Direct Laser Written Waveguide in Tellurite Glass for Supercontinuum Generation in 2 μm Spectral Range

A depressed cladding waveguide composed of 36 parallel tracks is inscribed in high purity 70TeO ₂ -22WO ₃ -8Bi ₂ O ₃ glass by femtosecond laser operating at 1030 nm. The Sellmeier formula for the refractive index of the investigated glass is obtained for the range of 1170-2350 nm. The module of the negative refractive index change in a track is found to increase with increasing wavelength in the range of 640-2000 nm. The waveguide shows single mode behavior in the wavelength range of 1700-2100 nm with mode field diameter (MFD) of 20 μm. The propagation loss is predominantly due to scattering in the waveguide. Spectrum broadening as large as 503 nm was demonstrated in a 14 mm long waveguide pumped by femtosecond pulses at 1950 nm. In the low input pulse energy region, the spectrum broadening is well described by generalized nonlinear Shrödinger equation (GNLSE) taking into account Kerr and the Raman nonlinearities under the assumption of constant MFD along the waveguide. Under higher energy pumping, an extra broadening was observed that is attributed to the focusing effect of Kerr lens in the waveguide mode.