【作者】 侯尚林；

【导师】 任晓敏；

【作者基本信息】 北京邮电大学 ， 电磁场与微波技术， 2008， 博士

【摘要】 光学纤维以优良的光传输特性被广泛地应用到通信系统、传感、医疗器械和各种光学器件等众多领域,研究热点逐渐从研究衰减到研究光纤的色散和非线性,并有大量的有源和无源的光器件应运而生。近年来,特殊结构的光纤和光器件由于可以实现一些特殊的传输,满足常规光纤很难满足的要求和更容易的设计,越来越受到人们的关注,尤其在光器件设计上得到了广泛的应用。本论文理论和实验研究了采用新型材料包层结构（即采用单轴晶体材料包层）和基于全内反射微结构的两种新型光纤及光栅。首先提出了单轴各向异性材料为包层、其主轴沿光纤光栅轴线（Z轴）方向的布喇格光纤光栅模型,引入了单轴晶体材料主轴折射率比参数K_cl,从波动方程推出了理想正规模的特征方程,计算了基模HE₁₁模的有效折射率、色散和功率限制因子;应用耦合模理论研究了该类布喇格光纤光栅的反射率、布喇格波长、反射波带宽及色散,理论研究了对该类光纤的电光效应和弹光效应。本部分的研究对基于以单轴晶体材料为包层的光纤和光栅器件的研究提供了理论依据,可以根据这些结论设计新型可调谐滤波器、波长选择器和电压、应力等传感器。应用改进的有效折射率法,分别用标量和矢量计算了微结构光纤（Microstructured Fiber,MF）的传输特性和全内反射微结构光纤Bragg光栅（MFBG）的反射特性和填充比的关系,提出了增大反射率的方法;应用BMP法设计了一种具有三层不同的空气孔直径的宽带色散补偿微结构光纤;设计和加工了长周期光纤光栅压力传感装置,对普通单模光纤进行了压力传感实验,实验表明传感器性能良好,线性度和灵敏度高;在高非线性微结构光纤上用机械压力法写制了一种长周期光纤光栅,测定了透射谱深度和压力大小的关系。本论文主要研究内容和创新点如下:1、单轴晶体包层光纤及光栅（1）提出了单轴各向异性材料为包层、其主轴沿光纤轴（Z轴）方向的光纤模型,矢量分析了特征方程、基模有效折射率和色散。研究表明光纤的色散随波长的增加而由负而正的增大,但零色散波长随K_cl的增加而减小。当K_cl＜1时,零色散波长随K_cl的增大而减小的很剧烈,但当K_cl＞1,零色散波长变化不明显。（2）研究了功率限制因子和包层单轴晶体材料主轴折射率比参数K_cl的关系,模拟了电光效应和弹光效应对此类光纤内光能量分布的影响。结果表明并且外加电场越强,纤芯内的光能量越少,光能量越集中到包层中;施加应变场越强,光能量越集中到纤芯中。（3）模拟计算了包层为单轴晶体材料的布喇格光纤光栅的反射率、Bragg波长、反射波带宽及色散和K_cl的关系,得出了单轴晶体包层光纤Bragg光栅比均匀各向同性包层的Bragg光栅更容易获得高反射率;单轴晶体包层折射率的变化可以使Bragg波长产生移动;包层为各向同性材料的光纤比包层为单轴晶体材料的光纤更容易把光能量集中在纤芯中传输;对光纤Bragg光栅来说,包层中传输的能量更容易耦合到反向导模中。（4）基于上述理论,提出了分别采用铌酸锂（LiNbO₃）和磷酸二氢钾（KDP）两种单轴晶体材料做包层的光电器件的设想,即分别利用铌酸锂的电光效应和磷酸二氢钾弹光效应设计可调谐滤波器、压力和电场（压）传感器方法。2、微结构光纤及光栅（5）应用改进的有效折射率方法（IEIM）分别用标量法和矢量法分析MF的有效折射率和基于全内反射MF的Bragg光栅的反射谱。计算结果表明标量法只适合填充比小于0.45的情况,对于比较大的填充比,要用矢量法来计算;包层中空气比分增大时,基空间填充模的有效折射率变小,Bragg波长移向短波长一边;随着包层中空气比分的增加,可以有效的提高微结构光纤Bragg光栅的反射率。（6）在高非线性微结构光纤上用机械压力法写制了10个周期,周期为1.2mm的长周期光纤光栅,测定了透射谱深度和压力大小的关系,表明长周期光纤光栅的透射谱透射深度随应力增加而单调增加,即能量从纤芯耦合到包层;当应力进一步增大,透射谱深度开始减小,即光开始从包层耦合回纤芯。（7）采用金属凹槽板完成了可调谐普通单模光纤的压力传感实验,结果表明在0-70N的测量范围内,透射峰衰减值随压力变化曲线的线性度达0.9915,灵敏度可达0.2dBm/N。（8）与他人合作,应用BMP法设计了一种1.55um波段宽带色散补偿微结构光纤,该光纤具有三层不同的空气孔直径,调节各结构参量得到最佳色散补偿光纤,在100nm范围内补偿普通单模光纤（G.652）,补偿倍数超过100倍,比目前已报道的都大。更多还原

