Multiobjective Optimization of Bespoke Gradient-Index Lenses: A Powerful Tool for Overcoming the Limitations of Transformation Optics

Gradient-index (GRIN) lenses have paved the way for electromagnetic wave tailoring due to their spatially varying permittivities, which enable continuous manipulation of the wave as it passes through the lens volume. However, traditional GRIN design methodologies, such as transformation optics or geometrical optics, often generate lens profiles that are limited to single-band performance. Here, we propose a multiobjective optimization strategy customized for designing dual-band GRIN lenses. Utilizing this powerful inverse-design tool, in conjunction with an advanced manufacturing technique, a GRIN lens with compact size and nonintuitive permittivity distribution is designed, fabricated, and characterized. The lens is capable of realizing two unique gain enhancement objectives at the L and C bands simultaneously, where different feeding sources are employed at the two bands.