Unidirectional Far‐Field Radiation of Surface Waves by On‐Chip Achromatic Metasurfaces

ABSTRACT Converting surface waves to unidirectional far‐field beams is crucial for information readout in on‐chip photonic applications, but conventional grating‐like couplers suffer from low‐efficiency issue due to multi‐mode generation. Although recently proposed metasurfaces have addressed this challenge, meta‐couplers realized so far exhibit inevitable frequency dispersions, restricting their practical applications. Here, we propose a scheme to design on‐chip achromatic metasurfaces that can decouple SWs within a continuous frequency band to far‐field beams traveling along the same direction. Our metadevices, composed of composite meta‐atoms exhibiting pre‐designed reflection phases with tailored frequency dispersion dictated by both resonant and Pancharatnam–Berry phase mechanisms, can compensate the desired frequency‐dependent wavevectors for SWs at different frequencies, thereby generating unidirectional far‐field beams. As a proof of concept, we design and fabricate two on‐chip achromatic metasurfaces working in the microwave regime and experimentally demonstrate that they can achieve in‐plane and out‐of‐plane unidirectional far‐field decoupling of SWs, exhibiting relative frequency bandwidths of 22.22% and 37.04%, respectively. Both microwave experiments and full‐wave simulations successfully confirm our theoretical predictions. These findings pave the way for on‐chip photonic manipulations and related applications, including wireless communication, signal processing, high‐sensitivity sensing, and so on.