【Abstract】 Optical fibers have many important applications in communication systems, sensors, medical instrumentation, and various optical components due to its super transmission properties, the hot research topics shifted from the attenuation to dispersion and nonlinearity research, and numerous passive and active optical components were invented. During the past few years, the optical fibers and optical components with special structure attracted much more attentions and were used wildly specially in optical components designing for its unique transmission characteristics and flexible designing that cannot be achieved from conventional fibers.In this dissertation, theoretical and experimental research on fibers and fiber gratings with a novel matieraial such as uniaxial crystal material and the Total Internal Reflection microstructured cladding.The model of fiber and fiber Bragg grating with cladding made of uniaxial crystal material whose optical axis is parallel to the axis （z-axis） of fiber was proposed, the parameter K_cl, i.e., the ratio of the extraordinary to the ordinary ray refractive index, were introduced, the characteristic equation of the ideal normal mode were derived from the wave equation, the effective index, dispersion and power confinement factor of the HE₁₁ mode of the fiber were simulated, the reflectivity, Bragg wavelength, bandwidth and dispersion of this kind fiber Bragg gratings were examined using coupled-mode theory and numeric solution and Electro-optic Effect and Elasto-Optic Effect of the fiber were theoretically investigated. These research results provide a theoretic basis for designing optical components based on fiber and fiber Bragg grating with cladding made of uniaxial crystal material, and a novel tunable filter, wavelength selector, voltage and strain sensors and etc can been designed according to the conclusions.The transmission properties of Microstractured fiber （MF）, the relationship between the filling factor and the reflectivity of fiber Bragg grating formed in the Total Internal Reflection microstructured fiber were investigated by the scalar and fully vectorial improved effective index method （FVIEIM）, and the ways to increase the reflectivity were concluded. The BeamPROP （BMP） method is used to design a broadband dispersion compensation MF whose structure is three-tier air hole with different diameters. A pressure sensor based on long-period fiber grating （LPG） were designed and fabricated, a pressure sensing experiment was conducted, and the results show that the LPG pressure sensor has great performance such as excellent linearity degree and high sensitivity. A kind of long-peroid fiber grating was inscribed in the high nonlinear microstructured fiber by mechanical pressure and the relationship between the depth of the transmission spectrum and the pressure was mensurated.The main contents and achievements are as follows.1, Fibers and fiber gratings with uniaxial crystal material cladding（1） The model of fiber with cladding made of uniaxial crystal material whose optical axis is parallel to the axis （z-axis） of fiber was proposed, the characteristic equation of the ideal normal mode were derived from the wave equation, the effective index, dispersion of the HE₁₁ mode of the fiber were simulated. The research results indicate that the dispersion increases from negative to positive with the wavelength increasing, the larger K_cl is, the less the zero dispersion wavelength changes. When K_cl <1, the zero dispersion wavelength decreases rapidly, but when K_cl >1, it decreases slowly.（2） The impact of K_cl on the power confinement factor of the HE₁₁mode of the fiber and the influence of Electro-optic Effect and Elasto-Optic Effect on the power distribution of this kind of the fiber was inverstigated. The calculated results indicate that the stronger the electri field is, the less optical power transmitted in the core, and more power was concentrated in the cladding. The stronger the strain is, the more energy is transmitted in the core.（3） The influence of K_cl on the reflectivity, Bragg wavelength, bandwidth and dispersion of fiber Bragg gratings with uniaxial crystal material cladding were demonstrated, the calculated results indicate that the reflectivity of the fiber Bragg grating with cladding made of uniaxial crystal material is much higher than that with cladding made of isotropy material, the Bragg wavelength could be shifted due to different index contribution of the uniaxial crystal material cladding. More power is confined in the core of the fiber with cladding made of isotropic materials than that with cladding made of isotropic material while keeping the other parameters of the fiber as constant. For fiber Bragg grating, the power transmitted by the cladding is more easily coupled into the backward-propagating guided fundamental mode.（4） The design of Optoelectronic devices with LiNbO₃ and KDP cladding, respectively, were predicted based on the above theory, i.e., a novel tunable filter, electric field （or voltage） and strain sensors and etc were proposed due to Electro-optic Effect of LiNbO₃ and Elasto-optic Effect of KDP crystal materials.2, Total Internal Reflection Microstructured fibers and gratings（5） The effective index of MF and the reflectivity of fiber Bragg grating formed in the Total Internal Reflection microstructured fiber were investigated by the scalar and fully vectorial improved effective index method （FVIEIM）, the calculated results indicate that the scalar approximation condition will not be satisfied and full vector should be used when the filling factor is more than 0.45, the effective index of the fundamental space filling mode （FSFM） decreases, the reflectivity increases and the Bragg wavelength shifts to shorter wavelength with the filling factor increasing. （6） A 10-peroids and 1.2mm-long-peroid fiber grating was inscribed in the high nonlinear microstructured fiber by mechanical pressure and the relationship between the depth of the transmission spectrum and the pressure was mensurated. The result indicates that the depth of the transmission spectrum increases with the pressure increasing, i.e., the optical energy transmitted in the core is coupled to the cladding, but when the pressure become larger, the depth of the transmission spectrum decreseas, i.e., the optical energy is coupled back to the core.（7） A pressure sensing experiment was conducted using a metal groove plate whose period can be tunable, the results show that when the pressure varies between 0 and 70N, the linearity degree of the pressure-transmission peak attenuation curve is as much as 0.9915 and the sensitivity is 0.2dBm/N.（8） The BeamPROP （BMP） method is used to design a broadband dispersion compensation MF in 1550nm wavelength range. The MSF structure is three-tier air hole with different diameters, the best structure with 100 nm bandwidth is found to compensate ordinary single-mode fiber （G.652） more than 100 times which is the largest, to our knowledge.更多还原