Design And Research Of Silicon-based Polarization Control Devices

In recent years,silicon materials on insulators（SOI）have attracted considerable attention in the field of photonic integration.However,the high refractive index difference between waveguide and cladding leads to significant polarization dependence,which greatly limits the application of Si-based photonic devices.As one of the solutions,polarization diversity system has become a hot research topic.As the key component of the system,polarization controller has important research significance.Therefore,the following work has done around the Si-based polarization controller in this paper.（1）Based on the principle of mode coupling,an asymmetric directional coupler（ADC）polarization beam splitter（PBS）is designed.Firstly,polarization beam splitting is achieved by adjusting the width and height of the waveguide to meet the phase matching condition.Secondly,the performance of the device is optimized by adding Si₃N₄ coating and arc waveguide.The simulation results show that the polarization extinction ratio of TM₀ and TE₀ polarization modes both increases significantly at 1550 nm wavelength,which is more than 29.8 dB;the loss is further reduced,which is less than 0.33 dB;and the total length of device is about 6 microns.（2）According to the principle of mode mixing,a polarization rotator（PR）based on surface plasmon（SPPs）waveguide is designed.By introducing Ag metal strip to form an asymmetric cross section,the two mixed modes,which interfere with each other,are stimulated,and polarization rotation can be realized after a certain distance.The simulation results show that at 1550 nm wavelength,the width of Ag strip has little effect on the conversion efficiency,and the values are more than 98%.By reasonably selecting the width and height of Ag strip（W₁=h₁=W₂=h₂=100nm）,a shorter polarization conversion length（L_C is only 1.26um）and a lower loss（Loss=2.06dB）can be obtained.（3）According to the mode coupling principle,a polarization beam splitter-rotator（PSR）based on hybrid plasma waveguide（HPW）structure is designed.By adjusting the width of straight waveguide（DW）and HPW,the effective refractive index of TM₀ polarization mode in DW is equal to that of TE₀ polarization mode in HPW,and polarization rotation occurs while polarization beam splitting is realized.The simulation results show that the polarization extinction ratios of TM₀ and TE₀ polarization modes are 34.6 dB and 24.8 dB respectively at 1550nm,and the losses are 1.688 dB and 0.072 dB respectively.At this time,the coupling length of the device is only 6.6 um.The designed Si-based polarization controller can be used not only in polarization diversity system,but also in polarization-mode division multiplexing system,which provides theoretical reference for expanding communication capacity.