A microcomb developed by researchers from Chalmers University of Technology has the potential to herald significant advances in a variety of technologies, spanning metrology and optical communication. The design is based on two microresonators and is coherent, tunable, and reproducible, and has up to 10× higher net conversion efficiency than current state-of-the-art devices. Microcombs generate a variety of uniformly distributed colors on a tiny cavity known as a microresonator. They can be used to measure or generate frequencies with extreme precision. Researchers at Chalmers University of Technology, Sweden, present a microcomb on a chip based on two microresonators instead of one. It is a coherent, tunable, and reproducible device with up to 10× higher net conversion efficiency than the current state-of-the-art. Courtesy of Yen Strandqvist, Chalmers University of Technology. “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 first author Óskar Bjarki Helgason, a Ph.D. student in the Department of Microtechnology and Nanoscience at Chalmers. The design overcomes several well-documented hurdles in the field, thanks in large part to its use of two optical cavities — microresonators — rather than one. The microresonators interact with one another, similar to how atoms bind together when forming a diatomic molecule — an interaction known as a photonic molecule. The device is small enough to place on the end of a human hair, and has very wide “teeth” — physical qualities that combine to establish numerous opportunities for researchers and engineers. Power consumption in optical communication, for example, could be drastically reduced, as tens of lasers could be replaced by a single chip-scale microcomb in data center interconnects. The design could also contribute to test and measurement applications in lidar for autonomous driving vehicles, where the microcomb could be implemented to measure distances. Calibration of spectrographs used in astronomical observatories is another potentiality. Their implementation could enable more effective identification of Earth-like exoplanets. Optical clocks and health-monitoring apps for mobile phones are further possibilities. In smartphones, the chip could be used to analyze the composition of exhaled air and detect 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 five to 10 years and an investment in engineering research,” said Victor Torres Company, lead on the research project at Chalmers. The research was published in Nature Photonics (www.doi.org/10.1038/s41566-020-00757-9).