Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have, for the first time, used a semiconductor laser to send and receive radio signals. The hybrid electronic-photonic device uses a laser to extract and transmit microwave signals, providing a data rate that may one day lead to ultra-high-speed Wi-Fi.

Hearing Dean Martin singing "Volare" on the radio may not seem that earthshaking, but when it's the first radio transmission and reception using lasers, it's something a little special. According to the team behind the new technology, the laser not only emitted microwaves wirelessly, but also modulated them and received outside radio signals.

Working on previous research by the team in 2017 and 2018, the laser radio works by means of an infrared laser frequency comb. A garden variety laser generates light at a single frequency, much like a violin playing a precise note as opposed to a white noise generator spewing out the whole spectrum of sound. In a frequency comb, the laser produces multiple beams at multiple frequencies that are evenly spaced apart like the teeth of a comb, hence the term.

In 2018, the SEAS team found that the light "teeth" of the laser comb could be made to resonate against one another, causing the electrons in the cavity of the laser to oscillate at microwave frequencies in the radio band of the spectrum. In the top electrode of the device, there's an etched slot that acts as a dipole antenna, like the rabbit ears on an old-fashioned analog television.

By modulating the comb, the team was able to encode data on the microwave emission. This was then transmitted by the antenna to its reception point, where it was picked up by a horn antenna before being filtered and decoded by a computer. In addition, the laser technology could also receive radio signals, and the laser's behavior could be controlled remotely using microwaves from a second device.

"This all-in-one, integrated device, holds great promise for wireless communication," says Marco Piccardo, a postdoctoral fellow at SEAS. "While the dream of terahertz wireless communication is still a ways away, this research provides a clear roadmap showing how to get there."

The research was published in the Proceedings of the National Academy of Sciences.

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