Dip-Type Probe Based on a Guided-Mode Resonance Sensor at the Facet of an Optical Fiber

This study presents a dip-type probe that was designed by integrating a polymer GMR sensor at the facet of an optical fiber to sense changes in the refractive index of sugar water. The polymer GMR probe was fabricated by nanoimprinting UV-cured resin and fixing it to the facet of a single-mode optical fiber using a silicon tube. A divergent beam from the fiber facet passes through the GMR sensor of the probe and then a polarizer to form a nearly straight dark line in the output beam. Instead of a spectrometer, a low-cost CMOS image sensor is utilized to detect the position shift of the dark line caused by the change in the refractive index on the surface of the GMR sensor. The experimental results show that its detection sensitivity and limit are approximately 42.2°/RIU (or 88500 pixels/RIU) and $1.13\times 10~^{-5}$ RIU/pixel, respectively, demonstrating its potential as a low-cost, compact commercial biosensor.