Tech Briefs Magazine - November 2021 - PIT-25

ers. The comb generates a billion pulses
of light per second, which bounce back
and forth inside an optical cavity. This
creates millions of spikes of optical frequencies
that look like rainbow-colored
teeth on a comb (hence the name). The
first tooth in that comb is set to a known
frequency, which gives scientists a starting
point to read the other frequencies.
Much like a ruler, if you know the first
marker is one millimeter and each marker
is a millimeter apart, you can easily
start measuring. Similarly, because they
know exactly how far apart these frequencies
are, scientists can translate these optical
signals to microwaves with a simple
mathematical formula, joining the two
ends of the electromagnetic spectrum.
This opens a lot of research doors.
The scientists used this new technology
to make better clocks, eventually developing
clocks that are 100 times better than
the cesium clocks used for civilian time
standards. More accurate and precise
clocks are critical for GPS navigation,
which relies on precise time signals to
determine your location. Better clocks
also have research advantages, from
detecting tiny changes in gravity to studying
phenomena of the quantum world
and perhaps finding dark matter. These
clocks may eventually change how we
define a second.
All atoms and molecules emit unique
frequencies of light when they jump
between energy states, not just the atoms
used in clocks. If one of the frequencies
from the comb hits an atom or molecule
with the exact same frequency, scientists
can identify what kind of atom or molecule
they've hit. Using the optical frequency
comb, scientists could study the
composition of stars in exquisite detail.
Astrophysicists can tell if they've found a
new planet by measuring the changes in
frequencies of the starlight. Using frequency
combs, we can improve lightranging
systems, which bounce light off
objects to detect them like radar or sonar.
They can see objects through flames,
helping NIST scientists study how structures
fail during a fire. The comb is also
being used to detect even the smallest
amounts of greenhouse gases in the air or
look for disease in human breath.
For more information, contact Chad
Boutin at chad.boutin@nist.gov.
Unique Amplifier Could Change Optical Communication
Chalmers University of Technology, Gothenburg, Sweden
esearchers at Chalmers University of
Technology have developed an optical
amplifier that they expect will revolutionize
both space and fiber communication.
The new amplifier offers high performance,
is compact enough to integrate into
a chip just millimeters in size, and crucially,
does not generate excess noise.
Optical communication makes it possible
to send information over very long
distances. The technology is useful in a
range of applications, such as space
communication and in fiber optic cables
for internet traffic.
With communication based on light,
rather than radio waves, we could, for
example, quickly send high-resolution
images from Mars. The information, carried
by laser beams, could be sent with
high speed from a transmitter on the
75
70
60
50
40
30
20
10
cm
Chalmers' new amplifier offers high performance, is compact enough to integrate into a chip just millimeters
in size and does not generate excess noise. (Illustration: Yen Strandqvist)
Photonics & Imaging Technology, November 2021
Cov
ToC
R
planet to a receiver on Earth or on the
Moon. Optical communication also
allows us to use the internet around the
world - whether the signal is transferred
in optical fiber cables under the
seabed or transmitted wirelessly.
Because the light - carrying the
information between two distant points
- loses power along the way, a large
number of optical amplifiers are needed.
Without amplifiers, up to 99 percent
of the signal in an optical fiber cable
would disappear within 100 kilometers.
A well-known problem in optical communication,
however, is that these amplifiers
add excess noise that significantly
impairs the quality of the signal you want
to send or receive. The light amplification
in the Chalmers project is based on a principle
known as the Kerr effect, which so
far is the only known approach that amplifies
light without causing significant
excess noise. The principle has been
demonstrated before, but never in such a
compact format - previous versions were
too bulky to be useful. The new amplifier
fits in a small chip just a few millimeters in
size, compared to previous amplifiers that
have been several thousand times larger.
Additionally, the new amplifiers offer
a level of performance high enough that
they can be placed more sparingly, making
them a more cost-effective option.
They also work in a continuous wave
(CW) operation rather than a pulsed
operation only.
" What we demonstrate here represents
the first CW operation with an extremely
low noise in a compact integrated chip.
This provides a realistic opportunity for
practical use in a variety of applications.
Since it's possible to integrate the amplifier
into very small modules, you can get
cheaper solutions with much better performance,
making this very interesting
for commercial players in the long run, "
said Professor Peter Andrekson. " It can
have many practical uses, not only in
communication, but in areas including
quantum computers, various sensor systems,
and in metrology when making
atmospheric measurements from satellites
for Earth monitoring. "
For more information, contact Mia
Halleröd Palmgren at mia.hallerodpalmgren@
chalmers.se
25

http://info.hotims.com/79419-902

Tech Briefs Magazine - November 2021

Table of Contents for the Digital Edition of Tech Briefs Magazine - November 2021