Design And Research Of Wideband Polarization Splitter Rotator Based On Silicon Mode-evolution

In recent years,Silicon on insulator（SOI）has attracted wide attention as an important silicon-optical integration platform.Due to the high refractive index difference between the SOI waveguide core and cladding materials,and the high compatibility with complementary metal oxide semiconductor（CMOS）process,The platform has the advantages of strong light binding ability,easy development of ultra-small functional devices and easy realization of large-scale photon integration.However,the inherent high refractive index difference of the SOI platform causes polarization sensitivity issues such as polarization mode dispersion and polarization-related losses,ultimately leading to degradation of optical communication system performance.The polarization splitter rotator（PSR）is a key device to control the polarization state of optical waves in the on-chip photonic integration circuit,which can effectively solve the polarization dependence problem in optical communication systems.In this paper,two types of PSRs with low insertion loss,low crosstalk and high polarization extinction ratio based on SOI platform are proposed respectively,and the polarization splitter rotator principle and optimization process of structural parameters are studied respectively.The transmission characteristics and fabrication tolerances are analyzed using the finite difference time domain method.The research results obtained in this paper are as follows:1.Based on the principle of mode evolution,a compact polarization splitter rotator with low loss,low crosstalk and high polarization extinction ratio in C band is proposed.The structural parameters of the device are optimized using PSO algorithm and spline interpolation optimization principle,and the polarization splitter rotator function is finally realized with the device length of only 45μm.The results show that the insertion loss in the1500nm-1600nm waveband is less than 0.007d B,the crosstalk is less than-28.7d B,and the polarization extinction ratio is greater than 49.1d B when input TE₀mode;the insertion loss in the whole C-band is less than 0.34d B,the crosstalk is less than-47.1d B,and the polarization extinction ratio is greater than 47.1d B when input TM₀mode.The insertion loss value at the center wavelength（1550nm）is only 0.06d B.Meanwhile,the device has a large manufacturing tolerance.2.An ultra-wideband polarization splitter rotator based on the mode evolution principle is proposed.Compared with conventional ridge or cone waveguide,the proposed device uses Direct Binary Search（DBS）to etch freely distributed air holes in the original waveguide.The defect holes make the cross section of the waveguide constantly change along the transmission direction,thus achieving refractive index tunability in a large bandwidth range.The optimized results show that the insertion loss is less than 0.23d B,the crosstalk is less than-13d B,and the polarization extinction ratio is more than 32.6d B for TE₀polarized light input in the operating waveband of 1300nm-1700nm;the insertion loss is less than 0.35d B,the crosstalk is less than-12.8d B,and the polarization extinction ratio is more than 26.3d B for TM₀polarized light input.The device has simple structure,small size,easy integration and large manufacturing tolerance.