光子学报  2017, Vol. 46 Issue (9): 0923002  DOI: 10.3788/gzxb20174609.0923002
0

引用本文  

冯序, 杨晓占, 黄国家, 邓大申, 秦祥, 冯文林. 基于铜离子沉积石墨烯涂层锥形光子晶体光纤的硫化氢传感器[J]. 光子学报, 2017, 46(9): 0923002. DOI: 10.3788/gzxb20174609.0923002.
FENG Xu, YANG Xiao-zhan, HUANG Guo-jia, DENG Da-shen, QIN Xiang, FENG Wen-lin. Hydrogen Sulfide Gas Sensor Based on Cu ion-deposited Graphene-coated Tapered Photonic Crystal Fiber[J]. Acta Photonica Sinica, 2017, 46(9): 0923002. DOI: 10.3788/gzxb20174609.0923002.

基金项目

国家自然科学基金(No.51574054)、重庆市高校创新团队项目(No.CXTDX201601030)、重庆市和重庆理工大学研究生创新项目(Nos.CYS16215,YCX2016213)资助

第一作者

冯序(1992-), 男, 硕士研究生, 主要研究方向为光纤传感与检测.Email:903694948@qq.com

通讯作者

冯文林(1976-), 男, 教授, 博士, 主要研究方向为光电功能材料与器件.Email:wenlinfeng@126.com

文章历史

收稿日期:2017-03-31
录用日期:2017-05-31
基于铜离子沉积石墨烯涂层锥形光子晶体光纤的硫化氢传感器
冯序1, 杨晓占1, 黄国家3, 邓大申1, 秦祥1, 冯文林1,2    
(1 重庆理工大学 理学院 物理与能源系, 重庆 400054)
(2 现代光电检测技术与仪器重庆市重点实验室, 重庆 400054)
(3 广州特种承压设备检测研究院, 广州 510663)
摘要:提出一种基于铜沉积石墨烯涂层光子晶体光纤马赫-曾德干涉的硫化氢气敏传感器.将45 mm光子晶体光纤两端与单模光纤进行拉锥熔接,使得光子晶体光纤的空气孔熔接时形成塌陷层,更好地激发包层模式,形成基于马赫-曾德结构的干涉仪.采用单层石墨烯粉体,加入异丙醇分散液,反复浸涂至光子晶体光纤包层表面形成石墨烯涂层,并沉积铜纳米颗粒,使传感器对硫化氢气体具有高的响应度.实验结果表明,在硫化氢气体浓度为0~60 ppm范围内,随着被测气体浓度不断增大,其输出光谱呈现明显蓝移,传感器灵敏度为0.042 03 nm/ppm,且线性度良好.该传感器成本低、灵敏度高、结构简单,适用于低浓度硫化氢气体的在线监测.
关键词光纤锥    光子晶体光纤    马赫曾德干涉仪    石墨烯    气体传感器    
中图分类号:TN201      文献标识码:A      文章编号:1004-4213(2017)09-0923002-5
Hydrogen Sulfide Gas Sensor Based on Cu ion-deposited Graphene-coated Tapered Photonic Crystal Fiber
FENG Xu1, YANG Xiao-zhan1, HUANG Guo-jia3, DENG Da-shen1, QIN Xiang1, FENG Wen-lin1,2    
(1 School of Science, Chongqing University of Technology, Chongqing 400054, China)
(2 Chongqing Key Laboratory of Modern Photoelectric Detection Technology and Instrument, Chongqing 400054, China)
(3 Guangzhou Special Pressure Equipment Inspection and Research Institute, Guangzhou 510663, China)
Foundation item: The National Natural Science Foundation of China (No.51574054), the University Innovation Team Building Program of Chongqing (No.CXTDX201601030), and the Postgraduate Research Innovation Project of Chongqing and CQUT (Nos.CYS16215, YCX2016213)
Abstract: A hydrogen sulfide gas sensor based on Cu-deposited graphene-coated tapered Photonic Crystal Fiber (PCF) Mach-Zehnder Interferometer (MZI) was proposed and fabricated. The PCF-MZI was formed by fusion splicing a PCF with length of 45 mm which was sandwiched between two Single-Mode Fibers (SMF), and the air holes of PCF in the splicing regions were fully collapsed, and then it could motivate the cladding modes better. Using isopropanol as dispersion agent, the monolayer powders of graphene were added in the solution and fully dispersed, and then the PCF was dip-coated and sintered repeatedly. Cu-deposited graphene-coated PCF was used to make the sensor produce high sensitivity. The results show that with the increasing concentration of hydrogen sulfide, the output wavelengths appear blue shift, and a high hydrogen sulfide gas sensitivity of 0.042 03 nm/ppm and good linear relationship are obtained within a measurement range from 0 to 60 ppm for hydrogen sulfide gas. The system has the advantages of low cost, high sensitivity and simple structure, especially suitable for low concentration and on-line monitoring of hydrogen sulfide gas.
Key words: Fiber tapers    Photonic crystal fiber    Mach-Zehnder interference    Graphene    Gas sensor    
OCIS Codes: 230.0040;230.0250;060.2370; 070.4790;260.3160
0 引言

