Wideband Tunable Microwave Signal Generation With low Spurs in Self-Feedback Injection-Locked Optoelectronic Oscillator

A delay-matched self-feedback injection-locked optoelectronic oscillator (SIL-OEO) is proposed to realize wideband tunable microwave signal generation, which are featured with ultra-low phase noise and low spurs. In the OEO cavity, two cascaded electro-optic Mach-Zehnder modulators (MZMs) are used to form two loops with an identical time delay. Thereinto, one loop serves as the oscillation path, and the other acts as the self-feedback injection locking path. Benefited from the delay-matched self-feedback injection locking effect, the gain of the dominant oscillation mode far exceeds that of the unwanted side modes, largely suppressing the spurs in the generated microwave signal. In addition, the usage of self-feedback injection locking avoids the requirement of an external precisely-tunable microwave source and the phase noise degradation due to external injection in the high-frequency range, which facilitates freely wideband frequency tuning by using a tunable bandpass filter. In a proof-of-concept experiment, tunable microwave signals from 2.99931 GHz to 20.0013 GHz are generated. The side-mode suppression ratios (SMSRs) reach beyond 65.3 dB within the whole frequency tuning range, and the phase noise is superior over -120 dBc/Hz@1 kHz and -142 dBc/Hz@10 kHz. Moreover, the power fluctuation during frequency tuning is smaller than 3.2 dB.