一种新型折射率掺镱双包层光纤

为了提高光纤放大器单纤输出功率,设计了一种新型折射率掺镱双包层光纤,纤芯直径30μm,包层直径125μm。采用一种改良的高温气相掺杂技术和改进的化学气相沉积法制作,纤芯折射率分布为凹陷型结构,掺杂区为低折射率区。对光纤的荧光特性、模场特性以及放大特性进行了测试。试验结果表明,该新型折射率分布设计有利于纤芯对抽运光吸收,荧光输出平坦,对光纤进行弯曲处理可实现平坦模场的能量输出,5m光纤实现了40dB 高功率飞秒信号光放大,输出功率30kW。     

锥形光纤的功率分布特性

从波动理论出发,对锥形光纤的纵向传播常数进行泰勒(Taylor)级数展开,经近似得到了锥形光纤功率分布的解。基于此理论,对锥形光纤的功率分布特性进行了讨论,并分析了锥形光纤的长度、锥度和光纤折射率等参数对锥形光纤不同模式功率分布的影响。为了减小功率泄漏,当光从锥形光纤大端入射时,应当减小锥长,减小锥度,增大纤芯包层折射率差;当光从锥形光纤小端入射时,应当增加锥长,增加锥度,增大纤芯包层折射率差。在长锥长、大锥度情况下,光纤折射率分布的影响相对较小。     

一种低损耗低模式串扰渐变型少模光纤

提出了一种纯二氧化硅纤芯、渐变折射率分布的 两模光纤,实现了渐变折射率少模光纤低差分模式群时延和纯二 氧化硅芯光纤低损耗优点的有效结合。采用全矢量有限元方法研究表明,所提出的少模光纤 纤芯采用纯二氧化硅实现了 低损耗,采用纤芯渐变折射率实现了低差分群延迟,包层处采用凹陷折射率实现了低弯曲损 耗,采用模式大折射率差实 现了低模式串扰,采用大有效面积实现了低非线性系数;该光纤具有非线性系数和差分模式 群时延在1.5～1.65 μm波长范围内平坦特性。     

掺铒光纤的纤芯折射率

在光纤研制过程中掺铒光纤(EDF)的纤芯折射率控制尤为关键。对采用改进型化学气相沉积(MCVD)技术沉积纤芯疏松层,并用溶液浸泡法,采用不同铝离子浓度的氯化铒溶液制作的四种掺铒光纤进行了折射率测试和电子探针微小分析(EPMA)。提出了掺铝将改变原疏松层中的二氧化硅和二氧化锗的比例,铝离子进入疏松层越多,最后得到的掺铒光纤纤芯的二氧化锗的摩尔分数就会越少,用氧化铝生成和二氧化锗挥发两个化学反应式进行了解释。掺铝和掺锗都会提高纤芯的折射率,但由于锗减少引起的折射率降低量大于铝提高引起的折射率提高量,导致掺铝后纤芯的整体折射率下降。     

光纤模群时延差的测量

一、绪言多模光纤基带特性主要取决于各模群速度差而产生的模式色散。因而为了得到宽频带多模光纤,使纤芯的折射率分布与最佳分布形状完全一致,这对均衡各模群延迟时间是重要的。然而,光纤的折射率分布通常是采用干涉显微镜来测量的,因为标准光纤的芯径只有50μm,纤芯中最大折射率差小于0.015,故采用此方法来评价能够反馈制造条件那样的高精     

光学结晶光纤概论

1前言 目前,包括CATV光纤线路在内的光通信系统所用的光纤,都是采用在石英(硅Si)玻璃中掺杂一些元素,使纤芯截面形成预期的折射率分布的折面图形状,使用折射率高的纤芯来实现光的波导传送的.厂家为了实现设计的传送性能,如:多模(MM)、单模(SM)和折射率的突变阶跃(SI)型、渐变(GI)型以及色散位移(DSF)光纤等,而对纤芯折射率分布的断面图作了不断地改进(参阅图1).     

