Fibre Bragg grating temperature sensors for high-speed machining applications

This paper reports the design, characterization and implementation of a fiber Bragg grating (FBG) temperature sensor in a power electronic inverter which has a high electromagnetic interference (EMI) radiation. The performance and characteristics of the sensor are investigated by monitoring the temperature variation of the insulated gate bipolar transistor (IGBT) in photovoltaic (PV) arrays inverter. The thermal expansion of the optical fiber is enhanced by mounting the FBG sensor to a metal sheet. Due to this enhancement, the FBG temperature sensor recorded an improvement in terms of linearity and sensitivity. A comparison is made between the performance of the enhanced FBG sensor and a thermocouple in a high EMI environment, and the results show that the FBG sensor performs better.

A novel packaging method for FBG temperature sensors based on ultrasonic-assisted soldering technology

In this paper, a novel fiber Bragg grating (FBG) temperature sensor system with low cost demodulation mechanism was proposed. The broadband light source was demodulated by a long period fiber grating (LPG) with an appropriate attenuation band. The sensing FBG was encapsulated with aluminum groove to make the FBG have a higher thermal expansion coefficient. The sensor with enhanced sensitivity 0.02°C was realized.

In this research, fiber Bragg grating (FBG) temperature sensors are embedded in composites in order to detect highly localized temperature gradients in the composite structures. The primary goal is to perform structural health monitoring on a composite structure. A secondary goal is to use the sensors as a diagnostic tool to determine the optimal composite materials, architectures, or structures that are the least susceptible to thermal damage. Initial results will be discussed for two composite materials using a single sensor to measure temperature variations. The tests include measurements of the temporal and spatial thermal response of the composite resulting either from an applied heat source or to high energy radiation incident on the surface. Additional tests demonstrate the response using a 3x2 array of sensors to simultaneously measure the temperature at three varying depths in the composite, using three FBGs aligned with the heat source, and three FBGs located a short lateral distance (3cm) away from the heat source. In addition, since FBGs respond to strain as well as to temperature, any strain in the composite is coupled into the embedded fiber and is also detected by the FBG sensors. Initial measurements demonstrate the simultaneous response of FBG sensors to both temperature and strain. The various components of strain that are observed in the composite will be discussed, and possible methods to isolate these components and mitigate their response will be considered.

A portable and high-precision magnetic testing system for optical fiber gyroes with low power consumption is designed and introduced. The magnetic sensitive detector contains a temperature sensor and six hyper sensitized Hall elements that are inlaid into six surfaces of a cube. The Hall elements and temperature sensor turns the magnetic intensity into electrical voltage. After signal conditioning, the analog value is transmitted into digital signal by high-precision analog-digital converter. After demarcated and temperature compensated in FPGA, the transmitted signal will be displayed on the LCD instantly and sent to PC by USB. Via the designed system, a precise survey of magnitude and direction of the magnetic field can be more effectively done. Moreover, direction of the detector can be freely deposited without adjustment.

The upside down taper lens (UDTL) optical fiber ends are formed by a heating method. This new type of microlens can be used to make optical fiber connector between two fibers. In this paper, using plastic optical fiber, a single installation which are needed in the making UDTL fiber ends is described. The making method of this type plastic optical fiber end is introduced. Theoretically, using 1D heat conductor model, we analyze the forming tendency during the heating of the end of a plastic fiber. Experiments of the coupling between two plastic optical fibers with UDTL ends are given. The testing results of the connector shows that this novel optical fiber device can improve the coupling efficiency and provided a potentially inexpensive, simple and direct coupling method for fiber optic communication and fiber sensor systems.

