Time-domain finite-difference beam propagation method

A new technique to model the behavior of pulsed optical beams in waveguides is proposed and analyzed. The technique is an extension of the traditional continuous-wave beam propagation method (BPNI) to include time dependence, therefore called the time-domain BPM (TD-BPM). The method was tested using different waveguide examples and it is concluded that the technique is simple and accurate. Compared with the finite-difference TD method, the new TD-BPM is more efficient in terms of computer memory and execution time especially for large optical devices     

Slow-wave finite-difference beam propagation method

By invoking the slow-wave approximation, the wave equation resumes the form of the Fresnel equation. Codes developed previously for the paraxial beam propagation can be extended to simulate the backward reflection and diffraction at any angle. Results of planar waveguide gratings and a beveled corner bend are presented     

A finite-difference vector beam propagation method forthree-dimensional waveguide structures

A finite-difference vector beam propagation method (FD-VBPM) for three-dimensional waveguide structures is developed. The polarization dependence and coupling of the optical guided-waves in the 3-D structures can be modeled and simulated     

Explicit finite difference vectorial beam propagation method

A vectorial beam propagation method (VBPM) is formulated and implemented using the explicit finite difference (EFD) scheme. The accuracy of semivectorial EFD-BPM, where the polarisation coupling is ignored but polarisation dependence is included, is found to be as good as that of full-vectorial EFD-BPM.<>     

Dielectric lens analysis using vectorial multimodal gaussian beam expansion

A dielectric lens is analyzed using vectorial multi-modal Gaussian beams. The basic points are reminded and theoretical tools are developed to treat a complete lens. Results are finally presented which allow discussion about the multiple reflections and the radial truncation effect on the radiation pattern.     

The finite-difference vector beam propagation method: analysis andassessment

The newly developed finite-difference vector beam propagation method (FD-VBPM) is analyzed and assessed for application to two-dimensional waveguide structures. The general formulations for the FD-VBPM are derived from the vector wave equations for the electric fields. The stability criteria, the numerical dissipation, and the dispersion of the finite-difference schemes are analyzed by applying the von Neumann method. Important issues regarding the implementation, such as the choice of reference refractive index, the application of numerical boundary conditions, and the use of numerical solution schemes, are discussed. The FD-VBPM is assessed by calculating the attenuation coefficients and the percentage errors of the propagation constants of the TE and TM modes of a step-index slab waveguide. Several salient features of the FD-VBPM are illustrated     

Spurious modes in the DuFort-Frankel finite-difference beam propagation method

In this letter, we analyze the DuFort-Frankel beam propagation method (BPM) which is a modification to the known explicit finite-difference beam propagation method (EFD-BPM) and found that there are some precautions that must he taken before using the method. The accuracy and the efficiency of this method has been shown and compared with the most popular FD-BPMs.     

Novel finite-element formulation for vectorial beam propagationanalysis in anisotropic medium

A novel full-vectorial finite-element beam propagation method for dielectric anisotropic media is presented. This computationally efficient approach uses only the transverse magnetic field components and is free of spurious solutions. Comparisons with other numerical and experimental results validate the method     

An improved finite-difference vector beam propagation formulationfor graded-index waveguides

An improved finite-difference vector beam propagation formulation for graded-index waveguides is presented. The modification over the existing version involves a more accurate representation of the Fresnel operator in finite-difference form that accounts for the gradient of the refractive index in the vector Hehmholtz equation. The modified scheme is assessed by calculating the TM mode propagation constants of single-mode planar guides that yield better agreement to the exact values over the existing scheme. Furthermore, the calculated coupling lengths of a vertical directional coupler show improved comparison to experimental data     

三维有限差分光束传输法在AWG中的应用

文章以亥姆赫兹方程为基础,推导了三维有限差分光束传输法(FD-BPM),并在阵列波导光栅模拟计算中采用该方法对光场在阵列波导中的传输过程进行了计算和模拟.结果表明,采用三维FD-BPM可提高计算精度.另外由于三维FD-BPM对纵向步长不敏感,可通过加大步长来减少计算时间,在提高精度的同时,不影响计算时间.     

非傍轴矢量离轴椭圆高斯光束的矩孔衍射

根据矢量瑞利衍射积分公式,对非傍轴矢量离轴椭圆高斯光束的矩孔衍射进行了系统的研究,给出了矩孔衍射的解析表达式,并将非傍轴矢量离轴椭圆高斯光束矩孔衍射轴上、近场、远场和单缝衍射光场分布,非傍轴离轴矢量高斯光束以及非傍轴矢量高斯光束的自由空间传输作为特例统一于一般表达式中,研究表明,在矩孔衍射中,f参数,截断参数以及相对离轴参数共同决定着光束的非傍轴行为.     

