High Q Brillouin fiber lasers with Hz level linewidths

We demonstrate a tunable dual polarization Brillouin fiber laser with a Q-factor of 2.4 billion with an intrinsic relative linewidth of approximately 1 Hz, establishing the potential of such systems for fiber based compact frequency references for precision metrology applications. Mode hops are avoided by implementation of self-injection locking, which also obviates the need for electronic locking of the pump laser frequency to the 100 m length fiber laser cavity. The mode hop free tuning range of an individual laser can be as large a 300 MHz with an integrated linewidth of 20 Hz.