| Surface plasmon polaritons(SPPs) are electromagnetic(EM)modes propagating along metal-dielectric interfaces,and nano scale optical waveguide devices based on the properties of SPPs can break the diffraction limit to confine the electromagnetic fields to the magnitude of far below the input wavelength.Because of these unique properties,with the increasing demand for the miniaturization of optical components and circuits,various nano scale sub wavelength optical waveguide structures based on SPPs have received great attention in different research areas.At the same time,the intensive studies on SPPs based nano scale optical waveguide devices have also accelerated the development of interdisciplinary fields,e.g.,micro&nano fabrication and molecular level biochemical detection and sensing.In recent years,surface plasmon optical waveguide devices based on Metal-Insulator-Metal(MIM)structure,such as splitter,combiner,coupler,filter,and absorber have become a research hotspot.In this paper,we firstly introduce the background and characteristic of SPPs,SPPs based MIM type surface plasmon waveguide(SPW)and SPW filter based on MIM.Secondly,the numerical methods used in this paper are explained.Finally,two new types of surface plasmon waveguide filters are presented,and their transmission characteristics are discussed in detail.The main research contents of the thesis are organized as follows:(1)In this paper,a new type of MIM type SPW filter structure is proposed.It consists of two MIM type linear waveguides connected directly to two face to face placed concentric semi rings with different radii,which shows the characteristic of stop band filter.Theoretical analysis shows that changing the geometric parameters of the structure will affect its transmission characteristics,and this is proved by numerical method.The simulation results show that increasing the inner radii will lead to the red shift of the transmission spectra,and the transmission valley and bandwidth will be affected.Meanwhile,the study found that the more obvious the asymmetry of the structure,the better the filtering effect.In addition,when the width of the insulator slit increases,the center wavelength of the transmission spectra will be blue shifted,the minimum transmittance will be reduced,and the bandwidth will be widened.Moreover,when the refractive index of the slit insulator medium increases,the valley wavelength of the transmission spectra will be red shifted and the band will also be widened slightly.In a word,the proposed SPW filter structure has a good performance of band stop filtering,which is simple in structure and easy to fabricate,and has a potential application in the field of high integrated optical devices and sensors.(2)This paper presents another type of SPPs based side coupled semi annular filter structure in terms of MIM SPW model.This type of filter structure is composed of a straight waveguide side coupled with a semi ring resonator.The simulation results show that the special structure can not only show the characteristic of stop band filter,but also make the resonant mode split.And at this time,there will be two transmission valleys formed in the transmission spectrum,and between them,a smaller transmission peak will appear,which is called as plasmon induced transparent(PIT)effect in many reported literatures.In addition,changing the outer radii of the semi ring will change the shape and location of the transmission spectrum.We also carried out further studies of filter structure including two semi ring cavities placed on both sides of the bus waveguide.And the transmission characteristics are studied by changing the geometrical parameters of the structure and the relative position of the two semi ring cavities.In sum,this filter is also very simple in structure and has a good stop-band filtering effect.The structure can also be applied to the integration of high density nano optical devices,nano optical communication and high sensitivity photon chip level biochemical sensors. |
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