Showing papers on "Fiber Bragg grating published in 2014"

Fiber Bragg grating sensors toward structural health monitoring in composite materials: challenges and solutions.

Abstract: Nowadays, smart composite materials embed miniaturized sensors for structural health monitoring (SHM) in order to mitigate the risk of failure due to an overload or to unwanted inhomogeneity resulting from the fabrication process. Optical fiber sensors, and more particularly fiber Bragg grating (FBG) sensors, outperform traditional sensor technologies, as they are lightweight, small in size and offer convenient multiplexing capabilities with remote operation. They have thus been extensively associated to composite materials to study their behavior for further SHM purposes. This paper reviews the main challenges arising from the use of FBGs in composite materials. The focus will be made on issues related to temperature-strain discrimination, demodulation of the amplitude spectrum during and after the curing process as well as connection between the embedded optical fibers and the surroundings. The main strategies developed in each of these three topics will be summarized and compared, demonstrating the large progress that has been made in this field in the past few years.

Handbook of Optical Fibre Sensing Technology

Abstract: PART ONE: PRELIMINARY OVERVIEW Introduction to Fibre Optic Sensing Technology (J.M. Lopez--Higuera) The Commercialisation of Fibre Optic Sensors (S.D. Crossley) PART TWO: FUNDAMENTALS OF PHOTONICS AND COMPONENTS FOR SENSING Light and Waveguiding (J.L. Arce--Diego) Optical Waveguides and their Manufacture (J. Zubia and M. Lomer) Passive Bulk Optical Components for Sensing (C. Gomez--Reino, V. Perez and C. Bao) Fibre and Integrated Optic Components for Sensing (R. Willsch and W. Ecke) Semiconductor Optical Sources for Sensing Technology (I. Esquivias and J. Arias) Photodetectors for Sensing (J.M. Lopez--Higuera and J. Madruga) Optical Amplifiers (M.A. Rebolledo and M. Lopez--Amo) Superfluorescent Fibre Optic Sources (J.M. Lopez--Higuera) PART THREE: PRINCIPLES AND TECHNIQUES FOR SENSING Transduction Techniques based on Intensity Modulation of Light (A.C. Garcia and J. Echevarria Cuenca) Interferometry and Polarimetry for Optical Sensing (DC. Jones) Gas Spectroscopy Techniques for Optical Fibre Sensors (B. Culshaw) Distributed Optical--fibre Sensing (A. Rogers) Principles of Laser Doppler Velocimetry (D.A. Jackson and C.N. Pannell) Fibre Gyroscope Principles (S. Merlo, M. Norgia and S. Donati) Fibre Grating Technology: Theory, Photosensitivity, Fabrication and Characterization (R. Khasyap and J.M. Lopez--Higuera) Fibre Bragg Grating Interrogation Techniques (J.L. Santos and W.N. MacPherson) Discrimination Techniques for Optical Sensors (J.D.C. Jones and W.N. MacPherson) Optical Reliability of Fibre Gratings (S. Kannan and P. Lemaire) Passive Fibre Optic Sensor Networks (A. Dandridge and C. Kirkendall) Active Fibre Optic Sensor Networks (S. Abad, M. Lopez--Amo and I.R. Matias) PART FOUR: APPLICATIONS Optical Fibre Gratings Applications (S.T. Vohra) Laser Doppler Velocimetry Applications (D.A. Jackson and C.N. Pannell) Phototonic Sensing Technology in Civil Engineering Applications (D. Inaudi) Applications of Optical Fibre Sensors for the Nuclear Power Industry (P. Ferdinand and S. Magne) Optical Fibre Current and Voltage Sensors for the Electric Power Industry (A.H. Rose and G.W. Day) Fibre Optic Gyroscope for Industrial Applications (T. Kumagai and H. Kajioka) Optical Fibre Sensors for Fly--By--Light Aircraft (M. Kobayashi and K. Toyama) Optical Fibre Sensing of Electrical Discharges and Plasmas (G. Woolsey) Fibre Optic Sensors for Oilfield Services (R.J. Schroeder, R.T. Ramos, T. Yamate and E. Udd) Fibre Optic Biosensors (C.A. Rowe--Taitt and F.S. Ligler) Biomedical Fibre Optic Sensors (F. Baldini and A.G. Mignani) Fibre Optic Sensors for Environmental Applications (G. Holst and B. Mizaikoff) The Optical Nose (D. Walt and S. Stitzel) A New Approach to optical Fibre Sensing Techniques based on the Sensory Systems of Living Bodies (J.A. Martin--Pereda and A.P. Gonzalez--Marcos) Acronyms. Index.

