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 (IUV = 1.5 -90~kW/cm2 ) and scan velocities (VSCAN = 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.
Arshad K. Mairaj, Ping Hua, Harvey N. Rutt, and Daniel W. Hewak, "Fabrication and Characterization of Continuous Wave Direct UV (λ=244~nm ) Written Channel Waveguides in Chalcogenide (Ga:La:S) Glass," J. Lightwave Technol. 20, 1578- (2002)