Variable-Focus Liquid-Crystal Fresnel Lens

Abstract

Liquid-crystal lens-cells shaped like a plano-convex Fresnel lens with homogeneous alignment are prepared. Their focal length can be varied from the value f e for an extraordinary ray to nearly f o for an ordinary ray by applying an electric field across the cell. The response and recovery times within several seconds are attained in the liquid-crystal lenses. More transparent (\gtrsim80%) variable-focus liquid-crystal lenses are achieved in the double-layered structure of two identical liquid-crystal Fresnel lenses with a mutually orthogonal optic axis.

Switchable Liquid Crystal Contact Lenses for the Correction of Presbyopia

“…Lensing occurs when the LC is switched to create a phase grating [43,44]. (3) Fresnel shaped LC lens: Use of a Fresnel lens geometry, where a Fresnel lens structure is index matched to the ordinary index of the liquid crystal [45,46]. (4) Electrode patterned LC lenses: The LC layer is evenly spaced and is switched so that it produces a gradient refractive index propagating radially from the lens axis.…”

“…This approach uses components of a comparable curved lens segmented into sections, illustrated in Figure 11, to make the lens thinner and therefore likely to be more comfortable to wear [45,46]. A spherical lens design can typically have a minimum cell gap of 30 µm.…”

“…Therefore, the LC layer is also a Fresnel lens, but its focal power is switchable. The Fresnel lenses can be designed to have either a positive [45,46] or negative [52,53] focal power. These devices follow a similar convention to those discussed in Figures 2 and 4.…”

“…This means that the switching fields are both non-uniform and high. Alternatively, the electrode can be deposited on top of the Fresnel structure [46]. However, the contours of the Fresnel shape would result in inhomogeneity in the shape of the electric field.…”

Tunable-focus lens for adaptive eyeglasses

“…Graded index (GRIN) LC lenses are attractive because they require very little electrical power. LC lenses works very well at small apertures (a few mm in diameter) but GRIN LCs cannot provide the phase changes needed for larger aperture lenses with the notable exception of "collapsed" grooved Fresnel configurations [28][29][30]. Fresnel configurations generally have image quality issues related to the visibility of the grooves and circular noise due to diffraction [28,29,31].…”