Subwavelength resolution of conical Fresnel zone lens

Abstract

Compared to the bulky and heavy ordinary lens the Fresnel zone (FZ) plate has the advantage of being thin, light and easy to manufacture. The ordinary lens, however, has a broadband and effective focusing. For a better FZ lens efficiency the next techniques are employed: subzone phase-correcting, curved (3D) zone surface or both put together. Here the second technique is illustrated in a Conical Fresnel Zone (CFZ) lens of Metal rings (Soret-type CFZM.υ.α lens), and both techniques are applied in a CFZ lens of Dielectric rings (Wood-type CFZD.υ.α lens) rings, where υ is the number of rings and α is the cone half-opening angle.