Ion-implanted waveguide formation in silica

The optimum processing parameters for the fabrication of low-loss waveguides in fused silica by ion implantation and annealing have been determined through a comparison of implantation-induced physical and optical properties. The step height at an implanted/unimplanted boundary resulting from Si implantation was measured as a function of ion dose (2×10¹²-6×10¹⁶/cm²), post-implantation annealing temperature (200-900°C) and time (0-2.5 hr). For a given ion energy (5 MeV), the compaction increased for doses <~10¹⁵/cm² and thereafter, saturated. Isochronal and isothermal annealing both resulted in a non-linear reduction in compaction, typical of a thermally-induced process. In contrast to the continual reduction in compaction observed during isochronal annealing, the loss coefficient exhibited a distinct minimum of ~0.15 dB/cm at an intermediate temperature of 500°C. This feature was consistent with the removal of a specific defect or colour centre. Investigation of the annealing behaviour of the B₂-band indicated that this defect was not responsible for the observed loss behaviour nor was the decrease in refractive index. Surface cracking was observed for C, Si, and Ge-implantations at doses around 8×10¹³/cm², an effect exaggerated for the lighter ions