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This PDF file contains the front matter associated with SPIE Proceedings Volume 9157, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
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Surface plasmon resonance (SPR) has been actively researched for sensor applications. Based on the subwavelength scale enhancement of light field and its sensitivity to refractive index, SPR can be used for surface enhanced Raman spectroscopy and various bio and chemical sensors. This talk will provide comparative overview of the potentials of SPR for optical sensors and its practical limitations in implementation.
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Compact ferrule-top nano-mechanical resonators with all-fiber optical interrogation are demonstrated. The resonators comprise of a suspended multi-layer graphene film supported by a ceramic ferrule with a bore diameter of 125 μm. The mechanical resonance of the graphene film is excited and detected via a single optical fiber cable, and experimental test shows that the resonant frequency and quality factor of the resonators are in the range of 170-520 kHz and 58.4-250, respectively. The integration of graphene resonator with optical fiber transmission and interrogation would allow the development of practical fiber-optic sensors for force, mass and pressure measurements.
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We report an electric field sensor based on a charged microparticle that is optically trapped, and moved to and
fro, inside a hollow-core photonic crystal fibre (PCF). Transverse electric fields displace the particle, altering
the transmitted optical power. The transmission change is found to be linear with fields in the 0.1-50 kV/m
range, with a flat frequency response from 0.01 to ~1 kHz. In a first test, the field pattern near a multi-element
electrode was resolved with a spatial resolution of 1 mm. This unique "flying particle" sensor allows electric
field mapping over long distances (the lowest loss hollow core PCF has a 3 dB length of ~3 km) and is
suitable for inaccessible or harsh environments.
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We report the first fabrication of polarization rocking filters in a highly birefringent elliptical microfiber. The rocking filters are made by periodically heating/twisting a microfiber with an ellipticity of ~0.7 and a diameter of ~2.8 μm along its major axis. Strong input polarization suppression of ~20 dB is achieved at a resonant wavelength of ~1556.4 nm with a device length of ~3.12 mm. High-order polarization rocking filter was used to measure the refractive index with sensitivity of 32036 nm/RIU.
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We describe a novel strain sensor based on a fiber Bragg grating (FBG) ring resonator. The spectrum of this resonator consists of equally-spaced resonances, exhibiting a frequency splitting proportional to the reflectivity of the intracavity FBG. A strain applied to the FBG causes a shift of the bragg wavelength, and thus a variation of the resonance splitting. The splitting is insensitive to the thermal/strain noise affecting the fiber in the region outside the FBG. The sensitivity and resolution of the sensor are analyzed in detail, showing that a subpicostrain resolution can be easily achieved with an optimized setup.
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Additive manufacturing or 3D printing of structural components in metals has potential to revolutionise the manufacturing industry. Embedded sensing in such structures opens a route towards SMART metals, providing added functionality, intelligence and enhanced performance in many components. Such embedded sensors would be capable of operating at extremely high temperatures by utilizing regenerated fibre Bragg gratings and in-fibre Fabry-Perot cavities.
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We proposed and experimentally demonstrated a novel tapered polarization-maintaining fiber (PMF) sensor based on analysis of polarization evolution. The unique structure of the tapered PMF demonstrates extraordinary polarization characteristics under external disturbance such as twists and magnetic fields, exhibiting great advantages of compactness, high sensitivity, and versatility.
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A differential extrinsic optical fiber Fabry-Perot based pressure sensor has been developed and benchmarked against a conventional piezoresistive Kulite pressure sensor. The sensors were placed on the fuselage of a 1:10/3 sub-scale model of a Scottish aviation Bulldog, which was placed in a wind-tunnel. Pressure tappings that surrounded the sensors aided the mapping of pressure distribution around this section of the fuselage. The results obtained from the fibre optic pressure sensor are in good agreement with those obtained from the Kulite and from the pressure tappings.
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Multicore optical fibre can be used to implement multidimensional optical fibre sensors. In this paper, an array of four multiplexed FBGs is inscribed in a multicore optical fibre in order to obtain a multipoint curvature sensor. An improved FBG inscription technique is used in order to mitigate the several issues that arise during the inscription of FBGs in this kind of optical fibres. The optical fibre sensor is described and theoretically analysed in order to obtain the magnitude and direction of the curvature and also the strain produced by external forces.
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A bench-top resonator fiber optic gyroscope (RFOG) was assembled and tested, showing encouraging progress toward
navigation grade performance. The gyro employed a fiber length of 19 meters of polarizing fiber for the sensing coil
which was wound on an 11.5 cm diameter PZT cylinder. A bias stability of approximately 0.1 deg/hr was observed over
a 2 hour timeframe, which is the best bias stability reported to date in an RFOG to our knowledge. Special care was
taken to minimize laser phase noise, including stabilization to an optical cavity which was also used for optical filtering,
giving angle random walk (ARW) values in the range of 0.008 deg/rt-hr. The ARW performance and bias stability are
within 2x and 10x, respectively, of many civil inertial navigation grade requirements.
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We report on an all fiber polarimetric optical detector system suitable for sensor applications that rely on fast polarization measurements. Our device exhibits an RF bandwidth of 500 MHz and an optical calibration bandwidth of over 30nm in the S-C-L-bands (1460-1625 nm) and above, with minimal PMD, PDL, and return loss when used in-line. A set of automated self-calibration procedures ensure high accuracy without the need for external polarization optics or reference polarimeters. We integrated our polarimeter into an acquisition systems capable of measuring fast polarization rotation events over long period of time with 250 MS/s peak sampling rate.
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We report an experimental fiber optic gyroscope (FOG) utilizing a 1085-m coil of 8-cm diameter driven with a laser of 10- MHz linewidth, with a record rotation-rate noise as low as 0.2 deg/h/√Hz and a drift below 0.038 deg/h. Simulations and comparison to the measured performance of a similar 150-m FOG show that the noise is limited approximately equally by coherent backscattering and polarization coupling in the sensing coil, and unaffected by the Kerr effect.
