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

摘要

Conventional lens technologies face great challenges in applications requiringlarge apertures and small f-numbers, while a liquid crystal (LC) lens based ongeometric phase is a potential solution. However, the challenge ofmanufacturing a large size LC flat lens with high efficiency and high phasegradient still remains. Here, an improved interferometric exposure system isproposed to acquire a large-size vectorial optical field for photo-alignment.Bifacial LC layers are applied to reduce the focal length while maintaining alarge aperture, high diffraction efficiency, and light weight. LC layers aredeposited 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 efficiencyis fabricated by using optical elements smaller than 2 in., while the effectivefocal length is reduced from 91.5 cm to 46 cm comparing to the single side LClens. This work demonstrates the great advantages of LC-based flat lenses forflat optical systems with large aperture.