# Nonlinearity Induced Anomalous Mode Collapsing and Non-chiral Asymmetric Mode Switching around multiple Exceptional Points

## TL;DR

This paper investigates how nonlinear effects in a specially designed optical waveguide cause mode collapsing and asymmetric mode switching around multiple exceptional points, revealing new topological and dynamical behaviors.

## Contribution

It introduces a novel multi-mode waveguide design that exhibits multiple second-order exceptional points and explores their encirclement, leading to unique nonlinear mode dynamics and switching mechanisms.

## Key findings

- Multiple EPs are realized in a three-mode waveguide.
- Nonlinear effects induce asymmetric mode switching.
- Mode collapsing occurs due to nonadiabatic corrections around EPs.

## Abstract

The dynamical encirclement around a second order exceptional point (EP) and corresponding chirality driven nonadiabatic modal dynamics have attracted enormous attention in the topological study of various non-Hermitian systems. However, dynamical encirclement around multiple second-order EPs in a multi-state system is yet to be explored. Here, exploiting an exclusive design of a planar gain-loss assisted three-mode supported optical waveguide with local Kerr-nonlinearity, we encounter multiple second-order EPs. Judiciously, choosing a specific parameter space by varying the unbalanced gain-loss profile, we encircle multiple EPs simultaneously, and explore the beam-dynamics toward corresponding chiral or non-chiral aspects of the device. While propagating through the designed waveguide, three coupled modes are collapsed into a specific dominating mode, owing to corresponding nonadiabatic corrections around multiple EPs. Even in the absence of chirality, here, the same amount of focusing and de-focusing type nonlinearity gives different dominating output, irrespective of the choice of inputs, for the same topological structure of the waveguide. This exclusive topologically robust compact scheme of nonlinearity induced asymmetric and non-chiral light dynamics should provide a promising opportunity to switch or retrieve a selective mode from a multi-mode signal in integrated devices.