Single longitudinal mode all-optical microwave oscillator based on parity–time symmetric torsional radial acoustic modes

With the wide application of all-optical microwave oscillators in future communication, radar detection, and other fields, the combination of the parity-time (PT) symmetry with the forward higher order mode is expected to realize a higher-performance all-optical microwave oscillator with a narrow linewidth single longitudinal mode (SLM), which can output a purer microwave photon signal.An SLM all-optical microwave oscillator based on torsional radial acoustic mode PT symmetry is proposed and verified.The design includes a single-mode fiber main ring that realizes TR 2,7 mode locking and a Sagnac loop that ensures PT-symmetric SLM output.The experiment shows that, upon the breaking of PT symmetry, a side mode suppression ratio of 52.8 dB, a linewidth of 6.176 Hz, and a phase noise of -115 dBc/Hz at a frequency offset of 10 kHz are achieved.This achievement is expected to promote technological progress in fields such as optical communication, fiber optic sensing, and radar detection.