Refractive Index, Temperature, and Heat Source Origin Sensing with Dual U-shaped Fiber Probes

Multiparameter sensors have become more valuable in the context of real-time monitoring system, where various measurand attributes affect the sensor response. Such feature is useful to accurately pinpoint the information of the measurand of interest in the presence of extraneous parameters. Most fiber optic sensors with multiparameter sensing capability are developed based on the interferometric scheme, where a bulky and costly detector is required. Single U-shaped fiber optic sensors, thus far, are limited to detecting only two parameters at most, with no spatial information provided. In this paper, we propose to assemble two U-shaped fiber probes to simultaneously detect refractive index, temperature, and heat source origin. The recorded sensor sensitivities for refractive index are -141.75%/RIU and -280.71%/RIU, and for temperature, 0.0535%/°C and 0.0931%/°C. Moreover, the sensor is able to estimate the heat source origin from two directions – front and back of the prototype. While the dual U-shaped fibers are able to measure refractive index and temperature simultaneously, they also provide spatial information regarding the positions of the heat emitting source, thereby enabling the multiparameter sensing capability. However, this paper reports only on the initial investigation of the prospect of multiple U-shaped fiber probes to achieve the multiparameter sensing capability.