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THE EXPERIMENTAL RESEARCHES OF THE MANDELSTAM – BRILLOUIN SCATTER CHARACTERISTICS IN ERBIUM OPTICAL FIBERS OF VARIOUS KINDS
Igor V. Bogachkov, Omsk State Technical University (OmSTU), Omsk, Russia, bogachkov@mail.ru
Abstract
The crucial subject in monitoring of the fiber optical communication lines (FOCLs) is a premature diagnostics of segments with high mechanical strain, longitudinal strain, sections with changed temperature, segments with bends in optical fibers (OFs) and so on. It allows us to recover such segments before a breakdown of FOCL. The longitudinal mechanical strain in OFs in FOCL can lead to a breakdown of the OF. Therewith, the problems in the FOCL can be originated by temperature transformations in the OFs. To detect segments of the OFs with changed temperature and longitudinal strain the Brillouin time-domain reflectometers (BOTDRs) are applied, in which the features of a Mandelstam — Brillouin backscatter spectrum (MBBS) along the OF are analyzed. The erbium-doped fiber (EDF) is used in the erbium-doped fiber optical amplifiers (EDFA), which are widely applied at this time, especially as a part of the FOCL with wavelength division multiplexing (WDM). To improve a radiation tolerance of an EDF the doping of erbium ions, as well as other additives as cerium is carried out.
Studies have shown that a structure of an OF core, a configuration and a composition of its layers influence on the MBBS properties. It is possible to detect the different kinds of OFs (including EDF), as part of a light-pipe using a BOTDR, and classify the OFs according to a shape of the MBBS. Taking into account the fact that the power levels of a signal launched into the OF are significant in BOTDR, for this reason the study of MBBS in some kinds of EDFs at different power levels of the input signal and influences is of particular interest. The experimental studies using the BOTDR «Ando AQ 8603» were carried out to consider the MBBS features in some kinds of erbium-doped optical fibers of different manufacturers. The results of tests of MBBS in EDF of various kinds are given, the influence of the structure of an OF core and the composition of OF layers on Brillouin frequency shift and MBBS profile is considered. The reflectograms of the BOTDR are shown, which demonstrate the MBBS distribution along the light-pipe, the strain distribution and the level of the backscattered signal. The segments with EDF are clearly visible in the reflectograms. The level graphs of a backscattered signal along the OF demonstrates the rise («hump») of about 3 dB at the EDF initial (at a distance of about 1 m from the joint), and a sharp drop in the backscattered signal level (more than 4 dB/m) after the «hump» is observed. As a result, the OFs following the EDF (length is more than 3m) are not visible in the BOTDR-traces. The reason for this is that the active EDF layers absorb the input BOTDR signal in the absence of pump radiation, which leads to the depletion of the backscattered MBS signal. This behavior in OFs of other kinds is not observed. If we change the power level of the input signal, this effect will be maintained.
Keywords: erbium-doped optical fiber, Mandelstam – Brillouin scatter, strain, Brillouin frequency shift, early diagnostics, Brillouin reflectometer, spectrum profile.
References
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- Bogachkov I.V. Detection of initial level of Brillouin frequency shift in optical fibers of different types. Journal of Physics: Conference Series, 2018. Vol. 1015 (2018), pp. 1-6.
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- Bogachkov I.V., Trukhina A.I., Inivatov D.P., Kireev A.P., Gorlov N.I. A classification of optical fibers types on the spectrum profile of the Mandelstam – Brillouin backscattering. Dynamics of Systems, Mechanisms and Machines (Dynamics–2018). Proceedings. Omsk, 2018, pp. 1-6.
- Certificate 23734 of electronic resource registration. Program for automatically detection the of optical fiber types on Brillouin traces. I.V. Bogachkov, D.P. Inivatov, A.G. Choban (Russia, OmSTU), publ. 14.08.2018.
Information about authors:
Igor V. Bogachkov, Associate professor (docent) of «Communication means and information security» department of Omsk State Technical University (OmSTU), Omsk, Russia