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Principal and Independent Component Analysis are used in this paper to provide a discrimination among those species participating in the plasma of welding spectra. This approach might be useful for spectral line identification for emission spectroscopy, especially for online welding diagnostics and laser induced breakdown spectroscopy. In this case, the feasibility of this proposal will be analyzed by means of arcwelding experiments where different plasma species will be separated by the proposed processing scheme.
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This work presents a demonstration of the potential of fiber cavity ring-down for remote sensing, by using an OTDR to send impulses down ~20 km of optical fiber at the end of which the fiber ring cavity was placed. The OTDR showed almost no losses in the fiber, so other ring-down cavities could be spliced along the same fiber. To study the sensitivity of the cavity ring an intensity sensor based on a taper was placed in the ring and glued to a translation stage. A displacement of the stage imposes a curvature on the taper and an associated loss. The configuration had a sensitivity of (11.8±0.5) μs/mm.
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We have developed an 8-element fibre laser seabed array demonstrating state-of-the art performance characteristics for a fibre laser sensing system and highlighting the advantage this technology provides in the underwater sensing domain. The system employs sea-state-zero sensitivity hydrophones with a flat acoustic response over a bandwidth exceeding 5kHz and very low inertial sensitivity. The system contains no outboard electronics and few metal components making it extremely light, compact, and low complexity. The array may be deployed up to 4 km from a land or sea based platform to a depth of up to 80m. Power delivery and telemetry for all 8 sensors is achieved via a single 2mm diameter optical fibre cable weighing less than 5kg per km. We report here results of the first field trials of this system.
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A fibre optical sensor for the simultaneous measurement of pressure, temperature and refractive index has been demonstrated. The sensor is based on a multi-cavity design and employs a monolithic sapphire transducer element.
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Novel FBG sensors based on cladding microstructures are proposed, which include micro-holes array, single or double spiral and straight groove types. Through depositing different sensitive film, the microstructured FBG sensors can be applied to fiber optic magnetic field sensor, hydrogen sensor and humidity sensor. As a developing example, a spiral type microstructured FBG magnetic field sensor is demonstrated. The testing results show that, the sensitivity of the spiral types probe can be promoted 4-6 times more than that of the non-microstructured standard FBG probe. The double spiral probe is better than the single spiral type.
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The fluctuation of polarization may cause wrong demodulation results in high-resolution static-strain sensing based on FBG-FP. This paper presents a polarization-insensitive demodulation algorithm using time-wavelet energy spectrum for single mode fiber (SMF) based FBG-FP sensor. This method can eliminate the influence of polarization instability effectively. Time-wavelet energy spectrum is calculated to get the energy distribution of the reflectance spectrums of FBG-FP on the timeline. The maximum value of the energy distribution is used to obtain the strain signal. In the laboratory, a high-resolution strain demodulation result without polarization controller is obtained.
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In this paper, π-phase-shifted FBG (π-FBG) is used for high-resolution static-strain sensing. A novel laser tuning technique based on triangle-wave voltage driver is proposed to improve wavelength scanning stability of tunable laser. And a static-strain demodulation algorithm based Gauss curve fitting and peak detection is tested. As the reflectance spectrum of π-FBG have high signal-to-noise ratio, a static-strain resolution of 0.83 nε is obtained in a vacuum environment, which shows that the proposed system have a good application prospect for geophysics applications.
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This paper introduces a highly-sensitive fiber optical acoustic emission (AE) sensor and a parameter analysis method aiming at concrete structure health monitoring. Distributed feedback fiber-laser (DFB-FL), which is encapsulated to have a high acoustic sensitivity, is used for sensor unit of the AE sensor. The AE signal of concrete beam in different work stages, based on the four-point bending experiment of the concrete beam, is picked up, and the relationship between the concrete beam work stages and the AE parameter is found. The results indicate that DFB-FLAES can be used as sensitive transducers for recording acoustic events and forecasting the imminent failure of the concrete beam.
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The polarimetric sensing characteristics of multi-mode-fiber based tilted fiber Bragg grating (MMF-TFBG) have been analyzed and experimentally demonstrated. The physical “enlarged” fiber core enables the tilted gratings to excite multi high-order core modes with significantly different polarization dependence and well-defined “comb” profiles which are spectrally separated at different wavelength. Orientation-recognized twist/rotation measurement (-90o to 90o) has been achieved with sensitivity of 0.075 dB/deg by using a cost-effective double-path power detection (power monitoring of two orthogonal-polarimetric odd core-modes, i.e. LP11 and LP12).
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A new technique to distributedly monitor intense current along high energy electric cables is presented and experimentally validated. The new technique is based on the distributed polarization measurement of Rayleigh backscattered light and on Faraday rotation of polarization induced by the electric current owing in the cable. While current monitoring by Faraday rotation in optical fibers is among the first examples of optical fiber sensors, this is the first time, to best of our knowledge, that a distributed current sensor is implemented. Preliminary experimental tests have been performed on a 40-m-long electric cable, with currents varying from 0 kA to 2:5 kA, using standard telecommunication fibers non-optimized to the specific aim. Results confirm the viability of the approach.
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An inline fiber-optic micro Fabry–Perot (MFP) cavity and a short fiber Bragg grating (SFBG) is overlapped to form a highly integrated MFP/SFBG sensor for simultaneous measurement of temperature and strain under high temperature (300°C). The F-P cavity is fabricated on an all-silica fiber by using the 157nm laser micro-machining technique while the SFBG is written on a GeO2 doped high temperature photon sensitive fiber at the same position of the MFP cavity. As the MFP cavity and the SFBG have different sensitivity coefficients to temperature and strain, they can be utilized for realization of dual parameters measurement. Experimental results show that simultaneous measurement of strain and temperature is achieved under high temperature up to 300°C.
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A highly sensitive current sensor based on an optical microfiber loop resonator (MLR) incorporating low index polymer is proposed and experimentally demonstrated. The microfiber with a waist diameter of 1 μm is wrapped around the nicrhrome wire with low index polymer coating and the optical MLR is realized. The use of the microfiber and low index polymer with high thermal property can effectively improve the current sensitivity of the proposed MLR-based sensing probe to be 437.9 pm/A2, which is ~10 times higher than the previous result.
