Spectroscopy of thulium-doped fibers with depressed cladding for sources emitting around 1700nm

We present a study of spectroscopic properties of several thulium-doped silica-based fibers with depressed cladding, aimed at potential applications in efficient fiber sources emitting around 1700nm. The fibers were characterized in terms of refractive index profiles, absorption and emission spectra, and fluorescence lifetimes. Additionally, the influence of inner structure dimensions on bend-induced losses was investigated. The results demonstrate that this fiber design effectively suppresses long-wavelength amplified spontaneous emission. The findings provide a basis for the design of a new fiber optimized for emission around 1700nm.