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

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 n(e) and n(o) of the LC materials. By rotating the polarisation direction of the incident light for 90 degrees, 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 mu m and a fill factor of 82.2%, the cell gap is 20 mu m. Changing the voltage from 0 to 0.7 V-rms allows the focal length to be adjusted from -4 mm to infinity; in turn, varying the voltage from 1 to 10 V-rms results in the focal length from 6.0 to 4.5 mm.

Automated summary

In this study, an LCMLA with a tunable focal length was designed using a self-assembled polymer convex array. By rotating the polarization direction of the incident light or changing the electric field, the focal length of the LCMLA can be continuously tuned from negative to positive.