Erbium-doped fiber compound-ring laser with a ring filter

A new all-fiber, diode-pumped laser with a compound-ring structure has been demonstrated. A double-coupler fiber ring filter formed by two in-line low-loss couplers is used as an intracavity mode selection element. It functions as a filter which provides a larger free spectral range for the compound laser cavity and serves as a ready port for the laser output. The fiber laser is pumped at 980 nm with a threshold of 7.9 mW and a slope efficiency of 0.11. The condition for a maximum output power can be obtained by tuning an in-line polarization controller.>