5G will be followed by 6G: The 6th generation of mobile communications promises even higher data rates, shorter latency, and strongly increased densities of terminal devices while exploiting Artificial Intelligence (or AI) to control devices or autonomous vehicles in the Internet-of-Things era. To simultaneously serve as many users as possible and to transmit data at the utmost speed, future wireless networks will consist of a large number of small radio cells. In these radio cells, distances are short so that high data rates can be transmitted with minimum energy consumption and low electromagnetic emission. The associated base stations will be compact and can easily be mounted to building facades or streetlights.
To form a powerful and flexible network, these base stations need to be connected by high-speed wireless links that offer data rates of tens or even hundreds of gigabits per second. This may be accomplished by terahertz carrier waves, which occupy the frequency range between microwaves and infrared light waves. However, terahertz receivers are still rather complex and expensive and often represent the bandwidth bottleneck of the entire link.
Researchers at Karlsruhe Institute of Technology (or KIT) have now developed a novel concept for low-cost terahertz receivers that consist of a single diode in combination with a dedicated signal processing technique. In a proof-of-concept experiment, reported in Nature Photonics, the team demonstrated transmission at a data rate of 115 Gbit/s and a carrier frequency of 0.3 THz over a distance of 110 meters.
At its core, the receiver consists of a single diode, which rectifies the terahertz signal. The diode is a so-called Schottky barrier diode, which offers large bandwidth and that is used as an envelope detector to recover the amplitude of the terahertz signal. Correct decoding of the data, however, additionally requires the time-dependent phase of the terahertz wave that is usually lost during rectification. To overcome this problem, the researchers used digital signal processing techniques in combination with a special class of data signals, for which the phase can be reconstructed from the amplitude Using their receiver concept, the scientists achieved a transmission rate of 115 Gbit/s at a carrier frequency of 0.3 THz over a distance of 110 m. This is the highest data rate so far demonstrated for wireless terahertz transmission over more than 100 meters. The terahertz receiver developed by KIT stands out due to its technical simplicity and lends itself to cost-efficient mass production.