Sensitivity measurement and analysis of an ErAs:GaAs coherent photomixing transceiver

A frequency domain transceiver is implemented with a pair of 780-nm-based ErAs:GaAs photomixers, one serving as the transmitter and the other as the receiver. The transceiver is all solid state, operated at room temperature, and has a fast response. The receiver detects the amplitude of the incoming electric field coherently and the sensitivity is limited by 1∕f mechanisms which are excited by a photovoltage that is always present in the receiver photomixer. This letter reports the first measurements and calculations of the signal-to-noise (S/N) ratio in the transceiver. Measurement yields a differential terahertz power-to-current sensitivity of 4mA∕W and noise equivalent power of 0.1pW∕Hz. The maximum S/N ratio was 58dB∕rtHz around 86GHz which is 17dB lower than our theoretical estimate. The discrepancy is attributed to radiative coupling losses and nonoptimal laser spatial overlap.