Hidden singularities in 3D optical fields

TL;DR

This paper reveals two unique types of hidden singularities in 3D optical fields—spin density phase and vector singularities—and explores their properties and interrelations, advancing fundamental understanding of 3D optical phenomena.

Contribution

It introduces the concept of two distinct SD singularities in 3D optical fields and analyzes their behaviors and connections, which were previously unrecognized.

Findings

Identification of spin density phase and vector singularities as unique to 3D fields

Mapping between the two types of SD singularities in purely transverse spin density fields

Provision of a fundamental theoretical framework for SD singularities in 3D optics

Abstract

In this article we show that in a three dimensional (3D) optical field there can exist two types of hidden singularities, one is spin density (SD) phase singularity and the other is SD vector singularity, which are both unique to 3D fields. The nature of these SD singularities is discussed and their connection with traditional optical singularities is also examined. Especially it is shown that in a 3D field with purely transverse spin density (`photonic wheels'), these two types of singularities exhibit very interesting behaviors: they are exactly mapped to each other regardless of their different physical meanings and different topological structures. Our work supplies a fundamental theory for the SD singularities and may provide a new way for further exploration of 3D optical fields.