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 proposed<sup>1-4</sup>. 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 <i>m</i> the focal length is
changed from f to f/m based on the digitized Fresnel zone equation: <i>f = r<sub>m</sub> <sup>2</sup>/2mλ</i>, where <i>r<sub>m</sub> </i>is <i>m<sup>th</sup></i>
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.
We demonstrate that, by using circular array of electrode pattern and applying multi-level phase modulation in each zone, a high-efficiency switchable electro-optic diffractive lens using liquid crystal as the active medium can be produced as a switchable eyewear. The lens is flat and the thickness of the liquid crystal is 5 μm. Two different designs are presented. In one design, all the patterned electrodes are distributed in one layer with a 1-μm gap between the electrodes. In the other design, the odd- and even-numbered electrodes are separately patterned in two layers without any lateral gaps between the electrodes. In both cases, vias are made for interconnection between the electrodes and the conductive wires. With the one-layer electrode design, both 1-diopter and 2-diopter 8-level lenses are demonstrated with an aperture of 10 mm. With the two-layer electrode design, a 2-diopter, 15-mm, 4-level lens is demonstrated. The diffraction efficiency of the 8-level lens can be higher than 90%. The ON- and OFF-state of the electrically controlled lens allow near- and distance-vision respectively for presbyopic eyes. The focusing power of the lens can be adjusted to be either positive or negative. The focusing power of the 8-level lens can be adjusted for near-, intermediate-, and distance vision. The lens is compact and easy to operate with fast response time, low voltages and low power dissipation. This is the first demonstration of the switchable lenses that almost meet the requirements for spectacle lens.