After 5G: cue ultrafast WiFi

A technique to transfer data at superfast speeds using sound and light has been developed by UK researchers...

This new breakthrough involves sending a sound wave through a quantum cascade laser to achieve wireless data transfer rates of 100 gigabytes per second. At speeds like this, you could download tens of movies in less than the time it takes to say "Amazon Prime".

The approach is one of the first successful demonstrations of creating and using high frequency terahertz waves. This range of frequencies is famously referred to as the “terahertz gap”, because limitations in existing technologies hampered our abilities to make use of these frequencies in the past.

To create sufficiently short waves at such high frequencies, the source needs to be switched on and off very quickly. This process is called modulation. Most WiFi and mobile devices, including Bluetooth, cordless phones and your car keys, operate at a frequency of 2.4GHz. This is the same range used for microwave ovens, and it was adopted for these newer applications precisely because the required technology was already well developed. An additional benefit is that these frequencies do not interfere with the signals used for radio and TV transmissions.

But as more devices seek to exploit this space as the "Internet of things" takes off, the 2.4GHz bandwidth is getting crowded, which is degrading performance and hence user experience.

The much-hyped 5G network partially surmounts this problem by operating at higher 30 and 300GHz frequencies. At the moment, very few devices operate in those bandwidths, meaning that the airwaves are less crowded and there's plenty of electronmagnetic elbow room for new sensors and devices.

That's fine for the time being, but once we all start communicating with 3D holograms, watching live sports games in virtual reality, and streaming 8K movies, we'll become starved of bandwidth again.

This is where Nottingham University's Tony Kent thinks he can make a difference with a new approach that uses a terahertz quantum cascade laser to “modulate” a light pulse fast enough to reach terahertz frequencies.

In an experimental setup, Kent's team have managed to create 100 billion light pulses per second by propagating a sound wave we cannot hear through the laser.

To understand how it works, think of the cascade laser as a staircase with hundreds of steps. The wave is created by releasing an electron, which loses energy every time it drops down one of these steps. As it does so, the electron emits a photon, which is a quantum of light. The size of each step corresponds to a wavelength in the terahertz range. To make it lose energy sufficiently quickly, the researchers sent a sound wave through the laser. This shook up the whole cascade, creating the terahertz wave.

The device they used here was the size of a few millimetres, but it could be engineered to be small enough to fit into devices. But because they are so close in frequency to visible light, terahertz waves are also very susceptible to obstacles in their paths, just as we cannot see through walls. So this new technique would mostly be for point-to-point, short range data transfers. This means transmitters would need to be positioned in any locations where ultrafast data transfer is desired, but it would be particularly useful in spaces where there are no obstructions.

So there you go, next time you wonder what will happen after 5G, think terahertz cascade quantum laser transmission!