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PRINCIPLES OF AUTOMATED DATA PROCESSING OF MANDELSTAM – BRILLOUIN BACKSCATTER CHARACTERISTICS FOR EVALUATING THE STATE OF OPTICAL FIBERS
DOI: 10.36724/2072-8735-2020-14-8-47-52
Igor V. Bogachkov, Omsk State Technical University (OmSTU), Omsk, Russia,
bogachkov@mail.ru
Abstract
For early diagnostics of the state of optical fibers (OFs) located in the laid optical cables (OCs), it is necessary to identify potentially unreliable sections of the S in advance, which over time can lead to the destruction of fibers and disrupt the normal operation of fiber-optic communication lines (FOCLs). For diagnosis and forecasting of the state of the OFs that are in the laid OCs, Brillouin optical pulse reflectometers (BOTDR) are used, in which the back-reflected signal of the spontaneous Mandelstam – Brillouin scattering (MBS) is analyzed. In the process of obtaining a trace of the distribution of the Mandelshtam – Brillouin backscatter spectrum (MBBS) along the OF, the Brillouin frequency shift (BFS) is determined. After this, a graphs of the distribution of strain along the light-guide is constructed. A classification of varieties of single-mode optical fibers based on analysis of the MBS characteristics is discussed in this paper. It is shown how by the characteristics of the frequency profiles of the MBBS, one can determine the type of fiber and also evaluate the change in the strain and BFS. The MBBS profile come under influence by the functional dependence of the distribution of acoustic modes in the OF, their longitudinal direction. Both of them depend on the structure of the OF layers, as well as on the types and concentration of various alloying additives of the core OF. For single-mode OFs, when describing the MBS process, it is necessary to take into account the spatial distribution and interaction of the main optical and several acoustic modes. After uploading the data file from the BOTDR, it is necessary to process the information in order to determine the BFS and the strain along the light-guide. This process can be automatized, if a database has been formed. When a new Brillouin reflectogram appears, the MBBS profile from it must be compared with templates from the generated database. To classify the fiber types, it is necessary to evaluate the degree of matching of the explored MBBS profile with all the database templates. To assess the degree of coincidence of the considered MBBS profiles, needs to be defined the overall part of the frequency band for analysis. The programs for the automated processing of the Brillouin reflectograms data are presented. Based on the analysis of Brillouin reflectograms, it is possible to identify a factor that had a predominant influence on the characteristics of the MBS signal in the explored sections of single-mode optical fibers. As a result of the program’s work, a template is output that, according to the program’s estimates according to the algorithm described above, has the best match with the downloaded image. To increase the accuracy of assessing the similarity of the explored profiles, it is also recommended to carry out calculations according to the above-described algorithm when aligning not only the maximum levels, but also combine the graphs along the frequency axis. It is clear that during the overlay the frequencies of the «peaks» (BFS), there will be a very strong coincidence of the patterns, and the type of the OFs will be determined correctly, while at some temperatures a good degree of similarity with another pattern could be obtained. The obtained estimate of the BFS allows one to determine the degree of the OF strain. The identification of the MBBS profile and other characteristics of the MBS allows you to create a database various types of the OFs and different manufacturers, which can be used to classify the type of the OFs. The results presented in this exploratory development show how based on the analysis of BOTDR reflectograms, it is possible to automatically determine the type of the OF in OC, to identify a factor that has a predominant effect on the frequency response and strain in the explored sections of the OFs in FOCL, which can improve the efficiency of predicting the operational parameters of the physical channels of optical telecommunication systems.
Keywords:single-mode optical fiber, Mandelstam – Brillouin scattering, reflected signal, Brillouin frequency shift, profile of the backscatter spectrum.
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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), Senior Member IEEE, Omsk, Russia