高对称性模场分布的高双折射光子晶体光纤

设计了一种具有高对称性模场分布的高双折射光子晶体光纤(PCF)结构,由尺寸相同的椭圆空气孔菱形排列组成。利用全矢量有限元法对该种结构光子晶体光纤的基模场分布、有效模场面积、双折射和色散进行数值分析,所得结果与相同结构参数的圆形空气孔光子晶体光纤进行比较。这两种光纤的模场均具有高对称性,近似圆形,并且易于与光器件中其他光纤耦合。椭圆空气孔光子晶体光纤的双折射可达10-3。     

空气孔正方形排列光子晶体光纤的有限元分析

采用全矢量有限元法结合完美匹配层吸收边界条件对渐增型空气孔正方形排列的高双折射光子晶体光纤的模场分布、限制损耗及双折射特性进行了数值模拟。仿真结果显示：该种结构的光子晶体光纤可以在包层空气孔层数仅为四层的情况下即可将限制损耗控制在1.31×10E-6 dB/m附近;同时横排内层空气孔的直径的变化可以有效地改变光纤的模式双折射曲线的走向,在长波长区间这种影响更为明显。     

矩形晶格结构双芯光子晶体光纤偏振分束器的研究

椭圆形空气孔光子晶体光纤可以产生较高的双折射,使得不同偏振方向的光有不同的耦合长度.将光纤的双折射现象应用于双芯光纤中,可以实现偏振状态的分离.应用平面波扩展法分析了椭圆形空气孔、矩形晶格结构的双芯光子晶体光纤中结构参量对光束不同偏振方向的耦合长度的影响,设计了一种基于椭圆形空气孔、矩形晶格结构的双芯光子晶体光纤偏振分束器.应用全矢量光束传播法分析了这种光纤偏振分束器的性能.结果表明,在1.55 μm工作波长上,长度为1.055 mm的光纤即能实现偏振状态的隔离,隔离度达到-16.9 dB,隔离度＜-16 dB的带宽可达到270 nm.     

高双折射光子晶体光纤特性分析

建立了基于透明边界条件(TBC)的全矢量迦辽金有限元法(FEM)分析二维光子晶体光纤(PCF)的模型,并对椭圆芯等5种高双折射光子晶体光纤基模的模式双折射、限制损耗及色散特性进行了数值分析和比较.通过减小内包层中沿x方向的空气孔,增大沿y方向的空气孔构成的一种光子晶体光纤的模式双折射在波长1550 nm处高达5.96×10-3,而椭圆芯光子晶体光纤为1.52×10-3.研究表明,可通过增加内包层中两个正交方向上空气孔的尺寸差来获得高双折射;同时还得出内包层中放大的空气孔减小限制损耗,增加色散,而减小空气孔尺寸带来的影响则刚好相反;内包层上空气孔数量越少,色散越平坦.     

一种新型混合包层结构高双折射光子晶体光纤

针对光子晶体光纤中高双折射的应用需求,提出了一种基于全内反射导光机制的新型混合包层结构光子晶体光纤,采用全矢量有限元法分析了结构参数对该光纤双折射的影响,以及采用全矢量有限元软件对该光纤结构进行了仿真。仿真结果表明,通过调整包层椭圆孔的椭圆率和孔间距等参数,该结构的光子晶体光纤在1.55 μm波长处可实现10-2量级的高双折射。     

高双折射高非线性低损耗八边形光子晶体光纤特性

为了同时实现高双折射高非线性并得到低损耗,设计一种在光纤纤芯附近引入椭圆形空气孔和圆形空气孔组成的新型优化的八边形光子晶体光纤。采用全矢量有限元法结合各向异性完美匹配层,对该光纤的有效面积、非线性、双折射和损耗特性进行了模拟分析。数值模拟结果表明,通过选择适当的结构参数,在波长1.55 m处,该光纤具有高双折射高达B=1.6810-2,比普通光纤高两个数量级,高非线性系数为=60 W-1km-1和低损为0.6 dB/km。这种具有高双折射高非线性系数的光纤可用于光通信、偏振敏感的各种设备和产生超连续普等领域。     

高双折射全内反射光子晶体光纤的特性研究

文章应用全矢量有效折射率方法(FVEIM)对芯区具有两个椭圆小空气孔的全内反射光子晶体光纤(TIR-PCF)进行了研究.结果表明,光子晶体光纤(PCF)的芯区折射率与包层区等效折射率的差随波长的增大而增大;固定包层空气孔的相对孔径,PCF基模的两个正交偏振态简并被打破,呈现出模式高双折射;随着芯区小空气孔椭圆率变大,模式双折射增大,PCF的总色散曲线变平坦.     

