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A novel all-fibre highly sensitive strain sensor based on polarization-maintaining photonic crystal fibre (PMPCF) is proposed and demonstrated experimentally. The sensing structure is formed by splicing a segment of PMPCF between two segments of thin core fibres (TCFs). Since the responses of the resonance dips induced by different order cladding modes interference with core mode are different, the strain sensitivity can be obtained by monitoring the shifts of the resonance dips. The experimental results show that the sensitivity of strain of the MZI is 4.03 pm/µϵ within the strain range from 0 µϵ to 1600 µϵ, respectively. And the temperature characteristics are also researched. This type of sensor has outstanding advantages of convenient manufacture, high-cost efficiency and insensitivity to temperature, so it has potential application prospects in physical, biological and chemical sensing. [ABSTRACT FROM AUTHOR]

• Fiber-reinforced cementitious composites (FRCCs) columns under reversed cyclic loading were tested. • Impact of fiber dosage and the combination proportion of polyvinyl alcohol (PVA) and steel(ST) fibers on the seismic behavior of columns were investigated. • The cracking behavior, ductility, load-carrying capacity, stiffness degradation, energy-dissipation capacity, and strain profiles of the reinforcements were evaluated. • FRCCs made of 1% PVA and 1% ST fibers are better than traditional engineering cementitious composites (ECC) for engineering applications. This study aims to investigate the seismic performance of reinforced cementitious composites columns strengthen by different fibers addition strategies. Six fiber-reinforced cementitious composites (FRCCs) columns are tested under reversed cyclic loading to explore the impact of Cementitious composites with Polyvinyl alcohol (PVA) fibers and hybrid cementitious composites simultaneously containing PVA and steel (ST) fibers on hysteresis behavior of the columns, in which fiber dosage and the combination proportion of PVA and ST fibers in composites are focused. The structural performance of the tested columns is evaluated based on the characteristics of the cracking behavior, ductility, load-carrying capacity, stiffness degradation, energy-dissipation capacity, and strain profiles of the reinforcements. The test results indicate that columns with 2 % vol. fibers compared to those including 1 % vol. fibers presented the better performance in terms of cracking behavior, ductility, and energy dissipation. The cementitious composites reinforced by 1.5 % vol. PVA + 0.5% vol. ST fibers contributes to the column characterized by optimum ductility in comparison to all columns with the other fibers. The highest energy dissipation capacity among the tested columns is observed in the case of the composites with 1 % vol. PVA + 1 % vol. ST fibers. The column with 0.5 % vol. PVA + 0.5 % vol. ST fibers manifests the better load carrying capacity over the rest of columns. [ABSTRACT FROM AUTHOR]

• A suspended core fiber (SCF) is proposed to generate photon nanojet (PNJ). The SCF is robust and reduces the difficulty of handling. Optical fibers are far more convenient in practice than microspheres (microcylinders), and they can be obtained without complicated processing. • The FWHM of the PNJ is smaller than the wavelength of the beam. • The PNJ based on the SCF is more stable in the experiment and the annular cladding acts as a protective layer to protect the PNJ from the external environment. The photonic nano-jet (PNJ) generated by the suspended core fiber (SCF) is proposed and experimentally demonstrated. Gaussian light irradiates the suspended core fiber, the PNJ is formed at the shadow-side surface of the suspended core. The measured results show that the full-width half-maximum (FWHM) of the PNJ is smaller than the incident light wavelength, and the propagation distance is several times that of the light wavelength. The experimental results are in a good agreement with the theoretical calculations. As the incident wavelength or the fiber core diameter decreases, the FWHM and decay length of the PNJ are significantly reduced. The FWHM of 0.73λ is achieved. The calculation results show that the SCF-based PNJ can achieve non-contact capture of a single nanoparticle. Suspended core fiber is easy to fabricate, simple and convenient to operate experimentally, and can produce a more stable PNJ that is less contaminated. Fiber-based PNJs offer new applications in particle capture and biophotonic sensing. [ABSTRACT FROM AUTHOR]

• An intrinsically secure fiber optic MS monitoring system for rockburst is developed. • Performance of the optical system is superior to commercialized electrical system. • A large number of effective MS signals have been obtained in field tests. By capturing the micro-crack signals of rock mass structure, the microseismic (MS) monitoring technology is a good candidate for the forecasting and early warning of dynamic disaster. In this paper, MS sensors based on fiber optic interferometric scheme are studied and fabricated, and authors develop an 8-channel highly sensitive fiber optic MS system based on space division multiplexing technology to monitor the whole process of rock mass from micro-fracture to macro-damage. Field test of the system is carried out in Hanjiang River to Weihe River Water Diversion Project. The results show that it can realize continuously monitored with high accuracy and reliability in the tunnel and obtain the characteristic of temporal-spatio-strong of MS events, which are superior to the commercialized electrical monitoring equipment. This work shows that using fiber optic interference technology to develop accelerometer for MS monitoring system is both advantageous and feasible with the character of intrinsically safe. [ABSTRACT FROM AUTHOR]

