线性啁啾光纤光栅的优化设计

基于线性啁啾光纤布拉格光栅的色散补偿原理，探讨了不同的准高斯型耦合系数函数曲线对色散补偿特性的影响，建立使该光栅色散补偿曲线既具有高色散系数和宽带特点，同时对边峰还有相对的抑制能力的设计思想。文中讨论了相关参数对色散补偿曲线的影响。     

线性啁啾光纤光栅色散补偿性能的数值分析

对线性啁啾光纤光栅的色散补偿性能进行了数值分析。结果表明 ,啁啾光栅时延曲线的纹波大小和线性度是影响其色散补偿性能的两个重要因素。对高斯型耦合系数分布光栅而言 ,更长的光栅将具有更佳的色散补偿性能     

啁啾光栅色散及时延特性研究

基于耦合模理论，通过对耦合波方程进行相位共轭变换，将反向耦合波方程变换为Ｒｉｃｃａｔｉ微分方程，利用数值解法对常耦合系数和高斯型耦合系数线性啁啾光栅的反射特性、色散特性和时延特性进行了详细分析，为设计具有理想效果的色散补偿器件提供了有效的理论方法。     

基于啁啾光纤光栅的掺Yb3+光纤激光器

啁啾光纤光栅可用于光纤色散补偿及脉冲压缩。该文从光纤光栅的耦合模方程出发，对中心波长为1053nm的啁啾光纤光栅进行了研究，数值分析了啁啾光纤光栅长度、耦合函数、啁啾系数、切趾技术等因素对啁啾光栅反射率、时延特性、色散特性、压缩特性的影响，并将结论应用于掺镱超短脉冲光纤激光器的设计，提出基于啁啾光纤光栅的全光纤环形腔连接方案。与其它非全光纤结构光纤激光器相比，这种结构具有更小的损耗和更高的效率。     

变迹啁啾Bragg光纤光栅的矩阵分析

本文用传输矩阵法分析了各种变迹与线性啁啾Bragg光纤光栅的响应特性,构造了各种变迹函数,进行了比较.分析了变迹函数、啁啾系数、折射率变化量以及光栅长度对反射带宽、最大反射率的影响.找到了最佳变迹函数和量佳啁啾系数.特例中的数值分析表明,补偿100km光纤色散带宽为1nm的最佳光栅长度是140mm,最佳啁啾系数为0.048nm/cm.     

光纤光栅耦合系数对其色散补偿性能的影响

本文利用耦合模方程,对具有不同函数形状耦合系数的光纤光栅的色散特性进行了理论和数值研究。通过比较这些线性咽啾光纤光栅对10Gb/s光通信系统色散补偿的效果,揭示了光纤光栅的耦合系数与其色散补偿性能的关系。     

光纤光栅非线性时延对啁啾的电视信号的影响

分析了有线电视系统中,用作色散补偿的光纤光栅因色散抖动对信号载波互调比产生的影响,结果显示色散抖动对有线电视信号互调比的影响随拦动幅度、抖动周期、信道数目的加而增加,信道频率的分布也对其的影响。对光栅的色散特性进行数值估算,发现常耦合系数线性啁啾光栅不能用的有线电视系统中进行色散补偿。     

薄包层啁啾长周期光纤光栅的色散补偿

为了提高啁啾长周期光纤光栅(LPFG)光纤通信的色散补偿能力,提出了利用薄包层啁啾LPFG进行包散补偿的方法.首先介绍了根据传输信号确定啁啾LPFG的啁啾系数、光栅长度等参数的方法.然后利用上述方法设计了对光纤中传输的中心波长为1550 nm,带宽为0.2nm的信号进行色散补偿的薄包层啁啾LPFG.利用耦合模理论及传输矩阵法计算了约1m长的此种啁啾LPFG的色散,结果表明可以补偿该光信号通过46 km光纤所产生的色散.进一步分析了切趾函数、啁啾系数、交叉耦合系数等参数对薄包层啁啾LPFG色散的影响.     

