Universal method to determine the thermo-optic coefficient of optical waveguide layer materials using a dual slab waveguide

A dual slab waveguide device method for determining the thermo-optic coefficient of waveguide layer materials is demonstrated. Temperature change-induced optical path length imbalance between two single slab waveguide modes provides the primary mechanism for detection. The waveguide mode output field phase change differences are encoded in shifts in the far field interference pattern. To illustrate the method, the thermo-optic coefficients of two In_1-xGa_xAs_yP_1-y quaternary alloys, 1.3Q and 1.15Q, are measured at a wavelength of 1.55 μm and at a center temperature of 25.2 °C. Their ratio is in excellent agreement with previous work, in accordance with optical dispersion models.