Fiber Bragg Grating Sensor System Research Articles

Ultra-long-distance FBG sensor system based on spectrum-limited Fourier domain modelocking fibre laser with Raman pumps

A novel ultra-long-distance (up to 76 km) fibre Bragg grating (FBG) sensor system based on a spectrum-limited Fourier domain modelocking fibre laser is proposed. Raman pumps are employed to form a Raman amplifier to compensate the transmission loss of the long fibre and ensure ultra-long-distance sensing. Strain sensing based on such an ultra-long-distance FBG sensor system is demonstrated with a signal-to-noise ratio over 22 dB and a sensitivity of 1.03 pm/µɛ in the wavelength domain or 18.3 ns/µɛ in the time domain.

光纤布拉格光栅传感解调中的寻峰算法

光纤布拉格光栅传感解调中的寻峰算法

Spectrally-overlapped chirped fibre Bragg grating sensor system for simultaneous two-parameter sensing

A spectrally-overlapped chirped fibre Bragg grating (FBG) sensor system for simultaneous two-parameter sensing is presented. The chirped FBGs are amplitude-modulated in such a way that they can be spectrally overlapped with similar spectral characteristics, namely the centre Bragg wavelength and bandwidth. That is, the chirped FBGs are multiplexed via the spectral-overlap multiplexing scheme. Because of its compatibility with the wavelength division multiplexing scheme, the number of gratings to be multiplexed can be increased by several times. The multiplexed sensor signal is demultiplexed and demodulated using the discrete wavelet transform. The resolution, accuracy and crosstalk of the sensor system are investigated through strain measurements. The application of this sensor system is demonstrated through the simultaneous measurement of strain and temperature of a metal alloy plate.

Real-Time Monitoring Sensor System for Fiber Bragg Grating Array

A time-division multiplexed fiber Bragg grating (FBG) sensor system capable of real-time monitoring is proposed and experimentally validated. It is based on an unbalanced Michelson interferometer, a delay signal generator, and a tree-structured single-pole-double-throw switch array. Realization of real-time monitoring is because the arriving time of sensing signals is synchronized with the controlling signals of the switches. A phase meter is used to measure the strain of FBG sensors.

Ultra-Long-Distance Fiber Bragg Grating Sensor System

A long-distance fiber Bragg grating (FBG) sensor system has been developed using a wavelength-swept light source with output power turned on-off and timing synchronized to the sweep signal to reduce optical noise caused by Rayleigh scattering generated from the transmission fiber. This system can detect changes in the FBG reflection wavelengths even if the FBG is 120 km from the sensing position.

On a fiber grating sensor system with the capacity of cross-sensitivity discrimination

A novel fiber Bragg grating (FBG) sensor system based on an interrogating technique by two parallel matched gratings was designed and theoretically discussed. With an interrogation grating playing the role of temperature compensation grating simultaneously, the wavelength drifts induced by temperature and strain were discriminated. Additionally, the expressions of temperature and strain were deduced for our solution, and dual-value problem and cross sensitivity were solved synchronously through data processing. The influence of the FBG's parameters on the dynamic range and precision was discussed. Besides, the change of environment temperature cannot influence the dynamic range of the sensor system through temperature tuning. The system proposed in this paper will be of great significance to accelerate the real engineering applications of FBG sensing techniques.

Cure Monitoring and Internal Strain Measurement of 3-D Hybrid Braided Composites using Fiber Bragg Grating Sensor

Curing behavior and internal strain of 3-D hybrid braided composites is studied using embedded fiber Bragg grating (FBG) sensors. Thermo-optic coefficients and photo-elastic constant of fabricated FBG sensors are experimentally determined. A seven-layered three-dimensional (3-D) braided preform is fabricated. S2 glass fiber is used as the main braiding yarn, and Kevlar fiber is inserted in the exterior surface layer in the axial direction. Several nylon fibers are braided together in order to replace the FBG sensors after braiding. FBG sensors are embedded along the curved braiding yarn as well as in the machine direction. An FBG-embedded 3-D braided composite is fabricated using the resin-transfer molding (RTM) process. During the cure process, the expansion and contraction caused by the matrix cure as well as temperature changes are monitored. Local dimensional changes are measured quantitatively using an FBG sensor system. The FBG sensor embedded along a curved braiding yarn exhibited a relatively small amount of shrinkage. By using embedded FBG sensors and surface-bonded electric strain gages, internal strains of the 3-D braided composite are measured during compressive and flexural tests, and the results show good agreement with each other.

