| Silicon-based integrated circuits have completely changed the life of modern people,with the development of the integrated circuits,the integration level is constantly improving,and the metal wire interconnection is gradually unable to meet the demands of high-speed and high-density information transmission.Optical interconnection has the advantages of large bandwidth,low loss and anti-electromagnetic interference,which is considered as a very potential solution.Silicon-based photonics has attracted people's attention in this context.Silicon-based photonic devices are compatible with the existing complementary metal oxide semiconductor process,while having the advantages of high stability,low cost and large-scale and high-density integration,which have become a popular research area in the academic and industrial fields.Optical filters are fundamental devices in optical networks.The next generation optical communication systems use flexible network and super channel technology,which require highly dynamic channel allocation to greatly improve the spectral efficiency.Tunable optical filters are reconfigurable in the central wavelength and bandwidth,and can be extended to terahertz,which is very important for the next generation optical networks.Therefore,the research on silicon-based tunable filters is particularly important.This thesis studies the tunable filters based on the sub-wavelength grating(SWG).Firstly,the basic structures and principles of several kinds of tunable filters are introduced,to solve the problems that the free spectral range(FSR)of the above filters is small or the size is too large,we propose two kinds of tunable filters based on SWG,and we simulate and realize bandwidth tuning of two kinds of tunable filters.Besides,we fabricate and test one kind of tunable filter.Measured results show that the combination of the apodized SWG and the tapered strip waveguides not only effectively suppresses the sidelobes,but also makes the device very compact.The main work of this thesis is as follows:(1)Theoretical study on the transmission characteristics of couplers based on periodic dielectric perturbation.With the help of a periodic structure,such as grating structure,the optical signal can be efficiently coupled between waveguides with different effective refractive indices,especially the coupled optical signal has frequency selectivity,and the coupler can be used as a filter.In addition,we analyze the factors that affect the coupling efficiency,bandwidth and central wavelength,which lays the foundation for the design,simulation and optimization of subsequent devices.(2)Design of compact tunable filters based on SWG.FDTD Solutions is used to verify and optimize the proposed filters.After simulation and optimization,the optimal parameters of the two filters are obtained.The coupling lengths of the two types of filters is 100 ?m and 70 ?m respectively,which are much smaller than that of the tunable filters using Bragg grating.The simulation results show that the method of apodization can achieve high sidelobes suppression,and the combination of the apodization and the tapered waveguide can also effectively suppress the sidelobes,especially the sidelobes on the left side of the passband.(3)Fabrication and test of the tunable filters based on SWG.On the vertical coupling optical platform,the contra-coupling filter based on a single sub-wavelength grating waveguide and the cascaded tunable filter are tested.The experimental results show that there are no sidelobes on the left side of the passband in the transmission spectrum.The combination of the apodized SWG and the tapered strip waveguides effectively suppresses the sidelobes,the length of the coupling region is only 100 ?m.Upon testing the tunable filter,the tuning bandwidth of 6 nm and the central wavelength of 7 nm are realized.The tunable filters based on sub-wavelength grating have ultracompact structure,wide tunable bandwidth,which lay a foundation for further study on silicon-based tunable filters. |
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