Instituto de Óptica “Daza de Valdés”

Tunable bound states in the continuum in active metasurfaces of graphene disk dimers

Tunable bound states in the continuum in active metasurfaces of graphene disk dimers

Óptica Guiada No-Lineal y en la Nanoescala (N2GO)-en

  • Active metasurfaces allow us to modify their optical properties after manufacturing, during device operation.

Madrid / December 12, 2023

A research team made up of researchers from the Institute of Structure of Matter and the Optics Institute of the CSIC, the University of Valladolid, the University of Fribourg, and the Technological Innovation Institute from Abu Dhabi have managed to design a real-time tunable metasurface that is capable of supporting a bound state in the continuum. This development, published in the renowned scientific journal Nanophotonics, is one more step in the knowledge of light-matter interaction and opens new opportunities for the design of advanced photonic devices.

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What are states confined in the continuum?

When all the components of the moment of light are real, it can be emitted and propagated freely. These propagating light states are also known as continuum states. On the contrary, when some momentum component is imaginary, light cannot be emitted by an object and remains confined to a region around it. In this case we are talking about linked states.
A third possibility occurs when, despite having all the real momentum components, for reasons of symmetry, the light remains linked to an object. We know this new state as a Bound State In the Continuum (BIC).
These states offer the ability to store energy without losses and to increase the interaction between light and matter in an extraordinary way, which makes them very interesting tools for developing new technologies. That is why the leading groups in this field are investigating how to create different devices that support BIC states and that can be modulated by different external stimuli.
In this study, the researchers have proposed the use of structures formed by dimers of graphene disks, in which each pair behaves like a meta-atom of a square matrix in which the conditions under which the changes occur can be actively manipulated. BIC.

A flat mesh in which there are discs of two colors of the same size forming a network
Recreation of the metasurface composed of dimers of graphene disks / Institute of Optics
The team demonstrated that the existence of the BICs and their quality factor can be adjusted in real time by applying a different electrical potential to each of the disks in the dimer. This is equivalent to changing the diameters of the discs, but is much more convenient to achieve active manipulation of the BIC condition.
In addition, the team proposed exploiting the lattice resonances of the nanodisk structure to multiply the signal thanks to them and thus mitigate the non-radiative losses of graphene.

Graphene

Graphene is a two-dimensional material composed of carbon atoms that offers exceptional optical properties and the ability to support very intense plasmons when excited with electromagnetic waves in the terahertz (THz) range. This, and the ability to tune its plasmons, makes it an ideal platform for developing new photonic devices with applications in imaging, sensing, telecommunications and energy, for example.

Metasurfaces

Metasurfaces are artificial devices composed of elements smaller than the wavelength of light arranged in a two-dimensional structure. These devices are very interesting because they have optical properties that are impossible to achieve in natural materials.

IO-CSIC Communication
cultura.io@io.cfmac.csic.es

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