高斯涡旋光束在自由空间传输中电场和磁场的偏振奇点

利用矢量菲涅尔衍射积分公式, 以高斯涡旋光束为例, 推导出傍轴高斯涡旋光束在自由空间传输过程中电场分量和磁场分量的解析表达式, 详细研究了自由空间中电场和磁场的偏振奇点变化规律. 结果表明, 高斯涡旋光束在自由空间传输中, 存在二维和三维电场和磁场的偏振奇点, 其位置一般不重合. 改变光束束腰宽度比、 振幅比以及传输距离, 偏振奇点出现移动. 在二维电场和磁场中, 当满足一定条件时, 会有V点产生.     

双孔干涉产生偏振奇点分析

在近轴近似的条件下,采用标量衍射积分的方法,对电磁场的双孔干涉进行了研究,并对千涉场中产生偏振奇点的情况进行了推广。在研究中通过双孔的光电场为线偏振状态,具有不同的偏振方向。数值计算结果表明,即使通过双孔的光电场的相位相同,只要双孔的尺寸存在一定的差异,干涉场中除了能够产生普通的的线偏振外,圆偏振奇点也会出现。     

Structural stability of a nonparaxial singular mode beam

The exact explicit solution of the Maxwell equations for nonparaxial singular beams propagating in free space or in a homogeneous isotropic medium is considered. It is shown that, in the paraxial approximation, such solutions for mode beams of both lower and higher orders may turn into the solutions for guided modes or vortices of optical fibers. It is found that a variation of the Rayleigh length for a mode beam does not change the structure of phase and polarization singularities; it merely transforms their coordinates. In the paraxial limit, the singularities are shifted off the axis to regions with negligible light fluxes.     

聚焦高斯涡旋光束焦区电场和磁场的偏振奇点

以高斯涡旋光束为例,研究了聚焦场中电场和磁场的偏振奇点变化规律.结果表明,高斯涡旋光束经透镜聚焦后,在焦区存在二维和三维电场和磁场的偏振奇点,其位置一般不重合.适当改变与焦面的距离以及光阑截断参数等出现圆偏振奇点的移动、产生和湮没.不同二维和三维电场和磁场圆偏振奇点湮没所对应的各参数临界值不同.在二维电场中,几何焦面上会有V点的产生.     

Strong-field photoionization of intense laser fields by controlling optical singularities

The spatial features of a light field, such as in the form of the optical singularities, provide a new degree of freedom for the application of light fields in different areas of science and technology. However, although the exploration of structured light is growing rapidly, the investigation of strong-field photoionization using such light fields is noticeably lagging behind. Here, we present an experimental study that reveals the signatures of intense, structured light fields with controlled optical singularities in strong-field photoionization. The different types of optical singularities can be identified through photoionization observables,i.e., photoelectron momentum distributions(PMDs). By concurrently shifting the locations of the phase and polarization singularities, the focal electric field features can be designated, and subsequently, the photoionization appearances can be manipulated. In this process, the behaviors of the different intense optical singularities are clearly visualized by the PMDs. This work will advance both the strong-field science and singularity optics.     

Two-dimensional polarization distribution controller based on variable retarder array

Two-dimensional polarization distribution controller which can transform linearly polarized beam into two-dimensional polarization distributed beam has been presented and investigated. The two-dimensional polarization distribution controller consists of two quarter-wave plates and a variable retarder array. The principles of the two-dimensional polarization distribution controller are analyzed and calculated results show when the directions of fast axes of these three components meet a particular constraint equation set, these three optical components could be regarded as a two-dimensional polarization distribution controller. Experiments have been carried out, and the light intensity distribution of radially and azimuthally polarized beams after an analyzer are obtained.     

部分空间相干部分光谱相干厄米-高斯脉冲电磁光束的偏振特性

基于非稳态场的相干理论,对部分空间相干部分光谱相干二维厄米-高斯脉冲电磁光束在自由空间传输时的偏振特性做了详细的数值研究.结果表明,脉冲电磁光束的偏振度分布由光束阶数、光束的空间相关长度、时间相干长度和场点位置等因素共同决定.研究表明,当空间相关长度趋于零或无穷大时,轴上点偏振度趋于一固定值,与光束阶数和场点位置无关....     

