| With the development of industrial manufacturing technology,especially in recent years the development of the etching technique, it has been possible to manufacture micro and nano-scale (sub-wavelength)range of the device, which provided an experimental basis for researchers to study the interaction of light with micro- and nanostructures, thereby plasmonic nanophotonics began to rise. Photonic devices have a huge advantage of electronic device in terms of transmission bandwidth, but because of the limitation of diffraction limit in traditional photonic devices, they cannot achieve the miniaturization of electronic devices.Surface plasmon polaritons (SPPs), a kind of electromagnetic wave,which are formed by free-electron interaction with light on the metal surface. The SPP field profiles decay exponentially into the neighboring media from their maxima at the interface. SPPs can breakthrough diffraction limit, and have great local field enhancement effect, which provide great possibility for photonic device miniaturization and integration. And the the device parameters of the structure system were optimized by using of simulation software and numerical analysis. Details are as follows:1. By employing the finite element method (FEM), the filtering characteristics of the subwavelength metallic waveguide coupled with resonators are investigated. Introducing several side-coupled cavities into metal-insulator-metal (MIM) waveguide, a multi-channel adjustable wavelength demultiplexer (WDM) can be realized. Simulation results show that the resonant wavelength and the length of the side coupled cavity has a simple linear relationship, and are demonstrated bythe standing wave theory. It is worth mentioning that, a reflection cavity has been proposed to effectively enhance the transmittance of the each channel of WDM. The phenomena and results are well analyzed by FEM simulation method and temporal coupled-mode theory (CMT). After that a cascaded square cavity structure is proposed and a super-high-resolution WDM is achieved with the resolution of about ?10 nm, which is the minimum value in the previous reports. The coupling characteristics between the stub resonator and a metal baffle is studied, and an asymmetric Fano line is achieved. Based on this special asymmetric Fano profile, several high-resolution wavelength demultiplexer are designed,and then, the scattering matrix theory is used to analyze the above phenomena.2. Fano resonance phenomenon is studied in the MIM waveguide structure. A defect is placed at the bottom of the cavity to break the symmetry of the original structure for the first time, so as to the anti-symmetric waveguide mode is excited. The interaction between this new emerging anti-symmetric waveguide mode and the original symmetry waveguide mode, gives rise to the Fano resonance. Using the finite element method, the parameters of the proposed structure are studied, and the results are consistent with our theoretical analysis. Then we improve the structure, it is found that multiple Fano resonance peaks generated by the anti-symmetric mode are achieved in the transmission spectrum, and the theoretical analysis is also given. Finally, the interaction between metal baffles or metal groove with the ring, stub resonator or the side-coupled cavity is also investigated, and all the transmission spectra exhibit asymmetric Fano profiles. The analysis reveals that these kinds of Fano resonance spectra can be equivalent to the coherent superposition of the two modes. One is the discrete states provided by the baffle or groove, and the other is the continuous spectrum offered by the resonator. The simulation results also found that, there is a simple linear relationship between the Fano peak/valley and length of the stub resonator or the side coupled cavity, or the radius of the ring resonator. Finally, by taking advantage of the asymmetry of Fano line and the sensitivity to the change of the surrounding refractive index, we have proposed several novel, high sensitivity and high figure of merit (FOM)plasmonics sensors. This plasmonic refractive index sensor has important applications in disease surveillance and detection.3. Using the coupled mode theory (CMT), a parallel cavities system of class electromagnetic induced transparency (EIT-like) phenomena were analyzed. According to the equivalent model of dual cavities coupled to the waveguide, the EIT-like effect under the multi-mode is also achieved. Moreover, controlling the relative position of the dual cavities, we can get any mode of regulation of the transparency window.This ultra-compact structure with single and multiple EIT-like spectral responses has many important applications in complex functional optical devices. The system response of a side-coupled cavity and a ring resonator is investigated. Analyzing the transmission characteristics of the direct coupling between the bus waveguide and the resonator by FEM, we find that the transmission spectra exhibit a typical EIT-like response when the resonant waveguide satisfies the phase-match condition. By extending the basic structure, multiple EIT-like profile is realized in the transmission spectra. Finally a plasmonic splitting device based on EIT-like response is designed.4. The effects on the transmission characteristics of metal defect in the plasmonic system is investigated. First, a metal defect is introduced in the wide gap MIM waveguide center, keeping the symmetry of the original structure, to study its influence on the transmission characteristics of the system. FEM simulation results show that the presence of metal bar makes the transmission spectrum more abundant. Surface current and surface charge models can be well explained the system phenomenon in a qualitative way. The proposing of the fitting formula, makes the resonant wavelength and the metal bar dimension closely linked together, further increasing the flexibility of the design to make it more conducive to the all-optical integration. Anti-symmetric mode is excited due to the symmetry breaking, and a sharp and asymmetric Fano profile emerges in the transmission spectrum, which richer transmission characteristics of the system. The case of a metal bar, which fixed at the bottom of the square resonator, is also studied, and a mode splitting is achieved. The quality factor of a resonator is greatly improved (? 150) without increasing the overall system size, and a 1x2 channel wavelength division demultiplexer is designed and realized. The effect of changing the refractive index in the square cavity on the transmission characteristics is also studied, and a sensitivity of about 1320 nm / RIU refractive index sensors is designed. Adjusting the position of the metal around the bottom of the cavity in the square, to achieve a higher order mode excitation.Introducing defects can effectively regulate the transmission characteristics of the system and achieve a more complex multi-functional optical devices, but also provides a good idea for future researching. |
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