一种新型混合双包层光子晶体光纤的色散特性研究

以多极法理论为基础,设计了一种混合双包层结构的光子晶体光纤.通过改变其五层空气孔的四个结构参数（内层空气孔直径、外层空气孔直径、六边形孔间距和八边形孔间距）,理论上实现了色散绝对值在144—20 μm的波段内变化仅为125 ps·km^-1·nm^-1的平坦色散特性.在此情况下对其损耗进行了数值模拟,使所设计的光纤在144—20 μm的宽波段范围内具有小于0005 dB/km的低限制损耗特性.     

3～5μm宽带超低色散平坦硫系光子晶体光纤

利用硫系光子晶体光纤色散可控特性,设计了一种宽带超低色散平坦硫系光子晶体光纤,采用多极法研究了孔间距和占空比等参量对色散曲线的影响.通过优化包层中不同层数空气孔的直径,获得内两层气孔半径为0.7μm,外两层气孔半径为0.8μm和孔间距为5μm的光子晶体光纤结构.模拟结果显示,该光纤在3~5μm波段可实现宽带色散平坦,且色散绝对值低于3.8ps·nm-1·km-1.     

低损耗宽带近零色散高非线性光子晶体光纤设计

提出了一种兼具低损耗、宽带近零色散和高非线性的光子晶体光纤结构,该结构光纤包层空气孔直径从纤芯向外层方向渐进增加;应用多极法,通过改变包层空气孔间距Λ、各层空气孔直径和空气孔层数N_r,对光子晶体光纤色散、损耗和非线性特性进行分析,获得了各特性随包层结构参数变化的规律,并最终设计出最佳结构参数。计算结果表明,该结构光纤存在3个零色散点,在1.25～1.55 μm较宽的波长范围内,色散值波动小于0.27 ps·nm?1·km?1,色散斜率小于0.008 ps·km?1·nm?2,1.55 μm波长处损耗为0.021 dB/km,在常用的飞秒激光泵浦波长0.8,1.06,1.55 μm处非线性系数分别达到78.6,60.4,38.2 W?1·km?1。     

C波段具有平坦近零色散光子晶体光纤的一种改进设计方法

光子晶体光纤的最内层空气孔在拉制过程中容易发生形变,从而严重影响色散. 基于多极法,模拟了当最内层空气孔为不易发生形变的较小值时,第二、三层空气孔对色散的影响,结果表明这种简单的色散控制方法也可以实现零色散点的快速平移,且保持色散平坦. 以此为基础,设计了应用于C波段具有近零平坦色散的光子晶体光纤,色散系数为-0.24-0.33 ps/(km·nm). 模拟表明,从第五层开始增加空气孔的层数对已设计光纤的色散影响很小,可以通过增加空气孔的层数得到理想的限制损耗. 这一方法亦适用于S,L波段具有类似性质PCF的设计. 关键词： 光子晶体光纤 色散系数 多极法 限制损耗     

六角点阵蜂窝状包层光子晶体光纤中的高双折射负色散效应

设计了一种六角点阵蜂窝状包层光子晶体光纤,该光纤中心缺失一根空气柱形成纤芯,包层由椭圆空气孔和小圆空气孔组成.基于全矢量有限元法并结合各向异性完美匹配层边界条件,对其双折射、色散、非线性系数、约束损耗和模场等特性进行了数值模拟;计算了具有相同参数的椭圆状包层光子晶体光纤的双折射、色散及非线性系数.结果发现,若调整光纤结构参数为孔间隔Λ=1.15μm,空气孔椭圆率η=0.5,相对孔间隔比f=0.48,小圆孔直径d₁=0.4μm时,在波长1.55μm处,该光纤的双折射B高达1.02×10^-2,比传统光纤高约两个数量级,同时,该光纤在低损耗通信窗口C波段呈现负色散和负色散斜率,其色散斜率在整个C波段附近在-0.132—-0.121ps·km^-1·nm^-2范围内波动,非线性系数为45.7 km^-1·W^-1,约束损耗接近10² dB·km^-1.蜂窝状包层比椭圆状包层光子晶体光纤的双折射及大负色散特性明显提高,非线性系数低,更有利于进行色散补偿.     

