一种基于DSP的便携式光纤EFPI传感器解调仪

介绍了一种利用数字信号处理(DSP)芯片的便携式光纤外腔式法珀干涉型(EFPI)传感器解调系统。为了实现高速度、高精度的光纤EFPI传感器的解调,提出了一种测量EFPI透射波长的算法。利用DSP通过对EFPI反射波形的实时跟踪,计算透射出的波长值,并根据标定转换为被测量。实验结果表明,解调系统的波长分辨率可达到2pm,动态测量范围高达50nm。     

基于扫描光纤激光器的光纤传感解调仪研究

介绍了一种基于扫描光纤激光器的光纤传感解调系统.采用氰化氢（HCN）气体吸收池作为波长参考基准,采用三次多项式拟合的方法来确定光纤F- P可调谐滤波器的波长与驱动电压的对应关系,可调谐滤波器扫描过程中对扫描电压、多路光谱信号进行同步采样,实时标定.实验结果表明,该解调系统在1 510 nm到1 590 nm波长范围内对FBG反射峰值波长的分辨率为1.4 pm,长期波长重复性达到3.2 pm.利用该系统实现了对FBG反射峰值波长和光纤EFPI传感器腔长的高准确度解调.     

基于DSP的光纤光栅应变传感器信号检测实验研究

针对光纤光栅应变传感器接收信号弱且信噪比低这一问题,提出了应用DSP技术来抑制噪声,提高Bragg峰值波长检测精度的方法.实验结果表明所设计的498阶Kaiser窗低通FIR数字滤波器能够显著提高光纤光栅应变传感器的信号检测精度.采用DSP技术可以较好地解决光纤光栅传感器的波长解调这一技术难题.     

新型波长解调技术在干涉型光纤传感器输出解调中的应用

提出了一种改进型边缘滤波波长解调技术,解决干涉型或谐振型光纤传感器输出的干涉谱波长的快速解调问题。该波长解调技术基于啁啾光栅和长周期光栅的光谱特点,以啁啾光栅作为矩形滤波器,提取传感器输出干涉谱的一个干涉峰;以长周期作为边缘滤波器,将干涉峰的波长信息转化为光强信息进行检测。该波长解调技术波长解调范围为传感器输出干涉谱的一个自由光谱范围(FSR),解调速度快,克服了当前波长解调技术中存在的测量范围与测量速度难以同时提高的问题,同时还具有系统成本低 ,体积小,能够灵活多路扩展的特点。详细介绍了解调系统的工作原理以及系统结构,并将其实际应用于一种干涉型光纤电流传感器输出干涉谱的波长解调中。通过实验证明电流传感器工作在工频及脉冲电流(脉冲宽度25 μs)情况下,该解调系统对传感器输出干涉谱具有准确、快速的解调效果。该研究对推进干涉或谐振型光纤传感器的实际工程化水平的提高具有重要意义。     

基于阵列波导光栅的智能服装人体测温解调系统研究

研究并实现了一种应用于智能服装中人体温度测量的阵列波导光栅解调系统。分析了系统的解调原理,搭建了光纤布拉格光栅解调实验平台,采用了强度法解调出光纤光栅的布拉格波长,完成了光纤光栅传感器串联前后解调的实验。结果表明,系统对光纤布拉格光栅的布拉格波长的解调具有高线性度,波长测量精度可达0.001 nm,光纤布拉格光栅传感器间串扰所造成的解调误差为0.000 5 nm,人体温度的测量误差为±0.16 ℃。该解调系统精度高、串扰低,可适用于智能服装中人体温度的测量。     

