Tm3+-doped fluoride (ZBLAN) fibers offer amplification and lasing in a wide variety of wavelength ranges, including 810 nm, 1480 nm, 1900 nm, and 2300 nm.1 Amplification and lasing around 1480 nm through the 3H4→3F4 transition is of interest for extending the capacity of WDM transmission systems, as well as developing sources for pumping erbium-doped fiber and fiber Raman amplifiers. The 3H4→3F4 transition, however, poses a challenge due to its self terminating nature. As such, the 3F4 level can be depleted either by colasing at 1900 nm2 or by using upconversion pumping at 1064 nm. High-power 1480 nm Tm3+:ZBLAN fiber lasers with upconversion pumping at 1064 nm have been demonstrated.3-6 Recent research has focused on improving further the power conversion efficiency as well as the development of monolithic fiber lasers, e.g., by incorporating fiber Bragg gratings (FBGs) directly within the Tm3+: ZBLAN fiber gain medium.
Dual-wavelength and multi-wavelength sources can have many applications in instrumentation (e.g., component testing), LIDAR systems, and fiber optics sensing. There have been several reports of dual-wavelength Tm3+-doped fiber lasers. For example, Androz et al. demonstrated operation at 785 nm and 810 nm, corresponding to the 1G4→3H5 and 3H4→3H6
transitions, respectively, with a Tm3+:ZBLAN fiber gain medium.7 Wang et al. obtained dual-wavelength lasing around 2 μm with a tunable wavelength spacing from 1 nm – 40 nm in a Tm3+:silica fiber laser.8 We realized oscillation at 805 nm and 810 nm through the 3H4→3H6 transition in a Tm3+:ZBLAN fiber laser; we also reported wavelength switching capability as well as bistable operation in both single cavity and cascaded cavity configurations.9 In this paper, we
extend our work further and report a dual-wavelength Tm3+:ZBLAN fiber laser operating in the S-band. Wavelength spacings of 11 nm and as narrow as 0.6 nm are achieved in a linear cascaded cavity configuration with bidirectional upconversion pumping at 1064 nm.