Novel Technioue For Optoelectronic Phase Locking Of Microwave Signals Using A Laser-diode-based Electro-optic Harmonic Mixer

For measurement of cw microwave signals in discrete devices or MMIC's by either photoconductive or electro-optic sampling techniques, it is important to maintain phase coherence or time synchronization between the microwave signal and optical pulse train. To accomplish this, we have recently demonstrated compact laser-diode-based optoelectronic phase lock loops (OEPLL).[1,2] The key element of the OEPLL's is a laser-diode-activated GaAs:Cr photoconductive switch or a reflection-mode electro-optic sampler which functions as an optoelectronic harmonic mixer (OEHM) for intermixing microwave signal from the target VCO and the optical pulse train. In practice, the microwave or millimeter wave signal to be probed on the MMIC might not be from a VCO. To solve this problem, we show in this paper that synchronization can also be achieved by using the microwave signal to be probed as the clock to phase lock the optical pulse train.