Distributed temperature sensors have been proposed for a wide variety of scientific and industrial applications and represent an important technology for modern infrastructures. Due to the range of potential applications, distributed fiber optic sensors based on spontaneous Raman scattering have been studied both theoretically and experimentally. This paper presents the experimental evaluation of a distributed fiber optic temperature sensor based on spontaneous Raman scattering over a wide temperature range, from -196 °C to +400 °C. The sensor is implemented using a commercial OTDR, a standard EDFA amplifier and a standard optical fiber link. Besides, a special type of optical fiber for high temperature operation, featuring metallic coating, is also assessed as the sensor element. The integrity of the fibers following the exposure to the extreme temperatures is analyzed. The results provide values for the sensitivity, accuracy and resolution of the sensor in the wide range of temperatures.

Optical sensors that can measure multiple parameters is a promising area of research. This can also be attributed to the fact that monitoring two or more measurands at the same time is crucial in embedded systems, especially when they are interconnected, as is the case of temperature and corrosion, or temperature and refractive index. In this work, an optical fiber sensor based on Raman scattering in single-mode optical fibers to simultaneously monitor temperature, refractive index and corrosion is proposed and experimentally demonstrated. This sensor consists of a distributed temperature detection system based on Raman scattering with additional sensor heads: for multipoint corrosion monitoring and multipoint refractive index variation measurement. The multiparameter sensor was evaluated for solutions with refractive indices in the range of 1.3370 – 1.3840 RIU (Refractive Index Unit), for temperatures between 30 °C and 100 °C, and for aluminum thin-film corrosion in acid solution. The experimental results show that the sensor presents sensitivities of 0.5 dB/10 ^-3 RIU to refractive index variations, of 0.43 dB/nm for corrosion, and of 0.243 dB/°C for temperature, with resolution of 2 °C. The sensor system can also provide the corrosion rate and operate in fiber links several kilometers long.

Fiber-optic magnetic field sensors are attracting interest for applications in navigation, magnetic resonance, geophysics, space systems, power transformers and generators, especially for hash environments, at long distances and for multiple monitoring points. This paper presents a computational modeling for optical fiber based magnetic field sensors using the magneto-optical Faraday and Kerr effects on the polar configuration. We propose two sensor profiles, one using a thin film of Fe and the other using a Ce: YIG layer. A simplified analytical model based on Fresnel equations is used to guide the numerical modeling built on COMSOL Multiphysics. The sensors design methodology is also presented, which optimizes the sensor operating range and sensitivity. The proposed sensor sensitivity, resolution and operating range are presented and compared to others found in the literature. The results indicate the possibility of building high resolution sensors for a restricted range of magnetic field intensities or a wide operating range sensor.

This paper presents experimental results, approximate analytical formulations and numerical simulation results to analyze the reflectance from a metalized fiber tip under corrosion, which is part of a corrosion sensor. Moreover, the dynamics of corrosion on a thin metallic film is modelled computationally by considering a proposed roughness fitting function to consider the evolution of film thickness and shape during the corrosion process. For this modelling, COMSOL Multiphysics is used to simulate the optical signal reflected from the transducer element of the sensor. The simulation results for the optical signal reflected from a rough metallic film are compared with experimental and analytical results. The results reveal that the corrosion process generates an inhomogeneous metallic structure that allows the occurrence of surface plasmon resonance. And the proposed simple surface roughness model can be used to describe the dynamic process of corrosion of an aluminum film that is deposited on the end-facet of an optical fiber.

In this work, we demonstrate refractive index (RI) sensors based on the cascade of hetero-core structures using multimode and no-core optical fibers in sequence. The sensor device is engineered to have resonances at different wavelengths using different sensing region lengths. The device fabrication involves simple fiber cleaving and fusion splicing. For the experiments, the two sensor regions are exposed to liquids with different RIs. For the hetero-core fiber insertion length of 45 mm, the transmission valley is centered at 1082.5 nm with 15.1 nm full width at half-maximum (FWHM) for an external medium RI of 1.3370. Additionally, it shifts 4.1 nm towards longer wavelengths as the RI of the external medium increases to 1.3840. For the 30 mm long hetero-core structure, the valley is centered at 1599.7 nm with 23.3 nm FWHM for an external medium RI of 1.3370, which shifts 7.4 nm as the RI increases to 1.3840. The sensor sensitivities are up to − 476 d B / r e f r a c t i v e index unit (RIU) and 270 nm/RIU. The resolution of the devices is estimated to be 2 × 10 − 5 R I U .