MONOLITHICALLY INTEGRATED OPTICAL DIFFERENTIAL-AMPLIFIERS FOR APPLICATIONS IN SMART PIXEL ARRAYS

The design, fabrication, and characterization of monolithically integr ated single- and dual-stage cascadable optical differential amplifiers (ODA's) are presented, The circuits are realized with photodiodes (PD 's), metal-semiconductor field-effect transistors (MESFET's) and light -emitting diodes (LED's) in the GaAs-AlGaAs system. They are fabricate d with a process which uses trench technology for the separation of th e devices. The single-stage switching energy of 2.5 pJ is reduced to 0 .4 pJ by the addition of a second stage, thereby increasing the bandwi dth from 2 to 12 MHz. The output power is 30 mu W, and the measured co ntrast ratio is approximately 1000, Switching is possible over an inpu t power range of more than 5 decades, with a lower limit of 15 pW. We measure an optical open-loop gain of 2.10(6) and a power dissipation o f 15-20 mW.