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     

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.     

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.     

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.     

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。     

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.     

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.     

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...     

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。     

Multiple defect core photonic crystal fiber with high birefringence induced by squeezed lattice with elliptical holes in soft glass

We present a dual mode, large core highly birefringent photonic crystal fiber with a photonic cladding composed of elliptical holes ordered in a rectangular lattice. The fiber is made of borosilicate glass and has a regular set of elliptical holes with an aspect ratio of 1.27 and a filling factor near 0.5. The group birefringence (G) and effective mode area were measured at 1550 nm for the fundamental mode and were found to equal 2 × 10^?4 and 20 μm² respectively. We discuss the influence of structural parameters including the ellipticity of the air holes and the aspect ratio of the rectangular lattice on the birefringence and on the fundamental and second modes of the fiber.     

Polarization and dispersive properties of elliptical-hole photoniccrystal fibers

We survey the properties of photonic crystal fibers with elliptical air holes, examining mode shapes, birefringence, group velocity walkoff and dispersion, and cutoff conditions. We find new types of behavior for each quantity and demonstrate the possibility achieving large birefringence with zero walkoff in the single-mode regime. We show that the dispersive properties of the vector modes are closely tied to those of the so-called fundamental space filling modes, and that at long wavelengths, the fibers exhibit a single-polarization single-mode regime of propagation without the presence of material anisotropy     

Intermodal interference based refractive index sensor employing elliptical core photonic crystal fiber

A refractive index (RI) sensor based on elliptical core photonic crystal fiber (EC-PCF) has been proposed. The asymmetric elliptical core introduces the polarization-dependent characteristics of the fiber core modes. The performances of intermodal interference between the intrinsic polarization fiber core modes are investigated by contrast in two interferometers based on the Mach-Zehnder (M-Z) and Sagnac interference model. In addition, the RI sensing characteristics of the two interferometers are studied by successively filling the three layers air holes closest to the elliptical core in the cladding. The results show that the M-Z interference between LP01 and LP11 mode in the same polarized direction is featured with the incremental RI sensing sensitivity as the decreasing interference length, and the infilled scope around the elliptical core has a weak correlation with the RI sensing sensitivity. Due to the high birefringence of LP11 mode, the Sagnac interferometer has better RI sensing performance, the maximum RI sensing sensitivity of 12 000 nm/RIU is achieved under the innermost one layer air holes infilled with RI matching liquid of RI=1.39 at the pre-setting EC-PCF length of 12 cm, which is two orders of magnitude higher than the M-Z interferometer with the same fiber length. The series of theoretical optimized analysis would provide guidance for the applications in the field of biochemical sensing.     

双矩形纤芯光子晶体光纤偏振分束器

基于双折射效应设计了一种新颖的纤芯为椭圆空气孔,包层为圆形空气孔的矩形双芯光子晶体光纤偏振分束器。用半矢量光束传播法(BPM)数值模拟了基模情形下该偏振分束器的性能,结果表明:在工作波长为1.55μm,光纤长度为1659μm时,两个纤芯在X、Y方向偏振光的隔离度分别达到了-41.3 dB和-39.1 dB,隔离度小于-10 dB的带宽超过了80 nm,达到了良好的偏振分束性能。同时,模拟了实际加工误差对所设计的偏振分束器的影响,得出在1.55μm的工作波长下,误差达到±7%时,隔离度仍能小于-10 dB,具有较高的实际应用价值。     

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。     

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.     

双孔单元四边形晶格光子晶体光纤特性的研究

为了获得双空气孔单元四边形晶格排列光子晶体光纤的光学特性，采用有限元分析法对该型光纤进行了数值模拟计算，得到了该型光纤的双折射、限制损耗、偏振拍长及色散特性结果。结果表明，与椭圆空气孔方形晶格排列光子晶体光纤相比，在相同的空气占空比条件下，双空气孔单元方形晶格排列光子晶体光纤可以获得更高的双折射特性，达到10-2量级；该型光纤两偏振模的限制损耗差可达103量级。该型光纤易于制造，在光纤通信及光纤传感等领域有一定的应用前景。     

高双折射双芯光子晶体光纤偏振分束器

设计了一种基于双折射效应的新型矩形纤芯光子晶体光纤偏振分束器,通过在矩形晶格结构的光子晶体光纤的每个纤芯中引入一对椭圆来增加结构的双折射。应用全矢量有限元法（FEM）分析了双芯光子晶体光纤中结构参数对双折射和耦合长度特性的影响,数值模拟了该偏振分束器的性能。结果表明:增大椭圆率可以在增大结构的双折射的同时减小耦合长度,并且该分束器在工作波长为1.55 m、传输长度为282 m 的光纤中能够实现偏振状态的隔离,消光比达到最小值-45.42 dB,并且在1.507~1.596 m、带宽为89 nm 的范围内消光比小于-10 dB。     

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.     

高双折射双芯光子晶体光纤特性

提出一种新型的高双折射双芯光子晶体光纤(PCF)模型,通过将最内层8个空气孔替换为4个椭圆空气孔来增大光纤的结构不对称性;通过改变两纤芯间的空气孔大小、椭圆空气孔的椭圆度以及孔间距来分析光子晶体光纤的双折射度、耦合长度以及色散特性。结果表明,双芯光子晶体光纤的模式双折射度达到10-2量级,耦合长度达0.1367 mm,在1.0~1.6 μm波长范围内具有超平坦色散特性。     

椭圆孔光子晶体光纤的偏振特性

摘要采用正交函数算法，提出了一种新型椭圆孔光子晶体光纤的本地正交函数模型。采用两种周期性结构的叠加构造超格子，用以表征光子晶体光纤(PCF)的横向折射率分布，同时将横向电场展开为Hermite-Gaussian函数。从电磁场的波动方程出发得到关于传播常数的本征方程。进而得到光子晶体光纤的传播常数、模场分布、偏振特性等传输特性。应用此模型讨论了椭圆孔光子晶体光纤基模两个偏振模式的双折射和群速度走离特性。研究表明，椭圆孔光子晶体光纤具有较大的模式双折射和群速度走离，双折射、群速度走离与频率的依赖关系和普通保偏光纤不同。另外椭圆孔光子晶体光纤还可实现在单模区同时保持高双折射和零群速度走离，可用于研究光纤的非线性。