The Bound State In The Continuum Mechanism And Regulation Of Single/bilayer Micro-nano Periodic Structures

Bound states in the continuum(BIC)have intrinsic properties such as theoretically infinitely high quality factor and robustness to system parameter changes,which make it have broad application prospects in many fields such as photonics,optical communication,biosensing and photovoltaics.This dissertation mainly studies the characteristics and regulation of BIC in nanohole and nanobar photonic crystal slabs,and studies BIC on the number of layers of photonic crystal slabs.Finite difference time domain(FDTD)and coupled mode theory(CMT)are compared to each other to improve the plausibility of the findings.The research contents of this paper are as follows:First,exploring the mechanism and regulation of BIC of monolayer H-shaped nanopore arrays.By adjusting the center position and size of the H-hole,the refractive index of the surrounding medium and lattice constant,the BICs of the two modes are obtained,and study the regulatory effect of structural parameters on it.Second,study the mechanism and regulation of BIC of one-dimensional nanowire arrays.By adjusting the nanowire size,position and refractive index,discuss the mechanism and regulation of BIC.Then,the mechanism and regulation of BIC of bilayer one-dimensional nanowire arrays are analyzed.By adjusting the size and position of the bar and the spacing of the bilayer structure and the refractive index of the surrounding medium,observe the change of incident angle and central wavelength and quantity of BIC.The research results show that both at-Γ BIC and off-Γ BIC can appear in the three micro-nano structures,and the former is protected by the symmetry of the structure and disappears when the symmetry is destroyed,and the latter has little to do with the symmetry of the structure.It can be tuned under various structural parameters.The BIC of both modes has high quality factor,theoretically reaching infinity.In addition,in the study of the nanowire structure,it was found that the resonance peaks of the two modes in the reflection spectrum of the single-layer nanowire structure appeared once each.However,in the reflection spectrum of the double-layer nanowire structure,the resonance peaks of the two modes appear twice each,which indicates that the number of BICs can be adjusted by increasing or decreasing the number of layers without introducing the structural complexity of each layer.The research results can provide some theoretical guidance for the design of new photonic devices.