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Highlights: [•] We fabricated a refractive index sensor based on in-fiber Michelson interferometer. [•] The sensor has the advantages of short size (less than 2mm) and easy fabrication. [•] We use the method of intensity-modulated to solve cross sensitivity. [•] The sensor has the sensitivity of −208.24dB/RIU at the refractive index of 1.440. [•] The sensor could apply in the fields of chemical and biomedical sensing. [Copyright &y& Elsevier]

We demonstrate a surface plasmon resonance refractive sensor based on the side-polished single mode optical fiber and investigated the sensor performance decay induced by silver coating degradation. The sensor showed fast response to the refractive index liquid in the range from 1.32 to 1.40 RIU. The highest sensitivity up to 4365.5 nm/RIU and a FOM of 51.61 RIU −1 were achieved, which were comparable to the reported polished-fiber-based SPR sensors. Characteristics of the silver-coated sensor after exposure to the air as well as to the liquid environment were investigated. The sensor always stored in dry air could respond stably two weeks later with sensitivity comparable with the fresh one and lower resolution due to the broadened resonant dip. But the sensor immersed in the refractive liquid for 30 min firstly and then exposed to ambient air for hours decayed dramatically due to silver degradation. The presented silver-coated SPR sensor could be used as a simple, cost-effective, disposable device in bio-chemical, environment, and food safety detection. [ABSTRACT FROM AUTHOR]

Breath, as an important health monitoring indicator, provides valuable diagnostic information for cardiovascular disease and pulmonary function. Humidity can act as a bridge between breath and sensing signals. Current monitoring methods depend on humidity-sensitive material characteristics. In this work, an all fiber-optic flexible humidity sensor for wearable breath monitoring is reported. An eccentric fiber Bragg grating (EFBG) is inscribed in a single mode fiber to excite a stable core mode and sensitive cladding modes. The core mode is shown to maintain stable spectral features under a high-humidity atmosphere and can be used to calibrate the wavelength and power of the system. Importantly, the interface evanescent field of the cladding mode is highly sensitive to the ambient refractive index (RI) and even humidity-induced RI variation. Without combining any sensitized material, EFBG can directly perceive humidity fluctuations during breath with fast response (92 ms) and recovery times (100 ms). Different breathing patterns can be recognized, and breathing frequency can be extracted by sensor responses. The EFBG humidity sensor demonstrates great reproducibility, fast response, high flexibility, excellent robustness, and self-compensation capability, showing promising potential for wearable breath monitoring. • A novel all-fiber humidity sensor without any additional sensitive material is proposed for human breath monitoring. • The proposed sensor is successfully applied to monitor human breathing with different breathing pattern. • The proposed sensor offers self-compensation for source power fluctuation and temperature effect. • The long-term stability, reliability and reproducibility of proposed sensor are superior to most sensitized material based sensors. [ABSTRACT FROM AUTHOR]