Elliptical micro‐fresnel lenses fabricated by electron‐beam writing technique

Abstract

AbstractElliptical micro‐Fresnel lenses can exhibit astigmatic characteristics; and hence, an astigmatic optical system made of a conventional combination lens can be made much thinner by their use. The authors have developed an electron‐beam writing system which has a function suitable for fabrication of thin‐film micro‐optical elements. The function of this writing system has been expanded so that elliptical micro‐Fresnel lenses can be fabricated. It has been confirmed that the fabricated lenses have a good sawtooth cross section. For the focusing characteristics of the lens, the eccentric ratios and the observation position dependence have been investigated theoretically and experimentally. The obtained focused spots almost reach the theoretical diffraction limit in both the major and minor directions. The intensity distribution of the focusing spots agree with the theoretical prediction. Hence, the fabricated lenses have focusing characteristics in agreement with the designed ones. Compared to the conventional microlens, these elliptical Fresnel lenses have a size smaller by one order of magnitude and their focusing efficiency is as high as 72 percent. Hence, it is expected that these lenses are new elements for micro‐optics.