Loss Reduction of GeO2-Doped Silica Waveguide with High Refractive Index Difference by High-Temperature Annealing

The effect of a GeO2-doped core on high-temperature annealing has been investigated to reduce the propagation loss of a waveguide device with high refractive index difference (Δ). A SiO2–GeO2 waveguide core was prepared on a fused silica substrate by rf magnetron sputtering and reactive ion etching. With increasing the annealing temperature, the roughness of the core side-wall gradually disappears and the rectangular core gradually becomes rounded. The effect of smoothing and rounding the cores was a significant reduction of the scattering loss, and moreover, it enabled the complete embedding of narrow gaps between cores in cladding glass using conventional plasma chemical vapor deposition. The propagation loss of the waveguide with a Δ of 1.5% was 0.07 dB/cm at 1.55 µm wavelength, the effect of which was demonstrated in the fabrication of an arrayed-waveguide grating demultiplexer.