Flexible, stretchable device allows full-colour tuning

A team of researchers from Pohang University of Science and Technology (POSTECH) have developed a novel stretchable photonic device that can control light wavelengths in all directions. Their research findings were published in Light: Science & Applications.

Structural colours are produced through the interaction of light with microscopic nanostructures, creating vibrant hues without relying on traditional colour-mixing methods. Conventional displays and image sensors blend the three primary colours (red, green and blue), while structural colour technology leverages the inherent wavelengths of light, creating more vivid and diverse colour displays. This approach is gaining recognition as a promising technology in the nano-optics and photonics industries.

Traditional colour mixing techniques, which use dyes or luminescent materials, are limited to passive and fixed colour representation. In contrast, tuneable colour technology controls nanostructures corresponding to specific light wavelengths, allowing for the free adjustment of pure colours. Previous research has been limited to unidirectional colour tuning, shifting colours from red to blue. Reversing this shift — from blue to red, which has a longer wavelength — is challenging.

Current technology only allows adjustments towards shorter wavelengths, making it difficult to achieve diverse colour representation in the ideal free wavelength direction. Therefore, a new optical device capable of bidirectional and omnidirectional wavelength adjustment is needed to maximise the utilisation of wavelength control technology.

The researchers from POSTECH, led by Professor Su Seok Choi, addressed these challenges by integrating chiral and liquid crystal elastomers (CLCEs) with dielectric elastomer actuators (DEAs). CLCEs are flexible materials capable of structural colour changes, while DEAs induce flexible deformation of dielectrics in response to electrical stimuli. The researchers optimised the actuator structure to allow expansion and contraction, combining it with CLCEs, thereby developing a highly adaptable stretchable device. This device can adjust the wavelength position across the visible spectrum, from shorter to longer wavelengths and vice versa.

In these experiments, the researchers demonstrated that the CLCE-based photonic device could control structural colours over a range of visible wavelengths (from blue at 450 nm to red at 650 nm) using electrical stimuli. This represents an advancement over previous technologies, which were limited to unidirectional wavelength tuning.

This research establishes a foundational technology for advanced photonic devices and highlights its potential for various industrial applications. “This technology can be applied in displays, optical sensors, optical camouflage, direct optical analogue encryption, biomimetic sensors and smart wearable devices, among many other applications involving light, colour and further broadband electromagnetic waves beyond visible band. We aim to expand its application scope through ongoing research,” Choi said.

Image credit: iStock.com/Pobytov