聚合物脊形光波导的变分有效折射率法分析

聚合物脊形光波导是聚合物集成光电子器件的重要构成单元.利用有效折射率法计算聚合物脊形光波导的横向折射率分布及有效折射率,将各区域中的光场分布近似用分段函数表达.基于导模满足的标量波动方程,利用变分法确定变分参量,以求得准确的横向光场分布.对聚合物脊形多模光波导基模和高阶模的色散特性与横向场分布进行分析,研究了波导结构参数对色散特性的影响,计算出TM基模和高阶模的光场分布,得出了聚合物脊形光波导的单模传输条件.研究表明,该方法计算量小、精度高,对聚合物光电子器件中脊形光波导的理论分析与设计优化提供了简单高效的方法.     

包含左手材料的四层平板波导中的光导模

研究一个芯子层是左手材料,其他三层由传统材料构成的四层平板光波导系统,利用图解法对各种TE偏振的导波模式的解进行详细分析.研究表明,四层左手材料光波导既能支持振荡导模,也能支持表面导模,与三层左手材料光波导相比较,此四层波导的导波模式呈现一些新的特性.对于中间传统材料层存在振荡场的情形:芯子层支持振荡导模的光波导中存在基模,并且高阶振荡导模出现模式缺失的性质;芯子层支持表面导模的光波导可以支持基模和多个高阶模式,并且存在模式兼并的性质.对于中间传统材料层存在衰减场的情形,此四层波导结构可等效为三层左手材料光波导.这些新的光波导传输性质对各种光波导器件的制作有潜在的应用价值.     

单模波导参数的双偏振测量

本文提出了单模波导参数(薄膜的折射率和厚度)的双偏振测量方法,给出了单模波导参数及其测量误差的计算公式,并测量了单模玻璃波导参数。测量结果表明,这个方法比单模波导参数的多波长测量简单,其测量精度接近波导参数的多模测量方怯。     

利用可见光测量近红外单模光纤的模场

光纤的模场分布是光纤最基本的特性,它包含了很多光纤的有关信息,单模光纤都工作在不可见的近红外波长范围内,且在可见光范围并非单模工作。提出了一种利用可见光测量近红外单模光纤模场直径的新方法,导出了一个考虑光纤材料色散的更精确地计算不同V值时模场直径的公式,设计了利用可见光直接拍摄模斑的系统,采用缠绕法提取基模,消除了高阶模对测量结果的影响,利用二元非线性曲面拟合,测得了光纤在近红外工作波长下的模场直径。由于无需红外光源、红外探测器以及精密的扫描装置,该方法具有成本低廉、测量速度快、调整容易等优点。     

聚合物脊形光波导TM模色散特性的偏振修正

有机聚合物脊形光波导的色散特性对聚合物光子学器件性能具有重要影响.本文利用标量变分理论计算脊形光波导的有效折射率,其用到的近似光场分布运用变分有效折射率法获得.考虑折射率分布的横向变化,基于导模满足的矢量波动方程,利用微扰法对标量变分理论所得有效折射率进行偏振修正,求得精度更高的色散特性.对聚合物多模脊形光波导基模和高阶模的色散特性进行分析,研究了波导结构参数对色散特性的影响,分析了单模波导TM、TE基模的偏振色散特性.研究结果表明,运用本征方程分析TM模的色散特性误差大,必须加以修正;而对于TE模,其误差相对较小.     

左手介质矩形波导导模和表面模的场分布

从麦克斯韦方程组出发,结合电磁场的边界条件,推导出介质矩形波导导模的一般色散方程.对普通介质矩形波导和左手介质矩形波导的导模场分布分别进行了数值模拟.通过对比两种介质矩形波导的导模场分布的模拟结果,发现左手介质矩形波导Ex22模的场分布比普通介质波导Ex00模的场更集中在波导中部.同时,根据处理普通介质矩形波导的Marcatili方法.类比得到左手介质矩形波导表面模的色散方程,并数值模拟了低阶模的场分布,结果表明,能量主要集中在波导的四个角区以及波导的边缘.     

测量单模光纤模场直径的一种新方法

本文根据单模光纤模场直径的横向位移定义,提出了一种测量模场直径的新方法——远场高斯掩模匹配法.讨论了几种测量及数据处理方法.最后给出了初步的实验结果.     

锥形光纤模场直径极小值特征研究

模场直径是光纤波导基模的特征参量。单模光纤中的功率密度与模场直径成反比。随着光纤激光器单模输出功率的不断攀升,纤芯中的功率密度不断增加,过高的功率密度会使光纤波导产生光学损伤和热损伤。基于锥形光纤模场分布近似模型,研究发现不同参数的拉锥光纤模场直径最小值位置对应的归一化频点具有规律性。采用有限差分波束传播法（FD-BPM）对不同波长、不同数值孔径下纤芯直径和模场直径的对应关系进行模拟,结果表明:模场直径最小值位置在归一化频率1.8附近,与光纤参数和波长的选取没有直接关系。这个特征参数可为高功率激光在光纤中功率密度最大值位置的快速确定提供依据,也为光纤光学理论增加了新的内涵。     

导模的功率衰减和转换特性的测量

本文在求解双模功率耦合方程的基础上,推得了导模的功率衰减和转换特性与光波导输入和输出功率的关系式.在离子交换玻璃波导上,将全息光栅和玻璃棱镜分别用作输入和输出耦合器,测得了光波导的输入和输出功率,并确定导模的功率衰减系数和功率转换系数.实验表明,这一测量方法是简便可行的,尤其适用于短波导样品的测量.     

五层MOS光波导TE模光学特性的简化分析

应用一种简化的方法对五层MOS光波导的光学特性进行了分析,给出了TE模传播常数和吸收损耗系数的近似计算公式,并结合计算结果检验了本方法及公式的精度,为实现波导中TE_0模低损耗单模传输,讨论了某些波导参量的选择.     

