Long-period Gratings in-situ Sensing for Flow Monitoring in Liquid Composite Molding

Liquid composite moulding (LCM) processes are used to manufacture high quality and complex-shaped composite parts in the automotive, marine, aerospace and civil industries. On-line sensing plays an important role in controlling the quality of the final product in the LCM manufacturing environment. The long-period fiber grating (LPG) technology, a new real-time fiber optic sensor system, was developed to monitor the flow front progression. The sensor operation and characterization under various process conditions were discussed in detail. The experimental results showed that LPG sensors were robust and reliable to detect the arrival of resin at pre-selected locations in structures with low-medium fiber volume fraction; however were limited at different depths in structures with high fiber volume fraction.

Ag-coated Long-period Fiber Grating

Based on coupled-mode theo ry , the eigenvalue equation of five-layered long-period fiber grating(LPFG) sens or with Ag film and gas-sensitive film overlays are firstly studied. The probl em of resolving complex eigenvalue equation on five-layered LPFG is analyzed, a nd the method of resolution is also given. Then the eigenvalue equation of three -layered metal cladding LPFG is analyzed, and the complex transcendental equati on is also discussed. The computing result shows that the coupling between the l ow-order EH modes and the core mode is much stronger than that between the low -order HE modes and the core mode.

Fabrication of long-period fiber gratings by CO_2 laser in fiber under tension

We demonstrate experimentally fabrication of CO2 laser written long-period fiber gratings （LPFGs） in single-mode fiber （SMF） under tension. New transmission dips can be generated due to the frozen-in stress in the fiber under tension. Dynamics analysis of laser writing process is performed to study the mechanism of the grating inscription. Experimental results show that the wavelength shift of new generated resonance dips can shift towards the longer or shorter wavelength with the increase of laser scanning cycles for gratings with different pitches.

Convention of Optical Vortices in Two-Helix Long-Period Fiber Gratings

An effective method to fabricate two-helix long-period fiber gratings （TH-LFGs） is presented. Based on the coupling mode theory, the conversion of optical vortices （OVs） in TH-LFGs are analyzed in detail. The conversions of OVs with different topological charges： 0 → ±2 and 1 → 3 are simulated as three examples and the conversion efficiency higher than 98% can be realized.

Hybrid Long-Period Fiber Grating with Multimode Fiber Core for Refractive Index Measurement

A refractive index （RI） sensor based on hybrid long-period fiber grating （LPFG） with multimode fiber core （MMFC） is proposed and demonstrated. The surrounding RI can be determined by monitoring the separation between the resonant wavelengths of the LPFG and MMFC since the resonant wavelengths of the LPFG and MMFC will shift in opposite directions when the surrounding RI changes. Experimental results show that the sensor possesses an enhanced sensitivity of 526.92nm/RIU in the RI range of 1.387-1.394 RIU. The response to the temperature is also discussed.

Sensing characteristics of a metal film coated long-period fiber grating

To obtain the influence rules of the coating parameters of a long-period fiber grating(LPFG)with respect to temperature,strain and refractive index sensing properties,based on the mode coupling theory,a strict four-layer theorietical model of a metal film coated LPFG is established,and these parameters that affect the spectral characteristics of the metal film coated LPFG are studied.The simulation results show that there is an optimal metal film thickness on the surface of the LPFG that will induce the surface-plasmon resonance(SP R)effect,which results in higher sensitivity to the environmental temperature and refractive index but has little influence on the strain There is theoretical evidence that when the silver thickness is between0.8and1.2nm,the refractive index sensitivity will reach the peak point of42.4026,at which the refractive index sensor sensitivity is increased by4.S%.The theoretical results of coating a long-period fiber grating provide a good theoretical basis and guidance for LPFG design and parameters optimization

Tunable wavelength filters using polymer long-period waveguide gratings based on metal-cladding directly defined technique

In this work, long-period waveguide grating-based tunable wavelength filters using organic–inorganic grafting poly（methyl methacrylate）（PMMA） materials are designed and fabricated by metal-cladding directly defined technique.The thermal stabilities and optical properties of the organic–inorganic grafting PMMA core materials are analyzed. Structures and performance parameters of the waveguide gratings and self-electrode heaters are designed and simulated. The contrast of the filter is about 15 d B and the resonant wavelength can be tuned by different electric powers applied to the metal-cladding self-electrode heaters. The temperature sensitivity is 3.5 nm/℃ and the switching time is about 1 ms. The technique is very suitable for realizing the optoelectronic integrated wavelength-division-multiplexing systems.

