Processing and optical properties of Nd³⁺-doped SiO₂-TiO₂-Al₂O₃ planar waveguides

We report here the processing and optical characterization of Nd³⁺-doped SiO₂-TiO₂-Al₂O₃ planar waveguides deposited on SOS (Silica on silicon) substrates by the sol-gel route combined with spin-coating and rapid thermal annealing (RTA). The recipes used for preparing the solutions by sol-gel route are in mole ratio of 93SiO₂: 7TiO₂: 20AlO_1.5:×ErO_1.5 (x = 0.5, 1, 1.5 and 2). In order to verify the residual OH content in the films, FTIR spectra were measured and the morphology of the material by the XRD analysis. Five 2-layer films annealed at a maximum temperature of 500 °C, 700 °C, 900 °C, 1000 °C, 1100 °C respectively were fabricated on silicon. The FTIR and XRD curves show that annealing at 1050 °C for 15s effectively removes the OH in the material and keeps the material amorphous. The propagation loss of the planar wavehuides was measured by using the method based on scattering measurement and the result was obtained to be 1.54 dB/cm. The fluorescence spectra were measured with 514 nm wavelength of Ar⁺ laser by directly shining the pump beam on the film instead of prism coupling. The results show that the 1 mole Nd³⁺ content recipe (93SiO₂:7TiO₂:20AlO_1.5:1NdO_1.5) has the strongest emission efficiency among the four samples investigated.