包层折射率调制LPFG理论、传感和带通滤波特性研究

发布时间：2018-05-17 16:34

本文选题：长周期光纤光栅 + 包层折射率调制　；参考：《湖南大学》2016年博士论文

【摘要】：光纤光栅是近二十年来传感和通信领域发展最为迅速的无源光器件之一。光纤光栅传感技术具有灵敏度高、抗电磁干扰以及与现有光电器件兼容性好等优点,已成为实现智能材料与结构的重要途径之一。长周期光纤光栅(LPFG)能够实现同向传输纤芯导模和包层模间的能量交换或模式耦合,从而在其透射谱谐振波长处产生分立的谐振峰。目前LPFG及其相关器件的研究主要集中于带阻型纤芯折射率调制LPFG,且已报道了较完善的理论体系。然而,随着工程建筑和环境安全等问题越来越受到人们的重视,探索更多类型的能“感知”工程结构以及环境变化的高灵敏光纤传感方案已成为人们的迫切愿望。本文系统研究了新型包层折射率调制LPFG(C-LPFG)及其相关器件的模式耦合原理以及折射率传感特性,并取得了以下几个方面的研究成果:1.应用光纤分层和离散化处理方法,详细推导了三层模型开放波导光纤光栅线偏振模色散方程以及分层耦合模理论(MCMT)。将分层光纤光栅折射率调制函数应用到封闭波导光纤光栅复耦合模理论(CCMT),从而扩展了MCMT和CCMT理论的应用范围,为复杂折射率调制光纤光栅的仿真分析提供了强有力的理论基础。2.复杂包层折射率调制可简化为三个参量:调制角度?θ、调制深度?r以及调制幅度clδn。研究表明,非均匀包层折射率调制引起纤芯导模同时耦合至低阶LP0j和高阶LP vj(v≥1)包层模;高阶模式耦合的谐振峰LP01,vj(v≥1)是由相应的两个偏振模式(C vj LP和S vj LP)耦合谐振峰合成,且随?θ变化具有典型的周期特征;谐振峰强度01,res vj T会出现与耦合相位以及模场分布相关的极值点;谐振波长01,res vjλ会出现相应的红移(?θ变化时)或蓝移(?r变化时);clδn变化引起01,res vj T线性变化;在不考虑偏振时,低阶和高阶模式谐振峰LP01,vj具有类似的折射率传感特性,其平均灵敏度达到01,S vj≈760nm/RIU。在此基础上,初步研究了包层折射率调制倾斜LPFG(TLPFG)的折射率传感特性,其最大灵敏度达到01,0S j=1918.4nm/RIU,高于非倾斜LPFG的灵敏度。3.提出一种高灵敏镀银膜C-LPFG的SPR折射率传感方案(C-LPFG型SPR)。通过对SPR模式的色散曲线及其导数、模场分布因子等参量的研究,揭示了SPR模式的激励原理以及折射率传感原理:SPR模式来源于有效折射率实部接近于环境折射率SRI的高阶EH包层模,SPR模式色散曲线随SRI变化发生整体漂移而保持形状不变,导致SPR模式谐振波长出现漂移,从而实现高灵敏C-LPFG型SPR传感。研究发现,当包层半径从62.5cl r=μm减小至22.25cl r=μm时,C-LPFG型SPR的折射率灵敏度从2900/SRI S≈nm RIU提高至4900/SRI S≈nm RIU(SRI的变化范围为1.33 1.337SRI≤n≤),均高于普通的纤芯折射率调制LPFG的SPR传感灵敏度。4.提出一种高灵敏带通型C-LPFG折射率传感方案。其基本原理为:输入光直接耦合至光纤包层并激励起包层模式,其中满足PMC条件的包层模式传输至包层中的光栅区域时再次耦合至纤芯并输出,从而其输出光谱具有典型的带通特性。研究发现,谐振波长处于TAP附近的带通型C-LPFG具有非常高的折射率灵敏度;减小包层半径后(14.6cl r=μm),其最大平均折射率灵敏度高达SRI=4757.6nm/US RI,相应的最大局部折射率灵敏度达到6000/SRI≈n S m RIU(1.33 1.36SRI≤n≤),高于同类型传统的带阻型LPFG传感。5.提出一种高灵敏带通型镀非金属膜C-LPFG(CC-LPFG)的折射率传感方案。镀非金属膜C-LPFG的模式发生模式转化后,其模场分布转移至膜层内,从而增大了光纤模式与外界环境的相互作用。研究表明,带通型CC-LPFG(17.56cl r=μm)的最大平均折射率灵敏度和最大局部灵敏度高达4S SRI2.12×=10 nm/RIU和3.5 104/SRI=×nm IUS R(1.33 1.34SRI≤n≤),具有非常明显的传感优势。6.初步研究了带通型C-LPFG的带通滤波特性,为后续可调谐宽带以及窄带带通滤波器的研究提供了理论基础。
[Abstract]:Fiber Bragg grating (FBG) is one of the most rapidly developing passive optical devices in the field of sensing and communication in the past twenty years. Fiber Bragg grating sensing technology has the advantages of high sensitivity, anti electromagnetic interference and good compatibility with existing optoelectronic devices. It has become one of the most important ways to realize intelligent materials and structures. Long period fiber gratings (LPFG) can be realized. The energy exchange or mode coupling between the guide and cladding modes of the core is transmitted at the same direction, thus generating a discrete resonant peak at the length of the resonant wave of the transmission spectrum. The current research on LPFG and its related devices is mainly focused on the band resistance fiber core refractive index modulation (LPFG), and has reported a more perfect theoretical system. However, with the safety of engineering and environmental safety More and more attention has been paid to such problems. It is an urgent desire to explore more types of high sensitive optical fiber sensing schemes which can "perceive" engineering structures and change the environment. This paper systematically studies the mode coupling principle of the novel cladding refractive index modulation LPFG (C-LPFG) and its related devices, as well as the sensing characteristics of the refractive index. The following achievements are obtained: 1. using the optical fiber layered and discrete processing methods, the three layer model open waveguide fiber grating line polarization mode dispersion equation and the layered coupled mode theory (MCMT) are derived in detail. The refractive index modulation function of the layered fiber grating is applied to the closed waveguide fiber Bragg grating complex mode theory (CCMT). The application range of MCMT and CCMT theory is extended, which provides a strong theoretical basis for the simulation analysis of complex refractive index modulation fiber Bragg gratings..2. complex cladding