Highly sensitive refractometers based on a side-polished single-mode fibre coupled with a metal oxide thin-film planar waveguide

Refractometric sensor elements were studied consisting of a side-polished single-mode optical fibre covered by a pulsed laser deposited ZnO thin film. A measurement scheme was used for in situ control of the film thickness during the deposition process. Highly sensitive sensors were produced based on the interaction with the zero- and first-order modes of the ZnO planar waveguide. The sensors' applicability to the two spectral regions for communications, namely 800–1000 nm and 1300–1600 nm, was demonstrated. A high sensitivity of the order of 3000–6700 nm per refractive index unit change was obtained for sensor elements utilizing the interaction of the fibre mode with the TE0 or TM0 mode of the ZnO thin-film waveguide.