Chiral Metamaterials for THz Polarisation Control

Project Information

CHARTIST

Grant agreement ID: 101007896

DOI

10.3030/101007896

Project closed

EC signature date 27 November 2020

Start date 1 October 2021

End date 31 March 2026

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 745 200,00

EU contribution

€ 726 800,00

Coordinated by

ITA-SUOMEN YLIOPISTO
Finland

Periodic Reporting for period 1 - CHARTIST (Chiral Metamaterials for THz Polarisation Control)

Reporting period: 2021-10-01 to 2024-03-31

Summary of the context and overall objectives of the project

The main goal of the CHARTIST is to provide theoretical basis, perform proof of concept experiments, and build prototype devices for control of THz-wave polarization. The project relies on solid theoretical background that will enable analytical and numerical modelling interaction of the THz radiation with chiral metamaterials and metasurfaces and will also reveal the most promising techniques to control helicity in the THz range by external stimuli. CHARTIST brings together experimentalists and theoreticians working in synergy to build prototypes of components for THz photonics based on chiral metamaterials and metasurfaces. This project aims at providing theoretical basis, performing proof of concept experiments, and building a prototype device for unprecedented dynamic control of THz-wave polarization. The project relies on solid theoretical background that enables analytical and numerical modelling interaction of the THz radiation with chiral metamaterials and metasurfaces and also reveals the most promising techniques to control helicity in the THz range by external stimuli. The chiral metamaterials and metasurfaces are fabricated by advance techniques including femtosecond micromachining of multilayer substrates and e-beam lithography. The enhancing of the fabricated chiral structures with graphene provides additional channels for manipulating the helicity-sensitive transmittance and reflectivity, which can be employed for the THz polarization control. The proposed research program implemented via intersectoral and international mobility and connected training, dissemination and outreach activities will enable the knowledge and technology transfer, wider professional networking, acquiring new skills and exploitation of project results by European THz industry. In parallel, the world-wide professional CHARTIST network considerably enhances the future career prospects of ESRs and widen the professional opportunities for ERs involved. In the course of the project implementation special attention is paid to the personalized training of ESRs in topics and skills needed to succeed in their research carrier in THz photonics, nanofabrication and 2D materials domains.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

According to the project schedule person-months secondments have been executed in the Period 1. 13 articles, 4 of which involved two or more project teams, were published in high-impact international journals. Several articles are in preparation or submitted.

In the Period 1, our scientific results include:
- We proposed realistic material platform to implement nonreciprocity in mid-infrared spectral range. The proposed concept can be employed to design devices that serve a wide range of applications from signal isolation and wave circulation to unidirectional propagation and asymmetric power amplification.
- There was designed a chiral metamaterial having a unit cell composed of a pair of vertical U-shape THz resonators featured with “twisted” arms. Such a metamaterial possesses a strong optical activity at negligible circular dichroism in the low THz frequency range. The performed experiment revealed that 130 µm-thick structure is capable to rotate polarization azimuth of transmitted wave by 25 degrees for an unmatched bandwidth of 1 THz. The proposed approach enables easy fabrication opening avenues to efficient polarization control in the low THz frequency range.
- We proposed the original technique for the fabrication of THz metasurfaces comprising a 3D printed regular array of polymer hemispheres covered with a thin conductive layer and demonstrated that such a metasurface possesses nearly zero reflectivity . Scaling up of the proposed technique makes it possible to tailor the electromagnetic responses and to design novel components of THz photonics.
- We introduce a concept of scattering suppression at arbitrary polarization and angle of incidence accompanied with accumulation of the electromagnetic energy in the near-field zone of a scatterer at anapole resonance. Combining such scatterers into three- or two-dimensional arrays enables metamaterials and metasurfaces having transmittance virtually independent on the irradiation conditions.
- Babinet principle-based metasurface made of two complimentary metal/hole checkerboards was proposed. We demonstrated both theoretically and experimentally that coupling of the currents generated in the layers by the incident electromagnetic wave enables absolute transmission of or the Cu-based Babinet metasuface at GHz frequencies. The proposed reproducible and scalable approach paves the way for the fabrication of a variety of THz devices based on the transmittance control.
- It was demonstrated that ultrafast laser writing in silica glass depends on the grade of silica glass associated with the method of its manufacture. This was interpreted in terms of the higher concentration of oxygen deficient centers in the electrically fused silica glass, which can confine self-trapped holes and prevent the nanopores formation.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

- We demonstrated that a decreased energy density achieved through increased scanning speed and without thermal accumulation leads to a more significant modification of silica glass. This counterintuitive phenomenon is attributed to the nonlocality of light-matter interaction at tight focusing, and ca lead to a tenfold increase in the writing speed of the polarization multiplexed data storage.
- The designed chiral metamaterial with a unit cell composed of a pair of vertical U-shape THz resonators possesses a strong optical activity at negligible circular dichroism in the low THz frequency range. The fabricated 130 µm-thick structure is capable to rotate polarization azimuth of transmitted wave by 25 degrees. The proposed approach enables easy fabrication opening avenues to efficient polarization control at THz frequencies.
- We proposed and fabricated the Babinet principle-based metasurface comprising two complimentary metal/hole checkerboards. The fabricated metasurface demonstrated absolute transmission in the frequency range spanning from 4.5 to 6.62 GHz at the interlayer distance of 1.2 cm. The proposed reproducible and scalable approach paves the way for the fabrication of a variety of THz devices, which will be fabricated in the period 2 of the project.
- We proposed an original technique for the fabrication of terahertz (THz) metasurfaces comprising a 3D printed regular array of polymer hemispheres covered with a thin conductive layer. This thin metal layer suppresses the THz reflectivity of the metasurfaces, while the frequency range of such a suppression can be considerably broadened by enhancing the structure with graphene. Scaling up of the proposed technique makes it possible to create novel components of THz photonics.

Chiral metasurface comprising metallic meta-atoms on a silicon substrate