Research Progress from Suzhou Laboratory Published in Nature

On February 26, 2025, a groundbreaking paper titled "Disorder-assisted real-momentum topological photonic crystal" published in Nature by Professor Song Qinghua, Professor Li Bo from Suzhou Laboratory, alongside Professor Zhou Ji from Tsinghua University, Professor Qiu Cheng-Wei from National University of Singapore and Professor Romain Fleury from École Polytechnique Fédérale de Lausanne. This research introduces a novel concept of real-momentum topological photonic crystals, which can incorporate disorder as information carrier without compromising the topological properties of optical singularities, addressing a significant challenge in the field of topological photonics.

A Major Challenge in Topological Photonics

In topological photonics, Bound States in the Continuum (BICs) are specific optical singularities where energy is localized and cannot radiate outward. These states form non-radiative, high-Q polarization singularities in momentum space, with non-trivial topological charge in their surrounding polarization distributions. BIC hold great promise for applications in vortex beam generation, field enhancement, and high-Q optical systems.

Conventional BICs in metasurfaces and photonic crystals rely on strict periodic structures. Disorder in these structures can disrupt periodicity, causing BIC to degrade into quasi-BIC (QBIC) and losing their topological properties. Consequently, past research has mainly focused on minimizing the impact of disorder. However, disorder also provides additional degrees of freedom for structural control, which is crucial for wavefront manipulation applications. Thus, one of the major challenges in topological optics is how to introduce effective disorder into BICs without compromising their topological characteristics.

The Unique Concept of Real-Momentum Topological Photonic Crystals

To address this challenge, the research team proposed the concept of real-momentum topological photonic crystals for the first time (Figure 1). They discovered a unique BIC resonance mode in photonic crystals, where the electric field distribution exhibits a topological singularity at the structural center. Encircling this singularity, vortex phase profile with a non-trivial topological charge is formed. Remarkably, this topological resonance mode is immune to structural perturbations. When the structure undergoes minor changes, the resonance mode remains unaffected due to the topological protection of the singularity, thereby significantly enhancing the stability of BICs (Figure 2).

In the future, the research team will continue to address key challenges in this important field, and aim to apply it in optical communication, holographic displays, and special-shaped lasers.

Figure 1: Schematic of the effect of real-momentum space topological photonic crystal

Fig. 2 Topological resonance modes with immunity to structural perturbations

Its electric field distribution presents a singularity at the center of the structure, and the phase distribution has a non-trivial topological charge that is not affected by structural perturbations

Link to paper：https://www.nature.com/articles/s41586-025-08632-9