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STIMULATED BRILLOUIN-BASED SCATTERING, FAST SPEED ... · There was a case of repair job for a...
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Copyright © 2010 SubOptic Page 1 of 8 conference & convention enabling the next generation of networks & services STIMULATED BRILLOUIN-BASED SCATTERING, FAST SPEED DETECTION, ANALYSIS ON REAL APPLICATION DURING MALFUNCTION IN SUBMARINE OPTICAL CABLE Zai QingHua ([email protected] ) ZTT Submarine Cable Co., Ltd. Nantong, Jiangsu 226010 Dr Shen YiChun ([email protected] ) International Electromagnetism Institute, Zhejiang University Branch ZTT-Zhejiang University, Joint Laboratory, Hangzhou Zhejiang Abstract: the passage put forward a measurement on BOTDR against malfunction in submarine cable during test. Key Words: Brillouin-based Scattering, Malfunction point and Measurement. INTRODUCTION Following China strategic development in the oceanic economy, it has lay in recent year and plans to lie in near future greater lengths of Submarine Optical Fiber Cable and Submarine Optical-Fiber Composite Power Cable for both transmission of communication and power signal. In submarine cable repair process, the key technique lies in the measuring and locating of malfunction point(s), especially in the precise location in a sea water environment. General methods in locating malfunction point of submarine cable include; OTDR measuring, voltage tests, capacitance tests, audio frequency and supervising system testing. There was a case of repair job for a Submarine Optical-Fiber Composite Power Cable, where the cable integrity is good but optical fiber damaged and needing repair. Under circumstances, the general testing method for voltage test, capacitance, audio- frequency and line supervising cannot be used and where OTDR machine is only able to show the length of breaking point. It is hard to precisely locate the malfunction position. As such, fast and precise locating of malfunction position has become the primary issue in cable repair engineering. This passage has thus fast forwarded the process of determining of SOFC and SPC malfunction point base on stimulated Brillouin-based scattering theory. Basing on this theory, ZTT and Zhejiang University’s joint laboratory developed ZTT_BR, a set of high intelligent test instrument used for pin pointing the position of malfunction of SOFC. The ZTT_BR produces excellent result when used for experiment in real application. THEORY ANALYSIS
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STIMULATED BRILLOUIN-BASED SCATTERING, FAST SPEED
DETECTION, ANALYSIS ON REAL APPLICATION DURING MALFUNCTION IN SUBMARINE OPTICAL CABLE
Zai QingHua ([email protected]) ZTT Submarine Cable Co., Ltd. Nantong, Jiangsu 226010 Dr Shen YiChun ([email protected]) International Electromagnetism Institute, Zhejiang University Branch ZTT-Zhejiang University, Joint Laboratory, Hangzhou Zhejiang Abstract: the passage put forward a measurement on BOTDR against malfunction in submarine cable during test. Key Words: Brillouin-based Scattering, Malfunction point and Measurement. INTRODUCTION
Following China strategic development in the oceanic economy, it has lay in recent year and plans to lie in near future greater lengths of Submarine Optical Fiber Cable and Submarine Optical-Fiber Composite Power Cable for both transmission of communication and power signal.
In submarine cable repair process, the key technique lies in the measuring and locating of malfunction point(s), especially in the precise location in a sea water environment. General methods in locating malfunction point of submarine cable include; OTDR measuring, voltage tests, capacitance tests, audio frequency and supervising system testing.
There was a case of repair job for a Submarine Optical-Fiber Composite Power Cable, where the cable integrity is good but optical fiber damaged and needing repair. Under circumstances, the general testing method for voltage test, capacitance, audio-frequency and line supervising cannot be used and where OTDR machine is only able to show the length of breaking point. It is hard to precisely locate the malfunction position. As such, fast and precise locating of malfunction position has become the primary issue in cable repair engineering. This passage has thus fast forwarded the process of determining of SOFC and SPC malfunction point base on stimulated Brillouin-based scattering theory.
Basing on this theory, ZTT and Zhejiang University’s joint laboratory developed ZTT_BR, a set of high intelligent test instrument used for pin pointing the position of malfunction of SOFC. The ZTT_BR produces excellent result when used for experiment in real application.
