Synchronization of electrical and optical signals by using an optoelectronic timing discriminator in a phase-lock loop

A GaAs:Cr photoconductive switch is employed as an optoelectronic timing discriminator or phase detector in the phase lock loop. Timing information is derived from the temporally sloped output of the switch, which is the cross-correlation function of the electrical signal and the photoconductive response induced by the laser pulse train. Optoelectronic synchronization of microwave signals up to 12 GHz in a laser-diode-based system has been demonstrated. The long-term relative timing jitter between the electrical and optical signals is estimated from the error signal in the PLL to be less than 500 fs. This technique can also be used to synchronize lasers.<>