A refractive index sensor based on a three-layered polymeric waveguide was proposed and demonstrated. A high-index
thin film in TiO2 was placed on top of the waveguide in the sensing region, playing the role of strengthening the
evanescent field to enhance the sensitivity of the sensor. The refractive index of the analyte applied to the surface of the
sensor was estimated by observing the count of the polarimetric interference between the TE and TM polarizations,
which is manifested as a periodic variation in the optical output of the sensor. For a fabricated sensor involving a 20 nm
thick TiO2 film, the sensitivity was found to be equivalent to 1.8x10-3 RIU. It was found to be enhanced by increasing the
thickness of the high-index overlay to a certain degree.