Three-Dimensional Needle Shape Reconstruction Using an Array of Fiber Bragg Grating Sensors

Abstract: We present a prototype of a flexible nitinol needle (φ 1.0 mm and length 172 mm) integrated with an array of 12 Fiber Bragg Grating (FBG) sensors. These sensors measure the axial strain, which enables the computation of the needle curvature. We reconstruct the three-dimensional (3-D) needle shape from the curvature. Experiments are performed where the needle is deflected in free space. The maximum errors between the experiments and beam theory-based model are 0.20 mm (in-plane deflection with single bend), 0.51 mm (in-plane deflection with double bend), and 1.66 mm (out-of-plane). We also describe kinematics-based and mechanics-based models for predicting the 3-D needle shape during insertion into soft tissue. We perform experiments where the needle is inserted into a soft-tissue simulant, and the 3-D needle shape is reconstructed using the FBG sensors. We compare the reconstructed needle shape to deflection obtained from camera images and our models. The maximum error between the experiments and the camera images is 0.74 mm. The maximum errors between the kinematics-based and mechanics-based models and the camera images are 3.77 mm and 2.20 mm, respectively. This study demonstrates that deflection models and needles integrated with FBG sensors have the potential to be used in combination with clinical imaging modalities in order to enable accurate needle steering.

Graphene-coated microfiber Bragg grating for high-sensitivity gas sensing

Abstract: A graphene coated microfiber Bragg grating (GMFBG) for gas sensing is reported in this Letter. Taking advantage of the surface field enhancement and gas absorption of a GMFBG, we demonstrate an ultrasensitive approach to detect the concentration of chemical gas. The obtained sensitivities are 0.2 and 0.5 ppm for NH3 and xylene gas, respectively, which are tens of times higher than that of a GMFBG without graphene for tiny gas concentration change detection. Experimental results indicate that the GMFBG-based NH3 gas sensor has fast response due to its highly compact structure. Such a miniature fiber-optic element may find applications in high sensitivity gas sensing and trace analysis.

Photonic crystal fiber based surface plasmon resonance chemical sensors

Abstract: Research developments of the photonic crystal fiber based surface plasmon resonance (PCF-SPR) chemical sensors were intensively reviewed Photonic crystal fibers, such as the microstructured optical fiber, the photonic bandgap fiber and the Bragg fiber with various structures were applied to the SPR sensors, including fuse-tapered fiber structure, D-type fiber structure and cladding-off fiber structure Those sensors were classified as three kinds of configurations which were respectively based on the inner metal layer, the metallic nanowire and the outer metal film What's more, the principles, superiorities and problems of the PCF-SPR sensors were also discussed in detail

Multicore fiber sensor for high-temperature applications up to 1000°C

Abstract: A novel high temperature sensor based on customized multicore fiber (MCF) is proposed and experimentally demonstrated. The sensor consists of a short, few-centimeter-long segment of MCF spliced between two standard single-mode fibers. Due to interference effects, the transmission spectrum through this fiber chain features sharp and deep notches. Exposing the MCF segment to increasing temperatures of up to 1000°C results in a shift of the transmission notches toward longer wavelengths with a slope of approximately 29 pm/°C at lower temperatures and 52 pm/°C at higher temperatures, enabling temperature measurements with high sensitivity and accuracy. Due to its compact size and mechanical rigidity, the MCF sensor can be subjected to harsh environments. The fabrication of the MCF sensor is straightforward and reproducible, making it an inexpensive fiber device.

