Showing papers on "Fiber optic sensor published in 2015"
TL;DR: In this paper, different kinds of sensing techniques, including change of light intensity, interferometry, fiber Bragg grating, adsorption measurement and distributed sensing, are briefly reviewed to introduce the basic sensing principles.
Abstract: Optical fiber sensor (OFS) technologies have developed rapidly over the last few decades, and various types of OFS have found practical applications in the field of civil engineering. In this paper, which is resulting from the work of the RILEM technical committee “Optical fiber sensors for civil engineering applications”, different kinds of sensing techniques, including change of light intensity, interferometry, fiber Bragg grating, adsorption measurement and distributed sensing, are briefly reviewed to introduce the basic sensing principles. Then, the applications of OFS in highway structures, building structures, geotechnical structures, pipelines as well as cables monitoring are described, with focus on sensor design, installation technique and sensor performance. It is believed that the State-of-the-Art review is helpful to engineers considering the use of OFS in their projects, and can facilitate the wider application of OFS technologies in construction industry.
270 citations
TL;DR: A surface plasmon resonance (SPR) sensor based on photonic crystal fiber with selectively filled analyte channels with maximum amplitude sensitivity and maximum refractive index (RI) sensitivity is proposed, suitable for detecting various high RI chemicals, biochemical and organic chemical analytes.
Abstract: We propose a surface plasmon resonance (SPR) sensor based on photonic crystal fiber (PCF) with selectively filled analyte channels. Silver is used as the plasmonic material to accurately detect the analytes and is coated with a thin graphene layer to prevent oxidation. The liquid-filled cores are placed near to the metallic channel for easy excitation of free electrons to produce surface plasmon waves (SPWs). Surface plasmons along the metal surface are excited with a leaky Gaussian-like core guided mode. Numerical investigations of the fiber’s properties and sensing performance are performed using the finite element method (FEM). The proposed sensor shows maximum amplitude sensitivity of 418 Refractive Index Units (RIU−1) with resolution as high as 2.4 × 10−5 RIU. Using the wavelength interrogation method, a maximum refractive index (RI) sensitivity of 3000 nm/RIU in the sensing range of 1.46–1.49 is achieved. The proposed sensor is suitable for detecting various high RI chemicals, biochemical and organic chemical analytes. Additionally, the effects of fiber structural parameters on the properties of plasmonic excitation are investigated and optimized for sensing performance as well as reducing the sensor’s footprint.
239 citations
TL;DR: This work allows the feasibility of using the D-shaped hollow-core MOFs to develop a high-sensitivity, real-time and distributed SPR sensor to solve the phase matching and analyte filling problems in the microstructured optical fiber (MOF) sensors.
Abstract: To solve the phase matching and analyte filling problems in the microstructured optical fiber (MOF)-based surface plasmon resonance (SPR) sensors, we present the D-shaped hollow core MOF-based SPR sensor. The air hole in the fiber core can lower the refractive index of a Gaussian-like core mode to match with that of a plasmon mode. The analyte is deposited directly onto the D-shaped flat surface instead of filling the fiber holes. We numerically investigate the effect of the air hole in the core on the SPR sensing performance, and identify the sensor sensitivity on wavelength, amplitude and phase. This work allows us to determine the feasibility of using the D-shaped hollow-core MOFs to develop a high-sensitivity, real-time and distributed SPR sensor.
233 citations
TL;DR: Experimental results show that the proposed sensor can provide an ultra-high RI sensitivity of 30899 nm/RIU, which has potential applications in fields such as gas concentration analyzing and humidity monitoring.
Abstract: An ultra-high sensitivity open-cavity Fabry–Perot interferometer (FPI) gas refractive index (RI) sensor based on the photonic crystal fiber (PCF) and Vernier effect is proposed and demonstrated. The sensor is prepared by splicing a section of PCF to a section of fiber tube fused with a section of single mode fiber. The air holes running along the cladding of the PCF enable the gas to enter or leave the cavity freely. The reflection beam from the last end face of the PCF is used to generate the Vernier effect, which significantly improves the sensitivity of the sensor. Experimental results show that the proposed sensor can provide an ultra-high RI sensitivity of 30899 nm/RIU. This sensor has potential applications in fields such as gas concentration analyzing and humidity monitoring.
