• Photonics Research
  • Vol. 9, Issue 12, 12002388 (2021)
Feng Zhao1、2, Zicheng Shen2, Decheng Wang1, Bijie Xu1, Xiangning Chen1、3、*, and Yuanmu Yang2、4、*
Author Affiliations
  • 1School of Space Information, Space Engineering University, Beijing 101416, China
  • 2State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Beijing 100084, China
  • 3e-mail: xn_chen_edu@163.com
  • 4e-mail: ymyang@tsinghua.edu.cn
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    Abstract

    Metalenses are ultrathin optical elements that can focus light using densely arranged subwavelength structures. Due to their minimal form factor, they have been considered promising for imaging applications that require extreme system size, weight, and power, such as in consumer electronics and remote sensing. However, as a major impediment prohibiting the wide adoption of the metalens technology, the aperture size, and consequently the imaging resolution, of a metalens are often limited by lithography processes that are not scalable. Here, we propose to adopt a synthetic aperture approach to alleviate the issue, and experimentally demonstrate that, assisted by computational reconstruction, a synthetic aperture metalens composed of multiple metalenses with relatively small aperture size can achieve an imaging resolution comparable to a conventional lens with an equivalent large aperture. We validate the concept via an outdoor imaging experiment performed with a synthetic aperture metalens-integrated near-infrared camera using natural sunlight for target illumination.

    1. INTRODUCTION

    While conventional refractive optical components are typically bulky and heavy, the demand for compact, lightweight optical components is growing rapidly for various applications ranging from consumer electronics to remote sensing based on unmanned aerial vehicles or satellites [1,2]. In recent years, metasurfaces have emerged as a novel platform for wavefront control [311]. Composed of an array of subwavelength-spaced dielectric or metallic antennas with thickness less than or on the order of the wavelength of light, metasurfaces can accurately adjust the phase, amplitude, and polarization of light [1230], with versatile imaging capability in a compact form factor. Currently, one of the major hurdles for the wide adoption of the metalens technology is its aperture size. Increasing the size of the lens aperture can result in a higher imaging resolution that is critical for both microscopy and long-distance imaging applications. Optical metalenses, with their nanometer-sized, aperiodic feature, are typically fabricated by processes such as electron-beam lithography (EBL) that are costly and time-consuming. Despite the recent adoption of scalable manufacturing techniques such as nanoimprinting and ultraviolet stepper lithography in metalens fabrication [3134], the preparation of a lithography mask or imprinting mold still cannot be avoided. To date, the largest optical metalens can have an aperture size on the order of a few centimeters [32,3537]. For certain applications, such as a space telescope, which requires a lens aperture size on the order of meters, the manufacturing of a single metalens of such scale can be extremely challenging, if not impossible, limited by the current semiconductor fabrication infrastructure.