Output-Noise Statistical Characterization for Digital-Phase-Demodulation Systems With Intensity-Based Input Noise

A large fraction of fiber-optic-sensor systems make use of interferometry in the measurement process, implying the need for demodulation to obtain the encoded signal of interest. Of great interest for sensor characterization is the performance of the demodulation scheme under the influence of noise. In this paper, we construct a very general transfer function that relates intensity-induced input noise to its phase noise realization in the output for a wide class of digital-demodulation techniques. We proceed to compute analytically a probability density function of this output noise and use this to compute low-order statistical moments of the output noise. We compare the analytical formulations with simulated data from a representative demodulation scheme used in a currently existing fiber Bragg grating (FBG) sensor system and find excellent agreement

S-Band long-distance fiber Bragg grating sensor system

We propose and investigate experimentally a sigma fiber laser scheme, which uses multiple fiber Bragg grating (FBG) sensors as the feedback elements, for a long-distance sensor system with 20-km long in S-band at first. By tuning a wavelength selective filter located in a laser cavity over the gain bandwidth, the laser selectively lases at each of the fiber Bragg wavelengths of the sensors, thus allowing strain-induced shifts in the Bragg wavelengths to be monitored. In our experiment, an S-band four-sensor system is proposed and investigated experimentally.

Strain and damage monitoring of CFRP in impact loading using a fiber Bragg grating sensor system

A fiber-optic system featuring strain measurement and ultrasonic detection was constructed with fiber Bragg gratings based on wavelength–light intensity conversion technique. This fiber Bragg grating sensing system consists of a broadband light source, a broadband optical filter for strain measurement and a narrowband tunable filter for ultrasonic detection. The system was applied to strain measurement in impact loading to carbon fiber-reinforced plastics and the subsequent impact damage detection. Experimental results demonstrated that fiber Bragg grating sensors could measure strain with higher resolution compared with conventional strain gauges. Furthermore, ultrasonic inspection in which ultrasonic sensitivity was maximized by controlling the transmissive wavelength of the tunable filter could detect a 6.3 × 9 mm 2 impact damage.

A FBG sensor system with cascaded LPFGs and Music algorithm for dynamic strain measurement

A Mach-Zehnder (M-Z) interferometer formed by two cascaded long-period fiber gratings (LPFGs) serving as ‘many’ multi-channel edge filters is used to detect the wavelength shift, induced by measurand of fiber Bragg grating (FBG) sensors with high optical SNR of >60dB due to the use of a fiber ring laser, for the first time to our knowledge. Advantages of such a demodulation device are low-cost, compact, easy fabrication and implementation, good immunity of vibration and temperature, etc. In addition, in order to improve the resolution for dynamic strain measurement, a spectral analyzing algorithm called Music modern spectrum estimation is adapted. The experimental results show that a dynamic strain resolution of 0.1μɛ/Hz1/2 at 700Hz is obtained, which is 10 times improvement in strain resolution when compared with conventional FFT method.

Long-distance fiber Bragg grating sensor system with a high optical signal-to-noise ratio based on a tunable fiber ring laser configuration

A novel tunable fiber ring laser configuration with a combination of bidirectional Raman amplification and dual erbium-doped fiber (EDF) amplification is proposed for realizing high optical signal-to-noise ratio (SNR), long-distance, quasi-distributed fiber Bragg grating (FBG) sensing systems with large capacities and low cost. The hybrid Raman-EDF amplification configuration arranged in the ring laser can enhance the optical SNR of FBG sensor signals significantly owing to the good combination of the high gain of the erbium-doped fiber amplifier (EDFA) and the low noise of the Raman amplification. Such a sensing system can support a large number of FBG sensors because of the use of a tunable fiber Fabry-Perot filter located within the ring laser and spatial division multiplexing for expansion of sensor channels. Experimental results show that an excellent optical SNR of approximately 60 dB has been achieved for a 50 km transmission distance with a low Raman pump power of approximately 170 mW at a wavelength of 1455 nm and a low EDFA pump power of approximately 40 mW at a wavelength of 980 nm, which is the highest optical SNR achieved so far for a 50 km long FBG sensor system, to our knowledge.

