Photonic generation of high-performance microwave frequency combs using an optically injected semiconductor laser...

An approach to generating microwave frequency combs (MFCs) with superior performance is proposed and experimentally demonstrated based on an optically injected semiconductor laser (OISL). The OISL operates at the period-one (P1) oscillation state under proper injection conditions. A sinusoidal voltage signal is used to modulate the P1 state for the initial MFC generation, and then two optoelectronic feedback loops are introduced to enhance the performance of the MFC: a short-delay feedback loop is firstly applied to improve comb contrast based on Fourier domain mode locking (FDML), and a long-delay feedback loop is added to reduce the comb linewidth based on the self-injection-locking technique. In the proof-of-concept experiment, a K-band MFC (18-26 GHz) with a line spacing of 8.45 MHz is obtained, where a comb linewidth of approximately 500 Hz and a comb contrast over 45 dB are simultaneously achieved. Additionally, each comb component exhibits superior performance in terms of phase noise, all below -90dBc/Hz at 10 kHz offset, demonstrating an excellent coherence among these combs.