• A novel high spatial resolution quantum dots (QDs) optical fiber micro-probe temperature sensor is developed. • The sensor can high-efficiently excite and collect fluorescence. • The sensor production only requires 400 pL of QDs ink, which greatly saves expensive QDs materials and improves the spatial measurement accuracy. • The sensor based on selective etching and fiber end-face inkjet printing has a simple structure and good consistency, which has great application potential. A novel quantum dots (QDs) optical fiber micro-probe temperature sensor fabricated using selective etching and fiber end-face inkjet printing is proposed. The high-efficiency fluorescence excitation and collection of QDs micro-probe (QMP) are enabled using ingenious combination of controllable selective etching and precise inkjet printing. The production of the micro-probe only requires 400 pL of QDs ink. The small sensing point significantly saves expensive QDs materials and improves spatial measurement accuracy. The fabricated QMP sensors exhibit outstanding consistency and fluorescence stability. High sensitivity of 113 pm/°C and good repeatability are obtained. The performance of the QMP sensor is demonstrated by comparing it with that of an infrared thermometer. The proposed sensor provides a new fluorescence sensing strategy that allows the design of high-spatial-resolution sensors with stable and reliable performance and offers a great potential for medical diagnosis, environmental measurement, and industrial production. [ABSTRACT FROM AUTHOR]

In order to control the divergence angle of the optical fiber and reduce the focal spot size of the beam, we have proposed and experimentally proved a simple and low-cost method for fabricating microlens on the end facet of the fiber, which involves only two steps: dripping and curing. We successfully fabricated hemispherical microlenses with different sizes on the fiber end facets and proved that the shape of microlens can be adjusted through multiple titration and curing processes. The measured characteristics of the beam output from a lensed fiber are in agreement with numerical simulation results. [ABSTRACT FROM AUTHOR]

A high sensitivity temperature sensor is numerically and experimentally investigated in liquid filled eccentric hole-assisted dual-core fiber (EHADCF). The sensor is constructed by cascading two single mode fibers (SMFs) with an intermediate liquid filled EHADCF segment. The light couples periodically between the center and suspended cores due to small core distance. Refractive index (RI) matching liquid with high thermo-optic coefficient is filled into the air-hole of the EHADCF as the cladding of the suspended core. The dispersion curves of the center and suspended cores of the EHADCF change with the temperature, leading to the shift of the resonance peak. The measured temperature sensitivity of the sensor is −562.4 pm/°C. In addition, the stability of the sensor is also measured. Due to high sensitivity, good stability, compact size and large temperature range, the proposed sensor shows promising potentials for temperature sensing in environment monitoring. • A novel high sensitive temperature sensor based on liquid filled fiber directional coupler is developed. • The liquid is filled into the air-hole of the eccentric hole-assistant dual-core fiber as the cladding of the suspended core and the heat-sensitive material. • Compared with other temperature sensors based on directional coupler with liquid core, the proposed sensor has a much larger temperature range. • The proposed temperature sensor has a good stability. The maximum fluctuation of the center wavelength of the resonance dip is less than ±0.1 nm. [ABSTRACT FROM AUTHOR]

• A fibre inline temperature-insensitive Fabry–Perot interferometer is demonstrated as vibration sensor. • A section of hollow core photonic crystal fibre is employed to form a cavity by a CO 2 laser fusion splicer. • The sensor is temperature insensitive (−0.04 pm/°C), high sensitive (5.04 μg/√Hz) and miniaturised. • The sensor is anticipated to have wide application prospects in microseism monitoring in coal mines. This study proposes an inline temperature-insensitive Fabry–Perot interferometer (TI-FPI) for coal mine microseism sensing based on a cantilever structure. The sensor is fabricated by splicing a section of hollow core photonic crystal fibre (HC-PCF) between a lead-in polarisation-maintaining fibre (PMF) and a multi-mode fibre (MMF) using a CO 2 laser splicer. The HC-PCF and MMF are employed as a cantilever beam. An air cavity of the TI-FPI formed by the HC-PCF is modulated via external vibration, leading to a variation in the length. Sensors with air cavities of 407 μm, 698 μm, and 1069 μm are demonstrated. The experimental results show that the lowest temperature response is −0.04 pm/°C. The flat frequency band of the acceleration response can be adjusted by the cantilever beam's length, and the best average sensitivity and resolution of the sensors are 3.45 mV/g and 0.26 mg/√Hz (g is gravity of 9.8 m/s2), respectively. The minimum resolution is 5.04 μg/√Hz at a resonance frequency of 1500 Hz. The sensor is anticipated to have wide application prospects in microseism monitoring in coal mines. [ABSTRACT FROM AUTHOR]

A low cost, compact-extrinsic Fabry–Perot interferometer (EFPI) based on a polyethylene diaphragm for vibration detection is proposed. A fiber optic Fabry–Perot accelerometer (FOFPA) with a diameter of 10.0 mm is fabricated and a silica gel is adhered to the middle of polyethylene diaphragm as a mass load to form a compact structure. Theoretical simulation, modal analysis, and experimental tests are carried out to evaluate the performance of this FOFPA. Experimental results show that the measured sensitivity and acceleration resolution are 135 mV/g and 24.4 μ g/Hz 1∕2 , respectively. The sensor has a flat frequency response in the range of 20 Hz–1.5 kHz and is expected to be used for micro vibration monitoring. [ABSTRACT FROM AUTHOR]