Space Technology Special Report - Version B. July 2023 - 31

Lunar Lens: First Compact Flat Metalens Images Moon Surface
A research team has created the first ultrathin, compact metalens telescope capable of
imaging far-away objects, including the Moon.
Penn State College of Engineering, University Park, PA
A
stronomers and amateurs alike
know the bigger the telescope, the
more powerful the imaging capability.
To keep the power but streamline
one of the bulkier components, a
Penn State-led research team created
the first ultrathin, compact metalens
telescope capable of imaging faraway
objects, including the Moon.
Metalenses are comprised of tiny,
antenna-like surface patterns that can
focus light to magnify distant objects in
the same way as traditional curved glass
lenses, but they have the advantage
of being flat. Though millimeters-wide
metalenses have been developed in
the past, the researchers scaled the
size of their lens to eight centimeters
in diameter, or about four inches wide,
making it possible to use them in large
optical systems, such as telescopes. They
published their approach in Nano Letters.
" Traditional camera or telescope
lenses have curved surfaces of varying
thickness, where you have a bump
in the middle and thinner edges,
which causes the lens to be bulky and
heavy, " said corresponding author
Xingjie Ni, associate professor of
electrical engineering. " Metalenses
use nano-structures on the lens
instead of curvature to contour light,
which allows them to lay flat. "
That is one of the reasons, Ni said,
modern cell phone camera lenses
protrude from the body of the phone:
the thickness of the lenses takes up
space, though they appear flat since
they are hidden behind a glass window.
Metalenses are typically made using
electron beam lithography, which involves
scanning a focused beam of electrons
onto a piece of glass or other transparent
substrate to create antenna-like patterns
point by point. However, the scanning
process of the electron beam limits the
size of the lens that can be created, as
scanning each point is time-consuming.
SPACE TECHNOLOGY SPECIAL REPORT
Xingjie Ni (center), Penn State associate professor of electrical engineering, manipulates a
conventional telescope lens. In the foreground, Lidan Zhang, electrical engineering graduate
student, holds the metalens prototype, which is much smaller, flatter, and more compact. (Image:
Jeff Xu/Penn State. All Rights Reserved)
To create a bigger lens, the
researchers adapted a fabrication
method known as deep ultraviolet (DUV)
photolithography, which is commonly
used to produce computer chips.
" DUV photolithography is a highthroughput
and high-yield process that
can produce many computer chips within
seconds, " Ni said. " We found this to be a
good fabrication method for metalenses
because it allows for much larger pattern
sizes while still maintaining small details,
which allows the lens to work effectively. "
The researchers modified the method
with their own novel procedure, called
rotating wafer and stitching. Researchers
divided the wafer, on which the metalens
was fabricated, into four quadrants,
which were further divided into 22 by
22 millimeter regions - smaller than
a standard postage stamp. Using a
DUV lithography machine at Cornell
University, they projected a pattern
onto one quadrant through projection
lenses, which they then rotated by
90 degrees and projected again.
They repeated the rotation until all
four quadrants were patterned.
" The process is cost-effective because
the masks containing the pattern data
for each quadrant can be reused due to
the rotation symmetry of the metalens, "
Ni said. " This reduces the manufacturing
and environmental costs of the method. "
As the size of the metalens increased,
the digital files required to process
the patterns became significantly
larger, which would take a long time
for the DUV lithography machine
to process. To overcome this issue,
the researchers compressed the
files using data approximations and
by referencing non-unique data.
" We utilized every possible method
to reduce the file size, " Ni said. " We
identified identical data points and
JULY 2023 31

Space Technology Special Report - Version B. July 2023

Table of Contents for the Digital Edition of Space Technology Special Report - Version B. July 2023