Relaxed fabrication tolerances for low-Fresnel-number lenses

Numerical simulations have been performed to study the influence of resist-developing errors on continuous-relief microlenses. For very low Fresnel numbers (N < 4), the focal shift counteracts changes in the radius of curvature that are due to the depth errors and stabilizes the focal length. For higher Fresnel numbers (N > 2), the focal length is essentially determined by the diffraction at the lateral pattern of the segments, and deviations from the ideal blaze influence only the efficiency. A qualitative picture based on Fourier optics is given to explain these markedly relaxed tolerances with respect to depth errors for planar optical elements and even for low Fresnel numbers. (C) 1997 Optical Society of America.