一种实现光纤激光器高功率输出的方法

 介绍了一种实现光纤激光器高功率输出的新方法——采用螺旋芯光纤，这种光纤是在光纤制作过程中按照一定的弯曲半径使纤芯呈螺旋状排布在光纤包层中。介绍了这种螺旋芯光纤的原理和其提高输出功率的能力，以及目前的理论与实验研究现状。基于该光纤，提出了一种光纤激光器相干合成新思想。     

一种实现高功率输出的新型光纤激光器

介绍了一种实现光纤激光器高功率输出的新方法--采用螺旋芯光纤,这种光纤是在光纤制作过程中按照一定的弯曲半径使纤芯呈螺旋状排布在光纤包层中.介绍了这种螺旋芯光纤的原理和其提高输出功率的能力,以及目前的理论与实验研究现状.基于该光纤,提出了一种光纤激光器相干合成新思想.     

多层光纤布拉格光栅的理论与实验研究

从理论和实验两方面研究了在非周期性多层光纤上写入布拉格光栅的光学特性。从耦合模理论出发,讨论了光纤具有多于一个光敏层的情况。在实验室自制的两类多层光纤上写入光栅的实验也表明,该类光栅具备有一般光栅的普遍光学特性,说明在使用多层光纤作为关键部分构建器件时,需要的各类光栅部件能够通过直接在该类光纤上写入光栅实现。紫外光在氢载掺铒多层光纤上写入光栅的实验说明分层的异种元素掺杂将导致芯区应力增加,从而辅助提高光纤的光敏性。     

相移长周期光栅长度切趾光谱特性

应用耦合模理论和传输矩阵法分析了长周期相移光栅的光谱特性,比较了折射率切趾和长度切趾所产生的不同光谱结构,并分析了长度切趾中不同的切趾函数及光栅长度对光谱结构的影响.讨论了长度切趾的旁瓣增强效应,发现了一些新的有益结果.     

Theoretical analysis of novel fiber grating pair

A novel fiber grating pair that consists of a conventional long-period fiber grating and a fiber Bragg cladding grating (FBCG) is proposed. The FBCG is a new type of fiber grating in which refractive index modulation is formed in the cladding. Through the coupled-mode theory, we accurately calculate the coupling coefficients between modes supported in the fibers. And some other mode coupling features in the fiber cladding gratings are analyzed in detail. The calculation of the modes involved in this paper is based on a model of three-layer step-index fiber geometry. Then, we have investigated the sensitivity characteristics for variation of the modulation strengths of the fiber Bragg cladding gratings’ resonance peaks and the long-period cladding gratings’ (LPCGs) dual resonant peaks. Finally, the modulation strength sensitivity of the grating pair’s three resonant peaks is demonstrated, and the results indicate that these grating pairs may find potential applications in optical fiber sensing.     

Cladding-mode-assisted recouplings in concatenated long-period and fiber Bragg gratings

We investigate new types of mode recouplings in a concatenated grating structure comprising a long-period grating and a fiber Bragg grating. It is demonstrated that the light coupled out to the cladding mode by one of these gratings can be recoupled back to the guided mode by the other grating. Theoretical analysis based on the coupled-mode theory is presented, together with experimental results.     

长周期光纤光栅透射谱计算方法的比较与分析

长周期光纤光栅透射谱的求解方法有多种,本文以耦合模理论为基础,对常用的积分法、公式法、传输矩阵法求解长周期光纤光栅的透射谱进行比较与分析,指出这三种求解方法各自的特点和适用条件.积分法可在较宽波长范围内直接得到多个模式透射谱的精确解,但求解过程繁琐,运算量大;公式法虽然在表述和计算上较为方便,但只能在较小波长范围内直接求解单个模式的透射谱;传输矩阵法求解过程简便、准确度高、计算量相对较小,特别适合计算一些非均匀光纤光栅的透射谱.该研究为选择一种精确度高且理论和计算都较简单的计算长周期光纤光栅透射谱的方法提供理论依据.     