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A specific temperature and pressure optical fiber transducer is presented in this paper. By using a customized fiber reinforced plastic membrane with embedded Fiber Bragg Gratings, the fluid pressure and temperatures changes are converted in optical wavelength displacements. The membrane and the transducer custom design allows a suitable measurand discrimination. The transducer is implemented, characterized and calibrated. Its feasibility to be used on large diameter water pipes has been successfully validated by means of field trials. Many of these transducers will be optically multiplexed to monitoring these infrastructures.
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We investigate the effect of a waist diameter of a polarization-maintaining fiber (PMF) on ambient index and temperature sensitivities by configuring a Sagnac loop interferometer. To make the PMF sensitive to external index change, a micro-tapering technique is exploited to fabricate the tapered PMF. The Sagnac loop interfoermeter is fabricated by using the tapered PMF with various waist diameters. The reduction of the PMF diameter results in the enhancement of the ambient index sensitivity of the tapered-PMF-based Sagnac interferometer. However, the temperature sensitivities of the proposed Sagnac interferometers are not changed by reducing the waist diameters of the PMFs.
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A simple technique for simultaneous measurement of the concentration of ethylene glycol and temperature by using a hybrid Sagnac interferometer is proposed and experimentally demonstrated. The hybrid Sagnac interferometer is configured by inserting a long-period fiber grating (LPFG) and a D-shaped polarization-maintaining fiber (PMF) into a Sagnac interferometer. By partially removing the cladding of the PMF, we make the Sagnac interferometer sensitive to ambient index by exposing the core region of the D-shaped PMF to external circumstance. The determinant of the sensitivity matrix of the proposed sensing probe is improved by using the negative temperature sensitivity of the LPFG.
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A Fiber Bragg Gratings(FBG) have been used as a sensor head for measurement of temperature and static strain. However, a standard FBG sensor, which is constructed on single-mode fiber, cannot simultaneously measure both temperature and static strain since the sensor has cross-sensitivity between them. The cross-sensitivity problem can be solved by using an FBG constructed on a polarization maintaining fiber(PM-FBG) instead of a standard FBG. In this paper, we report improvement on the sensing resolution for the simultaneous measurement of temperature and static strain. An Fabry-Perot interferometer constructed with PM-FBG(PM-FBG-FPI) is introduced as a sensor head. The fine structure of an PM-FBG-FPI reflection spectrum enables high resolution detection of wavelength shifts. The resulting high resolution measurement is demonstrated experimentally.
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In this work, we describe improvements in the performance of fiber-bending pressure sensors by using depressed cladding erbium doped fiber (DC-EDF). In this study, we compare the accuracy of DC-EDF sensor with bending sensor using standard single-mode fiber. Furthermore, we present a new technique to use this sensor in such way their response to pressure variation is dependent only with the amplified spontaneous emission (ASE) peak wavelength in S-band. In other words, we demonstrate that they are insensitive to the signal and pumping power variations.
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We propose a fiber-optic dynamic electric field sensor using a nematic liquid crystal (NLC) Fabry-Perot etalon and a
wavelength-swept laser. The transmission wavelength of the NLC Fabry-Perot etalon depends on the applied electric
field intensity. The change in the effective refractive index of the NLC is measured while changing the applied electric
field intensity. It decreases from 1.67 to 1.51 as the applied the electric field intensity is increased. Additionally, we
successfully measure the dynamic variation of the electric field using the high-speed wavelength-swept laser. By
measuring the modulation frequency of the transmission peaks in the temporal domain, the frequency of the modulated
electric field can be estimated.
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The radiation resistant sensor system for measuring deformations of the fuel channels of the RBMK-1000 nuclear power reactor is by now developed and tested. Concept of the system is the application of metal-coated radiation resistant nitrogen-doped-silica-core fiber and Bragg gratings written in it. Performance of the fiber and sensor elements measured in conditions of the extreme radiation environment inside core of operating nuclear reactors is being reported.
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A technique to enhance the response of Brillouin distributed sensors is proposed and experimentally validated. The method consists in creating a multi-frequency pump pulse interacting with a multi-frequency continuous-wave probe. The power of each pulse at a distinct frequency is lower than the threshold for nonlinear effects, while the sensor response remains given by the total power of all pulses. Distinct frequency pulses are delayed to avoid temporal overlapping and cross-interaction; this requires to smartly reconstruct the traces before photo-detection. The method is validated in a 50 km-long sensor using 3 frequencies, demonstrating a signal-to-noise ratio enhancement of 4.8 dB.
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A magnetic field sensor using a non-adiabatic tapered optical fiber (NATOF) interacting with magnetic fluid (MF) nanoparticles is proposed and experimentally demonstrated. The NATOF is surrounded by a MF whose RI changes with external magnetic field which MF is as a cladding of tapered fiber. The Output interference spectrum is shifted by the change of the applied magnetic field intensity in the range up to 44 mT with a sensitivity of -7.17×10-2 nm/mT.
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Cardiovascular health of the human population is a major concern for medical clinicians, with cardiovascular diseases responsible for 48% of all deaths worldwide, according to the World Health Organisation. Therefore the development of new practicable and economical diagnostic tools to scrutinise the cardiovascular health of humans is a major driver for clinicians. We offer a new technique to obtain seismocardiographic signals covering both ballistocardiography (below 20Hz) and audible heart sounds (20Hz upwards). The detection scheme is based upon an array of curvature/displacement sensors using fibre optic long period gratings interrogated using a variation of the derivative spectroscopy interrogation technique
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A novel magnetic field sensor consisting of magnetic fluid (MF) and etched highly birefringent fiber loop mirror (Hi-Bi FLM) is proposed in the paper. The sensor is based on the etched FLM interferometer by using the property of the controllable refractive index of MF under external magnetic field. The refractive index of MF is changed by a tunable magnetic field and the resonant dip wavelength produced by the FLM shifts correspondingly. The magnetic field intensity can be measured by detecting wavelength shift. High sensitivity of 11.31pm/Oe and a resolution of 0.1Oe are obtained for the proposed magnetic field sensor.
