Design Of Dual-band Bandpass Filter Based On Compound Micro-nano Metallic Grating Waveguide Structure

With the advent of high-speed developing information age, the demand for devices’ miniaturization and integration is becoming more and more strong in both military or civilian fields. However, the biggest obstacle of present mainstream integrated circuit is "electronic bottleneck", which attributes to the "physical limits" in devices, and the photonic integration is one of the most promising technology to solve the "bottleneck". The discovery of surface plasmon polaritons, whose optical properties are unique, opens up the constraint and control for photons with subwavelength metallic structure. Therefore, the production and application of micro-nano devices, based on surface plasmon polaritons, laid the foundation of photonic integration, and is also becoming a hot spot in current scientfic research. In the analysis of the optical properties and applications of micro-nano devies, traditional scalar diffraction theory are no longer applicable, and the vector diffraction theory must be applied. In this paper, the finite-difference time-domain method was used to analyze the effect of all kinds of metal materials on the extraordinary optical transmission of metallic gratings, and then a subwavelength compound metallic grating waveguide structure is present, which demonstrates two transmission peaks with a dip in-between at normal incidence. The main research contents of this paper are listed as follows:1. After reviewing and comparing various numerical analysis method of micro-nano devices, and combining the unique structure of micro-nano metallic gratings and the research needs, the FDTD method was choose as our theoretical research method, and the commercial FDTD Solutions was selected as our numerical modeling tools. FDTD method has has much more advantages, such as strong commonality, direct calculation in time domain, easy to master, suitable for parallel computing and high accuray and so on. The algorithm of FDTD method was deduced from classical Maxwell’s equations. We also analyse the dispersion properties of metal materials where SPPs were excited and several kinds of commonly used numerial model:Lorentz model, Drude model, and Drude-Lorentz model. Finally, the parameter values in the Drude-Lorentz model we adoped were given.2. In view of the research gap that the effect of metallic material properties on the extraordinary optical transmission in the micro-nano metal gratings, we analyzed the influence of material properties of precious metals(Ag, Au, Cu) and non-preciou metals(Cr, Ni, W) whose dispersion relations were Drude-lorentz model on the extraordinary optical transmission in one dimensional metallic gratings. Numerical results show that Ag, Au, Cu show even larger transmittance peaks due to both a largr effective slits area and smaller absorption with the same parameters; In the case of Ni and Cr, the transmittance is much smaller due to absorption. In addition, by analyseing the spatial distributions of electromagnetic field in the values of peaks and velleys and comparing the dispersion relations of SPPs and the relation between the values of peaks and valleys and the period of metallic gratings, we find that SPPs modes sustained by the metallic gratings are responsible for the extraordinary optical transmission phenomenon.3. We present a subwavelength compound metallic grating waveguide structure which can provide two transmission peaks with a dip in-between at normal incidence. The groove in the designed structure plays an important role in the formation of two narrow bandwidth and high depth transmission peaks. So the existence of groove makes it an excellent candidate for dual-band bandpass filter. Mode coupling and resonance interactions among three types of resonance mode: F-P like resonance, waveguide resonance mode and SPP modes generate two transmission peaks. Such mechanism is further confirmed by analyzing the influence of incident angle on the two transmission peaks. It is also possible to realize the structure with a two-dimensional grating for applications that require unpolarized light.