Spiral Transformation for High-Resolution and Efficient Sorting of Optical Vortex Modes

Abstract

Mode sorting is an essential function for optical multiplexing systems that exploit the orthogonality of the orbital angular momentum mode space. The familiar log-polar optical transformation provides a simple yet efficient approach whose resolution is, however, restricted by a considerable overlap between adjacent modes resulting from the limited excursion of the phase along a complete circle around the optical vortex axis. We propose and experimentally verify a new optical transformation that maps spirals (instead of concentric circles) to parallel lines. As the phase excursion along a spiral in the wave front of an optical vortex is theoretically unlimited, this new optical transformation can separate orbital angular momentum modes with superior resolution while maintaining unity efficiency.

Sorting of spatially incoherent optical vortex modes

“…concept and principle. The spiral transformation method has been successfully applied for high resolution sorting of coherent OAM modes of light 10 . In this work we have applied it to OAM mode sorting of spatially incoherent OAM modes.…”

“…However, the most used optical beam is the OAM beam called Laguerre-Gauss (LG) beam 6 which can be decomposed in terms of orthogonal components allowing being space-divided with low inter-modal crosstalk among multiple modes 2,3,7 . This beam has a finite spatial extend and due to its azimuthal phase dependence can be sorted [8][9][10] , being ideal to optical communications.…”

“…The second type of ray-optics coordinate transformation is the spiral transformation that maps spirals to parallel lines. In this case, the tilt of the plane waves is theoretically unlimited and, in practice, the resolution of the mode separation is considerably improved 10 .…”

Generation and decomposition of scalar and vector modes carrying orbital angular momentum: a review

“…The second element has to correct the relative phase between these copies at the Fourier plane of the fan-out element. [205][206][207] Recent research work has also demonstrated that performing a spiral transformation instead of a log-polar transformation can also improve the resolution of the mode-sorter output. 208 However, all these methods improve resolution at the expense of making the setup more complex.…”

Tunable Polycyclic Chiral Beams

“…[ 1,2 ] OVs are characterized by a twisting wavefront, phase singularities, orbital angular momentum (OAM), [ 3–6 ] and null intensity in the beam center. These unique properties have been employed in many applications, such as optical communication, [ 7–9 ] optical manipulation, [ 10–14 ] super‐resolution microscopy, [ 15,16 ] quantum information communication, [ 17–19 ] and laser micromachining. [ 4 ] The OAM carried by each photon deliver energy to particles and can cause them to rotate.…”