| In recent years,with the advancement of the manufacturing process,people can produce optical devices of micro-nano scale.Some metal nanostructures based on surface plasmons and local surface plasmons(mainly nano-optical antennas)have the ability to break through the diffraction limit.By concentrating electromagnetic radiation to sub-wavelength scales to produce extremely strong and highly localized electromagnetic fields(called hotspots),it has attracted the attention of many researchers and attempts to explore the potential applications of this phenomenon.This optical property provides researchers with a way to manipulate light in a nanoscale size,and this method is only affected by the shape,size,material,and surrounding medium of the metal nanostructure itself.However,the current laboratory is investigating the optical properties of such nanostructures,often using complex and expensive optical path systems,which limits the further application of these photonic devices.Therefore,based on the coupled mode theory,metal surface plasmon theory and transmission line impedance matching theory,this paper first designs an integrated photonic platform consisting of four parts: silicon dioxide substrate,tapered nano-fiber,strip single-mode waveguide and connector.The connector is the core component of the entire integrated photonic platform.The connector can realize high-precision alignment connection between the tapered nano-fiber and the single-mode waveguide,and fix the optical fiber on the substrate,thereby achieving efficient coupling between the optical fiber and the waveguide(coupling efficiency is as high as 96%),and also proves the connector can prevents the background radiation from penetrating into the optical circuit.After that,the optical properties of common and optimized bowtie aperture antennas integrated on the top of the photonic platform were studied in depth.The influence of geometric parameters on the electric field enhancement factor and waveguide transmission of these types of antennas was discussed.The results show that the transmittance of the silicon waveguide is affected by the interference between the waveguide mode and the surface plasmon mode excited by the antenna,and the field enhancement factor of the antenna is mainly determined by the local plasma generated in the antenna nanogap.The corresponding wavelength at the maximum field enhancement factor of the antenna does not match the wavelength corresponding to the minimum transmittance through the silicon waveguide,which indicates that direct measurement of the transmission spectrum of the silicon waveguide may cause large errors in some multi-mode transmission cases.The numerical simulation results show that by changing the size parameters of the bowtie aperture antenna,the local surface plasmon resonance wavelength and the area and shape of the hot spot can be effectively adjusted.In addition,we have found that electric field enhancement can be further achieved by optimizing the bowtie aperture antenna by adding additional rectangular and bowtie cavities in a direction perpendicular to the waveguide mode propagation.The above research lays a foundation for further optimization of the on-chip bowtie aperture optical antenna and its application to surface enhanced Raman spectroscopy,near-field optical microscopy,high sensitivity sensor and plasmonic optical tweezers. |
