Metasurface Enabled Wide‐Angle Fourier Lens

• Published in: Advanced materials (Weinheim) 2018-06, Vol.30 (23), p.e1706368-n/a
• Main Authors: Liu, Wenwei, Li, Zhancheng, Cheng, Hua, Tang, Chengchun, Li, Junjie, Zhang, Shuang, Chen, Shuqi, Tian, Jianguo
• Format: Article
• Language: English
• Subjects: Data processing; Fourier lenses; Fourier transforms; Holography; Materials science; Metasurfaces; Microscopes; Numerical aperture; Optical components; Optics; spatial spectra
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201706368

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. The Fourier metalens based on amorphous silicon working beyond the paraxial regime up to 60° can not only resolve large Fourier components of the incident light but also exhibit accurate amplitude of each Fourier component. The Fourier metalens maintains its functionality and efficiency up to about 50% over 600 nm bandwidth in the near infrared region.