Stable and tunable narrow-linewidth erbium-doped fibre laser based on polarization-maintaining fibre ring filter and PM-FBG

A tunable, narrow-linewidth, ring-cavity, erbium-doped fibre laser (EDFL) incorporating a polarization-maintaining fibre ring filter (PMF-FRF) and a polarization-maintaining fibre Bragg grating (PM-FBG) was designed and used in experiments. In the proposed configuration, the PM-FBG was used as a wavelength selector and the PMF-FRF was fabricated by a 3 dB coupler and a 2 m polarization-maintaining fibre. In order to constrain the mode hopping, a 1 m long segment of erbium-doped fibre was inserted between the circulator and the PM-FBG as a saturable absorber. Based on these enhancements, the side-mode suppression was improved and a stable and tunable single-wavelength laser was achieved within the tuning scope of 1534.36-1535.07 nm by adjusting the polarization controller. In the tunable scope, each wavelength space was <= 0.1 nm, the maximum power drift was <= 0.35 dB, and the 3 dB linewidth was <= 0.15 nm. In the experiment, dual-and triple-wavelength laser emissions were also realized by modifying the polarization condition of the cavity. Over a 20 min monitoring period at room temperature, the wavelength shift and power fluctuation of the single-wavelength emission were <= 0.01 nm and 0.11 dB respectively, while wavelength shift and power fluctuation of the dual-wavelength emission of 1534.39 and 1535.07 nm were <= 0.02 nm and 0.7 dB respectively.