Study On Sensing Properties Of MIM Waveguide Coupled With Defected Resonator System

Nowadays,as optical technology is rapidly developing,the requirements of miniaturization and integration on optical devices are significantly increasing.Surface plasmon polaritons(SPPs),an electromagnetic wave that only propagates on the interface between metal and insulator,are generated by the interference of free electrons on metal and incident photons.SPPs can break the diffraction limit and control light within nanoscale.Therefore,SPPs can potentially be applied to integrated optical circuits and sub-wavelength photonic devices.Many waveguide structures can excite SPPs.Among them,metal-insulator-metal(MIM)waveguide has various excellent properties,including lower cost,stronger light confinement,lower propagation loss,ease to integrate and so on.SPPs-based waveguide coupling structures can generate many unique phenomena.Among them,Fano resonance is one of the most interesting phenomena.Fano resonance,originating from the interaction between continuous broadband mode and discrete narrowband mode,characters a sharp asymmetric outline on transmission spectra.The variations of surrounding environments and geometric parameters have huge influence on Fano resonance.Thus,the MIM waveguide structures that can generate Fano resonance have wide applications in sensing.In our work,four kinds MIM structures based on Fano resonance are designed,which are studied by finite element method(FEM)and coupled mode theory(CMT).The detailed work is as follow:1?A nanostructure of waveguide with two stubs coupled with circular split-ring resonance cavity(CSRRC)is proposed.It is found that this structure can excite Fano resonance.The reasons for the arousing of Fano resonance are investigated,the effects of geometric parameters on Fano resonance and sensor properties are studied.It is obtained that the best sensitivity is 1500 nm/RIU with a figure of merit of 65.2.2?A nanostructure of waveguide with a stub coupled with circular ring cavity with a stub(CRCS)is proposed.The reason for the generation of Fano resonance is analyzed,the effect of structural asymmetry on the splitting of Fano resonance mode is studied.It is found that the splitting of Fano resonance mode can greatly improve the figure of merit with a slight loss of sensitivity.Additionally,when this structure serves as a refractive index sensor,the sensitivity can reach 1420 nm/RIU with a figure of merit of 76.76.When this structure acts as a temperature sensor,the sensitivity can reach 0.8 nm/?.3?A nanostructure of waveguide coupled with rectangle cavity without a long side(RCWALS)is proposed.The propagation characteristics are analyzed.Comparing single RCWALS structure with two contrastive structures,it is observed that single RCWALS structure has better propagation properties and stronger resonant effects,and it can excite Fano resonance.According to calculation,a sensitivity of 1840 nm/RIU with a figure of merit of 51.11 is attained.Furthermore,three derived structures are presented.They have lower sensitivity but higher figure of merit,and they provide more detection positions.4?A nanostructure of waveguide coupled with inverted M-type cavity(IMTC)is proposed.Due to the interference between different light pathways,Fano resonance is excited.By comparing with contrastive structures,an appropriate interference area between waveguide and resonator can improve transmission characteristics.Additionally,four derived structures illustrate that the effects on sensitivity are structural sizes rather than shapes.Furthermore,the applications on temperature sensing and NaCl solution concentration monitoring are studied,whose sensitivities are 1.444 nm/? and 6.6 nm/%,respectively.Herein,four kinds of MIM coupling structures are presented,the effects on sensing properties are studied,new ideas for designing and fabricating microminiature structures with excellent properties are provided.The proposed structures,possessing advantages of small volume and high integration,can be applied to the micro-nano sensing system.This can further promote the development of optical devices integration.