Modélisation numérique et optimisation d’une métasurface non linéaire aux fréquences térahertz (THz)

Abstract

The frequency range from 300 GHz to 10 THz in the electromagnetic (EM) spectrum, simply defined as the terahertz (THz) window, lies between the fields of electronics and optics. Many fundamental resonances of materials coincide with this range, and THz waves are suitable to interact with them for various applications. From the other side, there is an increasing interest in controlling the propagation of EM radiation by means of periodically or randomly arranged artificial structures composed of dielectrics, metals, or other materials. Such artificial 2D arranged structures of sub-wavelength nature, which behave as a continuous medium for the EM waves, are called metasurfaces. However, nonlinear metasurfaces are considered to provide much flexibility, multifunctionality and their nonlinear responses can be used for secure communication. It is clear that these applications, and possibly new ones, require an adequate understanding and mastery of all the nonlinear properties they present. Therefore, a mathematical model is proposed that best describes the excitation characteristics of the nonlinear split-ring resonator in the THz frequency range. Complex phenomena including periodic oscillations and chaos, caused by the motion of charge carriers under intense EM radiation at the gap of the material are highlighted using tools such as the two-parameter Lyapunov exponent, bifurcation diagrams, frequency spectra, time profile, and phase image. Relevant regions of the material where hysteresis and multistability occur are revealed and studied in detail. Hysteresis regions are localized by means of two-parameter diagrams, while multistability is characterized by means of a crosssection basin of attraction. Finally, based on the Helmholtz formula, the physical energy to promote the EM wave propagation and to support a continuous oscillation in the material is evaluated.

Date	6 May 2024
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	François Blanchard (Supervisor)