Single-polarization single-mode photonic crystal fibers

A new structure of single-polarization single-mode (SPSM) photonic crystal fiber (PCF) is proposed and analyzed by using a full-vector finite element method with anisotropic perfectly matched layers. From the numerical results it is confirmed that the proposed fiber is low-loss SPSM-PCF within the wavelengths ranging from 1.48 to 1.6 /spl mu/m, where only the slow-axis mode exists and the confinement loss is less than 0.1 dB/km.     

单偏振单模微结构聚合物光纤的设计

设计了一种聚甲基丙烯酸甲酯(PMMA)基的单偏振单模(SPSM)微结构聚合物光纤(MPOF)。采用全矢量平面波展开法并结合完美匹配边界条件,对其偏振特性进行了理论模拟。详细讨论了微结构光纤参数的变化对单偏振单模带宽和工作波长的影响,发现在0.57～0.71μm的可见光波长范围,由于基模两个正交偏振模的截止波长不同,这种微结构聚合物光纤只能传输基模中的一个偏振模。光束传播法计算表明,在波长0.65μm处具有7圈空气孔的单偏振单模微结构聚合物光纤的传导偏振模约束损耗仅为1.24dB/m,这种低损耗的单偏振单模微结构聚合物光纤可有效消除传统保偏光纤固有的偏振串扰和偏振模色散。     

Design of Wideband Single-Polarization Single-Mode Photonic Crystal Fiber

The present paper proposes a novel design for achieving single-polarization single-mode (SPSM) operation in photonic crystal fiber (PCF), using a rectangular-lattice PCF with two lines of three central air holes enlarged. The proposed PCF that is composed entirely of silica material is modeled by a full-vector finite element method with anisotropic perfectly matched layers. The position of the region of single polarization can be tuned freely by adjusting the size of the central enlarged air holes. Using this structure, an SPSM PCF with confinement loss less than 0.1 dB/km within the wavelength range from 1.20 to 1.66 mum and effective mode area about 5.9 mum² at 1.55 mum has been successfully designed. The proposed fiber is a nonlinear SPSM, which may be useful for nonlinear optical applications or applications with a wide SPSM operating bandwidth requirement     

Design of single-polarization single-mode photonic crystal fiber at 1.30 and 1.55 /spl mu/m

Single-polarization single-mode (SPSM) operation of a highly birefringent (HB) photonic crystal fiber (PCF) is investigated in detail by using a full-vector finite-element method (FEM) with anisotropic perfectly matched layers (PMLs). The cutoff wavelengths of the two linearly polarized principal states can be designed by varying the structure parameters of the PCF. The confinement loss and splice loss to standard single-mode fiber for particular SPSM PCFs are calculated and optimized at both 1.30 and 1.55 /spl mu/m.     

2 μm波段7-cell空芯光子带隙光纤的特性研究

扩大传输容量已然成为现代光通信技术发展的首要任务。2μm波段属于人眼波段,并具有大气通信窗口,是未来光通信系统亟待开发的领域。软玻璃材料相比于石英玻璃,具有更宽的透光范围,并且可扩展到中红外波段,恰好配合2μm波段光通信系统。空芯光子带隙光纤(hollow core photonic bandgap fiber,HC-PBGF)由于光纤带隙的存在,提供了独一无二的导光模式。HC-PBGF具备灵活的光纤结构、较低的损耗,可控的色散特性,是非常适合光通信的传输媒介。设计了一种7-cell HC-PBGF,对该光纤的色散、模场面积、限制损耗和弯曲损耗等特性进行仿真分析。     

具有混合形状空气孔的OAM传输光纤设计研究

本文提出了一种新型轨道角动量模(OAM)传输的光子晶体光纤(PCF)结构,该光纤由最中心空气孔、高折射率环形层和外包层构成,其中外包层由一圈椭圆形空气孔和多圈呈周期排列的扇形空气孔共同组成,无需通过额外的掺杂,就可以使中心空气孔和外包层空气孔之间形成一个用来传输OAM光束的等效高折射率环形区。通过对该PCF的传输特性进行仿真分析,发现在1.55μm处,各模式的限制损耗维持在10^-6 dB/m-10^-10 dB/m,在C波段的色散值均维持在310 ps/(nm×km)以下,HE2,1模在1.55μm-1.6μm波段内的色散变化为3.1 ps/(nm×km)。在1.55μm处最大的Δnneff能够达到4.83×10^-3,大的有效折射率差可有效地抑制了模式间的简并,避免HE模和EH模耦合成LP模。验证了该光纤具有大带宽、小而平坦色散、大有效折射率差、低限制损耗和低非线性系数等优良性能。在1.25μm-2.0μm波段内共可以支持34个OAM模式的有效传输,每个模态都可作为独立的信道传递信息,适合用于大量数据的传输,大幅提高了光通信的系统容量和频谱效率。     

