Multi-channel bound states in the continuum in coaxial cylindrical waveguide

Pilipchuk, A. S.; Pilipchuk, A. A.; Sadreev, A. F. Source: PHYSICA SCRIPTA, 94 (11):10.1088/1402-4896/ab1e9b NOV 2019

Bound states in the continuum (BICs) or embedded trapped modes are widely studied in different physical systems. The studies are restricted to a single open scattering channel. In the present paper we consider BICs embedded into several continua in a cylindrical resonator opened by two coaxially attached cylindrical waveguides with different radii. We demonstrate that engineering the BICs requires a degeneracy of three eigenmodeds of the closed resonator. That is achieved by variation of both the length and the radius of the resonator.