated. The implementation of different delay times in this optical time-shifter via bias control of detectors integrated monolithically on a GaAs wafer is described.

Conformal pixellated MQW modulator structure for modulating retroreflector applications

We have developed a conformal optical modulator structure comprising pixellated InGaAs-InAlAs multiple-quantum-well (MQW) electroabsorption modulators embedded in a polymer membrane for operation in the 1550-nm optical region. The MQW modulators retain their electrical and optical characteristics after the polymer embedding process, with leakage currents of less than 50 nA and modulation contrast ratios of 2 : 1. The radio frequency response of these modulators was shown to be dependent on the pixel size, with a 3-dB modulation frequency of over 200 MHz for a 225/spl times/125 /spl mu/m/sup 2/ pixel. The conformal MQW modulator structure developed here can be used in applications requiring placement on a curved surface, such as in cats eye modulating retroreflectors.

Protective broadband window coatings

Optical windows employed in current and future airborne and ground based optical sensor systems are required to provide long service life under extreme environmental conditions including blowing sand and high speed rain. State of the art sensor systems are employing common aperture windows which must provide optical bandpasses from the TV to the LWIR. Operation Desert Storm experience indicates that current optical coatings provide limited environmental protection which adversely affects window life cycle cost. Most of these production coatings also have limited optical bandpasses (LWIR, MWIR, or TV-NIR). A family of optical coatings has been developed which provide a significant increase in rain and sand impact protection to current optical window materials. These coatings can also be tailored to provide either narrow optical bandwidth (e.g., LWIR) or broadband transmittance (TV- LWIR). They have been applied to a number of standard optical window materials. These coating have successfully completed airborne rain and sand abrasion test with minimal impact on optical window performance. Test results are presented. Low cost service life is anticipated as well as the ability to operate windows in even more taxing environments than currently feasible.

Wideband impedance-matched integrated optoelectronic transmitter

ABSTRACT A GaAs/GaAlAsintegrated optoelectronic transmitterhas been developed for wideband operation at 1 to4 GHz. This transmittercombines a GaAS/GaA1AS single-quantum-well (SQW) ridge-waveguide laserwith a GaAs MESFET driver circuit The single-stage driver circuit has an rfgain of9 dB and is impedance matched to both the low resistance laserload and the 50 fl microwaveinput by using reactive MMIC components. This design results in a nearly flat frequency response in the band of interest Acombination of both laser and MMIC fabrication processes has been used to realize the transmitter in the vertically integratedMOVPE-grown material. 1. INTRODUCTION Monolithically integratedoptoelectronic transmittershavedemonstratedvery high speedoperauonandcanbeusedin microwave-modulatedopticallinks orhigh-speeddigital interconnects. Small-signal analog modulation frequencies of3 to6GHz and digitalmodulation rates as high as 10 Gb/s have been reported.15 By combining these transmitters with integrated receivers and optical

GaAs/GaAlAs integrated optoelectronic transmitter for microwave applications

A monolithically integrated optoelectronic transmitter is being developed for wideband microwave-modulated links. The transmitter is designed to operate at signal frequencies of several gigahertz. It combines a GaAs/GaAlAs ridge-waveguide laser with a GaAs MESFET driver circuit. The laser has one of its cavity mirrors formed by dry etching so that the die size of the transmitter is not limited to the laser cavity length. The single-stage driver circuit is matched to both the low impedance of the laser and the 50 (Omega) microwave input by the inclusion of reactive components. A single-growth, vertically integrated material structure is used. Potential step-coverage problems that might result from this vertical integration are avoided by the use of air-bridge connections. The submicrometer FET gates are formed by direct-write electron-beam lithography.