基于光纤Bragg光栅的量测锚头压力研究

锚头的受力情况对整个锚杆的安全性有着重要影响。为了实时反映锚头的受力状态,将2只光纤Bragg光栅沿45°粘贴在轮辐式结构锚头的两根对称辐条中点处表面上,形成轮辐式测力传感结构,辐条在压力作用下产生剪切变形,引起辐条表面的光纤Bragg光栅中心波长移位。通过对光纤Bragg光栅中心波长移位的测量,实现在锚头处锚杆轴向拉力的在线监测。锚头压力实验表明:光栅1的测力灵敏度为108.8pm/kN,线性度为0.042%FS;光栅2的测力灵敏度为115pm/kN,线性度为0.023%FS。     

A gain-clamped S-band erbium-doped fiber amplifier using fiber Bragg grating

We propose and investigate experimentally a gain-clamped S-band erbium-doped fiber amplifier module, employing a fiber Bragg grating to serve as a reflected element to lase a saturated tone injected into the module, by forward optical feedback method. In addition, different injected powers of the saturated tone are used to realize the performances of gain and noise figure for the proposed amplifier over the effectively wavelength range of 1478-1520 nm.     

Acousto-optic superlattice modulator using a fiber Bragg grating

A modulator is reported in which an extensional acoustic wave is launched along a fiber Bragg grating. The acousto-optic superlattice effect causes an enhancement in reflectivity within a narrow spectral region on both sides of the Bragg wavelength. For a fixed acoustic propagation direction, the Doppler shift can be either positive or negative, depending on whether the wavelength of the incident light lies above or below the Bragg condition. The device can function as a Bragg cell and a tunable filter.     

Multi-component force measurement using embedded fiber Bragg grating

The development of new fiber Bragg grating (FBG)-based multi-component force sensors is described. A two-component and a three-component force sensor have been fabricated and tested. The two-component force sensor measures the normal and the longitudinal shear component of the force. The three-component force sensor measures the normal, the longitudinal shear and the transverse shear component, and thus provides the magnitude as well as the direction of the force in the three-dimensional space. In the two-component sensor, one FBG is embedded rectilinearly and another non-rectilinearly within carbon composite layer. In the three-component force sensor, one FBG is embedded rectilinearly and two mutually perpendicular FBGs non-rectilinearly within the carbon composite layer. This paper presents the basic sensor structure and the proof-of-concept experimental demonstration of the two sensors. Force measurement within the range 0–15 N has been successfully conducted within 10% deviation.     

Dynamic strain measurement using two wavelength-matched fiber Bragg grating sensors interrogated by a cascaded long-period fiber grating

In this work, we describe a fiber Bragg grating (FBG) sensing system using two wavelength-matched FBG sensors for static and dynamic strain measurement. A cascaded long-period fiber grating (CLPG)-based demodulation technique has been used to interrogate the two wavelength-matched FBG sensors. Experimental results of static strain measurement show that the proposed system has a strain resolution of 1 με. This system has also been used for dynamic strain measurement. An eddy current displacement meter-based system has been used as a comparison measurement. Experimental results of dynamic strain measurement have proved that the FBG sensing system has a good performance in the measurement of dynamic strain. The results of static and dynamic strain measurement indicate that the sensing system using two wavelength-matched FBG sensors is superior to the single FBG sensor system.     

Time-resolved photoacoustic spectroscopy using fiber Bragg grating acoustic transducers

An acoustic transducer based on a fiber Bragg grating (FBG) is presented and characterized for use in time-resolved laser-induced photoacoustic spectroscopy (PAS) on solid samples. The photoacoustic wave was generated by pulsed laser excitation of immobilized carbon black or erbium oxide powder, and detected by recording either the transmission or reflection spectrum of a clamped fiber Bragg grating (FBG). The characterization of the FBGs photoacoustic response is based on the experimental comparison with a static lateral strain source and on theoretical analysis using the piecewise-uniform approach to photoelastic theory. The temporal resolution of the response is determined by the arrangement of the FBG with respect to the source of the acoustic wave and is better than 150 ns, as was verified in a deconvolution analysis.The method has not only a fast time response but also is simple, inexpensive, and accurate as indicated by the good agreement of the experimental photoacoustic spectrum with previous measurements.     