硫化氢(H2S)是一种在自然界广泛存在的有毒有害气体,天然气和石油的燃烧、制药与合成化学纤维等都会产生大量的H2S气体,H2S气体所引起的灾害事故在国内外也常有报道[1-2].目前国外常用的H2S气体检测方法有气相色谱法[3]、电化学分析法[4]、传感器法[5]以及分光光度法[6]等.光纤马赫-曾德干涉型(Mach-Zehnder interference, MZI)传感器在液体折射率、光压和调制器等方面有诸多应用[7-10],但目前未见基于光纤马赫-曾德传感器的检测方法对H2S气体进行测试的报道.在气体的检测中,由于气体响应过程主要发生在敏感材料的表面,所以对气敏材料的选取十分重要.石墨烯是碳原子基于sp2杂化组成的六角蜂窝状结构,拥有极大的比表面积、极优的导电率以及极高的光学透射率[11],因此,在光伏[12]、生物成像[13]、光发射二极管及传感器[14]等领域有巨大的应用价值.

由于Cu沉积可增强对H2S气体的吸附性能[15],本文构建了一种基于铜沉积石墨烯涂层锥形光子晶体光纤(Photonic Crystal Fiber, PCF)的马赫-曾德干涉型气体传感器.该传感器仅需在PCF两端熔接普通单模光纤(Single Mode Fiber, SMF)并拉锥即可制得,其纤芯的光可更好地激发到包层,增加传感区的长度,并增大纤芯模式与包层模式的耦合程度,有效地提高传感器的灵敏度,同时该结构对温度灵敏度极低,在测量中能够克服温度交叉敏感问题.

1 基本原理

基于石墨烯纳米涂层锥形PCF气体传感器的结构是将一段PCF的两端分别与SMF进行拉锥熔接制得,如图 1,拥有两个锥形区域,形成SMF-PCF-SMF的结构,可看出制作的锥形结构在光纤熔接机监测精度范围内没有观测到熔接损耗.光从输入端单模光纤进入,在经过第一个锥形熔接区域时,一部分光传输至PCF包层,以包层模式传输,而另一部分光则继续在PCF纤芯中以纤芯模式传输.当到达第二个锥形熔接区域时,PCF包层中的光会与PCF纤芯中以纤芯模式传输的光汇聚发生干涉,同时两束光耦合至SMF纤芯继续进行传输,形成马赫-曾德干涉, 其干涉光强为

图 1 锥形结构制作示意图 Fig.1 Structure of tapered PCF before coating
$I = {I_{{\rm{cor}}}} + {I_{{\rm{cla}}}} + 2\sqrt {{I_{{\rm{cor}}}}{I_{{\rm{cla}}}}} \cos \Delta \varphi $ (1)

式中,IcorIcla分别为PCF中传输的纤芯的光强与包层中的光强,Δφ为两束光的相位差,即

$\Delta \varphi {\rm{ = }}\frac{{2{\rm{\pi }}\Delta {n_{{\rm{eff}}}}L}}{\lambda }$ (2)

式中,λ为传输光的波长,L为两个锥形熔接区域之间的干涉长度,Δneff是光纤纤芯有效折射率neffcor和光纤包层有效折射率neffcla之间的差值,当包层模和纤芯模之间的差值等于(2m+1)π时,光纤芯层和包层中的光的干涉会导致相消干涉,也就是说,会产生干涉波谷.m阶干涉波谷可表示为[16-17]

${\lambda _m}{\rm{ = }}\frac{{2\Delta {n_{{\rm{eff}}}}L}}{{2m + 1}}$ (3)

因此,m阶干涉波谷的波长将随着包层折射率的改变而改变[19-20],且变化量可表示为

$\Delta {\lambda _m} = \frac{{2\left( {\Delta {n_{{\rm{eff}}}} + \Delta n} \right)L}}{{2m + 1}} - \frac{{2\Delta {n_{{\rm{eff}}}}L}}{{2m + 1}} = \frac{{2\Delta nL}}{{2m + 1}}$ (4)

PCF包层的有效折射率会随着外部检测气体浓度的变化而变化,而PCF纤芯的有效折射率则保持不变[18-19].

2 实验过程与分析 2.1 光纤的拉锥熔接

实验中使用的PCF为长飞光纤光缆股份有限公司(Yangtze Optical Fibre and Cable Joint Stock Limited Company, YOFC)全内反射型PCF,其包层直径为125μm,具有多层空气孔,呈六边形结构排列.拉锥熔接机为古河S178C光纤熔接机;光源为康冠ASE宽带光源;光谱分析仪使用的是横河AQ6370D型光谱分析仪.传感器制备过程中采用的是手动设置拉锥熔接程序,用自动拉锥熔接的方式对SMF和PCF进行熔接,程序中首次放电开始强度+100,首次放电结束强度+100,再次放电开始强度+100,再次放电结束强度+100,清洁放电时间+200 ms,预熔时间+160 ms,首次放电时间+1 000 ms,再次放电时间+2 000 ms,此时PCF和SMF溶解点完全塌陷,从而能更好地激发包层模式.

