Analysis and Design of Photonic Crystal Fibers Based on an Improved Effective-Index Method

The modal characteristics of photonic crystal fibers (PCFs), with guiding cores consisting of one or seven missing airholes, are investigated with the finite element method and compared to those of step-index fibers (SIFs). To extend the applicability of the classical SIF theories to PCFs, the effective refractive index of photonic crystal cladding and the effective core radius of a PCF are studied systematically, based on simple physically consistent concepts. With the new effective cladding index and core radius of PCFs, the classical definition of the V parameter for SIFs is extended to PCFs, and a highly efficient approach based on the effective-index method is developed for the design of PCFs. The new design approach has been successfully employed to analyze the modal properties of PCF lasers with depressed-index cores and further tested by using it to effectively estimate the number of guided modes for PCFs with large cores     

Determining Properties of Fabricated Index-Guiding Photonic Crystal Fibers Using SEM Micrograph and Mode Convergence Algorithm

We develop a method for modeling properties of fabricated (realistic) air-silica photonic crystal fibers (PCFs). Our approach involves extracting the transverse refractive index (RI) profile of the drawn PCF from its scanning electron micrograph on which is operated a precise and fast mode-analysis recipe based on a finite difference (FD) field convergence scheme. From the digitized scaled RI distribution, we evaluate propagation characteristics of guided modes of PCFs, examining modal shapes, birefringence, dispersion, and other relevant properties. Naturally, our true-structure study of PCFs using FD algorithm exhibits results that are more close to measured data, establishing its practicality as compared with idealized-structure modeling. To demonstrate the efficacy of our method, we investigate some application-specific experimentally drawn PCFs, well known for their study in the literature. The key results that fairly predict experimental measurements are presented. Besides modeling fabricated fibers, this analysis will be very useful to realize PCFs with targeted specifications using feedback of estimation and characterization of trial fabrications.     

Design and optimization of photonic crystal fibers for broad-band dispersion compensation

Design of photonic crystal fibers (PCFs) for application of broad-band dispersion compensation is investigated by using an improved design model based on combination of a rigorous vector solver for modal properties and a scaling approach for dispersion characteristics. The newly designed PCF is shown to exhibit large normal dispersion up to -474.5 ps/nm/km, nearly five times of conventional dispersion compensating fibers, and compensate conventional single-mode fibers within /spl plusmn/0.05 ps/nm/km over a 236-nm wavelength range. Furthermore, the design model and methodology can be applied to design other dispersion-based devices such as dispersion flattened fibers and dispersion shifted fibers.     

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.     

高双折射光子晶体光纤研究进展

首先对高双折射光纤的基本原理和概念作了介绍,并简要讨论了用于分析高双折射光子晶体光纤的常用数值方法及其特点。在此基础上,提出可将高双折射光子晶体光纤归纳为四种基本类型,并对每一种类型的原理、特点和典型结构作了介绍和分析。还简要介绍了高双折射光子晶体光纤的典型应用,最后对高双折射光子晶体光纤的发展方向和前景进行了展望。     

激活或高折射率介质掺杂同轴光子晶体光纤增益特性的研究

文中在缺陷介质中掺入激活杂质或高折射率杂质时,数值研究了同轴光子晶体光纤的掺杂局域场特征以及受激辐射增强使透射率大于1现象和掺杂层复有效折射率负的虚部之间的内在规律,由此进一步说明,因受激幅射放大,而在掺杂同轴光子晶体光纤中获得窄的高增益透射带,由此带隙结构形成波分复用技术的多个传输信道,可应用于密集波分复用(DWDM)光通信系统.     

椭圆芯光子晶体光纤的偏振特性

采用全矢量模型研究椭圆芯光子晶体光纤(photonic crystal fibers,PCFs)的偏振特性。研究表明：椭网芯PCF基模的两个正交偏振态不再简并,模场具有较强的线偏振特性;模式双折射可达10^-3量级,该数值比传统椭圆保偏光纤至少高一个量级;在比传统椭圆保偏光纤更长的波长处获得零走离点和负走离区。椭圆芯PCF的偏振特性与光纤结构参数有较强的依赖关系,通过适当选择光纤的相对孔径和孔距,有望在给定的波长上实现高双折射和零走离单模运转,或设计出高双折射、大走离的单模光纤,为研制高性能保偏光纤提供了一个新的途径。     

Design of photonic crystal fibers with anomalous dispersion

Photonic crystal fibers (PCFs) have attracted greatattentionin recent years due to their interesting proper-ties ,such as endless single-mode operation,unique dis-persion and nonlinear characteristics[1 ,2].It has been re-ported that PCFs offer a wide range of potential applica-tions ,such as 2Rregenerators ,optical parametric ampli-fiers ,dispersioncompensationandsuper-continuumgen-eration[3].Also called holey fibers or microstructure fi-bers ,PCFs are optical fibers possessing periodic a…     

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.     

