NTU researchers with their terahertz chip. From left: Abishek Kumar, Associate Professor Ranjan Singh, and Dr Yihao Yang. Photo credit: Lester Kok.
With the recent news of 5G network rollout in Singapore, many are anticipating improvements in the speed and reliability of wireless communications, which has become an important part of our lives. Scientists from Nanyang Technological University, Singapore (NTU Singapore) and Osaka University in Japan have now developed a communication chip based on “photonic topological insulators” that may enable the next generation of ultra-fast wireless communications.
Publishing in the journal Nature Photonics, the researchers revealed that their chip can transfer data far more efficiently and quickly than 5G networks, using terahertz (THz) waves. THz waves are a class of electromagnetic waves that lie between microwaves and visible light in the electromagnetic spectrum and are a leading candidate for beyond-5G wireless communications.
Left: Close up view of the terahertz chip. Right: Size of the chip relative to a Singapore 5-cent coin. Photo credit: Lester Kok.
At the present moment, the theoretical speed limit for 5G wireless communications is 10 gigabits per second (Gbit/s) – a whopping 10 billion bits of data transferred per second. The team from Singapore and Japan team showed, however, that their prototype chip transmits at a rate of 11 Gbit/s, which is already above the theoretical limit for 5G. With further development, this rate can be increased even further.
In recent years, researchers have been looking into using THz waves for telecommunications. One major obstacle to these efforts is that THz waves are particularly susceptible to transmission errors, which are commonly caused by device defects and environmental interference. This imposes severe limitations to the rate at which information can be reliably transmitted.
The new chip overcomes this problem by using a new design concept called a “photonic topological insulator”, which supports a new type of electromagnetic wave called a “topological state.” Such waves can flow effortlessly around obstacles and corners without being reflected or lost. The theoretical concept originated in solid state physics, where the theoretical physicists who came up with it were awarded the 2016 Nobel Prize in Physics.
To apply the idea of topological states to THz waves, the team created a silicon chip with a special pattern of triangular holes. A channel within this pattern of holes allows light to flow in a topological state, unobstructed by bends, corners, or defects. In the prototype chip, the THz waves are routed around 10 sharp corners, maintaining a rate of 11Gbit/s with negligible loss in transmission.
In a practical demonstration, the researchers were able to show that their chip supports real-time streaming of 4K high-definition video.
“The whole process of designing, fabricating, and testing the chip took us two years,” said Associate Professor Ranjan Singh of NTU Singapore, the leader of the project. The fabrication of the silicon chip was performed at Osaka University under the leadership of Professor Masayuki Fujita, an expert in silicon photonic crystals.
According to Associate Professor Singh, this is the first ever practical application of a photonic topological insulator for THz waves, turning a previously theoretical concept into a useful technology.
“With the rapid adoption of IoT [Internet-of-Things] devices, including remote cameras and sensors, we need to handle high volumes of data wirelessly, with ultra-high speeds and low latency,” says Associate Professor Singh. “Our new THz technology can play an important role in this. For example, we envision self-driving cars using THz waves to communicate quickly and reliably with each other, allowing them to navigate better and avoid accidents.”
For their next project, the team is using the photonic topological insulator concept to develop THz interconnects – devices that connect different components within electromagnetic circuits. They hope that these interconnects, operating at 10 to 100 times current 5G speeds, will be integrated into future wireless communication appliances.
References
- NTU News Release: “NTU Singapore and Osaka University scientists build ultra-high-speed Terahertz wireless chip“
- Yihao Yang, Yuichiro Yamagami, Xiongbin Yu, Prakash Pitchappa, Julian Webber, Baile Zhang, Masayuki Fujita, Tadao Nagatsuma, and Ranjan Singh, “Terahertz topological photonics for on-chip communication,” Nature Photonics 14, 446 (2020).
- Video credit: Associate Professor Ranjan Singh