Could laser frequency combs be the future of Wi-Fi

May 03, 2018 // By Jean-Pierre Joosting
In 2017, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) discovered that an infrared frequency comb in a quantum cascade laser could offer a new way to generate terahertz frequencies. Now, those researchers have uncovered a new phenomenon of quantum cascade laser frequency combs, which would allow these devices to act as integrated transmitters or receivers that can efficiently encode information.

Wi-Fi and cellular data traffic are increasing exponentially but, unless the capacity of wireless links can be increased, all that traffic is bound to lead to unacceptable bottlenecks.

Upcoming 5G networks are a temporary fix and there is already talk of 6G. For a long term solution, esearchers have focused on terahertz frequencies, the submillimeter wavelengths of the electromagnetic spectrum. Data traveling at terahertz frequencies could move hundreds of times faster than today's wireless.

"This work represents a complete paradigm shift for the way a laser can be operated," said Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering and senior author of the paper. "This new phenomenon transforms a laser – a device operating at optical frequencies – into an advanced modulator at microwave frequencies, which has a technological significance for efficient use of bandwidth in communication systems."

See also: Manufacturing technology for integrating terahertz systems developed

Frequency combs are widely-used, high-precision tools for measuring and detecting different frequencies of light. Unlike conventional lasers, which emit a single frequency, these lasers emit multiple frequencies simultaneously, evenly spaced to resemble the teeth of a comb. Currently, optical frequency combs are used for everything from measuring the fingerprints of specific molecules to detecting distant exoplanets.

See also: What needs to happen for 5G to be a reality?

This research, however, wasn't interested in the optical output of the laser.


Inside an infrared frequency comb in a quantum cascade laser, the different frequencies of light beat together to generate microwave radiation. Illustration courtesy of Jared Sisler, Harvard University.


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