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A DETECTION OF STRAINED SECTIONS IN OPTICAL FIBERS ON BASIS OF THE BRILLOUIN RELECTOMETRY METHOD
Igor V. Bogachkov,
Associate professor (docent) at the "Communication means and information security" department of Omsk State Technical University (OmSTU), Omsk, Russia, bogachkov@mail.ru
Keywords: Brillouin reflectometry, early diagnostics, Brillouin scatter, strain, dispersion shift, optical fiber.
The results of experimental researches of the strain characteristics (longitudinal stretching mechanical loadings) of various types of optical fibers based on Brillouin backscatter spectrum (SBS) analysis are presented in this work. The important problem of the monitoring and early diagnostics of fiber optical communication line is an obtaining authentic information about physical states (strain, temperature) of optical fibers in the optical cables. Usual optical timedomain reflectometers (OTDR) cannot define a fiber ten-sion. To detection of mechanically stretched fibers sections (strain of fibers) Brillouin optical timedomain reflectometers (BOTDR) are applied.
The SBS and strain characteristics of usual single mode fibers (G.652), dispersion-shifted single mode fibers (DSF - G.653) and non zero dispersion-shifted optical fibers (NZDSF - G.655) are discussed in this paper.
The graphs of the Brillouin backscatter spectrums, Brillouin frequency shift dependences and corresponding strain characteristics of these optical fibers are presented.
The NZDSF according to the characteristics of SBS and strain occupies an intermediate posi-tion between the usual OF (G.652) and DSF (G.653). The received results have confirmed an opportunity of detection of mechanically stressed (strained) sections and estimations of strain fiber degree on the basis of SBS analysis at various ten-sile forces. Thus BOTDR it is connected only to one of fibers ends that is its important advantage, in comparison with other methods.
The strain control of fibers in ready optical cables by manufacture should be spent phase meth-ods as access by both ends of fibers in this case is possible, but BOTDR does not find out danger-ous fibers strain because of protective elements of optical cables.
Для цитирования:
Богачков И.В. Обнаружение натяжённых участков в оптических волокнах на основе метода бриллюэновской рефлектометрии // Т-Сотт: Телекоммуникации и транспорт. 2016. Том 10. №12. С. 85-91.
For citation:
Bogachkov I.V. A detection of strained sections in optical fibers on basis of the brillouin relectometry method. T-Comm. 2016. Vol. 10. No.12, pp. 85-91.
One of important problems of the monitoring and early diagnostics of liber optical communication line (FOL) is an obtaining trustworthy information about physical states of optical fibers (OF) in the optical cables (OC).
Significant quantity of communication OC now is laid under ground. Ground deformations, arising for this or that reason (displacement bases of high-altitude buildings, communications and engineering constructions and so on), will influence occurrence of mechanical pressure in OF. Even insignificant displacements Of the ground layers can cause to local fibers deformations in OC and appear fatal to integrity OF in OC.
Using of overhead technology (for example, raising aerial OC to high-voltage columns) at FOL cabling, the problem, connected with icing of the open OC sections during the winter time, is arisen. Some OC sections under weight of ice can be deformed, that will lead to occurrence of the raised strain in fibers which can reduce considerably longevity of FOL [1 - 3].
Thus, it is necessary to have authentic information about OF strain for estimation of the FOL reliability [I - 5].
Usual optical time-domain re Hectometers (OTDR) cannot define a fiber tension. To detection of mechanically stretched sections FOL (strain of Fibers) Brillouin optical time-domain reflec-tometers (BOTDR) are applied.
One of effective methods of definition of the fibers strain degree is the Brillouin refleclometry method [1-3] in which basis registration and the subsequent analysis of the Brillouin scatter (BS) spectrum in fiber. BS is nonlinear effect which is arisen at input in OF an optical signal with raised intensity.
BS depends on such parameters of the fiber, as a mechanical stretching (strain) and temperature. It is known [I —6], that spectral components, caused by BS, have important property for next practical applications, that their frequency is displaced on the value, which proportional to the strain degree of the fiber.
