Refractive Index Sensing Using Small-Period LPGs in Transmission and Reflection Configurations

Long-period gratings (LPGs) are promising photonic chemical sensors since they can excite cladding modes that interact with the surrounding medium. Small-period long-period gratings (SP-LPGs) allow the excitation of higher-order cladding modes, providing enhanced sensitivity and improved noise performance compared to conventional LPGs. In this work, we present both simulation and experimental results on refractive index sensing using SP-LPGs, specifically comparing their operation in transmission and reflection configurations. We experimentally demonstrate that the two configurations exhibit comparable performance in terms of sensitivity and noise, thus offering flexibility for sensing applications where access to both fiber ends is limited. The experimental results show an excellent agreement with simulations, highlighting the robustness and versatility of SP-LPG-based sensors.