Bragg Wavelength Of Fiber Bragg Grating Research Articles

Reliable self-healing FBG sensor network for improvement of multipoint strain sensing

In this paper, we proposed and designed reliable self-healing fiber Bragg grating (FBG) sensor network for improvement of multipoint strain sensing. We use an optical switch (OSW) to reconfigure the sensor network and improve the self-healing function during fault happen in the sensor network. In this work, to prove and validate the detection performance of our proposed Bragg wavelength detection technique even when the number of overlap spectra of FBGs increases, we conduct three experiments and collect three different cases of strain data (namely case 1, case 2, and case 3) by applying different strain steps to FBGs. In case 1 experiment, strain was applied to only FBG1 sensor, while the other four FBGs keeps fixed. In case 2 experiment, strain was applied to FBG1 and FBG2 sensors at the same time and with different strain steps. In case 3 experiment, strain was applied to FBG1, FBG2 and FBG3 sensors at the same time and with different strain steps. As a result, in all cases of the experiment, three situations of spectra were introduced between FBGs like non-overlapped, partially overlapped and completely overlapped spectra. To solve this overlap problem, we used deep learning technique to accurately identify the Bragg wavelength of FBGs in the condition of the partially or fully overlapped spectra. Therefore, our proposed FBG sensor system can improve the reliability and detection accuracy of the sensor system even the number of overlaps FBGs spectra increases.

Design Reliable Bus Structure Distributed Fiber Bragg Grating Sensor Network Using Gated Recurrent Unit Network.

The focus of this paper was designing and demonstrating bus structure FBG sensor networks using intensity wavelength division multiplexing (IWDM) techniques and a gated recurrent unit (GRU) algorithm to increase the capability of multiplexing and the ability to detect Bragg wavelengths with greater accuracy. Several Fiber Bragg grating (FBG) sensors are coupled with power ratios of 90:10 and 80:10, respectively in the suggested experimental setup. We used the latest IWDM multiplexing technique for the proposed scheme, as the IWDM system increases the number of sensors and allows us to alleviate the limited operational region drawback of conventional wavelength division multiplexing (WDM). However, IWDM has a crosstalk problem that causes high-sensor signal measurement errors. Thus, we proposed the GRU model to overcome this crosstalk or overlapping problem by converting the spectral detection problem into a regression problem and considered the sequence of spectral features as input. By feeding this sequential spectrum dataset into the GRU model, we trained the GRU system until we achieved optimal efficiency. Consequently, the well-trained GRU model quickly and accurately identifies the Bragg wavelength of each FBG from the overlapping spectra. The Bragg wavelength detection performance of our proposed GRU model is tested or validated using different numbers of FBG sensors, such as 3-FBG, 5-FBG, 7-FBG, and 10-FBG, separately. As a result, the experiment result proves that the well-trained GRU model accurately identifies each FBG Bragg wavelength, and even the number of FBG sensors increase, as well as the spectra of FBGs, which are partially or fully overlapped. Therefore, to boost the detection efficiency, reliability, and to increase the multiplexing capabilities of FBG sensor networks, the proposed sensor system is better than the other previously proposed methods.

High-Resolution FBG-Based Inclination Sensor Using Eigen Decomposition of Reflection Spectrum

This article addresses the analysis and design of a high-resolution and temperature-insensitive inclination sensor using fiber Bragg grating (FBG). The sensor uses a pendulum-based structure with FBG attached to its cantilever arm. Initially, strain analysis of the proposed inclination sensor is carried out using the finite-element method (FEM) to optimize the structure and materials for its fabrication. Experimental analysis is carried out on the inclination sensors by varying the inclination angle, and its results are compared with the FEM-based results. The shift in Bragg wavelength of FBG due to the generated strain at the cantilever arm is observed on optical interrogator. To measure the subpicometer wavelength shift with enhanced resolution and lower uncertainty, eigen decomposition of the reflection spectrum using Karhunen–Loeve transform (KLT) is implemented. The range of measurement of tilt angle is found to be 0°–3° with a resolution of 0.0008°. The satisfactory linearity of the measured angle versus true angle, excellent repeatability, and very high resolution validates the feasibility of the proposed inclination sensor.