For several decades silica-based optical fibres have been used for telecommunication and sensor purposes. The single-mode fibre is frequently employed in long-distance networks, whereas the multi-mode fibre is the preferred means of signal transport in campus and in-building networks. Because of the huge bandwidth of optical fibres in comparison to its electrical wireless and copper-based counterparts, the demand for optical fibres keeps increasing. In a competitive market, fibre manufacturers aim to produce ever better fibres that are as cheap and easy to employ as possible. As fibre research, development and manufacturing is a mature discipline, improvements in fibre design can only be achieved through the construction of robust, accurate and efficient numerical fibre models for the computation of those quantities that determine the behaviour of the fibre. We have developed a modular software code, based on Maxwell’s equations, to compute these quantities in a vectorial full-wave way for both single-mode and multi-mode optical fibres. Key is the refractive-index profile, or, more specifically, the dopant profile, as it defines the propagation, splicing and bending-loss characteristics of the fibre. For the single-mode fibre, the fibre quantities that we have concentrated on are dispersion, dispersion slope, mode-field diameter, effective area, bending loss, effective and theoretical cut-off wavelength and MAC-value. We highlight one fibre quantity in particular, viz. the computation of the bending loss in a single-mode fibre. Many approximate modelling techniques have been developed to estimate this loss in a fast way. Our numerical scheme, however, is the first rigorous one, as we have performed a vectorial full-wave analysis of the bent optical fibre. In this context, triple integrals involving products of Bessel functions with large, complex order and argument appear. Due to cancellations in the pertaining computation, a high relative accuracy is needed for the computation of each product. As a result, it takes weeks on a contemporary computer to compute the bending loss as a function of the radius of curvature. We have used the vectorial full-wave bending-loss results to determine the most appropriate approximate method. Subsequently, we have extended that approximate method to compute the bending losses of higher-order modes, since the required effective cut-off wavelength depends on the bending loss of the first higher-order mode. The selected approximate method has been used in the ensuing bending-loss calculations. Since the fibre properties are often conflicting, it is a challenging task to adapt the radial dopant profile to meet a set of predefined design goals. A design goal is a combination of desired values for (some of) the aforementioned fibre quantities, and can mathematically be translated into a cost function. The minimisation of this cost function provides us with the optimal dopant profile for that specific set. For the single-mode fibre, we have performed this minimisation for piecewise-linear profiles, by employing various global and gradient-based local optimisation strategies to speed up the design step considerably. Frequently,these optimisation strategies lead to counter-intuitive dopant profile designs that could not have been contrived otherwise. We have selected a deliberate mix of several optimisation routines and have compared their performances. Perhaps the most important conclusion is that there still appears to be room for improvement in the design of the radial dopant profile of commercially available fibres. For the multi-mode fibre, vectorial full-wave optimisation is not feasible yet because of the long computation times for the large number of propagating modes. Still, our numerical scheme allows for a manual fine-tuning of the popular power-law profile to minimise differential mode delay. Further, we have included mode coupling and differential mode attenuation in our model to obtain intensity patterns that match closely with measurements. We have also analysed the influence of profile variations, e.g. on-axis dips and kinks, on the intensity pattern. A selective excitation of different mode groups in a multi-mode fibre, offers the possibility to create several independent transmission channels, and thus a higher information capacity. Recently, the feasibility of this so-called mode group diversity multiplexing technique has been demonstrated. Simulations provide us with a means to better understand its operation and possibly increase its efficiency. The channel separation may be enhanced by employing a lens between the fibre and the detector, which is called mode-selective spatial filtering. Our numerical simulations of a mode group diversity multiplexing link, with and without mode-selective spatial filtering, are in agreement with the measurements. The above discussion makes clear that the developed software code has a wide range of applicability. Moreover, it is built in a modular way and thus extensions, like the inclusion of more fibre quantities or different profile dopants, are straightforward.

Many pipelines are built in regions affected by harsh environmental conditions where changes in soil texture between winter and summer increase the likelihood of hazards. Pipeline routes also cross mountains that are characterized by steep slopes and unstable soils as in the Andes and along the coastal range of Brazil. In other cases, these pipelines are laid in remote areas with significant seismic activity or exposure to permafrost. Depending on weather conditions and location, visual inspection is difficult or even impossible and therefore remote sensing solutions for pipes offer significant advantages over conventional inspection techniques. Optical fibers can help solve these challenges. Optical fiber based geotechnical and structural monitoring use distributed measurement of strain and temperature thanks to the sensitivity of Brillouin scattering to mechanical and thermal effects. The analysis of scattering combined with a time domain technique allows the measurement of strain and temperature profiles. Temperature measurement is carried out to monitor soil erosion or dune migration through event quantification and spatial location. Direct measurement of strain in the soil also improves the detection of environmental hazards. As an example, the technology can pinpoint the early signs of landslides. In some cases, actual pipe deformation must be monitored such as in the case of an active tectonic fault crossing. Pipe deformation monitoring operation is achieved by the measurement of distributed strain along fiber sensors attached to the structure. This paper comprehensively reviews over 15 years of continuous development of pipeline geohazard risk monitoring with optical fiber distributed sensors from technology qualification and validation to its implementation in real cases as well as its successful continuous operation. Case studies presented include pipeline monitoring in Arctic and Siberian environment as well as in the Andes which illustrate how the technology is used and demonstrate proof of early detection and location of geohazard events such as erosion, landslide, settlement and pipe deformation.

Recent progress in research on optical fiber devices, especially optical fiber couplers and optical fiber grating couplers are reviewed. Add-drop multiplexer operation by optical fiber grating couplers has recently attracted attention, because of its inherent low-insertion loss, simple implementation, and potential low-cost.