The longitudinal stretching force, enclosed to the fiber, changes its Young's modulus which in turn influences change of hyperacoustic wave speed.
The basic expression fl - 3] connecting the frequency shift (fB) of Brillouin backscatler spectrum (SBS) and the fiber strain degree, is the formulas:
fb = 2nvjk , v0 = y/Ee ! p , (I)
where n is the refraction index of the fiber core; X is the wavelength of the input light signal; v„ is the velocity of hyperacoustic wave; Er - Young's modulus (strain characteristics, module of elongation); p - quartz glass density [1,2],
Testing OF by short-pulses and scanning carrier frequency of this pulses the distribution along fiber of SBS and, respectively, the peak (maximum) signal frequencies in this spectrum can be found. By measuring distribution amount of Brillouin frequency shift (/¡,) along OF (/B(.Tt)), it is possible lo find out of the location of distributed irregularities (mechanical stressed sections) in OF and determine their characteristics [i —5].
It will allow to find out the distributed irregularities along OF and in view of the formula (I) to define the OF strain degree on the basis of dependence SBS fa^&e) [6 - 8j:
' •'/ <--> , (2)
fM-Cf /„(0 )-Cf
where s^z) is the dependence of the fiber strain ratio from the longitudinal coordinate z along OF; Av^z) is a change of the fiber strain concerning initial value; f{sc, z) - dependence of the frequency shift from strain and coordinatez;/B(0> is initial value of/«; Cf~ 493 MHz/°C (typical value; for various types of fibers there are differences in temperature dependence); Afa (z) -change of Brillouin frequency shift (fB) alone coordinate z [6-8].
Ouestions of mathematical modeling BS in the OF and research of influence of fiber tension parameters on its SBS have been considered in works [1 - 6].
In relation to detailing the models discussed in [1 - 6] and verifying the simulation results, experimental researches with BOTDR «Ando AQ 8603» with the assistance of «Moskabel-Fujikura» were carried out. The fiber sections with the changed longitudinal stretching force were researched.
3D-refiec tog rams - a SBS distribution (a function of the reflected signal intensity from longitudinal coordinate Z and Brillouin frequency shift (/«) along OF) BOTDR "Ando AQ 8603" for OF, being inside of laid OC by length about 80 km, is presented in Fig. 1.
Each part of the 3D-refleclograms along an axis of longitudinal coordinate z is the fiber reflectograms of some current frequency in view: of BS in OF.
Each section along a frequencies axis (z = const) is SBS structure in this fiber section. Arrows designate changes SBS along OF (coordinate z).
The peak (maximum) of SBS for the set coordinate line is displayed in the right bottom comer, and also the characteristic of the SBS structure in given OF section is shown.
BS shift in the FOL
fx: «j quunu y
sr.flrt- i n O , 7QOOHK Sompl o i 1^/1? Sfcon t iO . HPOOHx Rwnnn i IOMIIt;
Fig. 1. BOTDR 3D-reHectograms (SBS distribution) along the fiber, which is located in laid OC with length about 80 km
• 6N
OF1 I 1 (INT of: \ OF 3 TON
100. o
MHz/
D.S. Width
| J
±. o
dB/
Bistnucc: 1. Q 6 O K m Distance Seile: O.Ol km/
Frequency: 10.640GHz Pre(]uency Scale: 100 MHz/
Lange : Skm IOR : 1. 46810
F.W. : ]Ons
Ava. 1 2^11 Ras. I 0. 20m
Frequency Start: 10. 420GHz Sa^file: 46/50 Stop : 11.400GHZ Sweep : 20HHi
Fig. 6. Multi-reflectograms forNZPSF (G.655) at longitudinal stretching force 6 N
f, GHz (peak SBS)
>**
G.652 (1^- * G.i • 2 *
.0 »52 (2) *
» 3
J** * ** ♦ F. N
0 OJ 1 1JJ 2 IJ J JJ 4 i
rig. 7, Dependence of maximum (peak) SBS frequency from longitudinal tensile force
S trail t, % (°/! »= 104 US) i
G .652 (1 i 2 .....
