THE RESEARCH ON DISPERSION CONTROL OF DISPERSION UNSHIFTED SINGLE-MODE OPTICAL FIBER

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1 Journal of Theoretical an Applie Information Technology 3 st March 03. Vol. 49 No JATIT & LLS. All rights reserve. ISSN: E-ISSN: THE RESEARCH ON DISPERSION CONTROL OF DISPERSION UNSHIFTED SINGLE-MODE OPTICAL FIBER XIANGJUN WANG Department of Water Conservancy an Architectural Engineering, Beijing Vocational College of Agriculture, Beijing, 044, China. xjlucky@sohu.com ABSTRACT The ispersion unshifte optical fiber is in favor of communications construction project, because of its mature manufacturing technique, low loss, large banwith, transmission istance, low engineering cost, the relate erivative proucts, easy realiation. In orer to pursue a better communication quality, ispersion control has become an important inex of engineering. In this paper, base on the characteristics of ispersion unshifte optical fiber, ispersion mechanism is analye on theory, an the methos of ispersion management technology are contraste. Keywors: Optical Fiber(OF, Dispersion Compensation(DC, Fiber Communication(FC. INTRODUCTION Optical fiber communication system is the use of electromagnetic wave which is visible light or high frequency near infrare region in electromagnetic spectrum. As the meium, the information is transmitte from one en to the other en of the communication system by optical fiber. With the eman of high spee, large capacity information system currently, that the establishment of greater capacity optical fiber communication systems has become the most important problem. The fiber loss an ispersion are two big bottleneck for optical fiber communication. At present, the compensation of fiber loss is relatively easy to solve by to increase amplification equipment to compensate for loss. Because the ispersion problem involves many factors, it is particularly important. Dispersion unshifte single-moe optical fiber is the most commonly use currently. An it can be accounte for more than / of the volume of all fiber use. Dispersion unshifte single-moe optical fiber has the avantages of low loss, large banwith, transmission istance, easy upgrae an low cost, so it can be wiely applie in high spee, long istance transmission of information. For example in the long-istance communication, metropolitan area network, wie area network, an park trunk network. It iscusse the non ispersion shift fiber ispersion control technology in this paper. The research results mainly comprises the following elements. The secon section analyses the non ispersion shift fiber characteristics an its ispersion control importance. The thir section iscusses non ispersion shift fiber ispersion calculation. The fourth section stuies two kins of commonly use methos of ispersion management eeply. The fifth section is the conclusion of the research.. DISPERSION UNSHIFTED SINGLE- MODE OPTICAL FIBER The optical signals has a certain frequency spectrum with in optical fiber transmission. In another wor, light signal has a number of ifferent frequency components. In the optical fiber transmission, ifferent frequencies or ifferent patterns of light signal (pulse is transmitte with ifferent velocity. When it reaches a certain istance to be separate. The phenomenon is calle the fiber ispersion or ispersion. Dispersion causes the pulse broaening, strength reuction, bit error rate increases, egraation of communication quality. Especially for the long istance igital communication system, it is particularly serious, an bit error rate is increase to limit the transmission banwith. Dispersion unshifte single-moe optical fiber has two winows of 30nm an 550nm.The minimum attenuation is locate in the 550nm winow, an ero ispersion point locate 30nm winow. The winow of 550nm has large ispersion, an the maximum ispersion coefficient 93