光纤法布里-珀罗传感器阵列串扰抑制方法

本文提出了一种基于多波长平均的五步相移解调方案,解决非本征光纤法布里-珀罗（F-P）传感器阵列的串扰问题。以光纤F-P传感器的两基元并联复用系统为研究对象,探讨了基于五步相移解调方案的基本串扰理论以及多波长解调抑制串扰的具体方法。通过数值仿真研究了串扰与传感系统的消光比、平均波长数、波长间隔以及不同传感器基元腔长的关系,对单波长解调方案和多波长解调方案的串扰抑制效果进行了对比分析。结果表明,相较于单波长解调方案,多波长解调方案通过对多个连续工作点处的五步相移信号解调结果进行平均,降低了传感阵列的串扰。同时,该解调方案降低了对传感阵列光开关消光比和不同基元间腔长一致性的要求,有效推进了光纤F-P传感器阵列大规模复用的发展。     

动态匹配光栅解调方法波长读出优化研究

提出了采用一支价格低廉的微测力传感器作为匹配光栅解调系统的波长读出单元,不同于以往动态匹配光栅解调法采用拉伸匹配光栅的PZT驱动电压作为解调系统波长读出单元.当匹配光栅和传感光栅布喇格中心波长重叠时,光电探测器将接收到最大光信号.利用光纤光栅轴向受力和反射波长漂移的数学关系得到光纤光栅传感器的波长漂移.该解调系统解决了传统动态匹配解调系统中PZT本身特性对系统的影响,探测到的光纤光栅传感器反射波长和匹配光栅轴向受力大小具有很好的线性,系统线性大于0.999.本系统对于探测布喇格传感器应变分辩率达到1 με以下.     

基于宽谱光源的光纤传感波长解调系统的研究

研究制作了基于宽谱光源的光纤传感波长解调系统, 以多光纤光栅作为波长参考基准、采用可调谐光纤法布里-珀罗(F-P)滤波器作为波长扫描器件。系统中采用三次多项式拟合的方法对滤波器锯齿波的扫描电压与透射波长关系曲线进行非线性拟合, 解决可调谐光纤F-P滤波器的电压—波长非线性关系对系统测量带来的较大误差问题, 实现波长的高精度解调。采用五光纤光栅做波长参考, 单根光纤光栅传感器的解调实验结果表明：待测光纤光栅布拉格波长短期测量分辨率为3.5 pm, 长期测量稳定性为7 pm。采用该系统对光纤非本征法布里-珀罗干涉型(EFPI)应变传感器的测试结果表明, 测量应变灵敏度为2.41 nm/με, 并且应变和波长之间存在良好的线性关系, 线性相关度达到0.99991。     

基于色散补偿光纤的高速光纤光栅解调方法

本文提出并论证了一种光纤光栅高速解调的新方法, 利用色散补偿光纤的色散效应, 将光纤光栅的波长漂移信息转换成时域信息. 采用脉冲激光器作为光源, 仅需一个光脉冲可获取单根光纤上所有光纤光栅的反射光脉冲, 再根据各个光栅反射回光脉冲的延时变化即可实现波长的解调. 本方法可用于准分布光纤光栅传感网络解调, 系统采用全光纤结构, 无需波长扫描, 大大提高了解调速度. 本文搭建了测试系统进行实验验证, 对3个光纤光栅组成的准分布式传感网络进行了解调, 实验结果表明, 解调出的光纤光栅布喇格波长线性度好, 解调速度最高可达1 MHz, 采样数据取10次平均后解调线性度可达0.9969, 解调误差约为27.8 pm.     

光纤法布里-珀罗腔传感器双波长解调法及波长优化设计

提出了光纤法布里珀罗(F-P)腔传感器的双通道双波长解调方法,并在此基础上建立了传感器的实验解调系统。理论分析与实验研究了双波长法解调光纤法布里珀罗腔传感器的基本原理,证明了双波长双通道解调法可以补偿传感器光网中和波长无关的变动引起的误差。根据已知的法布里珀罗腔传感器初始腔长和腔两端面反射率,从腔长变化的动态范围、线性、灵敏度等方面考虑,对工作波长以及线宽进行了优化设计。对双波长双通道解调系统进行了实验和数据分析,经最小二乘法拟合后的线性拟合度达到98.35%。实验结果表明:该方法可满足解调光纤法布里珀罗腔传感器在灵敏度、响应速度以及稳定度上的要求。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.