Composite metalens enables distortion-free imaging over a wide field of view.

In a recent study, researchers developed a composite metalens that enables distortion-free imaging. The study, published in the journal Engineering, presents a new approach to on-demand strain engineering using composite metalenses.

Metalens has emerged as a promising technology with applications in beam steering, imaging, depth sensing, and display projection. However, optical distortion, a key element in optical design, is relatively unexplored in the context of meta-optics. Researchers addressed this gap by demonstrating a general method to control distortion.

Composite metalens architectures are composed of doublet metasurfaces, which provide additional degrees of freedom compared to single-layer metalens. This allows for custom adjustment of angle-dependent image height relationships, allowing distortion to be controlled while minimizing other monochromatic aberrations.

The research team experimentally verified their design by fabricating a composite fisheye metalens. The metalens exhibited diffraction-limited performance over a wide field of view of 140°, with significantly low barrel distortion of less than 2%. In contrast, the distortion of the uncompensated reference metalens was up to 22%.

The metasurface of the metalens consists of amorphous silicon nanopillars on a glass substrate, encapsulated with a polymethyl methacrylate (PMMA) coating. The researchers designed the metalens using numerical simulations and an analytically derived design, followed by ray-tracing optimization. The device was fabricated using laser direct writing for the field aperture stop and electron beam lithography for metasurface patterning.

Characterization of the metalens included measuring the point spread function (PSF) using a customized setup with a rotatable optical axis. The Strehl ratio and modulation transfer function (MTF) were calculated to evaluate the focus quality. Results showed excellent agreement with the design and demonstrated good fabrication fidelity and diffraction-limited performance over the entire field of view.

Optical distortion was evaluated by recording the image height versus angle of incidence (AOI). The composite metalens demonstrated a linear dependence of image height on AOI, validating the design goal.

To demonstrate distortion-free imaging capabilities at wide viewing angles, images of a cylindrical panoramic target were captured using customized imaging settings. The images captured by the composite metalens showed minimal distortion compared to the singlet metalens images.

The design principles and manufacturing approaches of composite metalens have the potential to impact various fields such as consumer electronics, automotive and robotic sensing, medical image processing, and machine vision systems. This research opens new possibilities for the development of high-performance optical devices with reduced distortion and improved image quality.