Optical gain control of GaAs microwave monolithic integrated circuit distributed amplifier

Claim 1

An optical gain control circuit for controlling the gain of a GaAs MMIC distributed amplifier comprising a GaAs MMIC distributed amplifier having a dc bias control for controlling the gain of the amplifier; a light source for emitting light at a wavelength in the region of 0.5 micrometers to 1 micrometer; control means coupled to said light source for controlling the intensity of the light emitted from said source; a fixed resistance; a GaAs multi-finger FET having parallel connected sources, parallel connected drains and parallel connected gate fingers; circuit means for connecting the sources and drains of said FET in series circuit with said fixed resistance across a source of positive dc voltage; gate biasing means coupled to the gates of said FET for biasing said FET to a point near pinch-off to maximize the light sensitivity of the FET; dc amplifier means having an input coupled to the circuit junction of said fixed resistance and said FET and an output coupled to said dc bias control of said GaAs MMIC distributed amplifier; and means optically coupled to said light source and said FET for focussing light from said light source on the surface of said FET between the sources and the drains of the FET and covering substantially all of the gate fingers of the FET, whereby changes in the intensity of light from said light source change the voltage drop across said FET and the input applied to said dc amplifier means to thereby change the gain of said MMIC distributed amplifier.