长周期光纤光栅的分析和优化设计

利用传输矩阵法对相移和变迹长周期光纤光栅的传输特性进行了计算和分析,提出长周期光纤光栅传输谱的相移优化设计方法.采用非均匀相移的设计思想,优化长周期光纤光栅的传输谱.和传统的均匀相移和变迹长周期光纤光栅相比,可以有效消除长周期光纤光栅谐振波长附近的旁瓣,并保证其传输性能.计算和分析结果表明:这种方法比传统的变迹优化设计方法更有效.     

高频CO2激光脉冲写入的相移长周期光纤光栅

运用矩阵传输法，并结合长周期光纤光栅的模式耦合理论，阐述了相移长周期光纤光栅传输光谱的形成原理.利用高频CO2激光脉冲制作出相移长周期光纤光栅.该方法仅需用计算机绘制光栅结构图形，再由计算机依照此图形控制CO2激光器对普通光纤曝光，就可自动完成光纤光栅的制作.实际制造出一条相移长周期光纤光栅，在1520~1570 nm和1610~1670 nm波长范围内分别呈现出相移图样，相移波段的通带中心波长分别为1546 nm和1640 nm.对光栅进行温度测试，观测1610~1670 nm范围内相移光谱的变化，发现相移光栅的通带及阻带中心波长具有相同的温度变化系数，其数值为0.064 nm/℃，另外又测试了光栅的应变特性，灵敏度约为－0.51 nm/mε.因此在利用光栅温度特性或应变特性做传感的过程中，可以仅测试通带中心波长的变化，实现低成本多样化的测量手段.     

级联长周期光纤光栅的光谱特性研究

级联长周期光纤光栅的透射谱具有干涉峰的振幅大、谱型丰富等优点。利用传输矩阵法分析了级联及相移长周期光栅的光谱特性,研究了级联光栅间距、位置和相移对光栅谱的影响,并对级联及相移长周期光栅谱进行了比较。结果表明:两者光谱特性在光栅间距长度与光栅周期之比较小或级联位置靠近光栅两端时具有较强的一致性。对相移长周期光栅而言,当引入多个相移时,两个主阻带间的通带宽度随着引入的相移个数的增多而逐渐变宽。     

级联长周期光栅光谱特性

利用传输矩阵法分析了级联长周期光栅的光谱特性,讨论了级联处光纤的长度、位置以及包层模损耗系数对级联长周期光栅光谱的影响,并对级联长周期光栅和相移长周期光栅的光谱进行了比较。结果表明两者光谱存级联光纤长度较小或级联位置靠近光栅两端时具有较强的一致性,而在级联处光纤较长并且级联位置在中间时,两者表现出截然不同的光谱特性;在不考虑其他损耗的情况下,如果只改变级联处光纤长度,级联长周期光栅总量守恒;此外,当级联长周期光栅在级联处光纤包层模损耗系数较大时,级联长周期光栅的光谱等效于两个长周期光栅光谱的非相干叠加,从而为长周期光栅增益均衡器的优化设计和制作提供了一个简便有效的方法。     

级联长周期光纤光栅对的干涉谱分析及其在多信道滤波器中的应用

分析了由光纤级联的两个相同的长周期光纤光栅形成的干涉谱。根据设计中的关键技术,利用粒子群优化算法设计了长周期光纤光栅传输损耗为50％的平坦传输损耗谱.将相同的两个优化设计的长周期光纤光栅级联,可以实现一种实用的可调谐多信道隔离滤波器.讨论了级联长周期光纤光栅对之间光纤的偏振特性对干涉谱的影响.     

