Detection and mixing of two modulated optical signals using only a single GaAs FET (experimental study)

GaAs FET´s are widely used in system such LNA, PA, mixers, frequency multipliers, oscillators and attenuators. Recent works have shown the usefulness of these transistors in the optoelectronics field, as photodetectors or optoelectric mixers. In this paper an experimental study explores the idea of unifying the detection and mixing of two optical modulated signals at different wavelengths, using a single GaAs FET. The FET is biased at fixed V_GS and V_DS and loaded to 50 Omega, while two optical modulated signals of different wavelength and frequencies are illuminating the gate of the FET. The results show that the FET can detect both signals and by means of the inherent nonlinearity in the channel of the FET, the sum and difference of both frequencies appear (up and down conversion). Moreover, this type of architecture demonstrates low distortion in contrast to its counterpart (electric and optoelectric mixers) and also, to obtain the same power level for the up and down conversion frequencies, the power level required for the RF and LO signals are much lower than the case of electric and optoelectric mixers. To our knowledge this is the first time that a single FET is used for detecting and mixing two optical modulated signals at the same time