A Submillimetric 3-DOF Force Sensing Instrument With Integrated Fiber Bragg Grating for Retinal Microsurgery

Abstract: Vitreoretinal surgery requires very fine motor control to perform precise manipulation of the delicate tissue in the interior of the eye. Besides physiological hand tremor, fatigue, poor kinesthetic feedback, and patient movement, the absence of force sensing is one of the main technical challenges. Previous two degrees of freedom (DOF) force sensing instruments have demonstrated robust force measuring performance. The main design challenge is to incorporate high sensitivity axial force sensing. This paper reports the development of a submillimetric 3-DOF force sensing pick instrument based on fiber Bragg grating (FBG) sensors. The configuration of the four FBG sensors is arranged to maximize the decoupling between axial and transverse force sensing. A superelastic nitinol flexure is designed to achieve high axial force sensitivity. An automated calibration system was developed for repeatability testing, calibration, and validation. Experimental results demonstrate a FBG sensor repeatability of 1.3 pm. The linear model for calculating the transverse forces provides an accurate global estimate. While the linear model for axial force is only locally accurate within a conical region with a 30° vertex angle, a second-order polynomial model can provide a useful global estimate for axial force. Combining the linear model for transverse forces and nonlinear model for axial force, the 3-DOF force sensing instrument can provide sub-millinewton resolution for axial force and a quarter millinewton for transverse forces. Validation with random samples show the force sensor can provide consistent and accurate measurement of 3-D forces.

Simultaneous measurement of refractive index and temperature based on a core-offset Mach–Zehnder interferometer combined with a fiber Bragg grating

Abstract: An all-fiber sensor for simultaneous measurement of refractive index and temperature in solutions is proposed and demonstrated. The sensing head contains a core-offset Mach–Zehnder interferometer (MZI) and a fiber Bragg grating (FBG). The interference fringe of the MZI and the Bragg wavelength of the FBG would shift with the variation of the ambient refractive index (RI) and/or temperature. The experimental results show that the RI sensitivity and the temperature sensitivity for the sensor are 13.7592 nm/RI and 0.0462 nm/°C, respectively. Its low fabrication cost, simple configuration and high sensitivity will have attractive potential applications in chemical and biological sensing.

Cascaded fiber-optic Fabry-Perot interferometers with Vernier effect for highly sensitive measurement of axial strain and magnetic field

Abstract: We report a highly sensitive fiber-optic sensor based on two cascaded intrinsic fiber Fabry-Perot interferometers (IFFPIs). The cascaded IFFPIs have different free spectral ranges (FSRs) and are formed by a short section of hollow core photonic crystal fiber sandwiched by two single mode fibers. With the superposition of reflective spectrum with different FSRs, the Vernier effect will be generated in the proposed sensor and we found that the strain sensitivity of the proposed sensor can be improved from 1.6 pm/μe for a single IFFPI sensor to 47.14 pm/μe by employing the Vernier effect. The sensor embed with a metglas ribbon can be also used to measure the magnetic field according to the similar principle. The sensitivity of the magnetic field measurement is achieved to be 71.57 pm/Oe that is significantly larger than the 2.5 pm/Oe for a single IFFPI sensor.

