Numerical analysis of planar multimode optical sensor with active nanolayer

In the paper, numerical studies of the model of an optical sensor, based on interference of modes in a planar one-dimensional step-index configuration, are presented. Calculations are performed using the method of mode field analysis. The structure consists of the single-mode input waveguide, the multimode waveguide that guides only a few modes and the single-mode output waveguide.The structure is covered by a nanometer active sensor layer of a high refractive index, which changes its optical properties in contact with the measured external surrounding. The refractive index variation of an active sensor layer affects the modal properties of the multimode waveguide and the output optical field distribution. By the proper selection of the active layer, the considered configuration can be used for gas detection.