ft ..... G.652 (2) J •
-1 ..... » •
1 ..... • F, N
0 OS J 1,5 2 2.5 3 3.5 4
Fig. 8. Dependence of fiber strain from longitudinal tensile force
Comparing the OF SBS-proftles, which shown in Fig. i -Fig. 6, except for the main peak, designated by large arrow, which is observed in G.652 in Fig. 1, there are additional 2 small peaks, although not explicitly expressed, as in DSF |9, 10]. (The SBS-profileS of DSF have three "humps", separated by two minimums [10].)
The peak of SBS (JB) is shifted to the frequency 10.96 GHz at longitudinal stretching force 6 N on NZDSF section.
Analysis of NZDSF strain leads to such results.
NZDSF under normal conditions (without stretching at room temperature) has a negative strain -0.39%. The strain of G.652 (0F1) is -0.06% (SBS maximum (/¿) is at the frequency 10.83 GHz) at the same time and the same conditions.
If the NZDSF exposed to longitudinal stretching force, the strain increased to -0.29% at the force 1 N and reached level of +0.21% at force 6 N,
The experiments with DSF [9, 10| show that the strain of the DSF in normal conditions (at room temperature without stretching) has an even larger displacement of the SBS peak to smaller frequencies. The estimation on the first maximum gives an even greater removal of the strain in the negative side, compared to NZDSF (0.4% compared to NZDSF and 0.8% compared to G.652).
The linear dependence displaced downwards concerning usual fiher (G.652) oil 0.4 % is observed at changes of longitudinal tensile loadings.
The received dependence of SBS peak frequency from longitudinal tensile force value is presented in Fig, 7.
The corresponding graph of the strain is shown in Fig. 8.
The received experimental results have qualitative similarity to the results presented in |9 - 12].
The strain control of fibers in ready OC by manufacture should he spent phase methods as access by both ends OF in this case is possible, but BOTDR does not find out dangerous fibers strain because of protective elements of OC.
Because of strong protective elements of cable, which protect it and all fibers inside OC against mechanical damages, BOTDR have not discovered "problem" sections of fibers in OC until the critical levels of stretching forces (about 11-12 kN), which lead to destruction of OC [7].
An analysis of the experimental data received by phase methods has shown, these methods allow to find out occurrence of fibers strain at tensile force less than 10 kN, which yet does not lead to destruction of OC so, it is possible to find the "problem" place and eliminate dangerous influences [8, 9].
The received results have confirmed an opportunity of detection of mechanically stressed (strained) sections and estimations of strain fiber degree on the basis of SBS analysis at various tensile forces. Thus BOTDR it is connected only to one of FOL ends that is its important advantage, in comparison with other methods.
The NZDSF according to the characteristics of SBS and strain occupies an intermediate position between the usual OF (G.652) and DSF (G.653).
References
1. Bogachkov I. V.. Gorlov N.I. Components of fiber optic communication systems and methods of their parameters control. - Omsk: Publishing house OmSTU, 2013. 192 p. (In Russian)
2. Bogachkov I. V.. Gorlov N.I. Designing, construction and technical operation of fiber-optical communication lines. Vol. I - Vol. 5 -Omsk: Publishing house OmSTU, 2013 -2015 (/« Russian}
3. Listvin A. V., List\'in KN, Reflectometry of optical Fibers for communication lines, M: L.ESARart. 2005, 208 p. (In Russian)
4. Bogachkov I,K, Ovchinnikov S.V., Gorlov N.I. Accuracy Enhancement of Distributed Irregularities; Estimation in Optical Fiber // IEEE 2012 1! ih International Conference on Actual Problems of Electronic Instrument Engineering Proceedings. Vol. I, P. 60-62.
5. Bogachkov I.V.. Ovchinnikov S.V., Maistrenko V.A. Applying of Brillouin Scatter Spectrum Analysis for Detection of Distributed Irregularities in Optic Fibers and Estimation of Irregularities Parameters II International Siberian Conference oil Control and Communications (SIBCON) 2013, Proceedings, Krasnoyarsk: Siberian Federal University, 2013, Pp. 1-3.
