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Keeping the next generation of atomic clock ticking

August 10, 2022 | Julie Robert

Update : August 10, 2022

INRS Professor Roberto Morandotti contributes to international breakthrough in photonics.

INRS Professor Roberto Morandotti contributes to international breakthrough in photonics

Atomic clocks are among the most accurate timekeepers in human history. An accurate time reference is essential for systems such as global navigation, satellite mapping, establishing the next generations of telecommunication (5 and 6G+, fibre communication). But atomic clock are currently massive devices – weighing hundreds of kilograms – which need to be housed within precise, difficult-to-maintain conditions. That’s why scientists around the world are racing to build portable versions that will work in real-world settings, and could replace existing satellite navigation systems, such as GPS and Galileo.

Now, an international research team based in the United Kingdom, in partnership with the Institut national de la recherche scientifique (INRS), has solved a major stumbling block in the development of these portable atomic clocks, by working out how to reliably switch ‘on’ their counting device – and keep them running. Their work was published today in the journal Nature.

Microcombs are a fundamental part of future optical atomic clocks – they allow one to count the oscillation of the ‘atomic pendulum’ in the clock, converting the atomic oscillation at hundreds of trillions of times per second to a billion times a second – a gigahertz frequency, that modern electronic systems can easily measure.

Based on electronic compatible optical microchips, the microcombs are the best candidates to miniaturise the next generation of ultraprecise timekeeping. They are cutting-edge laser technology sources, made up of ultraprecise laser lines, equally spaced in the spectrum.

However, microcombs are typically produced by devices so sensitive, that when someone talks or enters a room, they cannot maintain their state. They lose stability and the microcombs shut down.

An ‘eternal engine’

The research team found a way to allow the system to start by itself and remain stable in state – essentially being self-recovering. This work was conducted under the leadership of former INRS post-doctoral fellow Professor Alessia Pasquazi in partnership with, among others, Professor Roberto Morandotti from the Research Centre Énergie Matériaux Télécommunications at the Institut national de la recherche scientifique (INRS).

“We have basically an ‘eternal engine’ – like Snowpiercer if you watch it – which always comes back to the same state if something happens to disrupt it. Now, we have a start and a recovery button,” says Professor Pasquazi, who began this work at the University of Sussex before moving to Loughborough University last month.

“This collaborative work is a key milestone in the development of microcombs because the stabilization of the system we have developed is very useful for real-world applications. It could be used for optical radar, machine learning applications and spectroscopy. It will also eliminate our dependence on GPS.”

Roberto Morandotti who specializes in nonlinear optics and in the micro and nanofabrication of structures for photonics.

Revolutionizing telecommunication networks

“A well-behaved microcomb uses a special type of wave, called a cavity-soliton, which is not simple to get. Like the engine of a petrol car, a microcomb prefers to stay in an ‘off-state’. When you start your car, you need a starter motor that makes the engine rotate properly,” explains professor Pasquazi. “At the moment, microcombs do not have a good ‘starter-motor’. It is like having your car with the battery constantly broken, and you need someone to push it downhill every time you need to use it, hoping that it will start.” 

In 2019 the research team had already demonstrated that they could use a different type of waves called laser cavity solitons to get microcombs, by embedding directly the microchip in a standard laser and obtained a great boost in terms of efficiency. Now, researchers have shown that soliton can be naturally turned into the only state of the system.

According to the researchers, microcombs are expected to revolutionize telecommunication networks, which use many different colours to transfer as much information as possible. “While networks currently use separate lasers for every colour, microcombs will provide a compact and power-efficient alternative, with the possibility of also transferring ultra-precise timekeeping,” concludes Pasquazi.

About the study

The paper, Self-emergence of robust solitons in a micro-cavity, has been published on August 10th in collaboration with colleagues at the University of Sussex, City University of Hong Kong, the Xi’an Institute of Optics and Precision Mechanics, in China, Swinburne University of Technology in Australia, the INRS-EMT, in Canada and the University of Strathclyde.