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多模干涉(MMI)耦合器需要精确定位成像位置,以便器件的设计制作。针对强限制和弱限制的三维多模波导干涉耦合器,采用三维交替方向隐式有限差分光束传输法(BPM),数值计算得出多模波导长度、输入波导和输出波导位置。首先通过对对称干涉多模干涉耦合器的数值分析求得多模干涉耦合器的等效宽度Weq及最低二阶模之间的拍长Lc,然后将这些参量结合光束传输法直接用于器件设计。计算显示该方法得到的成像位置和导模传输分析法(MPA)的理论预测比较接近,但Weq和Lc却是由光束传输法计算得到的,导模传输分析法理论只能在得到Weq和Lc的前提下才能得到成像位置。该方法直接针对三维波导进行,没有采用基于等效折射率方法的从三维波导到二维波导的简化处理,并且也没有采用导模传输分析法所采用的近似,保证了计算精度,对于实际多模干涉器件的设计制作可起参考作用。
Multimode Interference (MMI) couplers require precise positioning of the imaging location for the design of the device. For the three-dimensional multi-mode waveguide interference coupler with strong and weak restrictions, the three-dimensional alternating direction implicit finite difference beam transmission method (BPM) is used to calculate the lengths of the multimode waveguide, the input waveguide and the output waveguide. Firstly, the equivalent width Weq of the multimode interference coupler and the beat length Lc between the lowest order modes of the multimode interference coupler are obtained through the numerical analysis of the symmetric interference multimode interference coupler, and then these parameters are combined with the beam transmission method directly for the device design . The calculated results show that the imaging position obtained by this method is close to the theoretical prediction of guided mode transmission analysis (MPA), but Weq and Lc are calculated by the beam propagation method. The theory of guided mode transmission analysis can only be obtained after Weq and Lc Under the premise of the imaging position can be obtained. The method is directed to three-dimensional waveguides without the simplified processing from three-dimensional waveguides to two-dimensional waveguides based on the equivalent refractive index method and does not use approximations adopted by the guided-mode transmission analysis method to ensure the accuracy of calculation. Die interference device design and production can serve as a reference.