The Research Of Silicon-based Grating Coupler And Grating Filter

Silicon-on-Insulator(SOI)has been proven as an ideal platform for integrated optics because its high index contrast,which results in strong optical mode confinement,and makes it possible to scale photonic devices to the sub-micrometer level.However,there is a huge coupling loss caused by the mode size mismatch between the single mode silicon waveguide and the single mode fiber.The grating coupler can couple light into and out of silicon waveguides anywhere on the chip,providing more possibility and convenience for wafer scale testing.In this thesis,universal design methodologies of the grating couplers based on two platforms(SOI & Silicon Nitride)have been demonstrated and verified by numerical simulation and experiments.The simulated coupling efficiency of-4.3dB and the measured result of-6.5dB have been achieved with the proposed structure based on 220 nm SOI platform.To promote the coupling efficiency,some methods such as apodization,poly-silicon overlay and metal reflection mirror have been introduced.In addition,we have discussed the design differences between grating couplers based on SOI and silicon nitride platform.Meanwhile,a compact,high efficient and broadband mode-size converter has been proposed and optimized by combining the finite difference time domain and the particle swarm optimization method.For the mode coupling between a 12?m wide waveguide grating and a 0.4?m wide single mode silicon waveguide,a high conversion efficiency of 93.9% is obtained with a length of 30?m,which is only one fifth of the traditional linear mode-size converter.As one of the most important devices in integrated optics,waveguide Bragg grating filters have been widely used in wavelength-division multiplexing,pulse shaping,dispersion compensation and other fields.In the thesis,the waveguide Bragg grating filter based on the 0.5?m wide single mode silicon waveguide has been designed.The bandwidth of the grating filter is 15 nm with the corrugation width of 20 nm.The sidelobe of the waveguide Bragg grating filter has been suppressed by apodization,with the suppression ratio of 27 dB.Finally,we proposed a filter based on asymmetric multimode waveguide,the bandwidth of the filter is 2nm with the corrugation width of 100 nm.