227 citations
TL;DR: In this paper, a novel fiber optic temperature sensor has been proposed and experimentally demonstrated with ~9 times sensitivity enhancement by using two cascaded Sagnac interferometers, which consist of the same type of polarization maintaining fibers with slightly different lengths.
175 citations
TL;DR: In this article, a simple hexagonal lattice photonic crystal fiber biosensor using surface plasmon resonance phenomenon was proposed, where the analyte (sample) was placed outside the fiber structure instead of inside the air-holes.
Abstract: We propose a simple, two rings, hexagonal lattice photonic crystal fiber biosensor using surface plasmon resonance phenomenon. An active plasmonic gold layer and the analyte (sample) are placed outside the fiber structure instead of inside the air-holes, which will result in a simpler and straight forward fabrication process. The proposed sensor exhibits birefringent behavior that enhances its sensitivity. Numerical investigation of the guiding properties and sensing performance are conducted by finite element method. Using wavelength and amplitude interrogation methods, the proposed sensor could provide maximum sensitivity of 4000 nm/RIU and 320 RIU $^{-1}$ , respectively. The resolutions of the sensor are $2.5 \times 10^{-5}$ and $3.125 \times 10^{-5}$ RIU for wavelength and amplitude interrogation modes. The proposed sensor design shows promising results that could be used in biological and biochemical analytes detection.
175 citations
TL;DR: A fiber-optic sensor based on a silicon Fabry-Pérot cavity, fabricated by attaching a silicon pillar on the tip of a single-mode fiber, for high-resolution and high-speed temperature measurement, suggesting a maximum frequency of ~2 kHz can be reached to address the needs for highly dynamic environmental variations such as those found in the ocean.
Abstract: We report a fiber-optic sensor based on a silicon Fabry-Perot cavity, fabricated by attaching a silicon pillar on the tip of a single-mode fiber, for high-resolution and high-speed temperature measurement. The large thermo-optic coefficient and thermal expansion coefficient of the silicon material give rise to an experimental sensitivity of 84.6 pm/°C. The excellent transparency and large refractive index of silicon over the infrared wavelength range result in a visibility of 33 dB for the reflection spectrum. A novel average wavelength tracking method has been proposed and demonstrated for sensor demodulation with improved signal-to-noise ratio, which leads to a temperature resolution of 6 × 10−4 °C. Due to the high thermal diffusivity of silicon, a response time as short as 0.51 ms for a sensor with an 80-µm-diameter and 200-µm-long silicon pillar has been experimentally achieved, suggesting a maximum frequency of ~2 kHz can be reached, to address the needs for highly dynamic environmental variations such as those found in the ocean.
162 citations
TL;DR: In this article, an optical fiber Michelson interferometer (MI)-based sensor was proposed to overcome the cross-sensitivity problem between surrounding RI and temperature, which achieved a high resolution of 4.9 × 10−6 RIU and sensitivity of −202.46 dB/RIU.
Abstract: a b s t r a c t We demonstrated a refractive index (RI) sensor based on optical fiber Michelson interferometer (MI), which was fabricated by splicing a section of thin core fiber (TCF) to a standard single mode fiber with a core offset. Experimentally, such a MI-based RI sensor with a core offset of 8 m and a TCF length of 3 mm exhibits a high resolution of 4.9 × 10−6 RIU and sensitivity of −202.46 dB/RIU, which is two or three times higher than that of intensity-modulated RI sensors reported previously. In contrast, our MIbased RI sensor is insensitive to temperature, thus overcoming the cross-sensitivity problem between surrounding RI and temperature. Moreover, intensity modulation, rather than wavelength modulation, was used in the proposed MI-based RI sensor, and the sensor also has the advantages of compact size (8 mm), simple structure, easy fabrication, and good repeatability. © 2014 Published by Elsevier B.V.
156 citations
TL;DR: A compact, low loss, and highly sensitive optical fiber curvature sensor is presented, which allows for using either visibility or spectral shift for sensor interrogation when the device is bent.
