Active mode-locking optoelectronic oscillator based on a high-Q microring resonator

An active mode-locking optoelectronic oscillator (AML-OEO) utilizing a microring resonator (MRR)-based microwave photonic filter (MPF) is proposed. The active mode locking is achieved by inserting a Mach-Zehnder modulator (MZM) into a conventional OEO loop and varying the frequency of the signal apply to the MZM. Experimental results show that harmonic mode-locking at fundamental, second-order, fifth-order, and tenth-order produces microwave frequency combs (MFCs) with repetition frequencies of 4.4856 MHz, 8.9712 MHz, 22.428 MHz, and 44.856 MHz, respectively. Compared with the free-running OEO, the phase noise of MFCs is the same for different orders, all around -85 dBc/Hz@10 kHz, but the supermode noise rejection ratio is improved.