Ultra-thin flat lens has extreme depth of focus

March 18, 2020 //By Julien Happich
flat lens
Thanks to an innovative design methodology, solving a non-linear inverse problem via parameters optimization, a team of researchers from the University of Utah has designed an ultra-thin flat lens focused in a large focal range spanning several metres.

In a paper titled “Extreme-depth-of-focus imaging with a flat lens” published in the OSA Optica journal, the researchers report a very thin lens that does not require refocusing even to capture different object images separated by large distances, removing the need for refocusing mechanisms and drastically simplifying imaging systems.


Schematic of a multi-level diffractive lens (MDL)
that exhibits extreme-depth-of-focus (ExDOF)
imaging.

The so-called multi-level diffractive lens (MDL) described in the paper enhances the depth of focus by over 4 orders of magnitude compared to traditional fixed lenses.


Optical micrograph of the fabricated MDL, with the inset showing
a magnified view of the centre of the lens. Focal range is 5 to
1200mm, aperture is 1.8 mm.

In experiments using such a lens, the researchers were able to maintain focus for objects separated by as large a distance as 6 metres. When illuminated by collimated light at 0.85m, a 1.8mm diametre multi-level diffractive lens shaped with a distribution of concentric rings of varying thickness up to 2.6µm maximum, produced a beam which remained in focus from 5 to 1200 mm.

The researchers have founded a startup Oblate Optics in San Diego to commercialize planar optics with large bandwidths and a large depth of field. They are seeking collaboration with strategic partners.
 

Oblate Optics - www.oblateoptics.com

University of Utah - www.utah.edu


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