多层介质波导的一种新方法及其在非均匀介质平面光波导中的应用

本文提出求解多层介质平面光波导的一个简单而直接的方法。将其应用于非均匀平面光波导,可以求解任意折射率分布和TM模问题。以抛物线型和指数型分布为例,说明只要分层数目足够多,本文介绍的方法可以达到任意精度。     

宽带波长可调固体染料光放大的实现

对有机染料4－Dieyanomethylene-2-methjyl-6-(p-dimethylaminostyryl)-4H-pyran(DCM)掺杂的PMMA（聚甲基丙烯酸甲酯）以及DCM掺杂的PMMA／凝胶玻璃复合材料平面光波导中的放大自发辐射进行了研究。实验表明,通过合理地控制波导层的折射率及厚度,可以在较宽范围内选择放大自发辐射的波长,从而实现波长调谐,波长调谐范围可达30nm。该方法可应用于固体可调谐激光器及光放大器的宽带调谐。     

新型光波导阵列电光快速扫描器的光波导效应

对新型光波导阵列电光快速扫描器中的光波导效应进行了研究,分析了考虑光波导模式效应的光波导阵列电光快速扫描器的扫描特性,指出光波导模式特性主要影响新型光波导电光快速扫描器的扫描范围和效率,并研究了在应用该器件进行光束扫描时的技术要求.     

星形光波导耦合器的耦合特性分析

根据TE0模光波导的本征场分布、瑞利索末菲标量衍射积分公式和激励源与光波导耦合的匹配效率公式,给出光波导端面衍射和耦合的归一化发射系数和接收系数计算公式,推导出光波导端面非接触耦合的耦合效率计算公式。光波导模场分布采用高斯函数近似表达,给出简洁的计算光波导端面非接触耦合的耦合效率函数表达式。最后,基于星形光波导耦合器结构参量的特点,将累加运算采用积分运算近似表达,给出星形光波导耦合器接收光波导总的接收效率与耦合器基本参量的关系,阐明了星形光波导耦合器的耦合特性。     

W.K.B近似法应用的拓宽

本文将Ｗ．Ｋ．Ｂ近似法拓宽到缓变参量条件下的计算，类比了量子理论中的结果，并就渐变折射率光波导和平面分层介质两种模型为例做了探讨。     

新型电光扫描器中光波导阵列特性研究

利用有限差分光束传输法(FD-BPM)详细研究了光波导阵列电光扫描器的核心部件—光波导阵列的传输特性和辐射特性,分析了光波导阵列结构参量对其传输特性和辐射特性的影响.研究结果表明,光波导芯层厚度、光波导阵列的周期、长度和层数对光波导阵列输出面上的光场振幅、相位分布及光波导阵列输出光束主瓣的半峰值全宽度(FWHM)影响很大.通过与其它理论研究的结果进行比较指出,FD-BPM可以很方便地、更全面地描述光波导阵列的传输和辐射特性.另外,在研究光波导阵列光束扫描的基础上,根据光波导阵列电光扫描器的扫描探测要求,提出了光波导阵列结构优化设计的原则.     

左手介质椭圆光波导基模传播特性

在椭圆柱坐标系中,采用分离变量方法,得出了左手介质椭圆光波导本征方程的近似解,通过数值计算,分析了椭圆波导偏心率、左手介质的电容率、磁导率对椭圆光波导基模传播特性的影响,并将左介质光波导与右手介质光波导基模特性进行对比,得出左手介质光波导的基模特性与右手介质光波导基模特性差别不大的结论.     

基于硅波导的喇曼光放大器

在硅波导上添加反向偏压的PIN结构,当波导产生受激喇曼散射时,可以将波导中双光子吸收(TPA)产生的光生自由载流子扫出波导,降低了波导的非线性损失,极大地提高了硅波导中泵浦光对信号光的喇曼增益。为了应用已经非常成熟的硅工艺,并且应用硅波导使器件小型化,根据法布里-帕罗(F-P)腔和行波放大器理论,在硅波导两端的解理面蒸镀增透膜,应用这种波导的喇曼效应设计了一种光放大器,即基于硅波导的喇曼光放大器。建立了计算放大器增益的方程,给出了不同波导长度和输入功率情况下的放大器增益,得出适当增加波导长度和泵浦光功率可以得到较高喇曼增益的结论。基于硅的光放大器有较高的饱和功率且没有泵浦源的限制,通过调整泵浦激光的波长可以放大不同波长的信号光。     

