Quasi-phase-matching (QPM) has become one of the most common approaches for increasing the efficiency of nonlinear three-wave mixing processes in integrated photonic circuits. Here, we provide a study of dispersion engineering of QPM second-harmonic (SH) generation in stoichiometric silicon nitride (Si3N4) waveguides. We apply waveguide design and lithographic control in combination with the all-optical poling technique to study the QPM properties and shape the waveguide dispersion for broadband spectral conversion efficiency inside Si3N4 waveguides. By meeting the requirements for maximal bandwidth of the conversion efficiency spectrum, we demonstrate that group-velocity matching of the pump and SH is simultaneously satisfied, resulting in efficient SH generation from ultrashort optical pulses. The latter is employed for retrieving a carrier-envelope-offset frequency of a frequency comb by using an f−2f interferometric technique, where supercontinuum and SH of a femtosecond pulse are generated in Si3N4 waveguides. Finally, we show that the waveguide dispersion determines the QPM wavelength variation magnitude and sign due to the thermo-optic effect.

中文翻译：

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色散工程全光极化氮化硅波导中的宽带准相位匹配

准相位匹配 (QPM) 已成为提高集成光子电路中非线性三波混频过程效率的最常用方法之一。在这里，我们提供了化学计量氮化硅 (Si3N4) 波导中 QPM 二次谐波 (SH) 生成的色散工程研究。我们将波导设计和光刻控制与全光极化技术相结合，研究 QPM 特性并塑造波导色散，以实现 Si3N4 波导内的宽带光谱转换效率。通过满足转换效率谱的最大带宽要求，我们证明了泵浦和 SH 的群速度匹配同时得到满足，从而从超短光脉冲中有效地产生 SH。后者用于通过使用 f-2f 干涉测量技术检索频率梳的载波包络偏移频率，其中在 Si3N4 波导中生成超连续谱和飞秒脉冲的 SH。最后，我们表明由于热光效应，波导色散决定了 QPM 波长变化幅度和符号。