Wavelength and sensitivity tunable long period gratings fabricated in fluid-cladding microfibers

We report the fabrication of long period gratings in fluid-cladding microfibers by directly focusing a femtosecond laser beam on the microfibers surface to induce periodical modification a long one side of the microfibers.A long period grating is fabricated in a water-cladding microfiber with a diameter of~5μm,which demonstrates a resonant attenuation of 28.53 dB at wavelength of 1588.1 nm with 10 pitches.When water cladding is changed to be refractive index oil of n=1.33 and alcohol solution with concentration of 5%,the resonance wavelength shifts to 1575.1 nm with resonant attenuation of 24.91 dB and 1594.1 nm with resonant attenuation of 35.9 dB,respectively.The long period grating demonstrates different temperature sensitivities of-0.524 nm/℃,-0.767 nm/℃and-1.316 nm/℃for water,alcohol solution and refractive index oil cladding microfibers,respectively,which means the alterable liquid cladding allows the availability of tunable wavelength and sensitivity.The fluid-cladding protects the microfibers from external disturbance and contamination and allows more flexibility in controlling the transmission property and sensing characteristics of long period gratings,which can be used as fiber devices and sensors for chemical,biological,and environmental applications.

中大型蜗轮副动态检查仪结构设计与仿真分析

为提高蜗轮副传动误差的检测水平,设计了一台适用于中大型蜗轮副传动误差检测的仪器,其具有大尺寸、动态测量、多参数同时测量等优点。阐述了传动误差检测系统的基本构架,以及仪器的总体设计方案;介绍了仪器的工作原理,提出将时栅传感器与仪器相关部件一体化加工的构想,使用SolidWorks进行了关键零部件设计,完成了结构布局和虚拟装配;通过Ansys Workbench对横梁装配体进行有限元分析并进行了结构优化,优化后1阶固有频率提升23.95%,各阶固有频率对应振幅均明显减小。

Vector bending sensor based on chirped long-period grating with off-axis micro-helix taper

Vector bending sensing has been consistently growing in many fields.A low-cost and high sensitivity vector bending sensor based on a chirped long-period fiber grating[LPFG]with an off-axis micro helix taper is proposed and experimentally demonstrated.The grating is composed of several sections of single-mode fiber with gradually larger lengths,and the off-axis micro helix tapers with fixed lengths when they are fabricated by using the arc discharge technology.The large refractive index modulation in the micro-helix taper greatly reduces the sensor size.The total length of the sensor is only 4.67 mm.The micro-helix taper-based LPFG can identify the bending direction due to the asymmetric structure introduced by the micro helix.The experimental results show that the transmission spectra of the sensor have distinct responses for different bending directions,and the maximum bending sensitivity is 14.08 nm/m^(-1)in the range from 0.128 m^(-1)to 1.28 m^(-1).The proposed bending sensor possesses pronounced advantages,such as high sensitivity,small size,low cost,and orientation identification,and offers a very promising method for bend measurement.

莫尔条纹法测量微小旋转角度的频域分析

利用菲涅耳衍射的频域分析方法,对莫尔条纹复振幅分布公式进行了理论推导,得到了使用两块相同光栅组成的光栅付测量微小角度的原理公式,与利用几何光学等方法得到的结论一致.模拟结果表明:莫尔条纹是光栅付拍现象的最低频率含量,莫尔条纹内含有大量高次谐波;在探测器光学系统放大率一定的前提下,为通过直接测量莫尔条纹宽度的变化达到测量角度变化的目的,必须根据测角精度、探测器的尺寸和分辨率选择合适的光栅付光栅常数和光栅付初始夹角.

利用光纤光栅实现压力和温度同时测量

结合光纤光栅弹簧管压力传感器的结构特点 ,在悬臂梁的上下两面分别粘贴两个应力和温度灵敏系数基本相同的光纤光栅 ,通过分别测量光纤光栅对的波长位移 ,实现了压力和温度的同时测量 ,压力和温度测量的分辨率分别为 0 .1 4 MPa和 0 .5℃ .

