First data transmission through terahertz multiplexer

　　A method for multiplexing data carried on terahertz waves has been demonstrated by a team of scientists from Brown University and the University of Lille.

　　The researchers report the transmission of two real-time video signals through a terahertz multiplexer at an aggregate data rate of 50Gbits/s, which is said to be 100 times the optimal data rate of today's fastest cellular network.

　　"We showed that we can transmit separate data streams on terahertz waves at very high speeds and with very low error rates," said Brown Professor Daniel Mittleman. "This is the first time anybody has characterised a terahertz multiplexing system using actual data, and our results show that our approach could be viable in future terahertz wireless networks."

　　The team's multiplexing and demultiplexing approach uses two metal plates placed parallel to each other to form a waveguide. One of the plates has a slit cut into it. When terahertz waves travel through the waveguide, some of the radiation leaks out of the slit. The angle at which radiation beams escape is dependent upon the frequency of the wave.

　　"We can put several waves at several different frequencies – each of them carrying a data stream – into the waveguide, and they won't interfere with each other because they're different frequencies; that's multiplexing," Prof Mittleman said. "Each of those frequencies leaks out of the slit at a different angle, separating the data streams; that's demultiplexing."

　　According to the team, because of the nature of terahertz waves, signals in terahertz communications networks will propagate as directional beams, not omnidirectional broadcasts like in existing wireless systems.

　　A user at a particular location – and therefore at a particular angle – will communicate on a particular frequency.

　　"If the angle is a little off, we might be detecting the full power of the signal, but we're receiving one sideband a little better than the other, which increases the error rate." Prof Mittleman explained. "So it's important to have the angle right.