STIMULATED BRILLOUIN-BASED SCATTERING, FAST SPEED DETECTION, ANALYSIS ON REAL APPLICATION DURING MALFUNCTION IN SUBMARINE OPTICAL CABLE

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1 STIMULATED RILLOUIN-ASED SCATTERING, FAST SPEED DETECTION, ANALYSIS ON REAL APPLICATION DURING MALFUNCTION IN SUMARINE OPTICAL CALE Zai QingHua ZTT Submarine Cable Co., Ltd. Nantong, Jiangu Dr Shen YiChun International Electromagnetim Intitute, Zhejiang Univerity ranch ZTT-Zhejiang Univerity, Joint Laboratory, Hangzhou Zhejiang Abtract: the aage ut forward a meaurement on OTDR againt malfunction in ubmarine cable during tet. Key Word: rillouin-baed Scattering, Malfunction oint and Meaurement. INTRODUCTION Following China trategic develoment in the oceanic economy, it ha lay in recent year and lan to lie in near future greater length of Submarine Otical Fiber Cable and Submarine Otical-Fiber Comoite Power Cable for both tranmiion of communication and ower ignal. In ubmarine cable reair roce, the key technique lie in the meauring and locating of malfunction oint(), eecially in the recie location in a ea water environment. General method in locating malfunction oint of ubmarine cable include; OTDR meauring, voltage tet, caacitance tet, audio frequency and uerviing ytem teting. There wa a cae of reair job for a Submarine Otical-Fiber Comoite Power Cable, where the cable integrity i good but otical fiber damaged and needing reair. Under circumtance, the general teting method for voltage tet, caacitance, audiofrequency and line uerviing cannot be ued and where OTDR machine i only able to how the length of breaking oint. It i hard to reciely locate the malfunction oition. A uch, fat and recie locating of malfunction oition ha become the rimary iue in cable reair engineering. Thi aage ha thu fat forwarded the roce of determining of SOFC and SPC malfunction oint bae on timulated rillouin-baed cattering theory. aing on thi theory, ZTT and Zhejiang Univerity joint laboratory develoed ZTT_R, a et of high intelligent tet intrument ued for in ointing the oition of malfunction of SOFC. The ZTT_R roduce excellent reult when ued for exeriment in real alication. THEORY ANALYSIS Coyright 2010 SubOtic Page 1 of 8

2 The accuracy of meaurement, range and atial reolution achieved on temerature and train meaurement from ditribution of rillouin-bae cattering ening technology i higher than that of the fiber otic ditribution ening technology. Including thoe of Rayleigh-bae cattering and Raman-bae cattering; they too, have catured ma attention. A large number of theoretical and exerimental tudie have roven that the fiber of rillouin-bae cattering, ignal ower and otical fiber in which the ambient temerature and train are borne by certain condition. A linear relationhi between change in fiber and the ignaling ower of rillouin-bae cattering tudy i imortant. Stimulated rillouin-bae cattering in fiber i called the um-wave. Stoke-Wave function through non-linear acoutic effect. Pum wave generate ound wave through electrotriction and medium refractive index caued by the eriodic modulation. Pum induced refractive index grating through the um-wave ragg diffraction, reulting in frequency down the Stoke-Wave. Otical fiber rillouin-bae cattering roce i uming-wave and toke-wave carried out by non-linear interaction of ound wave. It i ued to decribe the roce of rillouin-bae cattering arameter mathematical model of the claic characteritic of the three couled amlitude equation. However, in a continuou um, or quaicontinuou uming condition and on aumtion of acoutic rillouin-bae cattering, the attenuate roce hall quicken. Three couled equation can be imlified under the condition of couling trength for the teady-tate equation: di dz di dz = g ( Δv) I I + αi (1) S = g ( Δv) I I αi (2) On equation, I i Stoke otical denity, I i um otical denity,α i otical fiber attenuation, g i rillouin gain coefficient,that i: 2 γ ( Δv / 2) g ( Δv) = g Δv + ( Δv / 2) On equation γ i ide amlitude coefficient,general ingle mode otical fiber value i 2/3 [6], Δv i rillouin Gain bandwidth (3) Δ v = ( v v ) v (4) v v On equation, i Stoke otical frequency, i um otical frequency, v i rillouin frequency hift,the value v = 2nV A λ, n i otical fiber refractive index, VA i acoutic Seed, λ i um wave length in otic fiber. Coyright 2010 SubOtic Page 2 of 8

3 g Peak gain coefficient 0 i : g n 12 = cλ ρ V Δv 2 π (5) 0 A ρ On equation 0 i material denity, 12 i material longitudinal elatic-otic coefficient. If ower to decribe rillouin cattering couled equation, equation (1), (2) can turn into : dp g (6) = P P + αp dz A eff (7) A On equation eff i otic fiber effective cro-ection, P i um ower, P = I Aeff P P Value, i toke ower,the value = I Aeff Conidering otical fiber and um lo, equation (6) & (7) ha no analytical olution,the calculation i to be comleted by numerical olution. It i firt order ordinary differential equation ytem. Given border incident um ower P (0) and end P (L) of toke otical ower, Such border condition cannot make olution by ordinary differential equation ytem. ut if we know the boundary condition z=0 or boundary condition at the ame time when z=l, we may reolute the couled equation. Therefore, we aume z=0,another P (0) boundary condition i given with initial value, for a given te ize h, uing fourth-order claical Runge-Kutta method along the otical fiber rior to the oint for equation (6) and equation (7),o that the fiber end at z=l, we can calculate the ' P ( L) Stoke ower.when in comarion with the given border P (L) and P (0) iterate P (0) until the difference to meet the requirement, then the can be derived thu olving equation (6) & (7). It hould be noted that the ditribution ening technology of rillouin-bae cattering often concern the temerature and train change for a certain egment of fiber. Thu, when olving equation we often refine the te ize nearer a certain egment of fiber. A a reult, it make the differential value of e maller to imrove the calculation accuracy a well a to determine the ower ditribution in the vicinity of the egment. For the other ection of fiber, we may take the bigger te ize and lower reciion in order to reduce the amount of calculation and imroving of eed in comuting. In ummary, rillouin-bae cattering, ZTT_R can detect change of continuou temerature and train. Any rie in otical fiber temerature and train of fiber change, ZTT_R act quickly to in-oint the recie fault location. A ingle terminal meaurement i only required to realize it convenience through uing the ontaneou rillouin-bae cattering. Coyright 2010 SubOtic Page 3 of 8