FBG-based Shape Sensing Tubes for Continuum Robots

Abstract: Fiber Bragg gratings (FBG)-based optical sensors are a promising real-time technique for sensing the 3D curva- ture of continuum robots. Existing implementations, however, have relied on embedding optical fibers in small-diameter metal wires or needles. This paper proposes polymer tubes as an alternative substrate for the fibers. This approach separates the sensors from the robot structural components while using a minimal amount of the robot's tool lumen and providing the potential of inexpensive fabrication. Since the fibers are stiffer than the polymer substrate, however, design challenges arise in modeling strain transfer between the fibers and the tube substrate. To investigate the potential of this approach, a strain transfer model is derived and validated through simulation and experiment. I. INTRODUCTION Continuum robots take the shape of three dimensional curves and are able to change their shape through a com- bination of bending, rotation and extension or contraction of their structural components. Because of these capabilities, continuum robots are ideally suited for applications such as minimally invasive surgery. Their flexibility, however, leads to uncertainty in the shape of their backbone curve as well as in the location of their tip. Approaches to real-time sensing that have been studied include imaging, electromagnetic (EM) tracking and force sensing for tendon-based actuation. These techniques all have shortcomings, however. For example, drawbacks with imag- ing include limited resolution (ultrasound), risk of ionizing radiation (x-ray or CT), and slow speed (MRI). Tendon length-based shape estimation is limited to single bends and its accuracy depends highly on the robot kinematic model. In contrast to these approaches, a real-time sensing tech- nology that could be easily inserted and removed from the robot is preferred because of its direct measurement, instant adaptability to the continuous shape change and ease of replaceability. Curvature sensing using fiber Bragg gratings (FBG) has received recent attention, due to its small size, biocompatibility and high sensitivity. Compared to EM sensors (1), FBG-based sensors are smaller, immune to EM noise and can contain multiple sensors along the length of a fiber. For example designs using attached (2) or embedded (3), (4) fibers have been implemented on 1mm diameter metal wires. Both approaches reasonably assumed a perfect strain transfer from the wire to FBG. While the small wire diameter had minimal effect on structural stiffness and made it possible to accommodate large curvatures (gratings

High-resolution and broadband all-fiber spectrometers

Abstract: The development of optical fibers has revolutionized telecommunications by enabling long-distance broadband transmission with minimal loss. In turn, the ubiquity of high-quality, low-cost fibers has enabled a number of additional applications, including fiber sensors, fiber lasers, and imaging fiber bundles. Recently, we showed that a multimode optical fiber can also function as a spectrometer by measuring the wavelength-dependent speckle pattern formed by interference between the guided modes. Here, we reach a record resolution of 1 pm at a wavelength of 1500 nm using a 100 m long multimode fiber, outperforming the state-of-the-art grating spectrometers. We also achieved broadband operation with a 4 cm long fiber, covering 400–750 nm with 1 nm resolution. The fiber spectrometer, consisting of the fiber, which can be coiled to a small volume, and a monochrome camera that records the speckle pattern, is compact, lightweight, and low cost while providing ultrahigh resolution, broad bandwidth, and low loss.

Humidity responsivity of poly(methyl methacrylate)-based optical fiber Bragg grating sensors.

Abstract: The humidity response of poly(methyl methacrylate) (PMMA)-based optical fiber Bragg gratings (POFBGs) has been studied. The characteristic wavelength of the grating is modulated by water absorption-induced swelling and refractive index change in the fiber. This work indicates that anisotropic expansion may exist in PMMA optical fiber, reducing the humidity responsivity of the grating and introducing uncertainty in the responsivity from fiber to fiber. By pre-straining a grating, one can get rid of this uncertainty and simultaneously improve the POFBG response time.

Long period grating in multicore optical fiber: an ultra-sensitive vector bending sensor for low curvatures

Abstract: Long period grating was UV inscribed into a multicore fiber consisting of 120 single mode cores. The multicore fiber that hosts the grating was fusion spliced into a single mode fiber at both ends. The splice creates a taper transition between the two types of fiber that produces a nonadiabatic mode evolution; this results in the illumination of all the modes in the multicore fiber. The spectral characteristics of this fiber device as a function of curvature were investigated. The device yielded a significant spectral sensitivity as high as 1.23 nm/m-1 and 3.57 dB/m-1 to the ultra-low curvature values from 0 to 1 m-1. This fiber device can also distinguish the orientation of curvature experienced by the fiber as the long period grating attenuation bands producing either a blue or red wavelength shift. The finite element method (FEM) model was used to investigate the modal behavior in multicore fiber and to predict the phase-matching curves of the long period grating inscribed into multicore fiber.

Advances in bio-tactile sensors for minimally invasive surgery using the fibre Bragg grating force sensor technique: a survey.

