【作者】 姜萌；

【导师】 张伟刚；

【作者基本信息】 南开大学 ， 光学， 2010， 博士

【摘要】 本文介绍了光腔衰荡光谱的技术背景、特点、意义和发展历程；综述了其在高反射率测量、原子分子吸收光谱研究、分析化学、痕量气体检测和大气环境检测等技术中的应用；概述了在此基础上发展起来的光纤腔衰荡技术及其优越性。本文的主要研究工作及研究成果如下：1、系统阐述了基于光强测量的CRDS技术和相移CRDS技术的原理；从技术角度分析了光源、增益放大器、耦合器件和探测器的参数选择和技术指标对测量精度和范围的影响；并重点分析了吸收单元——衰荡腔的分类,将其归纳为基于倏逝波原理的衰荡腔,引入微腔的衰荡腔以及引入光纤光栅的衰荡腔。对这三种结构进行了细致的总结,并指出了各自的优缺点。2、提出复折射率替代折射率的倏逝波模型计算流体吸收损耗,利用有限单元法建立了光纤四层折射率模型并计算得到了复折射率即消光系数；根据比尔-朗伯定律和倏逝波理论分别计算得到光纤的吸收损耗和传输损耗,并据此研究了当光纤包层被腐蚀后所泄漏的倏逝场及光纤的传输特性,并定量分析了被氢氟酸腐蚀的光纤包层直径对传输损耗的影响。3、采用氢氟酸腐蚀环内光纤的方法形成包层部分移除的吸收单元,设计并实现了免受温度影响的980nm光纤环衰荡腔系统和1560 nm皮秒级脉冲光纤环衰荡腔系统,利用5μL微流量注射器控制滴定浓度,检测二甲基亚砜溶液(DMSO)的折射率和浓度与损耗的对应关系。实现了对二甲亚砜溶液浓度的高精度测量,探测灵敏度达到1×10-3dB。4、提出并实验验证了碳纳米管涂覆的光纤倏逝波气体传感的新方法。在分析碳纳米管材料的发展和特性的基础上,总结了碳纳米管制备方法、碳纳米管和光纤的组装方法及其应用和发展。提出了利用碳纳米管的吸附和高温解吸附特性,将碳纳米管材料进行开口预处理并与光纤衰荡腔组装的方案,实现了对气体和易挥发有机溶剂(VOC)的实时初步传感测量。5、提出并实验验证了基于相移长周期光纤光栅(PS-LPG)的光纤环腔衰荡谱系统实现低损耗探测的新方法。采用耦合模理论分析了长周期光纤光栅的模式耦合和折射率传感特性,并用传输矩阵法分析了相移长周期光纤光栅的传输谱特性。根据理论分析结果选择适当的写制周期和长度,利用高频聚焦CO2激光脉冲技术在单模光纤上写制出低损耗(Loss<-0.74dB),谐振峰波长在1560nm的相移长周期光纤光栅,将其引入1560nm窄脉冲光纤环衰荡腔系统,避免了移除部分包层光纤的吸收单元结构脆弱的缺点,实现了对外界折射率和外界溶液浓度的实时检测。6、提出并实验验证了基于相移超长周期光纤光栅(PS-ULPG)的光纤环腔衰荡谱探测系统。利用超长周期光纤光栅谐振峰为高阶包层模与纤芯模式耦合,对外界环境变化更为敏感的特性,将高频CO2激光器写制的低传输损耗PS-ULPG作为吸收单元引入衰荡腔系统。根据耦合模理论的计算结果适当选择写制参数,在单模光纤上写制出谐振波长为1560nm超长周期光纤光栅以及相移超长周期光纤光栅,并将其引入1560nm的窄脉冲光纤环衰荡腔系统中。通过测量不同折射率的液体对光纤环衰荡谱衰荡时间的影响,实现了对外界直射率和外界溶液浓度的实时测量。7、在对目前单一组分、单一参量流体折射率传感分析的基础上,提出了以动态检测、传感单元设计等方式实现基于光纤腔衰荡光谱技术的多组分、多参量检测系统的思路,设计出典型的系统方案并进行了初步的应用探索。更多还原

