Injection-locked tunable integrated optoelectronic oscillator

Generating high-quality microwave signals using tunable integrated optoelectronic oscillators (OEOs) remains challenging due to the high losses and instabilities inherent to chip-based platforms. Here, we present an injection-locked tunable integrated OEO on a thin-film lithium niobate platform that mitigates these limitations. The proposed system generated a continuous frequency-tunable radio frequency signal from 7.5 to 22.5 GHz. At an injection power of -5 dBm, an average side-mode suppression ratio (SMSR) of 75 dB was observed, which, to the best of our knowledge, is the highest value reported for integrated tunable OEOs without long external fiber delay lines, along with an average phase noise of -105 dBc/Hz@10 kHz. When the injection power was increased to 5 dBm, the average SMSR was improved to 84 dB, while the average phase noise was reduced to -114 dBc/Hz@10 kHz. Time-domain stability measurements further confirm improved operational stability under injection locking. This approach reduces the reliance on ultra-high-Q filtering and supports integrated microwave generation under realistic fabrication constraints.