An optical measurement of vortex shape at a free surface

We have proposed an optical method of vortex shape measurement based on Fourier transform profilometry (FTP) and verified it by experiment. The results of our experiment proposed in this paper show that FTP can efficiently reconstruct the vortex shape at a free surface and this method is suitable for wide use in studying such problems as liquid shear flow, wake of an object, flow behind a bluff body, and wetting angle.     

Composite optical vortices in two noncollinear cosh-Gaussian vortex beams and their propagation properties in free space

The composite optical vortices (OVs) formed by superimposing two parallel, noncollinear cosh-Gaussian (ChG) vortex beams at the waist plane and their propagation in free space are studied. The dependence of the number, position and net topological charge of composite OVs on the control parameter, such as the relative phase, amplitude ratio, waist-width ratio, relative off-axis distance and decentered parameter, and on the propagation distance is illustrated numerically. A comparison with the previous work is also made.     

Enhancement of free space optical link in heavy rain attenuation using multiple beam concept

Free space optics (FSO) has attracted a lot of attention for a variety of applications in telecommunications area, and it is dream of every researcher and telecommunication society to make it a real alternative solution for the last mile problem, to replace fiber optics. FSO is much preferred because of its low maintenance cost and deployment time. FSO with single-beam system is vulnerable to atmospheric attenuation, so to overcome this, a multiple-beam FSO transceiver system has become prominent and is usually used. In this paper, average rain attenuation is evaluated from the collected rain intensity data which are collected for a period of seven months, and implemented in the study concerning results relating link distance, and received optical power of using multiple-beam FSO system in tropical rainy weather. Comparison is made in terms of received optical power, geometrical losses, atmospheric losses, and bit error rate (BER) on using different number of optical beams, based on simulation at data rate of 1 Gb/s. From the results it is clear that the quality of received power is improved by using up to four beams, along with link distance up to 1141.2 m as compared to one-beam, two-beam, and three-beam, with link distances 833.3 m, 991.0 m, 1075.4 m, respectively.     

离轴平顶高斯涡旋光束形成的合成光涡旋及其在自由空间中的传输

对两束拓扑电荷m_1,2=±1的平行、离轴平顶高斯涡旋光束在束腰面叠加形成的合成光涡旋及其在自由空间的传输做了研究.详细的数值计算和分析表明,合光涡旋的位置、数目和净拓扑电荷与光束的控制参数,包括相对位相,振幅比,束腰宽度比,相对离轴参数,光束阶数,以及传输距离有关,但拓扑电荷不总是守恒. 关键词： 奇点光学 合成光涡旋 平顶高斯涡旋光束 拓扑电荷     

Wavelength-scalable micro-fabricated wedge for generation of optical vortex beam in optical manipulation

An optical wedge phase plate is fabricated for the study of vortex beam generation in optical manipulation. It is demonstrated that the wedge phase element provides scalability for generating the vortex beam at different wavelengths as long as the incident beam size is adjusted accordingly. The presence of singularity for different wavelengths and the associated orbital angular momentum are confirmed experimentally in optical manipulation. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. PACS 41.85.Ct; 42.82.Cr     

Arbitrary laser beam propagation in free space

The propagation of arbitrary laser beams in free space is examined. For this purpose, starting with an incident field of arbitrary field distribution, the intensity at the receiver plane is formulated via Huygens Fresnel diffraction integral. Arbitrary source field profile is produced by decomposing the source into incremental areas (pixels). The received field through the propagation in free space is found by superposing the contributions from all source incremental areas. The proposed method enables us to evaluate the received intensity originating from any type of source field. Using the arbitrary beam excitation, intensity of various laser beams such as cos-Gaussian, cosh-Gaussian, general type beams are checked to be consistent with the already existing results in literature, and the received intensity distributions are obtained for some original arbitrary beam field profiles. Our received intensity formulation for the arbitrary source field profiles presented in this paper can find application in optics communication links, reflection from rough surfaces, optical cryptography and optical imaging systems.     

