New Work on 2D Materials Could Enable Cheaper and Effective Infrared Photonic Components

There are still mysteries of our planet and others to be unraveled. Recent work by a team including researchers from Northwestern Engineering could bring us closer to reshaping our understanding of life on Earth and its potential on other planets in our galaxy.

A group led by Koray Aydin, associate professor of electrical and computer engineering, in collaboration with Vinayak Dravid, Abraham Harris Professor of Materials Science and Engineering and founding director of the Northwestern University Atomic and Nanoscale Characterization Center (NUANCE), and Joshua Caldwell from Vanderbilt University, shed light on viable schemes for polarization-dependent infrared optical components that construct imaging systems. Using a combination of analytical methods and cross-polarization spectroscopy, the research demonstrated efficient modification of the infrared radiation.

By developing optical components for infrared, Aydin said, the work could revolutionize remote sensing for earth sciences such as hydrology, ecology, oceanography, and geology. The results could lead to advanced imaging systems that potentially offer new insights about the Earth, including detailed information about vegetation and patterns of deforestation, crucial to fighting global climate change.

“Polarization-sensitivity in optics offers more detailed information through imaging about the nature and characteristics of the organic and inorganic materials,” Aydin said. “However, optical elements for infrared technology were scarce due to the complications of material absorptions in this range.” 

The underlying physics and design principles for on-demand polarization and absorption were demonstrated using α-MoO₃ — a novel Van der Waals material where strongly bonded two-dimensional layers are bound in the third dimension through weaker dispersion forces — in infrared, which can be tailored to imaging, spectroscopy, light detection and ranging, remote sensing, and space exploration.

Imaging is crucial for important applications ranging from liquid-crystal displays on phones to biological tissue imaging that is pivotal for the research and development in biological sciences.

Though most of these technologies are developed for visible and near-infrared electromagnetic radiation ranges, researchers seek new applications and opportunities in other parts of the electromagnetic radiation spectrum.

Infrared range emerges as a candidate for remote sensing with high resolution and less noise, necessary in this project because it can perform the tasks more efficiently than other technologies.  

The team investigated the polarization-dependent optical characteristics of cavities formed. They then used the novel Van der Waals material to extend the degrees of freedom in the design of infrared photonic components, exploiting the in-plane variations in physical properties along different molecular axes of this material. The researchers reported absorption over 80 percent and polarization conversion without the need for nanoscale fabrication. 

This opens the door for development of superior infrared optical devices that are less expensive to make, require fewer materials, and avoid expensive fabrication methods. This is due to the unique optical properties of the 2D-layered material α-MoO₃ developed by the Dravid Group, and characterized at the NUANCE Center.

“This material has exciting properties that will open new possibilities in designing and demonstrating various infrared wavelength optoelectronic devices including chemical sensors, filters, polarization converters, and other applications,” said Sina Abedini Dereshgi, a PhD student in Aydin’s lab leading the study. 

Following the development of α-MoO₃ three years ago, most of the research surrounding this material has promising near-field optics and designed with metamaterials, which are artificially engineered materials that use polarization-insensitive metals and semiconductors with complicated micro/nanofabrication techniques. As a result, despite being efficient, the resulting components require time-consuming and high-budget methods and yield small device areas.

Aydin and his collaborators demonstrated that since α-MoO₃ is naturally polarization-sensitive, it does not require complicated fabrication schemes and is as high-efficient as its metamaterial counterparts.

“As the α-MoO₃ material quality matures, we envisage the possibility of large-area polarization-sensitive components. α-MoO₃ can be thinned down to a monolayer to become a two-dimensional material,” Aydin said. “The literature abounds with research on semimetal and insulator two-dimensional materials for infrared. The addition of α-MoO_3, which is a semiconductor, paves the path to the next generation of switchable photonic integrated devices in infrared.”

The paper, “Lithography-free IR Polarization Converters via Orthogonal In-plane Phonons in α-MoO₃ Flakes,” was published November 13 in Nature Communications. The study was funded by an Office of Naval Research Young Investigator Award and the Air Force Office of Scientific Research.