基于光子晶体光纤的色散补偿和色散平坦技术

本文介绍了在各种结构参数下光子晶体光纤的色散特性，总结了实现光子晶体色散补偿光纤和光子晶体色散平坦光纤的各种设计方法。利用光子晶体光纤结构设计的灵活性，可以设计出具有各种色散曲线的光子晶体光纤，而这些光纤大略可以分成两类：空气孔直径大小一致的普通光子晶体光纤和空气孔直径大小变化的光子晶体光纤。从数值仿真的结果来看，如果选择适当的空气孔分布结构，空气孔直径大小变化的光子晶体光纤可以具有非常优异的色散补偿和色散平坦特性。这些数值仿真为实际的光子晶体的制作提供了参考。     

国产化大模场掺镱光子晶体光纤的设计与制备

理论分析了空气孔尺寸与晶格常数对光子晶体光纤(PCF)单模特性的影响,设计了大模场双包层PCF的波导结构。采用自主知识产权的专利技术,制备出高数值孔径大模场掺Yb双包层PCF,其内包层数值孔径为0.65,纤芯数值孔径为0.06,有效模场面积为1 465.7μm2。     

Numerical and experimental analysis of polarization properties from hybrid PCFs across different photonic bandgaps

This work presents a numerical and experimental characterization of polarization properties from hybrid photonic crystal fibers (hybrid PCFs or HPCFs) across different bandgaps. Very high extinction ratio over at least three wide bands and single-mode and single-polarization operation over more than 320 nm have been obtained by using only one fiber. Furthermore, it is reported, for the first time, a multi- and broadband fiber-based optical polarizer. Numerical simulations and experiments of modal, birefringence and polarization properties have been carried out to demonstrate the remarkable performance of the proposed device.     

Study of Raman amplification properties in triangular photonic crystal fibers

The Raman properties of triangular photonic crystal fibers (PCFs) are analyzed in order to design a fiber for Raman amplification with enhanced performances. By casting the Raman intensity propagation equations, the Raman effective area and the Raman gain coefficient are introduced - two meaningful parameters that take into account the overlap between the pump and signal profiles. The behavior of these two parameters is examined in silica PCFs as a function of the geometrical characteristics of the triangular lattice. The numerical results show that a proper design of the hole diameter and the spacing between air holes can minimize the Raman effective area and maximize the Raman gain coefficient. The paper then focuses on PCFs with a germania-doped core. It is found that, for a given PCF cross section and dimension of the doped region, the Raman gain coefficient increases linearly with germania concentration. Moreover, by enlarging the doped region, it is discovered that a PCF with a germania-doped area internally tangent to the first ring of air holes has a maximum Raman gain coefficient. Finally, the calculated values of the Raman gain coefficient are compared with those of other highly nonlinear fibers presented in the literature, showing that a well-designed triangular PCF can significantly improve Raman gain performance.     

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.     

光子晶体光纤的研究新进展

国际上关于光子晶体光纤(PCF)的研究主要集中在改善PCF的性能和拓展PCF的应用领域两方面.文章介绍了光子晶体光纤的结构、导光原理和主要特性,并重点讨论了高性能光子晶体光纤的研制情况以及光子晶体光纤的在应用领域的新进展.     

Virtual boundary method for the analysis of elliptically cross-sectional photonic-crystal fibers with elliptical pores

This paper introduces a new semianalytical method for the analysis of propagation characteristics of elliptically cross-sectional photonic-crystal fibers (PCFs) with elliptical pores. This method known as a virtual boundary method (VBM) is based on the equivalency between an actual PCF and a three-layered, transversely inhomogeneous waveguide. The complicated refractive-index profile of the PCF is written as a double Fourier series, and an approximate separable wave equation is found in an elliptical coordinate system for the longitudinal field components. The exact solution to the derived equation is expressed in terms of higher order transcendental functions, such as regular and irregular Coulomb-wave functions and Mathieu functions. After having expressed all the field components, boundary conditions are imposed on the boundaries, and then, a transcendental equation for the propagation constant is derived, which is solved numerically. The validity of the method is ensured by comparing various quantities, such as effective indexes, modal birefringences, and electromagnetic field distributions, with those from an accurate full-vector finite-element method (FEM) simulator, showing relatively good agreement between the results. The method correctly confirms some of the unique PCFs' properties, such as strong localization of light within the fiber and enhancement of modal birefringence as a function of the topology of hole arrangement.     

基于光子晶体光纤的光学传感

光子晶体光纤(PCFs)的应用在很多方面改善了传统光纤传感器的性能.基于 PCFs的光纤传感器对应力和液体折射率具有较高的传感精度以及更好的温度特性,并且可以灵活引入各种耦合结构单元组成干涉仪,介绍了基于光纤布拉格光栅(FBG)、长周期光栅(LPG)和干涉仪的PCFs传感器的基本构造、工作原理和最新的研究进展.     

光子晶体光纤的后处理技术

对光子晶体光纤的后处理技术进行了详细的分析和讨论,包括拉锥、空气孔膨胀后拉锥、选择性空气孔塌缩。利用这些后处理技术,可以改变光子晶体光纤的结构参数,如空气孔大小、纤芯大小和形状等,制作各种不同类型的光子晶体光纤光器件。     

光子晶体光纤非线性光学研究新进展

光子晶体光纤(PCF),又称为多孔光纤(HF)或微结构光纤(MF),是一种单一介质,并由波长量级的空气孔构成微结构包层的新型光纤。光子晶体光纤呈现出许多在传统光纤中难以实现的特性,从1996年世界上制造出第一根光子晶体光纤以来,它便受到了广泛关注并成为近年来光学与光电子学研究的一个热点。介绍了光子晶体光纤的制作工艺、工作原理、基本特性、目前的研究重点和进展情况,重点评述了光子晶体光纤非线性光学方面的研究及其潜在的应用。     

Design of erbium-doped triangular photonic-crystal-fiber-based amplifiers

The amplification properties of erbium-doped triangular photonic crystal fibers (PCFs) are analyzed by varying the pitch, the hole diameter, and the dopant radius by means of a full-vector finite-element modal formulation combined with a population and propagation rate equation solver. Fiber designs which allow us to greatly reduce splice losses are presented and it is demonstrated that PCF amplifiers may deliver gains of more than 47 dB with splice losses lower than 0.3 dB.