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A novel fiber-optic surface plasmon resonance (SPR) hydrogen sulfide gas sensor based on silver/3-aminpropyltriethoxysilane/cuprous oxide modified graphene sheets (Ag/APTES/ ${\text{Cu}}_{x}\text{O}$ (${x}=1$ , 2)-MGS) composite membrane coated no-core fiber (NCF) was proposed and fabricated. The NCF is sandwiched between two segments of multi-mode fiber (MMF), forming the fiber-optic sensing unit with MMF1-NCF-MMF2 structure. The comparative experiment of sensing performance of two sensors coated respectively by Ag/APTES and Ag/APTES/ ${\text{Cu}}_{x}\text{O}$ (${x}=1$ , 2)-MGS film is investigated in detail. The results show that the sensor with Ag/APTES/ ${\text{Cu}}_{x}\text{O}$ (${x}=1$ , 2)-MGS film has better sensing performance for hydrogen sulfide in the concentration range of 10–60 ppm. After adsorption of hydrogen sulfide, the resonance wavelength of the sensor with Ag/APTES/ ${\text{Cu}}_{x}\text{O}$ (${x}=1$ , 2)-MGS film shows the red shift, and the total shift is about 132.642 nm. In the concentration range of 10–40 ppm, the sensitivity is 3385.67 pm/ppm, the detection limit is 0.56±0.12 ppm, and the response time is 27 s. The sensor has good temperature, humidity, time stability and excellent selectivity, and can be potentially used in the trace hydrogen sulfide detection. [ABSTRACT FROM AUTHOR]

A ring-shaped structure based on polymer coated no-core fiber (NCF) is presented for simultaneous temperature and pressure measurements. The sensing structure is fabricated by splicing the partially coated NCF between single-mode fibers and bending it into a loop. The anti-resonance effect is formed in the NCF and the resonant dips have wavelength shift responses to the temperature and displacement variations. It should be noted that the increase of temperature leads to a decrease in the polymer coating refractive index and changes the displacement measurement sensitivity, thus, the compensation algorithm is required to resolve this cross-sensitivity problem. Combining the ring-shaped structure with the elastic diaphragm encapsulation can convert seawater pressure into structural deformation displacement to achieve pressure measurement. The experimental and simulation results show that this sensor offers a high temperature sensitivity of −5.098 nm/°C with the resolution of $2\times 10^{-4}$ °C and a pressure sensitivity of −2.368 nm/MPa with the resolution of $0.4\times 10^{-3}$ MPa. In addition, the sensing performances could be changed by adjusting the NCF size and the ring-shaped structure diameter, which enables this sensing structure to have a broader application potential for seawater parameter measurement. [ABSTRACT FROM AUTHOR]

In this work, we thoroughly evaluate different types of lateral-offset Mach-Zehnder interferometers (MZIs) to search for the optimized design. Three different structures (SNS, SMNMS, and SNNNS. S: single-mode fiber; N: no-core fiber; M: multi-mode fiber) are proposed and their performances are compared numerically. Besides, for the SNNNS sensor, the effect of different no-core fiber (NCF) diameters on the sensor performance is discussed. The numerical analyses demonstrate that the SNNNS sensor with NCF diameter of $61.5{\mu m}$ shows the best performance among all the sensors. The experimental results confirm that, when compared with the SNS sensor, the SNNNS sensor is insensitive to the lateral-offset distance. It ensures an excellent interference performance within a large offset range, which facilitates the sensor fabrication. The optimized design of the sensor device shows the potential integration applications in the ultra-low concentration biomolecule detection field. [ABSTRACT FROM AUTHOR]

A singlemode-multimode-singlemode (SMS) fiber structure consists of a short section of multimode fiber fusion- spliced between two SMS fibers. The mechanism underpinning the operation of an SMS fiber structure is multimode interference and associated self-imaging. SMS structures can be used in a variety of optical fiber systems but are most commonly used as sensors for a variety of parameters, ranging from macro-world measurands such as temperature, strain, vibration, flow rate, RI and humidity to the micro-world with measurands such as proteins, pathogens, DNA and specific molecules. While traditional SMS structures employ a short section of standard multimode fiber, a large number of structures have been investigated and demonstrated over the last decade involving the replacement of the multimode fiber section with alternatives such as a hollow core fiber or a tapered fiber. The objective of replacing the multimode fiber has most often been to allow sensing of different measurands or to improve sensitivity. In this paper, several different categories of SMS fiber structures, including traditional SMS, modified SMS and tapered SMS fiber structures are discussed with some theoretical underpinning and reviews of a wide variety of sensing examples and recent advances. The paper then summarizes and compares the performances of a variety of sensors which have been published under a number of headings. The paper concludes by considering the challenges faced by SMS based sensing schemes in terms of their deployment in real world applications and discusses possible future developments of SMS fiber sensors. [ABSTRACT FROM AUTHOR]

We describe and demonstrate a liquid level sensor by parallel connection of two liquid level sensors that consists of single-mode-no-core-single-mode fiber structure followed by a fiber Bragg grating. The parallel connection can extend measurement range of liquid level. The structure parameters are optimized and the performance of the sensor is experimentally demonstrated. Results show that the sensor can achieve a linear sensitivity of 0.196 dB/mm within the liquid level range of 0–59 mm and 0.233 dB/mm within 59–117 mm. It has great potential in industrial applications due to its simple structure and extended measurement range, also it can be applied in multi-point measurement. [ABSTRACT FROM PUBLISHER]

In this paper, we propose and demonstrate a compact dual-parameter sensor for magnetic field intensity and temperature based on the singlemode no-core singlemode fiber. The no-core fiber (NCF) is coated with the magnetic fluid to detect the magnetic field and temperature simultaneously. The fundamental mode light launched from the singlemode fiber (SMF) will be decomposed into high-order modes lights in the NCF, and then, the high-order modes lights will finally interfere in the exit SMF. Because different interference dips have different sensitivities to the magnetic field intensity and temperature, the cross sensitivity of the magnetic field intensity and temperature can be effectively eliminated by monitoring two discrete interference dips. For the two dips monitored in the experiment, the proposed sensor has the magnetic field sensitivities of 7.43288 and 6.20037 pm/Oe, respectively, and the temperature sensitivities of −0.2469 and −0.28667 nm/°C, respectively. The proposed sensor is compact and easy to setup, and has good potential in applications. [ABSTRACT FROM PUBLISHER]

A fiber-optic strain and curvature sensor based on no-core fiber has been proposed and demonstrated. The sensor is fabricated using a multimode fiber without cladding, known as the no-core fiber with a thinner diameter. The jointing point between the no-core fiber and single-mode fiber is a taper, which will improve the sensitivity of the sensor. The peak wavelength shift of the sensor exhibits an excellent response for strain and curvature changes. [ABSTRACT FROM PUBLISHER]