Hybrid Plasmonic-photonic Resonators with Sharp Absorption Cross-section and Obvious Electric Field Enhancement
In recent years,the plasmonic-photonic hybrid system has attracted extensive attention and research from scholars at home and abroad because of its combination of the advantages of the plasmonic and photonic resonators.In previous works,the plasmonic-photonic hybrid system has demonstrated obviously enhanced Purcell factor due to the deep subwavelength confinement of localized surface plasmon resonance and the additional contribution of the ultra-small mode volume.Different from previous works,in this paper,we are focused on the extra contribution of optical resonator on plasmonic resonator in a plasmonic-photonic hybrid resonator consisting of a two-dimensional photonic crystal microcavity and Au nano-antennas.Firstly,the absorption cross section spectrum and the distribution of electric field intensity of the hybrid resonators are calculated by using the finite difference time domain method.By comparing the coupling characteristics of singe-NA model,three-NAs model and five-NAs model,the physical mechanism of the enhanced absorption cross section and the law of the enhanced electric field intensity are analyzed.The results prove that compared with pure plasmon resonators,the hybrid system demonstrates obviously enhanced absorption cross-section and electric field intensity.In particular,the hybrid resonator exhibits Fano-like lineshape and sharp peak in its absorption cross-section spectrum which can be modulated by changing the numbers of Au nano-antennas or the resonance wavelength detuning between the Au nano-antenna and PC microcavity.With the increase of the number of Au-NAs,the absorption cross section of the hybrid system is continuously enhanced,but the response is different at 657 nm and 576 nm.Due to the increasing loss of the Au NAs,the Fano-like lineshape at 657 nm are getting more and more unconspicuous,while the peaks at 576 nm are becoming sharper,which is due to the superposition of each Au NA coupled with the PC microcavity's higher-order mode at 576 nm.In general,the five-NAs model has the best absorption cross section enhancement.Contrary to the enhancement law of the absorption cross section,the enhancement effect of the electric field intensity of the hybrid systems decrease with the increase of the number of Au-NAs.Among them,the single-NA model has the best electric field enhancement,especially when the resonance wavelength detuning is Δλ=-27 nm.At this time,the electric field intensity of the hybrid system is about 12 times that of the single Au NA and 80 times that of the bare photonic crystal microcavity.In particular,the electric field enhancement factor of the hybrid resonator is three order higher than that of the single Au NA,which can be widely used in the field of surface enhancement spectroscopy.Then,we establish the coupling coefficient formula to describe the coupling efficiency of the electric field intensity at 657 nm.The results show that the coupling coefficient is not the highest when Δλ=0 nm.Actually,coupling coefficient will gradually increase as Δλ increases along the negative direction,which means a smaller Au NA corresponds to a higher coupling coefficient.We analyze that the above phenomenon are the results of the combined effect of the loss change of localized surface plasmon mode and the change of electric field intensity.For the three-NAs model and the five-NAs model,it is not difficult to make a conclusion that the electric field coupling coefficient is mainly determined by the PC microcavity's electric field intensity at the coupling position,that is,higher electric field intensity at the coupling position will result in larger electric field coupling coefficient.Finally,we also analyze the dependencies of linewidth and intensity of absorption cross section peaks at 657 nm and 576 nm on the resonance wavelength detuning.The results show that the relationship between them are almost linear,which is convenient for purposeful modulation in practical applications.In summary,this study provides a new platform for the study of photothermal detection and spectral enhancement.
Hybrid resonatorSharp absorption cross-sectionObvious electric field enhancementSurface plasmonPhotonic crystal
刘莹、朱泽斌、蒋立勇
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南京理工大学 物理学院 微纳光子学与量子调控研究所,南京 210094
南京理工大学 半导体微纳结构与量子信息感知工业和信息化部重点实验室,南京 210094
混合谐振腔 尖锐吸收截面 显著增强电场 表面等离激元 光子晶体
国家自然科学基金Fundamental Research Funds for the Centre UniversitiesFundamental Research Funds for NUSTPostgraduate Research Practice Innovation Program of Jiangsu Province
NETL
NSTL
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