High Power Highly Nonlinear Holey Fiber with Low Confinement Loss for Supercontinuum Light Sources

The high power holey fiber is an efficient supercontinuum light source by using picosecond pulse, which is a less expensive laser source compared with low power and expensive femtosecond laser sources. In this paper, a high power highly nonlinear holey fiber (HN-HF) with a low confinement loss is proposed for supercontinuum light sources. The finite difference method is used to calculate the different properties of the proposed HN-HF. High nonlinear coefficients are obtained at 1.06 μm, 1.31 μm, and 1.55 μm wavelengths with flattened chromatic dispersion and low confinement losses simultaneously. Moreover, numerical simulation results show that high power broad supercontinuum spectra with very short length of the proposed photonic crystal fiber are achieved.     

Single-polarization single-mode optical fibers

Strictly speaking, an ordinary axially symmetrical single-mode fiber is a "two-mode" fiber because two orthogonally polarized HE11modes can be propagated in it. This fact results in the instability of the polarization state of the propagated mode when geometrical perturbation exists in the fiber, and also the so-called polarization mode dispersion. These are harmful in some applications of single-mode fibers to communication and measurement. To prevent these adverse effects, single-polarization single-mode (SPSM) optical fibers have been developed. Three basic types of the SPSM fiber are elliptical-core fiber, stress-induced birefringent fiber, and side-pit fiber. This paper describes the principles of these three types, performance obtained experimentally, theoretical approaches, and measurement techniques related to the SPSM fibers. Finally, relevant technical tasks in the future are mentioned.     

Study of ultraflattened dispersion square-lattice photonic crystal fiber with low confinement loss

A new type ultraflattened dispersion square-lattice photonic crystal fiber with two different air-hole diameters in cladding region is proposed and the dispersion is investigated using a compact 2-D finite difference frequency domain method with the anisotropic perfectly matched layers (PML) absorbing boundary conditions. Through numerical simulation and opti- mizing the geometrical parameters, we find that the photonic crystal fibers proposed can realize ultraflattened dispersion of 0±0.06 ps/(km·nm) in wa...     

基于光子晶体光纤的宽带色散补偿光纤的设计

采用矢量光束传输法(VBPM)对小纤芯光子晶体光纤(PCF)的色散特性进行了数值分析,研究发现通过调节光子晶体光纤的结构参数可以灵活的对其色散补偿值进行调整,能够实现C L波段(1 530～1 565 nm)的宽带色散补偿功能,并且对标准单模光纤的色散斜率有很好的补偿.在∧=1.0μm,d/∧=0.7时,1 550 nm处的色散值可以达到-339.1 ps/(km×nm),相关色散斜率(RDS)可以达到0.003 2 nm-1,能够有效的对标准单模光纤进行色散斜率补偿.     

Novel fiber design for flat gain Raman amplification using single pump and dispersion compensation in S band

This paper reports on a novel fiber design that has an inherently flattened effective Raman gain spectrum. Simulations show that gain-flattened broad-band Raman amplification, using a single pump, can be achieved in any wavelength band by suitably choosing the fiber parameters and the pump wavelength. The fiber also has a high negative dispersion coefficient-(380-515) ps/km/spl middot/nm over the operating range of wavelengths-and the shape of the dispersion curve is such that the total link dispersion can be not only compensated but also flattened. Hence, the designed fiber can serve as a lossless, broad-band, dispersion-flattening, and dispersion-compensating module for the S band, wherein lossless operation is achieved using inherently gain-flattened single-pump Raman amplification. The performance characteristics of such a module was modeled taking into account wavelength-dependent splice loss as well as background loss, and it has been shown through simulations that lossless operation with /spl plusmn/0.2-dB gain ripple is achievable over (1480-1511) nm using a single pump. Moreover, dispersion compensation for five spans of transmission in a 10-Gb/s system, over this 32-nm bandwidth in the S band, should be attainable using the proposed design.     

