Southampton University researchers have created an 11km-long hollow-core photonic bandgap fibre, a significant increase on what was previously possible.
The low-loss, high-bandwidth fibre paves the way for the use of this type of revolutionary fibre - which can be made of a single type of glass - in telecommunications. This has previously been impossible due to the very short lengths that engineers were able to manufacture.
“Hollow-core photonic bandgap fibre has only had niche applications up until now because it was thought that it could not be manufactured in lengths suitable for telecoms applications,” said Marco Petrovich, a senior member of the Zepler Institute team at the University of Southampton. “Not only have we successfully made a photonic bandgap fibre in a suitable length, we have also engineered it to have the right properties for telecoms applications.”
The fibre, which supports 200nm bandwidth with a longitudinally uniform loss of approximately 5dB/km at 1560nm has a 19-cell core and five-cladding ring structure. It was fabricated using a conventional two-stage stack-and-draw technique.
The breakthrough was made possible due to an improved understanding of fibre properties deriving from various new numerical and experimental fabrication and characterisation tools recently developed by the team of researchers.
Petrovich and his colleagues have demonstrated that the fibre has error-free, low-latency, direct-detection 10Gbit/s transmission across the entire C-band.
While conventional solid optical fibres require additional chemical elements - so-called dopants - in order to carry light, the photonic band-gap fibres can be made entirely from one kind of glass. In conventional fibres, the material used dictates the properties of the fibre, but in a photonic bandgap fibre, the defining factor is its structure.
The nodes and struts that give photonic bandgap fibre its properties are usually on a sub-micron scale, with many only a few nanometres in size.
“Any small change in these structures can change the properties along the fibre,” said Petrovich. “We have shown that our fibre’s properties are consistent along its entire length.”
In microstructured fibres, the cladding region is peppered with many small air holes that run the entire fibre length. In photonic band-gap fibres, light guidance in the hollow core can be achieved via photonic band-gap effects.
The researchers believe they will be able to manufacture even longer fibres in the future.
The project received funding from the UK Engineering and Physical Sciences Research Council and the European Union’s Seventh Framework Programme.