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We investigate the strain and temperature sensing characteristics of an inline hybrid Mach-Zehnder interferometer (HMZI) formed by splicing a short section of asymmetric twin-core photonic crystal fiber (ATC-PCF) between two single mode fibers. For fixed polarization state of input light, two cores due to their asymmetric construction strongly support the propagation of few dominant core-modes, specifically, a lowest-order, and a set of lowest- and higher-order core-modes, respectively; this leads to a unique phase difference between inter-core and intra-core mode fiber interferometers in our ATC-PCF based HMZI. Experimental results reveal that, among different orders of interferometers involved in the HMZI, the interferometer with higher-value of modal refractive index difference exhibit larger phase-shift sensitivity to the surrounding perturbations.
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FBGs respond to external pressures in ways that reflect both the strain-optic effect and the geometrical variations, both induced by the applied pressure. While the response to static isotropic pressure is quite straight forward and intuitive, the response to anisotropic shock waves is much more complex and depends also on the relative orientation between the fiber and the shock propagation direction. We describe and explain experimental results for both cases.
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The authors present the development of a opto-magnetostrictive current monitoring device intended to be used in situations where high voltages are involved. The system offers not only measurement reliability, but to be also practical and light weighted. Fiber Bragg gratings (FBG) are employed in the measurement procedure: the current is acquired using a hybrid sensor head set-up, that is, an FBG together with a magnetostrictive rod.
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We demonstrate the fabrication of the long-period fiber gratings (LPFGs) in the thinned cladding fiber (TCF) using CO2 laser. The sensing response of the gratings to surrounding refractive index has been investigated experimentally. The LPFGs written in the TCF could be used as the high sensitive refractive index sensors.
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The design and development of a plastic optical fiber (POF) macrobend temperature sensor is presented. The sensor has a linear response versus temperature at a fixed bend radius, with a sensitivity of 8.2 ∙ 10−4(ºC)−1 and a 8% non-linearity full scale error. The sensor system uses the power variation between two discrete wavelengths for auto reference purposes. An analysis for selecting operation wavelengths has been carried out in order to optimize the response of the sensor. The proposed sensor can be used in harsh environment and has a low-cost.
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Tactile sensing technology can measure a given property of an object through physical contact between a sensing element and the object. Various tactile sensing techniques have been developed for several applications such as intelligent robots, tactile interface, medical support and nursing care support. A desirable tactile sensing element for supporting human daily life can be embedded in the soft material with high sensitivity and accuracy in order to prevent from damaging to human or object physically. This report describes a new tactile sensing element. Hetero-core optical fibers have high sensitivity of macro-bending at local sensor portion and temperature independency, including advantages of optical fiber itself; thin size, light weight, flexible transmission line, and immunity to electro-magnetic interference. The proposed tactile sensing element could detect textures of touched objects through the optical loss caused by the force applied to the sensing element. The characteristics of the sensing element have been evaluated, in which the sensing element has the monotonic and non-linear sensitivity against the normal force ranged from 0 to 5 N with lower accuracy than 0.25 dB. Additionally, texture detection have been successfully demonstrated in which small surface figures of 0.1 mm in height were detected with spatial resolution of 0.4 mm.
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Study of fiber optic extrinsic Fabry-Pérot sensors utilizing state-of-the-art MEMS technology mostly focus on sensor fabrication for various applications, while the signal interrogation is still insatiable to current application. In this paper, we propose a white light path matched differential interferometer dynamic sensing system utilizing phase generated carrier demodulation scheme. A step motor with a movable mirror and a fiber-wound piezoelectric transducer string are used to act path matching and phase modulation respectively. Experimental results show that the sensing signal could be correctly recovered with low distortion and the phase noise spectrum level is less than -100 dB re. rad/√Hz above 2.5 kHz.
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We tested the long term stability of first order Sapphire Fiber Bragg gratings (SFBG) at 1400°C for a period of 28 days in air. During the whole period temperatures detected by the SFBG differed less than ±2K°C from the temperatures measured by a type B thermocouple. The spectra at the beginning and the end of the installation were identical. The reliable practical application of wavelength-multiplexed two-grating SFBG arrays for quasi-distributed sensing at very high temperatures has been demonstrated.
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A dual side hole fiber (DSHF) with a pair of large air holes is proposed for free transducer temperature sensing in the infrared region (1500–1600 nm). The results of birefringence measurement based on a sagnac interferometer showed the linear group birefringence is from 4.35×10-5 at 1500 nm, to 1.14×10-4 at 1600 nm, respectively. The group birefringence of DSHF leads to a group temperature sensitivity from 3.9nm/°c at 1501nm to 1nm/°c at 1595nm, respectively.
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Operation of an optical fiber sensor based on an in-fiber Fabry-Perot interferometer using chirped fiber Bragg gratings is examined in the pulse-position modulation scheme, especially for mechanical vibration measurement. Emphasis is placed on the ability to measure vibration of larger amplitude. Although the magnitude of vibration that can be measured with a single Fabry-Perot resonance peak is rather limited, the limitation is expected to be overcome by use of multiple resonance peaks in the operation. The experiment with five resonance peaks shows the successful operation of the sensor and therefore the validity of the method proposed.
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We demonstrate the ability of a fiber grating laser with dual-polarization, single-longitudinal-mode output to measure an extremely small mass (or transverse load). The minimum detectable mass is 0.28 milligram by reducing the noise level of the output beat signal.
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We report on the development of a point temperature sensor, based on coating tellurite onto the tips of optical fibres. By doping the tellurite glass with rare earth ions such as erbium the tip of the fibre can act as a localized temperature sensor by monitoring the upconversion emission from the ions. This sensing geometry allows the temperature to be measured with good spatial resolution, while the strong response of the rare earth ions to changing temperature provides a temperature precision of 0.1-0.3 °C over the measured range.
