Double Fiber Bragg Grating Research Articles

A high-sensitivity fiber Bragg grating sensor for displacement measurement in structural health monitoring.

Displacement measurement is of great significance to monitor the crack variation and ensure the health of building structures. Aiming at the problems of low sensitivity and high temperature error of fiber Bragg grating (FBG) displacement sensors in displacement monitoring, this paper presents an adjustable cantilever beam displacement sensor with the FBGs as the sensing element. The sensor adds double FBGs on the relative surfaces of the equal-strength cantilever beam, which increases the bending deformation on the FBG of the beam surface to improve the sensitivity and realize the temperature compensation of the sensor. By adding an adjustable external rod structure between a flexible spring and a fixed foot stand, the sensor can regulate the range of initial crack width for different occasions. A theoretical analysis of the displacement sensor is performed, and the simulation analysis and optimization design for the structural parameters of the cantilever beam elastic sensitive element are implemented by adopting SolidWorks and ANSYS software. Finally, a displacement testing platform is constructed to test its performance. Experimental results show that this design has a high sensitivity coefficient of 39.47 pm/mm and a temperature coefficient of 1.04 pm/°C in the range of initial crack width from 0 to 110mm or from 0 to 130mm depending on different monitoring situations. Furthermore, good linearity, hysteresis delay, repeatability, and temperature compensation performance have also been demonstrated.

A Synchronous and Accurate Detection Method for Gas Pipeline Leakage Position and Flow Rate Based on Double Fiber Bragg Gratings

Fast and accurate detection of pipeline leaks plays an important role in reducing economic losses and ensuring the safety of personnel. However, for the two important indicators of gas pipeline detection, how to effectively detect the leakage location and leakage rate simultaneously is a serious challenge. In this paper, we present an innovative optical fiber detection method based on double fiber Bragg gratings (FBGs) string to solve this problem. Combined with the theory of material mechanics and fluid mechanics, the binary equations are derived as the demodulation formula. In the detection, the corresponding physical quantities can be calculated by substituting the center wavelength of the two FBGs after drift. The experiments demonstrate that this sensor’s gas flow rate sensitivity in different positions can be up to 466.67 pm∙s/m. Meanwhile, at the same flow rate and different leakage positions, the sensor has sensitive symmetrical performance. The error results manifest that the velocity error is not more than 0.13 m/s, and the relative position detection error is not more than 0.167%. Overall, besides the extended measurement range and excellent linearity, our method also has the advantages of low production cost, simple structure and ease of production, which is more suitable for gas pipeline health monitoring in the future.

A Simultaneous Distinguishing Measurement Method of Carbon Dioxide Gas Concentration and Air Humidity Based on Double Fiber Bragg Gratings

Due to the advantages of small size, high sensitivity and strong anti-interference ability, optical fiber sensors are widely used in gas detection. Meanwhile, concentration and humidity detection based on optical fiber sensing are paramount technologies in the field of gas sensing. However, how to solve the issue of cross sensitivity of concentration and humidity of optical fiber gas sensors and realize synchronous detection of two parameters are current common challenges. In this study, taking carbon dioxide as an example, a detection method based on double fiber Bragg grating (FBG) string is proposed to measure carbon dioxide concentration and air humidity simultaneously. Here, a pair of FBGs are welded in series on an optical fiber after being filled with special materials. Using the control variable method, the performance parameters of the sensor can be determined through calculation. The experimental results demonstrate that the gas concentration sensitivity is 0.5952 pm/ppm in the range of 0 ppm~2250 ppm. In the range of 25%~65%, the air humidity sensitivity is 28.62 pm/RH. Moreover, it is less affected by temperature and has satisfactory repeatability and reproducibility. The sensor realizes high sensitivity and low crosstalk measurement of concentration and humidity and can be applied to the simultaneous detection of carbon dioxide concentration and air humidity in specific confined space.

