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 (450 nm to 750 nm). 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 (300 nm 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.
Highlights
We demonstrate imaging over the visible band using a single planar diffractive lens
Metalenses require subwavelength features and large aspect ratios, making them impractical for low-cost manufacturing over large areas
We further emphasize that we previously demonstrated water-immersion diffractive lenses with numerical aperture (NA) as high as 1.4317
Summary
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). This means that for many photography applications, a diffractive lens would need an aspect ratio of only 1.7 This is considerably simpler to fabricate than a visible-wavelength metalens, where feature widths of 15 are required[5]. This preliminary design does not achieve diffraction-limited focusing at all the design wavelengths, these are sufficient for good image formation via post-processing using a-priori information of the focused spots as illustrated by the images formed by the fabricated NA = 0.18 lens above[23]. We believe that our approach will lead to considerably simpler, thinner and cheaper imaging systems
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