Ultra-narrow linewidth Brillouin-erbium fiber laser pumped by distributed feedback fiber laser

An ultra-narrow linewidth fiber laser in a Brillouin ring cavity structure pumped with a distributed feedback fiber laser is presented. A total cavity length about 10m is constructed to satisfy the single longitudinal mode working condition. As a part of the ring cavity, a 3m-long Erbium doped fiber pumped with a 980nm laser diode provides an additional linear gain for intra-cavity Brillouin laser. After an intra-cavity polarization control, a single longitudinal mode Brillouin laser with an unique polarization is achieved and its linewidth is measured and deduced to be narrower than 100Hz. The threshold for single longitudinal mode operation is about 20mW distributed feedback fiber laser and 50mW 980nm pump. A maximum laser output power of over 15mW can be obtained for a maximum 980nm pump power of 250mW.