“There may be some reluctance to build intensive FTTH if regulators subsequently force telcos to open up infrastructure access to competitors” John Williamson – see page 12
APPLICATIONS & RESEARCH
Stanford researchers build a ‘billion sensors’ earthquake observatory with optical fibres
Thousands of miles of buried optical fibres crisscross California’s San Francisco Bay Area delivering high-speed internet and HD video to homes and businesses. Biondo Biondi, a professor of geophysics at Stanford’s School of Earth, Energy & Environmental Sciences, dreams of turning that dense network into an inexpensive “billion sensors” observatory for continuously monitoring and studying earthquakes. Over the past year, Biondi’s group has shown that it’s possible to convert the jiggles of perturbed optical fibre strands into information about the direction and magnitude of seismic events. The researchers have been recording those seismic jiggles in a 3-mile loop of optical fibre installed beneath the Stanford University campus. “We can continuously listen to – and hear well – the Earth using Slow speeds and the Internet ‘rush hour’ could soon be a thing of the past with new hardware designed and demonstrated by University College London (UCL) researchers that provides consistently high-speed broadband connectivity, with rates at more than 10,000 Mbits/s, using new, simplified and low-cost receiver technology. “UK broadband speeds are woefully slow compared to many other countries, but this is not a technical limitation. Although 300 Mbits/s may be available to some, average UK speeds are currently 36 Mbits/s.
sensor coverage would also enable higher resolution measurements of ground responses to shaking.
smaller ones, in greater detail and pinpoint their sources more quickly than is currently possible. Greater
pre-existing optical fibres that have been deployed for telecom purposes,” Biondi said. Currently researchers monitor earthquakes with seismometers, which are more sensitive than the proposed telecom array, but their coverage is sparse and they can be challenging and expensive to install and maintain, especially in urban areas. By contrast, a seismic observatory like the one Biondi proposes would be relatively inexpensive to operate. “Every metre of optical fibre in our network acts like a sensor and costs less than a dollar to install,” Biondi said. “You will never be able to create a network using conventional seismometers with that kind of coverage, density and price.” Such a network would allow scientists to study earthquakes, especially By 2025, average speeds over 100 times faster will be required to meet increased demands for bandwidth- hungry applications such as ultra-high definition video, online gaming and the Internet of Things,” explained lead researcher Dr Sezer Erkılınç, UCL electronic & electrical engineering. “The future growth in the number of mobile devices, coupled with the promise of 5G to enable new services via smart devices, means we are likely to experience bandwidth restrictions; our new optical receiver technology will help combat this problem.” The UCL team notes that
The location of a 3-mile, figure-8 loop of optical fibres installed beneath the Stanford campus. Image: Stamen Design and the Victoria & Albert Museum.
UCL simplifies receivers for ultra-fast access
Networks Group, Professor Polina Bayvel, UCL Electronic & Electrical Engineering. The new, simplified receiver retains many of the advantages of coherent receivers, but is cheaper and smaller, requiring just a quarter of the detectors used in conventional receivers. Simplification was achieved by adapting a coding technique to fibre access networks that was originally designed to prevent signal fading in wireless communications. This approach has the additional cost-saving benefit of using the same optical fibre for both upstream and downstream data.
to maximise the capacity of optical fibre links, data is transmitted using di erent wavelengths of light and the ideal would be to dedicate a wavelength to each subscriber to avoid bandwidth sharing between users. Although this is already possible using highly sensitive coherent receivers, these are costly and only financially viable in core networks. “Their cost and complexity has so far prevented their introduction into the access networks and limits the support of multi-Gbits/s broadband rates available to subscribers,” said co-author and Head of the Optical
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| ISSUE 11 | Q4 2017
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