新型THz波超平坦色散光子晶体光纤

设计出一种新型的渐变空气孔径THz波超平坦色散光子晶体光纤.应用时域有限差分方法(finite-difference time-domain,FDTD)计算光纤色散,所得结果表明渐变空气孔径光子晶体光纤比孔直径不变光子晶体光纤控制色散的能力更强;且当第三层与第四层空气孔直径相同时,孔直径渐变的光子晶体光纤的色散更趋于平坦,而当空气孔直径取d₁=0.85d₄, d₂=0.95d₄,d₃=d₄(d₁,d₂,d₃,d₄分别为包层从内到外空气孔的直径)时,此种光子晶体光纤可以在波长60—65 μm(4.61—5 THz)范围内将波导色散值控制在-0.1±0.3 ps/(km·nm)范围内,得到趋于超平坦色散的、具有很好的束缚THz波的能力和良好的损耗特性的新型THz波光子晶体光纤. 关键词： THz波光子晶体光纤 时域有限差分方法 超平坦色散     

色散补偿光子晶体光纤结构参数对其色散的影响

光子晶体光纤由于其灵活可调的色散特性用作色散补偿具有极大的应用潜力. 设计了一种色散补偿光子晶体光纤, 并运用频域有限差分法模拟了其色散特性,从理论上分析了其结构参数孔间距Λ和空气占空比d/Λ对该光子晶体光纤的色散系数的影响, 并且实际制备出了3种不同结构参数的光子晶体光纤. 通过对其色散曲线对比分析表明: 当光子晶体光纤孔间距在1 μm附近时, 其色散系数随着孔间距Λ和占空比d/Λ的增大而增加, 但对于孔间距Λ的变化比占空比d/Λ更为敏感, 并且随着孔间距Λ的增加,其对色散系数的影响能力逐渐减小. 设计并制备的光子晶体光纤在1550 nm处的色散系数为-241.5 ps·nm^-1·km^-1, 相对色散斜率为0.0018, 具有较好的色散补偿能力. 关键词： 色散 色散补偿 光子晶体光纤 结构参数     

一种阶梯结构的色散平坦光子晶体光纤的研究

以多极法理论为基础,提出了一种阶梯结构的光子晶体光纤.通过改变其内四层的三个结构参量(内两层孔孔径,外两层孔孔径和孔间距),实现色散绝对值在1.1～1.8μm的波段内变化仅为0.05～2 ps/(km·nm)的平坦甚至超平坦的特性.在此情况下对其有效模场面积进行数值模拟,充分展示了达到色散平坦和超平坦时,相对于传统光子晶体光纤,此种结构的光纤对芯区内光场的局域能力有很大程度的增强,其有效模场面积可仅为传统光子晶体光纤的1/30.最后,经过大量的数值计算和理论分析,归纳出若要此种阶梯结构的光纤在1.1～1.8μm的波段内达到色散平坦甚至超平坦特性的设计依据.     

全固态八边形大模场光子晶体光纤的设计

提出一种新型的全固态八边形大模场低损耗的掺镱石英光子晶体光纤,利用多极法对光纤的结构和特性进行了模拟.这种结构的光子晶体光纤空气孔由掺有少量氧化硼的石英棒代替,简化了制备过程,提高了光纤的热损伤阈值.在波长为1064 μm处,光纤的模场面积可达2000 μm²,还可实现单模传输,而且其弯曲损耗很小,当弯曲半径为5 cm时弯曲损耗小于05 dB/m.这种光纤对光纤激光器和光纤放大器的发展有重要意义. 关键词： 光子晶体光纤 模场面积 弯曲损耗 限制损耗     

空气孔正方形排列的低损耗高双折射光子晶体光纤的数值模拟

提出了一种正方形排列渐增空气孔高双折射光子晶体光纤，并利用多极方法对光纤基模的模场分布、色散、双折射以及损耗特性进行了数值模拟.模拟结果表明利用这种结构可以在包层空气孔层数较少的情况下实现极低的限制损耗，通过调节内层空气孔的分布可以有效地控制光纤的双折射和色散特性.本结果对高双折射光子晶体光纤的制备具有一定的指导意义. 关键词： 光子晶体光纤 双折射 限制损耗 多极方法     

