Reserch And Development In The Silicon Based MMI Coupler And Polarization Beam Splitter

With the development of the optical communication/sensing systems, the requests for the optical waveguide based coupler/polarization beam splitter become increasingly higher. Silicon based multimode interference (MMI) coupler and polarization beam splitter are of important passive devices in optical communication/sensing, for their advantages of high stability, compact, mass fabrication and compatible with CMOS process. This thesis focuses on the Silicon based MMI coupler/polarization beam splitter as well as demonstrates the theoretical analysis and experimental testing.In the second chapter, the imaging principle of the offset excitation at the input port is derived, in which the resonance phenomena in the input single mode waveguide is analyzed. The MMI coupler without modulation module is proposed by using the offset excitation principle, which can attain tunable splitting ratio. By using the effective index method (EIM), the guided-mode propagation analysis (G-MPA) and the 3D finite difference beam propagation method (3D-FD-BPM), the 1×4 and 1×2 MMI coupler based on the offset excitation are analyzed and designed.In the third chapter, the perturbation theory based on the gap in the buffer layer is derived, in which the effect of the parameters for the gap on the mode distribution is analyzed. According to perturbation theory, the MMI based polarization beam splitter is proposed. The structure of the gap is optimizd and designed by using the full vector finite element method (FV-FEM). The optimal design for the MMI based polarization beam splitter is given, in which the width, the length of the multimode waveguide and the location of the input/ouput waveguides are optimizd and designed by using 2D-FD-BPM and 3D-FD-BPM, respectively.In the fourth chapter, the fabrication process and the testing methods for the Silicon based MMI coupler/polarization beam splitter is given as well as the testing platform is constructed. The coupler/polarization beam splitter chips are tested, in wich the experimental results are analyzed corresponding to the theoretical designing.Finally, the fifth chapter summarizes the whole and gives the next step of the work.