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Tiny photonic devices could help detect disease and spot exoplanets

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Researchers from Chalmers University of Technology, Sweden, have developed a new microcomb which could play a major role in many exciting applications, from fast disease detection to massively cutting the power consumption of optical communications systems.

A microcomb is a photonic device capable of generating a range of optical frequencies on a tiny optical cavity known as a microresonator. These colours are uniformly distributed, such that the microcomb behaves like a 'ruler made of light' for measuring or generating frequencies with extreme precision.

The Chalmers University researchers developed a new kind of microcomb of a chip, based on not one but two microresonators. The two microresonators interact with each other, similar to how atoms bind together when forming a diatomic molecule; this arrangement is known as a “photonic molecule”.

The device is a coherent, tuneable and reproducible device with up to ten times higher net conversion efficiency than the current state of the art devices.

“The reason why the results are important is that they represent a unique combination of characteristics, in terms of efficiency, low-power operation and control, that are unprecedented in the field,” said PhD candidate Óskar Bjarki Helgason.

While this is not the first time a microcomb on a chip has been demonstrated, this method overcomes a number of well-known limitations through the use of a second microresonator. This arrangement results in its unique characteristics. It is small enough to fit on the end of a human hair, and the gaps between the “teeth” of the comb are extremely wide. As almost any measurement can be linked to frequency, the large width of the teeth opens up the possibility of wide opportunities for both researchers and engineers.

The microcomb could, for instance, radically decrease the power consumption in optical communication systems, with tens of lasers being replaced by a single chip-scale microcomb in data centres. They could be used in lidar for autonomous driving vehicles in order to measure distances, or to calibrate the spectrographs used astronomical observations (such as for the discovery of exoplanets). Other possibilities include more accurate optical clocks, health monitoring apps for phones, and diagnostic tests based on analysis of exhaled air.

“For the technology to be practical and find its use outside the lab, we need to co-integrate additional elements with the microresonators, such as lasers, modulators, and control electronics,” said Dr Victor Torres-Company, who leads the Ultrafast Photonics Laboratory at Chalmers University. “This is a huge challenge, that requires maybe five to 10 years and an investment in engineering research, but I am convinced that it will happen.

“The most interesting advances and applications are the ones that we have not even conceived of yet. This will likely be enabled by the possibility of having multiple microcombs on the same chip. What could we achieve with tens of microcombs that we cannot do with one?”

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