All-fiber stimulated Brillouin ring laser with submilliwatt pump threshold

An all-fiber ring resonator, constructed from a single strand of single-mode optical fiber and a directional coupler, is shown to have a low threshold for stimulated Brillouin laser action. The 10-m-perimeter fiber ring resonator has a low round-trip loss of under 3.5% and an inherent pump-power enhancement of approximately 30. Lasing threshold for the 4.0-microm-core fiber occurred with a pump power of 0.56 mW at lambda = 6328 A and 1.74 mW at lambda = 5145 A.