Enhanced bandgap in annular photonic-crystal silicon-on-insulator asymmetric slabs

Photonic band structures of annular photonic-crystal (APC) silicon-on-insulator (SOI) asymmetric slabs with finite thickness were investigated by the three-dimensional plane-wave expansion method. The results show that for a broad range of air-volume filling factors, APC slabs can exhibit a significantly larger bandgap than conventional circular-hole photonic-crystal (PC) slabs. Bandgap enhancements over conventional air hole PC SOI slabs as large as twofold are predicted for low air-volume filling factors below 15%. This desirable behavior suggests a potential for APC SOI slabs to serve as the basis of various optical cavities, waveguides, and mirrors.     

Band-gap guidance in optically induced photonic lattices with a negative defect

We report the first experimental demonstration of band-gap guidance of light in an optically induced two-dimensional photonic lattice with a single-site negative defect (akin to a low-index core in photonic-crystal fibers). We discuss the difference between spatial guidance at a regular and a defect site, and show that the guided beam through the defect displays fine structures such as vortex cells that arise from defect modes excited at higher band gaps. Defect modes at different wavelengths are also observed.     

Polarization singularities in 2D and 3D speckle fields

The 3D structure of randomly polarized light fields is exemplified by its polarization singularities: lines along which the polarization is purely circular (C lines) and surfaces on which the polarization is linear (L surfaces). We visualize these polarization singularities experimentally in vector laser speckle fields, and in numerical simulations of random wave superpositions. Our results confirm previous analytical predictions [M. R. Dennis, Opt. Commun. 213, 201 (2002)] regarding the statistical distribution of types of C points and relate their 2D properties to their 3D structure.     

Birefringent fibre-optic pressure sensor

In this paper a birefringent optical fibre sensor is used to measure the external wall pressure of a pressurized resilient tube. In the design presented here, the sensing polarization-maintaining fibre is external to the tube and the interaction alters the polarization state of the guided light which can easily be measured by conventional techniques.     

Design of a wedge plate for polarization-preserving angular shifter

It is shown that by using a wedge plate, the incident direction of light propagation can be rotated as necessary while still preserving beam polarization. The basic conditions of these preservations of polarization are deduced. For numerical demonstration, it is shown that a collimated beam with +45° linear polarization can be guided to any pre-settled direction where the square of ellipse ratio variation in the polarization is less than 0.0001%, while the variation of squared ellipse ratio of a right circular polarization beam is kept under 0.1%.     

Polarization singularity democracy: WYSIWYG

The canonical point singularity of elliptically polarized light is a C point, an isolated point of circular polarization surrounded by a field of polarization ellipses. The defining singular property of a C point is that the surrounding ellipses rotate about the point. It is shown that this rotation is seen only for a particular line of sight (LOS) and, conversely, that there exists a unique LOS for every ellipse along which the ellipse is seen as a singularity. It is also shown that changes in LOS can turn singularities into stationary points and vice versa. The democratic behavior of polarization singularities and stationary points is a consequence of the fundamental "what you see is what you get" property of ellipse fields. Simple experiments are proposed for observing this unusual property of elliptically polarized light.     

基于光子晶体耦合波导的宽带慢光研究

提出了在完整三角晶格光子晶体中引入两线缺陷构成的耦合型波导结构。通过分析谱带形对不同结构参数的依赖关系,在最优化的光子晶体耦合波导中,找到了一种独特的、群速近似为零的谱带。通过对波导宽度的啁啾实现了不同频率光的色散补偿,最终得到了带宽为13.24nm、平均群折射率为28的宽带理想慢光,并进一步采用二维时域有限差分(FDTD)算法进行了验证。数值分析结果表明,高斯脉冲在耦合波导中传输后的相对时域展宽低于10%。     

Vectorial Pauli algebraic approach in polarization optics. II. Interaction of light with the canonical polarization devices

