Optical Directional Coupler Devices Based On Spps

In order to obtain the faster information transmission and greater capacity of information carrying now, photonic technology (we take photon as the carrier of information transmission) has become a focus for researchers, but compared with the traditional electronic devices (ultra large scale integrated circuit technology) , the miniaturization process of the photonic devices is far behind a lot. The size of current electronic devices has been reduced to the nanometer scale, while the horizontal size of a typical optical waveguide remains in the micrometer range, which due to the restrictions of diffraction limit. The emergence of surface plasmon provides a new solution of size matching problems. As the device based on surface plasmon has the advantages of both optical device and electronic device, so it points out a new direction to researches of optoelectronic integration and optical integration.Nowadays, the optical devices based on surface plasmon have been studied extensively. A large number of device structures have been proposed. Among the many optical devices which based on surface plasmon, the optical directional coupler device is a basic optical device, which is widely used as a spectrometer, optical switches, signal detection device, power splitter and so on. It is an important component of the integrated optical devices. Therefore the research on optical directional coupler device of high integration level has important practical application.In this paper we have mainly studied the optical directional coupler device based on the surface plasmon. First, we research the basic properties of surface plasmon by the Maxwell electromagnetic theory, discuss in detail the conditions of its production, dispersion relations, transmission mode, excitation mode, properties of stimulate light, electromagnetic field distribution and so on. Second, we introduce an important numerical simulation in the computational electromagnetic, that is, finite difference time domain method (FDTD). The time evolution equation of electromagnetic fields in uniaxial anisotropic perfectly matched layer (UPML) is derived in detail and the differential equations with time is also obtained by discretization. Finally, we have designed the branch directional coupler device, variable resistance branch directional coupler device, ring directional coupler device based on metal-insulator-metal (MIM) waveguide. The dimensions of these devices are all in the nanometer scale. We have achieved numerical simulations of these directional coupler devices in the MATLAB programming platform by the finite difference time domain method for electromagnetic waves. Through the analysis of the simulation results, we show that these structures can achieve the functions of the traditional directional coupler, and limit the light mode in a sub-wavelength area. We also give the characteristics parameters and quality factor of device designed.