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Temperature stability of magneto-optic sensor at a marked transient temperature gradient has been investigated. Our experimental study leads to the conclusion that the polarized gyro architecture with two quarter-wave retarders on the opposite sides of the fiber loop of Sagnac interferometer must be used to obtain a fiber-optic current sensor with the lowdrift behavior.
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A novel magnetic field sensor by using an optical fiber Bragg grating (FBG) cascaded by a cleaved optical fiber end, which is face surrounded with magnetic fluid (MF), is experimentally demonstrated. Through Fresnel reflection (FR) of the fiber end face, side mode suppression ratio (SMSR) of reflection spectrum of the FBG is tuned by refractive index (RI) of the MF, which is sensitivity to the external magnetic field. As a result, magnetic field measurement is successfully achieved. Compared with previously reported methods based on FR of a fiber end only, it eliminates the influence of power level fluctuation of the optical source and therefore improves the measurement accuracy and stability. Furthermore, temperature can be measured simultaneously by monitoring wavelength shift of the FBG.
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Cerenkov radiation, which is produced by charged particles that pass through optical fibers with a velocity greater than that of light, is frequently regarded as a severe noise signal in a fiber-optic radiation sensor consisting of a scintillator and an optical fiber. Since the spectral range of Cerenkov radiation is very broad and covers that of light outputs from a scintillator, Cerenkov radiation generated in optical fibers is also acquired by a photodetector. However, Cerenkov radiation can be a significant signal when we measure the intensities of Cerenkov radiation generated from fixed length of optical fibers because it is one of the signals induced by interactions between radiations and optical fibers. In this study, gamma-ray induced Cerenkov radiation generated in silica and plastic optical fibers was measured in order to select an efficient optical fiber for producing Cerenkov radiation. The intensities and the spectra of Cerenkov radiation generated in the optical fibers were measured using a spectrometer. As the results, the intensities of Cerenkov radiation generated in silica and plastic optical fibers have peak wavelengths at approximately 500 nm. Also, the intensity of Cerenkov radiation obtained using a plastic wavelength shifting fiber was the highest among all sample optical fibers.
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A highly sensitive fiber-optic mechanical vibration sensor is constructed by using a cascaded long period fiber grating (LPG) based on an intensity modulation scheme. In the fabrication process, the cascaded LPG, which is composed of a pair of identical LPGs with a certain distance, is inscribed in a length of photosensitive single-mode optical fiber by means of a point-by-point technique using a KrF excimer laser. Since the sensitivity of the intensity-based LPG sensor depends on a gradient of the slope of transmittance spectrum curve as well as the strain-sensitivity of the spectral shift, the channeled spectrum of the cascaded LPG provides a highly sensitive operation for the vibration detection. In the experiment, several kinds of cascaded LPGs have been fabricated and examined in terms of the sensor sensitivity. In addition, highly sensitive mechanical vibration detection has been successfully demonstrated.
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This paper presents the study on the acoustic response of pressure compensated fiber laser hydrophones. Both a theoretical model and a finite-element model are developed to describe the acoustic response of the hydrophone. The proposed theoretical model has been preliminarily validated by an in air test of a hydrophone sample. A further analysis is also made to evaluate the sensor performances and the results offer reference for performance optimization.
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Partial discharge in elastomeric high voltage insulations is a major reason for device failure. The special challenges of the high voltage environment limit the use of conventional acoustic emission sensors. Fibre-optic sensors can cope with these challenges thanks to their optical sensing principle and the use of all-dielectric materials. In this contribution, improvements to a previously introduced design of ultrasonic fibre-optic acoustic partial discharge sensors for elastomeric insulations are presented. The improved performance of fibre-optic acoustic sensors in detecting AC partial discharge is demonstrated. Furthermore, their ability to detect low-level damage processes in elastomeric insulation under DC dielectric stress is shown to outperform the highly sensitive electrical detection method.
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In this work, we propose a compact sensor head to perform cryogenic temperature measurements based on a long-period fiber grating. The presented configuration enables the sensor to be interrogated in reflection since a phase-shifted is produced by Fresnel reflection on the end-face of the fiber, cleaved at a quarter-period separation distance from the end of the grating.
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We report an all-fiber heterodyne interferometer for the measurements of laser-induced thermoelastic deformation to estimate the Gruneisen coefficient and the optical attenuation depth of a sample. The system comprises a Q-switched Nd-YAG laser providing a nanosecond excitation pulse and an all-fiber heterodyne interferometer that measures the induced displacement of the sample surface. To evaluate the system, phantom experiments were carried out with various gelatin-based models. The results show that the attenuation depth and Gruneisen coefficient of the phantoms were about 4.256 mm and 0.568, respectively. In addition, increase of the weight fraction of gelatin led increase in the Gruneisen coefficient.
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A polling topology that employs optical switching based on the properties of erbium-doped fibres (EDFs) is used to interrogate an array of FBGs. The properties of the EDF are investigated in its pumped and un-pumped states and the EDFs’ switching properties are evaluated by comparing them with a high performance electronically controlled MEM optical switch. Potential advantages of the proposed technique are discussed.
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In this work we present an innovative method of connecting metal coated optical fibers with metal surfaces. The process is based on electrolytic reaction between copper and allows to obtain a robustand inflexible connection. Furthermore reliability tests of such fiber to metal joints have been performed, with the results of mechanical strength and temperature resistance tests presented. Additionally, as accelerated oxidation of copper at elevated temperatures is a major concern in long term temperature stability of the connection, we propose a method of slowing down the oxidation process with chemical nickel coating. Analysis of the obtained results allows us to predict that the investigated connection may find applications in various industrial optical sensors with special focus on harsh environments.
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In-fibre microcavity Fabry-Perot interferometers were constructed by splicing single mode fibre to polarisation maintaining photonic crystal fibre (PCF), with the air in the PCF pressurised to 5.000±0.005bar. The response to transverse load was characterised, along with the influence of rotational orientation and the repeatability of the fabrication process. It was found that the features of the channelled reflected spectrum exhibited a blue wavelength shift with increasing applied transverse load.
