New self-calibrating photonic chip shines a light on ultrafast tech of the future

When it comes to advancements in technology, we’re always pushing for things to be faster, better, more efficient, more sustainable, and smaller.

This certainly applies to the burgeoning field of photonics – the use of light particles (photons) to store, transmit and manipulate information. In broad terms, photonics is a lot like electronics except the particles which are doing the work are photons, not electrons.

Researchers at Melbourne’s Monash University and RMIT have now developed an advanced photonic circuit which could transform the speed and scale of photonics technologies.

Publishing their findings in Nature Photonics, the team believes the efficiency of their new photonic chip can help advance research into artificial intelligence as well as in driverless cars, language processing, and data transfer.

In 2020, Monash University’s Bill Corcoran worked with RMIT researchers to develop a new optical microcomb chip. That single fingernail-sized chip was able to transfer 39 terabits per second – three times the record data rate for the entire National Broadband Network. The testing of the chip was widely regarded as a demonstration of the world’s fastest internet speed.

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Lead investigator of the latest collaboration Arthur Lowery, professor at Monash, says their work is now building on the 2020 optical microcomb chip.

Researchers say that the microcomb chip represents the building of a superhighway. The new “self-calibrating” optical chip incorporates on and off ramps, connecting a number of superhighways for even greater movement of data.

“We have demonstrated a self-calibrating programmable photonic filter chip, featuring a signal processing core and an integrated reference path for self-calibration,” Lowery explains.

The new chip turns an impressive initial demonstration into something that can be useful in engineering new technologies.

“Self-calibration is significant because it makes tunable photonic integrated circuits useful in the real world; applications include optical communications systems that switch signals to destinations based on their colour, very fast computations of similarity (correlators), scientific instrumentation for chemical or biological analysis, and even astronomy,” says Lowery.

As more and more advanced technologies like artificial intelligence and self-driving cars require greater volumes of data to be transmitted at even greater speeds, developments in photonics illuminate how this might be achieved.

“This research is a major breakthrough – our photonic technology is now sufficiently advanced so that truly complex systems can be integrated on a single chip,” says Professor Arnan Mitchell from RMIT’s Integrated Photonics and Applications Centre. “The idea that a device can have an on-chip reference system, allowing all its components to work as one, is a technological breakthrough that will allow us to address bottleneck internet issues by rapidly reconfiguring the optical networks that carry our internet to get data where it’s needed the most.”

“Electronics saw similar improvements in the stability of radio filters using digital techniques that led to many mobiles being able to share the same chunk of spectrum. Our optical chips have similar architectures, but can operate on signals with terahertz bandwidths,” says Lowery.

While photonics opens up massive opportunities, it is not easy going to make devices which can be programmed and reprogrammed. This is because the manufacturing needs to be done with precision down to the scale of the wavelength of light – nanometres.

So, making an optical chip that can be hooked up to existing infrastructure becomes a major issue.

“Our solution is to calibrate the chips after manufacturing, to tune them up in effect by using an on-chip reference, rather than by using external equipment,” explains Lowery. “We use the beauty of causality, effect following cause, which dictates that the optical delays of the paths through the chip can be uniquely deduced from the intensity versus wavelength, which is far easier to measure than precise time delays. We have added a strong reference path to our chip and calibrated it. This gives us all the settings required to ‘dial up’ and desired switching function or spectral response.”

Instead of dialling in a setting manually, the chip is tuned in one step allowing data streams to be switched seamlessly.

“As we integrate more and more pieces of bench-sized equipment onto fingernail-sized chips, it becomes more and more difficult to get them all working together to achieve the speed and function they did when they were bigger,” says Dr Andy Boes, a collaborator from the University of Adelaide. “We overcame this challenge by creating a chip that was clever enough to calibrate itself so all the components could act at the speed they needed to in unison.”