The group index and the effective index of a waveguide mode depends on the wavelength of the propagating light and the refractive index of the material. As the refractive index of the material depends on the temperature; together with the waveguide geometry, TE and TM light experience different propagation response due to the change in temperature. Here, the proposal is to use separate interferometer which only sustain either TE or TM mode, and from the shift of the interference pattern due to temperature, we can compare the effect on TE and TM modes.