Saturable absorber-based single-longitudinal mode tunable fiber laser using a Faraday rotator mirror as the rear cavity end

A single-longitudinal mode selection is realized in a linear-cavity tunable fiber laser constructed using a Faraday rotator mirror and a partial reflectance fiber Bragg grating as the cavity ends. At both tuning wavelengths of 1543.47 and 1557.52 nm, the measured optical signal-to-noise ratio is larger than 40 dB and a linewidth less than 1 MHz is obtained. It is based on the usage of a piece of gain fiber type saturable absorber as the mode filter. The pumping power efficiency is improved by 10% by recycling the residual pump power to the gain medium.