Linear frequency conversion with time-varying meta-surfaces
Frequency conversion is usually achieved using non-linear materials. However, the field of dynamic metamaterials is likely, at least from a theoretical point of view, to offer an alternative technique to these conversion processes. This has been demonstrated by researchers at Fresnel Institute, in collaboration with other international teams. Dynamic metamaterials are known to broaden or generate a continuum of frequencies in response to quasi-monochromatic radiation. This property is conferred on them by parallel excitation (electrical, optical, etc.) enabling their physical parameters to be modified in real time at high frequency (optical, RF). This pump-probe configuration introduces a susceptibility with 2 time variables, the first of which (t’) is associated with the causality principle (memory/inertia/dispersion/absorption), and the second (t) with the real-time modification of the material’s memory. This dual temporal aspect calls for a reconsideration of Maxwell’s equations, where new degrees of freedom appear notably related to the time dependence of dispersion. In this context, the researchers succeeded in identifying the class of susceptibilities capable of converting the frequency of the incident radiation into an arbitrary pre-established frequency, while respecting the principles of causality. This theoretical work has been established for conventional materials (notably linear) whose volume is reduced to the case of a meta-surface for simplification. The process can be generalized to a comb of arbitrary frequencies that could be imposed for reflection and/or transmission. However, the number of parameters involved in the analytical form of the susceptibilities (24 in a 2-frequency conversion process) increases rapidly with the number of frequencies to be imposed.
DOI : 10.1103/PhysRevResearch.6.013002
Reference : Claude Amra, Ali Passian, Philippe Tchamitchian, Mauro Ettorre, Ahmed Alwakil, Juan Antonio Zapien, Paul Rouquette, Yannick Abautret, and Myriam Zerrad, “Linear-frequency conversion with time-varying metasurfaces”, Phys. Rev. Research 6, 013002 – Published 2 January 2024
Partners : Institut FRESNEL, ORNL – Oak Ridge National Laboratory, IETR – Institut d’Électronique et des Technologies du numéRique, CUHK – City University of Hong Kong, LAM – Laboratoire d’Astrophysique de Marseille
Contact : Claude AMRA – claude.amra@fresnel.fr or Myriam ZERRAD myriam.zerrad@fresnel.fr
