Optical Transmission Characteristics And Its Application Of Metallic Nanostructures

Surface plasmon polaritons (SPPs) are the electromagnetic surface waves that travel along the interface between metal and dielectric with an exponentially decay to the both sides. SPPs have been considered as energy and information carriers in nanoscale optics for their ability of overcoming diffraction limit of light in conventional optics. We can use it can realize optical signal transmission, processing and related applications at the nanoscale. Analysis of the physical mechanisms and characteristics of the SPPs, it will deepen people’s understanding about the interaction law of light with metallic nanostructures in theoretically. Simultaneously, research on nanophotonics devices based on SPPs that will promote research progress in integrated optics, optical waveguides, bio-photonics and so on. In this paper, the finite element method (FEM) and finite difference time domain method (FDTD) are used for investigating the optical transmission characteristics, control means and sensing applications of the metallic micro-and nanostructures. The main contents and results of this paper are as listed below:(1) As for the study of the hybrid plasmonic waveguide, we proposed and analyzed a kind of structure which consists of double micro-rings and a thin metal film. Using the finite element method (FEM), the SPPs mode distribution between micro-ring and metal film, mode area and restrictions, long-distance transmission, and the coupling strength between SPPs mode and cylindrical dielectric waveguide mode are calculated and analyzed. The simulation results show that the structure can significantly enhance the coupling effect, it allows SPPs mode and dielectric waveguide mode realizing strong coupling at large slit width. More importantly, the study showed that the distance h between metal film and micro-ring media, and micro-ring diameter D have only a little effect on the mode coupling, which is very favorable for suppress the adverse effects caused by structural defects. The study shows the superiority of the hybrid plasmonic waveguide, which is important for the exploration and design of plasmonic micro-cavity nanolaser.(2) Through modeling and simulation with FEM business software COMSOL Multiphysics 4.3b, we proposed a high sensitivity refractive index sensor based on SPPs. The coupling structure consists of double SPPs waveguides and nanoscale resonant ring. First of all, the influence of the refractive index of the insulator on the effective refractive index of SPPs is analyzed in metal-insulator-metal (MIM) waveguide, and numerical calculation and analysis of the transmission characteristics of the proposed structure, then study on sensing characteristics of the structure by surveying the refractive index of detected sample impact on the transmission spectrum. Simulation results show that there are three peaks in the transmission spectrum of the structure, and all peak wavelengths shift have linear relationship with the refractive index of the detection sample. In addition, as a result of the investigation of the structural parameters impact on the sensitivity of the sensor, we are optimized the SPPs sensor. The refractive index sensitivity of the SPPs sensor exceeds previously reported, up to 3460nmRIU-’. Furthermore, the proposed structure can be designed as a nanoscale temperature sensor with a temperature sensitivity of 1.36nm/℃. This study established the theoretical work basis for designing and application of nanosensors.(3) We propose a MIM waveguide with a single triangle defect, compared with the conventional MIM waveguide, the proposed structure can cause localized surface plasmon resonances (LSPR) in the defect area that resulting resonance absorption, which can be achieved optical filtering function. The numerical study shows that there is a dip in the transmission spectrum due to LSPR absorption, the dip location is related to the height and the width of the triangle defect. In addition, optical wavelength of the dip appears in the defect area that will excite largest field enhancement effect. Because of LSPR is sensitive to changes in the refractive index of the surrounding dielectric materials, so the proposed structure can be used in the field of nano-sensing. By two-dimensional (2D) FEM modeling, we have analyzed the refractive index sensing characteristics and temperature sensing characteristics. The simulation results showed that the wavelength of the transmission spectrum dip has a linear relationship with the refractive index of the dielectric material and the ambient temperature. In summary, when the defect vertex angle is very sharp, this structure not only can achieve high sensor sensitivity (1736nmRIU-1), but also can be obtained a high quality factor (9.79). Simplification and miniaturization of the device structure make it to integration with the chip.(4) We propose a nanoscale temperature sensor, and systematic analysis of the temperature sensing characteristics of the device by means of theoretical analysis and FDTD numerical simulation. The temperature sensor is constituted of MIM waveguide and ethanol-sealed rectangular cavity. We have studied the transmission of the electromagnetic waves, the field intensity distribution, temperature sensing characteristics, structural parameters impact on the temperature sensitivity and the coupling strength of the structure. The simulation shows that the effective refractive index of SPPs linearly decreases with increasing temperature at MIM waveguide of silver-ethanol-silver structure. The temperature sensor have two transmission peaks in the presence of 600nm-1800nm, the peak wavelength will blue shift with the temperature increasing. Further analysis shows that the resonance wavelengths and temperature have a linear relationship, so we can get the ambient temperature by detecting changes of resonance wavelengths.2D FDTD simulation results show that the sensitivity of the temperature sensor has to do with the length and height of the rectangular nanocavity, and thermo-optic coefficient of liquid which sealed in the nanocavity, the temperature sensor sensitivity is about -0.65nm/℃. Furthermore, since the band-pass filtering characteristic of the device can be adjusted by temperature, so that the structure can be used as adjustable band-pass filter. The research results have certain guiding significance for the design of nanoscale optoelectronic devices.(5) A novel surface plasmon polaritons (SPPs) refractive index sensor based on a single defect nanocavity coupled with a metal-insulator-metal (MIM) waveguide is proposed. The refractive index sensing characteristics of this structure are analyzed by the finite difference time domain (FDTD) meth. The results show that there exist two Fano resonances in the transmission spectra, and both of which have a linear relationship with the refractive index of the detected sample. By optimizing the proposed structure parameters, we achieve a theoretical value of the refractive index sensitivity as high as 1800.4nmRIU-1. It could be utilized to develop ultracompact nanodevice for high-resolution biological sensing. Our study will help to better understand the physical meaning of Fano resonance, it has an important guiding significance for designing metallic micro and nanostructure that can support Fano resonance.(6) Characteristics of a plasmonic filter with double-nanodisk-shaped resonators are analyzed and demonstrated numerically by the finite difference time domain (FDTD) method. It is found that there are several types of modes in the transmission spectrums, and these modes can be easily adjusted by changing the radiuses of the nanodisk-shaped resonators or the coupling distances between the resonators and the waveguides. Furthermore, these modes are sensitive to variation of the refraction index of the material under sensing, which provides a potential way to realize multi-parameter sensing with high sensitivity and high figure of merit (FOM) in nanoscale. As an extension of this structure, a four-port wavelength demultiplexer is designed, which can separate resonant modes and be realized single band transmission of each channel. The proposed structure could be utilized to develop multifunction device for large-scale photonic integration.