Low-Cost Interrogation of Long-Distance and Multipoint FBG Sensor Using Incoherent-FMCW Optical Ranging System

More than a decade, multipoint sensor systems involving fiber Bragg gratings (FBGs) have been widely used in various implementations, especially the structural health monitoring system (SHMS). In this paper, a three-points FBG sensor was successfully analyzed by combination of incoherent frequency modulated continuous wave (I-FMCW) optical ranging system and a vertical-cavity surface-emitting laser (VCSEL) as a wavelength-tunable laser source. This system is not only capable of reading out the FBG sensors, but also identifying the location of the installed FBGs. The I-FMCW can be conducted by intensity modulation of a low-cost commercial VCSEL. Furthermore, the wavelength of the VCSEL can also be tuned by the injection current change to match the Bragg wavelength of FBGs. The detected signal from the FBGs and the reference signal from the signal generator are electrically mixed to obtain the beat frequency. A thermo-electric controller (TEC) controls temperature of one of the FBGs in the range of 25° C ~ 45° C, and contrary the others are kept at room temperature. As well as measuring temperature, one of the FBGs is strained in the range of $369~\mu \varepsilon \sim ~2137~\mu \varepsilon $ . The measurement result shows that the system can clearly distinguish all FBGs installed in totally 6.6 km-long optical fiber. In addition, the Bragg wavelength shift of the FBGs according to temperature as well as strain changes was successfully measured. The system can be scaled up more than three FBGs and extended scale area, and is a candidate as a low-cost and simple FBG interrogator for a long-range SHMS.

Simultaneous measurement of micro-displacement and temperature based on balloon-like interferometer and fiber Bragg grating

An optical fiber sensor based on balloon-like interferometer and fiber Bragg grating (FBG) for simultaneous measurement of micro-displacement and temperature has been presented and experimentally investigated. The single-mode fiber (SMF) with coating stripped is designed into a balloon-like shape to form a modal interferometer. The interference occurs between the core mode and cladding mode induced by the bending. With the micro-displacement increasing, the radius of balloon-like interferometer changes, which results in the variation of interference fringe of balloon-like interferometer, while the Bragg wavelength of FBG remains the same. With the change of temperature, the interference fringe of balloon-like interferometer and Bragg wavelength of FBG will shift. Thus the simultaneous measurement of micro-displacement and temperature can be achieved. From the experimental results, sensitivities of the balloon-like interferometer for the micro-displacement and temperature are 180 pm/μ m and 105 pm/°C.

High-precision FBG demodulation using amplitude ratio curve with sharp peak

Abstract For the fiber Bragg grating (FBG) sensor based on the reflection peak position searching demodulation algorithms, a key problem is that the demodulation precision of measurement signal is seriously limited by the full width half maximum (FWHM) of the FBG reflection spectrum. In this paper, in order to overcome this problem and enhance the measurement precision, we proposed a high-precision demodulation method based on amplitude ratio curve to instead of the FBG reflection spectrum, which can increase the sensing precision significantly. In this method, the Bragg wavelength of FBG is modulated periodically with a sinusoidal function to obtain a series of reflection spectra. Then at each wavelength the amplitude ratio between second harmonic frequency component and fundamental frequency component is calculated to create the amplitude ratio curve. Here, we present a comprehensive theoretical analysis and experimental demonstration to verify the advantages of this method. Comparing with the demodulation method based on the FBG reflection spectrum, the average maximum measure error (MME) of Bragg wavelength is reduced from ±1.54 pm to ±0.15 pm, which improved by 10.3 times. In addition, the influence of the modulation amplitude and sampling frequency on demodulation accuracy are also studied in this paper.

