Photo, left: Cut through a Hollow-core photonic bandgap fibre in which light propagates in the central hole. [Image: Gregory Jasion, University of Southampton].
A team from Southampton’s Optoelectronics Research Centre has demonstrated a specialty optical fibre with zero-sensitivity to temperature changes.
Published in the optical journal Optica, a paper entitled; “How to make the propagation time through an optical fibre fully insensitive to temperature variations”, reports a significant advance in stabilising the time that it takes for laser light to pass through an optical fibre.
The research has been conducted through a collaboration between the ORC’s Coherent Optical Signals & Microstructured Optical Fibre Groups. The collective team have explored the development of robust hollow core fibres suitable for use in various demanding applications, such as the distribution of accurate time signals, that are sensitive to environmentally-induced changes in fibre temperature.
Dr Radan Slavík, Principal Investigator for the project and leader of the Coherent Optical Signals group, says: “This represents an exciting new research direction for my group and I am happy that we have developed such a great collaboration with the Microstructured Optical Fibre group, without whom this work would not have been possible. Optical fibres have significantly lower thermal sensitivity than electrical cables.
he added, “Demonstrating that this can be reduced to zero makes optical fibres the ultimate technology for many applications that are sensitive to drifts in absolute propagation delay. I am starting to investigate some of these – e.g., through my recently-awarded UK Space Agency project that I have with UK’s National Physical Laboratory, which aims to use our technology on next-generation satellites”.
Sense and sensitivity
Propagation time through an optical fibre changes with the environmental conditions occurring where the fibre is laid, since changes in the temperature alter both the fibre length (by a tiny but still significant fraction) and the refractive index associated with the silica glass at its core. These changes have negligible impact in most fibre applications such as telecommunications, however, they can be greatly detrimental in many others such as fibre-based interferometric sensing.
In prior research we showed that hollow core photonic bandgap fibres (HC-PBGFs) have up to 18 times smaller sensitivity to temperature variations than traditional solid core fibres, making these fibres the most environmentally insensitive fibre technology available to date. However, in this current work we have managed to find a way to completely eliminate this sensitivity.
Dr Eric Numkam-Fokoua, the lead author of the paper commented, “What we predict theoretically and demonstrate experimentally is that it is possible to design a hollow-core fibre such that a temperature increase causes a propagating pulse to speed up and compensate exactly for the associated small fibre elongation. This remarkable property which cannot be achieved in any other fibre type represents the ultimate fibre solution for many time sensitive applications.”
The development of these new fibres underpins various key elements of research within the £6M “Hollow Core Fibre Photonics” Programme Grant recently awarded to the ORC by the UK Engineering and Physical Sciences Research Council (EPSRC). The paper can be found at: Optica and Optics and Photonics news.