Improving the Quality of Arbitrary Periodic Waveform via Injection-Locking of an Optoelectronic Oscillator

A novel method for improving the quality of arbitrary periodic waveforms is proposed via injection-locking of an optoelectronic oscillator (OEO). A low-quality arbitrary periodic signal with its frequency spectrum discretized by its repetition frequency is injected into the OEO system. When its repetition frequency equals an integral multiple of the free spectral range (FSR) of the oscillation loop, the injection-pulling mechanism triggers mode-locking in the frequency domain. Consequently, each oscillation mode synchronizes with the relative discretized frequency component of the injected periodic signal, and the gain accumulation for each frequency mode is improved through the pulling mechanism of the injection-locking process. In a proof-of-concept experiment, this approach successfully generates linearly frequency-modulated waveforms (LFMWs) with different bandwidths, a three-level frequency hopping (FH) microwave waveform covering an FH range of 400 MHz, and a 100-Mb/s phase-coded microwave waveform, respectively. This utilization of the injection-locking mechanism within a low phase noise OEO significantly enhances the spectral purity of the produced arbitrary periodic microwave waveforms.