有中心缺陷孔的矩形点阵PCF双折射特性研究

采用全矢量有限元法研究了具有中心椭圆缺陷孔的矩形点阵PCF(光子晶体光纤)的双折射特性。结果发现,该新型PCF的双折射特性对波长和光纤的结构参数具有较强的依赖关系,与无中心椭圆缺陷孔的矩形点阵PCF相比,在中心缺陷孔参数bc/Λ=0.075、中心空气孔椭圆率η=2.2、包层结构参数Λ=2.0μm和d/Λ=0.48时,该新型PCF具有更高的双折射。     

高非线性高双折射光子晶体光纤特性的理论研究

基于全矢量有限元法,设计了一种新型零色散波长为1550 nm的高非线性双折射光子晶体光纤(PCF),并分析了PCF的有效折射率、有效模面积、双折射、非线性系数以及色散特性。数值结果表明,当光纤包层孔间距Λ为1.6 μm,大空气孔直径d1为1.4 μm,小空气孔直径d2为0.74 μm和0.76 μm时,光纤的零色散波长都在1550 nm处,该PCF的双折射为4.049×10-3,非线性系数可达28.4 km-1·W-1。这种高非线性高双折射PCF,在1550 nm通信波段具有非常广泛的应用前景。     

椭圆芯扁六角聚合物光子晶体光纤的偏振特性

采用全矢量定域基函数模型,以聚合物PMMA为基材,研究了椭圆芯三角点阵扁六角结构光子晶体光纤(Photonic crystal fibers,PCFs)的偏振特性,分析了其相位模双折射和群模双折射与相对孔间隔比的依赖关系,并与椭圆芯三角点阵正六角结构PCFs的研究结论进行比较;研究发现,椭圆芯扁六角结构PCF的偏振特性强烈的依赖于光纤的结构参数,由于色度色散的存在,在短波长段,群双折射远远高于相位模双折射,通过适当调节光纤的相对孔径和相对孔间隔比,有望在给定波长实现高双折射和零偏振模色散单模运行.该研究为高双折射聚合物光子晶体保偏光纤的制备提供了理论依据.     

一种新结构光子晶体光纤的双折射特性研究

在普通正六边形光子晶体光纤的基础上,通过改变x轴方向空气孔的大小及分布构造了一种新结构的光子晶体光纤。利用多极法对该光子晶体基模的模场分布及双折射进行了数值计算,分析了光波长与结构参数对双折射的影响,同时对光子晶体光纤的色散特性进行了研究。结果表明,通过改变x轴方向空气孔的大小以及分布结构使光子晶体光纤比普通六边形结构光子晶体光纤的双折射率明显提高,并且具有较低的宽带反常色散,在光纤双折射效应的应用和光学器件的研制等方面具有独特的优势。     

Design of low-confinement-loss and highly birefringent index-guiding photonic crystal fibers

We present a systematic scheme to achieve both high birefringence and low confinement loss in index-guiding photonic crystal fibers （PCFs）, using a structurally-simple PCF with finite number of air holes in the cladding region. By increasing the size of the outermost-ring air holes in the cladding region, highly birefringent PCFs with low confinement loss can be successfully achieved. The design strategy is based on the fact that the modal birefringence of PCFs is dominated by the inner-ring air holes in PCF, which is verified by a full-vector finite element method with anisotropic perfectly matched layers. Numerical results show that modal birefringence in the order of 10-3 and confinement loss less than 0.1 dB/km can be easily realized in the proposed PCF with only four rings of air holes in the cladding region. We expect that such fibers will be much easier to be fabvicated than those with more air holes in the cladding region.     

