Grating couplerLumerical

Silicon-on-insulator has become a promising platform for high-density integrated photonics circuits. The large refractive index contrast between the functional silicon layer and its cladding raises a coupling issue between an optical fibre and on-chip devices. Grating coupler provides a compact and efficient way to tackle the coupling issue between the optical fibre and silicon waveguide. In this thesis, a universal design methodology, which accommodates various etch depths, silicon thicknesses, and cladding materials has been demonstrated and verified by both FDTD simulation and measurement results. A fully etched grating coupler with a sub-wavelength grating structure has been proposed to reduce the large back reflection of existing fully etched grating couplers. Back reflection of the proposed fully etched grating coupler has been reduced from more than 20% to about 5%. The insertion loss and bandwidth of the proposed structure have also been improved. In addition, a bidirectional grating coupler for vertical coupling has been proposed to improve the insertion loss and bandwidth of the traditional grating coupler. A simulated insertion loss of -1.5dB with a 3dB bandwidth of more 100nm has been achieved with the proposed structure.