THEORY ANALYSIS
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The accuracy of measurement, range and spatial resolution achieved on temperature and strain measurements from distribution of Brillouin-base scattering sensing technology is higher than that of the fiber optic distribution sensing technology. Including those of Rayleigh-base scattering and Raman-base scattering; they too, have captured mass attention. A large number of theoretical and experimental studies have proven that the fiber of Brillouin-base scattering, signals power and optical fiber in which the ambient temperature and strain are borne by certain conditions. A linear relationship between changes in fiber and the signaling power of Brillouin-base scattering study is important. Stimulated Brillouin-base scattering in fiber is called the pump-wave. Stokes-Wave functions through non-linear acoustic effect. Pump waves generate sound waves through electrostriction and medium refractive index caused by the periodic modulation. Pump induced refractive index grating through the pump-wave Bragg diffraction, resulting in frequency down the Stokes-Wave. Optical fiber Brillouin-base scattering process is pumping-wave and stokes-wave carried out by non-linear interaction of sound waves. It is used to describe the process of Brillouin-base scattering parameter mathematical model of the classic characteristics of the three coupled amplitude equations. However, in a continuous pump, or quasi-continuous pumping conditions and on assumption of acoustic Brillouin-base scattering, the attenuate process shall quicken. Three coupled equations can be simplified under the condition of coupling strength for the steady-state equation:
SspBs IIIvg
dzdI
α+Δ−= )( (1)
pspBp IIIvg
dzdI
α−Δ−= )( (2)
On equation， sI is Stokes optical density， pI is pump optical density，α is optical
fiber attenuation， Bg is Brillouin gain coefficient，That is:
22
2
0 )2/()2/()(
B
BB vv
vgvgΔ+Δ
Δ=Δ
γ (3)
On equation γ is side amplitude coefficient，general single mode optical fiber value is
2/3［6］， BvΔ is Brillouin Gain bandwidth
Bps vvvv −−=Δ )( (4)
On equation， sv is Stokes optical frequency， pv is pump optical frequency， Bv is
Brillouin frequency shift，the value λAB nVv 2= ， n is optical fiber refractive index，AV is acoustics Speed, λ is
pump wave length in optic fiber.
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Peak gain coefficient 0g is ：
BAp vVcpn
gΔ
=0
2
212
7
02ρλπ (5)
On equation 0ρ is material density， 12p is material longitudinal elastic-optic coefficient. If power to describe Brillouin scattering coupled equation, equation (1), (2) can turn into
：
sspeff
Bs PPPAg
dzdP
α+−= (6)
(7)
On equation effA is optic fiber effective cross-section ， pP is pump power ，
Value effpp AIP =， sP is stokes power，the value effss AIP =
。 Considering optical fiber and pump loss, equation (6) & (7) has no analytical
solution，the calculation is to be completed by numerical solution. It is first order ordinary differential equation system. Given border incident pump power )0(pP and end
of stokes optical power )(LPs ， Such border conditions cannot make solution by ordinary differential equation system.
But if we know the boundary condition z=0 or boundary condition at the same time when z=L, we may resolute the coupled equation. Therefore, we assume z=0，another
boundary condition )0(sP is given with initial value, for a given step size h, using fourth-order classical Runge-Kutta method along the optical fiber prior to the points for equation (6) and equation (7)，so that the fiber end at z=L, we can calculate the
Stokes power )(' LPs .When in comparison with the given border )(LPs and
iterate )0(sP until the difference to meet the requirement, then the )0(sP can be derived thus solving equation (6) & (7).
It should be noted that the distribution sensing technology of Brillouin-base scattering often concerns the temperature and strain changes for a certain segment of fiber. Thus, when solving equation we often refine the step size nearer a certain segment of fiber. As a result, it makes the differential value of ‘e’ smaller to improve the calculation accuracy as well as to determine the power distribution in the vicinity of the segment. For the other section of fiber, we may take the bigger step size and lower precision in order to reduce the amounts of calculation and improving of speed in computing.
In summary, Brillouin-base scattering, ZTT_BR can detect changes of continuous temperature and strain. Any rise in optical fiber temperature and strain of fiber change, ZTT_BR acts quickly to pin-point the precise fault location. A single terminal measurement is only required to realize its convenience through using the spontaneous Brillouin-base scattering.
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2 EXPERIMENT VERIFICATION 2.1 Changes of bare fiber temperature influence on strain-change
Method description: using 1km ~ 2km of long bare optical fiber and by part heating to a certain point. Observe strain changes of the point through using ZTT_BR. Determine the distance from the point to terminal of fiber and realize the position of heating point. Process of experiment: When ambient temperature is 22℃, making use of test device as shown in chart 1, Connect ZTT_BR and fiber tray, heating certain point to the tail of fiber. The relation between temperature and strain can be observed.