Abstract: A compact, low loss, and highly sensitive optical fiber curvature sensor is presented. The device consists of a few-millimeter-long piece of seven-core fiber spliced between two single-mode fibers. When the optical fiber device is kept straight, a pronounced interference pattern appears in the transmission spectrum. However, when the device is bent, a spectral shift of the interference pattern is produced, and the visibility of the interference notches changes. This allows for using either visibility or spectral shift for sensor interrogation. The dynamic range of the device can be tailored through the proper selection of the length of the seven-core fiber. The effects of temperature and refractive index of the external medium on the response of the curvature sensor are also discussed. Linear sensitivity of about 3000 nm/mm−1 for bending was observed experimentally.
153 citations
TL;DR: This review summarizes principles and current stage of development of fiber-optic chemical sensors (FOCS) and biosensors (FOBS) and analytical results reached with fiber- Optic chemical and biological sensors.
Abstract: This review summarizes principles and current stage of development of fiber-optic chemical sensors (FOCS) and biosensors (FOBS). Fiber optic sensor (FOS) systems use the ability of optical fibers (OF) to guide the light in the spectral range from ultraviolet (UV) (180 nm) up to middle infrared (IR) (10 μm) and modulation of guided light by the parameters of the surrounding environment of the OF core. The introduction of OF in the sensor systems has brought advantages such as measurement in flammable and explosive environments, immunity to electrical noises, miniaturization, geometrical flexibility, measurement of small sample volumes, remote sensing in inaccessible sites or harsh environments and multi-sensing. The review comprises briefly the theory of OF elaborated for sensors, techniques of fabrications and analytical results reached with fiber-optic chemical and biological sensors.
152 citations
TL;DR: A novel and highly sensitive liquid level sensor based on a polymer optical fiber Bragg grating (POFBG) is experimentally demonstrated and a novel multi-sensor arrangement proposed which has the potential to provide level readings independent of temperature and the liquid density is proposed.
Abstract: A novel and highly sensitive liquid level sensor based on a polymer optical fiber Bragg grating (POFBG) is experimentally demonstrated. Two different configurations are studied and both configurations show the potential to interrogate liquid level by measuring the strain induced in a POFBG embedded in a silicone rubber diaphragm, which deforms due to hydrostatic pressure variations. The sensor exhibits a highly linear response over the sensing range and a good repeatability. For comparison, a similar sensor using a FBG inscribed in silica fiber is fabricated, which displays a sensitivity that is a factor of 5 smaller than the POFBG. The temperature sensitivity is studied and a novel multi-sensor arrangement proposed which has the potential to provide level readings independent of temperature and the liquid density.
TL;DR: In this paper, the first inscription of fiber Bragg gratings (FBGs) in cyclic transparent optical polymer (CYTOP)-perfluorinated polymer optical fibers (POFs) was reported.
Abstract: We report on the first inscription of fiber Bragg gratings (FBGs) in cyclic transparent optical polymer (CYTOP)-perfluorinated polymer optical fibers (POFs). We have used a direct write method with a femtosecond laser operating in the visible. The FBGs have a typical reflectivity of 70%, a bandwidth of 0.25 nm, a 3-mm length, and an index change of $\sim 10^{-4}$ . The FBGs operate in the $C$ -band, where CYTOP offers key advantages over polymethyl methacrylate optical fibers, displaying significantly lower optical loss in the important near-infrared (NIR) optical communications window. In addition, we note that CYTOP has a far lower affinity for water absorption and a core-mode refractive index that coincides with the aqueous index regime. These properties offer several unique opportunities for POF sensing at NIR wavelengths, such as compatibility with existing optical networks, the potential for POF sensor multiplexing and suitability for biosensing. We demonstrate compatibility with a commercial Bragg grating demodulator.
TL;DR: In this paper, a distributed fiber sensing system based on phase-sensitive optical time domain reflectometer (Φ-OTDR) and phase-generated carrier demodulation algorithm is proposed.
Abstract: We propose a novel approach to generate distributed fiber sensing system based on phase-sensitive optical time domain reflectometer (Φ-OTDR) and phase-generated carrier demodulation algorithm. An unbalanced Michelson interferometer is introduced at the receiving end of the system. The back Rayleigh scattering light from a certain position along the sensing fiber would interfere to generate interference light signal versus time, whose phase carries the sensing information. Phase-generated carrier demodulation algorithm is proposed and carried out to recover the phase information. A single frequency vibration event is applied to a certain position along the sensing fiber and we realize to demodulate it correctly. The noise level of the phase sensitive OTDR system is about $3 \times 10^{-3}$ rad/SHz and a signal to noise ratio about 30.45 dB is achieved. The maximum sensing length and the spatial resolution of the Φ-OTDR system are 10 km and 6 m with pulse repetition rate at 10 kHz and 6 m fiber delay in MI with interrogating pulse width of 30 ns.