第四章 激光传输技术(续)

4 2　激光光纤传输技术4 2 1　光纤波导结构光纤是一种能够传送光频电磁波的介质波导。光纤的典型结构如图 4 5所示 ,它包括纤芯、包层和护套三部分。纤芯和包层构成传光的波导结构 ,护套只起保护作用。波导性质由折射率分布决定 ,图中第二排是两种典型的纤芯折射率剖面ｎ(ｒ)示意图 ,最下面一排给出了单模光纤和多模光纤的结构参量。α为纤芯半径 ,λ为自由空间光波长 ,Δ =(1-ｎ22 /ｎ21 ) /2图 4 5　典型光纤的术语、折射率分布和尺寸范围光纤作为信息传输介质的优点主要如下。(1)光纤的传输损耗低、信息容量大。与金属导线比起来 ,高…     

阶跃折射率光纤中的激光模式特性

研究了根据阶跃折射率光纤中传输的光场遵循贝塞尔分布的光纤中的激光模式特性,通过贝塞尔方程解析解的方法,利用计算机仿真得到了光纤内和光纤出射端外典型的低阶线偏振模(LPmn模)的光强分布特性和传输特性;同时,研究了大模场光纤参数如纤芯直径、纤芯折射率和包层折射率等不同时典型低阶LPmn模式的光强分布特性和传输特性的变化规律;并且计算了各典型的低阶LPmn模式的M2因子,讨论了光纤激光光束质量因子的特点及随光纤参数的变化规律。     

一种双模大模场面积多芯光纤的设计和特性分析

提出了一种具有双模大模场面积的多芯光纤,建立了该多芯光纤的电磁场模型并采用有限元方法对其进行求解。基于该模型研究了光纤的模式特性和弯曲特性,系统分析了纤芯间距、纤芯半径和芯包折射率差对光纤模式特性和基模有效模场面积的影响。结果表明:通过引入空气孔并适当减少纤芯间距、纤芯半径和芯包折射率差,该光纤能实现严格的双模传输。保持双模传输时,通过增大纤芯间距,减小纤芯半径和芯包折射率差均有助于增大基模的模场面积。通过调整结构参数,在近似满足双模传输的条件下,光纤的基模模场面积在平直状态下可达到3155μm²。     

光子带隙光纤中纤芯环掺杂对传输特性的影响

为了研究光子带隙光纤中纤芯环掺杂浓度的百分比对光纤传输特性的影响,利用全矢量有限元法在纤芯环掺杂浓度的百分比为1%～5%的条件下对7孔光子带隙光纤纤芯环掺杂和19孔光子带隙光纤纤芯环掺杂两种结构进行了仿真,比较了两种结构的纤芯模能量分布曲线,并且给出了19孔光子带隙光纤在不同的纤芯环掺杂浓度的百分比下,光纤带宽、色散、有效模面积和有效折射率的分布曲线图。结果表明,19孔光子带隙光纤比7孔光子带隙光纤具有更强的限光能力,且纤芯环掺杂浓度的百分比对光子带隙光纤的传输性能有显著的影响。     

有限元法求解任意折射率分布光纤波导截止波长

本文应用有限元方法,求解了任意径向非均匀折射率分布圆柱对称介质波导中纵向场耦合波动方程定解问题所对应的变分问题,计算了任意径向非均匀折射率分布介质波导的截止波长。阶跃光纤与幂指数折射率分布光纤计算结果与文献结果的比较表明,该方法计算结果精度高且不需要弱导或高斯模场分布等限制要求。然后本文研究了带阶跃环的三角型分段折射率分布光纤归一化截止频率随结构参数变化的规律。     

Chromatic dispersion characteristics of fibers with opticalKerr-effect nonlinearity

Chromatic dispersions of optical fibers with Kerr-effect nonlinearity are investigated. Under high optical intensity, dispersion characteristics become different from those of the linear state (or weak optical intensity) since the refractive index profile changes in accordance with the intensity profile. Nonlinear dispersion characteristics are calculated for step-index and quadratic profile fibers with core-cladding, core, and cladding nonlinearity. It is shown that although the propagation constant of the step-index fiber increases substantially from the linear value, the group delay and waveguide dispersion do not increase as much     

光纤有效面积与结构参数的关系

采用有限元法对任意折射率剖面光纤的有效面积 ( Aeff)和校正因子 k进行了精确计算 ,并首次系统地计算和讨论了决定光纤折射率剖面的各个结构参数与 Aeff的关系。结果表明 ,光纤内芯的幂指数 p,内芯半径 a1 ,内芯相对折射率差 Δ1 与 Aeff关系很大 ,减小 p,a1 和Δ1 可增大 Aeff;增加折射率外环的宽度和相对折射率差可以增大 Aeff;内芯和折射率外环之间的折射率凹陷层可减小 Aeff,但影响较小。     

Index profile measurements of fibers and their evaluation

The refractive index distribution in the core of a multimode optical-fiber waveguide plays an important role in determining the transmission properties of the guide. The closer the index profile is to the required ideal distribution, the greater the resulting information carrying capacity of the fiber. This review paper discusses methods for measuring the refractive index distribution in optical fibers and for predicting their impulse response and signal bandwidth from the measured profiles. Some attention is also given to preform and single-mode fiber profiling.     