6. Bogachkov I. V.. Maistrenko V.A. The Modeling of the Brillouin Backscaltering for Searching of Mechanical Strained Places in Optical Fibers // International Siberian Conference on Control and Communications (SIBCON) 2015. Omsk, 2015. Pp. 1-5.
7. Bogachkov I.V., Gorlov N.I. Experimental Examination of the Strain Characteristics of Optical Fibers // IFFE 2014 12th International Conference on Actual Problems of Electronic Instrument Engineering Proceedings, -Novosibirsk, 2014, Vol. 1, Pp. 223-227.
8. Bogachkov IV.. Maistrenko V.A. Experimental examinations of changes influence of the Brillouin backscattering spectrum in optical fibers on their characteristics II Dynamics of Systems, Mechanisms and Machines, Dynamics 2014. Proceedings. Omsk, 2014, Pp. 1-10,
9. Bogachkov I. V. Researching of Influence of the Strain Degree of Optical Fibers on the Brillouin Backscattering Characteristics // International Siberian Conference on Control and Communications (SIBCON) 2015. Omsk, 2015. Pp. 1-6.
10. Bogachkov I. V. Researching of features of the Brillouin Back-scattcring Spectrum in Dispersion-Shifted Optical Fibers // International Siberian Conference on Control and Communications (SIBCON) 2016. M.: 2016. Pp. 1-6.
11. Bel a! M, New son TP. Experimental Examination of the Variation of the Spontaneous Brillouin Power and Frequency Coefficients Under the Combined Influence of Temperature and Strain // Journal of Lightwave Technology, 2012. Vol. 30. No. 8. Pp. 1250-1255.
12. BOTDR Measurement Techniques and Brillouin Backscatter Characterisiics of Corning Single-Mode Optical Fibers // hi i p: //ww w.corning.com/media/world wide/coc/d ocuments/Fi ber/RC-%20Whiie%20Papers/WP-General/WP4259_01-l 5.pdf.
ОБНАРУЖЕНИЕ НАТЯЖЁННЫХ УЧАСТКОВ В ОПТИЧЕСКИХ ВОЛОКНАХ НА ОСНОВЕ МЕТОДА БРИЛЛЮЭНОВСКОЙ РЕФЛЕКТОМЕТРИИ
Богачков Игорь Викторович, к. т. н., доцент, Доцент кафедры "Средства связи и информационная безопасность" ("ССИБ"), ФГБОУ ВПО "Омский государственный технический университет" (ОмГТУ), г. Омск, Россия,
bogachkov@mail.ru
Аннотация
Представлены результаты экспериментальных исследований характеристик натяжения (продольных растягивающих механических нагрузок) в оптических волокнах с различными дисперсионными характеристиками на основе анализа спектра рассеяния Мандельштама - Бриллюэна (бриллюэновского рассеяния). Важной задачей мониторинга и ранней диагностики волоконно-оптических линий связи (ВОЛС) является получение достоверной информации о физическом состоянии (натяжение, температура) оптических волокон в оптических кабелях. Обычные оптические импульсные рефлектометры (OTDR) не в состоянии определить натяжение волокон. Для обнаружения механически напряженных участков ВОЛС (натяжения оптических волокон) применяются бриллюэновские оптические рефлектометры (BOTDR). Обсуждаются характеристики обычных одномодовых оптических волокон (G.652), волокон со смещённой дисперсией (DSF - G.653) и волокон c ненулевой смещённой дисперсией (NZDSF - G.655). Представлены рефлектограммы спектра бриллюэновского рассеяния (СБР) и бриллюэновского сдвига частоты и соответствующие графики натяжения этих разновидностей волокон, полученные в экспериментах. Исследования показали, что NZDSF по характеристикам СБР и натяжения занимает промежуточное положение между обычными одномодовыми оптическими волокнами (G.652D) и DSF (G.653). Полученные результаты подтвердили возможность обнаружения механически напряженных участков и оценки степени натяжения оптических волокон на основании анализа СБР при различных растягивающих нагрузках. При этом BOTDR подключается только к одному из концов ВОЛС, что является его важным достоинством, по сравнению с другими методами. Контроль натяжений оптических волокон в готовых оптических кабелях при производстве следует проводить фазовыми методами, так как в этом случае возможен доступ к обоим концам волокон, а BOTDR не обнаруживает опасного натяжения ОВ из-за защитных элементов кабелей.
