Liquid core optical fiber temperature sensors

An intensity-based, cost-effective liquid-core optical-fiber temperature sensor has been developed for the measurement of temperatures from 20°C to 185°C with a resolution better than ±20°C. The sensor is composed of a hollow-core optical fiber filled with a liquid of a known index of refraction which is slightly higher than that of the silica tube which acts as the cladding. The refractive-index fluid is chosen such that the variation of its refractive index with temperature is well defined and linear in the desired range of operation. As the temperature surrounding the liquid-core fiber increases, the index of the liquid decreases in a linear fashion until it reaches the refractive index of the cladding and the guided modes are no longer supported by the fiber. Calibration of the intensity changes with temperature yields a repeatable method to measure temperature. A simplified theoretical analysis of the decrease in transmitted signal intensity with increase in temperature has been performed, and it is shown that the obtained experimental results closely match the elementary theoretical analysis