Reflective-type guided-mode resonance sensor system based on interference line fringe shifting

A refractive index (RI) sensing system with a reflective-type guided-mode resonance (GMR) sensor based on interference bright fringe line shift on a bi-cell photodiode is proposed. A transmissive-type dark fringe line shift detected by an image sensor instead of a spectrometer to detect the RI change of aqueous sugar solutions has been reported previously. In this study, the proposed system employing a converging laser beam focuses on the GMR sensor, causing its reflection to create a bright fringe line on the bi-cell photodiode. The shifting of this line, caused by the surface RI change on the sensor, can be obtained by detecting the differential voltages between the two photodiodes on the bi-cell photodiode. The primary experimental results indicate that the system's average detection sensitivity is 15.8 V/RIU. This detection method enables the system to be low-cost, compact, and highly sensitive, with excellent potential for biosensing applications.