Tunable single-frequency fiber laser based on the spectral narrowing effect in a nonlinear semiconductor optical amplifier.

A wavelength-tunable single-frequency fiber laser based on the spectral narrowing effect in a nonlinear semiconductor optical amplifier (NL-SOA) is proposed and experimentally demonstrated. The single-frequency operation is achieved based on the spectral narrowing effect resulted from the inverse four-wave mixing in a NL-SOA. By incorporating the NL-SOA in the fiber laser cavity, single-frequency lasing is achieved. The lasing frequency can be tuned by tuning the center wavelength of a tunable filter (TF) incorporated in the laser cavity. The proposed wavelength-tunable single-frequency fiber laser is experimentally evaluated. Stable single-frequency oscillation with a side-mode suppression ratio (SMSR) as high as 55 dB and a spectral linewidth of less than 10.1 kHz over a wavelength tuning range of as wide as 48 nm is demonstrated.