Multi- and dual-wavelength Thulium-doped fluoride fiber laser assisted by four-wave mixing in S-band region

Abstract

In this work, multi-wavelength lasing in the S-band region using a Sagnac loop filter in a thulium-doped fluoride fiber laser (TDFFL) was demonstrated for the first time. The Sagnac loop served as a comb-like wavelength filter, while a 10-km long dispersion compensating fiber (DCF) was utilized to induce the four-wave mixing (FWM) effect in the cavity. The FWM effect was used to suppress mode competition in the TDFFL as well as to enhance the number of lasing lines. At its optimum polarization state, 17 stable lasing lines at peak powers of less than 10 dB from the highest peak power were observed, with these lasing lines having a uniform wavelength spacing of 0.23 nm. The multi-wavelength operation exhibited minimal wavelength drifts and power fluctuations of less than 0.01 nm and 1.2 dB respectively. A tunable dual-wavelength laser output was also demonstrated, with a constant wavelength spacing throughout the tuning range.