Continuously tunable phase controller for microwave oscillators by using optoelectronic phase-lock loop

We have successfully developed a laser-diode-based optoelectronic phase-locked loop (OEPLL) for phase-tracking free-running microwave signals beyond 20 GHz. In this work, we modify the OEPLL system to demonstrate a broadband, frequency-independent, and continuously tunable microwave phase shifter. The key parameters of the OEPLL-based phase shifter (OEPLL-PS) such as the maximum phase-shifting range, tuning accuracy, linearity, insertion loss, long-term phase stability as well as switching response were investigated. We also demonstrate the precise control of relative phase change between two phase-locked microwave oscillators by using the OEPLL-PS