Partner und Internationale Organisationen
(Englisch)
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B, CH, D, DK, E, FIN, I, NL, S, UK
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Abstract
(Englisch)
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Intra-core fibre gratings are a new kind of all-fibre components based on permanent periodic index modulation in the core of single mode optical fibre induced by UV laser light. The fibre grating couples light between different fibre modes. Examples for fibre gratings are long period gratings (LPGs), modeconverters, and fibre Bragg gratings (FBG), which are basic components for future telecommunication wavelength division multiplexing networks. FBGs can be used as reflection, loss, or transmission filters, as mirrors in fibre lasers, or as more complicated components like dispersion compensators (CDC), or optical add drop multiplexers (OADM). FBGs, LPGs, CDCs and OADMs are now being commercialised, although some fundamental reliability aspects like thermal stability and mechanical breaking strength are still under investigation. COST action 246 focused on the reliability of optical fibres and components. During an international workshop organised by the Institute of Applied Optics (IOA) and Swisscom in Bern, in October 1995, the topic of FBG reliability was introduced into the ongoing COST 246 action. A special working group was formed in order to address the characterisation, the thermal and mechanical reliability, and the influence of environmental condition on FBGs. A round robin on FBG characterisation was organised with the objective to elaborate a common standard for spectral and functional FBG measurements. Different European partners addressed thermal reliability issues of FBGs in B-co-doped and / or hydrogen loaded germanosilicate fibres. Preliminary experiments were conducted to identify possible problems with mechanical reliability due to environmental conditions. The mechanical reliability of FBGs fabricated on-tower during fibre drawing was studied by German partners. The outcome of this working group is summarised in Chapter 10 (edited by IOA) of the final COST report to be published by Springer Verlag, London. IOA-EPFL investigated the influence of mechanical reliability of FBGs fabricated after fibre drawing. In general, this fabrication procedure is used to fabricate components for telecom applications. Pre- and post fibre preparation procedures like Hydrogen loading, mechanical vs. chemical stripping of the coating, and recoating were investigated. The influence of pulsed and CW irradiation was studied. Chemically stripped samples with mechanical reliability similar to pristine fibres show strong mechanical degradation due to pulsed laser irradiation, where laser intensity and irradiation dose were major issues. Using a CW laser IOA has shown that it is possible to fabricate high strength FBGs with stress corrosion coefficient, Weibull m-value and median breaking strength similar to pristine fibre. A simple fibre lifetime model applied to such FBGs shows that these components withstand for 50 years a constant tensile stress which is only 6% lower than that of pristine fibres. The work lead to a Ph.D. thesis, which was accepted by the department of Microengineering at EPFL in July 1998. The results were also presented at international conferences in several contributed and invited papers and they were published in peer reviewed journals.
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