Frequency locking of an erbium-doped fiber ring laser to an external fiber Fabry–Perot resonator

An all-fiber, single-frequency, erbium-doped ring laser has been frequency locked to a resonance peak of an external fiber Fabry–Perot resonator by the Pound–Drever technique. In addition, feedback to the mode selection filter in the laser resonator eliminates occasional mode hopping completely, resulting in frequency-locked, stable, single-frequency operation of the laser for periods of several hours.