Abstract: The large interest in utilising fibre Bragg grating (FBG) strain sensors for minimally invasive surgery (MIS) applications to replace conventional electrical tactile sensors has grown in the past few years. FBG strain sensors offer the advantages of optical fibre sensors, such as high sensitivity, immunity to electromagnetic noise, electrical passivity and chemical inertness, but are not limited by phase discontinuity or intensity fluctuations. FBG sensors feature a wavelength-encoding sensing signal that enables distributed sensing that utilises fewer connections. In addition, their flexibility and lightness allow easy insertion into needles and catheters, thus enabling localised measurements inside tissues and blood. Two types of FBG tactile sensors have been emphasised in the literature: single-point and array FBG tactile sensors. This paper describes the current design, development and research of the optical fibre tactile techniques that are based on FBGs to enhance the performance of MIS procedures in general. Providing MIS or microsurgery surgeons with accurate and precise measurements and control of the contact forces during tissues manipulation will benefit both surgeons and patients.

Optical computation of the Laplace operator using phase-shifted Bragg grating.

Abstract: Diffraction of a 3D optical beam on a multilayer phase-shifted Bragg grating (PSBG) is considered. It is shown that the PSBG enables optical computation of the spatial Laplace operator of the electromagnetic field components of the incident beam. The computation of the Laplacian is performed in reflection at normal incidence. As a special case, the parameters of the PSBG transforming the incident Gaussian beam into a Laguerre-Gaussian mode of order (1,0) are obtained. Presented numerical results demonstrate high quality of the Laplace operator computation and confirm the possibility of the formation of Laguerre-Gaussian mode. We expect the proposed applications to be useful for all-optical data processing.

Spatial differentiation of optical beams using phase-shifted Bragg grating.

Abstract: We present a theoretical study of a new application of the phase-shifted Bragg grating (PSBG) as an optical spatial differentiator operating in reflection. We demonstrate that the PSBG allows to calculate the first-order spatial derivative at oblique incidence and the second-order derivative at normal incidence. As an example, the differentiator is numerically shown to be able to convert an input 2D Gaussian beam into a 2D Hermite-Gaussian mode. We expect the proposed application to be useful for all-optical data processing.

Wide wavelength selectable all-fiber thulium doped fiber laser between 1925 nm and 2200 nm

Abstract: We demonstrate an all-fiber Tm3+-doped silica fiber laser operating at a wide selectable wavelength range by using different fiber Bragg gratings (FBGs) as wavelength selection elements. With a specifically designed high reflective (HR) FBG and the fiber end as an output coupler, the lasing in the range from 1975 nm to 2150 nm with slope efficiency of >30% can be achieved. By employing a low reflective (LR) FBG as the output coupler, the obtainable wavelengths were extended to the range between 1925 nm and 2200 nm which is the reported longest wavelength from the Tm3+-doped silica fiber lasers. Furthermore, by employing a FBG array in the laser cavity and inducing bend loss between adjacent FBGs in the array, six switchable lasing wavelengths were achieved. © 2014 Optical Society of America.

3.77 μm fiber laser based on cascaded Raman gain in a chalcogenide glass fiber

Abstract: Laser emission is demonstrated at a wavelength of 3.766 μm in a cascaded Raman gain device. The laser cavity is made of two nested pairs of fiber Bragg gratings inscribed in a 2.8 m length of low-loss As2S3 fiber. An erbium-doped fluoride glass quasi-CW fiber laser emitting at 3.005 μm is used to pump the cascaded Raman cavity, which converts the pump wavelength successively to the first and second Stokes orders, respectively at 3.340 and 3.766 μm. A laser output peak power in excess of 100 mW is obtained with a lasing efficiency of about 8.3% with respect to the launched pump power. This represents the highest emission wavelength delivered by a fiber laser operating at room temperature.

