Single Microcomb Replaces Multiple Lasers

Microscope image of the frequency microcomb made of a microresonator device. (Source:A. Fülöp)

Every time we send an e-mail, a tweet, or stream a video, we rely on laser light to transfer digital infor­mation over a complex network of optical fibers. Dozens of high-perfor­mance lasers are needed to fill up the bandwidth and to squeeze in an increasing amount of digital data. Researchers have now shown that all these lasers can be replaced by a single device called a microcomb. A micro­comb is an optical device that generates very sharp and equi­distant frequency lines in a tiny microphotonic chip. This tech­nology was developed about a decade ago and is now reaching a maturity level that enables new appli­cations, including lidar, sensing, time­keeping and of course optical communi­cations.

The soul of a microcomb is a tiny optical cavity that confines laser light in space. Therefore, this tech­nology provides a fantastic playground to explore new nonlinear physical phenomena. These conditions have now been utilised by researchers at Chalmers Univer­sity of Techno­logy, Sweden, in coopera­tion with researchers at Purdue Univer­sity, USA. “We observed that the optical frequencies of the micro­comb interfered destruc­tively over a short period of time, thus providing the formation of a wave inside the cavity that resembled a “hole” of light. The interes­ting aspect of this waveform is that it yielded a sufficient amount of power per frequency line, which was essential to achieve these high-performance experi­ments in fiber communi­cation systems”, says Victor Torres Company.

The physical formation of these dark pulses of light is far from being fully understood, but the researchers believe that their unique properties will enable novel appli­cations in fiber-optic communi­cation systems and spectro­scopy. Victor Torres Company says: “This is a bright start to better understand the formation of dark pulses in micro­resonators and their potential use in optical communi­cations. The research could lead to faster and more power-efficient optical communi­cation links in the future.”

The results are the fruit of a collaborative effort between researchers at the School of Electrical and Computer Engi­neering at Purdue Univer­sity, who fabricated the samples, and the group of Professor Peter Andrekson at the Photonics Labora­tory at Chalmers, which hosts world-class experi­mental faci­lities for fiber-optic communi­cations research. “Our findings do not represent the first demon­stration of a microcomb in fiber communi­cations, but it is the first time that the micro­comb has achieved a perfor­mance compatible with the strong demands of future communi­cation systems”, says Peter Andrekson.

“Working with the micro­comb and this experiment has been a great experience. This proof-of-concept demon­stration has allowed us to explore the require­ments for future chip-scale data trans­mitters while at the same time proving the potential of this very exciting dark pulse comb techno­logy”, co-worker Attila Fülöp says. (Source: Chalmers Univ.)

Reference: A. Fülöp et al.: High-order coherent communications using mode-locked dark-pulse Kerr combs from microresonators, Nat. Commun. 9, Article number: 1598 (2018); DOI: 10.1038/s41467-018-04046-6

Link: Photonics Laboratory, Dept. of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden

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