Study On Grating Coupler And Waveguide Beam Splitter Based On Silicon Substrate

Silicon photonics is one of the popular research fields among current photonics. Its research is to achieve fabrication and integration of various photonic devices on silicon materials. Planar grating coupler has characteristics of high coupling efficiency, small size and easy for fabrication and encapsulation, which is applied to the coupling between fiber and waveguide. Silicon waveguide polarization beam splitter is an important part of the nano-integrated optics which can control the output of polarization.Based on the principle of the guided mode of planar waveguide, the Bragg condition of grating coupling, the properties of the surface plasmon between metal and dielectric, using the analytical method of rigorous coupled-wave theory and the calculation method of Finite Difference Time Domain, this paper mainly researched silicon grating coupler and waveguide polarization beam splitter, to solve the problem of high coupling efficiency between fiber and waveguide and meet the demand of polarization in nano-integration of silicon device.A number of novel achievements were obtained through the study:(1)A multilevel grating coupler based on SOI material structure is proposed to realize coupling between waveguide and fiber, which can realize coupling when the beams with TE polarization and TM polarization are incident at the same time, solving the problem of unique polarization in the past coupler. This coupler has the characteristics of non-polarization and extremely compact dimension(with the grating length of 3μm). Theory research and simulation results indicate that the wavelength range is 1533nm-1580 nm when the TE mode and TM mode coupling efficiency are both more than 40% as the grating period is 0.99μm. The coupling efficiencies of TE mode and TM mode incident are 49.9% and 49.5% at the wavelength of 1565 nm, and the difference between them is only 0.4%.(2) A high coupling efficiency full-etched grating coupler with reflector grating and refractive index matching layer is designed to realize vertical coupling between waveguide and fiber. Simulation results show that the coupling efficiency of TE mode can reach 87.6% at the wavelength of 1550 nm, which greatly improves the coupling efficiency of the full-etched grating coupler. We also use a FIB/SEM system to fabricate the grating coupler.(3)A novel polarizer with a silver nanoribbon added into a traditional waveguide directional coupler is designed to realize the polarized output of TE mode. A high extinction ratio can be obtained from this polarizer because of the selectivity of SPPs on polarization. Simulation results indicate that the novel polarizer has the characteristics of broadband, big angle tolerance and extremely compact dimension. With the optimized parameters(L=1.25μm, t=40nm, λ=1.55μm, α=13.9°, W=300nm, L1=0.15μm), the coupling efficiency for TE mode can reach about 95%, but only 3% for TM mode, with the extinction ratio of TE mode about 15 d B.