基于有限差分光束传播法的过渡波导功耗分析

为了在既定尺寸下减小斜坡波导和弯曲波导的功耗，设计了4种过渡波导形状函数，用有限差分光束传播法(FD—BPM)进行了模拟分析，发现过渡波导形状的选取与坡度和曲折角存在条件关系，并给出了条件表达式和详细说明。     

Application of the finite-difference vector beam propagation methodto directional coupler devices

The finite-difference vector beam propagation method (FD-VBPM) is applied to optical guided-wave devices based on two-dimensional directional couplers. The FD-VBPM is first validated for a parallel coupler made of two identical step-index slab waveguides by comparing with the exact analytical solutions. Subsequently, the polarization beamsplitters and wavelength filters based on directional couplers are simulated. The polarization properties of these devices are examined     

用有限差分光束传输法分析过渡波导损耗

为了减小弯曲过渡波导和斜坡过渡波导的功耗,设计研究了几种过渡波导形状函数,并用有限差分光束传输法进行了模拟分析,发现过渡波导形状的选取与坡度和曲折角存在一定的条件关系,经总结给出了该条件关系表达式;并且,在分析计算不同形状过渡波导损耗的过程中,凸现出了有限差分光束传播法在光波导器件及其单元器件模拟分析中的直观性与方便性。     

A full duplex capable retrodirective array system for high-speed beam tracking and pointing applications

A retrodirective array capable of full duplex communication is presented. The system is based purely on analog circuits for all signal-processing tasks including target tracking, beam pointing, and carrier recovery. Two types of receiver architectures are used, i.e., AM diode detectors for near-omni directional coverage and a digital beamforming receiver to enhance signal-to-interference ratio. This paper also discusses this technology in the context of development of a radar target/communication device, which is intended to both facilitate radar imaging and establish a self-tracking communication link between the ground terminal and mobile radar station. Demonstration of 10-Mb/s data receiving and transmitting functions are presented along with its automatic beam-steering ability and radiation patterns, as well as details about each major circuit component used in the array.     

Analysis of integrated optical corner reflectors using a finite-difference beam propagation method

Integrated optical corner reflectors in III-V semiconductors are analyzed employing a finite-difference beam propagation method and propagating the beam in parallel with the etched semiconductor-air interface. For this choice of propagation direction, the effects of mirror roughness, rotation, and displacement of the mirror surface from its ideal position can be assessed very easily. The integrated reflector whose mode size is larger shows less dependence on the mirror displacement error. The loss due to mirror surface roughness depends weakly on the mode size and strongly on the mode polarization, being larger for the quasi-transverse-electric polarization. The loss due to rotational errors of the mirror surface is not a strong function of polarization, but increases as the waveguide width increases. However, for a rotation error smaller than 0.1 degrees , which should be achieved easily, the excess loss is smaller than 0.2 dB at 1.3 % mu m regardless of the waveguide width.<>     

Efficient time-domain finite-difference beam propagation methodsfor the analysis of slab and circularly symmetric waveguides

The generalized Douglas scheme is applied to the time-domain finite difference beam propagation methods (TD-BPMs) in rectangular and cylindrical coordinates. High accuracy and efficiency are demonstrated through the analysis of optical pulse propagation in slab and circularly symmetric waveguides. As an example of a reflection problem, the TD-BPM in cylindrical coordinates is applied to the analysis of a fiber Bragg grating with a sinusoidal index change. Effectiveness of the present scheme is discussed in comparison with the conventional TD-BPM and the finite-difference time-domain method     

一种高精度的大点数二维FFT处理器设计

基于传统的频域抽取快速傅里叶变换(FFT)算法以及二维FFT算法,设计了一种高精度的大点数FFT处理器。该处理单元采用一个状态机控制整个运算流程,针对小点数情况的一维FFT算法和大点数情况的二维FFT算法,该处理器都可以智能地选择合适的处理流程和缓存管理,自动地完成整个FFT运算而无需软件介入。在支持大点数的二维FFT算法的基础上,该设计还通过对旋转因子计算过程的优化,以提高在大点数情况下的精度表现,在4M长度的输入序列时可以获得130 dB以上的信噪比。     

Modified finite-difference beam propagation method based on thegeneralized Douglas scheme for variable coefficients

The accuracy of the implicit finite-difference beam propagation method (FD-BPM), in which the phase term is not split, is improved using the generalized Douglas scheme. The propagation error of the fundamental mode in two- and three-dimensional waveguides is evaluated by the mode-mismatch loss calculation. It Is demonstrated that the truncation error is reduced to O(Δx)⁴ in the transverse direction, even when the parabolic wave equation contains variable coefficients, The computational time is almost identical to the conventional FD-BPM based on the Crank-Nicholson scheme     

E-beam lithography of computer generated holograms using a fully vectorial 3D beam propagation method

A fully vectorial 3D beam propagation method (BPM) has been applied to obtain a required pattern of computer generated hologram (CGH) with a variable profile of four phase levels. The computer reconstruction of the CGH image having one and two focal spots was performed by application of the fully vectorial 3D BPM method. After transferring the CGH by EBL technique an adequate phase profile was obtained. Inter-level parameter method was developed to obtain the estimated an electron beam dose required for the even topographical patterning. Using this method, an EBL exposure dose determined to achieve the required relief amplitude of 1.29 μm was 43 μC/cm². The manufactured holograms showed that the overall proposed production process, from the 3D BPM computer simulation to e-beam lithography, can be used to obtain good quality product with reasonable time and computational resources.