Multi-wavelength fiber lasers operated in stretched-pulse mode-locked regimes with a very compact configuration

A novel and compact configuration for the generation of tunable multi-wavelength fiber ring lasers by exploiting the intracavity birefringence filter is demonstrated. The fiber laser is passively mode locked by using a nonlinear polarization rotation technique. A single polarization controller (PC) and a polarization-dependent isolator combined with birefringence act as a tunable comb filter and the mode locker to generate the single-wavelength ultrafast oscillation and multi-wavelength lasing by finely adjusting the PC. Multi-wavelength lasing of up to 50 lines with a wavelength spacing of 0.8 nm within a 3 dB bandwidth has been obtained. The total group velocity dispersion of the ring cavity is designed to the near-zero regime, which indicates a stretched-pulse mode-locked state.