High-Q Resonant Modes in Periodic Stubbed Structure

Abstract

Bound states in the continuum (BICs) have unique properties and significant applications in photonics. In this paper, we show analytically and experimentally the existence of ( $$N-1$$ ) BICs (multi-BICs) in the flat band of a periodic photonic comb made of N stubs of length $$d_{2}$$ separated by segments of length $$d_{1}$$ . These BICs occur when $$d_{1}$$ and $$d_{2}$$ are taken commensurate at a given frequency, which turn to quasi-BICs (multi-Fano resonances) when $$d_{1}$$ and $$d_{2}$$ are taken slightly different from the BIC position. The signature of BICs and quasi-BICs can be observed in the transmission and density of states (DOS) spectra. We show that BICs are characterized by an infinite Q factor resonances, while quasi-BICs give rise to high-Q factor resonances that grow cubically with N. Our study improves the theoretical comprehension of BICs in stubbed structure and provides useful guidelines for future applications.