Study On The Improvement Of Coupled Mode Theory And Its Application In Devices Baded On Surface Plasmon Polariton Waveguides

In recent years, the progress of photonic integrated circuits has fallen far behind integrated circuits(IC) because of the limit of the diffraction,a key to make photonic have an electronics-like development is to confine the light into dimensions breaking the diffraction limit. Currently, the surface plasmom polarizations waveguides which can transmit the surface electromagnetic wave between the interface of metal and medium are arousing interest of the researchers. The lateral dimension of surface plasmom polariton waveguides is subwavelength scale, which break through the diffraction limit of the traditional optical waveguide, meet the need of the miniaturization and high-density integration of photonic integrated circuits and make it possible to construct subwavelength photonic devices.This paper begins with a brief summary of the research background,the research status and the history of development of surface plasmon polartion waves. The excitation and principle of surface plasmon polarization wave are elaborated and analyzed. The electromagnetic field distributions of the several representative surface plasmon polariton waveguides (such as metal belt, V-groove, triangular wedge) have been analyzed and contrasted carefully. And the simulation results reveal that the electromagnetic field distributions of the several representative surface plasmon polariton waveguides are entirely different from that of the tradition optical waveguides. Namely, the longitudinal electric field component can not be neglected in the total electromagnetic field of surface plasmon polariton waveguides.Then, this dissertation starts from the coupled mode theory of dielectric optical waveguides, deduces the expression of the coupled amplitude equations, amplitude coefficients and coupling coefficients in detail and points that the weakly guiding situations are used in the theoretical derivation. In other words, the longitudinal electric field component of traditional optical waveguides is neglected in the expression of coupling coefficient because of its weaking. However, the longitudinal electric field component of SPP waveguides can’t be neglected in related calculations. Therefore> in allusion to special modes supported by surface plasmon polariton (SPP) waveguides, explicit expression for mode coupling coefficient which plays a central role in coupled mode theory is redefined by adding the longitudinal electric field component and the coupled mode theory for SPP waveguides is proposed and deduced firstly. The mode coupling coefficients calculated by the proposed formula improve greatly compared with the coupled mode theory suited to conventional optical waveguides, which is the error of stripe is above10%, the CPP is almost zero, and the WPP is above95%, and reasonable explanations from the point of view of physics and mathematics have been given. Next, the coupling lengths, the transmission lengths, the normalized power exchanges and the crosstalk performances of adjacent parallel SPP waveguides with varying waveguide separation distances D and waveguide lengths L are investigated at telecom wavelength. The results are meaningful as they indicate that the coupled mode theory is developed in a self-consistent manner by retaining the longitudinal electric field component in the derivation and neglecting it only when the waveguides structure satisfies the weakly guiding situations.At last, the transmission characteristics, the coupling properties and the crosstalk performance of the wedge SPP waveguides which has a obvious feature that is the longitudinal electric field component is far stronger than the transverse electric field component are analyzed and discussed in detail. From the perspectives of transmission length and mode dimensions, the optimum structure size and the best separation distance of two Adjacent parallel WPP waveguides are listed according to the use of an optical coupler or an independent communication channel. That provides a reference for practical application of WPP waveguides.The overall results of this dissertation illustrate that the new mode coupling coefficient formula for SPP waveguides considered in this paper can provide more accurate theoretical basis and more effective computational methods to analyze the coupling characteristic and crosstalk performance which is important complements in the theory of SPP waveguides. This lays a theoretical foundation for constructing several optical devices based on SPP waveguides and offers a theoretical reference and direction for further deducing the coupled mode theory for SPP-WBG.