Broadband Wide Field-of-View Metalens by the Virtual-Diffraction- Aperture Method

Implementing a metalens with a wide field-of-view (FOV) is crucial for compact and practical imaging devices. To this end, a virtual-diffraction-aperture (VDA)-based synthesis method in combination with a numerical diffraction-field analyzer, dipole based model expansion, is proposed to efficiently and effectively extend the FOV of a given metalens. By introducing a virtual diffraction aperture (VDA), the method transforms the complicated optimization regarding complex amplitude distribution on the metalens, to a rather straightforward one regarding the aperture contour. Moreover, as an optimization method, the VDA provides extra degrees of freedom to modulate not only spatial resolution but also the focusing efficiency (FE) crucial to another key property of an imaging system, that is, temperature sensitivity. To demonstrate this method, a proof-of-concept single wide FOV metalens prototype with a numerical aperture of 0.81 for passive millimeter wave imaging is synthesized and fabricated. It generates the expected wideband tight focusing beams over an angular FOV of at least 90 degrees for a frequency range from 33 to 37 GHz while maintaining almost identical FE. The proposed VDA method may contribute to the evolution of the imaging equipment toward ultra-compact, large FOV, approaching a diffraction-limited resolution to meet diverse application demands.