Tokyo Researchers Give Optics Boost to Terahertz Radiation

3 months ago by Luke James

An underused part of the electromagnetic spectrum—terahertz radiation—has been given an optics boost from a ‘metasurface’ by Tokyo researchers.

Terahertz radiation, often referred to as ‘T-rays’, is an area that hasn’t been explored very much in contrast to most of the rest of the electromagnetic spectrum. Despite this, T-rays hold lots of potential for applications in next-generation wireless communications beyond even 5G (think 6G or 7G), security systems, and biomedicine.

Now, a new device developed by researchers from the Tokyo University of Agriculture and Technology, or TUAT, could help scientists begin to understand the potential of T-rays. The device has been made using a specially designed ‘metasurface’ that features properties that cannot be found in nature. The research team behind the device published their work in the journal Optics Express on July the 13th.

 

Closing the Terahertz Gap

The ‘terahertz gap’ is a term used by engineers to describe how there is very little technology that exists that makes use of the frequency band, which sits between microwaves and infrared radiation: terahertz radiation. This is because although it is easy to generate and manipulate both microwave and infrared radiation, practical technologies that can do the same with terahertz are inefficient and impractical, and many of them do not operate at room temperature.

If, however, engineers could harness T-rays, their properties would be very useful for a range of applications. For example, T-rays can penetrate opaque objects, but they are non-ionising (unlike X-rays). This means they are much safer. They can also go through materials like ceramic, plastic, clothing, and wood—making them useful in the security sector for body scanners. For this reason also, T-rays could be promising for art historians and cultural heritage scientists who would benefit from using a radiation-free, zero-risk alternative when investigating artefacts.

Although the terahertz gap has closed a little over the last decade (as terahertz technology has more recently taken off somewhat, the performance and dimensions of conventional optical components, which are able to manipulate terahertz waves, have not kept up. There are a few reasons for this, the main one being that there is a lack of naturally occurring materials that are suitable for the terahertz waveband.

 

A diagram that depicts a terahertz metasurface ultra-thin collimator for power enhancement.

A diagram that depicts a terahertz metasurface ultra-thin collimator for power enhancement. Image Credit: Takehito Suzuki, Tokyo Institute of Agriculture and Technology, via Phys.org.

 

A New Optical Component

The lack of terahertz-friendly natural materials could be about to change thanks to researchers at TUAT who claim to have developed an optical component that can more easily manipulate T-rays in a practical manner.

Known as ‘collimators’, conventional devices that can manipulate T-rays, are formed of a bulky three-dimensional structure that is made from naturally occurring materials. In contrast, the Tokyo team’s device is a much thinner (2.22 micrometres) plane made from a ‘metasurface’: a material that is engineered to exhibit properties that don’t appear in nature. Rather than from the materials themselves, these properties are borne from the geometry and arrangement of the materials in tiny repeating patterns that can bend electromagnetic waves in a way that natural materials cannot.

In this study, 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-in.

According to the Tokyo University of Agriculture and Technology research team, their design is unprecedented—“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.”

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