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A novel photonic crystal fiber (PCF) sensor for refractive index detection based on polydimethylsiloxane (PDMS) is presented in this research, as well as designs for single-channel and dual-channel structures for this PDMS-PCF sensor. The proposed structures can be used to develop sensors with biocompatible polymers. The performance of the single-channel PDMS-PCF sensor was studied, and it was found that adjusting parameters such as pore diameter, lattice constant, distance between the D-shaped structure and the fiber core, and the radius of gold nanoparticles can optimize the sensor's performance. The findings indicate that the detection range of the single-channel photonic crystal is 1.21–1.27. The maximum wavelength sensitivity is 10,000 nm/RIU with a resolution of 1 × 10 − 5 RIU, which is gained when the refractive index is set to 1.27. Based on the results of the single-channel PCF, a dual-channel PDMS-PCF sensor is designed. The refractive index detection range of the proposed sensor is 1.2–1.28. The proposed sensor has a maximum wavelength sensitivity of 13,000 nm/RIU and a maximum resolution of 7.69 × 10 − 6 RIU at a refractive index of 1.28. The designed PDMS-PCF holds tremendous potential for applications in the analysis and detection of substances in the human body in the future. [ABSTRACT FROM AUTHOR]

In this paper, a highly sensitive surface plasmon resonance sensor is proposed on the basis of a miniature tapered single-mode fiber. The sensing area of the tapered fiber is coated with graphene, silver, and titanium dioxide layer. The graphene layer is used to increase the light absorption rate, and the titanium dioxide layer is used to protect the silver layer from oxidation and improve the sensor sensitivity due to its high dielectric constant. According to the simulation results of COMSOL Multiphysics software, when the graphene is 15 layers, the silver layer is 40 nm, and the titanium dioxide is 20 nm, high-performance SPR can be obtained. The refractive index detection range of this sensor is 1.32–1.38, and its sensitivity can reach 8750 nm/RIU when the external refractive index is 1.38. The research results have potential application value for the design of high-performance SPR sensors. [ABSTRACT FROM AUTHOR]

A fiber-optics tapered sensor that is covered by an electrospinning polyvinyl alcohol (PVA) nanofiber film, is demonstrated to measure humidity and temperature simultaneously. A section multi-mode fiber (MMF) was sandwiched between two leading-in and out single mode fibers (SMFs), which was further tapered down to 29 μm to promote the humidity sensitivity of the sensor. A thin layer of electrospinning PVA nanofiber film was uniformly coated on the MMF taper region by electrospinning technology. In order to promote the humidity sensitivity and mechanical strength of electrospinning nanofibers, the carbon nanotubes (CNTs) were mixed into PVA to formed PVA/CNTs composite nanofiber film. A Fiber Bragg Grating (FBG) was cascaded with the humidity sensing fiber to monitor the ambient temperature simultaneously. The addition of CNTs effectively eliminated the cracks on the electrospinning nanofiber and made it more uniform and smoother. As experimental results show, the humidity sensitivity of the sensor with PVA/CNTs film was 0.0484 dB/%RH, an improvement of 31.16% compared to that of the sensor with PVA film, for which sensitivity is 0.0369 dB/%RH. The nanofiber humidity-sensitive film constructed using electrospinning had a satisfactory humidity response, special 3D structure and extensive application prospect. [ABSTRACT FROM AUTHOR]

In this paper, a carboxymethyl cellulose (CMC)/carbon nanotubes (CNTs) composite film was manufactured and used as a good humidity sensitive material to design a humidity and temperature simultaneous measurement sensor with simple structure, high sensitivity and fast response time. The sensor is constructed by a fiber Bragg grating (FBG) and then connected a hollow-core fiber (HCF) on the end face of which coated a CMC/CNTs hydrogel composite film. Through contrast experimental tests, the results show that the humidity sensitivity of the sensor with CMC film is 170.55 pm/%RH, while the sensitivity of the sensor with CMC/CNTs composite film is 230.95 pm/%RH. The humidity-insensitive FBG can be used to obtain accurate temperature information, and the temperature sensitivity is 26.35 pm/°C. This paper not only proves that CMC is an excellent humidity sensitive material for optical fiber sensors but also proves that carbon nanotubes can increase the humidity sensitivity of the hydrogel film effectively. This temperature and humidity simultaneous measurement sensor has a good application prospect. [ABSTRACT FROM AUTHOR]

Hydroxypropyl methylcellulose (HPMC) is a kind of water-soluble polymer material. The hydrogel formed by HPMC swelling in water is a polymer network system with a netlike cross-linked structure and it can absorb lots of water if it exposed to the water environment. Therefore, an optical fiber Fabry-Perot interferometer (FPI) relative humidity (RH) sensor based on hollow-core fiber (HCF) and HPMC hydrogel film is proposed and demonstrated. The experimental results show that the proposed sensor has a binomial humidity response and 2.25 s response time in the range of 40%–99%RH. The HPMC hydrogel with hydrophilicity, natural grid-like nanostructure and biocompatibility is an effective humidity-sensitive material for optical fiber RH sensor and has great application potential in various fields. [ABSTRACT FROM AUTHOR]