Photosensitivity of sol–gel derived inorganicxB₂O₃ : 20GeO₂ : (80 −x)SiO₂system with various boron concentrations

Abstract

Optical properties of sol–gel synthesized boron co-doped germanosilicate(xB2O3 : 20GeO2 : (80 − x)SiO2) thin films (single layer) were investigated by varying the molar concentration of B2O3 for x = 5, 10 and 20 under various annealing temperatures, ranging from 500 to 1000 °C. Densification of the thin film was found to be influenced by the concentration of boron under various annealing temperatures. Iterative deposition of the dense xB2O3 : 20GeO2 : (80 − x)SiO2 (for x = 5, 10 and 20) thin film was used to fabricate a few micrometre thick single-mode slab waveguides at 1.55 µm. Refractive indices and the propagation loss values of the waveguide samples were determined by using the prism-coupler technique. Under ultra-violet illumination, the refractive index change (Δn) of the xB2O3 : 20GeO2 : (80 − x)SiO2 increases with increasing B2O3concentration, for both transverse electric and transverse magnetic. The values of ΔnTE are ∼0.009, ∼0.012 and ∼0.014, for x = 5, 10 and 20, respectively. The high values of Δn, which increase with the B2O3 concentration are probably caused by the larger stress present in the boron doped films.