【作者】 卫延；

【导师】 简水生；

【作者基本信息】 北京交通大学 ， 通信与信息系统， 2008， 博士

【摘要】 特种光纤已广泛应用于光纤通信、光纤传感、医学、材料加工和军事科技等领域。本论文结合国家高技术研究发展计划（863）项目“通信用特种光纤—稀土掺杂光纤（2001AA312230）”和“光纤制造新技术及新型光纤—新型特种光纤（2002AA312190）”的实施，对掺铒保偏光纤、边孔光纤、孔辅助导光光纤和保偏光子晶体光纤等进行了深入研究，获得以下创新性成果：1．首次将二阶透明边界条件（2nd TBC）应用于光纤模式分析的伽辽金平面有限元模型，可用于分析任意非均匀和各向异性折射率分布的光纤的传输模特性。与一阶透明边界条件（1st TBC）相比，二阶透明边界条件提高了求解光纤模式限制损耗的精度，与多极法（MM）计算结果的相对误差在10％以内。2．采用基于2nd TBC的伽辽金平面有限元模型对单模光子晶体光纤（PCF）的温度特性进行了数值模拟，得出PCF有效折射率n_eff、模式场有效半径R_eff及限制损耗CL随温度变化的近似解析式。研究表明当折射率温度系数ζ在所研究的温度范围内变化缓慢时，随着温度的增加，n_ef线性增加，R_eff和CL线性减小，色散大小不受温度变化影响，n_eff，R（eff）和CL在数值上改变很小，表明PCF具有较好的温度稳定性。3．采用基于2nd TBC的伽辽金平面有限元模型结合有限元平面应变模型研究了圆芯边孔光纤和K型椭圆芯边孔光纤的应力区和固有双折射。分析了两种边孔光纤横截面上应力分量σ_x、σ_y的拉、压应力区以及应力双折射B_s的分布形态并给出了清晰的物理解释，指出了几何双折射、应力双折射与模式双折射之间的关系，并给出了它们随波长和光纤结构参数的变化特点。4．扩展了现有光纤应力分析的有限元平面应变模型，可用来计算任意横向外力作用下光纤截面各点的应力状态。分析了含孔光纤（包括边孔光纤、光子晶体光纤、保偏光子晶体光纤和孔辅助导光光纤）的压力感应双折射分布形态，给出了压力感应双折射灵敏度随光纤结构参数的变化关系。研究表明含孔光纤横截面上各空气孔应力集中的扩散和相互干涉造成了光纤中心区域压力感应双折射复杂的分布形态，压力感应双折射与横向压力大小成线性关系，对压力作用方向敏感。根据独立空气孔应力集中的线性叠加定性解释了各种含孔光纤压力感应双折射的横截面分布形态。5．提出了一种制作保偏光纤的新方法—光纤预制棒侧向开槽法，并建成了一套完善的制作工艺。相比于护套打孔法，开槽法可制作更长的保偏光纤预制棒，更易保证两应力施加区中心和纤芯中心三心共线，凹槽的对称性、直线度、内表面粗糙度要求更易实现。开槽法简化了保偏光纤预制棒制作工艺，降低了制作成本。另外开槽法还可用于制作边孔光纤、双芯光纤以及孔辅助导光光纤，丰富了特种光纤制作方法。6．采用基于2nd TBC的伽辽金平面有限元模型和有限元平面应变模型，根据模场直径、截止波长、双折射等性能指标对熊猫型掺铒保偏光纤进行了结构优化，给出了双折射达到3×10^-4时结构参量的取值范围。改进了MCVD法溶液掺杂技术的部分工艺和设备，在石墨电炉高温区下游安装气体冷却装置来提高沉积效率和纤芯疏松层的均匀性，设计了在MCVD车床上实现在线掺杂装置以保证溶液掺杂过程的洁净度。改进了特种光纤拉丝塔牵引系统，开发了六轮拉丝辅助牵引设备限制拉丝过程中光纤的扭转。在上述工艺改进的基础上，用开槽法结合MCVD法溶液在线掺杂工艺，试制出了高性能低成本的掺铒保偏光纤。所研制的掺Al³⁺、Er³⁺的保偏光纤在1530nm处的吸收系数为9.5dB／m，平均模式双折射和群双折射都为4.76×10^-4，1550nm处拍长为3.26mm；共掺Bi³⁺、Ga³⁺和Al³⁺的掺铒保偏光纤在1530nm处的吸收系数为19.5dB／m，1530-1560nm范围内模式双折射和群双折射平均值都为1.93×10^-4，1550nm处的拍长为8.05mm，且数值波动很小；两种光纤在波长1200nm附近的背景损耗都在30dB／km左右。更多还原