Novel integrated optical fiber sensor for temperature, pressure and flow measurement

A novel integrated optical fiber sensor was proposed for temperature, pressure and flow measurement. One fiber Bragg grating (FBG) was fixed in the target for temperature measurement. A couple of FBGs, which were stuck on the inner wall of a hollow cylindrical cantilever, were used to measure flow rate. Another couple of FBGs were fixed on the outer wall of a thin-walled cylinder to measure pressure. Theoretical relationships between the Bragg wavelengths of FBGs and temperature, pressure and flow rate, have been established by numerical analysis respectively. Meanwhile, experiments have been carried out to obtain the performance of the proposed integrated sensor. Experimental results showed that the resolutions of temperature, pressure and flow rate were 0.1 °C, 0.006 MPa, 0.17m3/h and the measurement ranges were 10∼95 °C, 0∼10 MPa and 0∼18.5m3/h, respectively. In addition, the precision of sensor in temperature, pressure and flow rate were 0.12%, 0.5%, 1.5%, respectively. As we know, the proposed flowmeter is more compact with good resolution, wide measurement range, high accuracy and easy fabrication.

Reflective mercury ion and temperature sensor based on a functionalized no-core fiber combined with a fiber Bragg grating

A reflective fiber optic sensor is proposed and experimentally validated, which enables simultaneous measurement of temperature and mercury ion (Hg2+) concentration. The sensor consists of a fiber Bragg grating (FBG) and a functionalized no-core fiber (NCF). The chitosan (CS)/poly acrylic acid (PAA), as Hg2+ sensitive film, is assembled on the surface of the NCF by layer-by-layer self-assembly method. Besides, the silver film is coated on the end of NCF to ensure the reflection of light. This reflective fiber structure forms a fiber modal interferometer. When the sensor is immersed in the test solution, the Hg2+ adsorption of sensitive film leads to change in its refractive index, and then the interference spectrum of the fiber modal interferometer will shift accordingly, which is the measurement principle of Hg2+ sensor. Meanwhile, when the surrounding temperature changes, the interference fringe of the fiber modal interferometer and the Bragg wavelength of FBG will shift simultaneously. Therefore, the Hg2+ concentration and temperature can be simultaneously measured by using dual-wavelength matrix method, and then the cross sensitivity problem of temperature and Hg2+ concentration can also be solved. The experimental results show that the detection sensitivity of Hg2+ concentration is 0.0823 nm/μM in the range of 0 μM–100 μM and 0.0178 nm/μM in the range of 100 μM–500 μM, respectively. The temperature sensitivity is 0.0147 nm/°C in the range of 20 °C–50 °C.

Optical fiber sensors based on novel polyimide for humidity monitoring of building materials

Abstract This paper presents novel preparation methods of polyimide and coupling agent, coated on the fiber Bragg grating (FBG) sensor for monitoring relative humidity (RH). The sensing mechanism that the volume change of the moisture-sensitive polyimide induces the shift of the Bragg wavelength of FBG is used in the RH sensor. The performance of the polymer-coated RH sensor was evaluated under laboratory conditions of temperature over a range of values (20.0–80.0 °C) and humidity over a range of RH values (25.0–95.0%). The time response and RH sensitivity of the sensor based on novel polyimide and coupling agent was improved, compared to the previous. A new packaged RH sensor was designed, which was used in detecting the moisture diffusion and evolutions inside of sample made of building materials which exposed to a controlled environment in the lab after casting. Relative humidity inside of sample with time was 100% in the first phase of vapor-saturated, slowly reduced in the latter phase. The results indicate the RH sensor developed provides a feasible method to detect the influence of environment on moisture inside the material in the drying process.

