Rigorous concept for the design of diffractive microlenses with high numerical apertures

Cylindrical dielectric diffractive microlenses are designed by the use of rigorous electromagnetic diffraction theory, and their performances are compared with microlenses based on a conventional scalar design concept. Microlenses with a relief of four depth levels are considered as well as binary microlenses with subwavelength structures. We show that the density of energy in the focus of high-numerical-aperture microlenses can be significantly increased if the phase distribution of the transmitted electrical field is optimized.