Comparative study of the temperature-sensitive materials for D-shaped optical fiber-based temperature sensor

Optical fiber-based surface plasmon resonance (SPR) sensors provide exceptional sensitivity, a compact design, and the capability for remote monitoring, making them ideal for advanced detection systems. Temperature-responsive liquids such as chloroform, chloroform-ethanol mixtures, and ethanol-glycerol mixtures hold significant potential in biomedical optical fiber sensors due to their ability to react to temperature changes. These liquids exhibit significant refractive index (n) changes with temperature (T), quantified by the thermo-optic coefficient (dn/dT), enabling precise, non-invasive, and real-time temperature monitoring. This study explores the incorporation of different temperature-sensitive analytes into a D-shaped double-channel optical fiber for a wide range of temperature sensing in a single sensing platform. The double-channel sensor employs gold as the plasmonic material and channel 1 is filled with a fluid having a constant refractive index of 1.33, while channel 2 is filled with temperature-sensitive liquids. The refractive index of channel 2 is modeled as the base refractive index adjusted by the product of dn/dT and the temperature difference relative to a reference. Sensitivity analyses span temperatures from 283.15 °K (10°C) to 343.15 °K (70°C), addressing biomedical and industrial sensing applications. The findings indicate that chloroform and mixtures of chloroform with ethanol demonstrate exceptional sensitivity as temperature-sensitive analytes. Chloroform achieves a maximum refractive index sensitivity of 429.82 nm/RIU in the RI range of 1.33–1.45 and temperature sensitivity of 5 nm/°K. A 50:50 chloroform-ethanol mixture enhances refractive index sensitivity to 714.28 nm/RIU in the range of 1.33–1.40 while maintaining 5 nm/°K temperature sensitivity. In contrast, a 34:66 ethanol-glycerol mixture exhibits a refractive index sensitivity of -453.72 nm/RIU in the range of refractive index 1.33–1.44 and temperature sensitivity of -5 nm/°K. These findings establish chloroform and its mixtures as highly promising candidates for efficient optical temperature sensing in both biomedical and industrial applications.