# Broadband lightweight flat lenses for longwave-infrared imaging

## TL;DR

This paper demonstrates ultra-thin, lightweight flat lenses for longwave-infrared imaging using multi-level diffractive optics, achieving good imaging performance despite material absorption, and suggests potential for high-efficiency lenses with alternative materials.

## Contribution

The work introduces a polymer flat lens for LWIR imaging with 10μm thickness, broadband correction, and low weight, showing practical imaging despite absorption losses and proposing high-refractive-index materials for improved efficiency.

## Key findings

- Achieved LWIR imaging with a 10μm thick polymer flat lens.
- Demonstrated field of view of ~35 degrees and angular resolution <0.013 degrees.
- Showed potential for >70% focusing efficiency using silicon-based lenses.

## Abstract

We experimentally demonstrate imaging in the longwave-infrared (LWIR) spectral band (8um to 12um) using a single polymer flat lens based upon multi-level diffractive optics. The device thickness is only 10{\mu}m, and chromatic aberrations are corrected over the entire LWIR band with one surface. Due to the drastic reduction in device thickness, we are able to utilize polymers with absorption in the LWIR, allowing for inexpensive manufacturing via imprint lithography. The weight of our lens is less than 100 times those of comparable refractive lenses. We fabricated and characterized two different flat lenses. Even with about 25% absorption losses, experiments show that our flat polymer lenses obtain good imaging with field of view of ~35degrees and angular resolution less than 0.013 degrees. The flat lenses were characterized with two different commercial LWIR image sensors. Finally, we show that by using lossless, higher-refractive-index materials like silicon, focusing efficiencies in excess of 70% can be achieved over the entire LWIR band. Our results firmly establish the potential for lightweight, ultra-thin, broadband lenses for high-quality imaging in the LWIR band.

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Source: https://tomesphere.com/paper/1904.09011