Research On A New Type Of Photonic Crystal Device Based On Surface Wave Modulation

Recently, dense wavelength division multiplexer (DWDM) technique has attracted more and more attention in point-to-point core networks, it immensely increases the message capacity on the basis of existing optical fiber communication system. Multiplexers and demultiplexers are the critical components of DWDM systems. Therefore, designing this kind of demultiplexer with small size, simple fabrication, easy to use and convenient for optical circuit integration is one of the critical technique to achieve all-optical network in the further. Surrounding this research hot, the thesis has put emphasis on studying how the 2D photonic crystal waveguide modulates the emerging beams, and based on this analysis designing a new type of wavelength division demultiplexer, achieved some innovative results. Main contents of the thesis are summarized as follows:1. Through investigating how the corrugated surface of 2D photonic crystal waveguide (PCW) modulates the emerging beams, we propose a new style of wavelength division demultiplexer based on surface wave modulation. Firstly, we use a simple diffraction sketch and a grating equation to understand the physical mechanism about corrugated surface adjusting emerging beams. Then by systematically investigating how the cylinders radius and refractive index of the corrugated surface affect the focus locations by means of the finite-difference time-domain (FDTD) numerical simulations, we find that at the same normalized frequency the focus moves away from the corrugated surface with the increasing of radius or refractive index of all cylinders, and for the same corrugated surface the distance between the focus and the PCW increases with the normalized frequencies and the focal length elongates along the radiation direction. According to the above physical mechanism and modulation regulation, we firstly realize an on-axis focus at a specific wavelength by using a PCW with asymmetric corrugated surface, for light source with other wavelengths the emerging beams are off-axis focused at different directions, therefore realization the function of demutiplexing. Furthermore, we discover the focus can also be affected by the vertical width of the corrugated surface and the waveguide width.2. We design a new type of 2D PCW with declining exit surface, this waveguide can focus emerging beams without revising the period of corrugated surface, which is the greatest difference between this structure and the waveguide with planar exit surface studied in the previous chapter. Similarly, we use a simple diffraction sketch to explain the physical mechanism about the declining surface waveguide focusing the emerging beams. We demonstrate, by using the FDTD numerical method, the focus moving toward the waveguide exit with the increasing of the angles of declining surfaces, and for the same decling surface the distance between the focus and the PCW increases with the normalized frequencies. Furthermore, we introduce two solutions to modify the exit surface to shape off-axis focus at the waveguide exit, when each side of exit surface with different declining angle or with same declining angle but different corrugated period at each side.