Liquid crystals open new route to planar optical elements

June 16, 2016, Osaka University
Schematic illustration of a cholesteric liquid crystal device with lens functionality (left) and photos of reflected beam spots (right). The parabolic profile of the helix phase converts the incident plane wave to a converging beam, which focuses to a spot. Credit: Osaka Univeresity

Researchers at Osaka University developed a technology to control the light wavefront reflected from a cholesteric liquid crystal - a liquid crystal phase with 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 catoptrics devices.

The cholesteric is a liquid crystal phase in which the constituent rod-like molecules spontaneously form a helical structure (Fig. 1). Owing to its structure, cholesteric liquid crystals exhibit Bragg-reflection for 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 papers. 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 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 (also known as the wavefront) determines how the light propagates; for example, light propagating along a straight line has a flat profile, whereas that converges has a curved (parabolic) profile. On the other hand, the helix phase defines the relative orientation of the at a particular position in space, and can easily be controlled by defining the orientation of the on a substrate. Therefore, by patterning the orientational easy axis in a standard, slab-like cholesteric liquid crystal device, the reflected wavefront can be designed arbitrarily. Figure 2 illustrates a planar lens device based on this concept; the parabolic distribution of the helix phase converts an incident planar wavefront to a parabolic profile that converges at a single point. The device shows high circular polarization selectivity even when the helix phase is patterned; the technology thus provides a platform to develop unique optical devices that can be tuned from being fully reflective to transmissive, depending on the incident polarization.

This research was featured in the electronic version of Nature Photonics on Monday, April 11, 2016.

Schematic illustration (left) and photos (right) of a standard cholesteric liquid crystal device. The green bars in the left figure are guides indicating positions with the same helix phase. Cholesteric liquid crystals reflect circularly polarized light with the same handedness as the helical structure and with wavelength fulfilling the Bragg condition (refractive index � helical pitch). In the right figure, purple light with right circular polarization is reflected. Credit: Osaka University

Explore further: Reconfigurable building blocks for the construction of photonic devices

More information: Junji Kobashi et al, Planar optics with patterned chiral liquid crystals, Nature Photonics (2016). DOI: 10.1038/nphoton.2016.66

Related Stories

What screens are made of: New twists (and bends) in LCD research

April 18, 2016

Liquid crystals, discovered more than 125 years ago, are at work behind the screens of TV and computer monitors, clocks, watches and most other electronics displays, and scientists are still discovering new twists—and bends—in ...

What scientists know about jewel beetle shimmer

July 23, 2009

"Jewel beetles" are widely known for their glossy external skeletons that appear to change colors as the angle of view changes. Now they may be known for something else--providing a blueprint for materials that reflect light ...

World's first microlaser emitting in 3-D

December 8, 2010

Versatile electronic gadgets should employ a number of important criteria: small in size, quick in operation, inexpensive to fabricate, and deliver high precision output. A new microlaser, developed at the Jožef Stefan ...

Plasmon-enhanced Polarization-selective filter

July 17, 2014

As we all know, some optical devices can only work with a certain incident polarization direction. In this case, a polarizer is necessary to shift the polarization direction of linearly polarized light. A common polarizer ...

Recommended for you

Hauling antiprotons around in a van

February 22, 2018

A team of researchers working on the antiProton Unstable Matter Annihilation (PUMA) project near CERN's particle laboratory, according to a report in Nature, plans to capture a billion antiprotons, put them in a shipping ...

Urban heat island effects depend on a city's layout

February 22, 2018

The arrangement of a city's streets and buildings plays a crucial role in the local urban heat island effect, which causes cities to be hotter than their surroundings, researchers have found. The new finding could provide ...

New quantum memory stores information for hours

February 22, 2018

Storing information in a quantum memory system is a difficult challenge, as the data is usually quickly lost. At TU Wien, ultra-long storage times have now been achieved using tiny diamonds.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.