2 Journal of Theoretical an Applie Information Technology 3 st March 03. Vol. 49 No JATIT & LLS. All rights reserve. ISSN: E-ISSN: is up to 8ps (nm km. Specific parameters is shown in Table. In 550nm the ban ispersion is large, from long-term consieration, it puts forwar higher requirements to ensure greater banwith an request communication system can work in a wie ban. Table : Attenuation Coefficient An Dispersion Properties Of Dispersion Unshifte Single-Moe Optical Fiber Attenuation Coefficient An Dispersion Properties Project Technical Specifications Grae A Grae B Grae C 30nm Maximum attenuation coefficient,b/km nm Maximum attenuation coefficient,b/km xx nm Maximum attenuation coefficient,b/km Zero ispersion wavelength range,nm 300~34 88~339nm The maximum absolute value 3.5 of the ispersion coefficient,ps/(nm km Dispersion 7~360nm The maximum absolute value characteristics 5.3 of the ispersion coefficient,ps/(nm km 550 The maximum absolute value of the ispersion coefficient,ps/(nm km 8 Polariing film ispersion(pmdcoefficient maximum,ps/ km 0.3 In G.65 coefficient inex PMD was not specifie. The type optical fiber, requirements: M(cable segment number=0,q(probability=0.0%,pmdq(link PMD coefficient esign value=0.5ps/ km The ispersion properties of ispersion unshifte single-moe optical fiber is showe in Figure. Dispersion System ps/(nm km Minimum loss point Zero ispersion point Wavelength (nm Figure.: The Dispersion Properties Of Dispersion Unshifte Single-Moe Optical Fiber 3. DISPERSION CALCULATION OF DISPERSION UNSHIFTED SINGLE-MODE OPTICAL FIBER In orer to obtain minimum loss an better banwith, 550nm wavelength ispersive research becomes very important in ispersion unshifte single-moe optical fiber. The ispersion unshifte single-moe optical fiber of 550nm ispersion can be expresse as : ( λ t( + + t = t( λ0 + λ 0 ( λ λ Where, λ is pulse center wavelength, is 0 λ 0 the spectral with, t is ispersion with, t ( λ0 =L/ υλ ( 0,Where, L is length of the link, is the light to transmit the group velocity 0 λ. 0 υλ ( It also can be expresse as: λ ( λ LD( + + t = λld( λ0 + λ0 ( Where First orer ispersion parameter 94

3 Journal of Theoretical an Applie Information Technology 3 st March 03. Vol. 49 No JATIT & LLS. All rights reserve. ISSN: E-ISSN: D( λ0 = λ ( υλ0 λ= λ0 (3 D'( λ0 = [ D( λ ] λ= λ0 λ (4 In 550nm winow,d 6 ps/(nm km,d 0.06ps/(nm km 4. DISPERSION MANAGEMENT APPROACH In the optical fiber communication system, information is encoe in the sequence of light pulses through the optical fiber communication. The optical pulse with is ecie by the bit rate B. The guarantee banwith cases, there may be pulse ispersion inuce pulse broaening, namely it is extene to a specifie bit slot (TB=/B. So it will interference etection an error coe. In long-istance communication lines, a ispersion shifte fiber ispersion value becomes larger. For the fixe transmission istance is L, an the group velocity ispersion (GVD will limit the bit rate B, for information transmission capacity of a useful measure is the prouct BL by bit rate an istance. In the actual use of GVD control, which will influence the system esign. It will bring new ispersion problems. For example in wavelength ivision multiplexing (WDM system, on the optical fiber ero-ispersion wavelength, it will arrange a maximum of one channel, which will effect banwith eman. In orer to pursue the GVD minimum, it also will appear very strong four wave mixing phenomenon an so on. In long istance propagation, it will generate a combination of two orer intermoulation CSO eterioration an so on. There are several ispersion compensation metho to stuy. 4. The ispersion compensation fiber for ispersion compensation Non ispersion isplacement optical fiber an ispersion compensating optical fiber are connecte for use. At the noes is use alternately as a communication meium. Dispersion compensation fiber in 550nm ispersion value is negative, an with the ispersion shift fiber is opposite, to be use for ispersion compensation by single moe optical fiber ispersion compensation. For the two segments of the fiber composition of the ispersion map, an the normalie amplitue U can use the following equation: i U( Lm, t = U(0, ωexp