Radiation field propagation in low-contrast single-mode optical waveguides

In short waveguides used in integrated optical circuits, the radiation field is often present in the guiding region of a waveguide as well as the guided modes. We show that this can be investigated efficiently by extracting the radiation part from the total input field and simulating its evolution along the waveguide by use of the beam propagation method. The results are presented for a single-mode waveguide and a waveguide junction excited by a Gaussian beam. For a noncentred excitation, a considerable fraction of the radiation power is still in the guiding region after propagation over several tens of micrometres, and can be coupled to guided modes past the junction.     

Analysis of waveguide dispersion characteristics of WI- and WII-type triple-clad single-mode fibers

Waveguide dispersion characteristics of two kinds of triple-clad single-mode fibers named WI and WII were examined in this paper. In view of the impossibility to deduce the expression of waveguide dispersion directly due to the complexity of the characteristic equations, a feasible approach to calculate waveguide dispersion was established. The calculated results indicate that the adjustable range of the zero-dispersion point of the triple-clad WI- and WII-type single-mode fibers is obviously wider than that of the conventional doubly clad W-type single-mode fibers in the same conditions. The influences made by the geometric parameters and optical parameters on the waveguide dispersion and cutoff characteristics of low-order modes for WI- and WII-type fibers were analyzed. The method presented to calculate waveguide dispersion can be applied to multi-clad fibers.     

Multi-layer cladding leaky planar waveguide for high-power applications

We design a multi-layer cladding large-core planar waveguide that supports a single guided mode. The waveguide works on the principle of higher-order mode discrimination. The cladding of the waveguide is formed by alternate low- and high- index regions, which helps leaking out of higher-order modes while retaining the fundamental mode over the entire length of the waveguide. The structure is analyzed by the transfer-matrix method and the leakage losses of the modes have been calculated. We show that a waveguide formed in silica with numerical aperture 0.24 and core width 10 μm can be designed to exhibit single-mode operation at 1550-nm wavelength. Such a structure should find applications in high-power planar waveguide lasers and amplifiers.     

Characterization of circumferential guided waves in a cylindrical cortical bone-mimicking phantom

The femoral neck cortical shell was recently demonstrated to act like a waveguide for circumferential waves. Femoral neck assessment with ultrasound could be enhanced by guided waves measurement. In this study, the decomposition of the time reversal operator (DORT) method is used to measure the phase velocities of circumferential guided modes in a circular tube with dimensions characteristic of femoral neck. The tube is made of a bone-mimicking material. Five guided modes are obtained and compared to theoretical predictions. The work substantiates the feasibility of measuring guided waves in a relatively thick tube of attenuating material with the DORT method.     

Large-core single-mode channel waveguide based on geometrically shaped leaky cladding

We propose a leaky channel waveguide structure for large-mode-area single-mode operation. The proposed structure is characterized by a uniform rectangular core and a specially designed cladding, through which all the confined modes are leaky. Single-mode operation is ensured by choosing the waveguide parameters properly so that the differential leakage loss between the first two modes is sufficiently high. A general power-law cladding geometry profile is considered, which is solved by the effective-index method in conjunction with the transfer-matrix-method to obtain the effective indices and leakage losses of the modes. We show that, with a suitable choice of cladding parameters, the waveguide can demonstrate extended single-mode operation in the wavelength range 750–1600 nm with a core area as large as 100 μm². Such a large confinement area for mode propagation can effectively suppress nonlinear optical effects. The waveguide is expected to find applications in the design of high-power lasers and amplifiers. PACS 42.82.-m; 42.82.Et; 42.79.Gn; 42.55.-f; 42.82.Bq     

转移矩阵法在负折射率介质材料平板波导中的应用研究

利用严格电磁理论，推导出了适用于负折射率介质材料光波导的转移矩阵，分析讨论了转移矩阵的性质和应用.利用转移矩阵方法，推导出导波层为负折射率介质材料、覆盖层和衬底为右手材料的三层对称介质光波导的本征色散方程.用图解法研究了负折射率介质波导中TE波的异常色散特性.在负折射材料介质波导中没有零阶模，最低阶为1阶模，并且有截止频率,只有波导参量满足一定条件的时候才会存在，导模的横向波数可以为实数和纯虚数，而正折射率介质波导导模的横向波数只能为实数.     

三包层WⅠ和WⅡ型单模光纤波导色散特性的研究

研究了三包层WⅠ和WⅡ型单模光纤的波导色散特性。结果发现在相同条件下，三包层WⅠ和WⅡ型单模光纤零色散点的调节范围比传统的双包层W型单模光纤明显增大。详细分析了几何参量P、Q和光学参量R1、R2对单模传输时的波导色散特性和低次模截止频率的影响。所得的研究结果为获得更为理想的色散补偿、色散平坦光纤及设计新型无源光器件提供了重要的依据。计算波导色散的方法可推广到多包层光纤。     

光折变表面波诱导的薄层波导中的导波模式

利用数值模拟对扩散非线性机制下由光折变表面波诱导的薄层波导中导模的形成和特点进行了研究。采用分布傅里叶法对导模的传输特性进行了模拟。通过求解本征方程,对光折变表面波诱导的薄层波导中存在的导波模式进行了数值求解。通过调节传播常数和波导参数的方法,可以控制导模的阶数和传播波形。随着阶数的增加,导模轮廓的对称性越来越差;随着波导参数的增加,导模的峰值振幅单调递增。导模的能量主要聚集在晶体薄层波导中靠近-c轴的一侧,随着传播常数的增大,导模能量先减小后增大,且导模可以稳定传播。