Injection Locking-Enabled Supermode Noise Suppression for Harmonically Mode-Locked Optoelectronic Oscillator

We propose and experimentally demonstrate an injection locking-enabled supermode noise suppression scheme for the harmonically mode-locked optoelectronic oscillators (OEOs). When a single-tone local oscillator (LO) signal with its frequency equal to that of an arbitrary oscillation mode arising in the OEO cavity is injected, the supermode noise under the harmonic mode locking is effectively suppressed, leading to the enhanced stability and coherence among the generated microwave pulses. In particular, we identify that the power of the injected LO signal should be properly set to ensure a negligible impact on the pulsewidth. Both numerical simulation and experimental verification are presented to justify the feasibility of our proposed method. In the experiment, when a 15-GHz LO signal with a power of −40 dBm is injected into the OEO cavity, the supermode noise suppression ratio achieves 52.7 dB, 55.4 dB, and 53.3 dB, respectively, under conditions of 2nd-, 12th-, and 50th-order harmonic mode locking. Meanwhile, the pulsewidth of the generated microwave pulse train is independent to the injection locking effect.