相移长周期光栅及其在增益谱平坦化中的应用

用耦合模方法和传输矩阵法相结合对长周期光栅的传输光谱特性进行了研究, 提出了用相移长周期光栅使双峰的增益谱线平坦化。理论证明, 实现这样的平坦化是可行的。     

相移光纤光栅耦合系数控制

为了通过遮挡法实现不同耦合系数π相移光纤光栅制作,分析了刻制过程中的相移形成原理,提出通过调整遮挡区长度和π相移周期次数控制π相移光纤光栅耦合系数的方法.采用传输矩阵法对刻制相移光纤光栅过程中的透射谱变化进行仿真计算,分析了不同光栅条纹可见度下遮挡区长度对相移光纤光栅透射谱的影响.基于不同遮挡区长度进行了相移光纤光栅制作实验,结果表明:通过调整遮挡区长度和π相移出现次数能够实现对相移光纤光栅耦合系数的有效控制.     

光纤光栅传输矩阵研究

利用模耦合理论给出并分析了一般坐标系下相移布喇格光纤光栅中的传输矩阵及其特性,所给出的传输矩阵具有分段不变性,而且不能被分解为一个矩阵和一个相移矩阵的乘积.利用该传输矩阵可以研究均匀、相移、啁啾、超结构等光纤光栅及光栅的级联等.计算了相移光栅的反射谱和相移量的关系,以及两个光栅级联时的反射谱.结果表明,同样相移量时的反射谱和已有文献不同,两个光栅级联时,也不同于已有文献,各自的谐振波长与光栅的级联没有关系.     

啁啾莫尔光纤光栅特性的研究

较全面地分析了啁啾莫尔光纤光栅的特性。介绍了啁啾莫尔光纤光栅的发展与应用前景。提出了利用薄膜传输矩阵的方法来计算光纤光栅 ,这种算法将光栅视为多层均匀薄膜的叠加 ,利用传输矩阵计算光栅特性 ,并将这种算法与其它相关算法进行了比较。作为一种滤波器 ,啁啾莫尔光纤光栅的透射特性尤为重要 ,针对这种光纤光栅的长度、啁啾量及相移等重要参数计算了光栅的透射率变化 ,并对结果进行了优化数值分析 ,得出了它们之间的关系     

长周期光纤光栅傅里叶模式耦合理论

建立了长周期光纤光栅傅里叶模式耦合理论.在分析同向模式耦合时,发现了同向耦合模式的振幅系数间存在傅里叶变换关系.推导了长周期光纤光栅的同向耦合谱和透射谱的通用表达式.该理论是用傅里叶变换分析得出长周期光纤光栅折射率微扰的空域谱,再对该空域谱进行模式同向耦合分析,从而得到长周期光纤光栅光谱特性的通用表达式.根据该理论模拟分析了长周期光纤光栅在不同长度和微扰幅值时的光谱特性,与传统耦合模理论进行了对比分析.结果表明,该长周期光纤光栅傅里叶模式耦合理论具有简单、精确和高效的特点,与实际长周期光纤光栅的透射谱特性一致.应用该理论可分析无过耦合的任意轴向折射率微扰分布的长周期光纤光栅光谱特性.     

光子晶体光纤中级联长周期光栅双谐振波长干涉的研究

通过分析单模光纤SMF中的LPG对的传输特性及几个因素对干涉透射谱的影响,并结合前期工作,主要研究光子晶体光纤(PCF)中的LPG对在1665 nm附近U波段传输特性.结合光栅耦合强度与波长的关系以及拍长与波长的关系,对PCF中LPG对的参数进行选择设计,得到双谐振波长的干涉谱,级联LPG对构成的MZI干涉光谱在两个谐振波长处由于耦合强度不同而不同.     

振幅掩膜紫外写入的长周期光纤光栅特性研究

振幅掩膜紫外写入的长周期光纤光栅的纤芯折射率分布函数为矩形波。以三层阶跃折射率光波导结构基础，用弱导标量近似和标量耦合模理论分析折射率调制类型为矩形波的长周期光纤光栅的特性。详细地给出耦合模方程近似处理的方法，并说明了其合理性。用数学软件Matlab进行了数值模拟计算，发现折射率调制类为矩形波的光栅传输谱不是由它的各次余弦光栅谱的线性叠加而成的。还研究了外部环境折射率、包层半径、栅占空比等光栅结构参量对矩形折射率调制的光栅传输谱的影响。同时指出了每阶包层模的双谐振峰位置随栅参量的变化规律。刊■刊『_型，刿j1     

Simultaneous spectral recovery of long-period grating sensor array using optical time-division multiplexing

A novel sensor network based on optical time-division multiplexing (OTDM) is proposed and demonstrated for simultaneous sensing of long-period grating (LPG) sensor array with overlapping spectra. A star network is configured by pairing a circulator with each of the LPG sensors. Experiments are conducted by measuring the changes of surrounding refractive index at different sensors, which show excellent agreement between the demultiplexed and pristine transmission spectrum of the LPG sensors.     

