In brief

Researchers discovered that a new nanophotonic coating made from stibnite achieved tuneable light absorption of up to more than 99 percent and a tuneable phase modulator that can adjust light over a wide range of angles.

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Light benders shape tomorrow’s tech

26 Apr 2024

An innovative thin film coating that controls how much light is absorbed over a wide range of viewing angles can revolutionise optical technologies.

Hidden in everyday devices are invisible materials with light-bending superpowers. Nanophotonic optical coatings shape beams of light for applications such as harvesting energy from the sun and powering display and communication technologies.

Jinghua Teng and K.V. Sreekanth, researchers from A*STAR’s Institute of Materials Research and Engineering (IMRE), said that despite the promise, conventional thin film coatings fall short in the face of next-generation technology demands.

The problem with current optical coatings is their inability to consistently absorb light when it strikes from different angles in an issue known as impedance mismatch. This discrepancy in the way light is transmitted from one medium, like air, to another, like the film, lessens at acute angles, paradoxically improving absorption only at those angles.

Teng and Sreekanth theorised that for strong and broad spectral light absorption, the refractive index of a coating must be tuneable, while its extinction coefficient (a measure of how much light it can absorb without reflecting) should remain largely stable. Finding materials that tick both boxes has, until now, been incredibly challenging.

Progressing from their previous research, the team discovered that enhanced light absorption at near-normal angles is possible with a distinct cavity design. To broaden this effect across all angles, they identified the need for a material with unique characteristics.

Their search led them to stibnite (Sb2S3), a versatile chalcogenide phase change material. Remarkably, Sb2S3 can rearrange its atoms to greatly vary its refractive index while maintaining its light absorption capacity.

Using silver coated with Sb2S3, the team achieved greater than 99 percent light absorption and created a phase modulator that can adjust up to 140 degrees. “We achieved near-perfect absorption even in the crystalline phase of Sb2S3, from normal incidence to a wide range of angles,” Teng and Sreekanth commented. This is contrary to previous findings where the crystalline form showed weaker absorption.

The researchers said that this pioneering work can lead to vibrant, adjustable colour filters for more dynamic and energy-efficient displays, or optical switches, crucial for rerouting light in high-speed data networks.

Moreover, the exceptional light absorption properties of Sb2S3 may lead to thinner, high efficiency solar panels, more responsive photodetectors, and compact lasers being developed, all of which are foundational elements for the impending optoelectronic revolution.

The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE).

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Sreekanth, K.V., Prabhathan, P., Chaturvedi, A., Lekina, Y., Han, S., et al. Wide-angle tunable critical coupling in nanophotonic optical coatings with low-loss phase change material. Small 18 (28), 2202005 (2022). | article

About the Researchers

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Jinghua Teng

Senior Principal Scientist and Senior Group Leader

Institute of Materials Research and Engineering (IMRE)
Jinghua Teng is a Senior Principal Scientist and Senior Group Leader in the Institute of Materials Research and Engineering (IMRE) and an Adjunct Professor at the Department of Electrical and Computer Engineering, National University of Singapore, and the School of Physical and Mathematical Science, Nanyang Technological University, Singapore. His research interests include nano-optics and photonics, metamaterials and metasurfaces, 2D optoelectronics, THz technology, plasmonics, semiconductor materials and devices. He holds editorial board positions at the Journal of Optics, Opto-Electronic Advances, PhotoniX, Journal of Molecular and Engineering Materials, Journal of Nonlinear Optical Physics and Materials, and A*STAR Research Publication. Additionally, he is recognised as a Fellow of SPIE and OPTICA.
KV Sreekanth is a Senior Scientist at A*STAR’s Institute of Materials Research and Engineering (IMRE). He received his PhD degree from Nanyang Technological University, Singapore. He has over 15 years of research experience in nanophotonics and thin film optics. His current research focuses include phase change materials for reconfigurable nanophotonics, biosensing and meta-optics. He is recognised as a World’s Top 2% Scientists (Applied Physics) in 2021-2022.

This article was made for A*STAR Research by Wildtype Media Group