Optical microwave generation with an ultra-stable Fabry–Perot cavity in a laser diode self-injection loop

The optical microwave generation scheme with an ultra-stable Fabry–Perot cavity (USC) in a self-injection loop of laser diode (LD) is proposed and experimentally demonstrated for the first time, to the best of our knowledge, in this Letter. Using an USC as the mode selector, an injection light is obtained with coherent and equidistant comb-like modes, which are separated by integer multiples of the free spectral range (FSR) of the USC in frequency domain. After injecting back to the LD, the lasing modes are referenced to these comb-like modes, and the microwaves with frequencies of integer multiples of the USC FSR are obtained from the beating signal of detection photodiode. For the microwaves at frequencies of one FSR and two FSRs, the signal-to-noise ratios are better than 60 dB, and the 3 dB linewidths are below 16 Hz. The phase noises and the frequency stability of the generated microwave are also investigated experimentally.