Optimization of a 2D photonic crystal add/drop multiplexer based on contra-directional coupling

We present a highly integrated add/drop multiplexer, where the contra-directional coupling is realized by phase matching two photonic crystal waveguides. The device band structure, the corresponding transmission and drop spectra, and the coupling length are carefully analysed. Different device configurations are discussed and by tailoring the coupling factor, we optimize the frequency response of the filter, obtaining a -sized channel selector, characterized by a very high drop efficiency.     

Design and analysis of two-dimensional photonic crystals channel filter

A novel three-port channel add/drop filter consisting of two waveguides and two cavities is proposed. One is used for a resonant tunneling-based channel add/drop operation from the bus waveguide to the add/drop waveguide, while the other is used to realize the wavelength-selective reflection feedback in the bus waveguide. By means of coupled mode theory in time, the conditions to achieve 100% add efficiency are derived thoroughly. Based on these theoretical analysis, the channel add filter and some other multi-channel filters are designed in two-dimensional photonic crystals (2D PCs) with square lattice of dielectric rods in air. The numerical results by using the finite-difference time-domain (FDTD) method demonstrate almost complete channel add/drop tunneling at resonance via the three-port systems.     

Analysis of reconfigurable multi-channel wavelength add drop multiplexer for intelligent optical networks

This paper presents design of an electro-optically tunable polymer multi-channel wavelength add drop multiplexer (WADM). The proposed WADM with trapezoidal waveguide geometry and poled electro-optical polymer material in the waveguide cores enables the wavelength tuning speed of WADM as 7.5 ps at the resonance wavelength of 1550 nm and coupling length of 1.5 mm. The device can be electro-optically tuned to add/drop multiple channels. Transmission spectra of the device with varying device parameters are simulated. The proposed WADM with high speed, small size and varying tuning capability makes this device, an important element in faster provisioning and routing of light paths in intelligent optical network.     

非对称熔锥法制作光纤光栅辅助耦合器型上下话路滤波器

通过在失配光纤消逝场间的耦合作用中引入光栅调制扰动效应，推导出用于解释光栅辅助耦合器响应特征的耦合模方程，在此基础上全面分析了两光纤间的失配度对上下话路滤波性能的影响.采用非对称熔融预拉锥工艺，调整光纤的结构参数，制成了性能良好的光栅辅助耦合器，实验测试结果与理论计算符合得很好. 关键词： 光纤光栅 光纤耦合器 上下话路滤波器 熔融预拉锥     

Complete pentagon orientational ordering in C60 fullerite charged with NO

Solid C₆₀ was stored in NO under high pressure, and the gas molecules NO were found to diffuse into the octahedral interstitial sites in its fcc crystal lattice. Its ¹³C NMR MAS spectra are composed of a primary resonance at 143.7 ppm accompanied by two minor peaks shifted 0.4 and 0.8 ppm downfield, respectively. The dopant was found to depress its phase transition temperature at 260 K in pure C₆₀ and to substantially reduce the drop Δ?′ at the phase transition temperature. Furthermore, the spectral features associated with relaxation during glass transition at lower temperature, as observed in impedance spectra, were smeared. The fraction of P-orientation below T _c was calculated to be larger than 11/12. These results show that a completely P-oriented phase occurred in (NO)_0.1C₆₀ and that this phase is favored by a negative pressure on the C₆₀ lattice exerted by NO, as well as by the electrostatic interaction between the two.