Li Chuntao, Yao Ni, Yu Huakang, Lin Jintian, Gao Renhong, Deng Jiale, Guan Jianglin, Qiao Lingling, Cheng Ya
East China Normal University, State Key Laboratory of Precision Spectroscopy, Shanghai 200062, China.
East China Normal University, The Extreme Optoelectromechanics Laboratory (XXL), School of Physics and Electronic Science, Shanghai 200241, China.
Phys Rev Lett. 2025 May 30;134(21):213801. doi: 10.1103/PhysRevLett.134.213801.
High-order nonlinear optical processes beyond four-wave mixing (χ^{(3)}) are crucial for advancing ultraviolet (UV) light sources and quantum technologies, yet their practical implementation remains challenging due to inherently weak high-order nonlinear susceptibilities and stringent broadband phase-matching requirements-limitations that persist even in state-of-the-art high-Q microresonators. A breakthrough transverse multiwave mixing scheme is proposed in a high-Q lithium niobate microresonator, only under a single continuous-wave (cw) laser pump. Our approach leverages self-organized subwavelength photorefractive gratings (SPGs) generated through a bidirectional stimulated Raman scattering (SRS) process in the microresonator, without using two external counterpropagating lasers. Under single-wavelength pumping (1546 nm), bidirectional SRS (1713 nm) spontaneously generates dynamic SPGs that enable dual-function control: (1) broadband momentum compensation (Δk≈2π/Λ, Λ=grating period) to resolve broadband phase-matching challenges in high-order nonlinear interactions and (2) preservation of ultrahigh-quality factor (Q>7×10^{6}) for enhanced nonlinear conversion. Moreover, unlike conventional longitudinal configurations requiring more rigid multiwavelength resonance alignment, our transverse architecture decouples nonlinear processes from cavity-mode constraints through SPG-mediated momentum engineering, enabling simultaneous support for sum-frequency generation to six-wave mixing processes across 500-nm bandwidth with high conversion efficiencies. Furthermore, the cascaded SRS process is simultaneously activated to generate a light signal for subsequent nonlinear interactions. Consequently, this novel approach enables the first demonstration of single-pump phase-matched transverse SFG with record conversion efficiency (590%/W), and transverse multiwave mixing processes from χ^{(3)} (four-wave) to χ^{(5)} (six-wave) processes are achieved for the first time using only the single cw pump, leading to efficient visible and UV light generation, representing a notable advance in nonlinear integration.
超越四波混频（χ^{(3)}）的高阶非线性光学过程对于推进紫外（UV）光源和量子技术至关重要，然而由于固有的高阶非线性极化率较弱以及严格的宽带相位匹配要求，其实际应用仍然具有挑战性，即使在最先进的高Q微谐振器中这些限制依然存在。在高Q铌酸锂微谐振器中，仅在单个连续波（cw）激光泵浦下，提出了一种突破性的横向多波混频方案。我们的方法利用了通过微谐振器中的双向受激拉曼散射（SRS）过程产生的自组织亚波长光折变光栅（SPG），而无需使用两个反向传播的外部激光。在单波长泵浦（1546 nm）下，双向SRS（1713 nm）自发产生动态SPG，实现双功能控制：（1）宽带动量补偿（Δk≈2π/Λ，Λ =光栅周期），以解决高阶非线性相互作用中的宽带相位匹配挑战；（2）保持超高品质因数（Q>7×10^{6}）以增强非线性转换。此外，与需要更严格的多波长共振对准的传统纵向配置不同，我们的横向架构通过SPG介导的动量工程将非线性过程与腔模约束解耦，能够在500 nm带宽内同时支持高达六波混频过程的和频产生，并具有高转换效率。此外，级联SRS过程同时被激活，以产生用于后续非线性相互作用的光信号。因此，这种新颖的方法首次实现了具有创纪录转换效率（590%/W）的单泵浦相位匹配横向和频产生，并且仅使用单个cw泵浦首次实现了从χ^{(3)}（四波）到χ^{(5)}（六波）过程的横向多波混频过程，从而实现了高效的可见光和紫外光产生，代表了非线性集成方面的显著进展。
