Six-wavelength-switchable narrow-linewidth thulium-doped fiber laser with polarization-maintaining sampled fiber Bragg grating

•A wavelength-switchable narrow-linewidth TDFL with a SFBG has been proposed.•The laser got 6 single-wavelength and 9 dual-wavelength operations.•The power/wavelength fluctuations of single-wavelength laser were 0.71 dB/0.02 nm.•The linewidths of single-wavelength laser were among 0.60–1.08 kHz.•The power/wavelength fluctuations of dual-wavelength laser were 0.95 dB/0.03 nm.