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Résumé |
Tailoring resonances has always been at heart of modern photonics: nurturing photons for cavity-quantum electrodynamics, minimizing attenuation of guided light in integrated circuit and optical fiber, sharpening photonic resonances for low-threshold lasing and high-sensitivity optical sensing, engineering emission pattern of light-emitting diodes via radiation-mode out-coupling, to cite a few examples. Most photonic resonances are dictated by the complex energy-momentum dispersion characteristic of which the imaginary-part corresponds to system losses and the real-part corresponds to light frequency.
In this presentation, we will discuss different novel concepts to harness the complex dispersion characteristics of photonic resonances in sub-wavelength scale via molding periodic arrangement of materials with different permittivity and geometry. To illustrate the engineering of the real-part, we show that the same photonic band can transform continuously from Dirac dispersion to flatband in a simple photonic structure, or undergo a series of magic flatband configurations in moiré superlattice. Moreover, when taking into account the losses in open system, the complex energy-momentum dispersions, theoretically described by non-Hermitian Hamiltonians, reveal unique features with no Hermitian counterparts such as the complex degeneracy at exceptional points, and the destructive interference of losses at bound states in the continuum. All of these concepts will be illustrated by experimental demonstrations. Finally, for applications, we will present some proof-of-concepts of original micro-lasers and optical trappings based-on non-Hermitian singularity.
[1] Symmetry breaking in photonic crystals: On-demand dispersion from flatband to Dirac cones, PRL120 (6), 066102 (2018);
[2] Magic configurations in moiré superlattice of bilayer photonic crystals: Almost-perfect flatbands and unconventional localization, PRR 4, L032031 (2022);
[3] Unveiling the Enhancement of Spontaneous Emission at Exceptional Points, PRL 129, 083602 (2022). |