匹配型熊猫光纤的相衬法定轴技术的仿真分析

从匹配型熊猫光纤的结构及相衬显微技术物理图像出发 ,建立起仿真数学模型 ,计算机仿真了相衬法定轴技术。仿真数学模型考虑了匹配型熊猫光纤的应力折射率分布、相衬成像原理、光纤在物镜观察面上的相衬成像偏差等物理图像。计算机仿真分析得到了相衬法确定匹配型保偏光纤双折射光轴的光强特征图像。仿真结果与实验得到的光强图像相符合。此方法已成功地应用于定轴实验 ,定轴分辨率小于 2°     

Modal bandwidth enhancement in a plastic optical fiber by W-refractive index profile

A plastic optical fiber (POF) having a W-shaped refractive index profile (W-shaped POF) was prepared for the first time that had a possibility to realize a higher bit rate transmission than those of the conventional silica-based multimode fiber and graded index (GI) POF links. Since the W-shaped POF has a valley of the refractive index at the boundary of the core and cladding of the conventional graded-index (GI) POF, the group delay of higher order modes is strongly influenced, and the modal dispersion in the GI POF is compensated. By comparing the propagating mode properties of the W-shaped POF with those of the GI POF, we clarified theoretically and experimentally that the index valley has a remarkable modal dispersion compensation effect.     

Fabrication of light-induced self-written waveguides with a W-shaped refractive index profile

This paper proposes a novel technique for automatic waveguide formation by means of the self-trapping effect of optical fiber irradiation into a photopolymerizing resin. We investigate experimentally the phenomenon of thin cladding layer formation surrounding the core following the core creation. In the proposed technique, a counterdiffusion effect involving polymerizing monomers via the core/cladding interface causes enrichment of a low refractive index monomer, and a resultant "W-shaped" refractive index profile is realized. The measured propagation loss of the fabricated waveguide is 1.7 dB/cm at 0.68 /spl mu/m wavelength. This technology is appropriate for the fabrication of large-core optical waveguides of greater than 0.5 mm in diameter and is useful for automating the optical fiber connection and packaging process by virtue of being an all-passive optically induced process.     

Control of Refractive Index Distribution for High-Bandwidth Graded Index Plastic Optical Fiber

The graded index plastic optical fiber (GI-POF) has been proposed as the transmission medium to realize high-speed information transmission. We have succeeded in fabricating a GI-POF by the coextrusion process, a method that allows continuous fabrication of GI-POF. Although it has been indicated that the refractive index distribution of GI-POF fabricated by this process is formed by Fick diffusion with diffusion coefficient dependent on dopant concentration, the method to control it remains unknown. The purpose of this paper is to establish the technology of controlling refractive index distribution in GI-POF fabricated by the coextrusion process. Therefore, we investigate the physical mechanism of the dependency of diffusion coefficient on dopant concentration. It has become clear that the dependency is affected by the decrease of glass transition temperature and the nonlinear increase of melt flow rate. Moreover, through simulation of dopant diffusion by our originally developed program, it has become evident that changing the molecular weight of the core and cladding material allowed control of fabricating a GI-POF with optimal refractive index distribution by this fabrication method.      

Microscopic computer tomography measurement of nonaxisymmetricallydistributed optical fiber refractive index

A nonaxisymmetrically distributed method for measuring the refractive index of an optical fiber is described. The light intensity distribution is observed with a microscope when an optical fiber is latterally illuminated by collimated light. The integrated refractive-index difference along the projective line is obtained by performing two integrations of the light intensity. The fiber is rotated, and the observation and calculations are repeated at each angle of rotation. The refractive-index pattern over the fiber cross section is reconstructed by computer tomography     

Skew evaluation using two-dimensional refractive-index profile insingle-mode fiber ribbons

The skew of fiber ribbons must be small for high bit rate parallel optical transmission systems. Accurate skew evaluation using fiber parameters is important for this purpose. A simple method, based on the calculus of variations, is proposed for evaluating the skews of fiber ribbons. This method employs only one mode field (LP₀₁ mode) of an ideal step-index fiber as a trial function and a two-dimensional (2-D) refractive index profile. The measured skews of a 16-fiber ribbon composed of fibers with different parameters are compared with calculated values and are found to be in good agreement. The influence on the skew of several refractive index profile deviations (including asymmetric profile deviations) are evaluated using the proposed method. It is found that the asymmetric core profile has a large influence on skew whereas that of the asymmetric core-cladding boundary is relatively small