First electricity, then light…now sound waves
A light scattering phenomenon long considered a nuisance by the electronics and communications industries is emerging as a possible new way to transform 5G and broadband networks, sensors, satellite communications and defence systems.
University of Technology Sydney (UTS) researcher Professor Christopher Poulton is part of a global renaissance of researchers exploring both the applications and “blue sky” potential of a phenomena that could lead to what has been described as a “third wave of integrated circuits.”
Known as “Brillouin scattering”, the phenomenon – first predicted in 1922, though not measured until 1958 - occurs when light and sound waves are “coupled” causing an enhanced feedback loop between photons (light) and phonons (sound). This can cause problems in high-power laser systems used for communications, sensing and defence, because when the light scatters the power of the signal is reduced.
Together with other global leaders in the field Professor Poulton has published a review article in Nature Photonics outlining the history and potential of what scientists refer to as ‘Brillouin integrated photonics’.
Lead author, and head of the Sydney Nanoscience Hub, Professor Ben Eggleton said the Brillouin scattering process offers “a completely new way to integrate optical information into a chip environment using sound waves as a buffer to slow down the data without the heat that electronic systems produce.”
Professor Poulton said: “The big advance here is in the simultaneous control of light and sound waves on really small scales.
“This type of control is incredibly difficult, not least because the two types of waves have extremely different speeds.
“The enormous advances in fabrication and theory outlined in this paper demonstrate that this problem can be solved, and that powerful interactions between light and sound such as Brillouin scattering can now be harnessed on a single chip.
“This opens the door to a whole host of applications that connect optics and electronics,” he said.
The review also highlights the diversity of skills and expertise required in this field. Professor Poulton explained that there was a long running collaboration between Sydney University (USyd), Macquarie University (MU) and the Australian National University (ANU).
“UTS provides the theory, ANU and MU the fabrication and USyd the experimental expertise. You need all three components. Without theory and good numerical methods you wouldn’t know where to look or what to make,” he said.
From his perspective as someone who bridges the gap between physics and mathematics Professor Poulton thinks the research is “inherently interesting” even if he doesn’t know exactly what all the applications will be into the future.
“However, I believe that some aspects will be incredibly useful,” he said.
“The frequency of sound waves is in the high gigahertz which is the same frequency used in radar. You can use that for extremely broadband tuneable filters. These aren’t glamorous devices but without them a lot of things don’t work, radar systems for example.
“Current high frequency electronic filters top out at around 10 gigahertz, and then become big and clunky and boxy. If on-chip Brillouin can be developed to reduce the size of filters then weight and power consumption issues can be overcome and this offers the possibility of high-speed, low-weight and flexible solutions in sensing and communications applications,” Professor Poulton said.
Professor Peter Rakich from Yale University; Professor Michael Steel at Macquarie University; and Professor Gaurav Bahl from the University of Illinois at Urbana-Champaign are also co-authors on the paper.
Brillouin integrated photonics Benjamin J. Eggleton Christopher G. Poulton, Peter T. Rakich, Michael. J. Steel, Gaurav Bahl Nature Photonics (2019)
Australian Research Council, Harris Corporation, US Office of Naval Research and US National Science Foundation.