Photonic flat‐band lattices and unconventional light localization

Abstract

Abstract Flat‐band systems have attracted considerable interest in different branches of physics in the past decades, providing a flexible platform for studying fundamental phenomena associated with completely dispersionless bands within the whole Brillouin zone. Engineered flat‐band structures have now been realized in a variety of systems, in particular, in the field of photonics. Flat‐band localization, as an important phenomenon in solid‐state physics, is fundamentally interesting in the exploration of exotic ground‐state properties of many‐body systems. However, direct observation of some flat‐band phenomena is highly nontrivial in conventional condensed‐matter systems because of intrinsic limitations. In this article, we briefly review recent developments on flat‐band localization and the associated phenomena in various photonic lattices, including compact localized states, unconventional line states, and noncontractible loop states. We show that the photonic lattices offer a convenient platform for probing the underlying physics of flat‐band systems, which may provide inspiration for exploring the fundamentals and applications of flat‐band physics in other structured media from metamaterials to nanophotonic materials.