Fabrication and characterization of continuous wave direct UV (λ=244 nm) written channel waveguides in chalcogenide (Ga:La:S) glass

Gallium lanthanum sulphide (Ga:La:S) optical glass is an interesting material for both fiber and planar technologies, as it offers possibilities for a wide array of devices suitable for use in both nonlinear applications and as IR lasers. Direct laser writing into this glass has yielded low-loss single-mode channel waveguides. Samples were exposed to above-bandgap illumination of focused UV (λ=244 nm) light at varying intensities (I_UV=1.5-90 kW/cm²) and scan velocities (V_SCAN=0.005-0.067 m/s). The exposed regions were evaluated through atomic force microscopy (AFM), and surface compaction (0.3-3.6 μm) was observed. Sample topography was examined using a scanning electron microscope (SEM) with analysis of chemical changes within the exposed regions performed with energy-dispersive X-ray microscopy (EDAX). Waveguide attenuation was measured to be 0.2±0.1 dB/cm at 1.3 μm with a positive change in refractive index (Δn=10^-3). The chemical mechanism for these photo-induced changes with resulting photodensification has been correlated with a relative increase in the lanthanum content within the waveguide core.