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In this work a novel optical fiber sensor based on silica microspheres array is proposed. Different sensing heads are presented and compared, differing on the number of microspheres. These structures, ranging from arrays of one to five, are spliced in series. The sensor is subjected to different physical parameters, such as strain, temperature, refractive index and bending. Depending on the number of microspheres the sensitivities to strain and bending are different. The sensor also presents a high sensitivity to temperature of 20.3 pm/°C.
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In this work we present a cost effective strain sensor based on micro-cavities produced through the re-use of optical fibers destroyed by the catastrophic fuse effect. The strain sensor estimated sensitivity is 2.22 ±0.08 pm/μƐ. After the fuse effect, the damaged fiber becomes useless and, consequently, it is an economical solution for sensing proposes, when compared with the cavities produced using other complex methods. Also, the low thermal sensitivity is of great interest in several practical applications, allowing eluding cross-sensitivity with less instrumentation, and consequently less cost.
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In this paper it is presented an all-fiber implementation of the hot-wire needle probe concept, widely used to measure the thermal properties of materials, particularly the thermal conductivity. It is based on the heating of a metal thin film deposited on the surface of the fiber induced by the coupling of laser light into the cladding via a long period grating, and determination, using a fiber Bragg grating, of the time dependence of the temperature of the surrounding medium at a fixed distance of the fiber. The medium considered in this research was the air and the results obtained indicate the feasibility of this approach and point out future developments.
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In this paper, we report the development of a reduced temperature sensitivity optical fiber sensor for refractive index measurement based on Superimposed Long-Period Gratings (SLPG) inscribed by the electric arc technique in standard fiber. The reduced sensitivity to temperature is achieved by calculation of the difference between resonance wavelengths of two guided cladding modes.
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The spatial sensitivity of an erbium doped optical fibre distributed feedback (DFB) laser to an external magnetic field is
reported. Intrinsic birefringence of the laser cavity allows lasing in two orthogonal modes. The polarisation beat frequency
between these modes is sensitive to magnetic fields aligned along the axis of the optical fibre due to the Faraday effect. The
interaction of magnetic field, generated by a permanent magnet, with the spatial mode profile of the laser is investigated.
Experimental measurements show a 3.82 MHz change in the beat frequency when a permanent magnet is scanned along
the fibre laser.
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Interferometric fiber optic based sensors, namely those based on the Fabry-Perot (F-P) configuration seem very attractive for biomechanical and biomedical applications. The present study is focused on the proof of concept of two developed FP based sensors, for high and low pressure measurements of fluids. For low pressure sensor, it was used a polymeric diaphragm in a microstrutured fiber. It was obtained a good agreement between wavelength shift and the pressure, for the two tested sensors.
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We have proposed an optical pulse correlation remote sensing technique, which has the advantages of high accuracy and good response linearity. To eliminate the impact of polarization fluctuation on sensing signals, we use a polarization scrambled pulse train (PSP), in which the polarization state of each pulse is randomized. We measure the stability of sensing signal under polarization fluctuation in optical pulse correlation sensing with the PSP light and obtain good stability. Moreover, we demonstrate tensile strain measurement using the optical pulse correlation sensing with the PSP and confirm the linear response to the tensile strain even under polarization changing.
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We have investigated the influence of side-polished multimode fiber (SPMMF) core diameters D and residual radius R (the minimum distance between side-polished surface and the center of multimode fiber) on the sensitivity of a SPMMF based refractometer. We show that the residual radius has significant influence on the refractive index (RI) sensitivity but the core diameter does not. A refractometer with a lower SPMMF core diameter has a higher sensitivity. Experimental investigations achieved a maximum sensitivity of 42.23 dB/RIU (refractive index unit) for a refractive index range from 1.300 to 1.440 for a refractometer with a SPMMF core diameter of 50 μm.
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In this work we show numerically the potential of using a metamaterial constituted by ordered arrays of silver nanowires as a sensor for refractive index changes of a surrounding dielectric medium. The results show a strong dependence of the reflectance spectrum on the refractive index of the dielectric medium.
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In this work a strain sensor based on a suspended core fiber is proposed. The sensor comprises a suspended core PCF between SMFs and is based on the multimode interference generated in these transitions. A strain sensitivity study for different sensing heads and stage separation lengths was carried out showing a sensitivity of -2.42 pm/με for the best case. Also the sensing head was tested for curvature and temperature, showing in the first case that it is insensitive to curvature effects, and secondly, that for small sensor lengths it was insensitive to temperature variations.
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We estimated the influence of polarization crosstalk in a Sagnac-type optical current transformer (OCT) against sensor sensitivity, and confirmed that temperature dependence of Faraday effect is canceled out by controlling the extinction ratio of transmission fiber with temperature change. Based on the above evaluation, we developed a temperature compensation element (TCE) consisting of metal-coated PM fiber. Its extinction ratio varies with temperature because of the difference between the linear expansions of metal and fiber. The ratio error of OCT using this TCE in the temperature range from -40°C to 80°C was within 0.1%, and satisfied the required accuracy for IEC 60044-8 class 0.2S.
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Laser pulse width is the limiting factor for high spatial resolution measurement with Raman distributed temperature sensor (RDTS). Typically a 10 ns laser pulse provides a spatial resolution of 1 m. Path delay multiplexing can be used to overcome this limitation. This paper presents formalism for two path delay multiplexing, taking into account the point response function (PRF) of the RDTS.
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In this work a simultaneous strain and temperature sensor based on a suspended core fiber is proposed. The sensor
comprises a 3mm suspended core PCF between SMFs and is based on the combination of two multimodal interferences
with different frequency fringe patterns. The interference of the both signal has different sensitivity responses to strain
and temperature. Thought a low-pass frequency filtering of the detected spectrum, the wavelength shift of the two
interferences can be measured allowing the discrimination of strain and temperature simultaneously. The resolutions of
this sensor are 0.45 ºC and 4.02 με.
