基于光纤光栅传感器的体外血管模型应力测量北大核心CSCD

血管中的血液流动会对血管壁产生周向应力,周向应力与血管的结构及功能变化密切相关,测量体外血管模型的周向应力是生物力学研究中较重要的问题。提出了利用光纤光栅测量血管周向应力的方法,基于微流控技术利用钢针模具建立了集成光纤光栅的三维圆形血管模型,通过仿真研究了不同流动速度与应力的关系。仿真结果得到流速在8 mm/s~75 mm/s范围内,应力随速度的改变呈线性变化。利用光纤光栅传感器测量了流体流动时产生的周向应力,根据实验得到了光栅波长改变量与速度的关系,流速范围在8 mm/s~75 mm/s之间变化时,速度引起波长的变化为0.173 nm。结合仿真实验得到了应力与光栅波长改变量的关系,为血液流动时产生周向应力的体外测量提供了新思路。     

Suspended-core fiber Bragg grating sensor for directional-dependent transverse stress monitoring

This Letter presents simulation and experimental results of orientation-dependent transverse stress fiber sensors using fiber Bragg gratings (FBGs) inscribed in four-hole suspended-core fibers. Resonant peak shifts and splitting of FBGs were studied as functions of the applied transverse load and fiber orientation. Both simulation and experimental results revealed that the response of FBGs in suspended-core fibers is sensitive to both the orientation and magnitude of an applied transverse stress.     

光纤Bragg光栅压力传感机理研究

对光纤Bragg光栅的压力传感机理进行了理论研究。分析了引起光纤光栅中心波长偏移的各种物理效应，并对几种不同形式压力下各种物理效应所引起的灵敏度系数进行了计算。计算结果表明，纵向和横向压力灵敏度系数相反，屏蔽一个方向可获得较大的压力传感灵敏度；波导效应所引起的应变灵敏度系数都比弹光效应小几个数量级，因此可以忽略。并首次提出在不同方向的压力作用下，弹光效应对应变灵敏度具有不同的贡献。     

Effects of distributed birefringence on fiber Bragg grating under non-uniform transverse load

Many theoretical and experimental studies have been developed to characterize the spectral response of an optical fiber Bragg grating (FBG) in axial strain fields in recent years. However, comparatively few works were devoted to the evolution of the spectrum when a FBG is subjected to non-uniform transverse load. In this paper, the effects of distributed birefringence on FBG under non-uniform transverse load are analyzed and a numerical simulation based on the piecewise-uniform approach is also discussed to simulate the responses of FBG under some typical non-uniform transverse strain fields. Experiment was carried out using different loads applied at different locations of the FBG. Good agreements between experimental results and numerical simulations have been obtained.     

Design of all-optical temporal differentiator using a Moir fiber grating

We design and demonstrate an all-optical temporal differentiator based on a simple Moir fiber grating operated in reflection. The simulation results prove that a single Moir fiber grating with only one π-phase shifted point can act as the first-order temporal differentiator and that a Moir fiber grating incorporating two symmetrical π-phase shifted points can act as the second-order temporal differentiator. A practical Moir fiber grating is fabricated, thereby proving that such a grating can act as the first-order temporal differentiator. Our results verify the feasibility, flexibility, and accuracy of the proposed method.     

非轴向力下埋入式光纤传感器应变传递分析

利用剪滞法建立了当光纤光栅传感器的轴线和基体主应力的方向成一定角度时,光纤光栅传感器的测量应变与基体结构实际应变之间的关系,进而得出了光纤光栅传感器的平均应变传递率的一般公式。采用裸光纤光栅传感器进行实验,在倾斜角度α为30.72°时,实验所得的波长变化之比分别为:0.727,0.738,0.746;理论计算所得的波长变化之比为0.739,相对误差都在2%以内。同时分析了埋设角度偏差对测量结果的影响。研究结果表明,非轴向力作用下光纤光栅传感器的应变与结构基体应变之间的传递关系与其在轴向力作用下存在明显的区别,埋设角度的偏差会给测量结果造成一定的误差。     

