The Research On Silicon-based Ultrabroadband Polarization Beam Splitter

Silicon-based optoelectronic integrated circuit,as a popular communication technology in recent years,has exerted great influence on people's production and life.As early as the 1970s,the idea of building an integrated optical path was boldly put forward.With the gradual deepening of research,the research on silicon-based optoelectronics and integrated chips becomes more and more important.Silicon-based integrated chip technology relys on mature and stable complementary metal oxide semiconductor?CMOS?process,with the advantages of low cost,easy to process,large-scale production and high integration.In this paper,finite difference time domain?FDTD?method is used to simulate and experimentally study the propagation characteristics of quasi-transverse magnetic mode?TM?and quasi-transverse electric mode?TE?in silicon nanowire waveguide,including the optical electric field distribution and transmission in polarization beam splitter.Due to that the operation wavelength range of conventional polarization beam splitter?PBS?is short,an ultra-compact polarization beam beam splitter based on tapered bent directional coupler?DC?structure is designed.The main work of this paper is as follows:?1?Using the finite difference eigenmode solver?FDE?method in MODE solutions software,the polarization characteristics of silicon nanowire waveguide were studied.Due to the height of silicon on insulator?SOI?wafer is 220 nm,so the height of the silicon waveguide is 220 nm in the simulation.By adjusting the width of the silicon waveguides,we get waveguide width range of the two single-mode polarization states.In that ranges,TE and TM modes in silicon waveguides are fundamental mode,which can be named TE₀mode and TM₀ mode.And the light can not be inspired higher-order modes,such as TE₁,TM₁,TE₂...And so on.It lays a foundation for further simulations and setting waveguide width parameters of the tapered bent DC.?2?The finite difference time-domain?FDTD?method was adopted,after setting the physical parameters of SOI model,the waveguide structure of DC was designed by software.After setting parameters,such as waveguides gap,width and height,the optimal parameters of PBS were obtained after several simulations and optimization.The simulation results show that the PBS can significantly improve the operation bandwidth and achieve higher extinction ratio and lower optical loss,comparing with the bent DC structure with constant waveguide width and the tapered DC structure based on the straight waveguide.In order to optimize the device performance,the method of cascading single tapered bent DC structure is adopted.It can be seen that PBS has very large broadband performance?1280 nm-1600 nm?.For TM mode optical signal,greater than 10.1 dB extinction ratio and s less than 1.37 dB optical coupling los can be obtained.When the TE lignt inputs,the extinction ratio is also greater than 10.5 dB and the optical insertion loss is less than 1.33dB.Therefore,both polarization modes can achieve lowinsertion loss and high extinction ratio when the input light wavelength is between 1280 nm and1600 nm.?3?By using waveguide parameters which were obtained through simulation calculation,we designed the corresponding layouts and processed silicon-based optical chips.Optical lasers with a wavelength range of 1280 nm-1360 nm and1510 nm-1590 nm were used for testing the device.The measurement results show that,for TE mode optical signals,greater than 10.94 dB extinction ratio and less than 1.61 dB optical insertion loss can be obtained in the wavelength range of 1280 nm-1360 nm.When the wavelength range is from 1510 nm to1590 nm,the extinction ratio is greater than 11.98 dB and the optical insertion loss is less than 1.39 dB.When the TM light inputs,the extinction ratio is greater than 12.25 dB and optical coupling loss is less than 2.22 dB in 1280nm-1360 nm.In 1510 nm-1590 nm,greater than 18.93 dB extinction ratio and less than 1.22 dB optical coupling loss can be obtained.The structure of the tapered bent DC-PBS is simple and it adopts the most common SOI structure.It is easy to design and process,and it is easy to integrate with other silicon-based photonic devices.Therefore,it has a broad application prospect in silicon-based integrated optical circuits.