In this work, we synthesized bulk amorphous GeGaS glass by conventional melt quenching technique. Amorphous nature of
the glass is confirmed using X-ray diffraction. We fabricated the channel waveguides on this glass using the ultrafast laser
inscription technique. The waveguides are written on this glass 100 μm below the surface of the glass with a separation of 50
μm by focusing the laser beam into the material using 0.67 NA lens. The laser parameters are set to 350 fs pulse duration at
100 KHz repetition rate. A range of writing energies with translation speeds 1 mm/s, 2 mm/s, 3 mm/s and 4 mm/s were
investigated. After fabrication the waveguides facets were ground and polished to the optical quality to remove any tapering
of the waveguide close to the edges. We characterized the loss measurement by butt coupling method and the mode field
image of the waveguides has been captured to compare with the mode field image of fibers. Also we compared the
asymmetry in the shape of the waveguide and its photo structural change using Raman spectra.
We report here, a finite difference thermal diffusion (FDTD) model for controlling the cross-section and the guiding nature of the buried channel waveguides fabricated on GeGaS bulk glasses using the direct laser writing technique. Optimization of the laser parameters for guiding at wavelength 1550 nm is done experimentally and compared with the theoretical values estimated by FDTD model. The mode field diameter (MFD) between 5.294 μm and 24.706 μm were attained by suitable selection of writing speed (1mm/s to 4 mm/s) and pulse energy (623 nJ to 806 nJ) of the laser at a fixed repletion rate of 100 kHz. Transition from single-mode to multi-mode waveguide is observed at pulse energy 806nJ as a consequence of heat accumulation. The thermal diffusion model fits well for single-mode waveguides with the exception of multi-mode waveguides.