Frequency comb lasers prove useful for wireless terahertz communication

Researchers have shown that so-called frequency comb lasers can be used to send and receive information. That opens the way to fast wireless communication on terahertz frequencies.

According to Harvard, the discovery is important for the use of terahertz waves for wireless internet. Science has been experimenting for some time with terahertz frequencies, which may be used for possible successors to 5G or WiFi. The terahertz sources currently being tested tend to have limited bandwidth.

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences discovered a phenomenon that turns a laser into an efficient modulator at microwave frequencies. They are building on research from last year, which discovered that the use of an infrared frequency comb in a quantum cascade laser could be used to generate terahertz frequencies.

Frequency comb lasers, unlike traditional lasers, emit several laser frequencies simultaneously, with a controllable and regular spacing between the frequencies. Due to their high precision, scientists use such lasers for frequency measurements, for example for spectroscopic observations in astronomy or the fingerprint of molecules.

For this study, the scientists were interested in the output, so they had to find out what was going on in the laser. They discovered that light in the laser causes electrons to oscillate at microwave frequencies. Those oscillations can be modulated externally to encode information on a carrier wave.

The researchers have published their work in the scientific journal Optica under the title ‘Time-dependent population inversion gratings in laser frequency combs’.