Research And Improvements On Transmission Channel Of Plasmonic Filter Based On Mim Waveguides

Surface plasmons (SPs) are special electromagnetic surface waves which travel along the interface between the metal and the insulator with an exponential decay in both the propagation and the transverse directions. Now, SPs have been considered as significant energy and information carriers in nano-scale optics, due to the capability of overcoming the diffraction limit in conventional optics, which will play an important role in the fabrication of the highly integrated photonic circuit and devices.Recently, a variety of metal structures have been used to design SPs waveguides, such as the metal-insulator-metal (MIM) waveguide, the metal rod, the V-shaped groove, and the wedge structure etc. In particular, the MIM waveguide has unique advantages over others, such as the confinement of SPs in a much smaller space and the simple, easy fabrication procedure. Thus, MIM waveguide and related devices have been widely investigated in recent years. In this thesis, due to the current performance limit on the peak-to-notch contrast, the3dB bandwidth and the uniformity among channels, associated investigations are performed to improve the related performances of the plasmonic filter based on MIM waveguide.Firstly, two approaches are presented for the single-channel plasmonic filter based on MIM waveguide, which can achieve the narrow-band channel in the common communication wavelength (i.e.1.3or1.5μm).(1) A narrow-band plasmonic filter based on dual-section MIM structure is proposed, which consists of two metal layers and two insulator layer sections separated by a metal film. Each section contains four insulator periodic units structured by alternately stacking two insulators with different refractive indices. The transmission characteristics of the proposed filter are numerically investigated by using the finite-difference time-domain (FDTD) method. A transmission peak with a3dB bandwidth of9.2nm and a peak-to-notch contrast ratio about37.2dB, has been confirmed in the1.3-μm range. To further increase the width of metal film to55nm, the3dB bandwidth can be reduced to be7.2nm and the peak-to-notch contrast ratio can be increased to be40.1dB.(2) Due to the introduction of one or multiple phase shifts into MIM waveguides, one or multiple channels can be formed in the insulator layer, like these in conventional fiber grating. Further, by setting an appropriate distribution of multiple p phase shifts, a single narrow channel or multiple high-uniformity channels could be obtained in the plasmonic filter. Secondly, a high-uniformity multichannel plasmonic filter based on MIM waveguide is proposed to greatly improve the uniformity among channels. It consists of two metal layers and sandwiched multiple insulator super units structured by alternately stacking two insulators with different refractive indices. Here all super units are the same and each super unit is comprised of K sub-units and each sub-unit has an insulator with a high refractive index and an insulator with a low index, except for the lack of one insulator in the K-th sub-unit of the N-th super unit. Numerical simulation results show that14comb channels with an excellent channel uniformity could be achieved in the range of1-2μm, revealing a great improvement in the channel uniformity (±0.2dB), and the peak-to-notch contrast ratio is greater than14.8dB.