【Abstract】 Special Optical Fibers are widely used in such fields as optical fiber communications, sensing, physic, material process and military technoloty. Research on erbium-doped polarization-maintaining fibers, side-hole fibers, hole-assisted lightguide fiber and polarization-maintaining photonic crystal fibers are deeply discussed in this dissertation. The work is supported by the National High Technology Research and Development Programs of China, "Rare-earth doped fibers" and "Novel special fibers".The main achievements of the dissertation are listed as follows:1) The 2nd transparent boundary conditions （2nd TBC） are first used in 2D Galerkin vectorial finite-element method （FEM）, by which the modes of fibers with arbitrary nonhomogeneous and anisotropic refractive indices distribution can be analyzed. Compared to 1st TBC, the confinement loss （CL） of modes of fibers can be solved more accurately using 2nd TBC. The relative error between results of FEM with 2nd TBC and multipode method （MM） is no more than 10%.2) On the basis of FEM with 2nd TBC, the temperature properties of a single mode PCF are numerically simulated. Then the approximate formulas for the change of effective refractive index n_eff, effective radius R_eff and CL of the PCF with temperature are constructed. The results show when the temperature coefficient of refactive indexξvaries slowly within the concerned temperature range, with the increasing of the temperature, n_eff increases linearly, R_eff and CL decrease linearly. But n_eff, R_eff, and CL change little as temperature increases. The dispersive properties of PCF are not affected by the change of temperature. That means the PCF shows good temperature stability.3) By FEM with 2nd TBC, together with FEM for plane strain model, the stress zones and inherent birefringence of circular-core side-hole fibers （CSHF） and K-type elliptical-core side-hole fibers （KESHF） are analyzed. The distributions ofσ_x,σ_y and Bs in the cross-sections are calculated and explained clearly. The relations among geometric birefringence B_g, stress-induced birefringence B_s and mode birefringence B_m is discussed, and the change of B_g, B_s and B_m change with wavelength and fiber structure parameters is illustrated.4) The current method based on FEM of the plane strain model is improved to calculate the stress at any point in the cross-section of the fiber when arbitrary transverse force is applied. By the improved FEM for plan strain model, the cross-section distribution of pressure-induced birefringence B_of in hole-contain fibers （HCF）, including SHF, PCF, PM-PCF and HALF, are calculated. The relationship between sensitivity of B_of and fiber structure parameters are discussed. It is shown that because of diffusion and interference of concentration stress near the boundary of holes in cross-section, the distributions of B_of near the center of HCF are extremely complex. These complex distributions of B_of can be qualitatively explained by the linearly superposed field of concentration stress of separated holes. It’s also shown that B_of is proportion to the pressure on fiber boundary and is sensitive to the pressure direction.5) A novel method, the fiber preform goniometric-groove method is first reported, and a set of perfect fabrication technics are developed. By goniometric-groove method, longer PMF perform can be fabricated and more easily the collineation of the centers of two stress-applied parts and the fiber core can be realized than by Pit-in-jacket method. The expected specification for symmetrical characteristic, linearity and surface roughness of the groove are easy to meet. Besides, SHF, twin-core fiber and HALF are fabricated by goniometric-groove method.6) By FEM with 2nd TBC and FEM for plain strain model, according to the property requirements for mode field diameter, cut-off wavelength and mode birefringence, the structure parameters of Panda type Erbium-doped polarization-maintaining fiber （EDPMF） are optimized and the value range of structure parameters for a birefringence no less than 3×10^-4 is given. Partial technology and related equipments of modified chemical vapor deposition （MCVD） and the solution-doped technique are improved. A gas-cooling attachment is installed at the down stream in the high-temperature region of the graphite oven to increase the deposition efficiency and soot layer uniformity in fiber core. The equipment for on-line doping is installed on the MCVD lathe to guarantee the purity in solution-doped process. A six-wheel fiber drawing equipment is developed to restrain twist rotation of the fiber in fiber drawing process. Under the improvement in technics mentioned above, by goniometric-groove method, MCVD and solution-doped technique, two PMEDFs with high quality and low cost are fabricated. The absorption coefficient of Al³⁺-codoped PMEDF at 1530 nm is 9.5 dB/m, both average mode birefringence and group birefringence are 4.76×10^-4, the bit-length at 1550 nm is 3.26 mm. The absorption coefficient of Bi³⁺-Ga³⁺-Al³⁺ codoped PMEDF at 1530 nm is 19.5 dB/m, in the range from 1530 nm to 1560 nm both average mode birefringence and average group birefringence are 1.93×10^-4, the bit-length at 1550 nm is 8.05 mm. The background loss of two PMEDFs at 1200nm is near 30 dB/km.更多还原