一种新型结构长周期光纤光栅光谱特性研究

基于长周期光纤光栅(LPFG)包层有效折射率与包层半径、折射率和环境折射率的良好相关性,提出一种LPFG的新颖结构。利用传输矩阵法和三包层光纤的色散方程对其建模,mathcad15计算软件进行数值仿真和模拟。得到新型结构LPFG谐振峰发生分裂,即一个透射峰分裂为两个;两个分裂峰谐振波长间距随着腐蚀段包层半径的减小或填充材料厚度的增大而增加,模式越高增加越快;同时分裂峰间距在填充材料折射率小于1.4和大于1.48时基本不变,而在1.4和1.48之间分裂峰间距变化显著,在1.44附近达到极值。此种结构LPFG设计上的特殊性即可弥补半腐蚀LPFG容易断的不足,又可通过填充敏感材料且利用分裂峰间距定标而提高气体或液体浓度传感灵敏度。     

薄包层长周期光纤光栅的折射率传感特性

长周期光纤光栅(LPFG)可用于折射率传感,同时利用折射变化可以实现谐振波长的调谐.不同的光纤包层半径和光栅周期对折射率灵敏度有较大影响.利用光波导的耦合模理论分析了LPFG的折射率传感特性,给出LPFG的折射率灵敏度的解析表达式,给出了利用不同包层模时的折射率灵敏度.利用三层介质光纤的纤芯模本征方程计算了薄包层LPFG的折射率灵敏度.结果表明,基于不同包层模的LPFG的谐振波长随折射率的变化有红移,也有兰移;基于低阶模序包层模的LPFG,折射率灵敏度较小,中间模序最大,而高阶模序则较大,薄包层LPFG对折射率具有更大的灵敏度.     

镀膜长周期光纤光栅透射谱研究

基于三包层长周期光纤光栅的耦合模型,研究了镀膜长周期光纤光栅的光栅参数和膜层厚度对长周期光纤光栅谐振波长的影响。研究发现,当长周期光纤光栅的纤芯半径、折射率和周期增大时,谐振波向长波方向漂移;当长周期光纤光栅的包层半径和折射率增大时,谐振波向短波方向漂移。不同折射率的膜层介质其所对应的最优厚度(Optimum Overlay Thickness,OOT)不同,薄膜介质的折射率越高,对应的最优厚度越小,敏感区域范围也较窄;不同包层模式对应的最优厚度具体位置区别不大,较高阶次包层模对应的谐振波长在敏感区域范围内漂移量较大。     

基于长周期光纤光栅的高灵敏度温度传感方案

长周期光纤光栅具有波长选择损耗的带阻滤波特性 .其谐振波长随光纤包层直径的减小而向长波方向漂移 .环境温度、外部折射率指数的变化会导致谐振波长位移 .由此提出一种敏感度增强的温度传感方案 .推导了长周期光纤光栅谐振波长与温度之间的关系模型 .在光纤纤芯中写入长周期光纤光栅 ,通过腐蚀方法减小其包层直径 ,随后在光栅外再涂覆聚合物包层 .用此器件测量所得温度传感特性 ,其实验结果与仿真结果基本一致。其温度灵敏度超过 5 .2 nm/℃ .     

基于微环谐振器的甲烷传感器

提出了一种新型的基于微环谐振器的甲烷传感器。该传感器通过微环表层的穴番A涂层来增加微环的有效折射率,使微环谐振器中谐振波长随甲烷浓度的增加而向右漂移;通过测量输出光信号的谐振波长推算出甲烷浓度。理论分析结果表明,该传感器的谐振波长变化范围在一个自由光谱范围内,甲烷浓度测量范围为0~15%;对比SOI材料和聚合物材料、单面敏感膜和三面敏感膜的测量结果,得出聚合物材料三面敏感膜微环的谐振波长变化幅度较大,测量灵敏度为60pm。     

基于长周期光纤光栅的生物传感器设计及仿真

利用生物活性物质高效、专一的催化特性,通过生化反应中生成的复合物对包层折射率和半径的直接调制,提出了基于长周期光纤光栅的、可用于蛋白质等生物物质鉴别与分析的传感方案,并用数值计算方法对检测中所生成复合物薄膜层的折射率和厚度变化对耦合波长偏移和衰减的影响进行了仿真研究,为新型高灵敏度生物传感器的研发提供了理论依据。     

