A liquid crystal and polymer composite film for liquid crystal lenses
Yi-Hsin Lin1*, Hung-Shan Chen1, Yu-Jen Wang1, Chia-Ming Chang1
1Department of Photonics, National Chiao Tung University, Hsinchu, Taiwan
* presenting author:林怡欣, email:yilin@mail.nctu.edu.tw
Liquid crystal (LC) lenses are versatile optical components for the applications of wearable devices, ophthalmic lenses, camera modules, pico projectors, endoscopes, and optical zoom systems owing to electrically tunable lens power. The optical mechanism of LC lenses is primarily to convert a plane wave to a parabolic wave by means of spatial phase difference resulting from inhomogeneous orientations of LC molecules induced by an externally electric field. However, two major essentials limit the applications of LC lenses. One is the requirement of a polarizer limits the optical efficiency(<50%) owing to polarization-dependent anisotropic properties of LC. To improve the optical efficiency, polarizer-free LC lenses have been developed. The other one is small aperture size (<2mm)because of the power law of the LC lens, the lens power (i.e. an inverse of focal length) is inversely proportional to squared aperture size under paraxial approximation. Excluding Fresnel types, we must choose either tunable lens power or aperture size according to the power law of the LC lens. Recently, we developed a liquid crystal and polymer composite film (LCPCF) as a separation layer and an alignment layer for a multi-layered structure of LC lenses in order to enlarge the polarization-independent optical phase modulation. The LC lens is polarizer-free because two eigen-polarization states of light see an identical optical phase. However, the physical properties and mechanical properties of the LCPCF are not clearly investigated. How to extend the concept of such a polarizer-free lens in order to further enlarge the aperture size without lowering the lens power, restricted by the power law, has not been discussed, either. In addition, the detail polarization dependency has not been discussed. In this paper, we prove theoretically and experimentally that the aperture size is not limited by the power law of the LC lens. We also show the mechanical and physical properties of the LCPCF. We also derive the related optical theory of the polarization independency of the LC lens and discuss the polarization dependency related image performance. This study helps to develop large aperture LC lenses for wearable devices and ophthalmic applications.

This research was supported partially by Department of Natural Sciences and Sustainable Development in Ministry of Science and Technology (MOST) in Taiwan under the contract no. NSC 101-2112-M-009 -011 -MY3 and partially by Liqxtal Technology Inc.

Keywords: Liquid crystals, LC lenses, phase modulations, polymeric film