The key role of off-axis singularities in free-space vortex transmutation

Abstract

We experimentally demonstrate the generation of off-axis phase singularities in a vortex transmutation process induced by the breaking of rotational symmetry. The process takes place in free space by launching a highly-charged vortex, owning full rotational symmetry, into a linear thin diffractive element presenting discrete rotational symmetry. It is shown that off-axis phase singularities follow straight dark rays bifurcating from the symmetry axis. This phenomenon may provide new routes towards the spatial control of multiple phase singularities for applications in atom trapping and particle manipulation.

Analytical solution for multi-singular vortex Gaussian beams: the mathematical theory of scattering modes

“…(1) valid for all z in terms of the scattering modes as φ(w, w, z) = Φ 11 (w, w, z) − (a 1 + a 2 )Φ 01 (w, w, z) + a 1 a 2 Φ −10 (w, w, z). (32) Note the following simple rules in the procedure used to obtain solution (32):…”

“…This can be obtained as a diffraction of an LG mode showing definite angular momentum (that is, a highly charged vortex) by a thin diffractive discrete element showing certain discrete symmetry, as described in [25,26]. The particular generation of these solutions -termed as discrete Gaussian beams-out of LG modes can show the phenomenon known as vortex transmutation, that is the inversion of the topological charge as a consequence of the discrete symmetry [27,28,29,30,31,32].…”

Optical Vortex Transmutation with Geometric Metasurfaces of Rotational Symmetry Breaking

“…[15] However, if a medium has the symmetry breaking from O(2) continuous symmetry into C N discrete rotational symmetry of N-th order, the vorticity conservation is not preserved and the vortex transmutation phenomenon is observed. [16][17][18][19][20][21][22][23][24][25][26] Many previous works have been done to show the vortex transmutation rule by using photonic lattices or diffractive optical elements with C N discrete symmetry. [20][21][22][23][24][25][26] By using polygonal lenses as diffractive optical elements, the free-space vortex transmutation has been realized for changing the central vorticity of a coaxially incident optical vortex.…”

“…[16][17][18][19][20][21][22][23][24][25][26] Many previous works have been done to show the vortex transmutation rule by using photonic lattices or diffractive optical elements with C N discrete symmetry. [20][21][22][23][24][25][26] By using polygonal lenses as diffractive optical elements, the free-space vortex transmutation has been realized for changing the central vorticity of a coaxially incident optical vortex. [22][23][24][25][26] Recently, the free-space vortex transmutation has also been observed in the vortex generation by the closed-path nanoslits, where…”

“…[20][21][22][23][24][25][26] By using polygonal lenses as diffractive optical elements, the free-space vortex transmutation has been realized for changing the central vorticity of a coaxially incident optical vortex. [22][23][24][25][26] Recently, the free-space vortex transmutation has also been observed in the vortex generation by the closed-path nanoslits, where…”