A wideband heterodyne optical phase-locked loop for generation of 3-18 GHz microwave carriers

Experimental results of a wideband heterodyne second-order optical phase-locked loop with 1.5-μm semiconductor lasers are presented. The loop has a bandwidth of 180 MHz, a gain of 181 dBHz, and a propagation delay of only 400 ps. A beat signal of 8 MHz linewidth is phase locked to become a replica of a microwave reference source close to carrier with a noise level of -125 dBc/Hz.

The total phase variance of the locked carrier is 0.04 rad2 and carriers can be generated in a continuous range from 3 to 18 GHz. The loop reliability is excellent with an average time to cycle slip of 1011 s and an acquisition range of 640 MHz