Research On Silicon Waveguide Grating Devices And Design Methods

The advent of the intelligent era of the Internet of Everything makes the information interaction between things more frequent,and the traditional optical communication network is facing great challenges,and it is urgent to realize the upgrading of the network infrastructure.Silicon photonic devices have attracted extensive attention due to the advantages of low cost,high integration,and compatibility with CMOS process.As one of the important components of silicon photonic devices,waveguide grating devices can realize optical filtering,optical coupling,optical delay,optical modulation,and other functions,which are widely used in optical communication,microwave signal processing,sensing,and other fields.Intelligent and complex applications require more functions and better performance of silicon waveguide grating devices.The conventional forward design methods use first-principles to analyze the semi-analytical relationship between the medium period perturbation and the spectral response,which is suitable for the optimization design of grating devices with conventional functions.However,for grating devices with special functions,such as arbitrary customized spectrum and polarization independent,the more advanced design methods are needed.In this thesis,the waveguide grating devices with different functions and structures are studied systematically by coupling mode analysis,layer peeling algorithm,intelligent optimization algorithm and other design methods focusing on the application scenarios of hitlessly reconfigurable filtering,multi-channel Hilbert transform and polarization independent coupling.The main research work and innovation achievements are as follows:（1）The add/drop filters based on the looped multimode waveguide grating has been demonstrated by adopting the forward design method based on coupled mode theory.And then a dual-channel reconfigurable optical add/drop multiplexer（ROADM）is realized,which supports gridless center wavelength tunability,gridless bandwidth tunability,and hitless reconfiguration.The center wavelength tuning range is 14.5 nm,the bandwidth tuning range is from 0.2 to 2.4 nm.By adjusting the switching state of the add/drop filters,the dual-channel add/drop multiplexer can be reconfigured hitlessly.The reconfigurable optical add/drop multiplexer supports gridless center wavelength,bandwidth tuning,and hitless reconstruction at the same time,and has wider bandwidth tuning range,lower download loss,and less control electrode.（2）The inverse design model of layer peeling algorithm is constructed and is suitable for multimode waveguide Bragg grating filter.The dispersionless filter,the dispersion compensation filter,the three-channel dispersionless filter,and the Hilbert Transformer are demonstrated by using the model.The corresponding 3 d B bandwidths of the three filters are 4.0 nm,4.7 nm,and 1.4 nm,respectively.The group delays in the passband are 0 ps/nm,5.7 ps/nm and 0 ps/nm,respectively.The group delay ripples are less than 1.7 ps,1.5 ps and 2.0 ps,respectively.The mesured results are basically consistent with the ideal design goals,and the precise control of the amplitude and phase of the reflection spectrum is achieved.Compared with the single-mode waveguide grating filter,the multimode waveguide grating filter designed by the TDLP algorithm have smaller group delay ripples,lower insertion loss,larger extinction ratio and larger feature size.（3）The high-efficiency polarization-independent grating couplers with conventional fabrication process constraints are proposed which is based on an adaptive genetic algorithm model.According to different design requirements,two polarization-independent grating couplers with different structures are obtained by adjusting the parameters of the fitness function.The coupling efficiencies of the first design are-7.6d B and-7.9 d B for the TE₀ and TM₀ modes at 1550 nm,respectively.1.0 d B PDL bandwidth is 25.0 nm.In contrast,the second design presents higher coupling efficiencies of-7.6 d B and-7.2 d B for the TE₀ and TM₀ modes at 1550 nm,respectively.while its 1.0 d B PDL bandwidth is reduced to 22.0 nm.The polarization independent grating coupler is one of the best performing polarization independent grating couplers which is designed by conventional silicon photonics process（220 nm thick Si layer and70 nm etch depth）.（4）An ultra-compact mode multiplexer based on asymmetric directional couplers with subwavelength grating（ADCSWG）is proposed.By introducing subwavelength grating structure in the coupling interval region of asymmetric directional coupler,the coupling strength between modes is enhanced,and then the coupling length is shortened from 17.0μm to 5.6μm.ADCSWGs are used to form a four-channel mode multiplexing link,the minimum insertion loss of mode conversion link TE₀-TE_0/1/2/3-TE₀ is-0.2/-0.7/-0.7/-0.9 d B.The worst crosstalk between the corresponding output port and the other three output ports is 18.0/19.1/16.0/18.2 d B.The scheme has the advantages of lower insertion loss,more compact footprint,lower resolution and easily to increasing the channel count.