Optical waveguide hosting multiple exceptional points: Toward selective mode conversion

TL;DR

This paper explores the physical properties of multiple exceptional points in a 1D optical waveguide, demonstrating topologically robust mode switching that can enable selective optical mode conversion devices.

Contribution

It introduces a novel waveguide design hosting multiple EPs with a topologically robust mode switching mechanism for selective mode conversion.

Findings

Multiple EPs are realized in a 1D waveguide with four modes.

Encircling EPs in parameter space causes topologically protected mode switching.

The mode switching is robust against variations in parametric loops.

Abstract

We investigate the astonishing physical aspects of Exceptional Points (EPs) in a 1D planar few-mode optical waveguide. The waveguide hosts four quasi-guided modes. Here interactions between the selected pair of modes are modulated by a spatial distribution of inhomogeneous gain-loss profile. Both the coupled pairs approach two different second-order EPs in parameter plane. Considering a proper parametric loop to encircle the identified EPs simultaneously, we establish a specific topological feature where one round encirclement in parameter space yields the switching between the propagation constants ({\beta}) of the corresponding pairs of couple modes in complex {\beta}-plane. Choosing two different patterns of the parametric loop, we establish the immutable topology in {\beta}- switching phenomena. This robust mode conversion scheme shall provide a platform to realize selective mode switching devices or optical-mode converters.