高斯脉冲在半导体光放大器中传输的解析表征

采用解析方法,在考虑材料损耗和色散的情况下,详细研究了无啁啾高斯脉冲和啁啾高斯脉冲在半导体光放大器中传输的物理过程,分析了强度增益、脉冲宽度和频率啁啾与线宽增强因子、色散系数、小信号增益特征参数及初始啁啾之间的关系。结果表明:当输入变换极限的高斯脉冲时,色散会引起增益压缩,脉冲展宽和频率啁啾;同样情况下,线宽增强因子越大,脉宽加宽越明显,输出脉冲啁啾越大,且随着线宽增强因子的增大,输出脉冲啁啾极大值向特征参数值较小的一边移动。当输入啁啾高斯脉冲时,初始脉冲啁啾越大,增益压缩越明显,啁啾系数为正时,脉冲单纯展宽,输出啁啾随特征参数的增大而逐渐减小,啁啾系数为负时,初始啁啾与群速度色散导致的啁啾相互竞争,致使脉冲先被压缩后被展宽;脉冲最窄处对应的特征参数随线宽增强因子的增大而先增大后减小,输出啁啾随特征参数的增大而经历振荡后趋于平稳。     

线性啁啾光纤光栅的耦合模理论分析

利用耦合模理论对线性啁啾光纤光栅的反射谱进行了分析,并详细讨论了耦合系数、啁啾系数、高斯分布参量、光栅长度对线性啁啾光纤光栅的反射带宽和最大反射率的影响.     

初始啁啾补偿光纤色散效应的适用范围

以啁啾高斯脉冲在单模光纤中的传输为例,分别就线性初始啁啾对光纤二阶和三阶色散的补偿进行了系统的理论分析和数值计算,结果表明：线性初始啁啾对光纤的二阶色散（线性色散）有一定的补偿作用,但不能有效地用于三阶色散的补偿.     

Optical pulse compression using the combination of phase modulation and high-order dispersion compensation

Optical pulse compression using high-order dispersion compensation is proposed and theoretically analyzed. Firstly, the required dispersion profile for the high-order dispersion compensation is derived, according to the linear chirp and the nonlinear chirp of a phase-modulated continuous-wave (CW) laser source. With the use of the high-order dispersion compensation, such as the combination compensation of the second order dispersion (SOD) and the fourth order dispersion (FOD), an efficient pulse compression having a less time-bandwidth product and a greater peak power is realized. A sampled fiber Bragg grating (FBG) with both the SOD and the FOD is then designed using the equivalent chirp and the reconstruction algorithm. Finally, in the numerical simulation an optical pulse with a time-bandwidth product of 0.79 is generated via high-order dispersion compensation that is performed by using the sampled FBG.     

色散渐减光纤中自相似脉冲传输特性研究

研究了在高阶色散影响下,自相似脉冲在具有正常色散的色散渐减光纤中的演化情况.结果表明:当考虑高阶色散的影响时,脉冲的啁啾仍然具有很强的线性特性,只是中心变得不对称,产生中心漂移.这种啁啾特性使得自相似脉冲在时域中的抛物线形状产生畸形,导致了脉冲峰向一边延迟,并使脉冲的中心位置漂移,同时伴随着脉冲边沿的振荡.但是通过采用色散补偿技术,自相似脉冲强的线性啁啾仍然可以得到高质量的飞秒量级压缩脉冲,与忽略三阶色散影响时得到的压缩脉冲的脉宽近似相等.     

Numerical Study on the Performance in High bit rate Optical Communication Systems

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Soliton switching and propagation in two-core nonlinear fiber coupler with high order coupling coefficient

We use the variational approach (VA) and the split-step Fourier transforms (SSFT) to study the transmission and switching characteristics inside the fiber nonlinear directional coupler (NDLC). The results, based on the VA, indicate that the second-order coupling coefficient dispersion and initiative chirp all reduce the coupling length, and the second-order coupling coefficient dispersion makes the switching characteristics become sharper and threshold power become bigger under the case of not having initiative chirp. The outcomes, based on the SSFT, indicate that the first order intermodal dispersion coefficient make optical pulses splitting in the propagation of fundamental solitons, and the second-order coupling coefficient dispersion reduces the coupling length, sharpens the switching characteristics and increases the switching threshold power, the results agrees well with those from the VA.     

