Tunable dual-wavelength single-longitudinal-mode fiber laser based on spectral narrowing effect in a nonlinear semiconductor optical amplifier

A tunable dual-wavelength single-longitudinal-mode (SLM) fiber laser based on a nonlinear semiconductor optical amplifier (NL-SOA) and an optical comb filter is proposed and demonstrated successfully. The SLM operation principle is based on the spectral narrowing effect resulting from the inverse four-wave mixing (FWM) in a NL-SOA. By inserting the NL-SOA inside the fiber laser cavity, SLM lasing can be possibly achieved when stable laser oscillation is established after many roundtrips through the NL-SOA. Further, tunable dual-wavelength SLM output can be obtained by incorporating a tunable optical filter (TOF) and a comb filter inside the laser cavity to perform dual-wavelength selection function. As a result, tunable dual-wavelength SLM oscillation with a wavelength spacing of 0.4 nm and a wavelength tuning range of about 56 nm has been achieved. Each wavelength has a linewidth less than 8 kHz and a side-mode suppression ratio (SMSR) larger than 40 dB.