Research Of Sub-wavelength Tunable Devices Based On Surface Plasmon Polaritons

Surface Plasmon Polaritons(SPPs)is an electromagnetic mode which is confined at the interface of conductor and dielectric.With the features of subwavelength localization,transmission enhancement,it has a broad application prospect in the region of near-field optics,biosensors,ultra-high resolution imaging and so on.In this paper,we present the Drude dispersion mode of metals and semiconductors,and introduce the theory of SPPs-excitation in detail.Based on these discussion,we researched the following contents:The mechanism of the excitation of SPPs by prism-couple method is analyzed theoretically,which is verified by the reflection spectrum.The effect of structure parameters and material properties on the excitation of SPPs is studied based on Kretschmann structure.A tunable filter in optical band incorporating a voltage controlled Polymer-dispersed liquid crystal layer is designed and its working performance is simulated.The working wavelength of the filter can be tuned in a certain range by control the refractivity of PDLC with the external voltage.The tunable band narrow down with the increase of incident angle.The tunable band varies form 184 nm to 93 nm with the incident angle increases from 68° to 80°.Simultaneously,the excitation band ?? narrow down with the increase of incident angle as well,improving the acuity at the working wavelength.Then,variation relations of the working wavelength and the acuity at working wavelength of the tunable filter with the incident angle and controlled refractivity are presented.Utilizing the Drude dispersion mode of semiconductors,the permittivity dispersion curves in THz range of several common semiconductors is deduced under room temperature condition.Through calculation and analysis,we obtain that there are big differences among the character parameters of SPPs excited on the surfaces of different semiconductors corresponding to their different carrier concentration.Then,the variation of carrier concentration and permittivity of indium antimonide(InSb)with temperature is discussed.The effect of temperature on the character parameters of SPPs in THz range excited on the surface of InSb is analyzed.A kind of tunable THz frequency filter is designed based on sub-wavelength grating structure.Simulations shows that the resonant frequency of surface plasma resonances excited on the InSb grating by THz wave goes higher with increasing temperature.The working frequency can be tuned from 0.425 THz to 1.364 THz while temperature increases from 225 K to 325 K.Furthermore,the relationship of working frequency and temperature is nearly in a linear fashion.Hence,the desired working frequency can be selected in a tuning range of 900 GHz in THz region.