Measurements of optical-heterodyne conversion in low-temperature-grown GaAs

A low-temperature-grown GaAs interdigitated-electrode photomixer is used to generate coherent power at microwave frequencies. An output power of 200 μW (−7 dBm) is generated by pumping the photomixer with two 70-mW modes of a Ti:Al2O3 laser, separated in frequency by 200 MHz. This represents an optical-to-microwave conversion efficiency of 0.14%, which is within 50% of a prediction based on optical-heterodyne theory. When two lasers are used and the frequency of one is tuned with respect to the other, the output frequency of the photomixer increases smoothly and the output power is nearly constant up to 20 GHz. At higher frequencies the power decays because of parasitic capacitance.