Silicon-based Passive Photonic Integrated Devices And Hybrid-multiplexing Transmission Technology On-chip

With the rapid development of information technology,the demands are increasing for communication networks,high-speed interconnection,information processing,and data storage,meanwhile the development directions of various communication networks and signal processing systems are tending to high-speed,large capacity,low power consumption,and low cost.Silicon-based photonic integrated devices with CMOS-compatible processing can be employed to realize the compact integration of different devices on-chip forming typical silicon-based photonic integrated circuits(PICs)and have great potential applications in optical communications on-chip,optical interconnects,data center,and high-performance computing due to their advantages of compact size,excellent performance,low power consumption,and low cost.Based on the intrinsic high-index-contrast of the silicon material,the component size can be effectively shrunk,while strong polarization dependence is also introduced,which has greatly limited its application in optical communications.Thus,high-efficient polarization control schemes are really required to extend the application scope of silicon materials.Moreover,mode converters,power splitters,waveguide crossings in PICs,and on-chip hybrid multiplexing transmission technologies are also the research hotspots recently that should be well addressed to boost the fast development of silicon photonics.Therefore,this dissertation aims to perform the corresponding research work around these issues.The first chapter briefly describes the advances of silicon photonics,focusing on the silicon-based passive photonic integrated devices(e.g.,mode converters,power splitters,waveguide crossings,polarization controllers)and on-chip hybrid multiplexing transmission technologies.Moreover,the key performance indicators of these photonic integrated devices are also summarized.Finally,the contents and contributions of this dissertation are presented.In chapter 2,the numerical analysis and optimization methods used in this dissertation are introduced,including finite-difference frequency-domain method,finite element method,beam propagation method,and finite-difference time-domain method.Their principles,calculation processes,application scopes,and boundary conditions are discussed.In chapter 3,a novel silicon-based strip-to-slot mode converter is proposed and analyzed in detail.Within this device,a subwavelength grating(SWG)multimode waveguide combined with two SWG-wire tapered transitions at its both ends is applied to connect the input strip and output slot waveguides.In the multimode region,a two-fold image can be easily formed based on the symmetric interference and then this image can be further converted into the output slot mode due to similarity of their field distributions.From results,the device length is 4.3?m and the bandwidth can cover the whole wavelength band of optical communications.In chapter 4,a new silicon-based polarization-insensitive strip-to-slot power splitter is proposed and optimized.By embedding an inverse-tapered SWG in the center of the multimode waveguide that is used to splitter the input power,the polarization dependent loss of the device is reduced and polarization-insensitive transmission is realized.The optimized length of the multimode region is only 1.92?m with excellent performance,having potential application in the silicon-based slotted modulator.Waveguide crossing that is inevitable in the planar on-chip dense PICs exhibits huge loss and crosstalk,so that high-efficient crossing schemes are really required.Accordingly,the slot waveguide crossing and hybrid waveguide crossing schemes are proposed in chapter 5.For the crossing core component,multimode waveguide with advantages of broadband and large tolerance is employed to enhance the device performance,and detailed device optimizations are performed.Furthermore,ultracompact size,multi-functions,and multiple types of the waveguide crossing can also be developed.In chapter 6,silicon-based polarization control devices are studied systematically,including polarization beam splitters(PBSs),polarization rotators(PRs),polarization splitter-rotators(PSRs),and polarizers.For the PBS,three different compact photonic devices are proposed,e.g.,compact PBS for silicon-based slot waveguides using an asymmetrical multimode waveguide,compact and high extinction ratio PBS using subwavelength grating(SWG)couplers,and high-efficient PBS using asymmetrical three-guide directional coupler.For the PR,two different photonic devices are proposed,e.g.,compact PR for silicon-based slot waveguide structures using anisotropic materials,and hybrid plasmonic PR for silicon-based slot waveguides.For the PSR,two different ultracompact photonic devices are proposed,e.g.,compact and integrated PSR for silicon-based slot waveguides,and ultracompact and high-efficient silicon-based PSR using a partially-etched subwavelength grating coupler.For the polarizer,two different photonic devices are also proposed,e.g.,TE-pass polarizer for silicon-based slot waveguides using vertical coupling,and compact,broadband and low-loss TE-pass polarizer using transparent conducting oxides.For these devices,their principles,design procedures and performance optimizations are analyzed in detail,including fabrication tolerance for the key parameters.The obtained device performance and size have obvious advantages over some previous reports.Based upon the study of these passive photonic integrated devices,a novel silicon-based wavelength-/polarization-division-multiplexing optical transmission system on-chip is proposed in chapter 7.To achieve this,polarization multiplexers/demultiplexers are designed,and the hybrid multiplexing transmission scheme is constructed and demonstrated by simulation,including the analyses of its structure,performance,and application.Finally,the summary of the whole dissertation and the outlook for the future work are drawn.