X-type vortex and its effect on beam shaping

Abstract

In this article we propose a new type of optical vortex, the X-type vortex. This vortex inherits and develops the conventional noncanonical vortex, i.e. it no longer has a constant phase gradient around the center, while the intensity keeps invariant azimuthally. The strongly focusing properties of the X-type vortex and its effect on the beam shaping in three-dimensional (3D) fields are analyzed. The interesting phenomena, which cannot be seen in canonical vortices, are observed, for instance the ‘switch effect’ which shows that the intensity pattern can switch from one transverse axis to another in the focal plane by controlling the phase gradient parameter. It is shown that by adjusting the phase gradient of this vortex, the focal field can have marvelous patterns, from the doughnut shape to the shapes with different lobes, and the beam along propagation direction will form a twisting shape in 3D space with controllable rotation direction and location. The physical mechanisms underlying the rule of the beam shaping are also discussed, which generally say that the phase gradient of the X-type vortex, the orbital angular momentum, the polarization and the ‘nongeneric’ characteristic contribute differently in shaping fields. This new type of vortex may supply a new freedom for tailoring 3D optical fields, and our work will pave a way for exploration of new vortices and their applications.

Manipulation of Energy Flow with X-Type Vortex

“…The X-type vortex is a type of noncanonical optical vortex, with an anisotropic phase distribution [36]. The transverse field of an optical beam embedded with an X-type vortex can be expressed as:…”

“…The vortex also plays a key role in most research on Photonics 2022, 9, 998 2 of 14 the manipulation of energy flows [12,[14][15][16][17][18][19][20]22]. Besides the well-known canonical vortex, there also exists the noncanonical vortex, which has not received as much attention in most studies [32][33][34][35][36]. For a noncanonical vortex, the phase gradient is no longer constant along the azimuthal direction; thus, there will exist an 'anisotropic parameter' characterizing the phase distribution, which actually provides more freedom for beam structure [33,36].…”

“…Besides the well-known canonical vortex, there also exists the noncanonical vortex, which has not received as much attention in most studies [32][33][34][35][36]. For a noncanonical vortex, the phase gradient is no longer constant along the azimuthal direction; thus, there will exist an 'anisotropic parameter' characterizing the phase distribution, which actually provides more freedom for beam structure [33,36]. Very recently, an X-type vortex, as one type of the noncanonical vortex, was proposed, and it was found that this noncanonical vortex could shape the intensity distribution in rich structures in 3D vector fields [36].…”

“…For a noncanonical vortex, the phase gradient is no longer constant along the azimuthal direction; thus, there will exist an 'anisotropic parameter' characterizing the phase distribution, which actually provides more freedom for beam structure [33,36]. Very recently, an X-type vortex, as one type of the noncanonical vortex, was proposed, and it was found that this noncanonical vortex could shape the intensity distribution in rich structures in 3D vector fields [36]. In this article, we will use the X-type vortex and show its effects on energy flows.…”