Polymer optical fibers (POF) have received increased attention in recent years in the fields of data communication and sensing applications. The lower cost and higher flexibility are the main advantages of POF compared to silica fibers and make them interesting candidates for Fiber Bragg grating (FBG) sensor applications. FBG are convenient measurement devices for strain and temperature measurements, as they can be multiplexed within one fiber yielding a sensor array and the fiber can be embedded in structures. This work investigated the possibility of producing FBG in polymer fibers and their use as sensor units. It could be shown that using excimer laser irradiation at 308 nm, it is possible to write FBG in single-mode POF employing a standard phase mask, side writing technique. Index changes of up to 1.7 × 10-4 and reflectivies of up to 87% could be reached. The induced refractive index change due to pulsed UV irradiation was shown to be negative. The polymer material of the core (Polystyrene (PS) / Polymethyl methacrylate (PMMA)) was not sensitized prior to irradiation. During the grating formation an irradiation induced insertion loss of up to 11 dB/cm was observed. Excimer laser written FBG showed stability of over 9 months for approximately 40% of written FBG. Results of FBG writing using femto second laser irradiation showed FBG with reflectivities of up to 1.2 × 10-4, however these POFBG were not stable. The POFBG were characterized using optical low coherence reflectometry (OLCR) which enables to calculate the FBG location and length as well as the induced amplitude Δnac and mean refractive index change Δndc. Taking into account fiber and insertion losses, good agreement of these calculations and measurements were found. The results show that large variations of the induced index change result from irradiation. Local index change peaks of up to 4 times the mean value were observed, indicating inhomogeneity of the fiber material. Birefringence in the core of the POF (≈ 1.2 × 10-3) is up to a factor 3 higher than in the cladding which is due to the PS content within the core. The birefringence is due to inelastic strain and stress induced in the drawing process. Annealing, uniform irradiation and FBG writing using 308 nm excimer laser light induces a decrease of the absolute birefringence value. The changes upon irradiation are confined to the core of the fiber. Large variations in the initial and final birefringence before and after irradiation support the findings of the OLCR measurements indicating material inhomogeneities in the fiber. POFBG were found to be sensitive to relative humidity, temperature and strain. This is in contrast to glass fiber FBG which do not show humidity sensitivity. POFBG relative humidity sensitivity is non-linear with a change of up to 8 nm for a RH change of ≈ 100%. The non-linearity is introduced by a non-linear water sorption process. The POF grating response to temperature changes under dry conditions (1.5±1 % RH) is –10±0.5 pm/°C. The temperature response of the FBG submerged in water is –36±2 pm/°C due to an increased thermal expansion coefficient and a change in polarizability. Under ambient conditions the grating response to heating is typically ≈ –138 pm/°C, predominantly due to a change in POF swelling, i.e changes in relative humidity and POF water content. The diffusion coefficient of water in this POF at 23.5°C is 6.7 × 10-9cm2/s for sorption and 10 × 10-9cm2/s for desorption. Equilibrium of water content within the fiber and the surrounding air is typically reached after approximately one hour. Calculation showed that a reduction of the fiber diameter can increase this humidity sensitivity response time down to approximately 5 minutes for a fiber diameter of 25 µm.

ABSTRACTA optical fiber device is described which can be used for wavelength division multiplexing, switching of opticalsignals and for optical fiber sensors. The device is formed by taking the central output port of 3 x 3 fused taper Bow-Tie optical fiber coupler back to the central input port to form optical fiber ring resonator with two inputs and two outputs. Keywords: Bow-Tie optical fiber, Optical fiber coupler, Optical fiber ring resonator1. INTRODUCTIONAs well known, an four-port optical fiber ring resonator can be made from a 3 x 3 single mode optical fiber coupler, which cross section of coupling range is plane. The devices can be used for wavelength divisionmultiplexing, switching of optical signals and as optical fiber sensor. Because of the fiuctuationof polarizationstate in single mode optical fiber, the signals of output of the fiber ring resonator with 3 x 3 single mode fiber coupler are unstable. In order to overcome this problem, we should use couplermade of polarization-maintainingoptical fiber. In this paper, we present the analysis and experiment of four-port optical fiber ring resonator witha 3 x