Ключевые слова: бриллюэновская рефлектометрия, ранняя диагностика, бриллюэновское рассеяние, натяжение, смещённая дисперсия, оптоволокно.
Литература
1. Богачков И.В., Горлов Н.И. Методы и средства мониторинга и ранней диагностики волоконно-оптических линий передачи: монография. Омск: Изд-во ОмГТУ, 2013. 192 с.
2. Богачков И.В., Горлов Н.И. Проектирование, строительство и техническая эксплуата-ция волоконно-оптических линий передачи: учеб. пособие: в 5 ч. Омск: Изд-во ОмГТУ, 2013-2015.
3. Листвин А.В., Листвин В.Н. Рефлектометрия оптических волокон связи. М.: ЛЕСА-Рарт, 2005. 208 с.
4. Bogachkov I.V., Ovchinnikov S.V., Gorlov N.I. Accuracy Enhancement of Distributed Irregu-larities Estimation in Optical Fiber // IEEE 2012 11th International Conference on Actual Problems of Electronic Instrument Engineering Proceedings. Vol. 1. Pp. 60-62.
5. Bogachkov I.V., Ovchinnikov S.V., Maistrenko V.A. Applying of Brillouin Scatter Spectrum Analysis for Detection of Distributed Irregularities in Optic Fibers and Estimation of Irregularities Parameters // International Siberian Conference on Control and Communications (SIBCON) 2013. Proceedings. - Krasnoyarsk: Siberian Federal University, 2013. Pp. 1-3.
6. Bogachkov I.V., Maistrenko V. A. The Modeling of the Brillouin Backscattering for Searching of Mechanical Strained Places in Optical Fibers // International Siberian Conference on Control and Communications (SIBCON) 2015. Omsk, 2015. Pp. 1-5.
7. Bogachkov I.V., Gorlov N.I. Experimental Examination of the Strain Characteristics of Optical Fibers // IEEE 2014 12th International Conference on Actual Problems of Electronic Instrument Engineering Proceedings. - Novosibirsk, 2014. Vol. 1. Pp. 223-227.
8. Bogachkov I.V., Maistrenko V.A. Experimental examinations of changes influence of the Brillouin backscattering spectrum in optical fibers on their characteristics // Dynamics of Systems, Mechanisms and Machines, Dynamics 2014. Proceedings. Omsk, 2014. Pp. 1-10.
9. Bogachkov I.V. Researching of Influence of the Strain Degree of Optical Fibers on the Bril-louin Backscattering Characteristics // International Siberian Conference on Control and Commu-nications (SIBCON) 2015. Omsk, 2015. Pp. 1-6.
10. Bogachkov I.V. Researching of features of the Brillouin Backscattering Spectrum in Disper-sion-Shifted Optical Fibers // International Siberian Conference on Control and Communications (SIBCON) 2016. M. 2016. Pp. 1-6.
11. Belal M., Newson T.P. Experimental Examination of the Variation of the Spontaneous Bril-louin Power and Frequency Coefficients Under the Combined Influence of Temperature and Strain // Journal of Lightwave Technology, 2012, vol. 30, no. 8. Pp. 1250-1255.
12. BOTDR Measurement Techniques and Brillouin Backscatter Characteristics of Corning Sin-gle-Mode Optical Fibers // http://www.corning.com/media/worldwide/coc/documents/Fiber/RC-%20White%20Papers/WP-General/WP4259_0l-l5.pdf.
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