Researchers combine piezoelectric thin film and metasurfaces to create
lens with tunable focus
Compact, inexpensive tunable lenses could be useful for portable medical diagnostics, miniature cameras and more
Date:
February 17, 2022
Source:
Optica
Summary:
Tunability in lenses typically requires bulky components,
but researchers have created a metasurface lens that uses a
piezoelectric thin film to change focal length when a small voltage
is applied. The compact and lightweight lens could be useful for
portable medical diagnostic instruments, drone-based 3D mapping and
other applications where miniaturization can open new possibilities.
FULL STORY ==========================================================================
For the first time, researchers have created a metasurface lens that uses
a piezoelectric thin film to change focal length when a small voltage
is applied.
Because it is extremely compact and lightweight, the new lens could be
useful for portable medical diagnostic instruments, drone-based 3D mapping
and other applications where miniaturization can open new possibilities.
========================================================================== "This type of low-power, ultra-compact varifocal lens could be used in a
wide range of sensor and imaging technologies where system size, weight
and cost are important," said research project leader Christopher Dirdal
from SINTEF Smart Sensors and Microsystems in Norway. "In addition,
introducing precision tunability to metasurfaces opens up completely
new ways to manipulate light." Dirdal and colleagues describe the new technology in the Optica Publishing Group journal Optics Letters.To change focal length, a voltage is applied over lead zirconate titanate (PZT)
membranes causing them to deform. This, in turn, shifts the distance
between two metasurface lenses.
"Our novel approach offers a large displacement between the metasurface
lenses at high speed and using low voltages," said Dirdal. "Compared
to state-of-the- art devices, we demonstrated twice the out-of-plane displacement at a quarter of the voltage." Combining technologies The researchers made the new lens using metasurfaces -- flat surfaces that are patterned with nanostructures to manipulate light. They are particularly interesting because they can integrate several functionalities into
a single surface and can also be made in large batches using standard
micro- and nanofabrication techniques at potentially low cost.
========================================================================== "Most systems incorporating metasurfaces so far are static, meaning
that the optical functionality is locked after fabrication," said
Dirdal. "However, many of the optical components that are critical
for cameras, 3D-mapping lidar systems and holographic displays require adaptivity." Tunability, or adaptivity, in conventional optical systems
is typically accomplished using bulky and power-consuming components such
as stepper motors, rotators or magnets. To create this capability on a
smaller scale, the researchers turned to MEMS technology. These chip-based electrically controlled mechanically moveable parts are fast, require
little power and are also compatible with high-volume batch processing techniques, which can reduce the size, cost and weight of optical systems.
Demonstrating a change of focus Although MEMS actuation has been used
recently to create tunable metasurface lenses, Dirdal and colleagues
wanted to see if they could achieve even better performance. They did
this by designing a device in which a metasurface is suspended on a
membrane ring made of a thin-film PZT film, which allows the PZT to move
the metasurface when a voltage is applied.
To demonstrate how MEMS-metasurfaces could function as a varifocal lens doublet, they placed a second metasurface lens after the MEMS-metasurface.
Varying the separation distance between the lenses through MEMS
displacement allows researchers to tune the focal point of the lens
doublet on the fly.
The researchers showed that applying 23 volts allowed the PZT membrane
to move the metasurfaces 7.2 microns, producing a focal length change of
around 250 microns. They note that this range can be further improved
with metalenses that have a stronger focusing power and by optimizing
the MEMS design for longer stroke actuation. Such tunability would,
for instance, be useful for imaging at various depths into tissue to
image neurons or blood vessels.
With additional development of the MEMS architecture, the researchers
say it will likely be possible to make a commercially relevant tunable
lens device.
They are also exploring how the MEMS-metasurface combination can be
applied to various applications that have a need for small, light and
cheap optics without compromising optical quality.
========================================================================== Story Source: Materials provided by Optica. Note: Content may be edited
for style and length.
========================================================================== Journal Reference:
1. Christopher A. Dirdal, Paul C. V. Thrane, Firehun T. Dullo,
Jo Gjessing,
Anand Summanwar, Jon Tschudi. MEMS-tunable dielectric metasurface
lens using thin-film PZT for large displacements at low
voltages. Optics Letters, 2022; 47 (5): 1049 DOI: 10.1364/OL.451750 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/02/220217122318.htm
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