Broadband Low‐Loss Unidirectional Reflection On‐Chip with Asymmetric Dielectric Metasurface

Metasurface has emerged as a powerful platform for controlling light at subwavelength thickness, enabling new functionalities for imaging, polarization manipulation, and angular momentum conversion within a flat surface. An integrated asymmetric metasurface simultaneously achieving broadband, low loss forward power transmission, and significant back reflection suppression in multi‐mode waveguides is explored. The tapering along the direction of light propagation leads to low loss and space‐efficient mode conversion. Enhanced by a double‐flipped structure, a thin (2.5 µm) metasurface can simultaneously achieve high conversion efficiency (>80%), and back‐reflection efficiency of 90% over a 200 nm wavelength range. Such single‐side reflectors can be one of the enabling components for gain‐integrated adaptive optics on a chip.