Work conducted by the team at the Canada Research Chair in Ubiquitous Terahertz Photonics, led by Professor Maksim Skorobogatiy, has been acclaimed among the most important discoveries of 2019 by a prestigious journal of the Optical Society.
Left to right: Kathirvel Nallappan, PhD candidate in electrical engineering; Maksim Skorobogatiy, professor of engineering physics; Hichem Guerboukha, PhD candidate in engineering physics; Yang Cao, PhD candidate in engineering physics.
Polytechnique engineering physics PhD candidates Hichem Guerboukha and Yang Cao, electrical engineering PhD candidate Kathirvel Nallappan, and professor of engineering physics Maksim Skorobogatiy conducted research on use of porous materials for manufacturing of high-performance terahertz optical components, in collaboration with Professor José Azaña and post-doctoral fellow Mohamed Seghilani of the Centre Énergie, Matériaux et Télécommunications at the Institut national de la recherche scientifique (INRS).
The team introduced low-refractive-index, low-loss subwavelength inclusions (tiny air holes) into solid material as part of the design of optical components destined for applications that use the terahertz (THz) frequency band. The resulting components have much lower power-absorption losses in comparison with all-solid components, while retaining identical optical properties.
These results are possible because the electric field is enhanced in the subwavelength pores, leading to a faster decrease in the material's effective losses compared with changes in its effective refractive index as porosity increases.
An article about the work by the Polytechnique and INRS researchers appeared in the August 2019 issue of the journal Advanced Optical Materials. The editorial panel of the journal Optics & Photonics News, published by the Optical Society, later selected the article for a special issue, published in December 2019, dedicated to "breakthroughs of particular interest" made during the past year.
"This is an important acknowledgement for us, because it shows that our work attracted interest in the broader optics community," said Mr. Guerboukha, who was the project lead with the Canada Research Chair in Ubiquitous Terahertz Photonics at Polytechnique Montréal.
Porosity for high performance
As Mr. Guerboukha explains, THz frequencies hold great promise in applications such as communications and imaging. However, power absorption losses in the optical components in THz instrumentation systems are a recurring problem. "Ideally, a terahertz lens should transmit 100% of the power of a terahertz-range wave. But this is currently not the case, especially at higher frequencies," he noted.
As part of work involving the use of porous metamaterials, the Polytechnique and INRS researchers showed that, with a porous lens instead of a variable-thickness lens, wave transmission losses at higher frequencies are reduced.
"The optical components were manufactured by laser engraving on a Plexiglas polymer, with pore position and size carefully controlled. This was done at the PolyFab Normand-Brais shop, demonstrating the components' minimal production cost," the PhD candidate explained.
Use of porous materials points the way toward manufacturing of optical components with novel functions. The process could have applications in sixth-generation (6G) wireless communication devices, but also in imaging, with terahertz radiation making it possible to "see" through most dielectric materials such as paper, cardboard, fabric, and plastic, enabling applications in quality control, biomedicine, pharmaceuticals, security, agriculture, and more.
"In principle, our methodology is scalable to the other frequency bands, by adjusting the size of the pores: this would enable unique opportunities for manufacturing optical components with exotic materials," Mr. Guerboukha added.
Mr. Guerboukha and Yang Cao are completing their doctoral studies in engineering physics with Professor Skorobogatiy as their thesis director. Kathirvel Nallappan's work, meanwhile, is supervised by Professor Skorobogatiy and Chahé Nerguizian, Professor of electrical engineering.
Congratulations to our researchers for this honour!
Learn more
Article in Advanced Optical Materials
Article in Optics and Photonics News
"L'ère des térahertz, c'est pour bientôt!" article published in Poly magazine (in French)
Expertise profile, Professor Maksim Skorobogatiy
Website of the Department of Engineering Physics
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