Single-loop tunable PT-symmetric optoelectronic oscillator based on a phase modulator.

In this paper, a single-loop tunable parity-time (PT) symmetric optoelectronic oscillator (OEO) based on a dual-mode optical phase modulator (PM) and a microwave photonic filter (MPF) has been proposed, analyzed, and designed. By adjusting the polarization angle between the input linearly polarized light and the axis of the PM, the two-mode splitting ratio of the PM can be controlled, which results in a PT-symmetric structure based on a single physical loop. By adjusting the pump light wavelength, the center frequency of the stimulated Brillouin scattering (SBS)-based MPF can be tuned, which enables a fine tunable output frequency. The results reveal that, by adjusting the pump light wavelength with a step size of 0.0001 nm, a frequency tuning accuracy of 12.5 MHz can be obtained. Simultaneously, the OEO output frequency can be tuned from 0.9 to 22 GHz, while the side-mode suppress ratio (SMSR) is 53 dB, and the phase noise is -133.8 / at a frequency offset of 10 kHz.