Effect of symmetry breaking on bound states in the continuum in waveguide arrays

0558679 - ÚFE 2023 RIV US eng J - Journal Article
Petráček, J. - Kuzmiak, Vladimír
Effect of symmetry breaking on bound states in the continuum in waveguide arrays.
Physical Review A. Roč. 105, č. 6 (2022), č. článku 063505. ISSN 2469-9926. E-ISSN 2469-9934
R&D Projects: GA ČR(CZ) GA19-00062S
Institutional support: RVO:67985882
Keywords : Waveguides * Anderson models * Spectral properties
OECD category: Electrical and electronic engineering
Impact factor: 2.9, year: 2022
Method of publishing: Limited access
https://doi.org/10.1103/PhysRevA.105.063505

We developed the theoretical framework based on the coupled-mode theory which describes spectral and scattering properties of the photonic analog of an extended Fano-Anderson model???a waveguide array with two additional side-coupled waveguides. The structure supports a rich spectrum of eigenmodes, including bound state in the continuum (BIC) and other bound and leaky modes, which can be classified according to the relation between the self-coupling coefficients and eigenvalues. We focus on the structures with broken vertical symmetry with their band structures revealing interesting phenomena, such as exceptional points and level repulsion, and offer a lossless platform for PT-symmetry phase transition. We interpreted the resonant features in the scattering spectra through a generalized Weierstrass factorization. The resonance related with quasi-BIC arises from the interference between two leaky modes: one of them representing a continuum spectrum and the other (quasi-BIC) discrete state. The reflectance near the resonance can be rewritten into the form of the Fano formula where the shape parameter f can be expressed in terms of the poles associated with the two modes. Our approach provides a flexible framework which allows to interpret and to engineer the resonant properties of more complex systems.
Permanent Link: https://hdl.handle.net/11104/0338332