Femtosecond laser writing of a depressed cladding single mode channel waveguide in high-purity tellurite glass

High-purity tungstate-tellurite glasses doped with molybdenum, lanthanum or bismuth oxides were investigated from a point of view promising medium for nonlinear optical devices fabrication. A tubular-like architecture was employed for fabrication of waveguides in the of tellurite glasses, in which refractive index change is negative under femtosecond laser writing at 1028 nm. Thermal, nonlinear optical properties and optimal laser writing conditions were determined. The glasses revealed a very high stability against crystallization, high transparency in the visible, near- and mid-IR regions, large values of Kerr nonlinear coefficient that are within the range of (4.3 ÷ 5.4)·10− 6 cm2/GW. The highest values of the nonlinear coefficient were found for bismuth containing glasses. The single mode waveguide with propagation loss of 0.15 dB/cm at 1064 nm was inscribed in tungstate-tellurite glass.