This is the first time a laser has been used as a radio frequency transmitter when researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences transmitted a recording of Martin's classic "Volare" wirelessly via a semiconductor laser.
The researchers published their paper in the Proceedings of the National Academy of Sciences, and the researcher demonstrated a laser that can emit microwaves wirelessly, modulate them and receive external radio frequency signals.
The senior author of the study and the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS, Federico Capasso said that the research opens the door to new types of hybrid electronic-photonic devices and is the first step towards ultra-high speed Wi-Fi.
This new study leans on the previous work from the Capasso Lab. Back in 2017, the researchers found out 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 platforms. In 2018, the group discovered that quantum cascade laser frequency combs could also act as integrated transmitter or receivers to efficiently encode information.
At present, the researchers have figured out a way to extract and transmit wireless signals from laser frequency combs.
Different from the 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 found out that inside the laser, the different rates of light beat together to generate microwave radiation. The light inside the cavity of the laser instigated electrons to move back and forth at microwave frequencies, which are within the communications spectrum.
A postdoctoral fellow at SEAS and first author of the paper, Marco Piccardo said that for anyone to use this device for Wi-Fi, the person needs to be able to leave valuable information in the microwave signals and extract that information from the device.
An antenna is the first thing the new device needs to transmit microwave signals. As a result, the team etched a gap into the top electrode of the device to create a dipole antenna similar to the rabbit ears on the top of an old TV. After that, the researchers modulated the frequency comb to encode information on the microwave radiation created by the beating light of the comb. Then, with the use of the antenna, the microwaves are radiated out from the device, containing the encoded information. A horn antenna receives the radio signal, filtered and sent to a computer.
Piccardo said that this all-in-one integrated device holds great promise for wireless communication. The study provides a clear roadmap revealing how to get terahertz wireless connection even though the dream of it is still ways away.
