Cladding–Thickness–Dependent Performance of SMS Optical Fiber Sensors

This study presents a detailed investigation of single-mode–multimode–single-mode (SMS) fiber sensors with varied cladding thicknesses of multimode fiber (MMF) (4, 3, 2, 1, and 0 μm). The refractive index (RI) sensing performance of these sensors was evaluated using sensitivity, limit of detection (LOD), full width at half maximum (FWHM), quality factor (Q-factor), figure of merit (FOM), and comprehensive evaluation index (CEI). The results demonstrate that the sensor with a multimode fiber (MMF) cladding thickness of 0 μm achieves the highest overall performance, characterized by a superior sensitivity of 106.00 nm/RIU and a maximum figure of merit (FOM) of 5.54 RIU−1. In comparison, the sensor with a 2 μm MMF cladding thickness exhibits minimized energy loss, resulting in the highest quality factor of 169.02 and the narrowest full width at half maximum of 8.02 nm. Additionally, sensor stability is found to be independent of MMF cladding thickness.