Study On Electromagnetically Induced Transparency And Absorption Effects Based On Photonic Crystal Nanobeam Cavity

Photonic crystal is a artificial microstructure that is periodically arranged by different dielectric materials.In the photonic crystal,artificial defects are introduced or the periodicity of the photonic crystal is destroyed,thereby forming a photonic crystal resonator.Photonic crystal nanobeam(PCN)cavity is a typical photonic crystal resonant cavity,because of its compact structure,high quality factor and relatively simple preparation advantages,it has wide applications in many aspects.In this paper,the electromagnetically induced transparency(EIT)and absorption(EIA)effects based on the PCN cavity are studied,and the loss of the PCN cavity is controlled by using the adjustable Fermi energy level of graphene to achieve EIT and EIA effects.At the same time,using a combination of theoretical analysis and numerical simulation to explore the physical mechanism and potential applications of electromagnetically induced transparency and absorption effects based on the PCN cavity.This paper focuses on the theme of electromagnetically induced transparency and absorption effects based on the photonic crystal nanobeam cavity,and elaborate two specific research work from the aspect of optical interference:(1)In this paper,a PCN cavity-waveguide coupling system consisting of a silicon waveguide and two PCN cavities and its theoretical model are designed and proposed.The transmission and resonance characteristics of the structure and the effect of EIT are studied by the finite difference time domain(FDTD)method.By optimizing the coupling distance between the two cavities,the transparent window generated by the EIT-like effect can be modulated,which is caused by the destructive interference caused by the near-field coupling of the two cavities.By further integrating graphene at the top of the dark mode cavity,the full on-off modulation of the EIT effect can be achieved by adjusting the Fermi energy level of the graphene without re-optimizing or restructuring the structure.Combined with the coupled mode theory(CMT),the theoretical analysis shows that the active modulation of the EIT-like effect is attributed to the change of the dark mode cavity loss.In addition,by changing the Fermi level of graphene,the active modulation of group delay is realized,so that the control of slow light is realized.(2)This paper designs and proposes a design of a PCN cavity-waveguide coupling system,which consists of a silicon waveguide with a PNC radiation cavity C1 and another PCN sub-radiation cavity C2 side coupled to study EIA effect.When the near-field coupling strength between the two cavities is strong enough,a significant absorption window appears at the resonance frequency in the transmission spectrum of the system.Theoretical analysis based on CMT shows that the formationand evolution of the absorption window are attributed to extremely strong destructive interference and the coupling distance between the radiation cavity and the sub-radiation cavity,respectively.By further integrating graphene at the top of the sub-radiation cavity,the on-off modulation of the EIA-like effect can be achieved by adjusting the Fermi level of graphene without re-optimizing or restructuring the structure.Theoretical analysis combined with CMT shows that the active modulation of EIA-like effect is due to the change of sub-radiation cavity loss.In addition,the slow light and absorption characteristics of the system were also studied.