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An investigation of performance of multiplexed displacement sensors based on extrinsic Fabry-Perot interferometers has been carried out. We have considered serial and parallel configurations and analyzed the issues and advantages of the both. We have also extended the previously developed baseline demodulation algorithm for the case of a system of multiplexed sensors. Serial and parallel multiplexing schemes have been experimentally implemented with 3 and 4 sensing elements, respectively. For both configurations the achieved baseline standard deviations were between 30 and 200 pm, which is, to the best of our knowledge, more than an order less than any other multiplexed EFPI resolution ever reported.
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In this paper three highly birefringent (HiBi) spun photonic crystal fibers (PCF) are fabricated and their performance are characterized for electrical current measurement. These fibers are tested by coiling them around an electric conductor using three distinct winding diameters with different turns. The results present a very good linear relation with the current and its sensitivity depends on the winding diameter and on the number of turns. For the larger winding diameter, the fiber with lower circular pitch had higher sensitivity and for the smaller winding diameter the best sensitivity result was for the fiber with higher circular pitch.
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In this paper we present a giant-area fiber-optic gyroscope (GAFOG) combining a Raman distributed temperature sensor (RDTS) for metrological monitoring of Earth rotation rate fluctuations. The GAFOG exhibits sensitivity limits in Earth rotation sensing associated to temperature variations along the fiber. Distributed temperature measurements providing an accurate fiber temperature mapping, enable tracking of the signal phase drifts. This allows reduction of the phase noise at low Fourier frequencies, and a corresponding enhancement of the Earth rotation rate variation sensitivity beyond the currently achieved 2•nrad/s for integration times of 1000 s.
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We demonstrated a high-sensitivity strain sensor based on an in-line Fabry-Perot interferometer with an air cavity whose was created by splicing together two sections of standard single mode fibers. The sensitivity of this strain sensor was enhanced to 6.02 pm/με by improving the cavity length of the Fabry-Perot interferometer by means of repeating arc discharges for reshaping the air cavity. Moreover, such a strain sensor has a very low temperature sensitivity of 1.06 pm/°C, which reduces the cross-sensitivity problem between tensile strain and temperature.
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We use digitally enhanced heterodyne interferometry to measure the stability of optical fiber laser frequency references. Suppression of laser frequency noise by over four orders of magnitude is achieved using post processing time delay interferometry. This approach avoids dynamic range and bandwidth issues that can occur in feedback stabilization systems. Thus long fiber lengths may be used resulting in better frequency discrimination, a reduction in spatially uncorrelated noise sources and an increase in interferometer sensitivity. We achieve an optical stability of 30 Hz/√Hz for quasi-static frequencies as low as 20 mHz.
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We have proposed a novel magnetic field sensor based on orthogonally-polarized dual-frequency fiber laser and Faraday effect. In this paper, we propose a method to enhance the sensitivity of such Faraday effect based heterodyning fiber laser magnetic field sensor by tuning the intra-cavity intrinsic linear birefringence. We demonstrate that the sensitivity to magnetic field intensity is inversely proportional to the linear birefringence. A CO2-laser treatment is therefore proposed to tune the intra-cavity linear birefringence. With CO2-laser treatment to lower the intra-cavity linear birefringence, the sensitivities of heterodyning fiber laser sensors to magnetic field can be enhanced.
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We demonstrate a temperature sensor with ~ 9 times sensitivity enhancement that consists of two cascaded sagnac interferometers and works analogously to a Vernier scale. Experimental results show that the temperature sensitivity is increased from -1.46 nm/°C based on a single sagnac configuration to -13.36nm/°C.
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We propose a refractive index insensitive temperature sensor based on hollow annular core fiber (HACF) Mach-Zehnder interferometer (MZI). The HACF is composed of a large-diameter air hole, an annular core around the air hole and a cladding. The MZI is fabricated by inserting a short section of the HACF between two short multimode fibers, and the interference occurs between the light beams transmitting along the air hole and the annular core of the HACF. Experimental results show that the MZI is insensitive to external refractive index and has temperature sensitivity of 30 pm/°C.
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We propose an ultra-high sensitive temperature sensor based on multimode fiber (MMF) Mach-Zehnder interferometer (MZI). The multimode fiber MZI is composed of a short section of MMF inserting between another two pieces of MMFs with large lateral offset. The sensing head is packaged in a capillary which is filled with glycerol-water solution. At the offset splice interface, part of the light in the lead-in MMF is coupled into the glycerol-water solution around the sensing MMF and the remainder propagates along the cladding of the sensing MMF. Due to the large thermo-optic coefficient of the glycerol-water solution, the transmission spectrum of the MMF-based MZI shift quickly with temperature variation. Experimental results show that the temperature sensitivity is as high as 8.23 nm/°C.
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A polarimetric Distributed Bragg Reflector (DBR) laser sensor in a low birefringent Er-doped fiber has been proposed. The spectral overlap of two uniform fiber Bragg gratings (FBG) has been employed as filtering technique to achieve a Single Longitudinal Mode (SLM) regime. By measuring the RF beat frequency between the two orthogonal polarized lasing modes and the absolute wavelength of one mode, both strain and temperature has been determined simultaneously.
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A dual-core fiber in which one of the cores is doped with Germanium and the other with Phosphorus is used as an in-line Mach-Zehnder (MZ) interferometer to perform high sensitivity strain and temperature sensing. Opposite sensitivities for high and low wavelength peaks were demonstrated when strain was applied. To our knowledge this is the first time that such behavior is demonstrated using this type of in-line MZ interferometer based on a dual-core fiber. A sensitivity of (78±2) pm/με, between 0-950 με and (1380±20) pm/ºC between 45 and 80ºC is demonstrated. It was also demonstrated that it is possible to use this configuration for simultaneous measurement of strain and temperature and a matrix equation to calculate them was given.
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We present a new method of reduction of the excess RIN (relative intensity noise) of the broadband source of a fiber-optic gyroscope (FOG). It is based upon the use of an interferometric filter which reduces the excess RIN at the proper frequency of the sensing coil. We demonstrate that a fiber-optic ring resonator can provide a RIN power density reduction (PSD) of 18dB allowing the FOG to operate near the photonnoise limit.
