Low-loss waveguides in ultrafast laser-deposited As_2S_3 chalcogenide films

Ultrafast pulsed laser deposition was used to successfully deposit atomically smooth 5-μm-thick ${\mathrm{As}}_2{\mathrm{S}}_3$ films. The as-deposited films were photosensitive at wavelengths close to the band edge (≈520 nm), and waveguides could be directly patterned into them by photodarkening using an argon-ion or frequency-doubled Nd:YAG laser. The linear and nonlinear optical properties of the films were measured as well as the photosensitivity of the material. The optical losses in photodarkened waveguides were <0.2 dB/cm at wavelengths beyond 1200 nm and <0.1 dB/cm in as-deposited films. The third-order nonlinearity, $n_{2,{\mathrm{As}}_2{\mathrm{S}}_3},$ was measured using both four-wave mixing and the Z-scan technique and varied with wavelength from 100 to 200 times fused silica $(n_{2,\mathrm{Silica}}\approx 3\times {10}^{-16} {\mathrm{cm}}^2/\mathrm{W})$ between 1500 nm and 1100 nm with low nonlinear absorption.