Study On Electric/Magnetic Localized Resonance Modulation And Its Sensing Performance In Metal Nanostructures

Surface plasmons（SPs）are collective oscillations of free electrons on the surface of metals,which can bind the light field to the surface of metal nanostructures and manipulate light at the nanoscale,and thus have special optical properties.It is well known that the SPs resonance properties can be tuned by adjusting the material,shape and size of metal nanostructures,which has important applications in the field of nanophotonics,and the SPs resonance-based refractive index biosensor is one of the hot research topics at home and abroad.In this paper,by investigating the strong coupling properties of electric/magnetic SPs resonance with dielectric waveguide film in metal micro-nano structures,two high-performance refractive index sensors are designed,which has potential applications in the field of label-free biosensing.This thesis firstly introduces the research background of SPs and describes the physical mechanism of surface plasmon polaritons,the theoretical basis of localized surface plasmons and the frontier applications based on SPs resonance.Then,we introduce the negative refractive index properties of metamaterials,the basic concept of magnetic surface plasmons,and the principle and application of refractive index biosensors based on localized surface plasmons resonance.Finally,we innovatively designed two high performance refractive index biosensors in this thesis.The research of the thesis includes the following two aspects:1.We proposed a refractive index biosensor designed based on a three-dimensional metamaterial consists of a composite structure of a periodic array of silver vertical split-ring resonators（VSRRs）on an indium tin oxide（ITO）optical waveguide layer that is sandwiched between a Si O₂ substrate and a air cover layer.The results show that the strong coupling effect between the magnetic surface plasmon resonance in the VSRRs and the optical waveguide mode propagating in the dielectric waveguide can form a hybridization mode with an ultra-narrow bandwidth and a huge magnetic field enhancement.More importantly,this hybridization mode is extremely sensitive to the refractive index change of the ambient medium.The 3D metamaterial has a very high sensitivity（S=300 nm/RIU,S*=16 nm/RIU）and quality factor（FOM=30,FOM*=390）,and thus has important applications in the field of label-free biosensing.2.We designed an optical waveguide mode enhanced biosensor with localized surface plasmon resonance,which consists of a composite structure of Au sphere array on an indium tin oxide glass（ITO）spacer on a Si O₂ substrate.It is shown that this structure can form two narrow-band hybridized waveguide modes when the zero-order TE and TM waveguide modes in the dielectric waveguide are resonantly coupled with the localized surface plasmons resonance of the metal nanoparticles at positive light incidence.By changing the array period of gold nanospheres,it is possible to selectively excite arbitrary waveguide modes（TM,TE or both）as well as to modulate the position of waveguide modes.The modulation of the waveguide mode position can also be achieved by varying the thickness of the indium tin oxide film.The full width at half maximum of the reflected resonance peaks of the zero-order TM and TE waveguide modes of this metal nanostructure are only 2.4 nm and 3.2 nm,which are very favorable for the sensing performance.The calculated results show that the refractive index sensor designed based on this metal nanostructure has a sensitivity of S=80 nm/RIU and a quality factor of FOM=32,which is promising for biomedical sensing applications.