PHASE-SENSITIVE FIBEROPTIC MONOPTODES FOR CHEMICAL SENSING

A highly sensitive measurement method and miniaturized all-fibre sensing device for the detection of small changes in refractive index caused by chemical or biochemical reactions are proposed. The optical principle is based on the differential phase modulation between the two orthogonal polarization modes of a single-mode fibre via evanescent-field interaction with sensitive thin films deposited on the side-polished fibre, a so-called 'monoptode'. Using the matrix method for an approximated planar five-layer waveguide, the influence of the main parameters of the system, such as film thickness, refractive indices and wavelength of operation, on the polarimetric interferometer efficiency has been theoretically studied. As an example, the method is applied to optimize theoretically the waveguide parameters of a humidity-sensing optode using porous TiO2-SiO2 thin film.