TL;DR: Fiber Bragg gratings have been analyzed in detail, because they have proved to constitute the most promising technology in this field, and two different alternatives for strain measurements are also described.
Abstract: Aircraft structures require periodic and scheduled inspection and maintenance operations due to their special operating conditions and the principles of design employed to develop them. Therefore, structural health monitoring has a great potential to reduce the costs related to these operations. Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors. Several practical applications for structures and engines we have been working on are reported in this article. Fiber Bragg gratings have been analyzed in detail, because they have proved to constitute the most promising technology in this field, and two different alternatives for strain measurements are also described. With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.
TL;DR: The results show that this system can well demodulate distributed acoustic signal with the pressure detection limit of 0.122Pa and achieve an acoustic phase sensitivity of around -158dB (re rad/μPa) with a relatively flat frequency response between 450Hz to 600Hz.
Abstract: We demonstrate a distributed sensing network with 500 identical ultra-weak fiber Bragg gratings (uwFBGs) in an equal separation of 2m using balanced Michelson interferometer of the phase sensitive optical time domain reflectometry (φ-OTDR) for acoustic measurement. Phase, amplitude, frequency response and location information can be directly obtained at the same time by using the passive 3 × 3 coupler demodulation. Lab experiments on detecting sound waves in water tank are carried out. The results show that this system can well demodulate distributed acoustic signal with the pressure detection limit of 0.122Pa and achieve an acoustic phase sensitivity of around −158dB (re rad/μPa) with a relatively flat frequency response between 450Hz to 600Hz.
TL;DR: In this article, a surface plasmon resonance (SPR)-based fiber optic sensor using graphene-carbon nanotubes/poly(methyl methacrylate) (GCNT/PMMA) hybrid composites for the detection of methane gas have been carried out.
Abstract: Fabrication and characterization of a surface plasmon resonance (SPR)-based fiber optic sensor using graphene-carbon nanotubes/poly(methyl methacrylate) (GCNT/PMMA) hybrid composites for the detection of methane gas have been carried out. Four kinds of probes with different over-layers on the silver-coated unclad core of the fiber have been fabricated to achieve the best performance of the sensor. The over-layers used are of reduced graphene oxide (rGO), carbon nanotubes (CNT), reduced graphene oxide-carbon nanotubes (GCNT), and GCNT/PMMA hybrid nanocomposite. The sensing ability of all the probes has been tested for the following gases: methane, ammonia, hydrogen sulfide, chlorine, carbon dioxide, hydrogen, and nitrogen. The SPR spectra of all the probes for different concentrations of gases have been determined. A red shift in the resonance wavelength has been observed with increasing concentration of gases around the probes. Out of all the probes, the one with GCNT/PMMA hybrid nanocomposite over-layer has been found to be highly selective towards methane gas. For maximum sensitivity, the performance of the probe has been evaluated using different doping concentrations of GCNT in GCNT/PMMA nanocomposite. The doping concentration of 5 wt.% has been found to give maximum sensitivity of the sensor. Since the probe has been fabricated on optical fiber, apart from high selectivity and sensitivity, it has additional advantages such as miniaturized probe, low cost, capability of online monitoring and remote sensing, and immunity to electromagnetic field interference.
TL;DR: In this article, three kinds of fiber optic sensors employing surface plasmon resonance (SPR) and lossy mode resonance (LMR) have been fabricated over unclad core of the fiber using zinc oxide (ZnO).
