Detection of degenerate Stokes index states

Gauri Arora,P Senthilkumaran,Saba N Khan,S Deepa

doi:10.1038/s41598-020-77365-8

Gauri Arora, P Senthilkumaran + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-77365-8

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Journal: Scientific Reports	Publication Date: Nov 27, 2020
Citations: 22	License type: open-access

Affiliation: Indian Institute of Technology Delhi

Abstract

Stokes phase is the phase difference between orthogonal component states in the decomposition of any polarization state. Phase singularities in the Stokes phase distribution are Stokes singularities of an inhomogeneous polarization distribution. Under circular decomposition, Stokes phase distribution (phi _{12}) represents polarization azimuth (gamma ) distribution and the singularities present in it are polarization singularities. Therefore, the charge of the Stokes vortices depicted as Stokes index sigma _{12} is an important parameter associated with the polarization singularity. The Hybrid order Poincaré sphere (HyOPS)/Higher order Poincaré sphere (HOPS) beams, all having same Stokes index, contain a Stokes singularity at the center of the beam as these beams are constructed by vortex superposition. These beams, being superposition of orthogonal orbital angular momentum (OAM) states in orthogonal spin angular momentum (SAM) states can offer great multiplexing capabilities in communication. In this article, we identify these degenerate Stokes index states and discuss the ways and means of lifting this degeneracy. Otherwise, there are limitations on intensity based detection techniques, where demultiplexing or segregation of different HOPS/HyOPS beams is warranted. The method adduced here uses the diffraction of these beams through an equilateral triangular aperture in combination with polarization transformation as a probe to lift the Stokes index/Stokes phase degeneracy. Successively, the novelty of the detection scheme is discussed in the context of beams with alike polarization distributions where even the technique of Stokes polarimetry fails to predict the OAM and SAM content of the beam.

Highlights

Stokes phase is the phase difference between orthogonal component states in the decomposition of any polarization state
Further discrimination among various state of polarizations (SOPs) distributions can be obtained by polarization transformations, and the patterns obtained are shown in the outermost ring
The input Hybrid order Poincaré sphere (HyOPS) beams’ SOP distribution and diffracted intensity patterns are depicted near the points along the longitude on the sphere, whereas for the equatorial points the diffraction patterns are further subjected to polarization transformations and are shown on the right side of Fig. 6 in a 4x4 frame along with their SOP distributions and Stokes phases

Summary

Introduction

Stokes phase is the phase difference between orthogonal component states in the decomposition of any polarization state. For a given Stokes index σ12 there can be a multitude of SOP distributions represented by non-polar points on a HOPS or on a HyOPS. Five representative degenerate Stokes phase states for a given Stokes index σ12 are chosen to describe the diffraction and polarization transformation patterns.

Results

Conclusion