A Nearly Perfect Implementation of a Broadband Optical Null Media via Space‐Folding

ABSTRACT Optical null media (ONM), a class of metamaterials with extreme electromagnetic parameters, enable perfect directional projection of incident waves. However, conventional ONM implementations suffer from narrow bandwidth and impedance mismatch, severely limiting their practical applicability. Here, we propose and experimentally demonstrate an ultrabroadband space‐folding ONM integrated with symmetric impedance‐matching transition layers. It replicates the directional projection behavior of an ideal ONM while also enabling precise wavefront engineering by tailoring two independent geometric parameters, i.e., the folding ratio and the dilution ratio. With the incorporation of impedance‐matching layers, the structure maintains high transmittance over a wide frequency range, effectively realizing a broadband ONM. A broadband, low‐dispersion, high‐efficiency transmissive beam‐focusing lens designed using this concept demonstrates consistent focusing performance across the entire bandwidth (5–9 GHz) and shows excellent agreement between numerical simulations and microwave experiments. Owing to its simple material requirements, broadband operation, and flexible wavefront control capabilities, the proposed space‐folding ONM opens new avenues for invisibility cloaking, on‐chip photonic integration, and advanced beam‐manipulation devices.