| Photonic integrated circuit(PIC)is one of the best options for developing high-capacity,high-speed and broadband optical interconnections in next-generation optical networks.Optical power splitters and wavelength demultiplexers are very significant in PIC to realize many complex photonic devices.However,most silicon-based optical power splitters and wavelength demultiplexers are polarization-dependence,which limits their application range to a certain extent.Therefore,it is of great significance to realize their polarization-independent function.In summary,two kinds of polarization-independent silicon-based optical power splitters and a polarization-independent silicon-based wavelength demultiplexer are designed in this paper.The specific research contents are as follows.(1)Based on a Si/Si N_x double-layer waveguide and a multimode interference waveguide,a polarization-independent uniform optical power splitter is designed.It will be used to realize 1×2uniform power splitting of 1550 nm wavelength optical signal.Meanwhile,the insertion loss and reflection loss are further reduced by optimizing the tapered waveguide.The results show that the size of the device is only 3μm×16.8μm.Its insertion loss and reflection loss are as low as 0.044 d B and-48.8 d B respectively,and the splitting uniformity is 1.00033.In addition,the bandwidth can reach 380 nm with insertion loss less than 1 d B.(2)Based on a Si/Si N_x/Si sandwich structure and an adiabatic coupler,a polarization-independent optical power splitter with designable splitting ratio is designed.It can be used to realize the power distribution with designable splitting ratio for the 1550 nm wavelength optical signal.The polarization-independent function is realized by adjusting the refractive index of the Si N_x,which is the material of the core layer of the sandwich structure.At the same time,the designable splitting ratio function is realized by changing the asymmetry of the waveguide gaps of the adiabatic coupler.The results show that the coupling length of the device is only 7μm,and the designable splitting ratio ranges from 0.5 to 0.95,and the insertion loss is less than 0.31 d B.Besides,the bandwidth can reach 100 nm when the deviation of splitting ratio is within±0.01.(3)Based on introducting Si N_x material in the gap of directional coupler,a polarization-independent wavelength demultiplexer is designed to separate 1310 nm and 1550 nm wavelengths optical signals.The polarization-independent function is obtained by adjusting the refractive index of Si N_x.Meanwhile,the wavelength separation function is realized by adjusting the coupling length ratio of the two wavelength optical signals by optimizing the gap.The results show that the coupling region length of the device is only 22.8μm,and the insertion loss and crosstalk are as low as 0.05 d B and-21.58 d B,respectively.Besides,the bandwidth with crosstalk less than-10d B can reach 79 nm.Finally,a feasible fabrication scheme is proposed,and the bandwidth and crosstalk are improved by optimizing the device structure.In summary,three kinds of devices are designed in this paper.The uniform optical power splitter has the advantages of small size,excellent performance and large bandwidth.The splitting ratio of the the optical power splitter with the designable splitting ratio can range from 0.5 to 0.95,and the polarization independence is realized.The wavelength demultiplexer also has the advantages of compact structure,small loss and large bandwidth.The designed devices have potential application value in the future PIC system. |
