Optical gain control of a GaAs MMIC transmit-receive module compatible with optical spatial filters

A description is given of the optical gain control of a microwave amplifier which could be used in antenna beamforming applications. The challenge in developing the experimental circuit was to devise a means for the optical control of the microwave subsystem consistent with microwave monolithic integrated circuits (MMIC) technology, and compatible with optical processing and computing techniques. The experimental circuit consists of four main sections on LED with pigtail, a light-sensitive FET, a DC amplifier, and a distributed microwave amplifier. The electronic circuits are standard GaAs MMIC components which can be integrated into a single chip. A 250- mu W optical signal provided by the LED gave rise to 15 HB of gain control. The approach has several important attributes such as: it is independent of the operating frequency of the microwave components and can be extended to the millimeter range. It is compatible with GaAs MMIC fabrication processes; it can be extended to phase control circuits for pulsed applications; it has a fast response and is cost-effective because it uses a low-cost, low power LED and standard MMIC; and it is totally compatible with parallel optical processing such as spatial filters.<>