| Summary: | 碩士 === 國立東華大學 === 光電工程學系 === 100 === Filters play an important role in versatile optical systems. It can optimize the performance of the optical system by modifying the optical properties of them. Transmittance and reflectance are the most common parameters for evaluating the performance of a optical element. This thesis is divided into two parts, simulation and experimental results The simulation results are further divided into two parts, the a reflective filter and transmittance one which will be analyzed and discussed in Chapter III and Chapter IV, respectively. Finally, in the experimental part, the optical properties of a nanoporous Au film will be discussed in Chapter V.
Traditional plasmonic filters are mostly used in the infrared (IR) spectral range owing to the high reflectivity of metals in IR range. In this thesis, we investigate the plasmonic T-shaped structure by modifying its geometric structure. The symmetric T-shaped structure shows a single resonance dip while the asymmetric T shaped structure presents two resonance dips owing the two metal/insulator/metal (MIM) cavities formed by the asymmetric structure. We further investigate the asymmetric T-shaped structure. By fine-tuning and controlling the size of the MIM cavity, the absorption dips can be controlled. Finally, a dual wavelength band stop optical filter is designed. The shift of the resonance wavelength is almost linear proportional to the length of the MIM cavity. This makes the filter with a potential of tunable feasibility. In addition, T-shaped structure has a large-angle tolerance than the traditional filter. The absorption position is not affected as a changing incident angle changes. This high angle-tolerance makes the filter is useful for practical applications.
The transmissive color filters, consisting of periodic array of MIM grating stacked on an anti-reflective layer (MgF2), discussed in Chapter IV is different from the traditional multi-layer stack filters. Through simply modulating the geometric parameters of the MIM cavity, the resonance optical properties can be manipulated.
According to the 3D RCWA simulation, it is found that the resonance wavelength redshift as a increasing thickness of insulating layer, grating period and duty cycle. Nevertheless, the geometric parameters and cannot be unlimited modulated but should be in a proper range. In addition, the angle tolerance is an important issue as well. Our plasmonic color filters also shows better angle tolerance than traditional filters. Finally, the grating period and the thickness of insulator is used to control the resonance wavelength to be 542nm for presenting the fabrication possibility of the plasmonic filter.
Through the understanding of the two plasmon filter simulations, we take these basic theory to explore a simple NIR plasma filter components. By forming an eutectic of Au and Cu at an annealing temperature around 200oC, nanoporous Au film can be made. The nanoporous Au film is proposed to use as a optical filter. Furthermore, plasmonic multilayer nanoporous Au film is alos made. In Chapter V, the we described in detail of the fabrication processes and presents the results of optical measurements. The preliminary data might provide a direction for future research.
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