Since the invention of the silicon subwavelength grating waveguide in 2006, subwavelength metamaterial engineering has become an essential design tool in silicon photonics. Employing well-established nanometer-scale semiconductor manufacturing techniques to create metamaterials in optical waveguides has allowed unprecedented control of the flow of light in photonic chips. This is achieved through fine-tuning of fundamental optical properties such as modal confinement, effective index, dispersion, and anisotropy, directly by lithographic imprinting of a specific subwavelength grating structure onto a nanophotonic waveguide. In parallel, low-loss mode propagation is readily obtained over a broad spectral range since the subwavelength periodicity effectively avoids losses due to spurious resonances and bandgap effects. In this review we present recent advances achieved in the surging field of metamaterial integrated photonics. After briefly introducing the fundamental concepts governing the propagation of light in periodic waveguides via Floquet–Bloch modes, we review progress in the main application areas of subwavelength nanostructures in silicon photonics, presenting the most representative devices. We specifically focus on off-chip coupling interfaces, polarization management and anisotropy engineering, spectral filtering and wavelength multiplexing, evanescent field biochemical sensing, mid-infrared photonics, and nonlinear waveguide optics and optomechanics. We also introduce a nascent research area of resonant integrated photonics leveraging Mie resonances in dielectrics for on-chip guiding of optical waves, with the first Huygens’ metawaveguide recently demonstrated. Finally, we provide a brief overview of inverse design approaches and machine-learning algorithms for on-chip optical metamaterials. In our conclusions, we summarize the key developments while highlighting the challenges and future prospects.

中文翻译：

---

超材料集成光子学的最新进展


自2006年硅亚波长光栅波导发明以来，亚波长超材料工程已成为硅光子学中重要的设计工具。采用成熟的纳米级半导体制造技术在光波导中制造超材料，可以对光子芯片中的光流进行前所未有的控制。这是通过直接将特定亚波长光栅结构光刻压印到纳米光子波导上来微调基本光学特性（例如模态限制、有效折射率、色散和各向异性）来实现的。同时，由于亚波长周期性有效地避免了寄生谐振和带隙效应造成的损耗，因此很容易在宽光谱范围内获得低损耗模式传播。在这篇综述中，我们介绍了超材料集成光子学领域的最新进展。在简要介绍了通过Floquet-Bloch模式控制光在周期波导中传播的基本概念后，我们回顾了亚波长纳米结构在硅光子学中主要应用领域的进展，并介绍了最具代表性的器件。我们特别关注片外耦合接口、偏振管理和各向异性工程、光谱滤波和波长复用、倏逝场生化传感、中红外光子学以及非线性波导光学和光力学。我们还介绍了一个新兴的谐振集成光子学研究领域，利用电介质中的米氏共振进行光波片上引导，最近展示了第一个惠更斯元波导。 最后，我们简要概述了片上光学超材料的逆向设计方法和机器学习算法。在我们的结论中，我们总结了主要进展，同时强调了挑战和未来前景。