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 formtwo 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 PTsymmetry 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.