Chart 1：Fiber Temperature and Strain Change test device
Experiment Phenomenon：show as Chart 2（a）strain change without heating（b）strain change with heating on 33℃ temperature。
（a） (b) Chart 2 Optical Fiber Temperature～Strain Change test drawing
Experiment conclusion: when fiber rises 11℃，distinct strain change can be seen, and heating point of fiber may be determined.
2.2 Temperature change of optical fiber influence on strain change
Method Description: Taking a 10m long cable with both ends of optical fiber in fusion and applies heat at any one point of the cable with ZTT_BR strain and observes the change at that point. Testing process: At ambient temperature conditions of 22℃ and using the experimental device shown in Chart 3, connect ZTT_BR with the fiber optic tray and then optical fiber with test optic cable A and B segment , heat any one point of the cable to observe the temperature and strain change relationship.
heating
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Chart 3：Testing device on cable temperature and strain change
Test phenomenon: show as Chart 4（a）non-heating strain change drawing（b）heating point under 38℃ influence on strain change drawing.
（a） (b) Chart 4 Optical Cable temperature～Strain Change test drawing
Test Results: when fiber optic temperature raises 16℃, we can see distinct changes in response to identified heating point in the cable. Combination of the above tests and accurate locating of heating point is possible through ZTT_BR measurement.
3 APPLICATION CASES 3.1 Submarine Optical Composite Power Cable structure in Chart 5 shows the use of the optical fiber signal to control equipment operation of the power station at both ends. The electric cable section supplies the DC power.
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Chart 5：optical composite power cable structure
3.2 Malfunction point locating process： 3.2.1 Malfunction locating point test shown as Chart 6；
Chart 6：Malfunction point location test
Measuring optical fiber length with ZTT_BR to first determine malfunction point of optical fiber with data information.
Based on data information and maintenance vessel to locate malfunction vicinity point
(closer to test side), as close as possible for convenience.
Salvaging of submarine cable, heating certain segment of cable to 70～80℃, apply test by ZTT_BR to find the heating point. Determine the displacement distance of maintenance vessel according to the distance between heating point and optical fiber breaking point. Salvage cable base on the malfunction point.
If random point test is not accurate, and no heating point is located. Then shift the
maintenance vessel to different position of test side to repeat the above step.
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3.2.2 Test data shown as chart 7： (a) Submarine cable strain change with non-heating in the vicinity of landing point；(b) strain change with heating point of induct optical cable；(c) strain change with heating point of submarine cable.
（a）
(a)
(b) (c) Chart 7 Strain Change Test
4 Conclusions
Above method suggest malfunction locating technology for submarine optical-fiber composite power cable with Brillouin-base scattering test. Theoretically, it analyses Brillouin-base scattering test mode and undertakes experimental research. At the same time, based on Brillouin scattering test theory, ZTT-Zhejiang university jointly developed ZTT_BR, a set of overall intelligence testing instrument. ZTT takes experimental research and actual engineering application upon the instrument to achieve perfect effects. Evidently, it shortens construction term, improves project efficiency, greatly decreases human resources for maintenances and reduces material costs.
.
Heating 热加 点 heating
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Reference Documents
[1] 1，Shenyichun, Songmouping, Zhangxianming. long distance optical fiber Brillouin scattering research [J]. optics paper, 33(8):931-934, August 2004.
[2] Shen, Y.C., Zhang, X. M. and Chen, K. S. Optical single sideband modulation of 11GHz RoF system using stimulated Brillouin-base scattering [J]. IEEE Photonics Technology Letters, 17(6):1277-1279, June 2005.
[3] Shen, Y.C., Zhang, X. M. and Chen, K. S. All-optical generation of microwave/ millimeter-wave using a two-frequency Bragg grating based Brillouin fiber laser [J]. IEEE Journal of Lightwave Technology, 23(5):1860-1865, May 2005.
[4] Shen, Y.C., Zhang, X. M., Shen, G. F. and Chen, K. S. Microwave photonic signals conversion using stimulated Brillouin scattering [J]. Optics Communications, 249(1-3):109-115, May 2005.
[5] Chen L, Bao X, Analytical and Numerical solutions for steady state stimulated Brillouin-base scattering in a single-mode fiber. Opt. Commun., 1998, 152(6): 65-70.