光栅面不平行对压缩脉冲时空特性的影响

推导了光栅对压缩器两光栅在垂直于刻线的平面(衍射面)内有一夹角时1至4阶色散变化量的表达式,以及脉冲超高斯光束经光栅对压缩后的场分布。并据此模拟分析了光栅表面平行性失调对输出脉冲时空特性的影响。结果表明:脉冲光束单次通过光栅对时其波形会产生扭曲,光栅对的失调会使脉冲扭曲更加严重;而两次通过光栅对时横向谱移动的影响会消除,但脉冲将出现旁瓣,光栅对的失调使得脉冲在时间上提前,且色散阶数越高色散变化量对压缩脉冲时空特性的影响越大。

一种新型齿电式时栅位移传感器研究

提出一种可同时兼顾动态测量、静态测量的齿电式时栅传感器,这种传感器把定子分为上、中、下三层,在三层槽齿上分别绕有对称的三相绕组,使传感器的极对数达到槽数的1/2,以达到用低等分的加工精度实现高精度测量的目的。实验结果表明,该齿电式时栅传感器精度达到2.1″,且成本低廉。

OPCPA系统中光栅对不平行度对脉冲时间波形的影响

利用光线追迹法和四阶龙格-库塔法分析了光参量啁啾脉冲放大系统中实际展宽器和压缩器所带来的各阶色散,并将其代入放大过程数值模拟了脉冲变化的情况,讨论了压缩器光栅对表面不平行、刻线不平行、信号光强度、泵浦光强度等因素对输出脉冲宽度和时间波形的影响。结果表明,光栅对表面不平行将引起脉冲宽度变大,且光栅顺时针旋转对脉冲宽度和波形影响更大。而光栅刻线不平行时,当仅考虑二阶色散时,夹角为0.8°时脉宽最小,考虑到三阶色散时,夹角为1°脉宽最小,且光栅顺时针和逆时针旋转对脉冲的作用相同。对实际OPCPA系统,当放大晶体材料及长度一定时,尽量调整压缩器光栅平行,信号光强度和泵浦光强度有一最佳值能使输出脉冲宽度达到最小。

单光栅与双光栅衍射角度检测对比分析

光栅副是增量式光电编码器最主要组成部分,它的结构和衍射效应直接与检测精度相关。文中深入地分析了单光栅与双光栅衍射特点,并且从空间调制模型的角度推导光栅副对莫尔条纹的影响。从宏观和微观两个角度分析光栅副的屏函数,研究莫尔条纹光电信号输出波形的不确定原因和反差对比度,进而证明单光栅测量可以减少输出信号的频率成分,获得较高的细分精度和反差对比度。为了证明单光栅角度检测的可行性,给出了一套完整的单光栅角度检测方法。

两相非等节距时栅位移传感器

在分析时栅位移传感器的一般信号模型的基础上,深入探讨了三相、两相时栅位移传感器的测量机理,进而提出了一种新型位移传感器——两相非等节距时栅位移传感器,然后详细介绍了它的结构和原理.通过和其它两种传感器的对比表明,该传感器可以在不增加加工难度的情况下,增加传感器的极对数.最后通过实验表明,该传感器的精度比其它两种传感器得到了提高.

提高叠栅条纹信号质量的一种新方法(英文)

在国内外普遍使用的细栅距幅光栅叠栅条纹系统中 ,衍射效应是很明显的 ,这是造成叠栅条纹信号的衬比 (度 )和正弦性不好的主要原因 .本文在分析了叠栅条纹信号的基础上 ,导出了衍射光栅副中± 1级叠栅条纹的相位与光栅副间隔 ,光线入射角等的关系 ,提出了用±1级叠栅条纹来提高叠栅条纹的信号质量 ,实验结果与理论分析一致 ,实际应用 。

光栅压缩器中色散的矩阵计算

在ABCD矩阵基础上 ,通过引入角度色散项获得了可以方便描述色散系统的 3× 3阶矩阵 采用这种矩阵方程方便、准确地计算了标准光栅对压缩器中的二阶、三阶以及四阶色散 。

有限束宽下超高斯光束经光栅对压缩的研究

利用有限束宽下入射脉冲通过光栅对压缩的理论模型,从脉冲光束的傅里叶角谱入手,分析了脉冲超高斯光束单次及两次通过光栅对时的变换特性,以及高阶色散对脉冲压缩的影响。结果表明,脉冲超高斯光束单次通过光栅对压缩器时,横向谱移动使得出射光束产生时间相关的空间移动而两次通过压缩器时则会消除此种影响。高阶色散不仅影响输出脉冲的时间特性同时还影响其空间特性,导致输出脉冲波形扭曲,产生时空畸变。