Optical Fiber Sensor Based on Localized Surface Plasmon Resonance Using Silver Nanoparticles Photodeposited on the Optical Fiber End

Abstract: This paper reports the implementation of an optical fiber sensor to measure the refractive index in aqueous media based on localized surface plasmon resonance (LSPR). We have used a novel technique known as photodeposition to immobilize silver nanoparticles on the optical fiber end. This technique has a simple instrumentation, involves laser light via an optical fiber and silver nanoparticles suspended in an aqueous medium. The optical sensor was assembled using a tungsten lamp as white light, a spectrometer, and an optical fiber with silver nanoparticles. The response of this sensor is such that the LSPR peak wavelength is linearly shifted to longer wavelengths as the refractive index is increased, showing a sensitivity of 67.6 nm/RIU. Experimental results are presented.

Chemical-assisted femtosecond laser writing of lab-in-fibers.

Abstract: The lab-on-chip (LOC) platform has presented a powerful opportunity to improve functionalization, parallelization, and miniaturization on planar or multilevel geometries that has not been possible with fiber optic technology. A migration of such LOC devices into the optical fiber platform would therefore open the revolutionary prospect of creating novel lab-in-fiber (LIF) systems on the basis of an efficient optical transport highway for multifunctional sensing. For the LIF, the core optical waveguide inherently offers a facile means to interconnect numerous types of sensing elements along the optical fiber, presenting a radical opportunity for optimizing the packaging and densification of diverse components in convenient geometries beyond that available with conventional LOCs. In this paper, three-dimensional patterning inside the optical fiber by femtosecond laser writing, together with selective chemical etching, is presented as a powerful tool to form refractive index structures such as optical waveguides and gratings as well as to open buried microfluidic channels and optical resonators inside the flexible and robust glass fiber. In this approach, optically smooth surfaces (~12 nm rms) are introduced for the first time inside the fiber cladding that precisely conform to planar nanograting structures when formed by aberration-free focusing with an oil-immersion lens across the cylindrical fiber wall. This process has enabled optofluidic components to be precisely embedded within the fiber to be probed by either the single-mode fiber core waveguide or the laser-formed optical circuits. We establish cladding waveguides, X-couplers, fiber Bragg gratings, microholes, mirrors, optofluidic resonators, and microfluidic reservoirs that define the building blocks for facile interconnection of inline core-waveguide devices with cladding optofluidics. With these components, more advanced, integrated, and multiplexed fiber microsystems are presented demonstrating fluorescence detection, Fabry–Perot interferometric refractometry, and simultaneous sensing of refractive index, temperature, and bending strain. The flexible writing technique and multiplexed sensors described here open powerful prospects to migrate the benefits of LOCs into a more flexible and miniature LIF platform for highly functional and distributed sensing capabilities. The waveguide backbone of the LIF inherently provides an efficient exchange of information, combining sensing data that are attractive in telecom networks, smart catheters for medical procedures, compact sensors for security and defense, shape sensors, and low-cost health care products.

Subwavelength grating filtering devices.

Abstract: We propose and simulate the characteristics of optical filters based on subwavelength gratings. In particular, we demonstrate through numerical simulations the feasibility of implementing SWG Bragg gratings in silicon-on-insulator (SOI). We also propose SWG ring resonators in SOI and verify their operation using numerical simulations and experiments. The fabricated devices exhibit an extinction ratio as large as 30 dB and a Q-factor as high as ~20,000. These fundamental SWG filters can serve as building blocks for more complex devices.

Modified cantilever beam shaped FBG based accelerometer with self temperature compensation

Abstract: This paper focuses on Fiber Bragg Grating (FBG) based accelerometer design. The accelerometer structure consists of inertial mass supported by an L-shaped modified cantilever beam having non-uniform cross section area connected to base by a thin neck element which acts as strain concentrated centre hence an optimum zone for FBG sensors placement. It has a working bandwidth below the structure's natural frequency and responds linearly to vibrations. The parameters for the structure design have been optimised on SolidWorks 2012 platform. Experimental trials yield sensitivity of 46 pm/g for frequency below 50 Hz and 306 pm/g for frequency above 150 Hz. A mathematical model for the accelerometer structure's natural frequency modes is also presented with detailed analysis for different combinations of inertial mass-frame assembly.

