A Microwave Photonic Oscillator Based on Self-Injection Locking to a Fabry-Perot Cavity

We demonstrate an efficient simultaneous self-injection locking of two semiconductor lasers to high-order modes of a stand-alone monolithic Fabry-Perot cavity. The lasers are used to generate a low noise microwave signal on a fast photodiode. The overall improvement of the laser spectral purity exceeds 80 dB. The observed single-sideband phase noise of X- to Ka-band signals is at the -110 dBc/Hz level and is limited by the funda- mental thermorefractive noise of the cavity. The demon- strated cavity-laser configuration can be tightly pack- aged and is promising for generation of high frequency RF signals as well as for referencing optical frequency combs.