Switchable vector vortex beam generation using an optical fiber

We present our experimental results on directly transforming a circular-polarized Gaussian beam into linear-polarized vector vortex beams using a two-mode fiber and demonstrate switching between the different 0th-order vector vortex modes excited and guided in the fiber. Depending on the handiness of circular-polarization of the input Gaussian light beam, its launch angle with respect to the fiber axis and by changing them appropriately it is possible to excite and switch between the different vector vortex modes and its coherent linear superposition supported by the two-mode fiber. The output optical beams due to the selectively excited vector modes in the fiber are characterized by using a rotating analyzer and a two-beam interferometer setup to study the polarization and the phase behavior of the vector vortex beam.     

Stochastic parallel gradient descent laser beam control algorithm for atmospheric compensation in free space optical communication

Atmospheric turbulence seriously degrades the performance of free space optical (FSO) communication systems, especially the coupling efficiency. In this paper, we propose a stochastic parallel gradient descent (SPGD) algorithm to compensate the atmospheric turbulence in FSO communication system. Theoretical analysis and work flow of the algorithm are given. Both simulation and experimental results indicate that the coupling efficiency can be increased from 12% to more than 80% after 270 iterations or more than threefold, which implies a significant improvement of the performance.     

Manifestation of mechanical properties of light waves in vortex beam optical systems

It is shown that variations in the frequency and phase of the light beam upon a deformation of the optical system can be caused by the work produced by the light pressure. It is proposed to use this fact to demonstrate and measure mechanical properties of the beam: the momentum, the angular momentum, and peculiarities of their spatial distribution. The possible schemes of experiments for determination of the angular momentum of the Laguerre-Gaussian beam with a screw dislocation of the wave front and the circularly polarized beam with a smooth front are presented. The relationship between the mechanical and geometric characteristics of such beams is discussed.     

Radially polarized hollow Gaussian beam with on-axis spiral optical vortex

The focusing properties of radially polarized hollow Gaussian beam (HGB) with on-axis spiral optical vortex are investigated theoretically by vector diffraction theory. The phase wavefront of HGB is the function of radial coordinate. Calculation results show that the focusing properties can be altered considerably by beam order of HGB, topological charge of the on-axis optical vortex, and phase parameter that characterizes the radial phase wavefront distribution. Higher topological charge induces focal evolution from one focal spot to annular focal pattern in transverse direction, while phase parameter can lead to focal shift along optical axis remarkably. In addition, focal shift direction can also be adjusted by changing varying direction of phase parameter.     

双光束干涉条纹间距的在线测量

双光束干涉是物理光学中的重要内容，也是全息光栅制作的光学原理．本采用CCD光电传感器^[1]在线测量双光束干涉条纹间距的方法，来确定全息光栅常量的实验原理及实验装置，对了解全息照相及计算机在线测量技术是有益的。     

无线激光通信协议的设计(英文)

研究了无线激光通信(FSO)与传统激光通信的区别,编制了一套FSO物理层收发协议。采用现场可编程门阵列(FPGA)完成收发机与外部电路的数据通信,利用先入先出(FIFO)存储器完成收发协议与外部系统的接口。设计的物理层收发协议主要完成发送数据的编码、串行化以及接收数据的解串行化和解码。仿真实验结果表明:设计的收发协议可实现在40 Mbps通信速率下的稳定工作,证明了该收发协议设计的可行性。     

Quantum cascade laser-based free space optical communications

The advent of the quantum cascade laser (QCL) with emission wavelengths available in the infrared range from 3 μm through more than 100 μm opens up the possibility of exploiting infrared atmospheric transparency windows for free space optical communications. In an effort to establish the efficacy of using directly modulated QCLs for free space communications we have conducted a series of investigations that demonstrate the potential advantages of this technology. In these experiments we first establish that the QCL has very high modulation bandwidth. We then implement a practical free space communications link that under conditions of atmospheric fog, dust and other obscurants offers significant transparency advantage when compared with near infrared wavelength sources presently used in commercial free space optical communications links.     

