When a theory becomes a reality – New Zealand’s world-leading photonics research

A miniscule ring, made on a microchip like the one inside our phones, can transform a single laser beam into thousands with different colours. The resultant “microresonator optical frequency combs” or "microcombs” are a new emerging technology with massive potential. They are poised to drive a giant leap forward in many applications, from telecommunications to sensing, giving us a bigger, better, faster internet, precision self-driving cars and much more.

Now, writing in the esteemed Nature Photonics journal, an international collaboration led from New Zealand  reports on the discovery of a new microcomb paradigm. Te Whai Ao — Dodd-Walls Centre Principal Investigator and University of Auckland Associate Professor Miro Erkintalo has collaborated with colleagues at the US National Institute of Standards and Technologies (NIST) and the University of Maryland, the University of Burgundy in France and the Université Libre de Bruxelles in Belgium, to experimentally demonstrate a new microcomb technology he theoretically conceived during COVID lockdowns.

In conventional microcombs, numerous equally spaced laser frequencies are generated around the frequency of the single input laser. The Auckland-led collaboration has now discovered that a whole new regime can be achieved by using two lasers with very different frequencies instead of one. Here the microcombs form with frequencies in between the two inputs and, unlike conventional microcombs, come in two distinct flavours.

“This represents a new paradigm that is wholly different from existing approaches. There’s so much to explore,” Erkintalo says.

Working with students in Auckland and collaborators from Europe, Erkintalo came up with the theory of how the new scheme might work during COVID lockdowns. In 2022, the group put their theoretical predictions out to the scientific world on pre-print (prior to formal publication). Then a few months later, out of the blue Erkintalo got an email from the States.

“Grégory Moille from NIST and the University of Maryland had seen our prediction and decided to give it a go in the lab. Apparently it worked right away. Normally experiments require a lot of head-scratching and problem solving, but this one seemed to just work immediately. Everyone was quite surprised,” says Erkintalo.

With the theory now supported with evidence, the New Zealand and European researchers joined forces with the American academics to undertake a combined experimental and theoretical effort into the new microcomb regime.

As to what this new technology might be specifically used for, Erkintalo says that it may allow some or all the many applications of conventional microcombs to now be realised in frequency ranges where conventional microcombs are not available. In addition, the two different flavours associated with the new microcombs could be seen as ones and zeros that can power new types of computers that use laser light instead of electronics.

“But before we can develop the applications, we need to completely understand how these things work. This calls for exploring the fundamental physics at play, and that’s what we’re focussing on next. We are very fortunate to have just received funding from The Royal Society Te Apārangi for this purpose,” Erkintalo says.

The published paper can be found here.

Image Credit: Sean Kelly/NIST