ω ( βl βl iωt ω π + (5 Where, ω is resonant frequency, β is moe propagation constant, Lm = L+ L is ispersion β iagram cycle, j L is the length of j GVD parameters(j=, First orer ispersion is D j = ( c/ π λ β j (6 The ispersion compensation conition can be written as: DL + DL = 0. As long as it s establishe, it will restore to its initial pulse with after each cycle. If the two segments of the fiber length is the same as GVD, an is opposite in sign. For the optical system has been built, it can choose a relatively short ispersion compensating fiber (DCF in orer to upgrae. The system implementation metho is shown in Figure. Pin PO PO EDFA EDFA L L EDFA DCF Figure : DCF Dispersion Compensation System In the long istance 550nm non-ispersion isplacement optical fiber transmission system, the focus of the stuy is choosing optimum length of two orer intermoulation CSO minimum ispersion compensating fiber. Accoring to the nonlinear Schröinger equation, we get the CSO. λ CSO = mω P D e + πc + D [ Pγ ( e + ( 0lg[ { 0γ 0 ( + Pγ e ]}] + 0log( Ncso (7 Where, P 0 is the fiber optical power of main communication lines, P is input optical power of DCF, D is ispersion constant, γ is nonlinear coefficient, is loss constant, is the length of DCF, Ω is channel angular frequency, NCSO is two orer parameter. 95

4 Journal of Theoretical an Applie Information Technology 3 st March 03. Vol. 49 No JATIT & LLS. All rights reserve. ISSN: E-ISSN: perioic linear change smaller. An it oes not have P0 γd ( e + + D [ ( Pγ e + + a high nonlinear, so this is the biggest isavantage of the ispersion compensation fiber. Chirp grating 0 ( Pγ e ] = 0 (8 has compensation ability, low cost, mature technology, an the optical fiber link upgrae When (8 is establishe, CSO can be eliminate. easily. Along with the evelopment of In orer to meet the conitions, the length of communication network transmission as well as the ispersion compensating fiber has a ecisive application of ense wavelength ivision influence. When = 0, it has no ispersion multiplexing, fiber chirp grating has showe its compensation; is smaller, it is less ispersion large ispersion, such as high reflectivity, broa compensation; is larger, it is ispersion reflection banwith an other unique avantages. When the bit rate is 0Gbit/s, the system of compensation. Therefore, is moerate, which are ispersion tolerance capacity is become from 450ps equal to full ispersion compensation. CSO will be to 60ps. In the ense wavelength ivision ero in theory, an the actual ata is minimum. multiplexing system, chirp fiber gratings can be Take non- ispersion isplacement optical fiber an conveniently on various channels of precise ispersion fiber ata for calculation, the ata is ispersion compensation. In orer to obtain a better shown in Table. The length relation of COS an network effect, chirp fiber grating ispersion DCF is shown in Figure 4. It can be seen from the compensation moule an EDFA are place apart, graph, when the DCF is -0ps/ nm /km, the an the position of DCM can be arbitrarily optimum length of ispersion compensation fiber is change. As shown in figure 4. slightly less than the /0 of non-ispersion shift fiber length. Non ispersion shift fiber(=5km Table : Optical Fiber Data Dispersion compensation fiber P 0 8Bm P 4Bm γ / W /m γ / W /m D 7ps/ nm /km D -0ps/ nm /km 0.5B/km 0.5B/km 4. Dispersion compensation with chirp fiber grating The fiber chirp grating for ispersion compensation is base on fiber prague grating technology. The ispersion compensation fiber grating cycle is chirp or along the fiber irection of Figure 3: The CSO An DCF Length Relationship Figure4: Chirp Fiber Grating Dispersion Compensation System The DCM can be seen as a special fiber which has great ispersion. Because the length is small, its amage an nonlinear is negligible. The output en CSO of long istance optical fiber system is as follows: λ CSO= 0lg{ mpω [ DSL [ ( + ( e SL ( ] M ( j j 0γ π c j= k ( j j g eff eff j CSO j= + D [ L ( + ( e L ( ] } + 0log( N (9 Where, L is fiber length; M- is total number of EDFA; K- is EDFA number between L an L lines. j 96

