Polarization state rotation filter for optical generation of continuously tunable millimeter-wave signal employing an external intensity modulator

A method to generate a continuously tunable millimeter-wave signal employing an optical external intensity modulator and polarization state rotation filter (PSRF) is proposed. The technique is based on the optical heterodyne, the Mach–Zehnder modulator (MZM) is biased to suppress odd-order sidebands, and the polarization-dependent PSRF is used to filter the optical carrier. A concept-proof experiment system is built to demonstrate the generation of microwave signal by beating the generated two second-order optical components. The results show that a high purity tunable microwave signal with very narrow linewidth at four times the frequency of microwave drive signal can be obtained. Moreover, the generated signal does not suffer obvious phase-noise degradation after transmission through a 25-km SSMF link. The operation principle of PSRF and the effect of its performance on the generated electrical signal are also analyzed. The proposed technique based on PSRF is very easy to implement, flexible and cost-effective to generate continuously tunable millimeter-wave signals.