Variable focal length microlenses

Refractive surface relief microlenses (150 mu m diameter) are immersed in n ematic liquid crystal in a cell. Application of a variable voltage across t he cell effectively varies the refractive index of the liquid crystal and r esults in a change of the focal length by the lensmakers formula (E. Hecht, Optics, 2nd edn., Addison-Wesley, Reading, Massachusetts, 1987, p. 138). W e describe the cell design and construction and demonstrate a range of foca l lengths from + 490 to + 1000 mu m for 2 to 12 V applied. A diverging lens results when the voltage is lower. Theoretical models are developed to acc ount for some of the observed aberrations. (C) 2000 Published by Elsevier S cience B.V. All rights reserved.