Bragg光纤光栅法布里-珀罗传感器的应变测量

提出了一种对静态应变进行高分辨率测量的方法。该方法是把Bragg光纤光栅(FBG)与全光纤法布里_珀罗传感器(FFPI)组合起来,利用FBG反射波长的漂移特性来测量干涉条纹的数目。通过利用FFPI和伪外差解调法对小数条纹进行解调,可实现高分辨率的测量。结果表明,静态应变的测量分辨率达到了33×10-9ε(ε为应变)。     

Slow and fast light using fiber Bragg grating F-P cavity

In this paper, we analyzed the properties of fiber Bragg grating F-P cavity with different grating parameters at two ends. The features of transmission spectra and group velocity were investigated under different parameters including slight increase for the differences of the lengths of the two gratings, the periods of the two gratings, the refractive index modulation depths of the two gratings. The characteristics of the slow light in fiber Bragg grating and fiber Bragg grating F-P cavity were also compared. The results of this study can be useful for actual experiments and applications in using the fiber Bragg grating F-P cavity in the slow light.     

Tilted fiber Bragg grating sensors

Optical fiber gratings have developed into a mature technology with a wide range of applications in various areas, including physical sensing for temperature, strain, acoustic waves and pressure. All of these applications rely on the perturbation of the period or refractive index of a grating inscribed in the fiber core as a transducing mechanism between a quantity to be measured and the optical spectral response of the fiber grating. This paper presents a relatively recent variant of the fiber grating concept, whereby a small tilt of the grating fringes causes coupling of the optical power from the core mode into a multitude of cladding modes, each with its own wavevector and mode field shape. The main consequence of doing so is that the differential response of the modes can then be used to multiply the sensing modalities available for a single fiber grating and also to increase the sensor resolution by taking advantage of the large amount of data available. In particular, the temperature cross‐sensitivity and power source fluctuation noise inherent in all fiber grating designs can be completely eliminated by referencing all the spectral measurements to the wavelength and power level of the core mode back‐reflection. The mode resonances have a quality factor of 10⁵, and they can be observed in reflection or transmission. A thorough review of experimental and theoretical results will show that tilted fiber Bragg gratings can be used for high resolution refractometry, surface plasmon resonance applications, and multiparameter physical sensing (strain, vibration, curvature, and temperature).     

Wideband tunable linear-cavity fiber laser source using strain-induced chirped fiber Bragg grating

A novel wideband tunable linear-cavity fiber laser source using strain-induced chirped fiber Bragg grating (FBG) and erbium–ytterbium co-doped fibers is proposed and demonstrated for the first time. The strain-induced chirped FBG, which acts as a partial-reflecting mirror, is achieved by bending a uniform FBG bonded at a slant onto the lateral surface of a simply supported beam. A single wavelength lasing with a maximum wavelength tuning range of 17 nm has been achieved experimentally.     

Intensity vibration sensor based on Raman fiber laser using a distributed mirror combined with Bragg grating structures

In this work, the authors propose a new configuration for an intensity vibration sensor based on a Raman fiber laser. The linear cavity of the Raman fiber laser relies on the combination of a distributed Rayleigh mirror and fiber Bragg gratings, which are used as the sensing element and intensity filter. The sensor was able to measure vibrations with frequencies of up to 350 Hz with more than 50 dB of signal-to-noise ratio (SNR) and also the amplitude of the vibrations with a sensitivity of up to 0.57 ± 0.07 dB/με for vibrations with a maximum strain variation of up to 35 με. The main advantages of the proposed configuration are the simple scheme with high SNR for remote sensing and the easy possibility of multiplexing.     

Hybrid fiber Bragg grating sensor for vibration and temperature monitoring of a train bearing

We report a fiber Bragg grating(FBG)-based sensor for the simultaneous measurement of a train bearing's vibration and temperature. A pre-stretched optical fiber with an FBG and a mass is designed for axial vibration sensing. Another multiplexed FBG is embedded in a selected copper-based alloy with a high thermal expansion to detect temperature. Experiments show that the sensor possesses a high resonant frequency of 970 Hz, an acceleration sensitivity of 27.28 pm/g, and a high temperature sensitivity of 35.165 pm/℃. A resonant excitation test is also carried out that demonstrates the robustness and reliability of the sensor.     