无线激光通信协议的设计

研究了无线激光通信（FSO）与传统激光通信的区别,编制了一套FSO物理层收发协议。采用现场可编程门阵列（FPGA）完成收发机与外部电路的数据通信,利用先入先出（FIFO）存储器完成收发协议与外部系统的接口。设计的物理层收发协议主要完成发送数据的编码、串行化以及接收数据的解串行化和解码。仿真实验结果表明：设计的收发协议可实现在40 Mbps通信速率下的稳定工作,证明了该收发协议设计的可行性。     

All-weather long-wavelength infrared free space optical communications

Long-wavelength infrared radiation possesses superior transmission through common atmospheric problems such as fog, clouds, and smoke than the shorter wavelength laser sources in use today. Recent improvements in LWIR laser and modulator design makes possible reliable optical replacements for radio and microwave communications links in many applications. This paper describes components and techniques developed for high-speed, full-duplex all-weather infrared communications systems.     

Focal patterns of higher order hyperbolic-cosine-Gaussian beam with one optical vortex

Intensity distribution in focal region plays an important role in many optical systems. In this paper, the focal patterns of higher order hyperbolic-cosine-Gaussian (HOCG) beam in focal plane were investigated. The HOCG beam contains one spiral optical vortex on its optical axis. Results show that the focal pattern can be altered considerably by beam order of the incident HOCG beam, and some novel focal patterns may occur, including foursquare focal pattern, cross-shaped dark focal focus, foursquare intensity peaks chain, and multiple intensity peaks array. Focal pattern evolution principle on increasing beam order also differs remarkably under condition of different topological charge of the optical vortex and displacement parameter associated with the cosh parts. And like topological charge and displacement parameter, the beam order and numerical aperture may affect focal pattern.     

径向洛伦兹阵列光束在自由空间的传输特性

推导出有初始相位分布的径向洛伦兹阵列光束在自由空间传输的解析公式,用以研究相干合成光束在自由空间的传输特性。结果表明:在远场,具有不同相位分布的光束光强剖面成为空心形状,具有相同相位分布的光束光强剖面中心为亮斑。合成光束束宽和桶中功率与子光束束腰宽度、径向阵列的初始相位分布和半径有关。对所得结果用数值计算例做了说明。当阵列半径较大和束腰宽度较小时,具有不同相位分布和相同相位的光束束宽随传输距离的变化曲线和桶中功率都趋于一致。     

Propagation dynamics of an optical vortex imposed on an Airy beam

In this Letter, we demonstrate the general propagation dynamics of an Airy beam (AiB) carrying unit phase singularity, i.e., optical vortices (OVs). For the OV with a unit charge, theoretical analysis indicates that the OV carried by the AiB will propagate along the parabolic trajectory with an acceleration velocity twice as fast as conventional AiBs before a critical position. Thereafter, the AiB main lobe destroyed by OV will be reconstructed and the phase singularity will reappear in the middle of the AiB profile.     

Analysis of free space optical link in turbulent atmosphere

Free space optical (FSO) communication is an upgraded supplement to the existing wireless technologies. FSO technology provides vast modulation bandwidth, unlicensed spectrum, cost effective deployment, low power consumption and less mass requirement. Today, researchers are preliminary focused to use the free space communication systems for inter satellites links. In this paper, the performance analysis of FSO communication link in weak atmospheric turbulence has been analyzed for different atmospheric transmission windows using OOK modulation. The analysis has been done using bit error rate as the performance metric. The effect of attenuation on the link performance has been investigated by varying distance between transmitter and receiver for a given power and data rate. Further, BER performance analysis has been carried out for varying data rate and transmitted power. Also, the effect of attenuation on received optical power has been studied. The work has been performed in OptSim environment.     

径向洛伦兹阵列光束在自由空间的传输特性

推导出有初始相位分布的径向洛伦兹阵列光束在自由空间传输的解析公式,用以研究相干合成光束在自由空间的传输特性。结果表明:在远场,具有不同相位分布的光束光强剖面成为空心形状,具有相同相位分布的光束光强剖面中心为亮斑。合成光束束宽和桶中功率与子光束束腰宽度、径向阵列的初始相位分布和半径有关。对所得结果用数值计算例做了说明。当阵列半径较大和束腰宽度较小时,具有不同相位分布和相同相位的光束束宽随传输距离的变化曲线和桶中功率都趋于一致。