Microwave applications of a laser-diode-based photoconductive harmonic mixer

Two applications of a compact laser-diode-based photoconductive harmonic mixer were demonstrated. One of the unique features of this approach is that the photoconductor functions not only as an optical receiver but also as an electronic harmonic mixer. In the first experiment, two 10-GHz microwave oscillators were phase-locked together. The relative phase between the phase-locked signals can be continuously tuned over a whole cycle by an optical delay line. Phase-locking of the two oscillators with a frequency offset of 10 kHz was also demonstrated. In another set of experiments, the waveform of an optoelectronically phase-locked 12.01-GHz microwave signal and the waveform and spectrum of picosecond electrical pulses generated by a step recovery diode were measured by this technique. In comparison with previous electrooptical sampling or photoconductive sampling experiments using mainframe lasers, the principal advantages of the present system are compactness, a large number of sampling points, and the ability to display the waveform and spectrum on any convenient time scale or frequency range.<>