Shortening Focal Length of 100‐mm Aperture Flat Lens Based on Improved Sagnac Interferometer and Bifacial Liquid Crystal

Abstract

AbstractConventional lens technologies face great challenges in applications requiring large apertures and small f‐numbers, while a liquid crystal (LC) lens based on geometric phase is a potential solution. However, the challenge of manufacturing a large size LC flat lens with high efficiency and high phase gradient still remains. Here, an improved interferometric exposure system is proposed to acquire a large‐size vectorial optical field for photo‐alignment. Bifacial LC layers are applied to reduce the focal length while maintaining a large aperture, high diffraction efficiency, and light weight. LC layers are deposited on both sides of the substrate with the same vector system. Finally, a bifacial LC flat lens with a 10 cm diameter and 88.37% diffraction efficiency is fabricated by using optical elements smaller than 2 in., while the effective focal length is reduced from 91.5 cm to 46 cm comparing to the single side LC lens. This work demonstrates the great advantages of LC‐based flat lenses for flat optical systems with large aperture.