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A novel and in-line fiber low-frequency vibration sensor based on Butterfly-Shape Mach-Zehnder Interferometer (BSMZI) is proposed and demonstrated experimentally. The sensing element is a tapered hollow-core fiber (HCF) sandwiched between two single-mode fibers (SMFs). The frequency measured by the Butterfly-Shape vibration sensor can well match with the applied frequency, and the presence of the higher harmonics can verify that the sensor does not distort the measured vibration signal. The maximum relative error of vibration frequency is 0.27%. The intensity of vibration signal (of the fiber sensor) is linearly proportional to the driving power of vibration platform. The vibration measurement sensitivity is 13.575 dB/w in the range of 0.1 w to 0.5 w under a constant vibration frequency of 50 Hz, and the linear fitting coefficient is 0.9556. The proposed sensor has a negligible temperature sensitivity in the range of 30.3 °C–69.5 °C. Because of its compact structure, easy preparation, low production cost, high frequency measurement accuracy of low-frequency vibration, and good linearity of vibration sensing, the proposed BSMZI sensor has potential application prospect in low-frequency vibration sensing field. [ABSTRACT FROM AUTHOR]

An optical fiber axial contact force sensor based on bubble-expanded Fabry–Pérot interferometer (FPI) is investigated in this paper. The FPI is packaged as a reflective sensing probe to measure the axial contact force which is applied on the end of sensing probe. To the best of the authors’ knowledge, this is the first time that intrinsic optical fiber FPI is used for axial contact force measurement, which has potential in application fields such as robotics. The sensing probe based on bubble-expanded FPI exhibits a high axial contact force measurement sensitivity of −750.17 pm/N, which is 3 times higher than that of the sensing probe based on traditional rectangular FPI fabricated in this work. This experimental results are well explained by the simulation analysis using Comsol software. The proposed optical fiber axial contact force sensor has advantages of compact size, simple structure and high sensitivity. [ABSTRACT FROM AUTHOR]

A novel Mach–Zehnder Interferometer (MZI) formed by cascading two vase-shaped tapers in a single mode fiber (SMF) is proposed in this work. The vase-shaped taper is fabricated by fusion splicing a fiber sphere with a fiber tip by applying strong arc discharge. The curvature sensing characteristic of the proposed vase-shaped taper-based MZI is experimentally investigated, displaying that the interference spectrum has a blue shift with the increase of applied curvature. The sensor realizes a large range measurement of curvature from 0.9284 m −1 to 4.0470 m −1 with sensitivities of −8.41 nm/m −1 and −16.72 nm/ m −1 in the curvature range of 0.9284 m −1 to 2.4564 m −1 and 2.6025 m −1 to 4.0470 m −1 , respectively. Its temperature-curvature cross-sensitivities are −0.0021 m −1 / °C and −0.0011 m −1 / °C in the two measurement ranges, which are lower than the corresponding curvature resolutions which are 0.0024 m −1 and 0.0012 m −1 . The proposed sensor exhibits the advantages of low cost, negligible temperature cross-sensitivity, fine curvature sensitivity and large measurement scale. [ABSTRACT FROM AUTHOR]

All-fiber Mach-Zehnder interferometers (MZIs) working as curvature sensors have been attracting increasing attention. However, previously reported MZI-based curvature sensors with offset or abrupt-taper structures suffer from weak mechanical strength and low curvature sensitivity. In this letter, a robust and highly-sensitive MZI-based curvature sensor formed by cascading two up-tapers in a single mode fiber (SMF) is proposed and experimentally demonstrated. By optimizing structural parameters of the MZI both in simulation and in experiment, a high quality interference spectrum with a maximum extinction ratio (ER) of around 20 dB is obtained, which is crucial in curvature sensing with spectrum intensity variation and interference dip identifiability being considered. Experimental results show that a high curvature sensitivity of −35.41 nm/m −1 is obtained in the range of 0.6846 m −1 – 1.0606 m −1 , which is 2.4 times higher than that of the interferometer with single-mode-multimode-single-mode (SMS) structure. The two up-tapers, featured by great mechanical strength, are fabricated by only fusion pushing together a whole SMF without cleaving procedure, contributing to excellent repeatability and consistency in the sensor fabrication process. Such an all-fiber sensor exhibits advantages of simple configuration, ease of fabrication, excellent mechanical strength, low cost, and high curvature sensitivity. [ABSTRACT FROM AUTHOR]

Abstract: A planar, valveless, microfluidic pump using electrostrictive poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] based polymer as the actuator material is presented. P(VDF-TrFE) thick films having a large electrostrictive strain ∼5–7% and high elastic energy density of 1J/cm3 have been used in a unimorph diaphragm actuator configuration. The microfluidic pump was realized by integrating a nozzle/diffuser type fluidic mechanical-diode structure with the polymer microactuator. The P(VDF-TrFE) unimorph diaphragm actuator, 80μm thick and 2.2mm×2.2mm in lateral dimensions, showed an actuation deflection of 80μm for an applied electric field of 90MV/m. The microfluidic pump could pump methanol at a flow rate of 25μl/min at 63Hz with a backpressure of 350Pa. The flow rate of this pump could be easily controlled by external electrical field. Two different sizes of nozzle/diffuser elements were studied and the pumping efficiency of these structures is 11 and 16%, respectively. [Copyright &y& Elsevier]