双芯复合格点光子晶体光纤的负色散特性

介绍了一种双芯复合格点负色散光子晶体光纤,其包层是由连续电介质纯硅背景上挖出的两种大小不同的空气孔构成,芯区是由掺锗的高折射率的材料构成。为了实现负色散,还移去了包层中的一圈空气孔。采用频域有限差分法对其负色散特性进行分析表明,通过调整空气孔间距和两种空气孔的尺寸,可以得到不同程度的宽带负色散。当内芯半径取0.95μm,孔间距取2.15μm,大空气孔直径取1.9μm,小空气孔直径取1.1μm时,可在1.55μm处实现宽带负色散,其半峰全宽超过了200 nm。这种光纤的包层中空气孔呈六边形分布,空气孔的尺寸均大于1μm,降低了制作的难度。这种光纤可以用于波分复用光纤通信系统中的宽带色散补偿。     

八边形高双折射双零色散点光子晶体光纤特性分析

针对光纤通信和传感系统中高双折射、多零色散点的应用需求, 设计了一种新型结构的光子晶体光纤.该结构包层为圆形空气孔按照八边形形状排列而成, 并在内包层对称位置中加入两个椭圆空气孔以获得高双折射特性. 通过有限元数值分析方法对光纤特性进行分析,仿真结果表明,该结构光子晶体光纤在波长0.8—2 μm 范围内双折射可达10^-3量级,满足高双折射的应用需求,并且满足两个零色散点的应用需求. 同时光纤的非线性系数达10^-2·m^-1·W^-1量级,可应用于对非线性要求较高的场合.     

Dispersion flattened photonic crystal fiber with high nonlinearity for supercontinuum generation at 1.55 μm

A robust design for a photonic crystal fiber (PCF) based on pure silica with small normal dispersion and high nonlinear coefficient for its dual concentric core structure is presented.This design is suitable for flat broadband supercontinuum (SC) generation in the 1.55-μm region.The numerical results show that the nonlinear coefficient of the proposed eight-ring PCF is 33.8 W -1 ·km -1 at 1550 nm.Ultraflat dispersion with a value between -1.65 and -0.335 ps/(nm·km) is obtained ranging from 1375 to 1625 nm.The 3-dB bandwidth of the SC is 125 nm (1496–1621 nm),with a fiber length of 80 m and a corresponding input peak power of 43.8 W.The amplitude noise is considered to be related to SC generation.For practical fabrication,the influence of the random imperfections of airhole diameters on dispersion and nonlinearity is discussed to verify the robustness of our design.     

Large negative dispersion in dual-concentric-core photonic crystal fiber with hybrid cladding structure based on complete leaky mode coupling

Considering the optical stability of solution, the sugar-solution is infused into the outer core ring of dual-concentric-core photonic crystal fiber (DCCPCF). The influences of structure parameters and solution concentration on the phase and loss matching are comprehensively analyzed. By choosing the appropriate outer core mode to completely couple with the inner core fundamental mode, the large negative dispersion PCF around 1.55 μm is designed, which has the dispersion value of − 39,500 ps/km/nm as well as bandwidth of 7.4 nm and effective mode area of 28.3 μm². The designed PCF with hybrid cladding structure can effectively compensate the positive dispersion of conventional single mode fiber, and suppress the system perturbation caused by a series of nonlinear effects. Considering the mode field mismatching between the DCCPCF and the tapered fiber, the calculated connection loss around 1.55 μm is below 3 dB. In addition, the equivalent propagation constants of two leaky modes are deduced from the coupled-mode theory, and the complete mode coupling case can be well predicted by comparing the real and imaginary parts of propagation constants.     

