A New Kind of Microcomb on a Chip

The new microcomb is a coherent, tunable and reproducible device with up to ten times higher net conversion efficiency than the current state of the art. (Source: M. Halleröd Palmgren, Chalmers)

Tiny photonic devices could be used to find new exoplanets, monitor our health, and make the internet more energy efficient. Researchers from Chalmers Univer­sity of Technology, Sweden, now present a game changing microcomb that could bring advanced appli­cations closer to reality. A microcomb is a photonic device capable of generating a myriad of optical frequencies on a tiny micro­resonator. These colours are uniformly distri­buted so the micro­comb behaves like a ruler made of light. The device can be used to measure or generate frequencies with extreme precision.

Now, eight Chalmers researchers developed a new kind of microcomb on a chip, based on two micro­resonators. The new microcomb is a coherent, tunable and repro­ducible device with up to ten times higher net conversion effi­ciency than the current state of the art. “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,” says Óskar Bjarki Helgason, a PhD student at the Department of Micro­technology and Nanoscience at Chalmers.

The researchers are not the first to demons­trate a microcomb on a chip, but they have developed a method that overcomes several well-known limi­tations in the field. The key factor is the use of two optical cavities – micro­resonators – instead of one. This arrangement results in the unique physical charac­teristics. Placed on a chip, the newly deve­loped microcomb is so small that it would fit on the end of a human hair. The gaps between the teeth of the comb are very wide, which opens great oppor­tunities for both researchers and engineers.

Since almost any measurement can be linked to frequency, the micro­combs offer a wide range of potential appli­cations. They could, for example, radically decrease the power consumption in optical communi­cation systems, with tens of lasers being replaced by a single chip-scale microcomb in data centre inter­connects. They could also be used in lidar for auto­nomous driving vehicles, for measuring distances. Another exciting area where microcombs could be utilised is for the calibration of the spectro­graphs used in astronomical obser­vatories devoted to the discovery of Earth-like exoplanets.

Extremely accurate optical clocks and health-moni­toring apps for our mobile phones are further possi­bilities. By analysing the compo­sition of our exhaled air, one could potentially diagnose diseases at earlier stages. “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.

This is a huge challenge, that requires maybe 5 to 10 years and an investment in engi­neering research. But I am convinced that it will happen,” says Victor Torres Company, who leads the research project at Chalmers. “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?” (Source: Chalmers U.)

Reference: Ó. B. Helgason et al.: Dissipative solitons in photonic molecules, Nat. Phot., online 25 January 2021; DOI: 10.1038/s41566-020-00757-9

Link: Dept. of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg, Sweden

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