State Key Laboratory of Advanced Optical Communication Systems and Networks, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, 200240, China.
School of Science, Jiangnan University, Wuxi, 214122, China.
Sci Rep. 2023 Feb 16;13(1):2750. doi: 10.1038/s41598-023-29621-w.
Wavefront manipulations have enabled wide applications across many interdisciplinary fields ranging from optics and microwaves to acoustics. However, the realizations of such functional surfaces heavily rely on micro/nanofabrication to define the structured surfaces, which are fixed and only work within a limited spectrum. To address these issues, previous attempts combining tunable materials like liquid crystal or phase-change ones onto the metasurfaces have permitted extra tunability and working spectra, however, these additional layers bring in inevitable loss and complicate the fabrication. Here we demonstrate a fabrication-free tunable flat slab using a nonlinear four-wave mixing process. By wavefront-shaping the pump onto the flat slab, we can successfully tune the effective nonlinear refraction angle of the emitting FWM beams according to the phase-matching condition. In this manner, a focusing and a defocusing nonlinear of FWM beam through the flat slab have been demonstrated with a converging and a diverging pump wavefronts, respectively. Furthermore, a beam steering scheme over a 20° angle has been realized through a non-degenerate four-wave mixing process by introducing a second pump. These features open up a door to manipulating light propagation in an all-optical manner, paving the way to more functional and tunable flat slab devices in the applications of imaging and all-optical information.
波前操控已经在许多跨学科领域得到了广泛应用，涵盖了从光学、微波到声学等多个领域。然而，这些功能表面的实现严重依赖于微纳加工来定义结构化表面，而这些结构化表面是固定的，只能在有限的光谱范围内工作。为了解决这些问题，之前的尝试将可调谐材料（如液晶或相变材料）结合到超表面上，从而实现了额外的可调谐性和工作光谱，但这些额外的层带来了不可避免的损耗并使制造过程复杂化。在这里，我们展示了一种免制造的可调谐平板，它利用非线性四波混频过程。通过对平板上的泵浦光进行波前整形，我们可以根据相位匹配条件成功地调整发射 FWM 光束的有效非线性折射角。通过这种方式，通过会聚和发散的泵浦波前，分别演示了 FWM 光束在平板中的聚焦和散焦非线性。此外，通过引入第二泵浦光，通过非简并四波混频过程实现了 20°角度的光束转向方案。这些特性为以全光方式操控光的传播开辟了道路，为成像和全光信息应用中的更具功能性和可调谐的平板器件铺平了道路。