Tunable and switchable erbium-doped fiber laser based on the parallel filter of the FBGs embedded in Sagnac ring and the in-line MZI

A tunable and switchable erbium-doped fiber laser (EDFL) based on the parallel filter is proposed and experimentally verified. The parallel filter is composed of two branches. One branch is double fiber Bragg gratings (FBGs) embedded in Sagnac ring filter, which can realize the selection of two wavelengths; the other branch is an in-line Mach Zehnder interferometer (MZI) filter, which is composed of a 10 cm polarization-maintaining fiber (PMF) fused in the middle of single mode fibers (SMFs) with spheres at both ends, which can realize the selection of five wavelengths. When the parallel filter is inserted into the fiber laser cavity and the polarization controllers (PCs) are adjusted, the laser excitation from single-wavelength to quadruple-wavelength can be realized, including 7 different single-wavelength laser states, 16 different dual-wavelength laser states, 11 different triple-wavelength laser states and 2 different quadruple-wavelength laser states. In addition, the intervals of the dual-wavelength laser states are relatively regular, and the dual-wavelength laser intervals are obtained every ∼ 2 nm from 7 nm to 18 nm. And the optical signal-to-noise ratios (OSNRs) are more than 43 dB, and the highest OSNR is 60 dB. Finally, by changing the temperature applied to the FBG, tunability of dual-wavelength intervals can be achieved with a range of 1.1 nm. Due to the variety of lasing laser states of the fiber laser, easy switching, and regular intervals between the dual-wavelength laser states, the fiber laser proposed can be better applied to wavelength division multiplexing (WDM)system.

Flexible Optical Fiber-Based Smart Textile Sensor for Human–Machine Interaction

Flexible sensors are the main components of wearable devices. Compared with flexible substrate-based skin-like sensors, flexible textile sensors have the intrinsic advantages of excellent breathability, compliance with the human body and comfort to human skin. In this article, a flexible optical fiber-based smart textile (FOFT) sensor has been proposed for the application of intelligent human–machine interaction (HMI) and healthcare. The FOFT sensor integrated fiber Bragg gratings (FBGs) with yarns in the way of the plain weave. A double-layer flexible optical fiber crossover structure is proposed to improve the measurement accuracy of the sensor for human body signals. Such a structure leads to a highly flexible textile and wearing comfort. The weak characteristic information of the human body can be extracted by the sensor based on the wavelength demodulation of double FBGs. Combined with the backpropagation (BP) neural network, an FOFT sensor-based gesture recognition application with an off-line accuracy of 97.02% has been developed. Furthermore, the FOFT sensor is used to monitor the human respiratory signals under different postures and obtain the respiratory rate. A series of experiments demonstrate that the FOFT sensor has a huge potential in HMI and healthcare.

A Double FBGs Temperature Self-Compensating Displacement Sensor and Its Application in Subway Monitoring.

In order to ensure the effective vibration–reduction and vibration–isolation of the steel spring floating plate rail and meet the safe operation requirements of the subway, a Fiber Bragg Grating (FBG) displacement sensor for the deformation monitoring of the subway floating plate is proposed. The sensor adopts double FBGs to realize temperature self-compensation. The elastic ring is used as the elastic conversion structure after the fiber grating is pre-stretched; the two ends are pasted and fixed in the groove in the diameter direction of the ring, which avoids the waveform distortion caused by the full pasting of the fiber grating. The combination of linear bearing and displacement probe rods can increase stability and reduce friction loss so that the sensor has the advantages of high sensitivity and accurate measurement results. The test results and error analysis show that in the range of 0~20 mm, the sensitivity of the sensor is 164.2 pm/mm, the accuracy reaches 0.09% F.S, and the repeatability error and hysteresis error are only 1.86% and 0.99%, respectively. The thermal displacement coupling experiment proves that the sensor has good temperature self-compensation performance. It provides a new technical scheme for the effective monitoring and condition assessment of the built-in steel spring floating plate rail.

A Synchronous and Accurate Detection Method for Gas Pipeline Leakage Position and Flow Rate Based on Double Fiber Bragg Gratings

A Synchronous and Accurate Detection Method for Gas Pipeline Leakage Position and Flow Rate Based on Double Fiber Bragg Gratings

A two-dimensional cantilever beam vibration sensor based on fiber Bragg Grating

A two-dimensional cantilever vibration sensor based on Fiber Bragg Grating (FBG) is proposed. The proposed sensor consists of a section of optical fiber with double FBGs and three different beams. After theoretical analysis and experimental verification, the proposed sensor has a high sensitivity response. The experimental result shows that the natural frequency of the sensor in the x/y direction of vibrations is respectively 505/177 Hz. The flat frequency of the sensor is 60–150 Hz and 30–150 Hz, respectively. And the sensor’s sensitivity is respectively 125.85/82.32 pm/g in the x/y direction of vibration. Compared with the traditional cantilever beam FBG sensor, the proposed sensor has the advantages of multi-directional detection, avoiding chirp and so on. Therefore, it has great application prospects in two-dimensional vibration signal detection of bridges, roads and buildings.

