Broadband imaging with one planar diffractive lens

TL;DR

This paper introduces achromatic diffractive lenses capable of broadband visible imaging with high efficiency and focus quality, demonstrating their potential for low-cost, large-area flat lens applications.

Contribution

The authors designed, fabricated, and characterized novel achromatic diffractive lenses with high NA and broad bandwidth, surpassing previous flat-lens technologies in performance.

Findings

Achromatic lenses achieve diffraction-limited focusing across visible spectrum.

Focusing efficiency exceeds 40% over 450-750nm wavelengths.

Lenses demonstrate video imaging under natural broadband illumination.

Abstract

We demonstrate imaging over the visible band using a single planar diffractive lens. This is enabled via multi-level diffractive optics that is designed to focus over a broad wavelength range, which we refer to as an achromatic diffractive lens (ADL). We designed, fabricated and characterized two ADLs with numerical apertures of 0.05 and 0.18. Diffraction-limited focusing is demonstrated for the NA=0.05 lens with measured focusing efficiency of over 40% across the entire visible spectrum (450nm to 750nm). We characterized the lenses with a monochromatic and a color CMOS sensor, and demonstrated video imaging under natural sunlight and other broadband illumination conditions. We use rigorous electromagnetic simulations to emphasize that ADLs can achieve high NA (0.9) and large operating bandwidth (300nm in the visible spectrum), a combination of metrics that have so far eluded other flat-lens technologies such as metalenses. These planar diffractive lenses can be cost-effectively manufactured over large areas and thereby, can enable the wide adoption of flat, low-cost lenses for a variety of imaging applications.