Those of us working from home who - out of necessity or by choice - have taken a closer look at their Wi-Fi network recently, will know that the router sends signals over two frequencies: 2.4 Gigahertz and 5 Gigahertz. The latter connection is faster, but also has a shorter range unfortunately, due to the shorter radio waves (6 centimeters instead of 12.5) - which is why an extra Wi-Fi point is sometimes needed to enhance the signal.

In order to provide everyone with ultrafast internet indoors and outdoors, to allow self-driving cars to communicate with each other, or to enable wireless data transfer within data centers, ‘data rates’ of several Gigabits per second are required. For this, even higher frequencies are needed, ranging from 30 to 300 Gigahertz, corresponding to wavelengths of a few millimeters.

Beat

This poses several challenges, doctoral candidate Álvaro Morales Vicente from Spain says. “Since short waves cover a smaller range, the signals need to be steered in a very specific direction over a short distance. That can be done with several antennas in a row.” In addition, generating such high frequencies with traditional electronics is no easy task in itself, Morales Vicente emphasizes. “The main problem is the limited bandwidth of the modulation that can be handled by traditional electronics, which means that you cannot achieve the desired high bit rates.”

There is an alternative: using laser light to very accurately generate the desired radio frequencies. Laser light has a much higher frequency than radio waves, but combining two laser beams with slightly different ‘colors’ leads to a periodic variation in light intensity caused by interference, Morales Vicente explains. “That difference frequency can be converted to a radio signal with the use of a light detector.” This phenomenon is comparable to the ‘beating’ you can hear when you pluck two strings of a slightly out of tune guitar.