A new semi-analytical method for the analysis of tapered optical waveguides

Tapered waveguide are used in number of integrated optic devices such as directional couplers, modulators, switches mode converters, etc. Most of the methods analyzing tapered waveguide are numerical in nature. In this paper we present a simple, fast and accurate semi analytical method for z-varying waveguide. However, very few idealized structures can be analyzed directly. The present method consists of separating transverse and longitudinal variation in the wave equation, leading to a differential equation with z-varying coefficients for the field variation along z-axis. For the transverse variation local normal theory is applied. Now this equation is applied to specific taper geometries like linear down taper. Computational are done assuming typical values. We observe variation of power mode profile and mode width. Waveguide loss is also including in the analysis. Finally the analytical simulation results have been verified by the commercial Opti-BPM software.     

Lorentz beams as a basis for a new class of rectangularly symmetric optical fields

In this work we present a new and wide class of scalar, rectangular symmetrical optical fields, the free-space propagation of which can be given in a closed-form in the paraxial approximation. In particular it is shown how such fields can be expressed as a finite linear combination of the recently introduced Lorentz beams [O. El Gawhary, S. Severini, J. Opt. A: Pure Appl. Opt., 8 (2006) 409.] that, in this way, act as a basis for the newly introduced class. Because of their mathematical form, we call such fields super-Lorentzian beams. Some common features of the class are pointed out and the concept of order of the beam introduced. Moreover, by using these results, we demonstrate the existence of a new family of mutually orthogonal paraxial fields with a related new class of orthogonal polynomials.     

Propagation of a Lorentz-Gauss beam through a misaligned optical system

Based on the generalized integral formula and the convolution theorem of the Fourier transform, an analytical propagation formula of a Lorentz-Gauss beam passing through a misaligned paraxial optical system is derived. As numerical examples, the propagation properties of a Lorentz-Gauss beam through a misaligned thin lens with the lateral displacement and the angle displacement are graphically illustrated, respectively. The influences of the lateral displacement and the angle displacement of the misaligned thin lens on the normalized light intensity and the phase distributions are also examined, respectively.     

使用离焦望远镜系统合成轴上平顶光束的一种新方法

提出了用平顶多高斯光束作为理想光束和使用离焦望远镜系统合成轴上平顶光束的一种新方法.在近轴近似下,基于柯林斯衍射积分公式推导出轴上光场和入射光场的解析表达式,并做了物理分析.光束阶数N,平顶长度参数L,平顶中心位置z_c和纵向中心空间频率S_c对轴上光强分布的影响用数值计算例做了说明.比较表明,该方法优于文献中使用矩形函数模拟理想光束合成轴上平顶光束的方法. 关键词： 轴上平顶光束 平顶多高斯光束 离焦望远镜系统 傅里叶变换     

The impact of the off-axis for the spatial light to multimode fiber coupling system

The electric field distribution of Gaussian beam and properties of Cassegrain optical antenna are discussed and their images have been simulated. By analysis of Cassegrain optical antenna with collimation and off-axis circumstance, laser power distribution and the curve of coupling efficiency are obtained. The question of spatial light to multimode fiber coupling efficiency with alignment and off-axis are researched. At last, taking into account off-axis situation of Cassegrain and laser beam to multimode fiber, the coupling efficiency of the whole system is discussed. These researches are necessary and useful for increasing spatial light to multimode fiber coupling efficiency.     

Studies of propagation characteristics of elliptical Gaussian beams through circular apertured optical systems

An approximate analytical propagation formula of the elliptical Gaussian beams through a paraxial ABCD optical system with a circular aperture is obtained on the basis of the expansion of a hard-edged aperture into a finite sum of complex Gaussian functions. And the parameter characteristics of the truncated beams including the beam propagation factor and the kurtosis parameter are also studied in detail by using the second-order-moments method.     

Numerical approach to laser beam propagation through turbulent atmosphere and evaluation of beam quality factor

In this paper, propagation of a Gaussian laser beam through turbulent atmosphere is evaluated numerically. The beam quality factor for the propagated beam has been estimated for different turbulent conditions that are characterized by parameter C_n. The calculations show that the beam quality can be affected dramatically by atmospheric turbulence and the laser beam size and wavelength have major role in the results. Furthermore, the propagation of laser beam in longer distance results in more spatial perturbation of the beam. The results of these calculations and evaluation of beam quality factor M² can be used for estimating the refractive index structure parameter (or atmosphere turbulent parameter) C_n.     

