Tunable multifocal liquid crystal microlens array based on three-electrode structure

The development of multifocal microlens array has paid many attentions recently with the applications of plenoptic cameras, stereoscopic displays, and beam homogenizers. A variety of technologies have been explored and applied to produce multifocal microlens arrays, however, most multifocal microlens arrays are limited due to structural modification, long fabrication time, and lack of tunability. In this study, we present a novel method of fabricating a tunable multifocal liquid crystal microlens array (TMLCMA) using the three-electrode structure composed of a large hole, small-hole array, and planar electrodes. Liquid crystals with positive dielectric anisotropy were filled in the TMLCMA sample and aligned planar with antiparallel rubbing treatment. A modal layer was deposited on the surface of the large hole electrode to assist in extending the fringing electric field into the TMLCMA center. The fringing electric field induced by the large hole electrode results in the microlenses have different focal lengths from the TMLCMA border to the center. The TMLCMA can be worked in concave and convex modes on the basis of signal control schemes. The beam patterns through the TMLCMA are observed and the phase shifts of the microlenses at various positions are reported. The optical imaging of the TMLCMA has been demonstrated practically. The results reveal that the proposed method is able to produce a tunable multifocal microlens array via a simple fabrication and addressing scheme. This study has proposed a strong basis for the further development of microlens array, and the optical characteristics of the TMLCMA are promising to applications of optical fields.