Multi-phase-shifted helical long period fiber grating based temperature-insensitive optical twist sensor

Abstract: A compact temperature-insensitive optical fiber twist sensor based on multi-phase-shifted helical long period fiber grating has been proposed and experimentally demonstrated in this paper. A multi-phase-shifted helical long period fiber grating is fabricated with a multi-period rotation technology. A π/2 and a 3π/2 phase shift is introduced in the helical long period fiber grating by changing the period. The helical pitch can be effectively changed with a different twist rate, which is measured by calculating the wavelength difference between two phase shift peaks. Although the wavelength of the phase shift peak also shifts with a change of the temperature, the wavelength difference between two phase shift peaks is constant due to two fixed phase shifts in the helical long period fiber grating, which is extremely insensitive to temperature change for the multi-phase-shifted helical long period fiber grating. The experimental results show that a sensitivity of up to 1.959 nm/(rad/m) is achieved.

A Novel Interrogation System for Large Scale Sensing Network With Identical Ultra-Weak Fiber Bragg Gratings

Abstract: A novel interrogation system for large scale sensing network with identical ultra-weak fiber Bragg gratings (FBG) is proposed, theoretically analyzed and experimentally studied. Based on time-division multiplexing (TDM) technique, two semiconductor optical amplifiers are introduced to the interrogation system to achieve fast and flexible demodulation. A simulation depending on the formula of reflected pulse spectra, derived by analyzing the source of disturbance along the optical path, is processed for evaluating the performance theoretically. Experiment was demonstrated on an 843 serial FBGs sensor network, with a peak reflectivity of -40 to -45 dB and a spatial resolution of 2 m along a single optical fiber by launching a 50 kHz scanning frequency with 20 ns effective pulse width to the system. Due to the low crosstalk, it is possible to integrate several thousands of FBG sensors in a single optical fiber.

Bragg grating writing in PMMA microstructured polymer optical fibers in less than 7 minutes

Abstract: We demonstrate fiber Bragg grating (FBG) writing in PMMA microstructured Polymer Optical Fibers (mPOFs) using UV Phase Mask technique with writing times shorter than 10 min. The shortest writing time was 6 minutes and 50 seconds and the longest writing time was 8 min and 50 sec. The FBGs were written in a 125 µm PMMA mPOF having 3-rings of holes, the reflection peaks were centred at 632.6 nm and have a reflectivity as high as 26 dB. We also demonstrate how the writing dynamics depends on the intensity of the writing beam.

Fiber Optic Fabry-Perot Magnetic Field Sensor With Temperature Compensation Using a Fiber Bragg Grating

Abstract: Based on the characteristic of magnetic-controlled refractive index, magnetic fluid was used as a sensitive medium in fiber optic Fabry-Perot (F-P) cavity. Combined with the temperature sensing property of fiber Bragg grating (FBG), a novel fiber optic F-P magnetic field sensor with temperature compensation was proposed. The sensor probe has the advantages of simple structure, low cost, and high magnetic field measurement accuracy. Magnetic field and temperature can be simultaneously measured by the proposed sensor. Sensing mechanism and experimental results indicated that the temperature cross effect on magnetic field measurement can be effectively compensated using a FBG. The maximal magnetic field intensity is up to 600 Gs with a sensitivity of 0.04 nm/Gs and measurement resolution is 0.5 Gs.

Large Frequency Range and High Sensitivity Fiber Bragg Grating Accelerometer Based on Double Diaphragms

Abstract: A fiber Bragg grating (FBG) accelerometer based on double diaphragms is presented and experimentally demonstrated. Design, fabrication, and optimization of the FBG accelerometer are analyzed. Experimental results indicate that the FBG accelerometer provides broad flat frequency range from 50 to 800 Hz, corresponding sensitivity range from 23.8 to 45.9 pm/G, while the flatness is <;3 dB. Cross-axis sensitivity is <;2.1% of the main-axis sensitivity, dynamic resolution can reach 0.385 mG/√(Hz), and dynamic range is 80 dB. Random error of the FBG accelerometer is analyzed by using Allan variance analysis method, which is promising in cross well seismic exploration.