Ultra-Broadband Mode Size Converter Using On-Chip Metamaterial-Based Luneburg Lens

A Luneburg lens with a gradient index distribution is an aberration-free and coma-free spherical lens. It has wide applications ranging from invisibility cloaks, illusion optics, and superlensing. However, it is challenging to realize an on-chip Luneburg lens with superior performance. In this paper, an on-chip Luneburg lens is implemented through the integration of gradient metamaterial structures and silicon waveguides. The filling ratio...