基于激光光束轨道角动量的8位数据信号产生与检测的实验研究

本文研究了利用激光光束的轨道角动量进行8位数据信息传输的技术. 建立了一套利用光束轨道角动量进行8位数据信息传输的系统, 在信息调制部分采用可选通控制的光源阵列和相位调制屏实现光束轨道角动量态的编码复用, 在信息解调部分采用二元振幅光栅进行轨道角动量态检测,实现了无误码的数据信息传输.     

Geometric metasurface fork gratings for vortex‐beam generation and manipulation

In recent years, optical vortex beams possessing orbital angular momentum have received much attention due to their potential for high‐capacity optical communications. This capability arises from the unbounded topological charges of orbital angular momentum (OAM) that provide infinite freedoms for encoding information. The two most common approaches for generating vortex beams are through fork diffraction gratings and spiral phase plates. While realization of conventional spiral phase plate requires complicated 3D fabrication, the emerging field of metasurfaces has provided a planar and facile solution for generating vortex beams of arbitrary orbit angular momentum. Among various types of metasurfaces, the geometric phase metasurface has shown great potential for robust control of light‐ and spin‐controlled wave propagation. Here, we realize a novel type of geometric metasurface fork grating that seamlessly combine the functionality of a metasurface phase plate for vortex‐beam generation, and that of a linear phase gradient metasurface for controlling the wave‐propagation direction. The metasurface fork grating is therefore capable of simultaneously controlling both the spin and the orbital angular momentum of light.

     

Spectroscopic observation of the rotational Doppler effect

We report on the first spectroscopic observation of the rotational Doppler shift associated with light beams carrying orbital angular momentum. The effect is evidenced as the broadening of a Hanle electromagnetically induced transparency coherence resonance on Rb vapor when the two incident Laguerre-Gaussian laser beams have opposite topological charges. The observations closely agree with theoretical predictions.     

Separation of spin and orbital angular coherence momenta in the second-order coherence theory of vector electromagnetic fields

In analogy with the separation of the total optical angular momentum into a spin and an orbital part in electrodynamics, we introduce a new concept of spin and orbital angular coherence momenta into the general coherence theory of vector electromagnetic fields. The properties of the newly introduced spin and orbital angular coherence momenta are investigated through the decomposition of the total coherence angular momentum into the sum of these two components, and their separate conservations have been derived for what is believed to be the first time.     

Poincaré-sphere equivalent for light beams containing orbital angular momentum

The polarization state of a light beam is related to its spin angular momentum and can be represented on the Poincaré sphere. We propose a sphere for light beams in analogous orbital angular momentum states. Using the Poincaré-sphere equivalent, we interpret the rotational frequency shift for light beams with orbital angular momentum [Phys. Rev. Lett. 80, 3217 (1998)] as a dynamically evolving geometric phase.     

利用振幅光栅生成拉盖尔、高斯光束的实验研究

拉盖尔高斯(Laguerre-Gaussian，LG)光束由于其独特的相位结构和轨道角动量特性在微粒旋转操纵和信息处理等方面得到了越来越多的重视.对利用振幅型叉状衍射光栅产生LG光束进行了理论分析，采用计算全息图的方法制作了振幅型叉状衍射光栅，实验上获得了角量子数为±1的LG光束，并对光束变换过程中影响光束特性的主要因素进行了讨论.     

利用振幅光栅生成拉盖尔-高斯光束的实验研究

拉盖尔高斯(Laguerre-Gaussian,LG)光束由于其独特的相位结构和轨道角动量特性在微粒旋转操纵和信息处理等方面得到了越来越多的重视.对利用振幅型叉状衍射光栅产生LG光束进行了理论分析,采用计算全息图的方法制作了振幅型叉状衍射光栅,实验上获得了角量子数为±1的LG光束,并对光束变换过程中影响光束特性的主要因素进行了讨论. 关键词： 信息光学 拉盖尔高斯光束 计算全息光栅 光束轨道角动量     

Angular momentum of gaussian light beams

Analysis of the orbital angular momentum of paraxial light beams shows that a key role in the formation of this quantity is played by phase relations between longitudinal and transverse radiation fields. When a light beam is circularly polarized or has a helical wave front, the azimuthal component of the Poynting vector and the density of orbital angular momentum prove to be non-zero. In the case of circularly polarized radiation, the azimuthal component of the Poynting vector and the density of the orbital angular momentum can change the sign at different points in the cross section of the light beam, while the total orbital momentum of the beam remains quantized.     

