近日，意大利米兰理工大学Marco Finazzi团队实现了纳米尺度非线性干涉全光偏振编码与调制。相关论文于2025年9月15日发表在《光：科学与应用》杂志上。

光学超表面实现了在亚波长厚度内进行复杂的光操作，并且它们正在迅速成为纳米光子学应用的关键使能技术。对光偏振的控制已经为超紧凑的基于超表面的偏振测量装置提供了一条途径。如果转化为非线性光学体制，它可能成为非线性成像，光学全息和传感的变革性工具。

研究组报道了利用非线性干涉技术实现全介质超表面上转换光的超快全光偏振调制。通过控制ω处的泵浦光束与其2ω处的倍频副本之间的相对相位，研究组可以设置3ω处的两个频率简并上转换过程之间的相位关系——和频产生和三次谐波产生——源自AlGaAs超表面。

通过利用两种非线性过程的相反宇称并调整它们的相对强度，研究组实现了上转换光的偏振态在线性和圆态之间的调制，圆偏振度高达83%。值得注意的是，相反旋向的圆偏振光在傅里叶空间中被对称地映射，与超表面的第一衍射阶一致。此外，通过施加π的相位延迟，可以在相同的衍射阶内完全反转手性。该工作为具有精确相位控制的全光路由增加了一个额外的调制层：偏振。在k空间中同时编码和调制不同偏振态的能力具有手性传感和先进成像技术的潜力。

附：英文原文

Title: All-optical polarization encoding and modulation by nonlinear interferometry at the nanoscale

Author: Luan, Yigong, Zilli, Attilio, Di Francescantonio, Agostino, Vinel, Vincent, Biagioni, Paolo, Du, Lamberto, Lematre, Aristide, Leo, Giuseppe, Celebrano, Michele, Finazzi, Marco

Issue&Volume: 2025-09-15

Abstract: Optical metasurfaces allow complex light manipulation within subwavelength thicknesses and are thus rapidly emerging as a key enabling technology for nanophotonics applications. The control over light polarization already provided a route towards ultracompact metasurface-based polarimetry devices. If translated to the nonlinear optical regime it may become a transformative tool for nonlinear imaging, optical holography, and sensing. Here, we report ultrafast all-optical polarization modulation of upconverted light by all-dielectric metasurfaces via nonlinear interferometry. By controlling the relative phase between a pump beam at ω and its frequency-doubled replica at 2ω, we can set the phase relation between two frequency-degenerate upconversion processes at 3ω – sum-frequency generation and third-harmonic generation – stemming from an AlGaAs metasurface. By leveraging the opposite parity of the two nonlinear processes and adjusting their relative intensities, we achieve a modulation of the polarization state of the upconverted light between linear and circular states with a circular polarization degree of up to 83%. Remarkably, circularly polarized light of opposite handedness is symmetrically mapped in the Fourier space, at coincidence with the first diffraction orders of the metasurface. Furthermore, the handedness can be completely reversed within the same diffraction order by applying a phase delay of π. Our work adds an additional modulation layer beyond intensity to all-optical routing with precise phase control: polarization. The capability to encode and modulate simultaneously different polarization states in the k-space holds potential for chiral sensing and advanced imaging techniques.

DOI: 10.1038/s41377-025-01948-1

Source: https://www.nature.com/articles/s41377-025-01948-1