Ren Peiwen, Zheng Junrong, Huang Zhuo, Liu Yan, Zhang Long, Zhang Hua, Ma Jingwen, Chen Zhanghai, Li Jian-Feng, Yi Jun, Yang Zhilin
Xiamen University, College of Physical Science and Technology, School of Electronic Science and Engineering, State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, College of Energy, Fujian Key Laboratory of Ultrafast Laser Technology and Applications, Xiamen 361005, China.
The University of Hong Kong, Department of Electronic Engineering, Hong Kong, China.
Phys Rev Lett. 2025 Aug 22;135(8):083803. doi: 10.1103/bzpw-7h2x.
The photonic flat band, defined by minimal dispersion and near-zero group velocity, has facilitated significant advances in optical technologies. The practical applications of flat bands, such as enhanced light-matter interactions, require efficient coupling to far-field radiation. However, achieving controlled coupling between flat bands and their corresponding localized modes with far-field radiation remains challenging and elusive. Here, we achieve the tunable far-field excitation of a flat band in the near-infrared spectral range by coupling it to a photonic anapole mode. Distinct from conventional multipolar resonances in both its physical nature and unique radiation dynamics, the anapole mode offers highly localized field distributions and tunable emission characteristics, enabling the realization of a photonic flat band and precise control over its transition from a nonradiative to a radiative state. We directly observed the flat band within ±25° experimentally by angle-resolved far-field transmissivity spectroscopy. Simulation results extending to 90° confirm the persistence of the band's flatness across all incident angles, validating the inherent flatness of the band. Our findings not only provide a viable approach to accessing photonic flat bands but also significantly advance the field of nanoscale photonic manipulation, offering broad potential applications in optical technologies.
由最小色散和近零群速度定义的光子平带推动了光学技术的重大进展。平带的实际应用，如增强光与物质的相互作用，需要与远场辐射进行有效耦合。然而，实现平带与其相应的局域模式与远场辐射之间的可控耦合仍然具有挑战性且难以捉摸。在这里，我们通过将近红外光谱范围内的平带与光子无偶极模式耦合，实现了其可调谐的远场激发。无偶极模式在物理性质和独特的辐射动力学方面都与传统的多极共振不同，它提供了高度局域化的场分布和可调谐的发射特性，从而能够实现光子平带并精确控制其从非辐射态到辐射态的转变。我们通过角分辨远场透射率光谱实验直接在±25°范围内观测到了平带。扩展到90°的模拟结果证实了该带在所有入射角上的平坦度持续存在，验证了该带固有的平坦性。我们的发现不仅提供了一种获取光子平带的可行方法，还显著推动了纳米级光子操纵领域的发展，在光学技术中具有广泛的潜在应用。
