A switchable soliton mode-locked and multi-wavelength operation in thulium-doped fiber laser (TDFL) is demonstrated based on nonlinear polarization rotation (NPR) technique. The TDFL produces a soliton pulse operating at 1917.66nm using a 5m long thulium-doped fiber (TDF) as a gain medium as well as nonlinear medium. The solitonic behavior is further identified with two orders of Kelly sidebands in the output spectrum. The mode-locked emission is obtained from threshold pump power of 522–1052mW with consistent pulse repetition rate of 14.7MHz. Maximum pulse energy is calculated as 0.89nJ at pump power of 1052mW, whereas the maximum pulse width is estimated to be approximately 1.36ps corresponding to sech2 pulse profile. By shifting the polarization orientation, the cavity can change to multi-wavelength operation with signal-to-noise ratio (SNR) higher than 53dB. At pump power of 1037mW, three stable peak wavelengths are generated with a power fluctuation and constant spacing of $\pm 1$ dB and 7.4nm, respectively.

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References

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