光电集成与器件

从信号光及泵浦光在波导内的模式分布出发,提出了一种新的重迭因子的分析方法,对1 480 nm波段泵浦的掺饵光波导放大器(EDWA)进行了研究。探讨了光波导截面面积对EDWA增益的影响,得出了波导获得最大增益的波导截面面积范     

应用光学——光学系统设计指南

第十三章集成光学和纤维光学 13.1.4 波能的耦合光从一元件传输到另一元件是通过辐射耦合方式完成的。当光从辐射源进入光波导和从光波导输入到探测器时,就会出现耦合问题,当光从一波导输入另一波导的时候,在这两个光波导之间也会出现这个问题。实现这种耦合可以采用多种机理。     

Linear and nonlinear coupling properties of a novel multicore circular dielectric waveguide

In this work we investigate the linear and nonlinear coupling properties of a novel multicore circular dielectric waveguide. The proposed device consists of a circular central core and many circular sectoral cores at the periphery, while the whole structure can be considered as a nonlinear multicore composite optical coupler. Hybrid guided modes in a circular sectoral dielectric waveguide are derived using circular harmonic expansion for the electromagnetic fields and the Point Matching Method (PMM) for the application of boundary conditions. Several cases are investigated varying some of the parameters of the geometry and the optical frequency in order to produce dispersion diagrams. In advance, the electric and magnetic field distributions for the fundamental guided modes are produced, while linear and nonlinear coupling coefficients as well as the sectoral waveguide mode effective area are derived.     

Optically S-polarized surface waves in symmetrical nonlinear sensors: Thermal effects

A surface wave in a planar nonlinear waveguide is a current problem that has several applications in modern electronics and optics such as optical sensors design. The effect of thermal stress on the optical performance of a nonlinear symmetrical sensor is studied. The mathematical forms of the dispersion equation and thermal-stress sensitivity are analytically derived and plotted numerically. It is found that the thermal sensitivity of the sensor can be controlled by tuning the core size, by changing the loading materials, and by carefully selecting the materials.     

Measurement of the nonlinear optical response of optical fiber materials by use of spectrally resolved two-beam coupling

We present measurements of the femtosecond nonlinear response of fiber waveguide materials, obtained with spectrally resolved two-beam coupling. This simple but sensitive technique provides all the parameters that characterize the third-order nonlinear optical response, including the dynamics. Measurements are made with nanojoule-energy pulses from a mode-locked Ti:sapphire laser and a few millimeters of waveguide preform, without the need for drawing fiber.     

Dispersion modified slot optical waveguides

Advent of slot waveguide structures had opened a new era where light can be confined in low index slot guarded by high index slabs. Already in use SOI slot waveguides (contrast ratio is 2.42) have two distinct properties over the conventional waveguides, i.e. high E-field amplitude, optical power, optical intensity in low index materials, and strong E-field confinement localized to nanometer-size low index regions. We hereby propose a low refractive index contrast ratio slot waveguide structure (ratio is 1.18) comprising of commercially available glass material. Novelty lies in showing high E-field amplitude, optical power, optical intensity, and strong E-field confinement in low index slot regions despite of lowest ever reported contrast ratio. A systematic numerical study on the higher order dispersion characteristics of the widely studied SOI-based slot structure and of our proposed low refractive index contrast slot structure is carried out. It has been demonstrated that low refractive index contrast ratio slot optical waveguide GVD properties are quite different than SOI slot optical waveguide. The less normal dispersion existing in this kind of waveguide could have an impact on their applications in various nonlinear or linear applications.     

The nonlinear refraction sign turned to reverse by intercalating cresyl violent dye into layered titanate nanosheets

Solid-state dye-doped materials are an attractive alternative to conventional liquid dye solution. In this study, the spectral characteristics of dye cresyl violet before and after intercalating into layered titanate nanosheets and forming a nanohybrid thin film were investigated by measuring absorption and fluorescence spectra. In addition, their nonlinear optical properties were studied using single beam z-scan technique under irradiation of low power continuous wave (CW) produced by DPSS laser with a wavelength of 532 nm. The nonlinear studying results reveal that the dye cresyl violet in solution has a negative nonlinear refractive index, but it reverses to positive after the dye is intercalated into layered titanate nanosheets with a negative nonlinear refractive index forming CV/HTO nanohybrid thin film. This method can provide a way to turn to reverse nonlinear refraction sign of the materials.     

