By Josh Perry, Editor
[email protected]

For the first time, researchers at the Harvard University (Cambridge, Mass.) Paulson School of Engineering and Applied Sciences (SEAS) used a semiconductor laser as a radio transmitter, demonstrating the ability of lasers to emit microwaves, modulate them, and receive external radio frequency signals, according to a report from the university.

For the first time, researchers at Harvard have used a laser as a radio transmitter and receiver. (Wikimedia Commons)

The engineers transmitted Dean Martin’s version of “Volare” and, in the process, showed a potential path towards ultra-fast Wi-Fi and hybrid electronic-photonic devices.

“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,” the report explained. “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.”

Researchers created a dipole antenna by etching a gap into the device’s top electrode and modulated the frequency comb to encode information on the microwave radiation created by the light of the comb. The antenna broadcast the microwaves with the information, they were received by a horn antenna, and sent to a computer.

“The researchers also demonstrated that the laser radio could receive signals,” the report continued. “The team was able to remote control the behavior of the laser using microwave signals from another device.”

The research was recently published in the Proceedings of the National Academy of Sciences (PNAS). The abstract stated:

“Since the days of Hertz, radio transmitters have evolved from rudimentary circuits emitting around 50 MHz to modern ubiquitous Wi-Fi devices operating at gigahertz radio bands. As wireless data traffic continues to increase, there is a need for new communication technologies capable of high-frequency operation for high-speed data transfer.

“Here, we give a proof of concept of a compact radio frequency transmitter based on a semiconductor laser frequency comb. In this laser, the beating among the coherent modes oscillating inside the cavity generates a radio frequency current, which couples to the electrodes of the device. We show that redesigning the top contact of the laser allows one to exploit the internal oscillatory current to drive a dipole antenna, which radiates into free space.

“In addition, direct modulation of the laser current permits encoding a signal in the radiated radio frequency carrier. Working in the opposite direction, the antenna can receive an external radio frequency signal, couple it to the active region, and injection lock the laser.

“These results pave the way for applications and functionality in optical frequency combs, such as wireless radio communication and wireless synchronization to a reference source.”