A Broad-Band Achromatic Polarization-Insensitive In-Plane Lens with High Focusing Efficiency

Until now, many pioneering studies have been conducted on multiwavelength achromatic lens designs that can eliminate chromatic aberrations at various wavelengths. In these studies, the working bandwidth is still not wide enough for practical applications, and an effective achromatic design is achieved with a long design cycle that determines critical elements of the unit cell. To solve the limitations of the unit cell method, we use inverse design to simultaneously explore structures with broad bandwidth and high efficiency. In this study, we show that it is possible to obtain an achromatic cylindrical lens that can focus transverse electric and transverse magnetic polarization between 1300 and 1750 nm using the objective-first algorithm. We implement the generalized Bruggeman effective medium theory to binarize the lens with randomly varying index profiles while maintaining the optical performance of the cylindrical inverse-designed lens. The binarized lens is produced via three-dimensional printing and tested in a microwave regime, exhibiting high bandwidth operation and high focusing efficiency (average 62%).