Coupling characteristics of the high-polarization dual-core photonic crystal fiber with mixing air holes

A high-polarization dual-core photonic crystal fiber (PCF) with mixing air holes is designed. The full-vector finite element method and coupled-mode theory are used to investigate the birefringence, coupling length, dispersion characteristics, normalized power and extinction ratio of this fiber. Numerical investigations demonstrate that by changing the structural parameters of the fiber, the birefringence is up to 1.48×10-2 at 1.55 μm, the coupling lengths are 79 μm and 94 μm for x-polarized and y-polarized modes, the fiber has two zero dispersion points, and the dispersion is very flat at the ultra-wide waveband scope from 0.7 μm to 1.7 μm.     

Broadband Single-Polarization Single-Mode Photonic Crystal Fiber Coupler

In this letter, a novel design for a photonic crystal fiber coupler with single-polarization single-mode (SPSM) functionality is proposed and investigated using a vector plane-wave expansion method and a vector finite-element method. We study the changes in the coupling lengths between the two orthogonal polarizations and the width of the SPSM coupling region with respect to the air-hole parameters. We demonstrate that the SPSM coupling range can be more than 200 nm wide for a variety of air-hole parameters and show that the position and width of the SPSM coupling region can be tailored via the diameters of the large inner air holes and the small cladding air holes.     

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。     

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。     

八角格子色散补偿光纤

为了消除光纤通信系统中色散,采用各向异性完全匹配层和全矢量有限元方法,进行了理论分析和实验验证,设计了一种基于八角格子晶体的同轴双芯色散补偿光子晶体光纤;得到了该色散补偿光纤的传输特性如基模有效折射率、色散、损耗和非线性系数方面的数据,并分析了光纤波导色散与色散补偿光纤结构参量之间的关系。结果表明,所设计的光纤在200nm的负色散范围内,拥有负色散值(在波长为1.55m处有最低负色散值-1500 ps/(nmkm)),同时在E+S+C波段有较低的限制损耗(小于3.3dB/km);非线性效应也得到显著抑制。     

小芯径折射率引导型光子晶体光纤的制备和研究

介绍一种小芯径折射率引导型光子晶体光纤(PCF)的拉制方法.制备出的光纤纤芯周围第一层空气孔发生形变,呈柚子形,其芯径为1.7μm,孔间距A和空气孔直径d分别为3.4 μm和2.8μm.由于光纤结构的特殊性,采用有限元法在200～1600 nm波段对其基模有效折射率、色散系数、有效模场面积以及非线性系数进行了数值模拟计算.经过理论计算,这种光纤在所研究的波段具有极高的非线性系数且表现为反常色散,这些特性十分有利于超连续谱的产生.在测量了光纤的损耗、色散等基本特性后,选取损耗较小凡位于光纤反常色散区域,中心波长为800 nm的飞秒激光作为光源,将不同功率的超短激光脉冲耦合入光纤,对这种小芯径折射率引导型光子晶体光纤产生超连续谱的过程进行了测量和分析.     

单偏振单模微结构聚合物光纤理论设计

采用全矢量有限元法并结合完美匹配边界条件,设计实现了一种新型结构的单偏振单模（single polarization single mode,SPSM）微结构光纤（Microstructured optical fibers,MOFs）,以聚合物聚甲基丙烯酸甲酯（polymethyl methacrylate,PMMA...     

Enhanced performance of WDM systems using directly modulated lasers on positive dispersion fibers

Cost-effective directly modulated distributed feedback lasers (DML) have attracted much attention recently for operation at the 1.55 μm wavelength band applications in metropolitan area networks. In this paper, we show by simulation that the effect of directly modulated laser chirp can be compensated by a negative dispersion fiber, but this only occurs in a specific range of DML output power, and that a pulse broadened by the positive dispersion fiber can be equalized using self-phase-modulation (SPM) in optical fiber. The majority of metro and access networks are made up of conventional single-mode fibers (SMF) which are positive dispersion fibers. We demonstrated that optimum compensation is always feasible for such fibers, since the magnitude of the SPM can be controlled by changing the optical power in the fiber. Furthermore, simulation suggests that this technique will enable directly modulated wavelength division multiplexed systems to enhance their performance if the power of each channel is appropriate.     

An asymmetric dual-core single-polarization single-mode photonic crystal fiber coupler

A vectorial finite element method (VFEM) is adopted to investigate the novel single-polarization single-mode (SPSM) photonic crystal fiber (PCF) coupler which has asymmetric dual-core and two lines of enlarged air holes. It is demonstrated that the SPSM region of the designed fiber can be more than 250 nm wide with a set of optimized air-hole parameters and the width of the SPSM region could change slightly by fine adjustment of the inner large air holes. The coupling length between the odd and even x-polarization modes is also investigated through fine-tuning the large and small air-hole diameters.