Monolithically integrated optical differential amplifiers for applications in smart pixel arrays

The design, fabrication, and characterization of monolithically integrated single- and dual-stage cascadable optical differential amplifiers (ODAs) are presented. The circuits are realized with photodiodes (PDs), metal-semiconductor field-effect transistors (MESFETs) and light-emitting diodes (LEDs) in the GaAs-AlGaAs system. They are fabricated with a process which uses trench technology for the separation of the 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 bandwidth from 2 to 12 MHz., The output power is 30 /spl mu/W, and the measured contrast ratio is approximately 1000. Switching is possible over an input power range of more than 5 decades, with a lower limit of 15 pW. We measure an optical open-loop gain of 2/spl middot/10/sup 6/ and a power dissipation of 15-20 mW.