Propagation Characteristics Of Quasi-Airy Vortex Beams In Random Media

Airy beam has attracted considerable attention due to its intriguing properties,such as non-diffraction,self-acceleration and self-healing during propagation.The quasi-Airy beams,which are obtained by modulating the intensity and phase of Airy beams,not only have the characteristics of Airy beams,but also have some advantages in certain characteristics to satisfy the special application,and the circular quasi-Airy beam arrays constructed by arranging quasi-Airy beam in a circular array has controllable self-focusing property which has important applications in particle manipulation,imaging and communication.In addition,vortex beams carrying orbital angular momentum(OAM)increase the degree of freedom of optical information manipulation.Furthermore,using orbital angular momentum as the information carrier can achieve higher spectral efficiency and greater information capacity.However,when the beam propagates through the random medium like atmosphere turbulence and so on,wavefront of vortex beam will be distorted,and will reduce information quality by diffusion of the orbital angular momentum even break the propagation information.In order to improve the quality of the optical information,it’s an effective method to modulate the vortex beam structure.Therefore,in this paper,we investigate the propagation properties of vortex beams and arrays generated by quasi-Airy beam as sub-beams in free space and random media as providing a theoretical basis for the application of vortex beam as information carrier in free space and random medium in random media.By means of numerical simulation,we have systematically studied the quasi-Airy vortex beams and circular quasi-Airy vortex beam arrays.We have explored the propagation properties of the circular quasi-Airy vortex beam arrays in two random media: turbulent atmospheric and uniform rough surface,its main content includes:(1)Based on Airy beams,we construct quasi-Airy beams by means of Fourier spectrum propagation inversion,and explore the self-acceleration,caustics and self-recovery properties of quasi-Airy beams according to their propagation trajectory.Then,several quasi-Airy beams are arranged in annular arrays to form a circular quasi-Airy beam array.Because each of sub-beams is self-accelerating,the circular quasi-Airy beam array gradually focuses as it propagates,forming a self-focused beam.In addition,we have obtained different circular quasi-Airy beam arrays by changing the topological angle of the quasi-Airy beams.By taking ring Airy beam as a reference,we can regulate and control the focusing properties of the circular quasi-Airy beam array.(2)Quasi-Airy vortex beam is obtained by introducing a vortex in the main lobe and gap between the side lobes of the quasi-Airy beam.Propagation properties of quasi-Airy beams with different initial parameters(topological angle,truncation factor,topological charge,etc.)are explored in free space.The results show that the topological charges of optical vortex can be determined by the far-field distribution of acute-angle quasi-Airy vortex beams.Using quasi-Airy vortex beams as information carriers can improve the capacity and information confidentiality of free space optical communication systems.(3)Circular quasi-Airy vortex beam array with central spiral phase is constructed by a annular arrangement of stepped phase.Taking the ring Airy vortex beam as a reference,we explore the influence of different initial parameters,such as topological angle,truncation factor,topological charges of quasi-Airy vortex beam on propagation properties.The results show that there is a weak caustic optical region around the main ring near the center focusing position due to the interaction between the caustic property and the vortex.In addition,we have obtained the relevant conditions for regulating the focusing of the quasi-Airy vortex beam arrays.(4)There is exploration of the circular quasi-Airy beam array’s propagation properties in turbulent atmosphere in detail.By using the crosstalk theory of orbital angular momentum modes,we investigate the degree of spiral spectrum dispersion of a quasi-Airy vortex beam array affected by turbulent atmosphere by changing the initial parameters of light field,such as truncation coefficient,topological angle of sub-beam and topological charge and so on.(5)There is exploration of the speckle field structures formed by the initial field(initial position z=0)and the focusing field(position at the center of focus)on a uniform rough surface.The results show that the density of phase singularities in the speckle field can be used to characterize the surface of a rough medium.