Xu Ding, Peng Zhi Hao, Trovatello Chiara, Cheng Shan-Wen, Xu Xinyi, Sternbach Aaron, Basov D N, Schuck P James, Delor Milan
Department of Chemistry, Columbia University, New York, NY, USA.
Department of Mechanical Engineering, Columbia University, New York, NY, USA.
Nat Nanotechnol. 2025 Mar;20(3):374-380. doi: 10.1038/s41565-024-01849-1. Epub 2025 Jan 15.
Van der Waals (vdW) semiconductors have emerged as promising platforms for efficient nonlinear optical conversion, including harmonic and entangled photon generation. Although major efforts are devoted to integrating vdW materials in nanoscale waveguides for miniaturization, the realization of efficient, phase-matched conversion in these platforms remains challenging. Here, to address this challenge, we report a far-field ultrafast imaging method to track the propagation of both fundamental and harmonic waves within vdW waveguides with femtosecond and sub-50 nanometre spatiotemporal precision. We focus on light propagation in slab waveguides of rhombohedral-stacked MoS, a vdW semiconductor with large nonlinear susceptibility. Our method allows systematic optimization of nonlinear conversion by determining the phase-matching angles, mode profiles and losses in waveguides without prior knowledge of material optical constants. Using this approach, we show that both multimode and single-mode rhombohedral-stacked MoS waveguides support birefringent phase matching, demonstrating the material's potential for efficient on-chip nonlinear optics.
范德瓦尔斯（vdW）半导体已成为实现高效非线性光学转换（包括谐波和纠缠光子产生）的有前景的平台。尽管人们主要致力于将vdW材料集成到纳米级波导中以实现小型化，但在这些平台上实现高效的相位匹配转换仍然具有挑战性。在此，为应对这一挑战，我们报告了一种远场超快成像方法，用于以飞秒和低于50纳米的时空精度跟踪vdW波导内基波和谐波的传播。我们重点研究了菱形堆叠的MoS平板波导中的光传播，MoS是一种具有大非线性极化率的vdW半导体。我们的方法能够在无需事先了解材料光学常数的情况下，通过确定波导中的相位匹配角、模式分布和损耗，对非线性转换进行系统优化。使用这种方法，我们表明多模和单模菱形堆叠的MoS波导均支持双折射相位匹配，证明了该材料在高效片上非线性光学方面的潜力。