Use of fiber Bragg grating (FBG) for stable and tunable erbium-doped fiber ring laser with single-longitudinal-mode (SLM) output

In this demonstration, we propose and investigate a stable C-band erbium-doped fiber (EDF) laser with compound-ring cavity. To achieve wavelength tunability with single-longitudinal-mode (SML) output, the sub-ring scheme and fiber Bragg grating (FBG) are used inside the ring cavity. Here, different lasing wavelengths can be selected by employing different Bragg wavelengths of FBGs. In this experiment, the obtained optical signal to noise ratios (OSNRs) and output powers are larger than 44.5 dB and 8.0 dBm respectively in the tuning range of 1531.70–1547.88 nm. Moreover, the output wavelength and power fluctuations of the proposed EDF laser are less than 0.02 nm and 0.1 dB in an observation time of 30 min, respectively.

A motor's rotational angle sensor based on fiber Bragg grating

ABSTRACTThis article develops an optical fiber sensor using a fiber Bragg grating (FBG) and a piezo‐electrical transducer (PZT) to measure a motor's rotational angle. By mounting an FBG on a PZT bar, a dynamic strain simulator was constructed. The equivalent voltage produced by the potentiometer caused by the rotational angle of a motor's shaft was applied to the PZT and converted to the dynamic variation of the FBG Bragg wavelength. The motor's rotational angle was attained by measuring the changing value of the wavelength. The experimental results demonstrate that a high sensitivity of 0.459 pm/deg is achieved over a range of 0° to 270°. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1449–1452, 2014

A reactive power sensor based on fiber Bragg grating and a piezo‐electric transducer

AbstractThis article develops an optical fiber sensor using a fiber Bragg grating (FBG) and a piezo‐electrical transducer (PZT) to measure reactive power. By mounting an FBG on a PZT bar, a dynamic strain simulator was constructed. The equivalent voltage produced by reactive power applied to the PZT was converted to the dynamic variation of the FBG Bragg wavelength. The reactive power was attained by measuring the changing value of the wavelength. Thus, the sensor can be used to measure reactive power without the use of a traditional power meter. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1692–1696, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27617

Measurement of active power using fiber bragg grating and a piezo‐electric transducer

AbstractThis article develops an optical fiber sensor using fiber Bragg grating (FBG) and a piezo‐electrical transducer (PZT) to measure active power.Mounting an FBG on a PZT bar, a dynamic strain simulator was constructed. The equivalent voltage produced by active power applied to the PZT was converted to the dynamic variation of the FBG Bragg wavelength. The active power was attained by measuring the changing value of the wavelength. Thus, the sensor can be used to measure active power without the use of a traditional power meter. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:682–686, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27394

Modeling and testing of static pressure within an optical fiber cable spool using distributed fiber Bragg gratings

Based on the force analysis, we establish a theoretical model to study the static pressure distribution of the fiber cable spool for the fiber optic guided missile (FOG-M). Simulations indicate that for each fiber layer in the fiber cable spool, the applied static pressure on it asymptotically converges as the number of fiber layers increases. Using the distributed fiber Bragg grating (FBG) sensing technique, the static pressure of fiber cable layers in the spool on the cable winding device was measured. Experiments show that the Bragg wavelength of FBG in every layer varies very quickly at the beginning and then becomes gently as the subsequent fiber cable was twisted onto the spool layer by layer. Theoretical simulations agree qualitatively with experimental results. This technology provides us a real-time method to monitor the pressure within the fiber cable layer during the cable winding process.

Monitoring of sea bed level changes in nearshore regions using fiber optic sensors

This work reports the implementation and test of a pressure optical sensor suitable to measure, in situ, the sea bed level changes in the nearshore regions. The sensor is based on a fiber Bragg grating (FBG) embedded in a polymeric resin block. The increase of the pressure on the top face of the sensor, due to the change of sediments layer height, results in a change of the FBG Bragg wavelength. The sensor response reveals the capacity to discriminate sea bed level changes down to 2.5cm, under field survey conditions. Finally, the sensor was successfully tested in a field trial survey at Costa da Caparica, Portugal.

