Research On Plasmonic Sensor Based On Metal-insulator-metal Waveguide

Surface plasmon polaritons(SPPs)are charge-density waves propagating along the surfaces of metal and dielectric materials that originate from the interaction between electromagnetic waves and the free electrons of the conductor.The interaction between SPPs and incident light waves can be controlled by changing the surface structure of metal.Moreover,SPPs has strong field limitations and strong field enhancement effects on electromagnetic fields,which provides a new choice for the development of miniaturized photonic devices.Refractive index sensors play an important role in biological and chemical detection.The SPPs refractive index sensors based on metal-dielectric-metal(MIM)waveguides have high sensitivity,simple structure and only nanoscale,which can meet the requirements of photonic devices for small size and low cost.The purpose of this paper is to improve the refractive index sensitivity and figure of merit(FOM)of the sensor by improving its structure.Firstly,the basic theory of SPPs on the interface of metal-insulator,the excitation methods of SPPs,the important parameters of SPPs,model of dielectric constant of metal and the basic theory of MIM waveguide are introduced.Secondly,the internal gear-shaped ring resonator(IGRR)based refractive index sensor is designed,and the influence of the size of the IGRR on the transmission characteristics of the sensor is studied.By optimizing the structure of the sensor,the refractive index sensitivity of the IGRR based refractive index sensor is 1225 nm/RIU,and the maximum FOM is 484.In order to improve refractive index sensitivity,the double internal gear-shaped ring resonator(DIGR)based sensor is proposed,which can split the tooth mode of the IGRR and form two resonance dips.The simulation results show that the sensitivity of the two dips is 1250 nm/RIU and 1300 nm/RIU,respectively.Compared with the single IGRR based sensor,the sensitivity is further improved.In order to improve FOM of the sensor,the internal six-gear-shaped ring resonator(ISRR)sensor is proposed.The full width at half maximum(FWHM)of the resonant dips of the ISRRbased sensor are 6 and 10 nm(the FWHM of the two dips is smaller than the FWHM of the resonant dip of the IGRR based sensor).Furthermore,a refractive index sensor based on stubISRR is designed.Because of the interaction between the teeth-mode of the ISRR and the resonant of the stub,Fano resonance is excited and plasmon-induced,and an asymmetric line of Fano resonance is formed in the transmission spectrum.Through parameter optimization,the refractive index sensitivity of the ISRR-based sensor is 810 nm/RIU,and the maximum value of the FOM is 3072,which is much higher than the previous designs.