Tech Briefs Magazine - November 2021 - PIT-23

A new MIT-fabricated metalens shifts focus without tilting, shifting, or otherwise
moving. The design may enable miniature zoom lenses for drones, cellphones,
or night-vision goggles. (Image courtesy of the researchers)
surface varies accordingly. In this case, when the material is at
room temperature, the metasurface focuses light to generate a
sharp image of an object at a certain distance away. After the
material is heated, its atomic structure changes, and in response,
the metasurface redirects light to focus on a more distant object.
In this way, the new active " metalens " can tune its focus without
the need for bulky mechanical elements. The novel design,
which currently images within the infrared band, may enable
more nimble optical devices, such as miniature heat scopes for
drones, ultracompact thermal cameras for cellphones, and
low-profile night-vision goggles.
" Our result shows that our ultrathin tunable lens, without
moving parts, can achieve aberration-free imaging of overlapping
objects positioned at different depths, rivaling traditional,
bulky optical systems, " says Tian Gu, a research scientist in
MIT's Materials Research Laboratory.
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.
Earlier this year, the researchers reported adding another element,
selenium, to GST to make a new phase-changing material:
GSST. When they heated the new material, its atomic structure
shifted from an amorphous, random tangle of atoms, to a more
ordered, crystalline structure. This phase shift also changed the
way infrared light traveled through the material, affecting
refracting power but with minimal impact on transparency.
The team wondered whether GSST's switching ability could
be tailored to direct and focus light at specific points depending
on its phase. The material then could serve as an active
lens, without the need for mechanical parts to shift its focus.
" In general, when one makes an optical device, it's very challenging
to tune its characteristics post fabrication, " said teamPhotonics
& Imaging Technology, November 2021
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Tech Briefs Magazine - November 2021

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