Planar liquid-crystal optical elements could help miniaturize mirror-based optical systems

June 20, 2016
Bragg-reflecting cholesteric liquid crystals can alter the reflected phase profile arbitrarily.

Researchers at Osaka University (Osaka, Japan) developed a technology to control the light wavefront reflected from a cholesteric liquid crystal, which is a liquid crystal phase that has a helical structure. Although known for their ability to Bragg-reflect light, cholesteric liquid crystals could only be used as flat mirrors, reflecting light at the same angle as the incident angle. The new technology enables planar optical components to be made with functionality by design, contributing to the miniaturization of catoptric devices (mirror-based optical systems).1

The cholesteric liquid crystal is a liquid crystal phase in which the constituent rod-like molecules spontaneously form a helical structure (see figure). Owing to its structure, cholesteric liquid crystals exhibit Bragg reflection for circularly polarized light with the same polarization handedness as the helix, over a wavelength range determined by the refractive index and the helical pitch.

Their characteristic optical properties, as well as the fact that structure is formed by self-organization, have made cholesteric liquid crystals attractive for use as circular polarizers, light reflectors, and electronic paper. However, their ability to function only as a flat dielectric mirror in which light must follow the law of reflection posed a limit on the performance they could achieve, and hence usage of devices based on these materials.

Hiroyuki Yoshida, Assistant Professor, Junji Kobashi, a graduate student, and Masanori Ozaki, Professor at the Graduate School of Engineering, Osaka University discovered that the optical phase reflected from a cholesteric liquid crystal varied depending on the phase of the helical structure.

The distribution of optical phase (otherwise known as the wavefront) determines how the light propagates; for example, the wavefront of light propagating along a straight line has a planar profile, whereas the wavefront of light that converges has a curved (spherical) profile. On the other hand, the helix phase defines the relative orientation of the helical structure at a particular position in space, and can easily be controlled by defining the orientation of the liquid-crystal molecules on a substrate. Therefore, by patterning the orientational "easy axis" (the axis of equilibrium) in a standard, slab-like cholesteric liquid crystal device, the reflected wavefront can be designed arbitrarily.

Source: http://www.eurekalert.org/pub_releases/2016-06/ou-lco061616.php

REFERENCE:

1. Junji Kobashi et al.,Nature Photonics (2016); doi:10.1038/nphoton.2016.66

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.

Sponsored Recommendations

Request a free Micro 3D Printed sample part

April 11, 2024
The best way to understand the part quality we can achieve is by seeing it first-hand. Request a free 3D printed high-precision sample part.

How to Tune Servo Systems: The Basics

April 10, 2024
Learn how to tune a servo system using frequency-based tools to meet system specifications by watching our webinar!

How Precision Motion Systems are Shaping the Future of Semiconductor Manufacturing

March 28, 2024
This article highlights the pivotal role precision motion systems play in supporting the latest semiconductor manufacturing trends.

Melles Griot® XPLAN™ CCG Lens Series

March 19, 2024
IDEX Health & Science sets a new standard with our Melles Griot® XPLAN™ CCG Lens Series fluorescence microscope imaging systems. Access superior-quality optics with off-the-shelf...

Voice your opinion!

To join the conversation, and become an exclusive member of Laser Focus World, create an account today!