The first step toward ultra-high-speed Wi-Fi: a laser-radio transmitter

Leaping toward the next generation of wireless-based data communications, researchers say they are making progress extracting and sending data using semiconductor lasers that churn out radio signals across multiple frequencies all at the same time. Data could conceivably be transmitted hundreds of time faster than today’s traditional Radio Frequency (RF) wireless, engineers believe.

It’s the “first laser-radio transmitter,” Harvard University proclaims of its invention in an article on its John A. Paulson School of Engineering and Applied Science (SEAS) website.

The group’s excitement is due in part because for the first time, they’re using a special laser frequency comb rather than radio or traditional laser to send signals. Frequency combs in photonics are roughly a set of equally spaced frequencies across the spectrum being exploited—mimicking the look of a comb’s teeth. Here, the wireless signals, which carry the data, are extricated and then disseminated from that laser spectrum.

In these experiments, multiple laser frequencies simultaneously emitted produce wireless microwave spectrum, the team explains. The light-based laser frequencies “beat” together to form microwave. And it’s that microwave radiation, rather than the light, that they say can be used for wireless, bandwidth-intensive communications.

Lasers can create modulated outgoing wireless microwaves. They can also receive them, the researchers say. It “opens the door to new types of hybrid electronic-photonic devices and is the first step toward ultra-high-speed Wi-Fi,” senior author Frederico Capasso, of the engineering school, says in the article.

Modulation is the process where one adjusts the signal properties of a wave in such a way that it can carry information. It’s basically a signal that contains information. The data is then read through a kind of decoding at the receiving end, performing the opposite process—demodulation.

The researchers modulate the laser frequency comb “to encode information on the microwave radiation created by the beating light of the [laser] comb.” An antenna then radiates data-encoded microwaves out of the apparatus. The received radio signal (the microwaves) are captured by a horn antenna, filtered and then sent to a computer for translation.

Controlling the laser remotely

As an added bonus, the researchers also discovered they were able to remotely control the laser’s actions by using microwave signals from another device, lending itself to, perhaps, chained and wide-reaching, controllable radio communications systems.

“This all-in-one, integrated device, holds great promise for wireless communication,” says Marco Piccardo, a postdoctoral fellow at SEAS and first author of the paper.

Frequency combs have been well explored by the team. An infrared comb in a laser was used in 2017 to generate sub-millimeter terahertz frequencies. And in 2018, the group used laser frequency combs for the actual transmitting and receiving of encoded information.

Counter-intuitively, though, in this case, lasers “beating together to generate microwave radiation” could mean we end up with not the imagined, open-air fiber-like laser beams criss-crossing the skies like a scene in a sci-fi-movie, producing state-of-the-art ultra-fast data pipes. Instead we could see that the lasers are used simply to create wide, bandwidth-friendly wireless microwave frequencies, and that they, in turn, are actually the carrier medium that will end up being used for sending and receiving the fast data.