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Influence of spin manufacturing process on properties of the spun single mode fiber is investigated, a unidirectional spinning preform during the drawing process. The drawing speed constant is 1 m/min. The results show that pitch of the spun fiber exists; that mode field diameter (MFD) is obviously smaller; that cutoff wavelength and polarization mode dispersion (PMD) are decreased significantly, and then the loss is increased significantly when the spun fiber pitch is lower than 1.5 mm. It is very important for the fiber-optic gyroscope and fiber-optic current sensors to optimize spinning design to obtain relatively good spun fibers.
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We demonstrated an in-line open cavity Fabry–Pérot interferometer (FPI) for liquid refractive index sensing with linear response and high sensitivity. The FPI was fabricated by splicing a short piece of C-shaped fiber (tens of micrometers) between two standard single-mode fibers. The refractive index response of the FPI was characterized by ethanol-water mixtures in the range of 1.33 to 1.36, and a high sensitivity of 1294 nm/RIU at the wavelength of 1550 nm was achieved. The sensor was used to measure the thermo-optic coefficient of pure water, and the results agree well with the literature.
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A setup simulating High Voltage DC (HVDC) transformers barriers was developed to demonstrate the effectiveness of an optical fiber (OF) sensor in detecting partial discharges (PD) under these peculiar conditions. Different PD detection techniques were compared: electrical methods, and acoustic methods. Standard piezoelectric sensors (R15i-AST) and the above mentioned OF sensors were used for acoustic detection. The OF sensor was able to detect PD acoustically with a sensitivity better than the other detection methods. The multichannel instrumentation system was tested in real HVDC conditions with the aim of analyzing the behavior of the insulation (mineral oil/pressboard).
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Thermal strain significantly affects stability of fiber optic gyroscope (FOG) performance. This study investigates thermal strain development in a lightweight carbon fiber reinforced plastic (CFRP) FOG under thermal vacuum condition simulating space environment. First, we measure thermal strain distribution along an optical fiber in a CFRP FOG using a Brillouin-based high-spatial resolution system. The key strain profile is clarified and the strain development is simulated using finite element analysis. Finally, several constituent materials for FOG are quantitatively compared from the aspect of the maximum thermal strain and the density, confirming the clear advantage of CFRP.
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In this work, both arterial pulse and respiratory rate have been successfully measured based on changes in speckle patterns of multimode fibers. Using two fiber-based transducers, one located on the wrist and another in the chest, both disturbances were transmitted to the fiber, varying the speckle pattern. These variations of the speckle pattern were captured using a commercial webcam and further processed using different methods. The achieved results have been presented and the simultaneous monitoring of both vital signs has been also discussed. The feasibility to use the proposed sensor system for this application is demonstrated.
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The polarisation state of light may be exploited in single-mode polymer mPOFs for sensing purposes.
The bend-induced birefringence varies linearly with the inverse square of the bend radius, whereas the
twist-induced polarisation rotation varies linearly with the bre twist angle. Both e ects are highly reproducible and show higher sensitivity than their glass counterparts.
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An ultra-short DBR fiber laser based device for arterial pulse wave monitoring is proposed and demonstrated. As the sensing element, the 10mm length laser cavity is mounted onto a soft plastic plate and then embedded into textile. Deformation of the textile, involving the transverse force subjected by the laser cavity, is proportional to the vibration caused by the arterial pulse. The sensing principle is based on the linear relationship between the beat frequency of the laser and the transverse force. Laboratory studies demonstrate that the sensor could achieve real-time and accurate measurement of the weak and dynamical arterial pulse signal.
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We propose and experimentally demonstrate a novel long period fiber grating (LPFG) in an embedded-core hollow optical fiber (ECHOF). Without the structural deformation of the air hole and the fiber core, the high-quality LPFG can be fabricated within a few scanning cycles by a high-frequency CO2 laser with a low energy density of 0.896J/mm2. The ECHOF LPFG reveals a high temperature sensitivity of 50.2 pm/°C and a low strain sensitivity of 0.4 pm/με. Due to the good performance and easy fabrication, the ECHOF LPFG will be important to develop novel in-fiber devices.
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A technique to enhance the response of Brillouin distributed sensors is proposed and experimentally validated. The method consists in creating a multi-frequency pump pulse interacting with a multi-frequency continuous-wave probe. The power of each pulse at a distinct frequency is lower than the threshold for nonlinear effects, while the sensor response remains given by the total power of all pulses. Distinct frequency pulses are delayed to avoid temporal overlapping and cross-interaction; this requires to smartly reconstruct the traces before photo-detection. The method is validated in a 50 km-long sensor using 3 frequencies, demonstrating a signal-to-noise ratio enhancement of 4.8 dB.
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In this paper, improved fabrication and calibration techniques of Fiber Bragg Gratings (FBG) for very high temperature sensing applications up to more than 1500 °C will be presented. The fibers used are single crystalline sapphire fibers, which are applicable in such high temperature ranges due to their high melting point at 2040 °C and their extreme thermal stability. The inscription of the FBGs was performed by the second harmonic wave of a Ti:Sa-femtosecond laser system. With pulses of 400 nm wavelength first order gratings could be achieved. Using a two-beam phase mask interferometer, grating arrays within a wide spectral range have been fabricated with only one phase mask and without additional calibration routine. The inscribed grating arrays were wavelength-calibrated using a reference FBG, and their temperature sensitivity was evaluated.
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This paper proposes a novel concept of refractive index sensing based on a high-refractive-index-contrast optical Tamm plasmon (OTP) structure, i.e., an air/dielectric alternate-layered distributed Bragg reflector (DBR) coated with metal. In the reflection spectrum of the structure, a dip related to the formation of OTP appears. The dip wavelength and reflectivity are sensitive to ambient refractive index, which provides a potential way to achieve refractive index sensing with a large measurement range and high sensitivity.
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We present a novel approach for short, medium, and long range displacement measurement. This approach
is based on the interrogation of the relative phase-shift between two orthogonally polarized sinusoidal optical
signals through cross-phase modulation. Displacement determines the power of the side-band generated from
cross-phase modulation. Displacement measurement over a range of 12 mm with sub millimeter resolution is
demonstrated.
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