Guo Quanbing, Ou Zhenwei, Tang Jibo, Zhang Jing, Lu Fengya, Wu Ke, Zhang Douguo, Zhang Shunping, Xu Hongxing
Institute of Photonics, Department of Optics and Optical Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China.
Nano Lett. 2020 Nov 11;20(11):7956-7963. doi: 10.1021/acs.nanolett.0c02736. Epub 2020 Oct 14.
Monolayer transition metal dichalcogenides possess considerable second-order nonlinear coefficients but a limited efficiency of frequency conversion due to the short interaction length with light under the typical direct illumination. Here, we demonstrate an efficient frequency mixing of the guided surface waves on a monolayer tungsten disulfide (WS) by simultaneously lifting the temporal and spatial overlap of the guided wave and the nonlinear crystal. Three orders-of-magnitude enhancement of the conversion efficiency was achieved in the counter-propagating excitation configuration. Also, the frequency-mixing signals are highly collimated, with the emission direction and polarization controlled, respectively, by the pump frequencies and the rotation angle of WS relative to the propagation direction of the guided waves. These results indicate that the rules of nonlinear frequency conversion are applicable even when the crystal is scaled down to the ultimate single-layer limit. This study provides a versatile platform to enhance the nonlinear optical response of 2D materials and favor the scalable generation of a coherent light source and entangled photon pairs.
单层过渡金属二硫化物具有可观的二阶非线性系数，但在典型的直接光照下，由于与光的相互作用长度较短，其频率转换效率有限。在此，我们通过同时提高导波与非线性晶体的时间和空间重叠，展示了单层二硫化钨（WS）上导波的高效频率混合。在反向传播激发配置中实现了转换效率三个数量级的增强。此外，频率混合信号高度准直，其发射方向和偏振分别由泵浦频率以及WS相对于导波传播方向的旋转角度控制。这些结果表明，即使晶体缩小到最终的单层极限，非线性频率转换规则仍然适用。本研究提供了一个通用平台，可增强二维材料的非线性光学响应，并有利于相干光源和纠缠光子对的可扩展产生。