Abstract: Fabrication and characterization of fiber optic sensors employing surface plasmon resonance (SPR) and lossy mode resonance (LMR) for the detection of hydrogen sulfide gas have been carried out. Three kinds of probes, two utilizing LMR technique and the one utilizing SPR technique, have been fabricated over unclad core of the fiber using zinc oxide (ZnO). The first LMR probe, named as LMR 1, has been fabricated by coating ZnO thin film with an over layer of ZnO nanoparticles while the second LMR probe, named as LMR 2, has a layer of ZnO nanoparticles over the unclad core of the fiber. The third probe, named as SPR probe, has been fabricated by coating silver film and a thin over layer of ZnO over unclad core of the fiber. The variation of peak absorbance/resonance wavelength with the concentration of the hydrogen sulfide gas has been used to calibrate all the three sensors having different platforms. The results show the maximum sensitivity to H 2 S gas for LMR 1 probe while the minimum for the SPR probe. In addition, the LMR 1 probe is highly selective to hydrogen sulfide gas in comparison to other two probes. This has been confirmed by performing experiments using different gases. The LMR 1 sensor probe has number of advantages, in addition to high sensitivity and selectivity, such as low cost, miniaturized probe, fast response, reusability of the probe, capability of online monitoring and remote sensing.
TL;DR: In this article, a surface plasmon resonance (SPR) based indium tin oxide (ITO)-silver (Ag) coated fiber optic sensing probe was proposed for refractive index sensing in visible regime of the electromagnetic spectrum.
TL;DR: A Mach-Zehnder interferometer based on a twin-core fiber that exhibited a high gas pressure sensitivity and a low temperature cross-sensitivity makes it very suitable for highly-sensitive gas pressure sensing in harsh environments.
Abstract: A Mach-Zehnder interferometer based on a twin-core fiber was proposed and experimentally demonstrated for gas pressure measurements. The in-line Mach-Zehnder interferometer was fabricated by splicing a short section of twin-core fiber between two single mode fibers. A micro-channel was created to form an interferometer arm by use of a femtosecond laser to drill through one core of the twin-core fiber. The other core of the fiber was remained as the reference arm. Such a Mach-Zehnder interferometer exhibited a high gas pressure sensitivity of −9.6 nm/MPa and a low temperature cross-sensitivity of 4.4 KPa/°C. Moreover, ultra-compact device size and all-fiber configuration make it very suitable for highly-sensitive gas pressure sensing in harsh environments.
TL;DR: In this paper, setups of flexible, unobtrusive body-monitoring systems based on optical fibers and the respective measured vital parameters are discussed as well as the interaction of light with tissue.
Abstract: Long-term monitoring with optical fibers has moved into the focus of attention due to the applicability for medical measurements. Within this Review, setups of flexible, unobtrusive body-monitoring systems based on optical fibers and the respective measured vital parameters are in focus. Optical principles are discussed as well as the interaction of light with tissue. Optical fiber-based sensors that are already used in first trials are primarily selected for the section on possible applications. These medical textiles include the supervision of respiration, cardiac output, blood pressure, blood flow and its saturation with hemoglobin as well as oxygen, pressure, shear stress, mobility, gait, temperature, and electrolyte balance. The implementation of these sensor concepts prompts the development of wearable smart textiles. Thus, current sensing techniques and possibilities within photonic textiles are reviewed leading to multiparameter designs. Evaluation of these designs should show the great potential of optical fibers for the introduction into textiles especially due to the benefit of immunity to electromagnetic radiation. Still, further improvement of the signal-to-noise ratio is often necessary to develop a commercial monitoring system.
TL;DR: A surface plasmon resonance (SPR) based fiber optic sensor with bi layers of metal-ZnO is proposed and theoretically studied in this paper, where the top ZnO layer is shown to protect the metallic layer from oxidation and to enhance the sensitivity of the SPR sensor.
Abstract: A surface plasmon resonance (SPR) based fiber optic sensor with bi layers of metal–ZnO is proposed and theoretically studied. Three metals: gold (Au), silver (Ag) and copper (Cu) have been exercised in the study. The top ZnO layer is shown to protect the metallic layer from oxidation and to enhance the sensitivity of the SPR sensor. Besides, increase in thickness of Au/Ag/Cu layer increases the sensitivity of SPR sensor for all thicknesses of ZnO layers. For a fixed thickness of ZnO layer, the sensitivity of sensor is larger for Au layer than that of Ag/Cu layer. Sensitivity also increases with increase in ZnO layer thickness for all thicknesses of Au/Ag/Cu layers. The SPR sensor based on bi layers of 40 nm Au–15 nm ZnO demonstrates the maximum sensitivity of 3161 nm/RIU.
