Two dimensional array of AR-coated diffractive microlenses fabricated by thin film deposition

Two dimensional arrays of Fresnel zone microlenses were fabricated and coated with antireflection layers by ion-beam-sputter deposition technique. The thickness of the layers was controlled by a reflection-wideband-monitoring system with high accuracy. The lenses have a circular aperture of 2 mm and focal lengths of 70 mm and 20 mm for the wavelength of 0.63 mu m and focal lengths of 29 mm, 8 mm and 5.7 mm for the wavelength of 1.52 mu m. The blazed profile in each zone was approximated by an eight level profile. Such stepped profiles were recorded with several masks, written with e-beam and with photolithographic technology. The measurements reveal that the spot-sizes of the fabricated microlenses are close to the diffraction limited values, and the diffraction efficiency for the eight level structure is 83 %.