基于光纤光栅的多腔Fabry-Perot滤波器透射特性理论分析

理论分析了基于光纤光栅的全光纤多腔Fabry-Perot(FP)结构透射谱特性,推出包含任意多个腔时的传输矩阵函数通用公式以及对称两腔结构的能量传输率具体计算公式,给出在光栅阻带内中心波长处产生单谐振传输峰需满足的条件,并通过数值计算进行了验证。在此基础上比较分析了单腔与两腔FP结构下,中心波长1550 nm处产生谐振透射峰的光谱特性,结果表明引入两腔结构后谐振峰的平坦性及其过渡带滚降特性都得到了改善。详细计算并模拟了腔长及光纤光栅特性变化对两腔FP结构透射谐振峰谱型造成的影响,总结出滤波器设计原则,并得出结论:增大光纤光栅反射率能够优化谐振峰滚降特性,通过适当选取腔长及光栅反射率大小,此结构能够用于窄带单通道选择或多通道波长的解复用。     

毛细石英管构成的温度不敏感的折射率传感器

设计并制作了一种基于单模光纤－石英毛细管－单模光纤的马赫－曾德尔干涉仪光纤传感器。该传感器对环境折射率敏感,但对环境温度不敏感,传感器的石英毛细管长度为3cm,内径为2μｍ,外径为150μｍ,毛细管壁由高纯熔融石英构成,根据传感器透射光谱的谐振峰(波谷)波长对环境折射率变化敏感的特点,通过监测谐振峰波长的移动,测量了环境折射 率。实验结果表明:当谐振峰波长为1555nm时,折射率最大灵敏度为122.3nm/RIU(RIU为折射率单位),而温度灵敏度很低,说明该传感器可以消除温度对折射率的交叉敏感性,该传感器具有制作简单、结构紧凑、成本低、重复性好、灵敏度高等优点,在环境折射率测量中具有一定的应用前景。     

长周期光纤光栅温度特性的理论与实验研究

利用模式耦合理论,对长周期光纤光栅透射谱谐振波长的温度特性进行了理论分析和数值模拟.结果表明,可以通过选择具有合适纤芯与包层热光系数匹配的光纤,从而制作出谐振波长对温度变化敏感或者不敏感的长周期光纤光栅;采用高频CO2激光脉冲三束对称写入法制作长周期光纤光栅,并进行温度特性测试,结果表明,谐振波长具有线性响应的温度特性,灵敏度约为0.088 nm/℃,而峰值损耗对温度不敏感,起伏不超过0.5 dB.     

采用拍频检测的内嵌型微环传感器研究

提出了一种内嵌型微环传感结构。利用内嵌型结构产生的高Q值滤波峰,采用拍频检测技术,可以实现高灵敏度传感器。采用传输矩阵法分析了内嵌微环半径对滤波峰位置及相邻滤波峰之间关系的影响。内嵌微环的滤波峰产生了分裂,其波长间距很小,且随折射率变化波长间距也会变化。利用该器件构建了拍频检测系统,并对该器件进行传感分析。仿真结果表明,该结构的传感灵敏度为1×10-4折射率单位(RIU),其频率偏移为4 MHz/1×10-4RIU。     

Sensitivity of guided mode resonance filter-based biosensor in visible and near infrared ranges

The sensitivity of guided mode resonance filter (GMRF) biosensors was analyzed when the initial peak wavelength (IPW) changed from 400 to 1600 nm. The sensitivity of the GMRF to the sample refractive index and thickness was analyzed using rigorous coupled wave analysis method. Results indicate that for a certain IPW, the sensitivity of the GMRF did not change when the sample refractive index varied, but drastically decreased and achieved constant sensitivity with increased sample thickness. When the IPW increased, the sensitivity improved in relation to both sample refractive index and sample thickness. Furthermore, the capability of sample thickness improved with longer IPW. These results are helpful in obtaining an optimal GMRF biosensor.     

Evanescent wave long-period fiber grating within D-shaped optical fibers for high sensitivity refractive index detection

By now long-period fiber gratings (LPFGs) represent a well-assessed in-fiber technology. Their peculiar spectral properties and the intrinsic surrounding refractive index (SRI) sensitivity, together with the well known advantages of optical fibers, make these structures one of the most powerful tools, especially in the sensing field. Unfortunately, their main limitation relies on the need of opportunely coating the glass substrate when significant sensitivity enhancement and/or specific functionalization are required. In this work, the possibility to realize a self-functionalized and high sensitivity LPFG is demonstrated. The principle of operation is based on the exploitation of the evanescent wave interaction of the propagating light with a periodically patterned overlay. A D-shaped optical fiber is used as fiber substrate, that is made SRI sensitive by means of wet chemical etching based on hydrofluoric acid. Due to its peculiar geometry the process results easier in comparison with that to perform with standard single-mode fibers. In addition the chemical step can be stopped once the desired sensitivity is achieved. Successively a high refractive index (HRI) overlay is deposited on the flat surface of the fiber. Finally the HRI layer is periodically patterned by means of laser micromachining technique. The spectral characteristics of the fabricated device, together with the flexibility of the adopted fabrication method could allow the realization of innovative LPFGs to be adopted as technological platform for a multitude of chemical sensing applications, depending on the nature of the material deposited onto the flat surface of the etched D-fiber.     

