Imaging from the visible to the longwave infrared wavelengths via an inverse-designed flat lens

It is generally assumed that correcting chromatic aberrations in imaging requires multiple optical elements. Here, we show that by allowing the phase in the image plane to be a free parameter, it is possible to correct chromatic variation of focal length over an extremely large bandwidth, from the visible (Vis) to the longwave infrared (LWIR) wavelengths using a single diffractive surface, i.e., a flat lens. Specifically, we designed, fabricated and characterized a flat, multi-level diffractive lens (MDL) with a thickness of <= 10 mu m, diameter of similar to 1mm, and focal length of 18mm, which was constant over the operating bandwidth of lambda=0.45 mu m (blue) to 15 mu m (LWIR). We experimentally characterized the point-spread functions, aberrations and imaging performance of cameras comprised of this MDL and appropriate image sensors for lambda=0.45 mu m to 11 mu m. We further show using simulations that such extreme achromatic MDLs can be achieved even at high numerical apertures (NA=0.81). By drastically increasing the operating bandwidth and eliminating several refractive lenses, our approach enables thinner, lighter and simpler imaging systems. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

By allowing the phase in the image plane to be a free parameter, it is possible to correct chromatic aberrations over an extremely large bandwidth using a single diffractive surface, leading to thinner, lighter, and simpler imaging systems with improved performance.