A fiber Bragg grating sensor system for simultaneously static and dynamic measurements with a wavelength-swept fiber laser

A novel fiber Bragg grating (FBG) sensor system for static and dynamic measurements with a wavelength-swept fiber laser is proposed and demonstrated. In this system, both static and dynamic perturbation of each FBG in the sensor arrays can be interrogated simultaneously. The experiments demonstrated the strain resolutions of /spl sim/1 μ/spl epsiv/ and 3.4 n/spl epsiv///spl radic/Hz at 500 Hz for static and dynamic measurements, respectively.

A fibre Bragg grating sensor system monitors operational load in a wind turbine rotor blade

A fibre Bragg grating sensor system has been installed and successfully operated in a horizontal-axis wind turbine since February 2004. We herewith report the requirements, design and construction parameters of the sensor system for continuous on-line monitoring of bending loads of the rotor blades and provide examples of the monitoring results.

Multiplexed fibre Fizeau interferometer and fibre Bragg grating sensor system for simultaneous measurement of quasi-static strain and temperature using discrete wavelet transform

We present a multiplexed fibre Fizeau interferometer (FFI) and fibre Bragg grating (FBG) sensor system for simultaneous measurement of quasi-static strain and temperature. A combined spatial-frequency and wavelength- division multiplexing scheme is employed to multiplex the FFI and FBG sensors. A demodulation technique based on the discrete wavelet transform with signal processing enhancements is used to determine the measurand- induced physical changes of the sensors. The noise associated with the sensor signal is reduced by the block-level-thresholding wavelet denoising method, which is applied via the demodulation technique. This sensor system yields a high accuracy and resolution, and low crosstalk. It is well suited for long-term quasi-static measurements, especially for the structural health monitoring of large-scale structures.

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.

Time- and wavelength-division multiplexing of FBG sensors using a semiconductor optical amplifier in ring cavity configuration

A fiber Bragg grating (FBG) sensor system based on a semiconductor optical amplifier connected in a ring cavity configuration is proposed. The proposed configuration produces high power signal with good extinction ratio for FBGs with /spl sim/1% reflectivity. A sensor system consists of four group of three FBGs of different wavelengths was constructed to demonstrate time- and wavelength-division multiplexing of FBG sensors.

Fiber Bragg Grating-Based Multiplexed Sensing System Employing Fiber Laser Scheme with Semiconductor Optical Amplifier

We propose and demonstrate experimentally a multipoint fiber Bragg grating (FBG) sensor system, based on fiber Bragg gratings (FBGs), using a semiconductor optical amplifier (SOA) as a gain medium. Multiple wavelength operation is based on the inhomogeneous broadening effect of the SOA of the sensing system. In addition, the behavior of the proposed sensor configuration is also studied.

Simultaneous measurement of strain and damage signal of composite structures using afiber Bragg grating sensor

For the simultaneous measurement of strain and a damage signal, a fiber Bragg gratingsensor system with a dual demodulator is proposed. The dual demodulator is composed ofa demodulator with a tunable Fabry–Perot filter measuring the low-frequency signalwith large magnitude such as strain and another with a passive Mach–Zehnderinterferometer measuring the high-frequency signal with small amplitude suchas a damage or impact signal. Using the proposed fiber Bragg grating sensorsystem, both the strain and the damage signal of a cross-ply laminated compositebeam under tensile loading were simultaneously measured. The strain and thedamage signal measured by the single fiber Bragg grating sensor showed thatsudden strain shifts were accompanied with vibration at a maximum frequency ofseveral hundred kilohertz at the instant of transverse crack propagation in the90° layer of the composite beam.

A field deployable, multiplexed Bragg grating sensor system used in an extensive highway bridge monitoring evaluation tests

A multiplexed optical fiber Bragg grating sensor system with a measurement bandwidth of up to 200 Hz enabling dynamic loading events, e.g., road traffic, to be observed has been designed, installed, and tested over an 18-month period on a 346-m road bridge in Norway, for design verification and structural integrity monitoring purposes. A network of 32 fiber Bragg sensors was surface bonded along with a corresponding set of resistive strain gauges for comparative tests to be made. The wavelength data were calibrated against two thermally stabilized (/spl sim/0.15 pm) reference gratings, which rejected common mode noise and provided absolute wavelength scaling. These data provides independent strain and temperature information. Long-term test results showed good linearity and repeatability of <10 /spl mu//spl epsiv/ over the test period with a precision of /spl plusmn/5 /spl mu//spl epsiv/ and a resolution of /spl plusmn/1 /spl mu//spl epsiv/. The readings from the FBG sensors were comparable to those from the foil gauge sensors to within /spl plusmn/4 /spl mu//spl epsiv/.