Thermonuclear controlled fusion research is a highly active branch of plasma physics. The main goal is the production of energy from the fusion reaction of hydrogen isotope nuclei, the same reaction that powers stars. The most promising present approach are Tokamaks, toroidal devices where high temperature plasmas are confined by means of magnetic fields. This thesis is devoted to a detailed and systematic study of plasma rotation nthe Tokamak à Configuration Variable (TCV), at the Centre de Recherches en Physique des Plasmas (CRPP) in Lausanne Switzerland. In a tokamak, confinement is limited by particle and energy transport from the hot core to the cold edge and by macroscopic perturbations of magnetic equilibrium. Recently, plasma rotation has been demonstrated to beneficially affect both confinement and stability, explaining the great recent interest in plasma rotation studies Relatively little is understood about plasma rotation physics and, in particular, the so called "intrinsic" rotation that will constitute the main component of plasma rotation in next generation machines. That is why a great theoretical and experimental effort is being deployed in studying intrinsic rotation and this work is part of this context. In TCV, plasma rotation is measured by the Charge eXchange Recombination Spectroscopy diagnostic (CXRS). The spectroscopic signal comes from the perpendicular observation of a low power Diagnostic Neutral Beam Injector (DNBI), which applies a negligible torque to the plasma. Hence, the DNBI/CXRS pair is an effective tool for the experimental study of intrinsic tokamak plasma rotation. During this work, the pre existing toroidal observation view was complemented with two new systems, permitting the measurement of toroidal rotation, on inboard plasma radius, and poloidal rotation in the plasma periphery. The implementation of an automated wavelength calibration procedure, based on reference Neon spectra, permitted the first viable (toroidal and poloidal) rotation measurements of TCV, with uncertainties down to 1km/s. Using upgraded light collection optics and fiber optic transmission lines, simultaneous measurement of core and edge plasma was achieved, with a doubling of of the radial resolution of the toroidal rotation measurements. The measurable range of plasma parameters was also extended to higher densities by the installation of back illuminated CCD detectors. In the present configuration (CXRS09), the diagnostic is capable of routinely measuring toroidal and poloidal plasma rotations with a radial resolution of ≲ 1 cm and a sample frequency of 10 ÷ 20 Hz, for plasma densities of 0.8 ≲ ne,av ≲ 8 × 1019 m-3. The basic scenario of Ohmically heated discharges in limiter L-mode configuration was initially addressed. A large core toroidal rotation up to uφ ≈ 50 km/s in the counter current direction is measured, reversing nearly exactly upon reversal of plasma current Ip. The toroidal rotation profile may be schematically divided into a core, a peripheral and an intermediate region. For qe ≈ 3 (magnetic safety factor at the plasma edge) the core region velocity is relatively flat or slightly "bulged" in the co current direction inside the sawtooth inversion radius. In the peripheral region, the toroidal rotation is small with a monotonic intermediate region. The central rotation appears to be limited to approximately its value at the sawtooth inversion radius. Poloidal rotation uθ ≲ 3 km/s, measured in Ohmic discharges, is only weakly dependent on plasma parameters but reverses with reversed magnetic field, with values and direction coherent with neoclassical predictions. Combining uφ and uθ measurements, the profile of the radial electric field Er was estimated through the radial force balance equation. Er down to 8 kVm (inward directed) is found in the plasma bulk, and close to zero at the plasma edge. A spontaneous reversal of the toroidal rotation profile is observed when the average density exceeds ne,av ≈ 4 × 1019 m-3 at low qe ≈ 3, with the plasma now rotating in the co current direction. The transition between the co and counter rotation regimes is studied dynamically using ne and Ip ramps and with the application of Electro Cyclotron Heating (ECH). The rotation reversal is weakly sensitive to impurity concentration and positive plasma triangularity appears to be a key ingredient. Whilst a physical explanation has not been identified yet, dynamic uφ reversal observations indicate that it results from a changed balance of radial non-diffusive fluxes of toroidal momentum. The study was extended to the divertor magnetic configuration in which the plasma column rotates in the co current direction at low ne, and uφ reverses at high ne opposite from the limited configuration. The rotation profile may again be divided into three regions, although the rotation at the plasma periphery does not always remain close to zero but evolves with the plasma parameters. In particular, independently on the core rotation regime, peripheral uφ decreases with ne and Ip and is strongly sensitive to the ion B→ × ∇B direction, suggesting a link with parallel fluxes in the Scrape-Off Layer (SOL). Combined measurements of of CXRS and Mach probe indicate that in the plasma edge toroidal rotation matches the toroidal component of SOL flows. From the analysis of toroidal rotation in stationary and transient phases, a characterization of the momentum transport is presented. The resulting radial momentum diffusivity, of the order of Χφ ∼ 0.1 – 0.3 m2/s, exceeds by 2 orders of magnitude the neoclassical estimation. A remarkable result is the existence of a "residual stress" component, which sustains a substantial stationary rotation gradient for null background rotation. Conversely, the analysis suggests a minor role for the convective (pinch) component, that is preliminarily confirmed by gyro-kinetic simulations including turbulent Coriolis convective pinch. Neoclassical predictions are in quantitative and qualitative disagreement with the experimental observations. The effect of the sawtooth instability on the core rotation was addressed in a specific experimental scenario where the inter crash evolution of the core uφ could be measured. The measurement required the development of a fast CXRS acquisition scheme based on a trigger constructed in real time from a Soft X-ray measurement. At the sawtooth crash the plasma core undergoes a strong acceleration in the co current direction (∆uφ ≈ 9 km/s in the experimental scenario), possibly related to a strong transient toroidal electric field. The systematic and varied observations reported in this work extend the experimental knowledge of bulk plasma rotation in low confinement regimes. In particular, the rotation reversal phenomena constitute an important test for momentum transport models of tokamak plasmas.