4 2 EXPERIMENT VERIFICATION 2.1 Change of bare fiber temerature influence on train-change Method decrition: uing 1km ~ 2km of long bare otical fiber and by art heating to a certain oint. Oberve train change of the oint through uing ZTT_R. Determine the ditance from the oint to terminal of fiber and realize the oition of heating oint. Proce of exeriment: When ambient temerature i 22, making ue of tet device a hown in chart 1, Connect ZTT_R and fiber tray, heating certain oint to the tail of fiber. The relation between temerature and train can be oberved. Chart 1:Fiber Temerature and Strain Change tet device Exeriment Phenomenon:how a Chart 2(a)train change without heating(b)train change with heating on 33 temerature heating (a) (b) Chart 2 Otical Fiber Temerature~Strain Change tet drawing Exeriment concluion: when fiber rie 11,ditinct train change can be een, and heating oint of fiber may be determined. 2.2 Temerature change of otical fiber influence on train change Method Decrition: Taking a 10m long cable with both end of otical fiber in fuion and alie heat at any one oint of the cable with ZTT_R train and oberve the change at that oint. Teting roce: At ambient temerature condition of 22 and uing the exerimental device hown in Chart 3, connect ZTT_R with the fiber otic tray and then otical fiber with tet otic cable A and egment, heat any one oint of the cable to oberve the temerature and train change relationhi. Coyright 2010 SubOtic Page 4 of 8

5 Chart 3:Teting device on cable temerature and train change Tet henomenon: how a Chart 4(a)non-heating train change drawing(b) heating oint under 38 influence on train change drawing. (a) (b) Chart 4 Otical Cable temerature~strain Change tet drawing Tet Reult: when fiber otic temerature raie 16, we can ee ditinct change in reone to identified heating oint in the cable. Combination of the above tet and accurate locating of heating oint i oible through ZTT_R meaurement. 3 APPLICATION CASES 3.1 Submarine Otical Comoite Power Cable tructure in Chart 5 how the ue of the otical fiber ignal to control equiment oeration of the ower tation at both end. The electric cable ection ulie the DC ower. Coyright 2010 SubOtic Page 5 of 8

6 Chart 5:otical comoite ower cable tructure 3.2 Malfunction oint locating roce: Malfunction locating oint tet hown a Chart 6; Chart 6:Malfunction oint location tet Meauring otical fiber length with ZTT_R to firt determine malfunction oint of otical fiber with data information. aed on data information and maintenance veel to locate malfunction vicinity oint (cloer to tet ide), a cloe a oible for convenience. Salvaging of ubmarine cable, heating certain egment of cable to 70~80, aly tet by ZTT_R to find the heating oint. Determine the dilacement ditance of maintenance veel according to the ditance between heating oint and otical fiber breaking oint. Salvage cable bae on the malfunction oint. If random oint tet i not accurate, and no heating oint i located. Then hift the maintenance veel to different oition of tet ide to reeat the above te. Coyright 2010 SubOtic Page 6 of 8

7 3.2.2 Tet data hown a chart 7: (a) Submarine cable train change with non-heating in the vicinity of landing oint;(b) train change with heating oint of induct otical cable;(c) train change with heating oint of ubmarine cable. (a) 加 heating 热点 Heating (a) (b) (c) Chart 7 Strain Change Tet 4 Concluion Above method ugget malfunction locating technology for ubmarine otical-fiber comoite ower cable with rillouin-bae cattering tet. Theoretically, it analye rillouin-bae cattering tet mode and undertake exerimental reearch. At the ame time, baed on rillouin cattering tet theory, ZTT-Zhejiang univerity jointly develoed ZTT_R, a et of overall intelligence teting intrument. ZTT take exerimental reearch and actual engineering alication uon the intrument to achieve erfect effect. Evidently, it horten contruction term, imrove roject efficiency, greatly decreae human reource for maintenance and reduce material cot.. Coyright 2010 SubOtic Page 7 of 8

8 Reference Document [1] 1,Shenyichun, Songmouing, Zhangxianming. long ditance otical fiber rillouin cattering reearch [J]. otic aer, 33(8): , Augut [2] Shen, Y.C., Zhang, X. M. and Chen, K. S. Otical ingle ideband modulation of 11GHz RoF ytem uing timulated rillouin-bae cattering [J]. IEEE Photonic Technology Letter, 17(6): , June [3] Shen, Y.C., Zhang, X. M. and Chen, K. S. All-otical generation of microwave/ millimeter-wave uing a two-frequency ragg grating baed rillouin fiber laer [J]. IEEE Journal of Lightwave Technology, 23(5): , May [4] Shen, Y.C., Zhang, X. M., Shen, G. F. and Chen, K. S. Microwave hotonic ignal converion uing timulated rillouin cattering [J]. Otic Communication, 249(1-3): , May [5] Chen L, ao X, Analytical and Numerical olution for teady tate timulated rillouinbae cattering in a ingle-mode fiber. Ot. Commun., 1998, 152(6): Coyright 2010 SubOtic Page 8 of 8