Investigation on Tunable Modulation Index in the Polarization-Modulator-Based Optoelectronic Oscillator

Tunable characteristic of the modulation index in the polarization-modulator (PolM)-based optoelectronic oscillator (OEO) is investigated and demonstrated experimentally. The PolM-based OEO is theoretically analyzed and a simplified analytical expression to reveal the variation of the modulation index is derived. Numerical results indicate that a tunable modulation index from 0 to 2.405 can be achieved for stable oscillation inside the OEO. In addition, a proof-of-concept experiment is carried out and the measured modulation indexes exactly follow the simplified analytical expression. Such a tunable modulation index enriches the applications of the OEO in the field of microwave/optical signal generation and processing, such as the generation of the return-to-zero (RZ) and the carrier-suppressed RZ optical pulse trains in our experiment.