Wideband finely tunable, ultralow-phase noise microwave generation in a Brillouin cavity.

A novel, to the best of our knowledge, approach to generate frequency-tunable microwave sources with low-phase-noise based on a Brillouin laser frequency comb is proposed and experimentally demonstrated. The Brillouin laser frequency comb is generated by combining stimulated Brillouin scattering, frequency shifting optical injection locking, modulation sideband optical injection locking (MSOIL), and four-wave mixing effects. By beating the generated comb lines, the microwave is generated with an extremely low-level phase noise of -120 dBc/Hz at a 10-kHz offset. The frequency of the microwave signal can be finely tuned in steps of a Brillouin cavity mode spacing (i.e., 2 MHz) and coarsely adjusted to integer times the applied RF signal frequency in the MSOIL unit. Remarkably, the phase noise of the microwave source can be kept at almost the same low level during the whole tuning process over the frequency range of 30-75 GHz. The proposed tunable low-phase-noise microwave generation approach has great potential applications in communications, radars, and metrology.