相变材料辅助的非易失性硅基偏振不敏感1×2模式光开关

Non-Volatile Polarization-Insensitive Silicon-Based 1×2 Optical Mode Switch Using Phase-Change Materials

提出一种相变材料辅助的非易失性硅基偏振不敏感1×2模式光开关,该器件包括偏振分束单元、偏振合束单元、定向耦合结构单元、偏振不敏感交叉波导以及模式转换单元。通过调谐相变材料的晶态与非晶态,可实现偏振不敏感的多模光开关功能。利用粒子群智能算法和时域有限差分法对所提出的器件进行优化并分析其性能。仿真结果表明,在1535~1569 nm波长范围内:输入TE_(0)模式时,所设计器件的插入损耗小于1.37 dB,串扰小于-13.12 dB;输入TM_(0)模式时,所设计器件的插入损耗小于1.61 dB,串扰小于-17.39 dB。

Objective The development of multicore processors has greatly relieved the pressure of data processing.However,the capacity requirement for data transmission and exchange is still a challenge.Multidimensional multiplexing technologies are explored to meet the growing bandwidth requirements and provide a promising solution to address such a challenge.Among these technologies,mode division multiplexing in which each guided mode acts as an independent data channel has attracted much attention.Siliconbased optical mode switches are indispensable for reconfigurable onchip mode division multiplexing.Previously,these switches have been demonstrated by a Yjunction combined with a multimode interference coupler and phase shifters,Yjunction couplers combined with 2×2 multimode interference couplers,and microrings.Although these devices can have good performance,sustained power consumption is required to maintain the switch states,which means they are volatile.In addition,due to the high refractive index contrast of the silicononinsulator platform,a strong polarization dependence would be formed.Thus,nonvolatile polarizationinsensitive siliconbased optical mode switches are highly desired.Owing to their outstanding properties,phase change materials are considered attractive candidate materials for realizing nonvolatile integrated optical devices.To the best of our knowledge,nonvolatile polarizationinsensitive siliconbased optical mode switches employing phase change materials are never discussed before.Therefore,we wish to propose,design,and analyze a nonvolatile polarizationinsensitive siliconbased 1×2 optical mode switch using phasechange materials.Methods The proposed nonvolatile polarizationinsensitive siliconbased 1×2 optical mode switch using phasechange materials is composed of a polarization beam splitter,a polarization beam combiner,two directional couplers with phasechange materials operating in the TE0 and TM0 modes,a polarizationinsensitive silicon waveguide crossing,and twomode converter operating in the TE0 and TM0 modes.The proposed polarization beam splitter/combiner is based on a triplewaveguide coupler comprising two silicon waveguides on both sides and a SiSi_(3)N_(4) hybrid waveguide in the middle.By optimizing the structural parameters in the coupling region,a lowinsertionloss,and highpolarizationextinctionratio polarization beam splitter/combiner can be obtained.For the two directional couplers with phasechange materials,a tapered silicon waveguide and a SiGe_(2)Sb_(2)Te_(5)-ITO hybrid waveguide are employed to form the coupling region.The finite difference time domain method and particle swarm optimization algorithm are adopted to optimize the coupling region to obtain low insertion loss and excellent crosstalk.Similarly,the twomode converters are based on countertapered couplers.With an aim at achieving high conversion efficiency in a wide wavelength range,the corresponding coupling regions are optimized through the finite difference time domain method and particle swarm optimization algorithm.The proposed polarizationinsensitive silicon waveguide crossing consists of two orthogonal multimode waveguides in which the input and output tapers are mirrorsymmetrical.The finite difference time domain method and particle swarm optimization algorithm are employed to optimize these tapers and finally realize low insertion loss and excellent crosstalk.As a result,a nonvolatile polarizationinsensitive siliconbased 1×2 optical mode switch with good performance can be achieved by tuning the phase state of phasechange materials.Results and Discussions The functionality of the designed nonvolatile polarizationinsensitive siliconbased 1×2 optical mode switch is executed well(Fig.13).When Ge_(2)Sb_(2)Te_(5) is in the amorphous state,the input TE0 and TM0 modes are transformed into TE1 and TM1 modes and emerge from the port output2.The input TE0 and TM0 modes will propagate forward and come out from port output1,if Ge_(2)Sb_(2)Te_(5) is in the crystalline state.When the designed device is operating in TE polarization,the crosstalk is less than−13.12 dB and the insertion loss is smaller than 1.37 dB within a bandwidth from 1535 nm to 1569 nm(Fig.14).For TM polarization,within a bandwidth from 1535 nm to 1569 nm,the designed device exhibits a crosstalk of lower than−17.39 dB and an insertion loss of smaller than 1.61 dB.The corresponding fabrication tolerance is also discussed(Fig.16).The waveguide width variationΔW and the variation of Ge_(2)Sb_(2)Te_(5) thicknessΔh exert great influence on the crosstalk and insertion loss of the designed device.Thus,the waveguide width and Ge_(2)Sb_(2)Te_(5) thickness should be precisely controlled.Ge_(2)Sb_(2)Se_(4)Te1 can be employed to improve the crosstalk and reduce insertion loss further(Table 5).Conclusions We propose a nonvolatile polarizationinsensitive siliconbased 1×2 optical mode switch using phasechange materials.The proposed optical mode switch consists of a polarization beam splitter,a polarization beam combiner,two directional couplers with phasechange materials operating in the TE0 and TM0 modes,a polarizationinsensitive silicon waveguide crossing,and twomode converter operating in the TE0 and TM0 modes.The polarizationinsensitive mode switching behavior is realized by adjusting the phase state of phasechange materials.The finite difference time domain method and particle swarm optimization algorithm are employed to design and analyze the presented device in detail.For the designed nonvolatile polarizationinsensitive siliconbased 1×2 optical mode switch using Ge_(2)Sb_(2)Te_(5),when the TE0 mode is input,the insertion loss is lower than 1.37 dB and the crosstalk is less than−13.12 dB within a bandwidth from 1535 nm to 1569 nm.As the TM0 mode is input,the insertion loss is smaller than 1.61 dB and the crosstalk is lower than−17.39 dB within a bandwidth from 1535 nm to 1569 nm.The results can provide references for optimizing the design of nonvolatile polarizationinsensitive optical mode switches.