2.2 基于Cu沉积石墨烯纳米涂层的制作

石墨烯涂层的制作方法是,将单层石墨烯片用玛瑙研磨锅充分研磨2 h后加入到50 mL的异丙醇溶液,异丙醇拥有分散作用,使得单层石墨烯可以在其中均匀分散,再将制作的锥形PCF放入其中进行多次浸涂后在真空80℃干燥3 h,再将PCF放置于管式炉,在氮气(N2)的保护下300℃煅烧2h,从而使石墨烯稳定地吸附在光纤表面,并将异丙醇充分挥发.

石墨烯在光纤包层外部成膜后,将Cu纳米颗粒在其外表面沉积,将镀有石墨烯涂层的PCF在直径为1~10nm的Cu纳米颗粒溶液中进行浸涂,再放入真空干燥箱80℃干燥2h,置于管式炉中300℃在N2保护下煅烧3h.沉积纳米Cu颗粒以提高对H2S气体的敏感特性.为进一步确定其元素成分,其X射线能谱分析(Energy Dispersive X-Ray Spectroscopy, EDX)如图 2.从图 2可知,测试样品中主要含有碳和铜两种元素.

图 2 铜沉积石墨烯涂层光纤表面EDX图 Fig.2 Image of EDX for Cu-deposited graphene-coated fiber
2.3 气敏传感实验

基于石墨烯PCF气敏性能的实验装置如图 3.ASE为宽谱光源,OSA为光谱分析仪,其中气室(Gas chamber)的设计是四端口的玻璃管,玻璃管左右两端分别用环氧树脂进行密封处理,上下两部分分别是所测气体的进出口.实验选择的检测气体为H2S,经过计算并与N2按比例混合,以制备出不同浓度的H2S气体,在实验中主要用注射器存放气体并将其通入气室进行测量.制备的马赫-曾德干涉仪在未通气体时的光谱测试结果如图 4.

图 3 实验装置图 Fig.3 Schematic diagram of the experimental setup
图 4 铜沉积石墨烯涂层锥形PCF MZI光谱图 Fig.4 Transmission spectra of the PCF MZI coated with Cu-deposited graphene film

每间隔一定时间对Cu沉积石墨烯涂层锥形PCF MZI光谱进行采样,如图 5,可以看出所制备的传感器具有良好的稳定性和一致性.

图 5 传感器稳定性曲线 Fig.5 Stability curvers of the sensor

不同浓度待测气体由N2和H2S按体积比混合而成,分别配制了浓度为2 ppm、5 ppm、10 ppm、20 ppm、30 ppm、40 ppm、50 ppm以及60 ppm的H2S气体.图 6为不同浓度H2S气体所对应的输出光谱.由图 6可见,在H2S气体浓度0~60 ppm范围内,随着通入H2S气体浓度的增大,传感器输出光谱呈现明显蓝移现象.其原因在于:当传感器包层上的Cu沉积石墨烯纳米涂层与H2S气体发生接触时,由于涂层对H2S气体具有良好的吸附作用,纤芯折射率不变,但是会使得包层折射率有所增加,且随着H2S气体浓度的增加,其折射率差的绝对值也不断减小.因此,由式(3) 可知,随着气体浓度的不断增加,该传感器的输出光谱将发生蓝移.实验结果与理论分析具有较好的一致性.

图 6 不同浓度H2S所对应的输出光谱 Fig.6 Spectral responses of the PCF -MZI sensor in various concentrations of hydrogen sulfide

图 7,通过实验测量对气敏传感的光谱进行分析,对光谱偏移量进行计算,得到输出光谱在1 567 nm波长附近偏移量与所测气体浓度的关系,并且线性拟合度良好,线性度值为0.963 91,该传感器灵敏度为0.042 03 nm/ppm.在检测过程中通入所测H2S气体时,记录响应时间,测试传感器的响应和恢复时间,由图 8可知,H2S气体在0到60 ppm范围内,该传感器的响应时间tr和恢复时间tf分别约为48 s和72 s.

图 7 光谱偏移与气体浓度的关系 Fig.7 Wavelength shift upon the concentration of hydrogen sulfide
图 8 传感器响应-恢复曲线 Fig.8 Dynamic responses of the hydrogen sulfide sensor
3 结论

本文提出了一种Cu纳米颗粒沉积石墨烯涂层PCF马赫-曾德气体传感器.它是在一段长为45 mm的PCF两端分别熔接SMF,并采用熔融拉锥法制得.对传感器进行了气敏性能测试实验.实验结果表明,随着H2S浓度的增大,其传输光谱中心波长呈现蓝移,在0~60 ppm的气体浓度变化范围内,传感器灵敏度为0.042 03 nm/ppm,且具有好的线性度.该传感器具有体积小、重量轻、易于制备、灵敏度高等优点,对不同环境的H2S气体浓度测量有潜在的应用价值.

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