Study on holographic grating diffraction for Laguerre--Gaussian beam generation

Laguerre-Gaussian beams, as a special model with spiral phase structure, have been intensively investigated. Holographic grating method is a convenient method of generating Laguerre-Gaussian beams and measuring their orbital angular momenta. But due to some inevitable adverse factors such as lateral displacement, angular deflection and elliptical incident profile of incident beam, the practical effectiveness should be reevaluated. This paper is devoted to the study on the influences of the abovementioned three adverse factors on the holographic grating method. The characteristics of the mode decomposition of diffractive order and the relative powers of the orbital angular momentum eigen-states are also given.     

Effects of atmospheric turbulence on the orbital angular momentum of multi-Gaussian Schell model beams

The effects of multibeams and partially coherent source on the orbital angular momentum transmission of multi-Gaussian Schell model beams in an atmospheric turbulence channel are analyzed. An effective crosstalk probability model of the orbital angular momentum is derived which leads to crosstalk probability function for eigenmodes of different orbital angular momentum states and beamlets. The work shows that the evolution of the effective spatial coherence radius with growing the rms width of the correlation of the partially coherent source and the number of the beamlet in multi-Gaussian model beams. The crosstalk probability of the orbital angular momentum of an effective Gaussian-Schell model beam decreases as increasing of the degree of the spatial coherence of the partially coherent source and the beamlet number of the multi-Gaussian Schell model beams.     

Linear and angular momenta in tightly focused vortex segmented beams of light(Invited Paper)

We investigate the linear momentum density of light,which can be decomposed into spin and orbital parts,in the complex three-dimensional field distributions of tightly focused vortex segmented beams.The chosen angular spectrum exhibits two spatially separated vortices of opposite charge and orthogonal circular polarization to generate phase vortices in a meridional plane of observation.In the vicinity of those vortices,regions of negative orbital linear momentum occur.Besides these phase vortices,the occurrence of transverse orbital angular momentum manifests in a vortex charge-dependent relative shift of the energy density and linear momentum density.     

Geometrical phase shift of the extrinsic orbital angular momentum density of light propagating in a helically wound optical fiber

We calculate the intrinsic spin and extrinsic orbital angular momentum densities of an electromagnetic plane wave propagating in a helically wound optical fiber. The geometrical phase shift of the extrinsic angular momentum density of light traveling in such a fiber is derived analytically and discussed in comparison with that of the intrinsic angular momentum density.     

Backscattered polarization patterns, optical vortices, and the angular momentum of light

We demonstrate that the polarization patterns observed in backscattering of linearly polarized light are a manifestation of the conservation of angular momentum of light. We will show that this phenomenon can be described in terms of phase vortices that are acquired by the right and left circularly polarized components. The helicity and orbital angular momentum of these components satisfy the requirement for conservation of angular momentum.     

Atmospheric turbulence and orbital angular momentum of single photons for optical communication

The effects of propagation through random aberrations on coherence for single-photon communication systems based on orbital angular momentum states are quantified. A rotational coherence function is derived which leads to scattering equations for azimuthal modes of different orbital angular momentum states. The effect on a single-photon communication system is quantified using the channel capacity. The work shows that the decoherence effect of atmospheric turbulence on such systems is important even for weak turbulence.     

