A photoconductive detector suitable for optical communications systems

This paper describes a photoconductive detector which, through the use of a microwave bias, is capable of demodulating a low-level signal at information bandwidths greater than 1 MHz. The principle of operation is described and the advantages over d.c. biased photoconductors highlighted. The dependence of photocurrent gain on semiconductor properties and limitations on performances are discussed. A system operating at 1 ¿m wavelength using a Gunn oscillator and miniaturized microwave components is described. This detector, which uses germanium as the photoconductor, has a noise equivalent power (n.e.p.) of 5×10¿1 W in a noise bandwidth of 10 MHz and a 10¿90% rise-time of 80 ns. The system has also been operated with silicon and indium arsenide. Finally, a comparison is made between microwave biased photoconductive detectors and avalanche photodiodes.