An Ultra-Thin Terahertz Metalens

Illustration of a terahertz metasurface ultra-thin collimator for power enhancement. (T. Suzuki, TUAT)

https://www.photonicsviews.com/an-ultra-thin-terahertz-metalens/

Terahertz radiation has barely been exploited compared to most of the rest of the electro­magnetic spectrum. Yet T-rays potentially have appli­cations in next-generation wireless communi­cations (6G/7G), security systems, biome­dicine, and even art history. A new device for controlling T-rays using a specially designed meta­surface with properties not found in nature could begin to realize this potential.

Terahertz technology that allows gene­ration, detection, and appli­cation of terahertz waves has taken off in the last decade or so, closing the terahertz gap somewhat. But the performance and dimensions of conventional optical components able to mani­pulate terahertz waves have not kept up with this rapid development. One reason is the lack of naturally occurring materials suitable for the terahertz waveband. However, researchers at Tokyo Uni­versity of Agriculture and Techno­logy (TUAT) led by terahertz wave engineer Takehito Suzuki have recently developed an optical component that can more easily mani­pulate T-rays and in a practical fashion by using a material that doesn’t occur in nature.

Conventionally, a colli­mator, typically consisting of a curved lens or mirror, can mani­pulate T-rays is a bulky three-dimensional structure made of naturally occurring materials. But the researchers Takehito Suzuki, Kota Endo, and Satoshi Kondoh, have devised a collimator as an ultra-thin (2.22 micro­meters) plane made from a meta­surface. These properties come not from whatever metal or plastic base substance they are composed of, but instead from the geometry and arrangement of the material in tiny repeating patterns that can bend electro­magnetic waves in a way that natural substances cannot.

In this case, the material has an extremely high refrac­tive index and low reflec­tance. The collimator consists of 339 pairs of meta-atoms arranged so that the refractive index concen­trically increases from the outside to the center of the device. “The meta­surface design is unpre­cedented,” said Suzuki, “delivering a much higher performance that should acce­lerate the development of a wide range of appli­cations, including next-generation wireless communi­cations (6G/7G) and even thermal radiation control devices.” (Source: U. Tokyo)

Reference: T. Suzuki et al.: Terahertz metasurface ultra-thin collimator for power enhancement, Opt. Exp. 28, 22165 (2020); DOI: 10.1364/OE.392814