Tunable single-mode microwave signal generation utilizing an all-optical coupled microwave oscillator

A tunable all-optical coupled microwave oscillator is proposed and experimentally demonstrated. This system has no any electrical microwave devices as well as photoelectric conversion and electro-optic modulation. In this scheme, a fiber ring laser not only provides a set of frequency references but also acts as an active optical resonator. The oscillation frequency selection is carried out by cavity modes transfer and injection locking process. Due to the mode pulling effect, a self-adapting oscillation frequency locking is achieved. Through the microwave envelope detection and feedback modulation in a semiconductor optical amplifier (SOA), a microwave signal can be generated by a pure optical oscillation. In the experiment, good quality and high stability single-mode microwave signals are obtained, whose frequencies can be tuned from 6.93 GHz to 25.54 GHz by simply adjusting the wavelength of the master laser. Under different operation frequencies, the measured single-sideband phase noises are approximately -95 dBc/Hz at a 10-kHz offset from the carriers.