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Propagation propertiesof off-axis elliptical vortex beams
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Zhu Zhengtian
1
, Zhang Mingming
2
, Zhao Qi
1
, Xin Yu
1
, Chen Yanru
1
, Yu Renlong
1
,
Song Mingming
3**
5
(1. School of Electronic and Optical Engineering, Nanjing University of Science and Technology,
Nanjing 210094, China;
2. School of Information Science and Engineering, Xiamen University, Xiamen 361005, China;
3. Shanghai Xinyue Instrument Factory,Shanghai Academy of Spaceflight Technology, Shanghai
200233, China) 10
Foundations: the National Natural Science Foundation of China (61107011 and 61077012), the Specialized
Research Fund for the Doctoral Program of Higher Education (20123219110021), the Fundamental Research
Funds for the Central Universities(30920130112005) , the Innovation Fund for the Shanghai Aerospace Science
and Technology (SAST201350)
Brief author introduction:朱正天(1991-),男,硕士,主要研究方向:光学工程
Correspondance author: 赵琦(1961-),男,教授,主要研究方向:光学工程. E-mail: zhaoqi@njust.edu.cn
Abstract: Based on the Fresnel diffraction integral and Fourier transform, the analytical expression for
the propagation of off-axis elliptical vortex beams in free space is derived, which is used to study the
intensity distribution and propagation of phase singularity by numerical simulation. The results show
that the intensity distributions of beams change significantly while propagating. Position and number of
phase singularities are dependent on the vortex position at the source plane, propagation distance and 15
topological charge number. This research is useful for a deep understanding of the propagation of
off-axis phase singularity, and provides guidance for the beam aligning.
Key words: off-axis, elliptical vortex beams, phase singularity
20
1. Introduction
Optical vortex, carrying a special spiral wave front, has been a hot research topic
in recent years. Vortex beam has attracted an increasing interest in optical trapping
[1,2]
, quantum communication
[3]
, biomedicine
[4]
, etc.There are a lot of methods to
produce vortex beams, such as astigmatic mode converter,computer generated or 25
holography technique using spatial light modulators as well as interferometric
methods
[5]
. In experiment, vortex beams are mostly produced by using laser beams to
pass through a spiral phase plate (SPP),when the laser beam passes through the SPP,
the beam will be with a phase factor of
, where m is the topological charge(can
have both positive and negative sign depending on the sense ofrotation of the 30
corkscrew) or the order of the vortex.But in practical application, the center of vortex
beam from laser cannot be completely aligned with the center of SPP which means
the projecting beams from the SPP are actually off-axis vortex beams
[6-11]
.
In this paper, we studieda kind of non-canonical off-axis vortex beams called
off-axis elliptical vortex beams
[12,13]
. Ref. [12] studied the elliptical vortex beams 35
passing through a slit hexagon aperture, the conclusions can be used to measure the
magnitude of topological charge of the vortex beams according to the diffraction
patterns. Ref. [13] studied the elliptical vortex beams propagating in atmospheric
turbulence, and found that using elliptical vortex beams can effectively reduce the
effect of atmospheric turbulence on beams propagation, which can effectively reduce 40
the scintillation index. Red.[14]introduced an asymmetry in the core of a high charge
opticalvortex and found that the splitting of high topological charge vortices into
vortices of single charge becomes more pronounced with increase in the asymmetry in
their experiments. After the splitting, the single charge vortices align themselves in a
straight row. 45
Although some of such studies about the elliptical vortex beams have already