Source: Content compiled from IEEE by Semiconductor Industry Watch (ID: icbank), thank you.
The University of Sydney researchers combined photonic filters and modulators on a single chip, allowing them to
precisely detect signals across a wide band of radio frequency (RF) spectrum. The work brings photonic chips one
step closer to replacing the larger and more complex electronic radio-frequency chips in fiber-optic networks.
The Sydney team used a technique called stimulated Brillouin scattering, which involves converting electric fields
into pressure waves in certain insulators, such as optical fibres. In 2011, researchers reported the potential of
Brillouin scattering for high-resolution filtering and developed new fabrication techniques to incorporate
chalcogenide Brillouin waveguides onto silicon chips. In 2023, they successfully combined a photonic filter
and modulator on the same type of chip. This combination gives the experimental chip a spectral resolution
of 37 megahertz and a wider bandwidth than previous chips, the team reported in a paper published Nov. 20
in Nature Communications.
"The integration of the modulator with the active waveguide is the key breakthrough here," said David Marpaung,
a nanophotonics researcher at the University of Twente in the Netherlands. Marpaung worked with the Sydney
group a decade ago and now leads his own research group, which is taking a different approach and seeking to
achieve broadband, high-resolution photonic radio sensitivity in tiny packages. According to Marpaung,
when someone achieves spectral resolution below 10 MHz in the 100 GHz band, they will be able to replace the
bulker electronic RF chips on the market. Another advantage of such chips is that they can convert radio
frequency signals into optical signals for direct transmission over fiber-optic networks. The winner of this race
will be able to tap into a huge market for telecom providers and defense manufacturers who need radio receivers
that can reliably navigate complex radio frequency (RF) environments.
"Chalcogenides have a very strong Brillouin effect; It's very good, but there's still the question of whether it's scalable...
It's still seen as laboratory material, "Marpaung said. The Sydney team had to find a new way to fit chlogenide waveguides
in 5mm square packages into standard-made silicon chips, which was no easy task. In 2017, the group figured out how to
combine chillers into silicon input/output rings, but no one managed the combination with a standard chip until this year.
Other research groups are working on different materials that may also offer similar properties. For example, lithium niobate
has better modulator properties than silicon, and Marpaung has shown in work still under peer review that lithium niobate
can provide similar high-resolution filtering via Brbrouin scattering. Another research group, led by Peter Rakich of Yale
University, showed last year that a combination of pure silicon waveguided and chips could achieve 2.7MHz filtering over the
6 GHz spectrum band. This work does not integrate modulators, but it hints at a potentially simpler manufacturing path that
involves fewer materials.
That said, the Sydney team's approach may require better acoustic performance than silicon. The Brillouin effect has been known
to researchers for more than 100 years, but there has been renewed interest in recent decades. In the past, researchers have used
it to store information in pulses of light before retransmitting it, a trick that avoids the need to convert light into electricity and back
again.
Of course, the dream of integrated photonic chips has many moving parts. Modulators made by others are rapidly improving, which
will also help their technology, the Sydney researchers wrote. Other advances in related technologies could benefit some other teams
working on integrated photonic chips. "If you solve the integration problem, the performance problem and the utility problem, you
will be recognized by the market," Mr. Marpaung said.