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RESEARCHERS in Japan have found a way to supply 90 watts of power over a 300m optical fibre system, potentially opening the way to powering mobile data networks via optical fibre.
Radio antenna units wirelessly transmit data from a central station to mobile devices at radio frequencies. The central station transmits data to the antenna units using radio over fibres.
With increasing data use, the radio antenna units that transmit data to mobile devices must deal with increased demand. By bundling data and power transmissions onto the same optical fibre systems, it might be possible to simplify infrastructures, and also remove the vulnerability of the system to mains power interruptions.
The research team at the University of Electro-Communications have demonstrated the ability to supply 60W over a 300m test fibre system, exceeding the power supplied in previous research.
Power supply over fibre is limited by the power transmission efficiency, which is impeded by the large fraction of power fed into the optical link that is lost as heat during transmission. This means that any such system is limited in power feed levels, as the waste heat could damage optical components in the link.
The researchers demonstrated that they could bundle together two multimode fibres for transmitting power, with a double clad fibre for transmitting the data. This bundle was tapered and fused to a double clad fibre output.
A laser diode with direct electrical modulation from a signal generator produced test signals at 1550 nm to the standard specifications of the Institute of Electrical and Electronics Engineers (IEEE) for the wireless local access network (WLAN) used in wi-fi (specifications IEEE 802.11 g). Commercial laser diodes also fed the optical power.
An erbium-doped fibre amplifier boosted the signal and increased the power level of the data signal for the transmission. The system also included elements to reduce the noise, including bandpass filters and cladding mode strippers.
However, power was lost in the tapered fibre bundle divider due to the lower cross-sectional area occupied by fibre in the cluster bundle. As a result the overall power transmission efficiency was only 20 percent, limiting the power that could be fed into the link to just 40W.
The researchers then increased the number of multimode power-carrying fibres to six, optimising the cross-sectional area of fibre in the bundle cluster without introducing other limitations, thereby maximising the power transmission efficiency.