Tech Briefs Magazine - May 2022 - PIT-28

could not be recovered otherwise. The
technique simultaneously increases the
energy of the signal of interest while reducing
its relative noise content.
To achieve this, the researchers exploit
the Talbot self-imaging effect, which is
observed when a periodic train of pulses
propagates through a dispersive medium
such as an optical fiber. It causes
different frequency components of light
(the different " colors " of light) to travel
at different speeds. The Talbot effect was
previously utilized to coherently " stack "
or combine consecutive pulses in an incoming
train, leading to a passive amplification
of the pulses' peak power.
Just like a physical lens can be used to
focus a weak and large image into a narrower
and more intense beam, the proposed
system can be used to redistribute
the energy of a weak signal into a series
of high intensity pulses. This power focusing
effect can be achieved without
distorting the signal shape (carried information)
and without increasing the
noise along the signal.
The researchers believe this discovery
opens many avenues for upcoming research
lines. It could be possible to also
adapt this technique for 2D or 3D spatial
images, a feat that may have important
applications in astronomy research,
photography, and holography, among
others. Furthermore, while the present
demonstration focused on optical waveforms,
such as the ones used in telecommunications,
this technique could be
adapted for different types of waves, including
radio, microwave, plasma, acoustic,
or even quantum waves.
For more information, contact Audrey-Maude
Vézina at audrey-maude.vezina@inrs.ca.
Terahertz Energy Focused by Credit Card-Sized Device to Generate
High-Resolution Images
Massachusetts Institute of Technology, Cambridge, MA
R
esearchers have created a device
that enables them to electronically
steer and focus a beam of terahertz electromagnetic
energy with extreme precision.
This opens the door to high-resolution,
real-time imaging devices that
are hundredths the size of other radar
systems and more robust than other
optical systems.
Terahertz waves, located on the electromagnetic
spectrum between microwaves
and infrared light, exist in a " no
man's land, " where neither classical
electronics nor optical devices can effectively
manipulate their energy. But
these high-frequency radio waves have
many unique properties, like the ability
to pass through certain solid materials
without the health effects of X-rays. They
may also enable higher-speed communications,
or vision systems that can see
through foggy or dusty environments.
The Terahertz Integrated Electronics
Group at MIT, led by Associate Professor
Ruonan Han, seeks to bridge this socalled
terahertz gap. These researchers
have now demonstrated a precise, electronically
steerable, terahertz antenna
array, which contains an extremely large
number of antennas. The antenna array,
called a " reflectarray, " operates like a
controllable mirror with its direction of
reflection guided by a computer.
The reflectarray, which has nearly
10,000 antennas on a device the size of a
credit card, can precisely focus a beam of
terahertz energy on a tiny area and control
it rapidly with no moving parts. Built
using semiconductor chips and innova28
This
image shows the semiconductor terahertz beam former, with almost ten thousand built-in elements.
(Photo: The researchers)
tive fabrication techniques, the reflectarray
is also scalable.
The researchers demonstrated the device
by generating 3D depth images of
scenes. The images are similar to those
generated by a lidar (light detection and
ranging) device, but because the reflectarray
uses terahertz waves instead of
light, it can operate effectively in rain,
fog, or snow. This small reflectarray was
also able to generate radar images with
twice the angular resolution of those
produced by a radar installation on Cape
Cod, which is a building so large it is visible
from space. While the Cape Code
radar is able to cover a much larger area,
the new reflectarray is the first to bring
military-grade resolution to a device for
commercial intelligent machines.
" Antenna arrays are very interesting because,
just by changing the time delays that
are fed to each antenna, you can change
the direction the energy is focused, and it
is completely electronic, " said Dr. Nathan
Monroe. " So, it stands as an alternative
to those big radar dishes you see at the
airport that move around with motors.
We can do the same thing, but we don't
need any moving parts because we are just
changing some bits in a computer. "
For more information, contact Abby Abazorius
at abbya@mit.edu.
Photonics & Imaging Technology, May 2022
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