Bending Effects on Highly Birefringent Photonic Crystal Fibers With Low Chromatic Dispersion and Low Confinement Losses

Photonic crystal fibers (PCFs) with elliptical air-holes located in the core area that exhibit high birefringence, low losses, enhanced effective mode area, and low chromatic dispersion across a wide wavelength range have been presented. The effects of bending on birefringence, confinement losses and chromatic dispersion of the fundamental mode of the proposed PCFs have been thoroughly investigated by employing the full vectorial finite element method (FEM). Additionally, localization of higher order modes is presented. Also, effects of angular orientation on bending loss have been reported. Significant improvement on key propagation characteristics of the proposed PCFs are demonstrated by carefully altering the desired air hole diameters and their geometries and the hole-to-hole spacing.     

A kind of photonic crystal fiber with high birefringence and low cofinement loss

The triangular-lattice highly birefringent photonic crystal fibers（PCFs） with gradually increasing diameter of the air holes along radial axis are put forward. The modal birefringence, dispersion and confinement loss of the fundamental mode are simulated by full vector Galerkin finite element method（FEM） with a perfectly matched layer（PML）. The results show that this PCF can keep low confinement loss when the rings of air holes are few. When the wavelength is 1.55 μm, the birefringence, the confinement loss of quick-axis and slow-axis are 1.365×10^-3, 0.017 dB/m and 0.051 dB/m, respectively. A new way is proposed to fabricate polarization-mainting fibers with high performance.     

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.     

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.     

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.     

Highly birefringent photonic crystal fibers with flattened dispersion and low confinement loss

A highly birefringent index-guiding photonic crystal fiber (PCF) with flattened dispersion and low confinement loss is proposed by introducing two small air holes with the same diameter in the core area. The fundamental mode field, birefringence, confinement loss, effective mode area and dispersion characteristic of the fibers are studied by the full-vector finite element method (FEM). Simulation results show that a high birefringence with the order of 10 -3 and a low confinement loss of 0.001 dB/km are obtained at 1550 nm. Furthermore, flattened chromatic dispersion from 1450 nm to 1590 nm is obtained.     

混合双包层高双折射光子晶体光纤的特性

提出了一种新型的混合双包层结构的光子晶体光纤。利用多极法对光纤基模的模场分布、双折射、限制损耗及色散特性等进行了数值模拟,通过调节包层空气孔的孔径大小可以有效地控制光纤的双折射和限制损耗特性。结果发现:新设计的光纤具有高双折射低限制损耗特性,光纤结构参数为=1.0 m,d1=d2=d3=0.8 m时,该光纤在C波段（1.53~1.565 m）及L波段（1.57~1.62 m）呈现负色散及负色散斜率。在波长为1.55 m处,双折射高达10-2,限制损耗小于10-5 dB/m。     

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.     

Confinement losses and optimization in rectangular-lattice photonic-crystal fibers

Confinement losses in highly birefringent rectangular-lattice photonic-crystal fibers (RLPCFs) are investigated by the multipole method. The losses are strongly polarization dependent, which is due to the anisotropic properties of the cladding. The feature is applied to construct a new kind of single-polarization single-mode photonic-crystal fibers (PCFs), which is based on large differential loss between the two polarizations of the fundamental mode. Furthermore, it is found that the birefringence of RLPCFs is determined mainly by the air holes near the defect core. Consequently, a sandwiching (between triangular structures) rectangular configuration that has the property of reducing leakage loss while simultaneously retaining the birefringence of RLPCF is proposed.     

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.     

Ultrahigh Birefringent Photonic Crystal Fiber With Ultralow Confinement Loss

A photonic crystal fiber (PCF) with circular air holes in the fiber cladding and elliptical air holes in the fiber core is proposed. According to calculation, both ultrahigh birefringence (larger than 0.01) and ultralow confinement loss (less than 0.001dB/km) can be achieved simultaneously over a large wavelength range for a PCF with only four rings of circular air holes in the fiber cladding. The confinement loss in this PCF can be effectively reduced while the birefringence almost remains the same. The proposed design of the PCF is a solution to the tradeoff between the birefringence and the confinement loss for the originally reported highly birefringent elliptical-hole PCF. Moreover, an approach to modify the effective index of fiber core is also suggested in this letter     

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。     

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.     

一种可用于化学传感的对角对称光子晶体光纤设计

本文提出了一种可用于化学传感的具有高双折射、低损耗的光子晶体光纤,并系统地分析了空气孔参数对光纤光学特性的影响.研究表明,最优结构的光纤在典型波长1.55μm时对水、乙醇和苯的相对灵敏度分别可达56.3％、59.9％和62.5％,相比现有光子晶体光纤分别提高1.05～6.25倍、1.05～4.99倍和1.03～4.63...     

六角芯高双折射光子晶体光纤

提出了几种六角芯高双折射光子晶体光纤的新型结构,在这些结构中,包层不对称和纤芯不对称都能形成双折射,所有的空气孔都是圆形的,只需调整空气孔的大小、位置就能得到高双折射,这种光纤比椭圆形或矩形空气孔光纤更容易制作.最后,用半矢量平面波法计算模式双折射和波长的关系以及截止波长特性.与全矢量解相比,其带给有效折射率的误差仅约10-5.     

宽带色散平坦光子晶体光纤的优化设计与特性分析

设计了一种第一层为椭圆空气孔缺陷的宽带色散平坦光子晶体光纤,借助全矢量有限元法对这种结构的光子晶体光纤的色散特性、模场面积、双折射和限制损耗特性进行了数值模拟.结果表明改进的光子晶体光纤的色散曲线可以在很宽的波长范围内保持色散平坦并具有较低的色散值,其模场面积较未改进光子晶体光纤的模场面积要大,光纤的限制损耗变小且双折射也相当小.主要分析了这种光纤的结构参数的优化后,光纤的色散特性、有效模面积、双折射以及限制损耗特性的变化规律,最终设计了在1 200～1 800 nm波长范围内超平坦色散的光子晶体光纤.     

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.     

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.     

椭圆孔微纤芯光子晶体光纤的数值模拟

提出了一种在纤芯引入四个近矩形排列的椭圆空气孔,包层空气孔呈阶梯结构的高双折射光子晶体光纤,采用全矢量有限元方法,对光纤基模的模场分布、双折射、色散、限制损耗、有效模面积及非线性系数等特性进行了数值模拟.这种设计为获得高双折射光子晶体光纤提供了一种新的方法,为改善光子晶体光纤其他性能(如色散、非线性特性)提供了一种新的...