Page 20 - Spring 2025 Electron

Industry News
NEW PHOTONIC CHIP
REVOLUTIONISES OPTICAL
AMPLIFIER PERFORMANCE
Scientists at Ecole Polytechnique Federale de
Lausanne and IBM Research have developed a
compact optical amplifier based on a revolutionary
photonic chip which is said to “vastly outperform”
traditional optical amplifiers in terms of both
bandwidth and efficiency with potential
implications for data centre interconnects, AI
accelerators and high performance computing.
The photonic-chip-based travelling-wave
parametric amplifier, or TWPA, achieves ultra-
broadband signal amplification in a highly compact
form. Using gallium on phosphide-on-silicon dioxide
technology, it attains a net gain of over 10dB across
a bandwidth of approximately 140nm, which is three
times wider than a conventional C-band EDFA.
Gallium phosphide is noted for its exceptional optical
properties, namely strong optical connectivity, such
that light passing through it can interact in a way that
boosts signal strength, and a high refractive index,
which allows light to be confined tightly within the
waveguide leading to more efficient amplification.
This meant that the team could achieve high gain
with a waveguide that was relatively short, only a few
centimetres.
Whilst most amplifiers rely on rare earth elements
to strengthen signals, the TWPA uses optical non-
linearity whereby light interacts with a material
and amplifies itself. Careful design of the tiny spiral
waveguide enabled creation of a space in which light
20
waves reinforce each other, enhancing weak signals
and maintaining a low noise level.
The TWPA was also found to enhance performance
of optical frequency combs and coherent
communication signals, two important technologies
in modern optical networks and photonics,
demonstrating that such photonic integrated circuits
can outperform traditional fibre-based amplification
systems.
Reference: Dykes, P., ‘Ultra-broadband Photonic Chip boosts Optical
Signals’, Optical Connections News, 25th. March
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NEW CHIP-BASED
SYSTEM FOR TERAHERTZ
WAVE GENERATION
The effective generation of Terahertz waves using
a semiconductor chip is known to be challenging.
Many current technologies are unable to generate
waves with sufficient radiating power without the
use of bulky and expensive silicon lenses, which
greatly restricts integration of a terahertz source
into an electronic device.
Terahertz waves, which occupy a position between
radio waves and infrared light, have shorter
wavelengths and higher frequencies than radio
waves meaning that they can enable faster data
transmission, more precise medical imaging and
higher resolution radar. Unfortunately, however,
the dielectric constant of silicon is much higher
than that of air, resulting in most terahertz waves
being reflected at the silicon-air boundary rather
than being transmitted. With most signal strength
being lost at this boundary, silicon lenses have to
be installed to increase the power of the remaining
signal.
In order to address this limitation, researchers at the
Massachusetts Institute of Technology (MIT) have
developed a scalable, low-cost terahertz amplifier-
multiplier system that can generate high-power
terahertz waves on a chip without the need for silicon
lenses.
By attaching a thin, patterned sheet of material to
the back of the chip and using higher-power Intel
transistors, the researchers created a more efficient,
yet scalable, chip-based terahertz wave generator.
The said chip can then be used to produce terahertz
arrays for applications such as improved safety
scanners and environmental monitoring, eg. for
detection of airborne pollutants.
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Industry News
The thin sheet utilises ‘matching’, which equals
out the dielectric constants of silicon and air,
minimising the amount of signal that is reflected at
the boundary. It consists of a low-cost, commercially
available substrate with a dielectric constant that
approximates to what is needed for the match. A
laser cutter was then used to punch holes in the
sheet until it reached the correct dielectric constant.
Special Intel transistors were then applied with a
higher maximum frequency and breakdown voltage
than standard CMOS transistors.
The resultant chip-generated terahertz signals
achieved a peak radiation power of 11.1 decibel-
milliwatts.
Jinchen Wang, graduate student at the MIT
Department of Electrical Engineering and Computer
Science, explains:
“ To take full advantage of a terahertz wave
source, we need it to be scalable. A terahertz
array might have hundreds of chips, and there is
no place to put silicon lenses because the chips
are combined with such high density. We need a
different package, and here we’ve demonstrated a
promising approach that can be used for scalable,
low-cost terahertz arrays.
Since the dielectric constant of air is 1, if you just
cut some subwavelength holes in the sheet, it is
equivalent to injecting some air, which lowers the
overall dielectric constant of the matching sheet.
Because the frequency and the power are so high,
many of the standard ways to design a CMOS chip
are not applicable here.”
Reference: Gittins, C., ‘MIT Researchers develop Chip-based System
for Terahertz Waves’, Electronic Specifier, 3rd. March
21