非线性光学频率转换效应，可以打破传统光源发光波段受限于增益介质能级分布的束缚，拓宽激光光谱的范围。周期极化铌酸锂微环腔具有微腔品质因子高、模式体积小的特性，以及波导器件良好的模场空间交叠特性。同时，周期极化结构的引入，有望充分利用铌酸锂晶体最大非线性系数d33，实现高效率非线性光学频率转换。本项目拟基于申请人在（周期极化）铌酸锂微腔高精度微畴制备和非线性光学效应方面的研究基础，将复杂周期极化结构引入铌酸锂微环腔，开展多非线性过程准相位匹配，及以此为基础的级联非线性光学效应的研究。通过优化周期极化微环腔设计方案、制备工艺，实现具有丰富倒易空间波矢、支持级联非线性过程的高品质因子周期极化微环腔的制备，实现高效率级联非线性光学效应。本项目的研究成果将显著拓宽铌酸锂晶体微腔非线性光学器件的频率覆盖范围，为量子光源制备、红外弱信号探测等应用提供高效解决方案。

Nonlinear optical frequency conversion can be used to expand the spectral range of the laser source without the limitation of the energy level of the medium. Periodically poled lithium niobate microring resonators with high quality factors, small mode volume and the remarkable mode overlap provided by the waveguide structures, have great potentials in efficient nonlinear optical frequency conversion. Especially d33, the largest nonlinear coefficient of lithium niobate could be utilized, due to the periodically poled structures. Based on our previous works on high-precision nano-domain fabrication and nonlinear optical frequency conversions, the project about the multi-nonlinear frequency conversions, especially cascaded nonlinear process and its phase-matching mechanism could be carried out with the method of fabricating complicated periodically poled structures in lithium niobate microring resonators. Benefiting from the various reciprocal space wave vectors of the quasi periodically poled structures, the efficient cascaded nonlinear frequency conversion could be achieved by optimizing the domain patterns and the fabrication processes. The work will dramatically expend the spectral range of the applications based on nonlinear frequency conversions in lithium niobate microresonators and pave the way to achieve quantum sources fabrication and weak light detection.