Transverse angular momentum in topological photonic crystals

TL;DR

This paper demonstrates the existence of transverse angular momentum modes in topological silicon photonic crystals, enabling robust, broadband unidirectional light transport for integrated photonic applications.

Contribution

It reveals transverse angular momentum modes in topological photonic crystals and their role in achieving broadband, unidirectional, and robust light transport.

Findings

Robust light flow along interfaces with opposite directions was observed.

A transverse orbital angular momentum mode with alternating topological charge was identified.

Unidirectional transport remains stable over a range of frequencies and structural variations.

Abstract

Engineering local angular momentum of structured light fields in real space enables unprecedented applications in many fields, in particular for the realization of unidirectional robust transport in topological photonic crystals with non-trivial Berry vortex in momentum space. Here, we show transverse angular momentum modes in silicon topological photonic crystals when considering transverse electric polarization. Excited by a chiral external source with either transverse spin or orbital angular momentum, robust light flow propagating along opposite directions was observed in several kinds of sharp-turn interfaces between two topologically-distinct silicon photonic crystals. A transverse orbital angular momentum mode with alternating-sign topological charge was found at the boundary of such two photonic crystals. In addition, we also found that unidirectional transport is robust to the working frequency even when the ring-size or location of pseudo-spin source varies in a certain range, leading to the superiority of broadband photonic device. These findings enable for making use of transverse angular momentum, a kind of degree of freedom, to achieve unidirectional robust transport in telecom region and other potential applications in integrated photonic circuits such as on-chip robust delay line.