Highly Birefringent Photonic Crystal Fibers With Ultralow Chromatic Dispersion and Low Confinement Losses

Highly birefringent photonic crystal fibers (PCFs) with low confinement loss with ultralow and ultraflattened chromatic dispersions at wide wavelength band are presented. The transverse electric field vector distributions of two linearly polarized fundamental modes, their effective indices, modal birefringence, confinement losses and chromatic dispersion of the proposed PCFs are reported by using full-vector finite-element method (FEM). Significant improvements of PCFs in terms of the birefringence, chromatic dispersion and confinement losses are demonstrated by careful investigation of all air holes in each ring, air holes diameters and hole-to-hole spacing. In addition to this, the polarization beat length results of the proposed PCFs are also reported and discussed thoroughly.     

Analysis on photonic crystal fibers with circular air holes in elliptical configuration

In this paper, two novel structures of photonic crystal fibers (PCFs) containing elliptical rings of circular air holes are presented. The circular air holes in both structures are arranged in seven elliptical rings, but the number of holes in each ring is different for these structures. Moreover, air hole diameter and hole-to-hole pitch are altered along the distance from the center of the fiber’s cross section. Properties, such as birefringence and confinement loss, of these structures with different numbers of air hole rings are numerically analyzed by using the multipole method. Numerical results show that a high birefringence of 1.626 × 10⁻³ can be reached at the wavelength of 1.55 μm, and a low confinement loss on the order of 10⁻⁸ dB/m can be achieved at the same wavelength. Furthermore, it is also found that elliptic ratio obviously affects birefringence and confinement loss, but the number of air hole rings has little impact on birefringence.     

Birefringence Characteristics of Squeezed Lattice Photonic Crystal Fibers

By using the supercell lattice method, we investigate the influence of the squeezing lattice on the birefringence characteristics of photonic crystal fibers (PCFs). We first define the concept of squeezing ratio and then present a model, with which several types of PCFs are simulated. Simulation results show that the squeezing of PCFs' lattice with the uniform air holes in the cladding can break the multifold symmetry of PCFs and make PCFs highly birefringent. Furthermore, it is reported for the first time to our knowledge that the polarity of PCFs' birefringence can change several times as the air-hole diameter changes.     

Dependence of birefringence on elliptical-hole orientation in photonic crystal fibers

In this paper, the dependence of birefringence on the orientation of elliptical holes in triangular-lattice elliptical-hole photonic crystal fibers (PCFs) is investigated numerically. A resonant enhancement of birefringence between the anisotropic lattice arrangement and oriented elliptical holes is observed, and the birefringence varies periodically with the elliptical-hole orientation. When the major axes of adjacent elliptical holes are parallel, the birefringence approaches the maximum. Based on the numeric analysis, a novel highly birefringent PCF is proposed, and the maximum modal birefringence of 0.086 is achieved.     

Polarization-dependent coupling in twin-core photonic crystal fibers

The polarization dependence of light coupling in photonic crystal fibers (PCFs) with sixfold symmetric dual cores and highly birefringent dual cores are numerically investigated. The characteristics of PCF-based couplers, such as coupling length, extinction ratio and form birefringence, are examined as functions of the air-hole size and pitch. The silica bridges between air holes take an important role in the energy transfer across the two cores. We believe that the mechanism of light coupling in PCF-based couplers is different from that of conventional waveguide couplers. The polarization dependent coupling can be reduced by adjusting the air holes around the cores of PCFs. On the other hand, the polarization dependent coupling can be enhanced by introducing high birefringence in the two cores.     

Design of a new type high birefringence photonic crystal fiber

A High birefringence microstructure fiber with four big elliptical air holes is investigated by using the finite-difference frequency-domain （FDFD） method. Based on the numerical simulations, the influence of the air-hole size and pitch upon the mode birefringence is analyzed. The work may be helpful for the design and fabrication of high birefringence PCFs.     

Numerical modeling of photonic crystal fibers

Recent progress on numerical modeling methods for photonic crystal fibers (PCFs) such as the effective index approach, basis-function expansion approach, and numerical approach is described. An index-guiding PCF with an array of air holes surrounding the silica core region has special characteristics compared with conventional single-mode fibers (SMFs). Using a full modal vector model, the fundamental characteristics of PCFs such as cutoff wavelength, confinement loss, modal birefringence, and chromatic dispersion are numerically investigated.