New Double Fiber Bragg Grating Static Level Based on Equal Strength Beams

New Double Fiber Bragg Grating Static Level Based on Equal Strength Beams

Research on one-piece structure target flow sensing technology based on fiber Bragg grating

In view of problems existing in the detection of the traditional hydraulic system, such as the large volume of sensor and the low measurement accuracy, a new one-piece target type flow sensor is designed and researched based on fiber Bragg grating (FBG). A compact structure is designed, which is convenient to be dismantled, processed, and installed, based on the analysis of the principle of FBG and the structure of target type flow sensor. The force of target put in fluid flow is turned into the FBG wavelength drift, with a corresponding relationship. The problem on the cross sensitivities of the temperature and strain is solved effectively by using double FBG symmetrically pasted on the both surfaces of the cantilever. The impact on the fluid state is analyzed through simulation in the software FLUENT, and the results show that the impact was smaller than that of the traditional structure. The results of experiments in the hydraulic system show that there is a good linear relationship between the change in the dual FBG central wavelength and mass loading on the target sheet has a good linear relationship, and the sensitivity is twice that of a single FBG sensitivity.

A Highly Sensitive Temperature Sensor Based on Power Changes of Fiber Bragg Grating Pairs

A highly sensitive temperature sensor based on power change of double fiber Bragg gratings (FBGs) structure is proposed in this letter. It consists of two identical FBGs (FBG1, FBG2), in which the Bragg wavelength of FBG1 is modulated by the temperature and its reflecting light is injected into FBG2. Thus, the power difference of two peaks that appear in the transmission spectrum of FBG2 can be modulated by temperature around FBG1. By shifting the Bragg wavelength of FBG2, the sensor can achieve the segmental measurement of temperature. In the experiment, dynamic range of 25 °C-135 °C and sensitivity of 1.35 ± 0.02 dBm/°C have been achieved.

Research of a double fiber Bragg gratings vibration sensor with temperature and cross axis insensitive

A novel double fiber Bragg gratings (FBGs) vibration sensor with temperature and cross axis insensitive is developed. In order to eliminate the influences of the temperature drift, the symmetrical pull–push structure is adopted. The sensor head is based on two elastic material cylinders, into which two matching FBGs are embedded respectively, loaded with a seismic mass. Closed-form analytical formulas describing the resonant frequency and sensitivity of the FBG vibration sensor are provided which may be utilized to tailor the sensor performance to specific applications. The phase generation carrier (PGC) interrogation technique based on the unbalanced Michelson interferometer is studied. Experimental results of a prototype vibration sensor show that the acceleration sensitivity of the FBG vibration sensor reaches 450pm/g in the frequency range of 5–100Hz. The resonant frequency of the FBG vibration sensor is 210Hz. For a temperature change from 0°C to 50°C, the wavelength shift of the sensor is almost 0 without any temperature compensation schemes. The noise floor of the FBG vibration sensor is obviously improved and reaches −100dB/Hz1/2 over the range of 40–100Hz. The experimental results prove the good performance of the FBG vibration sensor.

A Research on High-Precision Strain Measurement Based on FBG with Temperature Compensation

FBG (Fiber Bragg Grating) is a new type of optical passive device which can be used in sensing field. This paper demonstrates the feasibility and effectiveness of FBG as the new method of strain measurement, and improves the measuring precision. Based on the strain sensing property of FBG, the study adopts the differential method of double FBGs to make temperature compensation, and conduct the contrast experiment with resistance strain chip. The experimental results show that strain measurement based on FBG agrees well with theoretical calculation. The measurement error: no more than 1%, linear fitting correlation coefficient: almost 1, linearity: 0.17%, sensitivity: 7.92, hysteresis error: 0.347%, repeatability error: 0.333%. The results show FBG’s performance are superior to resistance strain chip, especially in aspect of measuring precision. Therefore, we can conclude that FBG is a feasible and effective method of strain measurement.

