Wavelength and composition dependence of the thermo-optic coefficient for InGaAsP-based integrated waveguides

A method to take into account the wavelength, composition, and temperature dependencies in the calculation of the refractive index and linear thermo-optic coefficient of In1−xGaxAsyP1−y alloys is presented. The method, based on the modified single oscillator model, shows a good agreement with experimental data for InP reported in literature at different wavelength and temperature ranges. Further, we exploit this approach with a Film-Mode Matching solver to calculate the linear thermo-optic coefficients of both phase and group effective indices of an InGaAsP-based waveguide. The same waveguide structure is also experimentally investigated through a reflectometric technique and results are found to be in accordance with the simulations performed exploiting the proposed method. In both cases, a dependence of the group index on temperature, almost twice that of the phase index, is observed. These results provide a deeper understanding on the influence of the temperature on the behaviour of optical waveguides and devices, making possible an accurate and realistic modelling of integrated circuits.