艾里光束由于具有无衍射、自弯曲及自愈合等良好的特性，在显微成像、激光微加工及光学显微操作等方面均有广泛的应用。近年来，研究人员报道了基于超表面的艾里光束产生器，其克服了基于透镜及相位板等传统光学器件产生艾里光束需要复杂光路、庞大体积等问题，具有紧凑、易集成等优势。但是，目前已报道的艾里光束产生装置大多基于共振原理，因此无法宽带工作。同时，由于金属的欧姆损耗在近红外波段较大，因此基于金属超表面的艾里光束产生器在近红外效率均较低。

为了克服窄带宽及低效率的问题，光电子集成与器件功能实验室陈林课题组提出了利用全硅超表面构建宽带高效艾里光束发生器的方案。通过设计硅纳米柱的结构参数可在宽带范围内引入高的双折射，并且由于硅在近红外的损耗低，为高效产生艾里光束提供了可能。研究人员推导了双折射纳米柱在线偏光入射时，其正交线偏振透射光的归一化振幅和相对相位和纳米柱旋转角之间的关系。通过空间排列不同旋转角度的硅纳米柱，提供艾里函数所需要的振幅和相位分布，构建了基于全硅超表面的宽带高效艾里光束产生器，并在1.1μm到1.7μm波段对其性能进行了仿真及实验验证，仿真效率最高可达78%。这项研究为同时需要振幅、相位调制的高效微纳光子器件提供了一种宽带的实现方案。

2020年11月，研究成果以“基于全硅超表面产生超宽带、高效的艾里光束”(Ultra-Broadband High-Efficiency Airy Optical Beams Generated with All-Silicon Metasurfaces)为题，发表在光学杂志《先进光学材料》(Advanced Optical Materials)上。

文章链接为：

https://onlinelibrary.wiley.com/doi/full/10.1002/adom.202001284

图1 器件示意图

图2 艾里光束仿真（a-d）及实验（e-h）验证

New advances in Airy beam generators

As one type of non-diffraction beams, Airy beams have received enormous interest due to the unique diffraction-free, self-accelerating, and self-healing properties. Airy beams have found a wide range of applications including optical micromanipulation, microscopy, micromachining of curved profiles. Conventional protocols for generating Airy beams rely on the utilization of bulky optical elements, which is against high-density optical integration on a chip. Metasurfaces have provided a compact method to generate Airy beams, but the reported Airy beam generators suffer from the issue of narrow bandwidth as they typically rely on resonance principles. In addition, the inherent ohmic loss of metal will remarkably deteriorate the efficiency of the Airy beams around near-infrared band if metasurfaces with metal are involved.

In order to address the above-mentioned issues, Prof. Lin Chen’s group from Optoelectronic Devices and Integration Division of Wuhan National Lab for Optoelectronics, proposes a scheme for the ultra-broadband high-efficiency generation of Airy beams based on all-silicon metasurfaces. Adjusting the structural parameters of nanopillars, the building blocks can maintain high birefringence, and low loss over a wide spectral range. The relationship between the normalized amplitude, relative phase distributions of the transmissive electromagnetic waves and orientation angles of nanopillars has been derived. Then, the local amplitude and phase distributions of the transmitted electromagnetic waves passing through such silicon nanopillars can be well adjusted to follow the Airy function within a wide spectral range by changing orientation angles of the nanopillars. High efficiency Airy beams were numerically and experimentally verified over an ultra-wide spectral band ranging from 1.1 to 1.7 µm with the maximum efficiency of 78% in simulaiton, which is the widest operation bandwidth achieved for Airy beams in the optical domain with metasurfaces to date. The proposed scheme can stimulate the design of high efficiency devices with the simultaneous requirement of controlling the amplitude and phase distributions over a wide spectral band.

This work, titled as "Ultra-Broadband High-Efficiency Airy Optical Beams Generated with All-Silicon Metasurfaces", has been recently published in Advanced Optical Materials.

Address:

https://onlinelibrary.wiley.com/doi/full/10.1002/adom.202001284

Figure 1. Schematic view of the high-efficiency broadband Airy optical beam generator.

Figure 2. Simulated (a-d) and experimental (e-h) demonstration of Airy beam generation.