Combination dual-tapered fiber with band-pass filter in generating multi-wavelength Er³⁺-doped fiber laser

we propose to add a bandpass filter into multi-wavelength Er³⁺-doped fiber laser to avoid the mode competition in the ring-cavity laser based on comb-like dual-tapered fiber. The bandwidth of bandpass filter is within 1543.5–1558.5 nm, excluding the gain peak of Er³⁺-doped fiber around 1530 nm. The gain of Er³⁺-doped fiber within the filter bandwidth is uniform. When realizing the multi-wavelength laser output, 1-, 2-, 3-, 4- laser lines are obtained by adjusting the polarization controller, and the laser lines distribute at the interference wavelengths of dual-tapered fibers within the bandwidth of bandpass filter. Tunability of the multi-wavelength laser are demonstrated, including tunability range and wavelength spacing. Tunability ranges of 12.10 nm for single-wavelength, 9.312 nm for dual-wavelength, 4.3 nm for three-wavelength are generated; wavelength spacing of 1/2/3/4/5 intervals for dual-wavelength, 5.2 nm/7.6 nm for three-wavelength, 5.26 nm/2.64 nm/5.0 nm for four-wavelength are all generated. Stability of laser output in 1 h are tested. The proposed gain-balancing BPOF scheme in multi-wavelength EDFL is simple and effective to suppress the mode competition. These results could be used to support the practical applications of multi-wavelength Er³⁺-doped fiber laser.