Researchers Transmit RF Signals via Laser Beams

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have demonstrated a laser that can emit microwaves wirelessly, modulate them, and receive external radio frequency signals. It is the first time a laser has been used as a radio frequency transmitter. Researchers transmitted recording of Dean Martin’s classic “Volare” wirelessly via a semiconductor laser.

This research opens the door to new types of hybrid electronic-photonic devices and is the first step toward ultra-high-speed Wi-Fi. This study builds off previous work from the Capasso Lab. In 2017, the researchers discovered that an infrared-frequency comb in a quantum cascade laser could be used to generate terahertz frequencies, the submillimeter wavelengths of the electromagnetic spectrum that could move data hundreds of times faster than today’s wireless. In 2018, the team found that quantum cascade laser frequency combs could also act as integrated transmitters or receivers to efficiently encode information.

Now, the researchers have figured out a way to extract and transmit wireless signals from laser frequency combs. Unlike conventional lasers, which emit a single frequency of light, laser frequency combs emit multiple frequencies simultaneously, evenly spaced to resemble the teeth of a comb. In 2018, the researchers discovered that inside the laser, the different frequencies of light beat together to generate microwave radiation. The light inside the cavity of the laser caused electrons to oscillate at microwave frequencies - which are within the communications spectrum.

The first thing the new device needed to transmit microwave signals was an antenna - so the researchers etched a gap into the top electrode of the device, creating a dipole antenna (like the rabbit ears on the top of an old TV). Next, they modulated the frequency comb to encode information on the microwave radiation created by the beating light of the comb. Then, using the antenna, the microwaves containing the encoded information radiate out from the device. The radio signal is received by a horn antenna, filtered, and sent to a computer.

The researchers also demonstrated that the laser radio could receive signals. The team was able to remotely control the behavior of the laser using microwave signals from another device.

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

The Harvard Office of Technology Development has protected the intellectual property relating to this project and is exploring commercialization opportunities.