Quasi-phase-matched interactions in waveguides with quadratic nonlinearities enable highly efficient nonlinear frequency conversion. In this paper, we demonstrate the first generation of devices that combine the dispersion engineering available in nanophotonic waveguides with quasi-phase-matched nonlinear interactions available in periodically poled lithium niobate (PPLN). This combination enables quasi-static interactions of femtosecond pulses, reducing the pulse energy requirements by several orders of magnitude compared to conventional devices, from picojoules to femtojoules. We experimentally demonstrate two effects associated with second harmonic generation (SHG). First, we observe efficient quasi-phase-matched SHG with $ {\lt} {100}\;{\rm fJ}$ of pulse energy. Second, in the limit of strong phase-mismatch, we observe spectral broadening of both harmonics with as little as 2 pJ of pulse energy. These results lay a foundation for a new class of nonlinear devices, in which coengineering of dispersion with quasi-phase-matching enables efficient nonlinear optics at the femtojoule level.

中文翻译：

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纳米光子周期极化铌酸锂波导中的超宽带非线性光学

具有二次非线性的波导中的准相位匹配相互作用可实现高效的非线性频率转换。在本文中，我们演示了将纳米光子波导中的色散工程与周期极化的铌酸锂（PPLN）中的准相匹配非线性相互作用相结合的第一代设备。这种组合实现了飞秒脉冲的准静态相互作用，与从皮焦耳到飞焦耳的常规设备相比，将脉冲能量需求降低了几个数量级。我们通过实验证明了与二次谐波产生（SHG）相关的两种效应。首先，我们观察到$ {\ lt} {100} \; {\ rm fJ} $的有效准相位匹配SHG脉冲能量。其次，在强相位失配的极限下，我们观察到两种谐波的频谱展宽，脉冲能量低至2 pJ。这些结果为新型非线性器件奠定了基础，其中色散与准相位匹配的协同工程实现了飞焦级的高效非线性光学。