# Exceptional Point and Toward Mode Selective Optical Isolation

## TL;DR

This paper presents a novel, topologically robust optical isolation scheme using a gain-loss assisted waveguide with an exceptional point, enabling highly nonreciprocal, mode-selective light transmission with enhanced contrast for integrated photonics.

## Contribution

It introduces a gain-loss assisted dual-mode waveguide exploiting exceptional point encirclement for highly nonreciprocal, mode-selective optical isolation with tunable nonlinearity effects.

## Key findings

- Achieved up to 40 dB nonreciprocal transmission contrast.
- Demonstrated a scalable, topologically robust mode-selective isolation scheme.
- Proposed device enables efficient mode filtering in integrated photonic circuits.

## Abstract

Dynamical encirclement of an Exceptional Point (EP) and corresponding time-asymmetric mode evolution properties due to breakdown in adiabatic theorem have been a key to range of exotic physical effects in various open atomic, molecular and optical systems. Here, exploiting a gain-loss assisted dual-mode optical waveguide that hosts a dynamical EP-encirclement scheme, we have explored enhanced nonreciprocal effect in the dynamics of light with onset of saturable nonlinearity in the optical medium. We propose a prototype waveguide-based isolation scheme with judicious tuning of nonlinearity level where one can pass only a chosen mode in any of the desired directions as per device requirement. The deliberate presence of EP enormously enhances the nonreciprocal transmission contrast even up to 40 dB over the proposed device length with a scope of further scalability. This exclusive topologically robust mode selective all-optical isolation scheme will certainly offer opportunities in integrated photonic circuits for efficient coupling operation from external sources and improve device performances.