Ultrawide dynamic modulation of perfect absorption with a Friedrich–Wintgen BIC

Dynamical control of perfect absorption plays an indispensable role in optical switch and modulators.However,it always suffers from the limited modulation range,small depth,and susceptible absorption efficiencies.Here,we propose a new strategy based on Friedrich–Wintgen bound states in the continuum(F–W BICs)to realize a tunable perfect absorber with large dynamic modulation range.For proof of concept,we demonstrate a pentaband ultrahigh absorption system consisting of graphene gratings and graphene sheets through elaborately tuning F–W BIC.The nature of the F–W BIC arises from the destructive interference between Fabry–Perot resonance and guided mode resonance modes in the coherent phase-matching condition.The radiation channels are avoided from crossing.The BIC can be dynamically modulated by engineering the Fermi level of graphene gratings,which breaks the traditional modulation methods with an incidence angle.Remarkably,the perfect absorber with this F–W BIC approach achieves the largest modulation range of up to 3.5 THz.We believe that this work provides a new way to dynamically engineer perfect absorption and stimulates the development of multiband ultracompact devices.

基于环形谐振器边耦合波导的多模光学滤波器

设计了一种含有矩形槽(RG)的方环谐振器边耦合金属-介质-金属(MDM)波导,运用Fabry-Perot(F-P)理论精确推导了谐振器的有效长度,并利用该结构实现了多模可调等离子体滤波器。在数值计算和理论分析的基础上,得到了除传统整数模式以外的非整数模式。非整数模式的波长随着RG长度的增加发生红移,这是因为RG位于磁场的波腹时,对磁场的影响最大;整数模式由于对RG不敏感,其波长保持不变,这是因为RG位于磁场的波节时,对磁场的影响最小。可以通过改变RG的形状、位置及数目来调控模式的数目和场分布。与传统的谐振器相比,所提结构和所得到的结果可以为灵活调控谐振波长提供更多选择,在光电子器件的设计上具有潜在的应用价值。