Model of the planar broadband differential waveguide interferometer as a humidity sensor

The paper presents a model of the planar broadband differential waveguide interferometer. Its response to a change in thickness and refractive index of the waveguide layer due to a change in humidity is presented. The analysis was carried out for the wavelength range from 450 to 850 nm. The orthogonal modes TE₀ and TM₀, which propagate in this wavelength range, are considered. It is shown that by using light near the maximum of the system characteristic, instead of the spectrometer, the total power at the system output can be measured.