Noise sensor based on a fiber Bragg grating and a Piezo‐electric transducer

AbstractThis article demonstrates an optical fiber sensor using fiber Bragg grating (FBG) and a Piezo‐electrical transducer (PZT) to measure noise.Mounting an FBG on a PZT bar, a dynamic strain simulator was constructed. The voltage produced by noise level applied on PZT was converted to the dynamic variation of FBG Bragg wavelength. The experiments showed that the sensitivity of center‐wavelength variations is 0.0129 nm/dB for noise measurement between 85.3 and 105.2 dB. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:958–961, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25844

A Simple Fiber Bragg Grating-Based Sensor Network Architecture with Self-Protecting and Monitoring Functions

A novel fiber Bragg grating (FBG)-based passive sensor architecture, which can be used to protect the fiber cut and monitor the multiple sensors simultaneously, is proposed and experimentally demonstrated. Here, we employ a wavelength-tunable erbium-doped fiber (EDF) laser scheme with 25 km cavity length acting as the detecting light source in central office (CO). Each FBG sensor, serving as a feedback element, is used in proposed sensor architecture. By tuning the tunable bandpass filter (TBF) placing inside cavity to match the corresponding Bragg wavelength of FBG over the amplification bandwidth, we can retrieve the related wavelength lasing for the FBG sensing and monitoring simultaneously. Moreover, the survivability and capacity of the passive FBG sensor architecture can be also enhanced.

Simultaneous demodulation technique for a multiplexed fiber Fizeau interferometer and fiber Bragg grating sensor system

We propose a demodulation technique for a multiplexed fiber Fizeau interferometer (FFI) and fiber Bragg grating (FBG) sensor system using the discrete wavelet transform with signal processing enhancements. This simple and flexible demodulation technique determines the cavity length of FFI and the Bragg wavelength of FBG simultaneously and is especially suited for quasi-static measurements. We demonstrate this demodulation technique by performing some strain measurements, and a strain resolution of 1.0 microepsilon and an accuracy of 2.6 microepsilon are obtained. The maximum cross-talk of the sensor system is 6% of the applied strains.

A study on the longitudinal mode behavior of Fabry-Perot cavity composed of fiber Bragg grating

The characteristics of transmission spectrum of Fabry-Perot(F-P) cavity composed of two fiber Bragg gratings(FBG) are analysed in this paper. As the influence factors, bandwidth of FBG, phase factor of reflection coefficient of FBG and length of cavity are included. The changes of its characteristics caused by temperature and strain are dicussed. Then the method of how to design this kind of F-P cavity with single mode at the Bragg wavelength of FBG is provided. The numerical simulation spectrum and experimental result are also given.

Characteristics between Injection Current and Optical Power of Strained-Layer Multiple Quantum Well Semiconductor Lasers Coupled to an Externally Distributed Fiber Bragg Grating Reflector.

For the first time, the effects of coupling efficiency and Fiber Bragg Grating (FBG) reflectivity to characteristicsbetween injection current and optical power of Strained-Layer Multiple Quantum Well (SL MQW) semiconductor lasers coupled to an externally distributed FBG reflector are demonstrated. In this paper, wedescribe the experimental and simulated results. Our simulations show good agreement with experimentalmeasurements. This kind of laser is investigated and demonstrated, since the lasing wavelengthcan bespecified by choosing Bragg wavelength of FBGs and also be stabilized. At present, 980 nm pumplasers usinga distributed FBG reflector are deployed to enhance stability of Erbium Doped Fiber Amplifiers (EDFAs).Furthermore, the potential for use in Wavelength Division Multiplexing (WDM) transmitters is investigated.This result is useful to design characteristics between injection current and optical power for such lasers. Weconclude that the optimum FBG reflectivity is 0.2 on our experimental configuration where couplingefficiency is 0.6.