Zhou Ji, Hu Jianqi, Clementi Marco, Yakar Ozan, Nitiss Edgars, Stroganov Anton, Brès Camille-Sophie
Photonic Systems Laboratory (PHOSL), STI-IEM, École Polytechnique Fédérale de Lausanne, CH-1015, Lausanne, Switzerland.
Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, China.
Nat Commun. 2025 May 1;16(1):4083. doi: 10.1038/s41467-025-59215-1.
Quasi-phase-matching (QPM) is a widely adopted technique for mitigating stringent momentum conservation in nonlinear optical processes such as second-harmonic generation (SHG). It effectively compensates for the phase velocity mismatch between optical harmonics by introducing a periodic spatial modulation to the nonlinear optical medium. Such a mechanism has been further generalized to the spatiotemporal domain, where a non-stationary spatial QPM can induce a frequency shift of the generated light. Here we demonstrate how a spatiotemporal QPM grating, consisting in a concurrent spatial and temporal modulation of the nonlinear response, naturally emerges through all-optical poling in silicon nitride microresonators. Mediated by the coherent photogalvanic effect, a traveling space-charge grating is self-organized, affecting momentum and energy conservation, resulting in a quasi-phase-matched and Doppler-shifted second harmonic. Our observation of the photoinduced spatiotemporal QPM expands the scope of phase matching conditions in nonlinear photonics.
准相位匹配（QPM）是一种广泛应用的技术，用于缓解诸如二次谐波产生（SHG）等非线性光学过程中严格的动量守恒问题。它通过对非线性光学介质引入周期性空间调制，有效地补偿了光学谐波之间的相速度失配。这种机制已进一步推广到时空域，其中非平稳空间QPM可引起所产生光的频移。在此，我们展示了一种时空QPM光栅如何通过氮化硅微谐振器中的全光极化自然出现，该光栅由非线性响应的同时空间和时间调制组成。在相干光电流效应的介导下，一个移动的空间电荷光栅自组织形成，影响动量和能量守恒，从而产生准相位匹配和多普勒频移的二次谐波。我们对光致时空QPM的观察扩展了非线性光子学中相位匹配条件的范围。
