
How to make a flat lens - bookofjoe
https://www.economist.com/science-and-technology/2019/07/25/how-to-make-a-flat-lens
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bariumbitmap
The article is open access (CC-BY 4.0) and is available here:

[https://doi.org/10.1038/s41377-018-0078-x](https://doi.org/10.1038/s41377-018-0078-x)

Fresnel zone plates are not new, but they only work at a single wavelength.

[https://en.wikipedia.org/wiki/Zone_plate](https://en.wikipedia.org/wiki/Zone_plate)

This means that they are not achromatic.

[https://en.wikipedia.org/wiki/Achromatic_lens](https://en.wikipedia.org/wiki/Achromatic_lens)

The Shrestha et al. article uses nano-structured silicon to focus wavelengths
between 1200 nm (near-infrared) and 1600 nm (short-wavelength infrared); for
comparison, the tail end of visible light is around 740 nm. It's impressive to
get such a large range of wavelength (bandwidth), hence the "broadband" and
"achromatic" in the title.

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wnkrshm
It's a very interesting technology, especially since it holds the promise to
directly realize an almost arbitrary phase-mask (analogous to a lens' shape)
that has been found using already existing optical design technologies. The
problem, as in the article is size though.

Apart from the optical (especially on-chip) applications, in theory, it's
possible to have a freeform surface and cover it with small meta-atoms
(subwavelength structures) so that reflected wave-fronts are planar again,
like the incoming one. With millimeter waves such structures are way easier to
make than on the tens-of-nanometer scale - these will be used in all kinds of
aerospace products. And iirc, the first application (according to Frederico
Capasso) was laser optics on a satellite that had to be compacted and have
their weight reduced.

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jaclaz
>The problem, as in the article is size though.

I see it more in the amount of light needed, 50% pass-through vs. roughly 90%
of conventional lenses seems to me "a lot".

Even if the researchers "hope" that they will be able to improve the
material/shapes/whatever, it doesn't seem like an easy chore.

~~~
Veedrac
I would not be surprised if there are many applications where removing 90% of
the weight and bulk of the lens, or adding this much flexibility in the lens'
functionality, would more than make up for having to double the sensor size or
light intensity.

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Veedrac
The press release has more info: [https://engineering.columbia.edu/press-
releases/nanfang-yu-f...](https://engineering.columbia.edu/press-
releases/nanfang-yu-flat-lens)

I'm impressed at the images these produce.

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goldenkey
This is basically a fresnel lens on steroids. Its basically taking a fresnel
lens and bump mapping the depth buffer using a dithering shader. Ingenius!
Likely to not be able to surpass 50% light though since that are fresnel lens
limits as well, could be a mathematical law.

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zamadatix
I thought this was going to be [https://en.wikipedia.org/wiki/Gradient-
index_optics](https://en.wikipedia.org/wiki/Gradient-index_optics)

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bookofjoe
[http://archive.is/eBiwD](http://archive.is/eBiwD)

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ot
It looks like a Fresnel lens taken to the limit.

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anovikov
I saw this thing somewhere in XVIII century book... Fresnel lens? What's so
new about it?

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iamleppert
Is it possible to flag or outright ban paywalls from HN? In my case I even
tried to sign up to read the article but their registration is currently
broken (gives an invalid code message).

~~~
dang
If there's a workaround, it's ok. Users usually post workarounds in the
thread.

This is in the FAQ at
[https://news.ycombinator.com/newsfaq.html](https://news.ycombinator.com/newsfaq.html)
and there's more explanation here:

[https://news.ycombinator.com/item?id=10178989](https://news.ycombinator.com/item?id=10178989)

[https://hn.algolia.com/?query=by:dang%20paywall&sort=byDate&...](https://hn.algolia.com/?query=by:dang%20paywall&sort=byDate&dateRange=all&type=comment&storyText=false&prefix&page=0)

