The Key Laboratory of Weak Light Nonlinear Photonics, Ministry of Education, School of Physics and TEDA Institute of Applied Physics, Nankai University, Tianjin, 300071, China.
The Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi, 030006, China.
Adv Mater. 2018 Jun;30(23):e1706368. doi: 10.1002/adma.201706368. Epub 2018 Apr 19.
Fourier optics, the principle of using Fourier transformation to understand the functionalities of optical elements, lies at the heart of modern optics, and it has been widely applied to optical information processing, imaging, holography, etc. While a simple thin lens is capable of resolving Fourier components of an arbitrary optical wavefront, its operation is limited to near normal light incidence, i.e., the paraxial approximation, which puts a severe constraint on the resolvable Fourier domain. As a result, high-order Fourier components are lost, resulting in extinction of high-resolution information of an image. Other high numerical aperture Fourier lenses usually suffer from the bulky size and costly designs. Here, a dielectric metasurface consisting of high-aspect-ratio silicon waveguide array is demonstrated experimentally, which is capable of performing 1D Fourier transform for a large incident angle range and a broad operating bandwidth. Thus, the device significantly expands the operational Fourier space, benefitting from the large numerical aperture and negligible angular dispersion at large incident angles. The Fourier metasurface will not only facilitate efficient manipulation of spatial spectrum of free-space optical wavefront, but also be readily integrated into micro-optical platforms due to its compact size.
傅里叶光学，即利用傅里叶变换来理解光学元件功能的原理，是现代光学的核心，已广泛应用于光学信息处理、成像、全息术等领域。虽然简单的薄透镜能够解析任意光学波前的傅里叶分量，但它的操作仅限于近正常光入射，即傍轴近似，这对可分辨的傅里叶域施加了严格的限制。因此，高阶傅里叶分量会丢失，导致图像的高分辨率信息消失。其他高数值孔径傅里叶透镜通常受到体积庞大和设计昂贵的限制。这里，实验演示了一种由高纵横比硅波导阵列组成的介电超表面，它能够在大入射角范围和宽工作带宽下执行一维傅里叶变换。因此，该器件通过大数值孔径和在大入射角下可忽略的角度色散，显著扩展了操作傅里叶空间。傅里叶超表面不仅有利于对自由空间光波光谱的有效控制，而且由于其紧凑的尺寸，易于集成到微光学平台中。