Schematics of the bare and the PDMS-coated in-line microfiber MZI for RI and temperature sensing are shown in Fig. 1 (a) and (b), respectively. The microfiber MZI which is fabricated by non-adiabatically tapering a single mode fiber is composed of two abrupt tapered regions and a uniform waist region. When the fundamental HE 11 mode is propagating through the first abrupt tapered region, only symmetrical high order modes (HE 1m) can be excited owing to the symmetry of the abrupt tapered regions. Besides the fundamental HE 11 mode, only the high order HE 12 mode is excited by the fabricated microfiber whose taper waist diameter is 4.8 μm. The mode profiles of HE 11 mode and HE 12 mode are shown in Fig. 1 (c) and (d). These two modes interfere with each other at the second abrupt tapered region, forming dual-path interference. • An in-line microfiber MZI is demonstrated for ultrasensitive surrounding RI and temperature measurement. • An ultrahigh RI sensitivity of 24,209 nm/RIU and a high temperature sensitivity of -2.47 nm/℃ are experimentally achieved. • By embedding this microfiber MZI into PDMS, the temperature sensitivity is improved from -2.47 nm/℃ to about 8.33 nm/℃. An in-line microfiber Mach-Zehnder interferometer (MZI) is demonstrated for ultrasensitive refractive index (RI) and temperature measurement by operating at two sides of the dispersion turning point (DTP), respectively. An ultrahigh RI sensitivity of 24,209 nm/RIU (RI unit) around 1.3320 and a high temperature sensitivity of -2.47 nm/℃ are experimentally achieved by a microfiber MZI with taper waist diameter of about 4.8 μm. By embedding this microfiber MZI into polydimethylsiloxane (PDMS), the temperature sensitivity is improved from -2.47 nm/℃ to about 8.33 nm/℃. The positive temperature sensitivity of this PDMS-coated microfiber MZI and the negative thermo-optic coefficient of PDMS show that this microfiber MZI has a negative RI sensitivity around the material RI of PDMS (about 1.405), which indicates that the microfiber MZI works at two sides of the DTP for RI measurement and temperature measurement, respectively. The PDMS-coated microfiber MZI could achieve a temperature measurement resolution of about 0.0024 ℃ if the resolution of the optical spectrum analyzer were 0.02 nm, making it suitable for temperature measurement applications with high precision requirement. The bare microfiber MZI is promising for liquid analytical measurement in fields like biochemistry for its advantages of ultrahigh sensitivity, small size, and little sample consumption. [ABSTRACT FROM AUTHOR]

A miniature and highly sensitive optic fiber temperature sensor using a PDMS-filled air-microbubble Fabry-Perot (FP) interferometer (PAFPI) in a hollow-core fiber (HCF) is proposed. The sensor is fabricated by fusion splicing a single mode fiber (SMF) with a HCF, which is filled with polydimethylsiloxane (PDMS) by capillary effect, to form an air microbubble cavity. As far as we know, this is the first time that PDMS is applied to fill the hollow core fiber. There are three main reflected surfaces in the PAFPI sensor, and the superimposed interference spectrum of double FPI (a thin FPI and a thick FPI) is formed. Hence, the proposed sensor combines two advantages that are the large free spectral range (FSR) of the thin FPI and the high resolution of the thick FPI, which improve the resolution of spectral demodulation while ensuring a large dynamic range. Experimental results show that the sensor has the high temperature sensitivity of 2.7035 nm/℃ with a high linear response (R-square: 0.9962) in the range of 51.2–70.5 ℃, which is almost three orders larger than that of the conventional all-fiber air-cavity FP temperature sensors (about 10 pm/℃). The stability experiment is also carried out, and the maximal variations of the wavelength shift and the extinction ratio of the interference fringes are 20.3 pm and 0.1262 dB, respectively, for a long-term testing. Therefore, it may be applied to the surrounding temperature sensing. [ABSTRACT FROM AUTHOR]

Highlights • A probe-type relative humidity sensor was proposed and developed by combination of a U-shaped microfiber coupler and a polyvinyl alcohol coating. • The PVA overlay coated on the outer surface of the waist region of MFC which can ensure the MFC structure not be destroyed in the process of bending into U-shaped and the humidity sensitive will be further increased. • The RH sensor also displays an excellent reproducibility to humidity sensing experiment compared sensing performance of two almost identical U-shaped MFC samples. • Experiment results indicated that the proposed sensor exhibited a good linear relationship between the wavelength and relative humidity over the 15%–85%RH range and which also exhibited sensitivity are about 318.1 pm/%RH. • And temperature experiment results showed that the temperature sensitivity of the proposed sensor is about 13.9 pm/°C over the 20 °C to 50 °C rang, which indicated that the proposed sensor has the performance of being low temperature sensitive. Abstract A probe-type relative humidity (RH) sensor was proposed and developed by combination of a U-shaped microfiber coupler (MFC) and a polyvinyl alcohol coating. Optical MFC is considered as an excellent kind of humidity sensor due to its highly sensitive to the environmental RI changes. By covering one layer of PVA film onto the surface of the waist region of the MFC, the sensitive of the proposed sensor was further increased. Experiment results indicated that the proposed sensor exhibited a good linear relationship between the wavelength and relative humidity over the 15%–85%RH range and which also exhibited sensitivity are about 318.1 pm/%RH. And temperature experiment results showed that the temperature sensitivity of the proposed sensor is about 13.9 pm/°C over the 20 °C to 50 °C rang, which indicated that the proposed sensor has the performance of being low temperature sensitive. [ABSTRACT FROM AUTHOR]