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