# Exceptional-point-encirclement emulation tailoring: multidimensional asymmetric switching of all-fiber devices

## TL;DR

Researchers developed a new fiber-based device that enables multidimensional asymmetric switching by emulating exceptional point encirclement, achieving high-performance switching of polarization, mode, and orbital angular momentum.

## Contribution

The novel topology-optimized architecture enables multidimensional asymmetric switching without inherent 3-dB loss and demonstrates asymmetric orbital angular momentum switching for the first time.

## Key findings

- A new architecture eliminates 3-dB loss by using (de)multiplexers instead of couplers.
- The device enables high-performance asymmetric switching of polarization, mode, and orbital angular momentum.
- This is the first experimental demonstration of asymmetric orbital angular momentum switching.

## Abstract

In non-Hermitian systems, the dynamic encircling of exceptional points (EPs) engenders intriguing chiral phenomena, where the resultant state characteristics are intrinsically dependent upon the encircling handedness. An ingenious approach using simple leaky optical elements has been presented to emulate this chiral behavior without physically encircling an EP. This innovative simplification of EP properties enables a more straightforward implementation of asymmetric switching of polarization and path. Given that photons inherently possess multiple physical degrees of freedom, the research focus has shifted from single-dimensional to multidimensional asymmetric switching. Hence, there is a fundamental challenge of how to achieve multidimensional asymmetric switching through a simple and universally applicable architecture. Here, we propose and experimentally demonstrate a novel topology-optimized architecture, termed EP-encirclement emulation tailoring, enabling multidimensional asymmetric switching. Theoretical analysis reveals that our architecture eliminates the 3-dB inherent loss in conventional architecture by replacing couplers with (de)multiplexers. Building upon this architecture, we harness all-fiber devices to implement a high-performance asymmetric switching of polarization, mode, and orbital angular momentum (OAM). To our knowledge, this is the first experimental demonstration of asymmetric OAM switching to date. Our work provides an efficient topology architecture for emulating dynamic EP encirclement, paving the way for universal and flexible asymmetric switching devices.