Numerical propagation of partially coherent laser beams through optical systems

The propagation of partially coherent beams through optical systems is computed numerically in one transverse dimension. The optical system is divided into different elementary segments, through which the propagation of light can be calculated by appropriate operators, working on the coherence function or the Wigner distribution function respectively. For the necessary changes between these two functions describing the partially coherent beams, the use of the remarkable z-transform seems to be an advantage. With this algorithm the grid and the resolution in the spatial frequency domain can be arbitrarily chosen in contrast to the usual Fourier transform, the influence of phase aberrations on the focusability of Gauss-Schell model beams is discussed as an application example of the numerical model. With the help of this tool, practical beam guiding systems can be simulated for use with multimode laser radiation.     

A new definition of the degree of paraxiality for vector light beams

A parameter, called the degree of paraxiality, is introduced upon examining the property of energies originating from the longitudinal as well as the transverse components of both the electric and magnetic fields. It is shown that this degree of paraxiality is determined by the magnitude of the plane-wave spectrum, without depending on the vectorial feature of the plane-wave spectrum. Its value ranges from 0 to 1. A larger value stands for a more paraxial beam. As an application, two examples are considered.     

Analysis of the power coupling efficiency of the relay mirror system with the transmitter composed of sub-telescope array

Model of the relay mirror system with the transmitter composed of sub-telescope array is established. With this model, the new system is theoretically analyzed in the paper. Power coupling efficiencies of the 3-sub-telescope array system and the common system are calculated. The results show that power coupling efficiency of the system with new configuration is significantly improved in comparison with the common relay mirror system.     

一种新的基于最小平方逼近的广角光束传播方法

用最小平方逼近展开传播算子，实现了一种新的半矢量显式高阶有限差分光束传播方法-这种方法中不需要选择参考折射率，并在整个传播常数（包括辐射模的传播常数）分布区域进行逼近，解决了在泰勒展开和庞德逼近中存在的参考折射率选择和远离展开点误差增大等问题-用这种方法对几种典型波导结构进行了数值模拟，模拟结果验证了算法的正确性和可靠性- 关键词： 光束传播方法 有限差分 集成光学 数值方法     

高库仑量大电流两电极气体火花开关研究

设计了一个两电极气体火花开关，开关的主体部分仅包括阴极、阳极两个主电极，以及金属外壳和绝缘支撑外壳，两电极结构取消了触发极，消除了由于触发极烧蚀影响开关寿命的问题。开关设计工作电压23 kV，单脉冲能量1.2 MJ，峰值电流300 kA，单次脉冲电荷转移量110 C。初步试验阶段开关工作电压达到15 kV，开关的通流180 kA，电荷转移量为47.85 C。开关触发性能可靠，电极烧蚀均匀。     

利用功率谱密度评价离子束抛光光学元件表面粗糙度

利用功率谱密度(PSD)评价光学表面粗糙度具有传统评价手段(Ra)所不具备的优势。给出了功率谱密度的计算方法,以及抽样方向与一维PSD曲线的关系。在离子束抛光K9玻璃实验中引入PSD曲线,以评价抛光光学零件的光学表面粗糙度,结合PSD曲线与Ra值能够更全面的指导光学加工。     

Optimized design of a new three branch optical waveguide

A new type of 1 × 3 Y-branch optical waveguide structure with a cone transitional section is introduced in this paper. The symmetrical branch ratio of the 1 × 3 Y branch optical waveguide is obtained by changing the width of this waveguide. The loss and the uniformity are obtained by using the finite difference beam propagation methods, and their values are 0.2 dB and 0.05 dB, respectively. Therefore, it provides some experimental basis for production of three branch optical waveguide.     

