A joint team of physicists from Skoltech, MIPT, and ITMO developed an optical component that helps manage the properties of a terahertz beam and split it into several channels. The new device can be used as a modulator and generator of terahertz vortex beams in medicine, 6G communications, and microscopy. The paper appears in the journal Advanced Optical Materials.

The rapidly evolving terahertz technology involves the transmission of signals at about 1 trillion hertz, or 1 THz—in between the microwave and the infrared frequency bands. It will be used in high-speed 6G communications, as well as in medicine, as an alternative to X-rays. Researchers are currently focusing on the creation of optical components adapted to these frequencies, and generators that can be used to transmit such signals.

Physicists from MIPT and Skoltech have jointly developed a varifocal Fresnel zone plate based on carbon nanotubes that enables focusing THz radiation and tuning the plate's properties by stretching. In their recent study, the researchers joined forces with ITMO to synthesize an optical component that works in the THz range.

"Together with Skoltech and ITMO, we won the Clover competition for a joint research project in photonics and decided to create a spiral zone plate. ITMO performed design calculations for the shape and behavior of the plate, Skoltech synthesized nanomaterials and fabricated a plate with intended geometry, and MIPT experimentally tested the plate using the facilities of the General Physics Institute of RAS," said Maria Burdanova, a senior researcher at MIPT's Laboratory of Nanooptics and Plasmonics.

Made of a thin film of carbon nanotubes, the new plate twists the wavefront of the THz beam passing through it. In the experiment, the team placed two plates side by side and then rotated them relative to each other, changing the distribution of radiation intensity and splitting the beam into several areas (modes) of different radiation intensities, each of which could be used as a channel for information transfer.

The team experimentally tested the plate's properties using the THz imaging method. A powerful radiation source was directed at the plate, and the distribution of the electromagnetic field intensity was detected using a subwavelength aperture and a 2D raster scanning system based on a Golay cell. The researchers used the resulting image to make sure the plate produced a twisted beam and to check the intensity pattern.

The new modulator is suitable for a variety of applications, including THz microscopy and biomedicine, that require focusing and repositioning the beam.

"Tapping into the THz band is an important challenge due to the lack of unified instrumentation and device standards. At the same time, it opens the door to competitive research and the creation of ingenious solutions. One of the key features highlighting the prospects of carbon nanotubes is the possibility to create multifunctional devices with properties that can be fine-tuned by different effects through responses at the atomic, supramolecular, and micron levels.

"For the first time, our joint team has succeeded in introducing an additional effect: interaction of different nanotube patterns. This paves the way for future devices. Amazingly, the research took less than nine months from original idea to proof-of-concept—one of the fastest projects in my career so far.

"This breakthrough would not have been possible without the concerted effort of ITMO, MIPT, and Skoltech. This underscores the potential of seed programs to enhance domestic collaboration between Russian research teams," Dmitry Krasnikov, an associate professor at Skoltech Photonics, commented.

"Our Clover project has been extended for this year. We plan to manufacture a THz adaptive varifocal device based on the same spiral zone plates, but enhanced with manipulation capabilities. We also expect to file a patent application for the device we already have," Burdanova added.

In 2023, Skoltech, MIPT, and ITMO University launched the Clover initiative to support collaborative research and promote cooperation between the country's three leading universities in the field of photonics. With its orientation toward students, researchers, and postdocs starting their scientific careers, Clover engages them in frontier research projects and facilitates mobility between top research teams.

The long-term goal is to initiate large-scale programs in photonics and related fields in Russia. The Clover competition brought together top researchers working in the fields of biophotonics, advanced photonic materials, topological photonics, optical computing, and laser physics and technology.