5 Journal of Theoretical an Applie Information Technology 3 st March 03. Vol. 49 No JATIT & LLS. All rights reserve. ISSN: E-ISSN: Accoring to the formula(9, fiber length is 00km, an fiber parameters are in Table. Hypothesis ispersion of DCM is -00ps/nm. Make =0~00km, step is km, in 00km fiber, the output en of CSO inicators is shown in Figure 5. It can be seen from the figure, there is an optimal position, an it can make DCM completely offset the istortion which is inuce by fiber. Figure 5: CSO Position Changes With DCM The chirp fiber grating can also be use for multi channel ispersion compensation. In orer to make better use of single-moe fiber, wavelength ivision multiplexing ( WDM technology becomes the solution. But the ispersion compensation has become a problem to be solve. Usually the ispersion compensation is only narrow ban light source, an grating to match the requirements. Using a plurality of such grating to multi channel for ispersion compensation grating. The multiple channels is similar to multiple single channel grating performance, but it has high stability,when it is writing only in a section of the fiber. An the multi-channel grating cost are relatively low, so it is the very goo solution in the WDM ispersion compensation. 5. CONCLUSIONS Although there are many ispersion compensation methos, each kin of metho has its own avantages an isavantages. So far there is not a technique is optimal, an it mast be uner certain conitions to achieve the optimal. In ifferent transmission istance, each paragraph must ajust parameters to achieve the best results. The chirp technology is very effective in short istance communication, but it can not meet the requirements for ispersion compensation in long istance communication. Dispersion optical fiber compensation technology is better for less noe system, when the noe is large, it is ifficult to achieve. At the same time the spectrum inversion an the chirp technology is ifficult to achieve, an the cost comparison is high. Therefore, it shoul also be base on the specific situation an analysis to choose the optimal technology of ispersion compensation. With the project construction as the foothol in this paper, it will provie a reference metho for the research an evelopment of communications proucts, but also it provies a theoretical basis. Currently, the stuy on ispersion has evelope eeply, but there is not a best metho. There is no uniform ispersion compensation metho in ifferent communication systems. At the same time, the intelligent equipment still nees to be improve. REFRENCES: [] H.C. Chang, H.S. Huang, J.S. Wu, Wave coupling between parallel single-moe an multimoe optical fibers, IEEE Trans. Microwave Theory Tech. Vol.34 No.,986,pp [] Ye Wang, Dajian Xue, Xuanhui Lu, Power transfercharacteristicsamong N parallel singlemoeopticalfibers. Optik, Vol.0,009, pp [3] Schermer RT. Moe scalability in bent optical fibers. Optics Express, Vol.5, 007, pp [4] Yao L, Birks TA, Knight JC. Low ben loss in tightly-bent fibers through aiabatic ben transitions. Optics Express, Vol.7 009, pp. 96. [5] C. Elosua, C. Bariain, I.R. Matias, Optical fiber sensors to etect volatile organic compoun in sick builing synrome applications, Open Construction an Builing Technology Journal, Vol.4,00,pp.3-0. [6] Maravelakis, P.E., Castagliola, P.. An EWMA chart for monitoring the process stanar eviation when parameters are estimate. Computational Statistics an Data Analysis, Vol. 53,009, pp [7] C. Elosua, C. Bariain, A. Luquin, M. Laguna, I.R. Matias, Optimiation of single moe fibre sensors to etect organic vapours, Sensors an Actuators B:Chemical, Vol. 57,0,pp [8] M.H. Tu, T. Sun, K.T.V. Grattan, Optimiation of gol-nanoparticle-base optical fibre surface plasmon resonance (SPR-base sensors, Sensors an Actuators B:Chemical, 0. [9] C.R. Zamarre no, M. Hernae, I. Del Villar, I.R. Matias, F.J. Arregui, Optical fiber ph sensor 97

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