Applications of gradient index multimode interference structures in the technology of optical sensor

The aim of the work is the presentation of operating principle and properties of multimode interference structure devices made in gradient index technology by K⁺ and Na⁺ ion exchange method from the point of view of optical sensor design. Numerical analysis was performed using beam propagation method. Analyzed sensor structures are covered by nanolayers whose refractive index higher than the multimode interference section index is the reason for the concentration of wave propagation energy in the sensor layer area and its vicinity. Modifications of external propagation conditions change the refractive index and extinction coefficient of a sensor layer. The variation of optical properties leads to the modification of waveguiding conditions in the multimode interference coupler.