MODELING OF NEGATIVE INFLUENCES AT THE SIGNAL TRANSMISSION IN THE OPTICAL MEDIUM. Rastislav Róka, Filip Čertík

Transcription

1 MODELING OF NEGATIVE INFLUENCES AT THE SIGNAL TRANSMISSION IN THE OPTICAL MEDIUM Ratilav Róka, Filip Čertík Intitute of Telecommunication, FEEIT, Slovak Univerity of Technology in Bratilava Received 29 April 2015; accepted 10 May Introduction Nowaday, an interet in the ignal tranmiion through optical fiber rapidly increae due to the tranmiion bandwidth. The increaing of optical high-peed data rate in tranmiion ytem lead to limitation caued by linear and nonlinear effect. Each nonlinear effect limit different part of optical ignal (e.g. amplitude, phae, frequency and polarization). It i neceary to examine above all negative influence ariing in the optical environment and their influence on different modulation technique for achieving deired ignal tranmiion parameter. The imulation give tranmiion boundarie of advanced ignal proceing technique for the conidered optical ytem and allow comparing all the olution before their deployment in real optical tranmiion path. Thi paper preent feature and way for modeling of negative effect uing MATLAB Simulation tool. Firt, the paper introduce detailed characteritic of nonlinear effectpreentedin the optical tranmiion medium. Alo, created block cheme for particular nonlinear effect are prepared for including into the model of optical tranmiion path. Then, the imulation of negative influence at the ignal tranmiion i hown for the noncoherent OOK modulated ignal via the environment of a tandard ingle mode fiber. 2. Characteritic of nonlinearitie in the optical tranmiion medium The optical tranmiion medium repreent a complex frequency dependent ytem that conit of linear and nonlinear effect. The attenuation and the diperion effect repreent linear effectariing in the optical tranmiion medium, where an attenuation decreae the power of the tranmitted ignal and a diperion broaden the ignal in the time and hiftit phae. Both effect are major limitation factor for the optical tranmiion. The attenuation can be uppreed uing optical Raman or Erbium Doped Fiber Amplifier. The diperion i much more difficult to compre. The Chromatic Diperion can be neglected uing an electric compenator or uing coherent ytem uch a BPSK or QPSK modulation technique. However, the Polarization Mode Diperion ha a tochatic character and therefore it repreent a limitation for higher data rate optical tranmiion ytem. More detailed analyi and deign i hown in [1]. The nonlinear effect play an important role epecially in the long haul optical ignal tranmiion. We can claify nonlinear effect by a following way: Kerr nonlinearitie are elf-induced effect, where the phae velocity of the pule depending on the pule own intenity. The Kerr effect decribe a change in the fiber refractive index due to electrical perturbation. Due to the Kerr effect, we are able to decribe FWM, SPM and XPM effect, Scattering nonlinearitie occur due to a photon inelatic cattering to lower energy photon. The pule energy i tranferred to another wave with a different wavelength. 304

2 2.1 The Four-Wave Mixing effect The Four-Wave Mixing FWM effect repreent a parametric interaction among wave atifying a particular phae relationhip called the phae matching. Thi nonlinear effect occur only in ytem that carry more wavelength through the optical fiber and it i claified a a third-order ditortion phenomenon. The nonlinear interaction generate new frequency component of the material polarization vector, which can interfere with input field if a phae matching condition i obtain. Frequency component that directly overlap with bandwidth will caue an interference with original wave. The power of new generated wave can be obtain by olving coupled propagation equation of four interacting wave, which lead to equation (1) that mainly depend on the power of neighbor channel, the channel pacing and on the diperion [2]. The FWM block i hown in fig e l Ak 4 de Le A1 A2 A3 (1) where factor η i the FWM efficiency, γ i the nonlinear coefficient, L e i the effective length, A 2 1 (z), A 2 2 (z), A 2 3 (z) are power of input wave, l i the fiber length, α i the attenuation and d e the o-called degeneracy factor (equal to 3 if the degenerative FWM i conidered, 6 otherwie). Fig.1: The FWM block. 2.2 Self-Phae and Cro-Phae Modulation effect The Self-Phae modulation SPM and the Cro-Phae Modulation XPM effect have an important impact on high data peed communication ytem that ue the Dene Wavelength Diviion Multiplexing DWDM. The SPM effect occur due to the Kerr effect in which the refractive index of optical fiber increae with the optical intenity decreaing the propagation peed and thu induct the nonlinear phae hift. The XPM effect i very imilar to the SPM in which the intenity from different wavelength channel change the ignal phae and thu the XPM occur only in WDM ytem. In fact, the XPM convert power fluctuation in a particular wavelength channel to phae fluctuation in other co-propagating channel [3]. Both, SPM and XPM effect reult to pectral broadening and ditortion of the pule hape. The pectral broadening can be decribed by equation (2) and the phae hift by equation (3). d ' 0 (2) dt whereω' i the ignal frequency influenced with the SPM effect, ω 0 i the initial ignal frequency 305