Simulation and design of MIM nanoresonators for color filter applications

We simulated metal–insulator–metal (MIM) nanoresonator structures that can be realized by sandwiching an insulator layer between two metal grating layers with subwavelength periods and heights. Simulation results indicate that it is possible to use relatively low refractive index polymeric materials as the insulator layer and such MIM structures can function as color filters with reasonably narrow bandwidths in transmission mode. Such color filters being superior in performance might find application in liquid crystal display devices replacing the conventional color filters. Simulations suggest that development of plasmonic modes at the metal–insulator interfaces might be responsible for the filter‐like transmission behavior of such structures. The transmission peaks can be tuned by changing the heights of the two grating layers and the refractive index of the insulator layer. Transmission peak is red‐shifted as insulator layer refractive index increases. Simulations were carried out using a home‐grown, monochromatic version of recursive convolution finite‐difference time‐domain method.     

Improve the refractive index sensitivity of gold nanotube by reducing the restoring force of localized surface plasmon resonance

The core refractive index sensitivity of a gold nanotube was investigated by calculating the shift of local surface plasmon resonance (LSPR). It was found that the core refractive index sensitivity can be improved by reducing the wall thickness or the surrounding refractive index. The sensitivity increases exponentially with decreasing wall thickness, but increases linearly with decreasing surrounding refractive index. This multi-factor controlled sensitivity of gold nanotube enlarges the ability of optimizing the refractive index sensors. The physical origin of this tunable refractive index sensitivity of gold nanotube was also investigated based on the plasmon hybridization and repulsive effects on the restoring force of plasmon oscillation. This physical mechanism can be used for designing core-shell metallic nanostructures for effective LSPR chemical and biological sensing.     

LiNbO3棱镜耦合双金属薄膜表面等离子共振传感器

高折射率铌酸锂(LiNbO3)(2.202)为棱镜耦合激发的角度调制型表面等离子共振传感器,利用反射率公式优化单层银膜、金膜和双层银/金膜传感器薄膜的厚度,分别计算了优化厚度的传感器在检测样品折射率为1.330时的共振角、灵敏度、峰值半宽度(FWHM)和品质因数(FOM),理论计算表明:双层金属薄膜,随着金膜厚度的增加,传感器灵敏度增加,但峰值半宽度增加,品质因数下降.综合考虑,选择银/金(41/5)优化组合,传感器品质因数为优化的单层金膜(47 nm)传感器品质因数的2倍以上,另外,与常用的BK7玻璃棱镜耦合相比,LiNbO3棱镜耦合具有较大的样品动态检测范围.优化厚度的传感器实验检测糖水浓度表明:糖水浓度与共振角为线性比例关系.     

镀有SiO2-WO3纳米复合薄膜LPFG气体传感特性研究

以钨粉和正硅酸乙酯为原料,采用溶胶-凝胶工艺和浸渍提拉镀膜方法,在玻璃衬底上制备出了具有气敏传感特性的SiO2-WO3纳米复合薄膜.采用原子力显微镜和X射线衍射仪表征了薄膜样品的表面形貌和物相结构.实验结果表明:掺杂SiO2使WO3薄膜中的颗粒尺寸减小,空隙率提高,比表面积增大.将SiO2-WO3复合薄膜镀于长周期光纤光栅上(LPFG),在室温条件下,将LPFG置于体积分数为2%的NO气体中,LPFG谐振峰红移了4.77 nm,损耗由-9.93 dB变为-8.53 dB,相应的气体传感灵敏度达到3%,元件响应时间10 s,恢复时间20 s.     

测量液体折射率与浓度的光纤光栅传感器

基于长周期光纤光栅的耦合模理论,从简化的三层光纤模型出发,研究了外界环境折射率变化时长周期光纤光栅传输谱的变化,并对氯化钠溶液的浓度和折射率进行了验证。实验结果发现,长周期光纤光栅的谐振波长与氯化钠浓度的变化近似成线性关系,而与折射率成二次曲线关系,这与数值模拟的结果一致。采用长周期光纤光栅测量液体的浓度和折射率的方法结构简单,且传感信号属于波长解调,避免了光强波动及光纤损耗的影响,整个传感系统全光纤化,能够实现对环境介质的在线、实时、快速、精确测量,还可用于特殊测量场合,实现远程遥测功能。     

光纤Bragg光栅与长周期光纤光栅比较及传感应用

阐述了光纤Bragg光栅(FBG)与长周期光纤光栅(LPFG)的常用制作方法、原理、特性,并对它们进行了比较,介绍了目前国内外光纤光栅的最新应用,特别是在传感领域的新应用。对今后的研究方向做了预测,适合于不同用途光纤光栅的写入技术有待于进一步提高,通过减小包层直径来改变光纤光栅特性的方法有待于进一步研究和利用,在折射率传感领域光纤光栅会有更广阔的天地。