Parity-time symmetric optoelectronic oscillator with high side-mode suppression and low phase noise

A novel, to the best of our knowledge, optoelectronic oscillator (OEO) based on parity-time (PT) symmetry is proposed and experimentally demonstrated. In the proposed PT-symmetric OEO, a PT-symmetric structure with a phase modulator and an interleaved optical filter is incorporated to achieve the balance between the loop gain and loss in the OEO cavity, which significantly improves the side-mode suppression ratio (SMSR) of the generated microwave signals. In the experiment, a 10-GHz microwave signal has been successfully generated by the proposed PT-symmetric OEO, the side-mode suppression ratio of the RF output can reach 62.5 dB, and the phase noise can reach -148.88 dBc/Hz at 10-kHz offset via a 4.4-km OEO loop. Furthermore, the significant contrast between the generated 10-GHz signal's SMSR and phase noise is presented by using different fiber lengths. A YIG filter is incorporated into the OEO loop to verify the PT-symmetric effects at various oscillation frequencies. Experiment results indicate that the single-frequency oscillation can be tuned from 8 to 11 GHz with the SMSR beyond 50 dB and phase noise better than -130 dBc/Hz at 10 kHz offset via a 1-km OEO loop.