# Full Asymmetric Radiation Control Through Multi‐Channel Bound States in the Continuum

## TL;DR

This paper introduces a method to fully control light radiation using bound states in the continuum, enabling precise manipulation of light direction and phase for advanced photonic applications.

## Contribution

The paper presents a novel approach to achieve full tunability of unidirectional guided resonances using co-propagating diffraction orders in superwavelength BICs.

## Key findings

- Co-propagating diffraction orders in one half-space enable full control over unidirectional guided resonances.
- Directionality of UGRs can be tuned continuously from -1 to 1.
- Relative phase difference between beams can be adjusted from -π to π.

## Abstract

Bound states in the continuum (BICs) are waves exhibiting theoretically infinite quality factors, offering a powerful mechanism for extreme light confinement in photonic structures. Although breaking vertical structural symmetry in BICs‐supporting systems can induce asymmetric radiation, the radiated power typically remains partitioned between opposing half‐spaces. Furthermore, achieving arbitrary control over the amplitude ratio and phase difference of these counter‐propagating beams presents a significant challenge, thereby limiting sophisticated beam manipulation within a single half‐space. In this work, we delve into BICs within the superwavelength regime, where photonic structures inherently support multiple diffraction orders. We systematically investigate the far‐field polarization states and associated topological properties of these individual diffraction channels. Critically, by engineering a configuration that supports two co‐propagating diffraction orders directed into the same half‐space, we demonstrate comprehensive and continuous control over the resulting unidirectional guided resonances (UGRs). Full tunability of both the directionality (spanning from −1 to 1) and the relative phase difference (spanning from −π to π) between these two co‐propagating beams is achieved. This versatile manipulation of multiple beams radiating concertedly into a specific direction opens new avenues for various advanced applications.

Bound states in the continuum (BICs) enable extreme light confinement via high Q‐factors, but their radiation splits into half‐spaces with limited beam control. Here, in super wavelength BICs (supporting multiple diffraction orders), we design co‐propagating orders in one half‐space, achieving full tuning of UGRs’ directionality (−1 to 1) and phase (‐π to π), boosting advanced applications.