ABSTRACT
An optical communications system requires both a source—laser or light-emitting diode (LED)—and a receiver—a photodetector. Historically, photomultiplier tubes and vacuum photodiodes were available as receivers, but smaller, less expensive wide-bandwidth semiconductor devices are now widely used. These gas-filled tube devices are limited in bandwidth to around 10 kHz [1], and in the case of the vacuum photodiode to relatively high minimum detectable optical powers. Choice of a photodetector is governed by the operating wavelengths of the system, the response to these wavelengths, the speed or frequency response requirements, and the dark current or noise performance of the device.
