Super quasi-bound state in the continuum

Abstract

Avoided crossing of resonances and merging multiple bound states in the continuum (BICs) are parallel means for tailoring the physical properties of bound states in the continuum. Herein, we introduce a new concept of super quasi-bound state in the continuum for photonic crystal systems where its Q factor is boosted in both parametric and momentum spaces. A super quasi-BIC with substantial enhancement of quality Q factor can be achieved in a finite PhC by combining avoiding crossing of two symmetry protected (SP) quasi-BICs in parametric space and merging BICs in momentum space simultaneously. More importantly, analytical results show that the proposed mechanism will modify the asymptotic behavior of the quasi-BIC's Q factor over the numbers of resonators from N 2 to N 3 , which is of vital importance for realizing quasi-BICs in a compact PhC. Microwave experiments are performed to validate the theoretical results. Our results provide a paradigm shift for manipulating the physical properties quasi-BICs in finite PhC structures, which would facilitate various applications, including but not limited to low threshold lasing, wireless power transfer and high figure of merit sensing etc.