DIFFRACTIVE MICROLENSES WITH ANTIREFLECTION COATINGS FABRICATED BY THIN-FILM DEPOSITION

Two-dimensional arrays of Fresnel zone microlenses were fabricated and coated with antireflection layers by an ion beam sputter deposition t echnique. The reflection of these lenses was analyzed on the basis of an angular spectrum approach for different substrate materials. A mini mum reflectivity as tow as 2x10(-4) was realized by means of in situ c ontrolled multilayers of TiO2 and SiO2. The lenses have a circular ape rture of 2 mm and different focal lengths for the wavelengths of 1.52 and 0.63 mu m, respectively. The kinoform profile in each zone of the Fresnel zone lenses was approximated by an eight-level profile. Such s tepped profiles were realized with several masks written with an elect ron beam and transferred by photolithographic technology. Our measurem ents reveal that the spot sizes of the fabricated microlenses are clos e to the diffraction-limited values, and the highest measured diffract ion efficiencies for the eight-level structures are greater than 80%.