Photonic instantaneous measurement of microwave frequency using fiber Bragg grating

A photonic approach to realizing instantaneous measurement of microwave frequency based on optical monitoring using a fiber Bragg grating (FBG) is proposed and demonstrated. In the approach, a frequency-unknown microwave signal is modulated on an optical carrier in a Mach-Zehnder modulator biased at the minimum transmission point. After detecting the transmission and reflection optical powers at the output of the FBG, the microwave frequency can be determined according to the value of transmission-to-reflection power ratio, due to the fixed relationship between the microwave frequency and the power ratio. A proof-of-concept experiment has been performed, which demonstrates that a measurement resolution of ±0.08 GHz over a 10 GHz measurement bandwidth is achieved. The measurement performance in terms of resolution is better than previously reported results.     

Spatial characterization of fiber Bragg grating structures using transversal pressure

A technique for low cost and high precision characterization of fiber Bragg gratings based structures, using transversal pressure, is presented. It is based on the analysis of the amplitude and wavelength changes of the structure reflection spectrum, while being precisely pressed by an electromechanically actuated arm. The theory and the experimental results, which are in good agreement with the expected ones, are also presented.     

光纤光栅法布里-珀罗温度传感器的理论分析

通过对弱反射率、长腔长布拉格光纤光栅Fabry-Perot腔(FBG-FP腔)的反射与透射理论分析,得出反射光相位变化与温度变化的关系式,得出了FBG-FP腔中心波长变化与温度变化的关系式,并提出了一种有效的实验解调方法,该方法通过对绝对相位的检测,得出温度的变化量。     

Multiplexing of fiber Bragg grating sensors using subcarrier intensity modulation

We report the theory and experimental demonstration of two multiplexing schemes for addressing fiber grating sensor arrays consisting of multiple branches. In the first scheme, light in each branch is intensity modulated at different subcarrier frequencies and signals from different branches are separated in frequency domain by using bandpass filters. In the second scheme, the modulation frequency in each branch can be the same and signal separation is performed in time domain by using an electronic switch after photodetection.     

Switchable triple-wavelength erbium-doped fiber laser using a single fiber Bragg grating in polarization-maintaining fiber

A stable and narrow wavelength spacing multiwavelength erbium-doped fiber laser is proposed and demonstrated. The laser can produce simultaneous dual- and triple-wavelength lasing oscillations with a narrow wavelength spacing of less than 0.1 nm via using a single fiber Bragg gratings written in polarization-maintaining (PM) fiber. By adjusting polarization controller, the wavelength spacing of dual-wavelength lasing oscillations can be tuned to as small as 0.032 nm. The maximum amplitude variation for every lasing wavelength is less than 0.5 dB. The room-temperature operation principle is based on the polarization hole burning and deeply saturated effect in an ordinary erbium-doped fiber ring laser (EDFRL). The laser has the advantages of simple all-fiber configuration, low cost, high stability and operating at room temperature.     

Detection of liquid-level variation using a side-polished fiber Bragg grating

A liquid-level sensor based on a side-polished fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The sensor can detect height variation of liquids of arbitrary refractive index (RI). For liquids with RI lower than that of fiber core, liquid-level variation can be monitored by the peak power difference of the grating segments surrounded by the liquid and air. For liquids with RI higher than that of fiber core, liquid-level information can be obtained from the influence of the shortening of the effective length of the immersed grating segment upon the reflection spectrum.     

光纤布拉格光栅及其应用

近年来新型的紫外激光写入的光纤布拉格光栅元件（ＦＢＧ）以其具有直接写人光纤芯区、插入损耗小、易于全光集成及波长选择性好、传感信息对波长绝对编码等优点,成为国内外光纤技术领域的研究热点。该论文综述了ＦＢＧ制作技术的进展,介绍和比较了各种制作方法的优缺点,对ＦＢＧ在光纤通讯、光纤传感器等方面的应用前景进行了分析和说明,结果表明ＦＢＧ将对整个光纤技术领域产生重要的影响。