New nonlinear and dispersion flattened photonic crystal fiber with low confinement loss

A new nonlinear dispersion flattened photonic crystal fiber with low confinement loss is proposed. This fiber has threefold symmetry core. The doped region in the core and the big air-holes in the 1st ring can make high nonlinearity in the PCF. And the small air-holes in the 1st ring and the radial increasing diameters air-holes rings in cladding can be used to achieve the dispersion properties of the PCF. We can achieve the optimized optical properties by carefully selecting the PCFs structure parameters. A PCF with flattened dispersion is obtained. The dispersion is less than 0.8 ps/(nm km) and is larger than −0.7 ps/(nm km) from 1.515 μm to 1.622 μm. The nonlinear coefficient is about 12.6456 W⁻¹ km⁻¹, the fundamental mode area is about 10.2579 μm². The confinement loss is 0.30641 dB/km. This work may be useful for effective design and fabrication of dispersion flattened photonic crystal fibers with high nonlinearities.     

New high negative dispersion photonic crystal fiber

A new high negative dispersion photonic crystal fiber is proposed. It has double-core structure. The inner core has a circle germanium-doped region. The outer core is formed by removing the 3rd ring air-holes around the core. There are two ring air-holes between the two cores, Diameter of the 1st ring air holes is bigger than that of the 2nd ring air-holes, this can make mode coupling between inner mode and outer mode and showed that the high negative PCF is the result of this structure characteristics. There are honeycomb photonic lattice in the PCF's cladding. The influence of the structure parameters deviated from the design those on the chromatic dispersion are evaluated. When the structure parameters Λ=1.50 μm, d_core=2.10 μm, d₁=0.90 μm, d₂=0.44 μm and d₃=1.04 μm, the dispersion coefficient D is −1320 ps/(nm·km) at 1550 nm. This is a new kind of chromatic dispersion compensation PCF.     

类矩形芯光子晶体光纤的色散与偏振特性

应用全矢量模型分析类矩形芯光子晶体光纤的色散和偏振特性，讨论了光纤结构参数对光纤特性的影响.研究表明：类矩形芯光子晶体光纤的模式双折射比普通椭圆保偏光纤至少高一个数量级.增大光纤的相对孔径，可获得更高的双折射.零走离点对应的波长也比普通椭圆保偏光纤长，随着孔距的增大，走离曲线将向长波长方向产生移位，零走离点发生红移，零走离点所对应的波长与孔距成正比.零走离点的出现，将有效地抑制一阶偏振模色散.通过调整光纤的结构参数，可以获得灵活的色散特性，在孔距Λ=2μm, 相对孔径d/Λ=03时，在波长155μm附近，获得近400nm的超平坦色散区.该光纤在偏振控制、色散控制和管理方面具有广泛的应用前景. 关键词： 导波光学 光子晶体光纤 类矩形芯 全矢量     

Design procedure for photonic crystal fibers with ultra-flattened chromatic dispersion

A simple design procedure is used to generate photonic crystal fibers (PCFs) with ultra-flattened chromatic dispersion. Only four parameters are required, which not only considerably saves the computing time, but also distinctly reduces the air-hole quantity. The influence of the air-hole diameters of each ring of hexagonal PCFs (H-PCF, including 1-hole-missing and 7-hole-missing H-PCFs), circular PCFs (C-PCF), square PCFs (S-PCF), and octagonal PCFs (O-PCF) is investigated through simulations. Results show that regardless of the cross section structures of the PCFs, the 1st ring air-hole diameter has the greatest influence on the dispersion curve followed by that of the 2nd ring. The 3rd ring diameter only affects the dispersion curve within longer wavelengths, whereas the 4th and 5th rings have almost no influence on the dispersion curve. The hole-to-hole pitch between rings changes the dispersion curve as a whole. Based on the simulation results, a procedure is proposed to design PCFs with ultra-flattened dispersion. Through the adjustment of air-hole diameters of the inner three rings and hole-to-hole pitch, a flattened dispersion of 0±0.5 ps/(nm·km) within a wavelength range of 1.239 – 2.083 μm for 5-ring 1-hole-missing H-PCF, 1.248 – 1.992 μm for 5-ring C-PCF, 1.237 – 2.21 μm for 5-ring S-PCF, 1.149 – 1.926 μm for 5-ring O-PCF, and 1.294 – 1.663 μm for 7-hole-missing H-PCF is achieved.