Tunable liquid crystal microlens array with negative and positive optical powers based on a self-assembled polymer convex array

Abstract

ABSTRACT In this report, an LCMLA with a negative-positive tunable focal length is designed using a self-assembled highly uniform polymer convex array. The polymer convex array was prepared by scribing UV-sensitive glue onto the indium tin oxide (ITO) substrate modified with a microhole array patterned hydrophobic layer. This substrate is assembled with another ITO substrate coated with a homogeneous polyimide alignment layer and rubbed in one direction, then filled with an LC material to form a sandwich structure. The refractive index of the selected polymer is kept between ne and no of the LC materials. By rotating the polarisation direction of the incident light for 90°, the focal length of the LCMLA can be switched from negative to positive. Otherwise, by varying the electric field, the continuous negative-to-positive tuning of the focal length of the LCMLA is implemented. For instance, an LCMLA with the aperture of 200 μm and a fill factor of 82.2%, the cell gap is 20 μm. Changing the voltage from 0 to 0.7 Vrms allows the focal length to be adjusted from −4 mm to ∞; in turn, varying the voltage from 1 to 10 Vrms results in the focal length from 6.0 to 4.5 mm.