折射率直流分量调制对光纤Bragg光栅的影响

从耦合模理论出发,推导了折射率直流分量调制函数与光纤Bragg光栅相位之间的关系式,分析了折射率直流分量调制对光纤Bragg光栅时延特性的影响.利用传输矩阵法进行了数值仿真,仿真结果与理论分析一致.在理论分析基础上,提出采用同一块均匀相位掩膜版灵活制作具有不同线性或非线性时延特性的啁啾光纤光栅的方法,可用于高速光通信系统中不同色散和色散斜率的补偿.     

Coupled-mode analysis of fiber-optic add drop filters for dense wavelength-division multiplexing

We present a coupled-mode theory of fiber-optic add-drop filters, which involve directional coupling between two fibers combined with fiber Bragg gratings defined inside the coupling region. The analysis self-consistently accounts for both the directional and the reflection coupling, and the propagation constants and structure of the supermodes of the combined structure are derived. We present a detailed analysis of a filter design based on identical fibers. The calculated device parameters satisfy the requirements for dense wavelength-division multiplexing applications.     

Characteristics of Multiply π Phase-shifted Long-period Fiber Gratings

The transmission spectra of multiply π phase-shifted long-period fiber gratings (LPFG's) are analyzed by a combination of coupled-mode theory and the fundamental matrix method. The theoretical simulation shows that the LPFG' s can act as novel bandpass filters with two dominant passbands when multiple π phase-shifts are introduced at particular locations along the grating.     

Characteristics of Multiply π Phase shifted Long period Fiber Gratings

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Bending sensitivity of in-series long-period fiber gratings

The interference fringes formed in a long-period fiber grating pair are sensitive to the loss in the cladding mode, which can be induced by bending or by coating on the fiber. Assuming that there is no loss and that both gratings are identical, the interference fringes are shown to have 100% contrast when each grating has 50% transmissivity. By contrast, if the cladding mode is absorbed or scattered the fringe contrast is shown to be degraded. The spectral behaviors of a long-period fiber grating pair with loss is analyzed by the coupled-mode theory and is compared with experimental results.     

Coupled-mode analysis for linear fiber Bragg grating made of metamaterial

We derive the coupled-mode equations for a metamaterial fiber Bragg gratings (FBGs). The coupled-mode theory describing wave propagation in periodic structures such as FBG is generalized for studying the transmission and reflection of electromagnetic waves through a FBG containing metamaterial layers. This approach shows that the band gap becomes broader in comparison with a conventional FBG. It is observed that the central frequency of the band gap has a shift in regard of changing metamaterial thickness. We verify this investigation through attaining the transmission and reflection spectra of a conventional FBG while we are setting related parameters. Furthermore, this proposed structure can be applied as a tunable filter.     

A New Method of Solving Multimode Coupled Equations for Analysis of Uniform and Non-Uniform Fiber Bragg Gratings and Its Application to Acoustically Induced Superstructure Modulation

A new and simple mathematical formulation that is employed to analyze numerically coupled-mode equations modeling uniform and non-uniform gratings in optical fiber is investigated. This method would be straightforward and thus beneficial to solve multimode coupled equations in comparison with a previously used fundamental matrix method, and the Runge--Kutta algorithm. The new formulation proposed in this study is applied to calculate transmission and reflection spectra of core mode and higher-order cladding modes of acoustically induced superstructure modulation caused by microbending through fiber Bragg gratings (FBGs). Co-directional and contra-directional couplings based on acoustically induced modulation in FBGs have been discussed for a variety of induced coupling coefficients.     

