设计了一种具有不同衬底折射率的新型多模干涉耦合器 ,在多模波导区引入了更强的光场限制 ,激发更高阶的导模 ,从而提高映像质量 采用二维有限差分波束传播方法模拟了这种新型的结构 ,结果表明 :与传统结构相比 ,以功率均衡性和附加损耗为衡量标准的映像质量有了明显提高 这种结构可以应用于三维SOI脊形波导中 A new type of multimode interference coupler with different substrate refractive index is designed, which introduces a stronger optical field limitation in the multi-mode waveguide and excites the higher order guided modes to improve the image quality. The two-dimensional finite difference beam Propagation method simulates this new type of structure. The results show that compared with the traditional structure, the image quality with power balance and additional loss as the standard has been obviously improved. This structure can be applied to three-dimensional SOI ridge waveguide