Fano to BIC Resonances Transitions in 3D Printed Photonic Crystals

Bound states in the continuum (BIC) originates in quantum mechanics as discrete solutions of the single-particle Schrödinger equation embedded in the continuum of positive-energy states [1]. For electromagnetic waves, several physical conditions leading to optical BICs have been identified [2]. Symmetry protected BIC (SP-BIC), due to the symmetry mismatch between the modes supported by a photonic structure and the continuum modes, are particularly interesting because are predictable and robust against small perturbations that preserve the symmetry. Since they possess a wave vector close to the resonant modes with high-quality factors (high-Q), they can be exploited for different applications [3]. For these reasons BIC particularly attractive to the THz community because they may solve the deficiencies in THz filters, sensors and nonlinear sources.