Evolutionary Design and Prototyping of Single Crystalline Titanium Nitride Lattice Optics

This paper describes the design and prototyping of single-crystalline TiN plasmonic metasurfaces based on subwavelength hole arrays. An evolutionary algorithm with a multiobjective fitness function was developed to produce a variety of three-dimensional (3D) light profiles with balanced intensities at the light spots. We also demonstrated a simple, efficient technique to prototype these lattice designs in large-area TiN films by combining focused ion beam milling and wet chemical etching. Multilevel phase control was achieved by tuning nanohole size, and multipoint focusing with arbitrary light spot patterns was realized. Using anisotropic nanohole shapes, the TiN lattice lenses could exhibit dynamic tuning of the focal profiles by changing the polarization of incident light.