Simultaneous optical and electrical mixing in a single fast photodiode for the demodulation of weak mm-wave signals

Abstract

In this work we demonstrate that the normal photomixing scheme, i.e. one built around a two-mode laser (or a mode-locked laser) as the source, and a fast photodiode acting as the optical mixer of the two modes, can be used also to perform the electrical demodulation of an incoming weak signal at the same frequency. In particular, we consider a mode spacing c/2L in the range of mm-waves, typically 60GHz for a practical WLAN communication system. With optical powers in the range of mW’s (or 0dBm) for each mode, and an optical power amplifier boosting powers up to 8-10 dBm, the two modes can be photomixed on a high frequency photodiode and obtain an electrical signal with power of about 0dBm at the carrier frequency of 60GHz. Now, if an electrical signal, with a frequency slightly different from 60GHz, is applied to the photodiode output, electrical mixing with the photomixing carrier takes place and demodulation of the weak signal is performed, down to the baseband.