Impacts of polarization mode dispersion on the pulse-width with considering initial pulse chirp and fiber GVD

The impacts of polarization mode dispersion (PMD) on the pulse-width in linear systems have been investigated. The analytical solutions, including the effects of initial frequency chirp and group velocity dispersion (GVD), are derived. Analyses show that the pulse broadening effects induced by the second-order PMD depend on GVD and chirp parameter, which are different from those induced by the first-order PMD. An initially chirped Gaussian pulse is taken as an example, upon which analytical solutions of rms pulse-width are derived before and after the first-order PMD compensation. The first-order PMD compensator is also evaluated based on these solutions. The results show that the pulse broadening effects will be resisted efficiently by choosing appropriate GVD and chirp parameter; in general, the post-transmission compensation method will be less efficient than the PSP-transmission method.     

Multiple-order adaptive dispersion compensation using polynomially-chirped grating devices

Devices such as the planar arrayed-waveguide grating or the distributed Bragg reflector (AWG and DBR, respectively) are assuming increasing importance in the areas of fibre point-to-point communication and networking. In the particular context of dense wavelength-division multiplexing (DWDM), these devices play a well-established role as wavelength-selective elements. More recently, chirped variants have found use as dispersion compensators, offering wideband reduction of both basic and higher-order departures from constant group delay. However, up to the present time, the existence of a systematic approach to higher-order dispersion compensation has not been recognised. Additionally, we have identified a comprehensive isomorphism between AWG and DBR devices that allows the design characteristics of the former transverse geometry to be mapped on to the latter longitudinal structure. Here, we present a systematic study of these important passive optical grating-based devices which considers, firstly, analytic solutions for 2nd-order dispersion compensation (DC), and then 3rd- and 4th-order dispersion compensators with 100 GHz bandwidth. We then review optimisation strategies for DC, 3 dB bandwidth, and passband dispersion ripple, as determined by device chirp, apodisation, coupling strength and polyphase transfer function superposition. We conclude with a preliminary discussion of grating parametric sensitivity as evidenced by Monte Carlo analysis. Received: 22 May 2001 / Revised version: 31 July 2001 / Published online: 2 November 2001     

Chirp elimination using a linearly chirped fiber grating

Gain-switched distributed feedback laser diodes (GS-DFB-LD) with high repetition bit rate have large frequency chirp. Conventionally, the F–P spectrum filter and normal dispersion fiber were used to eliminate chirp in GS-DFB-LD pulse sources. In this paper, a new method for eliminating chirp of high repetition pulses generated from DFB laser diodes is proposed. The use of a linearly chirped fiber grating for chirp elimination is discussed theoretically and numerically. A new apodized coupling profile function for the grating, which we call it the inverse Gaussian, is given. Its characteristics are analyzed and compared with other profiles. The numerical results are in agreement with the theoretical analysis.     

受激喇曼散射对自相似脉冲产生的影响

研究了在受激喇曼散射与三阶色散共同作用下,自相似脉冲在具有正常色散的色散渐减光纤中的演化情况.结果表明:在同一个传输距离上,当考虑受激喇曼散射与三阶色散的共同影响时,脉冲中心的不对称特性相对好转;产生中心漂移与边缘振荡较只有三阶色散作用时要减弱,啁啾仍然具有很强的线性特性,但是线性范围减小,导致频谱的窄化以及对接下来自相似脉冲的压缩产生了不利影响;而且光纤长度的延长并没有起到展宽啁啾线性范围的效果,反而导致严重的啁啾非线性;因此对脉冲进行压缩后,压缩脉冲质量较不考虑受激喇曼散射时要差.