Flying Electromagnetic Toroids

Project Information

FLEET

Grant agreement ID: 786851

DOI

10.3030/786851

Project closed

EC signature date 27 April 2018

Start date 1 October 2018

End date 30 September 2025

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 570 198,00

EU contribution

€ 2 570 198,00

Coordinated by

UNIVERSITY OF SOUTHAMPTON
United Kingdom

Periodic Reporting for period 5 - FLEET (Flying Electromagnetic Toroids)

Reporting period: 2024-10-01 to 2025-09-30

Summary of the context and overall objectives of the project

Conventional transverse electromagnetic waves propagate with electric and magnetic field vectors oriented perpendicular to the direction of propagation. The project revealed the existence of fundamentally different electromagnetic excitations that also propagate at the speed of light, but only as localised, ultrashort bursts of energy known as Flying Toroids (FTs). These pulses possess highly unconventional field topologies, broad bandwidths, and intrinsically coupled spatial–temporal structures. Flying Toroids exhibit a range of unique properties that open new avenues for light-based technologies. Their broadband and space–time non-separable nature enables novel schemes for information encoding and telecommunications, while their unusual interaction with matter provides access to otherwise hidden excitations, promising new forms of spectroscopy and metrology.

The primary objectives of the project were to:
• Develop generators of Flying Toroids;
• Construct detectors incorporating light-harvesting and light-rejecting nanostructures sensitive to FT pulses;
• Develop fundamental components for manipulating FTs, including concentrators, deflectors, absorbers, and splitters;
• Demonstrate free-space and waveguide-based communication schemes using FTs;
• Establish novel spectroscopic techniques using FTs to reveal new information about matter.

The successful completion of the project has resulted in the following major outcomes:
1. Proof-of-principle experimental demonstrations of the generation, detection, characterisation, and spectroscopic application of toroidal electromagnetic excitations.
2. The establishment of a comprehensive theoretical and experimental framework for toroidal electrodynamics, encompassing both free-space propagating toroidal pulses and toroidal excitations in matter.
3. The discovery of a broad family of information carriers, supertoroidal pulses, exhibiting skyrmion-like topology, non-diffractive propagation, Lorentz invariance, and space–time superoscillatory behaviour.

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

This project has established toroidal light pulses (Flying Toroids) as a new, experimentally accessible class of topologically structured carriers of energy and information. We introduced and demonstrated a complete experimental toolkit for their generation, detection, spatiotemporal characterisation, and spectroscopic exploitation. Our findings revealed fundamentally new propagation dynamics, including non-diffracting topological skyrmions, space-time superoscillations, and highly selective light-matter interactions, such as the excitation of otherwise hidden toroidal and anapole modes in matter. Collectively, these advances lay the foundations for a new branch of electromagnetism with implications for telecommunications, spectroscopy, imaging, and precision metrology.

Main Results

1.Experimental generation of Flying Toroids in the optical regime was demonstrated for the first time using specially designed metasurfaces that convert conventional ultrashort pulses into toroidal pulses. This enabled FT generation at near-infrared wavelengths. Complementary ultrafast techniques were developed to fully characterise the spatiotemporal electromagnetic fields of toroidal pulses.
Nature Photon. 16, 523–528 (2022). https://doi.org/10.1038/s41566-022-01028-5
APL Photonics 6, 116103 (2021) https://doi.org/10.1063/5.0056066
2.A compact, ultra-broadband detector for FTs was introduced and experimentally demonstrated for the first time. Based on Pancharatnam–Berry geometric phase effects, this detector is effectively wavelength-agnostic.
Opt. Express 33, 50496–50504 (2025) https://doi.org/10.1364/OE.578310
3.Discovery of the supertoroidal family of pulses, revealing that FTs are only a subset of a much broader class of electromagnetic excitations. These pulses exhibit skyrmion-like topological structures and propagate without diffraction or distortion.
Nature Comm. 12, 5891 (2021). https://doi.org/10.1038/s41467-021-26037-w
Nature Comm. 15, 4863 (2024). https://doi.org/10.1038/s41467-024-48927-5
4.Development of a new form of toroidal spectroscopy for detecting toroidal and anapole excitations. This approach, based on monitoring optical response under changes in dielectric environment, uniquely distinguishes toroidal and anapole modes from conventional excitations.
PhotoniX 3, 23 (2022). https://doi.org/10.1186/s43074-022-00069-x
5.Extension of toroidal spectroscopy to atomic systems, including theoretical predictions of toroidal transitions in hydrogen-like atoms.
ACS Photonics 10(3), 556–558 (2023). https://doi.org/10.1021/acsphotonics.2c01953
Science Adv. 8, 45 (2022). DOI: 10.1126/sciadv.abq6751
6.Discovery of space–time superoscillations in band-limited supertoroidal pulses, characterised by co-localised spatial and temporal field oscillations exceeding limits implied by the spectral bandwidth.
Nature Comm. in press (2026), DOI: 10.1038/s41467-025-68260-9
7.Experimental generation of FTs in the THz regime, achieved in collaboration with Prof. T. Ellenbogen’s group at Tel-Aviv University. This approach relies on metasurface-mediated conversion of ultrashort optical pulses into structured THz envelopes.
Nature Photon. 16, 523–528 (2022). https://doi.org/10.1038/s41566-022-01028-5
8.Experimental generation of FTs in the GHz regime, achieved in collaboration with Prof. Y. Shen at Nanyang Technological University. This approach relies on special types of horn antennas converting electromagnetic pulses into structured THz envelopes.
Appl. Phys. Rev. 11, 031411 (2024) https://doi.org/10.1063/5.0218207
9.Introduction of a quantum-inspired tomographic methodology for quantifying the spatiotemporal structure and non-separability of FTs. This methodology was applied across all FT generation experiments.
Phys. Rev. Research 3, 013236 (2021). https://doi.org/10.1103/PhysRevResearch.3.013236
J. Opt., in print (2026). https://doi.org/10.1088/2040-8986/ae36bf
10.Advanced theoretical description of FT propagation dynamics, accounting for their intrinsic space–time coupling, providing a foundation for future control of FT propagation and interactions.
Phys. Rev. A 102, 063512 (2020). https://doi.org/10.1103/PhysRevA.102.063512
11.Demonstration of selective light–matter interactions, showing that FTs can excite toroidal modes in dielectric particles while suppressing conventional responses.
ICEAA-IEEE APWC 2023, Venice, Italy, 9 - 13 Oct 2023.
12.Observation of non-reciprocal interactions between toroidal charge–current configurations, mediated by asymmetric optical forces.
ICEAA-IEEE APWC 2024, Lisbon, Portugal, 2 - 6 Sept 2024. (paper in preparation)
13.The understanding of complex structures of FTs has inspired the development of new imaging and metrology modalities.
Adv. Science. 8, 2002886 (2020). https://doi.org/10.1002/advs.202002886
Nature Mater. 22, 844–847 (2023) doi: 10.1038/s41563-023-01543-y
Nature Comm., in press (2026) doi: https://doi.org/10.1038/s41467-025-68260-9

The project resulted in 19 peer-reviewed journal publications and numerous conference contributions, including 12 plenary and keynote talks. The exploitation potential of the compact ultra-broadband FT detector is currently being pursued under the ERC PoC ASTRA.

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)

The results reported in the previous section are all novel, original and constitute significant advances in the science of light beyond the state-of-the-art.

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