Microwave signal generation from a parity-time-symmetric optoelectronic oscillator with optical injection locking

A parity-time (PT) symmetric optoelectronic oscillator (OEO) with optical injection locking is proposed and experimentally demonstrated to generate single-mode microwave signals. A distributed feedback laser is injection locked, which functions as a frequency multiplier for the coarse mode selection of the PT-symmetric OEO. The PT symmetry in the OEO is implemented by using a polarization-dependent Sagnac loop to form two identical loops for coupling. By tuning the two polarization controllers in the Sagnac loop, the gain/loss and coupling coefficient of the two loops can be controlled, and single-mode oscillation in the OEO could be achieved at the broken PT-symmetry condition. Microwave signal generation at the frequency of 6.427 GHz is obtained from the proposed OEO. The phase noise is about -105 dBc/Hz at an offset frequency of 10 kHz.