Abstract
The optical behavior of coupled systems, in which the breaking of parity and time-reversal symmetry occurs, is drawing increasing attention to address the physics of the exceptional point singularity, i.e., when the real and imaginary parts of the normal-mode eigenfrequencies coincide. At this stage, fascinating phenomena are predicted, including electromagnetic-induced transparency and phase transitions. To experimentally observe the exceptional points, the near-field coupling to waveguide proposed so far was proved to work only in peculiar cases. Here, we extend the interference detection scheme, which lies at the heart of the Fano lineshape, by introducing generalized Fano lineshapes as a signature of the exceptional point occurrence in resonant-scattering experiments. We investigate photonic molecules and necklace states in disordered media by means of a near-field hyperspectral mapping. Generalized Fano profiles in material science could extend the characterization of composite nanoresonators, semiconductor nanostructures, and plasmonic and metamaterial devices.
Highlights
The optical behavior of coupled systems, in which the breaking of parity and time-reversal symmetry occurs, is drawing increasing attention to address the physics of the exceptional point singularity, i.e., when the real and imaginary parts of the normal-mode eigenfrequencies coincide
Each of the four spectra (ATS and electromagnetic-induced transparency (EIT) with γ1/γ2 = 10 and 1.1) shows two crossings with its zero-value baseline and an opposite behavior between EIT and Autler–Townes splitting (ATS) profiles. These lineshapes arise from the interference of two resonances with the flat non-resonant scattering, showing a physical origin strictly related to standard Fano profiles
We introduced the family of generalized Fano profiles for describing the coherent optical response of coupled modes in the proximity to the exceptional point singularity
Summary
The optical behavior of coupled systems, in which the breaking of parity and time-reversal symmetry occurs, is drawing increasing attention to address the physics of the exceptional point singularity, i.e., when the real and imaginary parts of the normal-mode eigenfrequencies coincide At this stage, fascinating phenomena are predicted, including electromagneticinduced transparency and phase transitions. It was imported into photonics and plasmonics, describing a single or even double resonance systems[9,10,11], exploiting the asymmetric lineshape to enhance sensors sensitivity[12] and using their local changes as an intrinsic interferometer[13,14] In this picture, Fano profiles are the manifestation of the interference between a resonant mode and a flat background, whose phase difference generates a variety of lineshapes[15]. We employ generalized Fano profiles to discriminate individual localized modes versus necklace states in disordered photonics systems
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