Presbyopia is an age-related loss of accommodation of the human eye that manifests itself as inability to shift focus from distant to near objects. Assuming no refractive error, presbyopes have clear vision of distant objects; they require reading glasses for viewing near objects. Area-divided bifocal lenses are one example of a treatment for this problem. However, the field of view is limited in such eyeglasses, requiring the user to gaze down to accomplish near-vision tasks and in some cases causing dizziness and discomfort. Here, we report on previously undescribed switchable, flat, liquid-crystal diffractive lenses that can adaptively change their focusing power. The operation of these spectacle lenses is based on electrical control of the refractive index of a 5-m-thick layer of nematic liquid crystal using a circular array of photolithographically defined transparent electrodes. It operates with high transmission, low voltage (<2 V rms), fast response (<1 sec), diffraction efficiency > 90%, small aberrations, and a power-failure-safe configuration. These results represent significant advance in stateof-the-art liquid-crystal diffractive lenses for vision care and other applications. They have the potential of revolutionizing the field of presbyopia correction when combined with automatic adjustable focusing power.ophthalmic lens ͉ switchable lens ͉ vision correction T he use of nematic liquid crystals to implement switchable lenses has been proposed previously but had limited success for ophthalmic applications (1). Hybrid liquid-crystal refractive lenses incorporating convex and concave substrates have been demonstrated (2, 3). However, the large thickness of the liquidcrystal layers (Ͼ400 m) make their response and recovery times long and their transmission low because of optical scattering. To reduce the thickness of the active layer, surface relief Fresnel lens substrates have been proposed (4). However, in this geometry the lens is optically active in the electrically off-state, which is not desirable for ophthalmic applications where a loss of electrical power could suddenly result in near-vision correction during a critical distance vision task such as driving. In other approaches, thin uniform layers of liquid crystal were used, and refractive lenses were produced by the use of discrete electrodes (5), continuous highly resistive electrodes (6), or spatially distributed electric fields (microlenses) (7). However, in these lenses either the range of focal length or their small diameter made them unsuitable for ophthalmic applications. We employ a photolithographically patterned thin diffractive lens with large aperture, fast response time, and a power-failure-safe configuration to overcome these limitations. Although high-efficiency liquid-crystal-based diffractive devices have been demonstrated for beam-steering (8, 9), less effort was given to the development of switchable diffractive lenses. The diffraction efficiencies of the lenses achieved for imaging (10-15) and other applications (16, 17) we...

We demonstrate an innovative variable-focus flat liquid-crystal diffractive lens (LCDL) with 95% diffraction efficiency and millisecond switching times using a +/-2.4 V ac input. This lens is based on the electrical modulation of a 3 mum layer of nematic liquid-crystal sandwiched between a Fresnel zone electrode structure and a reference substrate. Each zone is divided into 12 subzones to digitize the phase profiles and define the phase wrapping points. The focusing power can rapidly be switched by electrically changing the number of subzones and re-establishing the wrapping points. Potential applications include zooms with no moving parts and autofocus lenses for compact imaging devices.

We report on a novel zoom lens with no moving parts in the form of a switchable Galilean telescope. This zoom telescope consists of two flat liquid-crystal diffractive lenses with apertures of 10mm that can each take on the focal lengths of -50 and +100cm, with a spacing of 50cm and, hence, a zoom ratio of 4x. The lenses are driven using a low-voltage ac source with 1.6V and exhibit millisecond switching times. The spectral characteristic of this diffractive zoom system is evaluated for light sources of various bandwidths. Potential applications for this technology include a zoom lens with no moving parts for camera phones and medical imaging devices.