Research On Polarization Devices With Silicon-based Surface Plasmonic Waveguide

Polarization beam splitter(PBS)and polarization rotator(PR)which can manipulate the polarization state,are very important in polarization multiplexing communication system,and integrated polarization devices are indispensable for photonic integrated circuits(PICs),which are sensitive to polarization,and polarization-diversity photonic integrated chips.In PICs,the polarization devices are required to have the characteristics of small size,high polarization extinction ratio(ER)and low insertion loss(IL),and the devices based on silicon and Surface Plasmon Polariton(SPP)waveguide match with these characteristics,which has been a hot research topic in recent years.In this paper,we have carried out some theoretical research work for designing integrated polarization devices.The main contents of this thesis are listed as follows:1)The development and challenge of polarization devices are introduced and the SPP is proposed to achieve subwavelength polarization devices.After that,we introduce the dispersion model and excitation methods of the SPP.Then the most commonly used waveguide structures in silicon-based devices are analyzed through FDTD method.2)A PBS based on silicon slot waveguide is proposed.Based on the strong local characteristics of the vertical slot for the TE mode,the PBS with the coupling length of 2?m,is realized by using asymmetric direction coupling method.Through the simulation and parameter optimization,the ER of TE mode is above 25 dB and IL is less than 0.1 dB;the ER of TM mode is more than 20 dB and IL is less than 1 dB in C band.Thus,based on this structure,a high performance and ultra-small PBS can be realized.3)A PBS based on bending SPP waveguide is proposed.Because of the same optical path length,TM mode can be coupled to cross waveguide to achieve beam splitting function.Through the parameter optimization,the coupling length is 3.95 ?m and the transmission of TE mode is above 98%,and the transmission of TM mode is above 90% in the wavelength range of 1450 nm to 1550 nm.Meanwhile,within the range of ±30nm fabrication tolerance,the extinction ratios of TE and TM modes are about 20 dB.Thus a PBS with smaller size,high extinction ratio and large fabrication tolerance can be realized with this proposed structure.4)A PR based on L-shaped surface plasmonic waveguide is proposed.Breaking through the limitation that the cladding and substrate are usually using different materials,we use L-shaped plasmonic waveguide to rotate optical axis and two hybrid modes interfere with each other.After 3-?m rotation length,the polarization extinction ratio of TM can reach 25.19 dB and TE mode is 33.85 dB.Thereby an ultra-high performance PR can be achieved with this waveguide.