磁光光纤Bragg光栅中圆偏振光的非线性传输特性

提出了磁光光纤Bragg光栅的理论模型,给出了圆偏振光在磁光光纤光栅中传播的非线性耦合模方程. 研究表明,在磁光光纤Bragg光栅中,光栅引起正反传播方向的导波光发生耦合,法拉第效应引起磁圆双折射效应,而非线性效应则将左旋和右旋圆偏振光耦合在一起,它们的共同作用可使双稳态状态发生反转、非线性光控光开关阈值功率降低. 与传统光纤光栅相比,利用左旋和右旋磁圆偏振光之间的交叉相位调制实现的脉冲整形具有磁光偏置可调特性,为基于磁光光纤光栅的动态灵活全光3R再生器的研制提供了理论基础. 关键词： 磁光光纤Bragg光栅 圆偏振光 脉冲整形     

Characteristics of light polarization in magneto-optic fiber Bragg gratings with linear birefringence

The coupling between guided optical waves in magneto-optic fiber Bragg gratings(MFBGs) with linear birefringence is investigated using the eigen-mode and coupled-mode approaches.The relationship between the polarization-dependent loss(PDL) and the eigen states of polarization(SOPs) in the MFBGs is discussed.Only the MFBGs with low linear birefringence are applied to the peak PDL-based magnetic field measurement,after which the linear dynamic range is determined using the relative magnitude of linear and mag...     

均匀光纤布拉格光栅的反射偏振相关损耗特性

研究了单模光纤布拉格光栅的偏振相关损耗(PDL)特性.运用耦合模理论和琼斯(Jones)矩阵提出了反射光的有效偏振相关损耗(PDLeff),并模拟r其随光栅参数和双折射量的变化性质.光栅反射光的偏振相关损耗在反射谱的带边处明显地表现出来,特别是带边比较陡峭时.结果表明,光栅的有效偏振相关损耗明显地依赖于光栅的结构参数和...     

Analysis of spectral characteristics for reflective tilted fiber gratings of uniform periods

On the basis of the coupled-mode theory, a detailed investigation of the optical spectral characteristics is presented for uniform tilted fiber gratings. Explicit expressions are derived for the spectral parameters of reflection and transmission spectra. Numerical simulations are carried on to show the dependences of grating spectral responses on the structural parameters, such as tilt angle, grating length, index modulation amplitude and polarization states. The effects of these parameters on shaping the grating spectra are discussed comprehensively. The physical mechanism and intuitive phase-matching vector model are provided to explain the unique behaviors of transmission loss spectra. The results are helpful for providing a better understanding of the spectral behavior of the tilted fiber grating.     

极窄带宽的布拉格光纤光栅光谱特性研究

根据理想模展开下的耦合模方程，对光纤布拉格光栅的峰值反射率公式进行了数学推导，得到了布拉格光纤光栅的光谱反射率表达式。全面讨论了光栅周期、光纤栅长、光致折射率微扰最大值等参数与光纤光栅反射光谱的关系。仿真结果显示了固定参数下布拉格光栅的极限窄带宽，得到的反射率为1、带宽为0.02nm的窄带宽布拉格光栅，比现今分布式传感系统中使用的布拉格光栅的带宽窄1个数量级。这种布拉格光纤光栅用于分布式传感系统，可大大提高分布式传感系统中光源的带宽利用率，消除各信号间的相互串扰，提高传感光栅复用数目，降低解调系统成本。     

金属镀层两层膜系长周期光纤光栅谐振特性研究

采用严格的耦合模理论,建立了镀会属膜和敏感膜的两层膜系长周期光纤光栅复特征方程,用微扰法对复数超越特征方程进行求解.结果和文献[5]给出的数据相符.理论模拟数据表明.金属的消光系数对功率密度和透射谱影响很大.低阶偶次模式在纤芯内的功率密度所占比重远大于奇次模式,其衰减峰幅度也比奇次模高,因此,金属镀层长周期光纤光栅实际应用时,需要选择偶次模作为研究对象.进一步理论分析了金属和敏感膜层参数对长周期光纤光栅谐振特性的影响,研究发现,金属膜厚、敏感膜厚和折射率对谐振波长有较大的影响,谐振波长随金属膜厚、敏感膜厚和折射率的增大向短波方向漂移.在某些区域谐振波长存在跳变现象,长周期光纤光栅实际应用时应避开此区域.