A tunable and stabilized single-frequency fiber ring laser based on hybrid amplifier and shorter length EDF with unpumped status

A novel fiber ring laser technique, which covers both C- and L-bands, with the function of wavelength tunability and single-longitudinal-mode oscillation, is proposed and demonstrated experimentally. We propose a two-stage hybrid amplifier, which consists of a semiconductor optical amplifier (SOA) and an erbium-doped fiber amplifier (EDFA) with cascade configuration, for the gain profile to achieve C- to L-band (1540 to 1610 nm). A saturated-absorber-based autotracking filter, which composes of an unpumped erbium-doped fiber (EDF) and an optical reflected mirror (ORM), is employed to provide fine mode restriction and guarantee the single-frequency operation. The unpumped EDF must use shorter length to retrieve the stabilized single-frequency operation while the EDF length is between 0.5 to 1 in long. The effectively operation range is from 1542 to 1618 nm. The maximal output power of 5.7 dBm is retrieved at near 1577 nm, and the output power will drop to 3.7 and -0.32 dBm at 1604 and 1616 rim, respectively. The SMSR can be up to 53.2 dB/0.05 nm at around 1577 nm. The performance of output power of > 2.1 dBm, power stability of <= 0.02 dB, wavelength variation of < 0.01 nm and side-mode suppression ratio (SMSR) of > 31 dB/0.05 nm has been demonstrated for this single-frequency fiber laser over the wavelength range of 1550 to 1608 nm. The linewidth (RF) spectrum of the proposed structure has also been studied.