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Photonic technology boosts microwave signals
Researchers at Chalmers University of Technology have investigated the possibility of using fibre optic technology to generate and distribute microwave signals in future wireless networks. This technology is important to meet the increase in demand for mobility and high data rates.
Using optical fibre for the distribution of microwave signals has several benefits compared to using electrical cables. Optical fibre has low loss and frequency-independent attenuation. It is also insensitive to electromagnetic interference, low in weight, small in size and low in cost.
To meet the future demand generated by the constantly increasing number of devices that are wireless connected, and at the same time maintain full mobility and high data rates, new higher frequencies must be brought into use, as the frequency space is becoming congested.
In a new PhD thesis by Andreas Wiberg at the Photonics Laboratory at Chalmers, research is presented which deals with optical generation, modulation and distribution of signals in micro- and millimetre-wave applications. The results obtained include demonstrations of transportation of 40 GHz signals over 44 km of optical fibre modulated with 2.5 Gbit/s data, transmitted through a wireless link in a laboratory environment.
"Fibre optic solutions are particularly beneficial at high frequencies and over longer distances. Combining photonic technology and microwave applications opens up new, interesting possibilities and technical solutions," says Andreas Wiberg.
In order to also maintain sufficient coverage at high frequencies, new wireless systems with distributed antennas are required for both indoor and outdoor solutions. These antennas can be managed from a central location and with centralised control; dynamic channel allocation is possible in order to follow fluctuations in traffic load and maintain good wireless coverage.
Researchers at the Department of Microtechnology and Nanoscience at Chalmers University of Technology have investigated the possibility of using fibre optic technology to generate and distribute microwave signals for future networks with wireless Gigabit/s data rates, so-called Radio-over-Fibre.
The work by Andreas Wiberg also presents details of how several frequencies and/or frequency bands can be sent in parallel through a microwave photonic system in which optical filtering is used to separate the different frequencies. It is also shown that optical techniques could be used to generate high-frequency harmonics from electrically generated signals.
The use of photonic technology in microwave applications is referred to as Microwave Photonics and has many applications apart from communication. Microwave Photonics can also be used in analogue applications, such as reference signal generation and distribution of these signals to antenna arrays. Examples of such applications could be phase-steered radar antennas or large antenna arrays for radio astronomy.
Source: Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg, Sweden
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