非均匀应变场下相移光栅光谱特性及其实验研究

采用传输矩阵法系统研究轴向非均匀应变场下相移光栅光谱特性,对均匀应变、线性应变、二次应变以及三次应变分布下相移光栅反射谱进行仿真,分析应变分布函数各项系数对反射率、通透带宽、透射窗口对应波长以及光谱形状的影响,并得出规律性结论。基于不同形状悬臂梁组建应变调谐实验装置,利用有限元法计算固定于不同形状悬臂梁表面相移光栅栅区应变分布,结合数值计算结果进行相移光栅应变调谐实验,研究相移光栅栅区轴向在均匀应变场、线性应变场以及二次应变场下相移光栅的反射光谱,实验结果表明在不同应变场下相移光栅反射谱呈现规律性变化,与仿真结果很好吻合。     

Hybrid FBG–LPG sensor for surrounding refractive index and temperature simultaneous discrimination

In this work, we propose a configuration of a hybrid fiber Bragg grating together with a long period grating sensor used for simultaneously detect surrounding refractive index and temperature to be applied in aqueous environment and to reveal pollution. We present the simulation of such sensor and analyze the reflected wavelength and amplitude variations of the fiber Bragg grating spectrum to obtain the temperature and the external refractive index variations, respectively. The results show that the fiber Bragg grating reflected amplitude change depends on the variation of the long period grating transmission spectrum with the surrounding refractive index modification and the reflected wavelength shift depends on the temperature of the aqueous solution.     

Numerical modeling of fiber grating

The numerical simulation of light wave transmission and reflection in fiber grating is presented. The simulation is based on three-dimensional finite difference time domain algorithm. A method that can make the faint reflected wave distinct and legible is also proposed. With this method, we exhibit light wave reflection and radiation in fiber grating and tilted fiber grating, respectively, in numerical simulation.     

倾斜Bragg光纤光栅反射谱特性理论和实验研究

光纤Bragg光栅在通信和传感领域有着广泛的应用。根据倾斜光纤Bragg光栅的结构特点，利用耦合模原理，运用传输矩阵法，模拟分析了倾斜角度对光纤Bragg光栅反射特性的影响，并用实验对模拟结果进行了验证。实验和模拟结果表明：随着倾斜角的增大，中心反射波长向长波方向移动，反射带宽变窄，反射率减小。这个结论对倾斜Bragg光纤光栅的生产和应用有一定的指导作用。     

Fiber optic liquid leak detection technique with an ultrasonic actuator and a fiber Bragg grating

We present a technique for liquid leak detection in which ultrasonic and optical waves are introduced into a fiber simultaneously. The system is based on an ultrasonic technique using an ultrasonic actuator and a fiber Bragg grating receiver. A fiber-guided ultrasonic wave is utilized to stress the fiber Bragg grating, which is remote from the ultrasonic transmitter. When the traveling ultrasonic wave encounters a liquid, part of the wave will leak out from the fiber, which results in an ultrasonic strain decrease in the fiber Bragg grating. The ultrasonic wave and its attenuation are detected by the light variation of a narrowband laser source reflected and transmitted from the fiber Bragg grating, and the amplitude variation of the ultrasound can eventually be correlated with the fiber area coupled with the liquid.     

Using of non-uniform stress effect to realize the tunable dispersion of the fiber Bragg grating with tapered metal coatings

A novel method of adjusting the dispersion of fiber Bragg grating is proposed using the non-uniform stress effect. By loading the axial stress on the fiber grating coated with non-uniform copper thin-film, the induced non-uniform stress effect can realize the tunable dispersion of grating. The non-uniform copper films are plated on the outer cladding of fiber grating and the thickness of the copper film gradually changes along the grating length. Numerical models are established to analyze the dynamic tunable characteristics of such grating when loading different axial stresses on it. The model is verified by experiments.     

Optimization of reversible LPFG for sensing application

We report here for the first time to our knowledge the characterization of mechanically induced long period fiber gratings in novel MSM fiber structure. Reversible grating of same period and length was induced in single mode fiber, multimode fiber and novel multimode-singlemode-multimode (MSM) fiber structure. The spectral response of reversible LPFG in SMF is verified experimentally as well as from simulation results and then compared with the experimental spectral response of reversible LPFG in multimode fiber and MSM fiber structure. Reversible LPFG in novel MSM fiber structure is the most optimized and suitable grating for sensing application. For this grating we have obtained single resonant wavelength over a wide wavelength range and maximum transmission loss peak of around 20 dB.     

