In previous field experiments, rates of 40 gigabits per second and transmission distances of more than one km were reached, researchers said.

For their latest record, the scientists at the Karlsruhe Institute of Technology in Germany applied a photonic method to generate the radio signals at the transmitter. After radio transmission, fully integrated electronic circuits were used in the receiver.

"Our project focused on integration of a broadband radio relay link into fiber-optical systems," Professor Ingmar Kallfass said.

"For rural areas in particular, this technology represents an inexpensive and flexible alternative to optical fiber networks, whose extension can often not be justified from an economic point of view," said Kallfass.
"At a data rate of 100 gigabits per second, it would be possible to transmit the contents of a blue-ray disk or of five DVDs between two devices by radio within two seconds only," said Kallfass.
In the experiments, latest photonic and electronic technologies were combined: First, the radio signals are generated by means of an optical method.
Several bits are combined by so-called data symbols and transmitted at the same time. Upon transmission, the radio signals are received by active integrated electronic circuits.
The transmitter generates the radio signals by means of an ultra-broadband so-called photon mixer made by the Japanese company NTT-NEL. For this, two optical laser signals of different frequencies are superimposed on a photodiode.
The frequency of an electrical signal result equals the frequency difference of both optical signals. The millimeter-wave electrical signal is then radiated via an antenna.
"It is a major advantage of the photonic method that data streams from fiber-optical systems can directly be converted into high-frequency radio signals," Professor Jurg Leuthold, former head of the KIT Institute of Photonics and Quantum Electronics (IPQ).
Leuthold proposed the photonic extension that was realized in this project.
"This advantage makes the integration of radio relay links of high bit rates into optical fiber networks easier and more flexible," said Leuthold.


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