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DETERMINATION OF MECHANICAL STRESSED PLACES OF OPTICAL FIBERS IN OPTICAL CABLES USING BRILLOUIN REFLECTOMETERS
Igor V. Bogachkov, Omsk State Technical University (OmSTU), Omsk, Russia, bogachkov@mail.ru
Abstract
An important task of an early diagnostics of optical fibers (OFs) is the timely detection and suppression of fiber segments with mechanical stress in optical cables (OC). The local inhomogeneities of quartz (including microcracks) may occur in the processes of fiber production. They create internal stresses, so the fiber becomes vulnerable to bending or vibration. The increased OF strain in the laid OC affects durability of them, although modern modular structures of OCs have a certain stock of OC protection against the dangerous tension. To detect such «problem» segments of an OF the Brillouin reflectometry or phase shift method is used. This method underlies the operation of Brillouin optical time domain reflectometers (BOTDR), which are able to provide correct information on a distribution of a strain degree along OF length. Also, this information allows us to predict the degradation of fibers.
It is necessary at various stages of OC production to control the characteristics of an OF, including such as OF strain. Investigation results of the strain in stressed optical fiber and optical cable in various processes of production using BOTDR are described in this article.
In the production process of OFs and OCs it is not difficult to get access to both ends of the OF. The phase shift method is effectively used to find the total optical fiber elongation.
During the construction and operation of the OCs, the access is possible only to one OF end, therefore only the reflectometry methods (BOTDR) can be used.
When laying OCs, the OF strains will be redistributed (all OF strains along the line will be averaged while meeting the requirements of cable laying), but obvious defects, such as segments with high strain are likely to continue, and therefore the OC life can be significantly reduced. It is recommended to include the BOTDR in the control systems of the OF characteristics to detect OF segments with high mechanical stress and temperature changes. This will make it possible to identify the potentially harmful segments in the OC at various stages of OC production and improve the technologies used in the production process.
Keywords: optical fiber, strain, optical cable, Mandelstam – Brillouin scatter, early diagnostics, Brillouin reflectometry.
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Information about author:
Igor V. Bogachkov, Associate professor (docent) of «Communication means and information security» department of Omsk State Technical University (OmSTU), Omsk, Russia