Refractive Index Sensor Based on Gradient Waveguide Thickness Guided-Mode Resonance Filter

In this article, a novel refractive index sensor based on gradient waveguide thickness guided-mode resonance (GWT-GMR) is proposed. The GWT can convert an spectral information into an spatial information, which can be measured using a charged coupled device (CCD) instead of a bulky spectrometer. A GWT-GMR sensor of size only 1261 × 200 μm² has a detection range of 0.109 refractive index units (RIU), sensitivity of 16 239 μm/RIU, and the limit of detection of 6.9 × 10^-4 RIU, which are sufficient for many practical applications. Multiplexing can be easily implemented because of sensor compactness and the simple readout of the CCD. Moreover, the system is suitable for handheld devices or integration with smartphones for potential biosensing applications.