基于扭曲长周期光纤光栅的高灵敏度压力传感器

研究了高频CO2激光脉冲写入的长周期光纤光栅在扭曲状态下的横向负载特性.发现扭曲降低了光纤光栅谐振波长横向负载灵敏度的方向相关性,使得这种光栅在各圆周方向上谐振波长对横向负载都不敏感,而谐振峰幅度随横向负载的增加线性减小,且谐振峰幅度的负载灵敏度随扭曲率的增加而提高.在扭曲率为1.8°mm－1时负载灵敏度可达0.47 dB/(g·mm－1),是自由状态长周期光纤光栅横向负载灵敏度的7倍,最后给出了利用这种扭曲长周期光纤光栅通过强度解调实现压力传感的实验研究结果.     

CO(2) laser writing of long-period fiber gratings in optical fibers under tension

We demonstrate experimentally that the efficiency of writing a long-period fiber grating in a single-mode fiber by CO(2) laser pulses increases significantly with the axial stress applied along the fiber. We attribute the enhancement in writing efficiency to the generation of nonuniform inelastic frozen-in strains across the fiber under tension by CO(2) laser heating. Controlling the axial stress distribution along a fiber during the CO(2) laser writing process thus provides an additional degree of freedom for control of the grating characteristics.     

基于紫外刻写相移光栅的温度应力同时测量传感器

传统光纤光栅传感器存在温度应力交叉敏感的问题,无法同时测量被测物体的温度应力变化情况.针对这种情况,提出一种新型的利用紫外光刻写相移光栅的方法,在刻写光栅前用电极放电的方法去除掉极小一段光纤的光敏性,使光纤原有的均匀周期分布状态被破坏,从而形成相移光栅,并对其进行理论分析.此种相移光栅的透射光谱存在2个明显的谐振峰,利...     

Simultaneous measurement of refractive index and temperature using dual-period grapefruit microstructured fiber grating

By cascading the long period fiber grating (LPFG) and fiber Bragg grating (FBG) in grapefruit microstructured fiber, a novel dual-period fiber grating sensor is proposed. The refractive index and temperature are measured simultaneously by using the different sensitivity of FBG and LPFG. The relationship between dual-period fiber grating transmission spectrum and refractive index, resonant wavelengths and temperature are analyzed theoretically, respectively. The simulation results show that the accuracy of the sensor in measuring refractive index and temperature is estimated to be 2319.6 nm/RIU in a range from 1.33 to 1.36 and 0.017 nm/°C from 0 °C to 100 °C, respectively. Thus, the sensor has high refractive index sensitivity, and can provide the theoretical foundation for the optical fiber biosensor.     

Transverse load sensing by use of pi-phase-shifted fiber Bragg gratings

The birefringence of a pi -phase-shifted fiber Bragg grating can be determined with high accuracy by measurement of the polarization-induced spectral splitting of its narrow central transmission window. The use of this feature for sensing of a load applied in the direction transverse to the optical fiber is demonstrated. A distributed force resolution of 1.4x10(-3) N/mm was obtained, which corresponds to a difference in the principal strains of the fiber core of 0.5mu? . We also show that the transverse load response of the sensor is insensitive to temperature.     

Investigations on the wavelength dependence of optically induced long-period Bragg gratings

We numerically analyze the conversion of transverse modes with optically induced long-period Bragg gratings. These gratings are generated by a recently developed technique which uses a writing beam guided within the fiber to introduce a transient grating via the optical Kerr effect. We demonstrate several settings for conversion between different transverse modes, including conversion over a broad spectral range of up to 60?nm. The tunability of the grating parameters could promote novel applications.     

光纤光栅法布里-珀罗传感器频分复用技术

理论分析了光纤光栅法布里-珀罗(F-P)传感器频分复用技术的原理,并给出了信号处理对腔长选取的要求。数值模拟结果表明,不同腔长的传感器具有不同的谐振条纹频率,为保证频域中的信号不发生重叠,要求不同光纤光栅法布里-珀罗传感器间的腔长之差必须大于光纤光栅的长度。进一步的实验及模拟分析结果发现,温度等待测量的变化仅仅使光纤光栅法布里-珀罗传感器的反射光谱整体平移,相应的频域信号只产生相移而形状不发生变化,因而不能采用普通光纤法布里-珀罗(FFP)传感器的腔长傅里叶变换解调法解调频分复用光纤光栅法布里-珀罗传感器的信号。根据这一特点,提出了利用自相关分析实现频分复用传感器系统信号解调的方案。