Novel smart pixels composed of a photoconductive switch and a VCSEL

We report on a new kind of active smart pixel. It consists of a special photoconductive switch and a VCSEL. Due to its high gain the switch provides sufficiently high currents for directly operating the laser with very low switching power. Fan-out values of 55 dB for quasi-d.c. operation at an optical output power level of 0.5 mW have been demonstrated for our nonoptimized hybrid prototype smart pixel. The optical switching energy was 1.2 pJ. The measured switching contrast was 35 dB. The observed 3 dB bandwidth of 42 MHz was limited by the high parasitic capacitance of the contact pads of the VCSEL (which was not designed for high frequency applications). We expect that a speed up to 1 Gbit/s with a fan-out >4 can be achieved. Our new concept is simple and appears particularly suitable for monolithically integrated 2×2 smart pixel arrays