29 Mars – Thesis defense - Alexandre Gras

16 h Room Pierre Cotton - Institut Fresnel Campus de Saint Jérôme (Marseille)

Hybrid resonance for sensing application.

The response of open optical resonators to excitation can be expressed as a superposition of their intrinsic resonances, their quasinormal modes (QNM), which are loaded by the driving field and decay exponentially in time due to power leakage or absorption. Quasinormal modes are the eigensolutions of the time-harmonic Maxwell’s equations et complex eigenfrequencies and allow more physical insight to be brought into the analysis of resonator dynamics. However, due to the complexity in modeling the open resonators and computing their modes, numerical tools such as linear eigenmode solvers are frequently called upon. The numerical discretization of the problem and some of the methods used to satisfy boundary conditions manifest themselves in the form of numerical modes that bear no physical meaning but complete the QNM basis and allow it to converge if many modes are included in the expansion. We also verify that the multiple formulas that exist for the auxiliary-field formulation of the QNM expansion have a similar origin and produce the same results. We compute the modes of periodic resonator structures to reconstruct the spectra on a wide spectrum of frequencies. We try to make the expansion converge with the least amount of modes by finding a way to classify them then explore the dependence of the modes on numerical parameters. Finally, we devised a way to obtain convergent results with few modes by interpolating from a few real frequency computations.

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