PROCEEDINGS ARTICLE | August 26, 2010
Proc. SPIE. 7786, Current Developments in Lens Design and Optical Engineering XI; and Advances in Thin Film Coatings VI
KEYWORDS: Lenses, Electrodes, Diffraction, Liquid crystals, Zoom lenses, Telescopes, Binary data, Refractive index, Silica, Space telescopes
Non-mechanical variable lenses are important for creating compact imaging devices. Various
methods employing dielectrically actuated lenses, membrane lenses, and/or liquid crystal lenses
were previously proposed1-4. Here we present tunable-focus flat liquid crystal diffractive lenses
(LCDL) employing binary Fresnel zone electrodes fabricated on Indium-Tin-Oxide using
conventional micro-photolithography. The phase levels can be adjusted by varying the effective
refractive index of a nematic liquid crystal sandwiched between the electrodes and a reference
substrate. Using a proper voltage distribution across various electrodes the focal length can be
changed. Electrodes are shunted such that the correct phase retardation step sequence is
achieved. If the number of 2π zone boundaries is increased by a factor of m the focal length is
changed from f to f/m based on the digitized Fresnel zone equation: f = rm 2/2mλ, where rm is mth
zone radius, and λ is the wavelength.
The lenses operate at very low voltage levels (±2.5V ac input), exhibit fast switching
times (20-150 ms), can have large apertures (>10 mm), and small form factor, and are robust and
insensitive to vibrations, gravity, and capillary effects that limit membrane and dielectrically
actuated lenses. Several tests were performed on the LCDL including diffraction efficiency
measurement, switching dynamics, and hybrid imaging with a refractive lens. Negative focal
lengths are achieved by adjusting the voltages across electrodes. Using these lenses in
combination, magnification can be changed and zoom lenses can be formed. The promising
results make LCDL a good candidate for non-mechanical auto-focus and zoom lenses.
