Flat optics with cholesteric and blue phase liquid crystals

ABSTRACT

The cholesteric (Ch) phase is an ancient liquid crystal (LC) phase, with its roots dating back to the days of Friedrich Reinitzer. It is most well known for its ability to selectively reflect circularly polarised light with the same rotation handedness as the helical structure, and have found applications in polarising and display devices. Most studies to date utilising the reflective properties of ChLCs, however, have treated ChLCs as simple dielectric mirrors in which light follows the law of reflection. We have recently shown that through controlling the phase of the Ch helix, it is possible to control the phase of reflected light. Because the phase can be controlled over 0–2π, the reflected wavefront from a planar device can be designed to possess non-specular properties, such as deflection and lensing. In this paper, we aim to provide a comprehensive understanding of the phenomenon by presenting theoretical and experimental results on the dependence of the reflected light phase on the helix phase, and the effect of chiral handedness on the phenomenon. Also, we show that wavefront manipulation based on the same concept can be achieved in Ch blue phases (BPs), which are chiral LCs with three-dimensional periodicity.

GRAPHICAL ABSTRACT

KEYWORDS:

• Cholesteric liquid crystal
• cholesteric blue phase
• Bragg reflection
• wavefront
• metasurface

Acknowledgements

The authors thank Prof. Masanori Ozaki (Osaka University, Japan) for discussions and Dr Junichi Fukuda (Advanced Institute of Science and Technology, Japan) for providing the order parameter tensor distributions for BPs I and II. We thank DIC corporation for providing the photoalignment material LIA-03, and Merck Japan for providing the chiral dopant CD-X.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Grant-in-Aid for the Japanese Society for the Promotion of Science (JSPS) Fellows [#15J00288], the Ministry of Education, Culture, Sports, Science and Technology in Japan (MEXT) Photonics Advanced Research Center (PARC) at Osaka University, and the Japan Science and Technology Agency, Precursory Research for Embryonic Science and Technology (JST, PRESTO) “Hyper-nano-space design toward Innovative Functionality” Program..