3 2 z n 2 i I i t 2 I j t (3) i j where the firt term in bracket repreent the SPM effect and the econd term repreent the XPM effect. In the equation (3), the factor 2 ha it origin in a form of the nonlinear uceptibility and repreent the XPM twice a effective a the SPM for the ame power amount. The XPM effect affect the ignal only the interacting ignal uperimpoe in time [3,4]. The XPM effect can decreae a ytem performance even greater than the XPM effect, epecially in cae of 100 channel ytem. The common SPM and XPM block i hown in fig. 2. Fig.2: The common SPM and XPM block. 2.3 Stimulated Raman and Stimulated Brillouin Scattering effect The Stimulated Brillouin Scattering SBS and Stimulated Raman Scattering SRS effect influence the intenity of the tranmitted ignal. In the SBS cae, the acoutic wave change the frequency of everal photon that reult to interference with a tranmitted ignal. Thi frequency hifted wave i propagating only in the oppoite direction a the tranmitted ignal and the power can be decribed by di gbi pi I (4) dz where the I p i a pump ignal, I repreent tranmitted ignal intenity, g R i timulated Raman gain coefficient and α and α p are loe of ignal. The SRS effect i imilar to the SBS, were the pectral width i wide and interfere with everal tranmitted ignal. The SRS effect propagate in both direction. Both timulated cattering effect repreent a noie in optical tranmiion ytem [4,5]. The power of the frequency hifted wave can be decribed by di gri pi I (5) dz where the I p i a pump ignal, I repreent tranmitted ignal intenity, g R i timulated Raman gain coefficient and α and α p are loe of ignal.a deign of the common SRS, SBS and attenuation block i hown in fig. 3. Fig.3: The common SRS, SBS and attenuation block. 306

4 3. Simulation of nonlinear effect in optical fiber The preented imulation model come out from the imulation model for optical communication introduced in [6-8]. A modeling i performed in the Matlab Simulink 2014a programming environment. The imulation model how an influence of nonlinear effect on tranmitted optical ignal. The imulation model i deigned for the Samung ingle mode UltraPa TM non-zero diperion-hifted fiber [9]. A deign of the FWM effect require utilizing of the WDM technology and thu the generation of additional wavelength channel i hown in fig. 1. Thee additional neighbor channel are mixed in the WDM block and driven to the FWM block. The FWM block cheme firt verifie the phae matching condition and then mixe neighbor ignal uing the equation (1) if phae condition are atified. The influence of the FWM effect on the OOK tranmitted ignal i hown in fig. 4. Fig.4:The OOK tranmitted ignalinfluenced by the FWM effect. A deign of the common SPM and XPM block i hown in fig. 2, where the SPM&XPM block calculate the amount of pectral broadening. Both output are driven to the Frequency Shifting block, where the ignal i pectrally broaden. The fig. 5 how the ignal phae hift due to phae modulation effect. Fig.5:The OOK tranmitted ignal influenced by the SPM and XPM effect. The SRS&SBS block can be deigned by adding additional ignal channel uing a combination of two equation. Thee equation include the tranmitted ignal attenuation coefficient and therefore the common SRS, SBS and attenuation block i deigned. Auming the tandard SM fiber, the SRS effect downhift neighbor ignal by about 13,2 THz with the Raman band around 5 THz and the SRS effect downhift about 11 GHz with the Brillouin band le than 20 MHz. The influence of SRS and SBS effect together with attenuation i hown in fig

5 Fig.6:The OOK tranmitted ignal attenuated and influenced by the SRS and SBS effect. Concluion Thi contribution analye a modelling of nonlinear effect in the optical tranmiion medium. Uing created pecific block in the Matlab Simulink programming environment, we can imulate the influence of each linear and nonlinear effect on tranmitted ignal utilized by WDM optical ytem. We preent change of the optical ignal modulated with noncoherent OOK keying due to nonlinear effect ariing in the tranmiion environment. In future analyi, we can deign new and advanced combination of high-bit rate coherent modulation format with different encoding technique or include optical ignal amplification into long-haul tranmiion path. Acknowledgement Thi work i a part of reearch activitie conducted at Slovak Univerity of Technology Bratilava, Faculty of Electrical Engineering and Information Technology, Intitute of Telecommunication, within the cope of the project KEGA No. 039STU-4/2013 Utilization of Web-baed Training and Learning Sytem at the Development of New Educational Program in the Area of Optical Tranmiion Media. Reference: [1] R. Róka, F. Čertík. Modeling of Environmental Influence at the ignal tranmiion in the optical tranmiion medium, IJCNIS, Vol.4, No.3, S , ISSN X. [2] R. Róka, F. Čertík. The Nonlinear FWM Effect and it Influence on Optical Signal Utilized Different Modulation Technique in the WDM Tranmiion Sytem, OK th Conference, Praha (Czech), , ISBN [3] F. Čertík, R. Róka. Nonlinear SPM and XPM Effect and their Influence on Optical Signal Utilized Different Modulation Technique in WDM Tranmiion Sytem,OK th Conference, Praha (Czech), [4] E. Iannone, F. Matera, A. Mecozzi, M. Settembre. Nonlinear Optical Communication Network, John Wiley and on, pp.20-50, TK N66, [5] K.P. Ho. Phae-Modulated Optical Communication Sytem,Springer Science+Buine Media, pp , 2005, ISBN , ISBN [6] R. Róka. Fixed Tranmiion Media, Technology and Engineering Application of Simulink, InTech, Rijeka (Croatia), May 2012, ISBN [7] R. Róka, F. Čertík. Simulation Tool for Broadband Paive Optical Network. In: Simulation Technologie in Networking and Communication: Selecting the Bet Tool for the Tet, CRC Pre, Boca Raton (USA), November 2014, ISBN [8] R. Róka. The Simulation of Negative Influence in the Environment of Fixed Tranmiion Media, In: APSAC 2015, Vienna (Autria), , pp.58-68, ISBN , ISSN [9] Samung Fiberoptic: 308