A Frequency-Tunable Parity-Time Symmetric Optoelectronic Oscillator With Two Coupled Loops Having a Rational Loop Length Ratio

A frequency-tunable Parity-Time (PT) symmetric optoelectronic oscillator (OEO) with two coupled optoelectronic loops having a rational loop length ratio is proposed and experimentally demonstrated. Compared with a PT-symmetric OEO with two coupled loops having an identical loop length, the proposed OEO has two loops with different loop lengths, making it have better mode selection capability thanks to the Vernier effect, leading to stable single-mode oscillation with increased sidemode suppression ratio (SMSR). The proposed OEO is studied theoretically and evaluated experimentally. The experimental results show that stable frequency-tunable oscillation from 2 to 12 GHz with an SMSR of 40.7 dB is achieved. The phase noise is measured to be -114 dBc/Hz at an offset frequency of 10 kHz. Compared with a dual-loop OEO utilizing solely the Vernier effect that exhibits an SMSR of 36.8 dB, the SMSR of the proposed OEO is increased by 3.9 dB. The stability of the proposed OEO is also improved.