【Abstract】 This thesis provides a comprehensive introduction of the technical background, characteristics, advantages, and historical progress of cavity ring down spectroscopy (CRDS); moreover, the applications of CRDS in high reflectivity measurement, atomic and molecular absorption spectroscopy, analytic chemistry, mark gas detection, and atmosphere environmental monitoring have been also generally discussed about; furthermore, CRDS technology and its advantages have been briefly introduced. The main content of this thesis include the following aspects:1. CRDS techniques based on the measurement of optical intensity and phase have been systematically introduced; from the technical perspective, the influence of parameter selection of light source, gain amplifier, coupling components, and detector along with the technical features on the measurement resolution and range have been analyzed; and in particular, the absorption cell—ring down cavity is classified into the cavity based on evanescent waves, the cavity with micro-cavity, and the cavity based on fiber gratings. The above three configurations have been summarized in detail, and their respective merits have also been pointed out as well as the disadvantages.2. The evanescent wave model using complex refractive index is presented to calculate the absorption loss of flow, and a four-layer refractive index model has been set up by using the finite element method to acquire the complex refractive index, namely the extinction ratio; furthermore, according to the Beer-Lambert law and evanescent wave principle, the absorption loss and transmission loss of the fiber have also been calculated, based on which the evanescent field leakage and transmission characteristics for the cladding-etched fiber have been investigated as well as the influence of cladding diameter of the HF-acid-etching fiber on its transmission loss has been quantitatively analyzed3. By using HF acid to etch the fiber inside the cavity, absorption cells with partially eradicated cladding are formed, based on which the temperature-immune 980nm fiber CRDS system and 1560nm pico-second pulse fiber CRDS system have been designed and experimentally achieved. With a 5-microliter injector to control the fluid concentration, the refractive index of DMSO solution as a function of the transmission loss has been experimentally calibrated. The high-precision concentration measurement of DMSO solution is achieved with a sensitivity of 1×10-3dB.4. A novel gas sensing technique based on the fiber evanescent sensor coated with carbon nanotubes is presented and experimentally validated. Based on the progress and characteristic introduction of the carbon nanotube materials, the preparation method of carbon nanotubes, the approach to assemble the carbon nanotubes with fibers, and their applications have been summarized. An assembly scheme is presented, which needs to preprocess the carbon nanotube materials with front opening considering the adsorption and de-adsorption characteristics of carbon nanotubes under high temperature. And by using this method, preliminary real-time measurement of gases and VOC is realized.5. A novel low loss measurement method based on the phase-shifted long-period grating (PS-LPG) is presented and experimentally validated. The mode coupling and refractive index sensing characteristics of the long-period grating are analyzed by using the coupled mode theory, and the transmission characteristics of the PS-LPG is analyzed based on the transfer matrix method. According to the theoretical results, appropriate grating pitch and length parameters are selected, and the PS-LPG with low loss ((Loss<-0.74dB) and a resonance wavelength of 1560nm, is inscribed onto a single-mode fiber under exposure of focused high frequency CO2 laser pulses. By introducing this grating into a 1560nm narrow line-width pulse CRDS system, the fragile structure of absorption cells with fiber cladding partially eradicated is avoided, and thus real-time measurement of environmental refractive index and solution concentration is realized.6. A fiber CRDS system based on the phased-shifted ultralong-period grating (ULPG) is proposed and experimentally validated. By exploiting the larger sensitivity of the resonance wavelengths resulting from the mode coupling between the core mode and higher order cladding modes, the low loss PS-ULPG fabricated by high frequency CO2 laser is introduced into a CRDS system as the absorption cell. According to the simulation results based on the coupled mode theory, appropriate grating parameters are selected, and the ULPG and PS-ULPG with resonance wavelengths of 1560nm are written onto single-mode fibers, which have been employed in a 1560nm narrow line-width pulsed fiber CRDS system. Through measuring the ring down time of the liquid with different refractive indices, the real-time measurement of environmental refractive index and solution concentration is achieved.7. Based on the present study on single-parameter refractive sensing of the flow with single constituent, the multi-parameter sensing system with multi-constituent is proposed based on the CRDS technology equipped with dynamic measurement and optimal design of sensing units. The typical scheme is presented and its preliminary application has been attempted as well.更多还原