A theoretical approach to the interaction between polarized light and polarization devices, based on the vectorial and pure operatorial form of the Pauli algebra, is presented. In the first part of the paper we have established the vectorial Pauli-algebraic forms of the operators corresponding to various polarization devices and states of light polarization. In this second part we give the vectorial Pauli-algebraic treatment of the interaction between the canonical polarization devices and the various forms of light polarization. Unlike the standard (Jones and Mueller) approaches, this formalism does not appeal to any matrix representation of the involved operators. This approach establishes a bridge between the Hilbert space of the density operators of the polarization states and the Poincaré space of their geometric representations and gives a rigorous justification of the handling of the interactions between the polarization states and polarization systems on the Poincaré sphere and in the Poincaré ball. In such an approach, unlike the standard ones, the three relevant quantities that characterize the interaction - the gain, the Poincaré vector of the outgoing light and its degree of polarization - result straightforwardly, in block. A generalized form of Malus’ law, for any dichroic device and partially polarized light is also obtained this way.     

Evolution of emergent C-points, L-lines, and C-lines in free space

Polarization singularities,which emerge from the incoherent superposition of two vector electric fields with the same frequency,and their evolution in free space are studied analytically and illustrated by numerical examples.It is shown that there exist C-points,L-lines,in particular,C-lines in incoherently superimposed two-dimensional wavefields.Usually,the C-lines are unstable and disappear during the free-space propagation.The motion,pair creation-annihilation process of the emergent C-points,as well as the distortion of the L-lines may take place,and the degree of polarization of the emergent C-points varies upon propagation and may be less than 1.     

部分相干刃型位错光束的谱Stokes奇点

利用交叉谱密度函数的传输公式,推导出部分相干刃型位错光束在自由空间中传输的解析表达式.结合谱Stokes参数,详细讨论了其Stokes场的奇点变化规律.结果表明,部分相干刃型位错光束在自由空间传输过程中存在谱s12,s23和s31奇点.改变刃型位错的离轴量、斜率、空间相关长度等光束参数以及随着传输距离的变化,会有谱Stokes奇点的移动、产生和湮没,也会有V点的产生和C点旋性的反转.     

紧聚焦轴对称矢量光场波前调控及应用

作为光波最重要的本征物理属性之一,光场偏振态在研究光与物质相互作用中占有重要地位。矢量光场的波前调控为其聚焦场提供了更加复杂、更加灵活可控的振幅、相位以及偏振态分布,丰富了光与物质相互作用的手段,为材料表征提供了传统线偏振、圆偏振光场所不可替代的研究方法,具有重要的物理意义和实际应用价值。本文将综述矢量光场最新的研究进展,详细介绍矢量光场的偏振态特性、产生方法,以及紧聚焦轴对称矢量光场波前调控在远场小尺度光斑的产生、磁光记录、单分子/颗粒取向探测、任意三维偏振态的产生、高密度数据存储、信息加密以及矢量光场波前重构等方面的重要应用。     

A novel polarization channel drop filter based on two-dimensional photonic crystals

<正>A novel polarization channel drop filter(PCDF) based on two-dimensional(2D) photonic crystals(PCs) is presented.It consists of two line defect waveguides and two point defect micro-cavities.In the line-defect waveguides,the transverse-electric(TE) and transverse-magnetic(TM) polarization lights are guided using photonic band-gap and total internal reflection effect,respectively.The light at the resonant frequency for TE polarization can be transferred from one waveguide to the other using the proposed system.Compared with the existing four-port PCDF based on PCs,the three-port structure can realize a multi-channel wavelength system of PCDF more easily and can be an essential device in future polarization wavelength division multiplexing(PWDM) systems.     

多功能太赫兹超表面偏振控制器

本文提出了一种“金属栅-开口环/硅环-金属栅”结构的透射式超表面偏振控制器, 研究了入射角度和抽运光对该器件传输及偏振态控制性能的影响. 研究结果表明, 当线偏振太赫兹波垂直入射时, 可对0.39-1.11 THz频段的太赫兹波实现偏振方向90°旋转, 偏振旋转效率为99%, 损耗为1 dB. 对于斜入射的情况, 偏振转换性能在0-60°范围内基本保持不变, 且透过率达到90%以上. 同时, 通过调控抽运光强度的方式, 该器件能够实现对透射与反射太赫兹光束的强度调制, 调制深度均达到90%, 且可以实现太赫兹波偏振分束功能. 该器件可以作为未来太赫兹空间光通信和信息处理的宽带、角度不敏感、可调谐的偏振转换器和分束器.