Low-frequency fiber Bragg grating accelerometer based on a double-semicircle cantilever

A compact double fiber Bragg gratings (FBGs) accelerometer based on an organic double-semicircle cantilever is proposed and experimentally demonstrated for low-frequency vibration measurement. The configuration is formed by two points of every FBG fixed at the two sides of the semicircle, efficiently avoiding the unwanted chirp effect of grating. The dynamic vibration measurements exhibit that the accelerometer provides an extremely high sensitivity of 1296pm/g and a considered frequency range from 0 to 25Hz, while the two FBGs is contributed to the sensitivity enhancement, temperature and transverse sensitivity independent. The smart device has a compact size and efficient fabricating cost, indentifying it a good candidate for the embedding structure monitoring.

Temperature insensitive fiber optical displacement sensors based on double fiber Bragg gratings

ABSTRACTA temperature insensitive fiber optical displacement sensor based on double Bragg gratings is presented and experimentally demonstrated. The sensor is constructed by a trapezoid slid block and two isosceles cantilevered beams, and two fiber Bragg gratings (FBG) that are glued on the two beams. The displacement can be measured by interrogating the wavelength difference of the two FBGs, and the temperature dependence is greatly reduced. Experimental results show that a displacement sensitivity of 120 pm/mm and a temperature dependence of 2.1 pm/°C are achieved. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:304–306, 2014

High-sensitivity bend angle measurements using optical fiber gratings

We present a high-sensitivity and more flexible bend measurement method, which is based on the coupling of core mode to the cladding modes at the bending region in concatenation with optical fiber grating serving as band reflector. The characteristics of a bend sensing arm composed of bending region and optical fiber grating is examined for different configurations including single fiber Bragg grating (FBG), chirped FBG (CFBG), and double FBGs. The bend loss curves for coated, stripped, and etched sections of fiber in the bending region with FBG, CFBG, and double FBG are obtained experimentally. The effect of separation between bending region and optical fiber grating on loss is measured. The loss responses for single FBG and CFBG configurations are compared to discover the effectiveness for practical applications. It is demonstrated that the sensitivity of the double FBG scheme is twice that of the single FBG and CFBG configurations, and hence acts as sensitivity multiplier. The bend loss response for different fiber diameters obtained through etching in 40% hydrofluoric acid, is measured in double FBG scheme that resulted in a significant increase in the sensitivity, and reduction of dead-zone.

Study and design of a low cost optical pickup based on double FBGs

A fiber Bragg grating (FBG) pickup exploiting Intensity Modulation-Direct Detection (IM-DD) interrogation system was put forward in this paper. The feasibility of detecting the vibration of the guitar was revealed by FFT analysis. There was certain correlation between the FBG pickup and the magnetic pickup. A high signal-to-noise ratio (42.85dB) was obtained. The FBG pickup has a frequency response range (0–3000Hz) that is comparable to the reference pickup. The results indicated that the proposed pickup is effective to pick up the vibration. A simple structure design and low-cost interrogation system set-ups were proposed.

基于双光纤布拉格光栅滤波的量子密钥分发误码率分析

基于双光纤布拉格光栅滤波的量子密钥分发误码率分析

A new micro/nano displacement measurement method based on a double-fiber Bragg grating (FBG) sensing structure

The trend toward miniaturization in manufacturing has led to a requirement for micro/nano measuring techniques capable of measuring tiny features on small components. In this paper we propose and demonstrate a novel scheme for micro/nano displacement measurement based on a double-FBG (fiber Bragg grating) sensing structure, a suspended FBG probe stem and a fiber fused micro-ball tip. Such a scheme has some advantages including robustness, sensitivity, small size with large aspect ratio attainable, simplicity and economy. The preliminary experiments showed that the prototype yielded a measurement resolution of 10 nm and a nonlinear error of 150 nm.

双光栅π相位差温度不敏感加速度传感技术研究

双光栅π相位差温度不敏感加速度传感技术研究