Railway tracks are the direct supporting structures of the trains, which are vulnerable to produce large deformation under the temperature stress or subgrade settlement. The health status of track is critical, and the track should be routinely monitored to improve safety, lower the risk of excess deformation and provide reliable maintenance strategy. In this paper, the distributed optical fiber sensor was proposed to monitor the continuous deformation of the track. In order to validate the feasibility of the monitoring method, two deformation monitoring tests on one steel rail model in laboratory and on one real railway tack in outdoor were conducted respectively. In the model test, the working conditions of simply supported beam and continuous beam in the rail model under several concentrated loads were set to simulate different stress conditions of the real rail, respectively. In order to evaluate the monitoring accuracy, one distributed optical fiber sensor and one fiber Bragg grating (FBG) sensor were installed on the lower surface of the rail model, the strain measured by FBG sensor and the strain calculated from FEA were taken as measurement references. The model test results show that the strain measured by distributed optical fiber sensor has a good agreement with those measured by FBG sensor and FEA. In the outdoor test, the real track suffered from displacement and temperature loads. The distributed optical fiber sensor installed on the rail can monitor the corresponding strain and temperature with a good accuracy.

Fiber Bragg gratings are widely used in electrical equipment monitoring, structural health monitoring, power system fault monitoring and other actual detection occasions due to the unique advantages of anti-electromagnetic interference, low fusion loss, high sensitivity, small size, and easy distributed measurement. Fiber grating has been widely used in actual detection occasions such as electrical equipment monitoring, structural health monitoring, and power system fault monitoring. The temperature measurement of the motor based on fiber grating sensing technology not only has strong anti-electromagnetic interference ability, but also can realize multi-point distributed temperature measurement. The research of fiber grating temperature measurement system for intelligent electrical equipment is of great significance. This article mainly studies the optical fiber grating temperature measurement system of intelligent electrical equipment. This paper designs the temperature measurement system architecture, including data acquisition layer, data monitoring layer and remote monitoring layer. Complete the system design from two aspects: hardware design and software design. In the hardware part, the functions of the temperature sensor module transmission system, signal demodulation system, PLC and host computer are analyzed. Use FTM3501 fiber temperature converter is used to realize the automatic electrical fiber grating. Experimental results show that the thermometer has alarm and display analysis functions. The measurement uncertainty is analyzed, and the uncertainty of the calibration result of the fiber Bragg grating temperature sensor is 0.0725 °C; the fault judgment time of the system in this paper does not exceed 4.73 s, while the fault judgment time of the control group is more than 4.73 s. Compared with the control group, it has a faster fault accuracy speed. The system has high measurement accuracy and good stability, can be applied to actual temperature measurement systems, and has certain practical value.

In recent years, Fiber Bragg Grating (FBG) has attracted increasing interest for sensing applications, due to its unique fiber structure which offers many advantages such as immunity towards Electro-Magnetic Interference (EMI), rugged structure, high sensitivity, and accuracy. Moreover, the FBG temperature sensor has greater sensitivity and inexpensive price, therefore it is increasingly used in several industrial applications. In this article, the design, construction, calibration, and testing of an FBG temperature sensor probe are presented with detailed experimental analysis. Due to passive characteristics, these sensors do not influence EMI during sensing. Therefore, it will be the best possible choice for high magnetics field areas like Aluminum electrolysis cells in potlines. The static characteristics of the FBG temperature sensor such as precision, sensitivity, accuracy, linearity, etc. are presented. A rod-type temperature sensor with a high resolution of 0.2051°C and higher sensitivity of 13 pm$/^{\circ}$C has been discussed. In a broad frequency range, the proposed sensor demonstrates outstanding temperature sensitivity with enhanced characteristics. In the Fial section, the difficulties and potential of FBG sensors for sensing applications are discussed.