Parity-Time Symmetric Optoelectronic Oscillator Based on an Integrated Mode-Locked Laser

Originating from the non-Hermitian quantum mechanics, the parity-time (PT) symmetry has been extensively explored to ensure a stable single-mode oscillation for optoelectronic oscillators (OEOs), while avoiding additional extremely challenging ultrahigh-Q filters. Enabled by the emerging photonics integrated circuit (PIC) technology, we report the tunable PT-symmetric OEO by using an integrated mode-locked laser, as a striking advance to reduce the footprint of OEOs. Stable single-mode oscillating signal at 24.5 GHz has been generated with a phase noise of -108 dBc/Hz @ 10 kHz frequency offset. In particular, a tunable frequency range from 24 to 25 GHz is achieved by manipulating the injection currents into the well-designed on-chip linear laser cavity. This work exhibits a breakthrough in conceptual integrated microwave photonic devices, and also accelerates the real-world applications of fundamental physical theory of PT symmetry to information industry.