Orbital angular momentum exchange in the interaction of twisted light with molecules

In the interaction of molecules with light endowed with orbital angular momentum, an exchange of orbital angular momentum in an electric dipole transition occurs only between the light and the center of mass motion; i.e., internal "electronic-type" motion does not participate in any exchange of orbital angular momentum in a dipole transition. A quadrupole transition is the lowest electric multipolar process in which an exchange of orbital angular momentum can occur between the light, the internal motion, and the center of mass motion. This rules out experiments seeking to observe exchange of orbital angular momentum between light beams and the internal motion in electric dipole transitions.     

光子高阶轨道角动量制备、调控及传感应用研究进展

光子既是经典信息也是量子信息的理想载体. 单个光子不仅可以携带自旋角动量(与光波的圆偏振相关), 还可以携带轨道角动量(与光波的螺旋相位相关). 而轨道角动量的重要意义在于可利用单个光子的量子态构建一个高维的Hilbert空间, 从而实现高维量子信息的编码. 自Allen等于1992年确认光子轨道角动量的物理存在以来, 轨道角动量在经典光学和量子光学领域展现了诸多诱人的应用前景, 目前已成为国际光学领域的研究热点之一. 本综述将着重介绍高阶轨道角动量光束的制备与调控技术, 特别是高阶轨道角动量的量子纠缠态操控、旋转Doppler 效应测量及其在远程传感和精密测量技术中的应用.     

Coherent-mode representation and orbital angular momentum spectrum of partially coherent beam

Orbital angular momentum of the coherent beam has been intensively studied and promises potential applications in free space optical communication. But the orbital angular momentum of partially coherent beam is not well known. In this communication the coherent-mode representation method is adopted to describe the partially coherent beam and the orbital angular momentum spectrum is introduced for the partially coherent beam. The characteristics of the orbital angular momentum spectrum of partially coherent beam are discussed. To study the influence of the partial coherence on the optical link, the channel capacity is studied, with two kinds of available mode separators included.     

Optical and sound helical structures in a Mandelstam-Brillouin mirror

It is shown theoretically that the phase conjugation of a speckle optical field in a Mandelstam-Brillouin mirror is accompanied by the excitation of helical hypersonic waves with a step equal to one-half of the optical wavelength. The excitation of these waves violates the initial isotropy of the dielectric medium. The predicted effect admits clear physical interpretation based on the angular momentum conservation. The angular momentum transfer from the light to the medium occurs in the vicinity of an optical singularity (optical vortex line) due to reversal of the light orbital angular momentum by the phase-conjugation mirror. The excitation of hypersonic waves transferring the angular momentum is the necessary condition for the reversal of the angular momentum of the reflected light.     

Entangled orbital angular momentum states of multi-Laguerre Gaussian Schell beams pumping in a Zernike tilt corrected turbulence

Based on the paraxial approximation of the beams propagation in communication system, the square approximation of the wave structure function, the Zernike polynomial expansion of the non-Kolmogorov atmospheric turbulence-aberration and the assumption of the signal photon propagation in slant Zernike tilt corrected turbulence-channel, we analyze the effect of the multi-beam on entangled orbital angular momentum states. The joint detection probability of orbital angular momentum state entangled photons is modeled. Our work shows that the correction of the Zernike tilt aberration by adaptive optics is a method to improve the joint detection probability of orbital angular momentum state entangled photons. The crosstalk probability of the entangled orbital angular momentum states decreases as increasing of the degree of the spatial coherence of the partially coherent source and the beamlet number of the multil-Laguerre Gaussian Schell model beams.     

柱矢量光束的角动量性质

介绍了非近轴光束的表示理论,利用该表示理论很好地解决了非近轴光束的角动量问题,发现非近轴光束的总角动量可以严格地分解成自旋和轨道两部分,但是两者都依赖于由偏振椭圆度表征的光束的偏振状态。主要研究了柱矢量光束的角动量问题。给出了动量空间和位形空间中的柱矢量光束表达式和角动量算符表达式。通过分析两个空间中的角动量算符及柱矢量光束表达式,发现在这两种空间中,具有螺旋型相位的柱矢量光束是角动量算符沿着传播方向的分量的本征态,其本征值与偏振椭圆度无关,这为计算这类特殊光束的角动量提供了一种新方法。