TL;DR: This talk reports the recent progress on FMF based optical sensors, shows two types of FMF sensor, and demonstrates the potential of multi-parameter sensing.
Abstract: Few-mode fibers (FMFs) have found applications in optical communications and sensors with attractive features that standard single mode fiber (SSMF) do not possess. We report our recent progress on FMF based optical sensors, and show the potential of utilizing the spatial dimension for multi-parameter sensing with discrimination capability. We first show a discrete type FMF sensor based on interferometer structure with a short FMF, utilizing the modal interference between either the polarizations (x and y) or the spatial modes (LP(01) and LP(11)). We then show a distributed type FMF sensor by generating the stimulated Brillouin scattering (SBS) in a long FMF. We characterize the Brillouin gain spectrum (BGS) with a pump-probe configuration, and measure the temperature and strain coefficients for LP(01) and LP(11) modes. The proposed FMF based optical sensor can be applied to sensing a wide range of parameters.
TL;DR: A fibre optic surface plasmon resonance (SPR) sensor system for smartphones is reported, for the first time, and offers the potential of monitoring a large variety of environmental or point-of-care parameters in combination with smartphones.
Abstract: A fibre optic surface plasmon resonance (SPR) sensor system for smartphones is reported, for the first time. The sensor was fabricated by using an easy-to-implement silver coating technique and by polishing both ends of a 400 µm optical fibre to obtain 45° end-faces. For excitation and interrogation of the SPR sensor system the flash-light and camera at the back side of the smartphone were employed, respectively. Consequently, no external electrical components are required for the operation of the sensor system developed. In a first application example a refractive index sensor was realised. The performance of the SPR sensor system was demonstrated by using different volume concentrations of glycerol solution. A sensitivity of 5.96·10(-4) refractive index units (RIU)/pixel was obtained for a refractive index (RI) range from 1.33 to 1.36. In future implementations the reported sensor system could be integrated in a cover of a smartphone or used as a low-cost, portable point-of-care diagnostic platform. Consequently it offers the potential of monitoring a large variety of environmental or point-of-care parameters in combination with smartphones.
TL;DR: In this article, a statistical model for the signals received in phase-sensitive optical time domain reflectometry (OTDR) probed by highly coherent sources is developed, where the backscattering process is modelled by a set of discrete scatterers with properly chosen parameters.
Abstract: The paper develops a statistical model for the signals received in phase-sensitive optical time domain reflectometry (OTDR) probed by highly coherent sources. The backscattering process is modelled by a set of discrete scatterers with properly chosen parameters. Explicit equations for calculating the amplitude and the phase of the backscattered signal are obtained. The developed model predicts spectral and autocorrelation characteristics of the amplitude signals that are validated by experimental results. Characteristics of the phase signals, practicable for studying the sensing applications of the OTDR system, are presented and studied as well, demonstrating good correspondence with experiment. A more detailed modelling of distributed vibration sensing systems and their response to disturbances along an optical fiber will be possible as an extension of the developed formalism.
TL;DR: In this paper, a two-dimensional curvature optical fiber sensor based on a nontwisted homogeneous four-core fiber has been implemented to verify the theoretical analysis with the experimental results.
Abstract: We have implemented a multipoint two-dimensional curvature optical fiber sensor based on a nontwisted homogeneous four-core fiber. A theoretical approach to model the mechanical behavior of these fibers under curvature conditions has been developed. Two shape sensors composed of an array of FBGs inscribed in the four-core fiber have been implemented to corroborate the theoretical analysis with the experimental results. The characterization of the proposed shape sensors showed their ability to measure the curvature radius, the curvature direction, and any external applied force related to both uniform and nonuniform curvatures with high accuracy.
TL;DR: A fiber-optic surface plasmon resonance (SPR) sensor for temperature detection has been proposed by utilizing a thermosensitive liquid as the intermediate and combining with the fiber SPR structure to achieve a sensitivity much higher than that of the traditional fiber SPR sensor.