refractive index modulation can be simplified as three parameters: modulation angle, theta, modulation depth, R and modulation amplitude CL delta n. research shows that the non uniform cladding refractive index modulation causes core conductance. The mode is coupled to the low order LP0j and the high order LP VJ (V > 1) cladding mode, and the resonant peak LP01 of the high-order mode coupling, VJ (V > 1) is synthesized by the corresponding two polarization modes (C VJ LP and S VJ), and has typical periodic characteristics with the variation of? Theta. The resonant peak intensity is 01, which is related to the coupling phase and the distribution of the mode field. The extreme value point; the resonance wavelength 01, res VJ lambda will appear the corresponding red shift (? Theta change) or blue shift (? R change); CL delta N changes cause 01, res VJ T linear change; in the absence of polarization, the low order and high order mode resonant peak LP01, VJ has the similar refractive index sensing specificity, the average sensitivity reaches 01, S VJ The refractive index sensing characteristic of the clad refractive index modulation inclined LPFG (TLPFG) is studied. The maximum sensitivity is 01,0S j=1918.4nm/RIU and is higher than the sensitivity.3. of the non inclined LPFG. A SPR refractive index sensing scheme (C-LPFG type SPR) for a highly sensitive silver coating C-LPFG is proposed. The dispersion curve and its derivative, the mode field distribution factor and other parameters are used for the SPR mode. The study of quantity reveals the excitation principle of SPR mode and the principle of refractive index sensing: the SPR mode comes from the high order EH cladding mode of the effective refractive index close to the environmental refractive index SRI, and the SPR mode dispersion curve keeps the whole drift with the change of SRI, which leads to the drift of the resonant wavelength of the SPR mode, thus realizing the high sensitive C-LP. FG SPR sensing. It is found that when the radius of the cladding is reduced from 62.5cl r= to 22.25cl r= mu, the refractive index sensitivity of the C-LPFG SPR is higher than that of the 2900/SRI S, which is higher than that of the ordinary fiber core refractive index modulation. The basic principle of the band pass type C-LPFG refractive index sensing scheme is that the input light is directly coupled to the fiber cladding and excites the cladding mode, in which the cladding mode satisfying the PMC condition is transmitted to the grating region in the cladding to be coupled to the core and output again, and the output spectrum has typical band-pass characteristics. The band pass type C-LPFG near TAP has a very high refractive index sensitivity; after reducing the radius of the cladding (14.6cl r= mu m), the sensitivity of its maximum average refractive index is as high as SRI=4757.6nm/US RI, and the corresponding maximum local refractive index sensitivity reaches 6000/SRI n S m RIU (1.33 < < < < < <). A highly sensitive birefringence sensing scheme for C-LPFG (CC-LPFG) with a non-metallic film is presented. After the mode transformation of the non metallic film C-LPFG, the distribution of the mode field is transferred to the film layer, thus increasing the interaction between the optical fiber mode and the external environment. The study shows that the maximum average refractive index of the band-pass CC-LPFG (17.56cl r= mu m) is the maximum index of refraction. The sensitivity and maximum local sensitivity are as high as 4S SRI2.12 x =10 nm/RIU and 3.5 104/SRI= * nm IUS R (1.33 1.34SRI < < n <). It has a very obvious sensing advantage.6. preliminary study on bandpass bandpass filter characteristics, which provides a theoretical basis for the study of subsequent tunable broadband and narrowband bandpass filters.
【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN253

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