Modal phase matching (MPM) is a widely used phase matching technique in Al $_x$ Ga $_{1-x}$ As and other $\chi ^{(2)}$ nonlinear waveguides for efficient wavelength conversions. The use of a non-fundamental spatial mode compensates the material dispersion but also reduces the spatial overlap of the three interacting waves and therefore limits the conversion efficiency. In this work, we develop a technique to increase the nonlinear overlap by modifying the material nonlinearity, instead of the traditional method of optimizing the modal field profiles. This could eliminate the limiting factor of low spatial overlap inherent to MPM and significantly enhance the conversion efficiency. Among the design examples provided, this technique could increase the conversion efficiency by a factor of up to $\sim$ 290 in an Al $_x$ Ga $_{1-x}$ As waveguide. We further show that this technique is applicable to all $\chi^{(2)}$ material systems that utilize MPM for wavelength conversion.

中文翻译：

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模态相位匹配 $\chi^{\hbox{{(2)}}}$ 非线性波导中的波长转换效率增强


模态相位匹配 (MPM) 是一种广泛应用于 Al $_x$ Ga $_{1-x}$ As 和其他 $\chi ^{(2)}$ 非线性波导中的相位匹配技术，可实现高效的波长转换。非基本空间模式的使用补偿了材料色散，但也减少了三个相互作用波的空间重叠，因此限制了转换效率。在这项工作中，我们开发了一种通过修改材料非线性来增加非线性重叠的技术，而不是优化模态场分布的传统方法。这可以消除 MPM 固有的低空间重叠的限制因素，并显着提高转换效率。在提供的设计示例中，该技术可以将 Al $_x$ Ga $_{1-x}$ 作为波导的转换效率提高高达 $\sim$ 290 倍。我们进一步表明，该技术适用于所有利用 MPM 进行波长转换的 $\chi^{(2)}$ 材料系统。