Abstract: A fiber-optic surface plasmon resonance (SPR) sensor for temperature detection has been proposed by utilizing a thermosensitive liquid as the intermediate and combining with the fiber SPR structure. The sensing element of the sensor has been fabricated by packaging the fiber probe coated with a silver layer into a capillary filled with thermosensitive anhydrous ethanol. This packaging can protect the metal layer from oxidation and damage. Moreover, this proposed sensor achieves a sensitivity of 1.5745 nm/°C, which is much higher than that of the traditional fiber SPR sensor according to the comparative experiments.
TL;DR: In this article, an ultra-weak fiber Bragg grating array has been proposed to generate strong and controllable reflections while providing acceptable insertion loss in phase-sensitive optical time-domain reflectometry (Φ-OTDR).
Abstract: Phase-sensitive optical time-domain reflectometry (Φ-OTDR) has been widely used in various applications for its distributed measurement capability of dynamic disturbance along the entire length of sensing fiber. However, traditional Φ-OTDR cannot make high-precision measurement on the external disturbance-induced strain due to the randomly distributed position and reflectivity of scattering points within the optical fiber. In this paper, ultra-weak fiber Bragg grating (UWFBG) array has been proposed to generate strong and controllable reflections while providing acceptable insertion loss. Active laser frequency sweeping and unwrapping algorithms were included to set up a definite relationship between strain value and variation of interference power between neighboring reflection lights. With the assistant of UWFBG array, the capability of Φ-OTDR has been upgraded to be able to take high-precision measurement on strain. In the experiment, multipoint μϵ level dynamic strain variation has been fully captured at the end of a 5-km long sensing fiber with 2 m spatial resolution. The measured strain value was compared to the calibrated one obtained with Mach–Zehnder Interferometer method. These two values fit with each other quite well with a maximum deviation of 6.2 nϵ, which confirmed the validity and accuracy of the proposed method.
22 Mar 2015
TL;DR: A 30-core fiber with heterogeneous cores that achieved large spatial multiplicity and low crosstalk of less than -40 dB at 100 km was demonstrated.
Abstract: A 30-core fiber with heterogeneous cores that achieved large spatial multiplicity and low crosstalk of less than −40 dB at 100 km was demonstrated. The correlation lengths were estimated to be more than 1 m.
TL;DR: In this article, a system based on phase-sensitive optical time domain reflectometry is proposed for simultaneously strain and vibration sensing, where the strain is detected by comparing the patterns of signal for different laser frequencies, and the vibration of fiber is detected simultaneously from the signals for any certain laser frequency.
Abstract: A system based on phase-sensitive optical time domain reflectometry is proposed for simultaneously strain and vibration sensing. The strain of fiber is detected by comparing the patterns of signal for different laser frequencies, and the vibration of fiber is detected simultaneously from the signals for any certain laser frequency. During the measurement, frequencies of the probe optical pulses are modulated sequentially in ascending or descending order. Using the signals generated by optical pulses with the same frequency, the vibration of fiber is detected with fast response speed; using that with different frequencies, the strain of fiber is detected with high resolution. In our experiment, a sensing system with 2-m spatial resolution, up to 1-kHz frequency measurement range and 10- $\text{n}{{\varepsilon }}$ strain resolution is realized for a 9-km sensing fiber length.
TL;DR: In this paper, a surface plasmon resonance based fiber optic sensor for the detection of melamine using molecular imprinting is reported, which is fabricated by coating a thin film of silver over the unclad core of an optical fiber.
Abstract: Fabrication and characterization of a surface plasmon resonance based fiber optic sensor for the detection of melamine using molecular imprinting are reported. The probe is fabricated by coating a thin film of silver over the unclad core of an optical fiber which is further coated with the molecular imprinted (MIP) polymer using melamine as template molecule. The MIP layer creates binding sites, complementary of the template molecule on the surface. The template molecules have the capability to bind with these active sites. The performance of the sensor is tested for the melamine concentration range from 10 −7 M to 10 −1 M. A shift of 19 nm in resonance wavelength is recorded for this concentration range. The sensitivity is maximized by optimizing melamine concentration in MIP layer formation and the pH of the sample solution. The selectivity of the probe is checked using different analytes and is found to be highly selective for melamine. The sensitivity of the sensor is improved by introducing a thin layer of aluminum between silver and MIP layer. The sensor has advantages of fast response, high selectivity and sensitivity, low cost and can be used for online monitoring and remote sensing applications.