建立聚焦光学系统三维衍射积分的新方法

本文介绍了一种建立聚焦光学系统三维衍射积分的新方法,该方法简单直观.利用所建立的三维衍射积分能方便地有效地研究光学系统,特别是大孔径光学系统聚焦衍射场的三维场分布.文中给出了光学系统聚焦面上光矢的各分量及总光矢的分布,并研究分析了像差对光矢三线分布的影响以及像差对称性与光矢分布的关系,得出了一些结论.     

The threaded BPM: A novel extension to the two-dimensional scalar beam propagation method

The two-dimensional scalar beam propagation method (BPM) is a widely used, computationally efficient tool for the analysis of planar optical waveguides and devices. The inherent paraxial limitations and rectilinear analysis grid limit its application to slightly curved structures and waveguides. In this novel extention to the BPM algorithm, the curvature restrictions are removed and in many cases the paraxial restrictions can be avoided, allowing for the first time, the efficient analysis of arbitrarily curved structures, such as S- or U-shaped bends, curved transitions of progressively varying curvature, and curved couplers. It can also handle concatenated devices and the curved interconnect sections between them. The process operates by the concatenation of micro-conformal maps, which progressively re-orientate the problem optimally towards a straight BPM analysis.     

Nonparaxial propagation of Hermite-Laguerre-Gaussian beams in uniaxial crystal orthogonal to the optical axis

Analytical expressions for the three components of the nonparaxial propagation of a Hermite-Laguerre-Gaussian （HLG） beam in uniaxial crystal orthogonal to the optical axis are derived. The intensity distribution of an HLG beam and its three components propagating in a uniaxial crystal orthogonal to the optical axis are demonstrated by numerical examples. Although the y and z components of an HLG beam in the incident plane are both equal to zero, they emerge upon propagation inside the uniaxial crystal. Moreover, the beam profile of the x component is relatively stable and the beam profiles of the y and z components have the same evolution law. If the ratio of the extraordinary refractive index to the ordinary refractive index is larger than unity, the beam profile of the HLG beam is elongated in the x direction and generally rotates clockwise. Otherwise, the beam profile of the HLG beam is elongated in the y direction and generally rotates anticlockwise. This research is beneficial to the optical trapping and nonlinear optics involved in the rotation of a beam profile.     

A simple experimental method to generate partially coherent optical bottle beam

An experimental study is carried out to investigate a special kind of three-dimensional intensity distribution of a partially coherent optical beam known as optical bottle beam produced by using an annular aperture and lens combination (Lens Aperture System). In this paper, we are demonstrating the experimental results of our observations. The investigation also includes the effects of coherence modulation and central obstruction of the annular aperture (used in Lens Aperture System) on the resultant partially coherent optical bottle beam. The method discussed in this paper is simple and cost effective.     

Propagation of a flattened Gaussian beam through multi-apertured optical ABCD systems

By expanding the hard-aperture function into a finite sum of complex Gaussian functions, the recurrence propagation formula of a flattened Gaussian beam through multi-apertured optical ABCD systems is derived, and the propagation of a Gaussian beam is regarded as a special case in our theoretical model. The extension to the three-dimensional case is described. Numerical examples of the beam propagation through a multiple aperture-lens system and an aperture-spatial filter are given and compared with those by the straightforward numerical integration of the Collins formula. It is shown that our analytical results give a good trade-off between the computational time and accuracy, and provide a useful tool for simulating the beam propagation through complicated optical systems including multiple apertures and spatial filters. Finally, a comparison with the previous work is made and the main results obtained in this paper are summarized.     

Effects of misalignments in the optical vortex transformation performed by holograms with embedded phase singularity

Spatial characteristics of diffracted beams produced by a “fork” hologram from an incident circular Laguerre-Gaussian beam whose axis differs from the hologram optical axis are studied theoretically. General analytical representations for the complex amplitude distribution of a diffracted beam are derived in terms of superposition of Kummer beams or hypergeometric-Gaussian beams. The diffracted beam structure is determined by combination of the “proper” topological charge m of the incident vortex beam and the topological charge l of the singularity “imparted” by the hologram. Evolution of the diffracted beam structure is studied in detail for several combinations of m and l and for various incident beam displacements with respect to the optical axis of the hologram. Variations of the intensity and phase distribution due to the incident beam misalignment are investigated and possible applications for the purposeful optical vortex beam generation and optical measurements are discussed.