基于双矩形腔边耦合波导的等离子体诱导透明效应

为了降低功耗、实现超快速响应,设计了一种基于双矩形腔边耦合等离子体波导系统,并研究了其等离子体诱导透明效应.采用光学Kerr效应超快调控石墨烯-Ag复合材料波导结构,实现1 ps量级的超快响应时间.动态调控等离子体波导的传输相移,当泵浦光强为5.83 MW/cm^2时,等离子体诱导透明系统能够实现透射光谱π相移,这是因为基于石墨烯-Ag复合材料结构等离子体波导具有大的等效光学Kerr非线性系数,表面等离子体激元局域光场和等离子体诱导透明效应慢光对光学Kerr效应产生了协同增强作用,大大降低了系统获得透射光谱π相移的泵浦光强.等离子体诱导透明效应透明窗口的可调谐带宽为40 nm,系统的群延时控制在0.15 ps到0.85 ps之间,并且光波通过间接耦合或者相位耦合机制实现了等离子体诱导透明效应相移倍增效应.耦合模式理论计算结果很好地吻合了时域有限差分法仿真模拟结果,研究结果对于低功耗、超快速非线性响应和紧凑型光子器件的设计和制作具有一定的参考意义.     

亮孤子在宇称时间对称波导中的传输和控制

基于光波在宇称-时间(PT)对称波导中传输的理论模型, 数值研究了亮孤子在呈高斯分布的PT对称克尔非线性平板波导中的传输和控制. PT对称波导, 要求波导的折射率分布呈偶对称, 而增益/损耗分布呈奇对称. 结果表明: 当波导的折射率分布强度为正时, PT对称波导的中心折射率最大, 即使没有自聚焦克尔非线性效应, PT对称波导也可以束缚光波, 形成波浪形光束且长距离传输; 当折射率分布强度为负时, PT对称波导的中心折射率最小, 光波的传输方向发生偏移. 而增益/损耗分布可控制光波的偏移方向: 增益/损耗分布强度为正, 光波向左偏移; 强度为负, 光波向右偏移; 强度为零时, 光波被分为两束. 且当折射率分布强度为负时, 可以很好地抑制相邻亮孤子间的相互作用. 该研究结果可为未来PT对称波导在全光控制方面的应用提供一定的理论依据.     

Enhanced nonlinear optical responses of materials: Composite effects

We review recent theoretical progress in understanding physical processes of composite effects on enhanced third-order nonlinear optical responses of various kinds of the recently-proposed nonlinear optical materials, namely, colloidal nanocrystals with inhomogeneous metallodielectric particles or a graded-index host, metallic films with inhomogeneous microstructures adjusted by ion doping or temperature gradient, composites with compositional gradation or graded particles, and magneto-controlled ferrofluid-based nonlinear optical materials.     

Optimization design of optical waveguide control by nanoslit-enhanced THz field

We discuss design issues of devices which were proposed recently [Opt. Lett. 37 (2012) 3903] for terahertz (THz) control of the propagation of an optical waveguide mode. The mode propagates through a nonlinear dielectric material placed in a metallic nanoslit illuminated by THz radiation. The THz field in the slit is strongly localized and thus significantly enhanced, facilitating nonlinear interactions with the dielectric waveguide material. This enhancement can lead to notable changes in the refractive index of the waveguide. The closer the waveguide is to the slit walls, the higher the nonlinear effects are, but with the cost of increasing propagation losses due to parasitic coupling to surface plasmon polaritons at the metal interfaces. We analyze several optical waveguide configurations and define a figure of merit that allows us to design the optimal configuration. We find that designs with less overlap of the THz and optical fields but also with lower losses are better than designs where both these parameters are higher. The estimated terahertz field incident onto the metallic nanoslit required to manipulate the waveguide mode has reasonable values which can be achieved in practice.     

辛体系下利用棱单元的电磁波导的计算

为了解决复杂形状横截面的电磁波导问题,根据电磁波导的Hamilton体系,在辛几何形式下采用有限元半解析横向离散的方法对电磁波导进行求解.该方法可应用于任意各向异性材料,且便于处理不同介质的界面条件,求解用解析方法难以求解的复杂问题.利用棱单元进行有限元离散,给出矩形波导、T隔膜矩形波导、分层波导等多种波导的具体算例,其数值结果逼近于真实解,且伪解消除,表明该方法有效.