Polished glass has been at the center of imaging systems for centuries. Their precise curvature enables lenses to focus light and produce sharp images, whether the object in view is a single cell, the page of a book, or a far-off galaxy.
Changing focus to see clearly at all these scales typically requires physically moving a lens, by tilting, sliding, or otherwise shifting the lens, usually with the help of mechanical parts that add to the bulk of microscopes and telescopes.
Now MIT engineers have fabricated a tunable "metalens" that can focus on objects at multiple depths, without changes to its physical position or shape. The lens is made not of solid glass but of a transparent "phase-changing" material that, after heating, can rearrange its atomic structure and thereby change the way the material interacts with light.
[...] The new lens is made of a phase-changing material that the team fabricated by tweaking a material commonly used in rewritable CDs and DVDs. Called GST, it comprises germanium, antimony, and tellurium, and its internal structure changes when heated with laser pulses. This allows the material to switch between transparent and opaque states -- the mechanism that enables data stored in CDs to be written, wiped away, and rewritten.
[...] "In general when one makes an optical device, it's very challenging to tune its characteristics postfabrication," Shalaginov says. "That's why having this kind of platform is like a holy grail for optical engineers, that allows [the metalens] to switch focus efficiently and over a large range."
[...] The experiments show that a metalens can actively change focus without any mechanical motions. The researchers say that a metalens could be potentially fabricated with integrated microheaters to quickly heat the material with short millisecond pulses. By varying the heating conditions, they can also tune to other material's intermediate states, enabling continuous focal tuning.
Additional coverage on Interesting Engineering.
Journal Reference:
Mikhail Y. Shalaginov, Sensong An, Yifei Zhang, et al. Reconfigurable all-dielectric metalens with diffraction-limited performance [open], Nature Communications (DOI: 10.1038/s41467-021-21440-9)
(Score: 0) by Anonymous Coward on Wednesday February 24 2021, @10:02PM (2 children)
This story sounds very familiar, that being a metalens that changes focus due to thermal input. I remember commenting on how it probably would not be useful for a cell phone because thermal changes are not very fast acting. Not that I'd accuse a university PR shop of rehashing old news, mind you, but I'll admit that I couldn't turn up what I think I remember using the Search.
(Score: 4, Insightful) by Immerman on Wednesday February 24 2021, @10:55PM (1 child)
>because thermal changes are not very fast acting.
I don't know - they say they're using a variant of the phase-change material used for writing CDs and DVDs, presumably the rewriteable kind which is heated through a phase change to write or clear it. And an old 54x CD burner can burn a whole CD in 1.4 minutes. Look at the data area of the CD - how many cell-phone camera lenses would cover the same area? Probably thousands? That would give a rough estimate of being able to change the phase of one such lens a dozen times per second using technology not remotely designed for the job. You could probably speed that up dramatically if you're not trying to change hundreds of thousands of tiny areas independently.
(Score: 1) by fustakrakich on Thursday February 25 2021, @03:39AM
Fast or slow, how long before the stuff wears out? You can't write to the same CD very many times.
A different "metalens" [sciencemag.org]?
La politica e i criminali sono la stessa cosa..
(Score: 0) by Anonymous Coward on Thursday February 25 2021, @03:42AM (1 child)
If I'm reading correctly then this is one of those flat lenses that works through diffraction. That kind of lens only works with a single frequency so it can't be used to take colour pictures.
(Score: 2) by bart9h on Thursday February 25 2021, @09:40PM
yet
(Score: 2) by FatPhil on Thursday February 25 2021, @11:48AM (1 child)
That is not changing focal length, that's changing from "can be focussed" to "can't be focussed".
Congratulations, MIT, it sounds like you've invented quantum cataracts.
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 0) by Anonymous Coward on Thursday February 25 2021, @05:42PM
I believe it is changing the metamaterial pattern on the surface depending upon what effective focal length you want to generate. So let's say that if it has a spiral pattern on it, it will focus at 3 mm and if it has a checkerboard pattern on it, it will focus at 5 mm, then my reading of this is the opacity of the material selectively changes to go from one pattern to the other.