Ultra-fast liquid crystal lens with variable focal length

Abstract

Conventional electrically driven lenses with an aligned nematic liquid crystal (NLC) as a responsive material show considerably wider range of refractive index and thereby the focal length variation in comparison with their solid counterparts, but are known to concede significantly by their operational speed. In this paper, we present electrically adaptive lenses in a cell assembled of two flat glass substrates with a plano-convex polymer lens fabricated of a photoresist seating on one substrate and a plano-concave lens formed by a shear-stressed LC polymer system, filling the remaining space in the cell. Under the voltage applied to the inner surfaces of the cell substrates, the NLC reorients, its refractive index changes and consequently, the focal lengths of such a plano-concave–convex lens decrease from about 360 mm at zero voltage down to 155 mm at high (about 60 V) voltages. The benefit of the stressed LC state allows one to reduce the switching (on–off) time down to 2–3 ms, which is more than an order of magnitude lower in comparison with conventional NLC lenses.