Optical Fiber Transmission Amplifications for Ultra Long Haul Applications

176 Optical Fiber Transmission Amplifications for Ultra Long Haul Applications Ahmed Nabih Zaki Rashed Electronics and Electrical Communications Engineering Department Faculty of Electronic Engineering, Menouf 3291, Menoufia University, EGYPT Abstract This paper has presented the transmission systems with employing Raman amplifier technology in forward pumping directions in order to have put up with much higher level of design complexities, when compared to conventional transmission lines with doped fiber optical amplifier. Even for the construction of a fundamental, basic building block a unit of a fiber Raman amplifier (FRA), the designer have to struggle with the problems associated with the interactions between pump / signal waves mediated by Raman process, have to wander within the vast degrees of freedom given the choice of pumping directions/ratios, and have to contemplate with the wavelength dependent fiber loss/noise figure profiles. Optimizing optical signal to noise ratio ( OSNR) and designing ultra-long haul links with best signal quality factor performances and minimum bit error rates, while adjusting variables in the fiber length, Rayleigh penalty, pump noise, nonlinear penalty, dispersion and gain distribution is a problem which can be easily stated, but in reality is not a process which can be easily achieved. Keywords Optical signal processing, Performance signature, Raman Amplifiers, and Photonic Communications Engineering. I. Introduction Wavelength division multiplexing (WDM) is basically frequency division multiplexing in the optical frequency domain, where on a single optical fiber there are multiple communication channels at different wavelengths [1]. A WDM system uses a multiplexer at the transmitter to join the signals together and a demultiplexer at the receiver to split them apart. By using WDM and optical amplifiers, they can accommodate several generations of technology development in their optical infrastructure [2]. Optical gain depends on the frequency of the incident signal and also on the local beam intensity. Dense wavelength division multiplexing (DWDM) is a technology that puts data from different sources together on an optical fiber, with each signal carried at the same time on its own separate light wavelength [3]. Optical amplifiers have several advantages over regenerators. Optical amplifiers can be more easily upgraded to a higher bit rate. In an optical communication system, as the optical signals from the transmitter propagate through optical fiber are attenuated by it and losses are added by other optical components, such as multiplexers and couplers which causes the signal to become too weak to be detected. Before this the signal strength has to be regenerated [4]. Most optical amplifiers amplify incident light through stimulated emission, its main ingredient is the optical gain realized when the amplifier is pumped to achieve population inversion. The optical gain, in general, depends not only on the frequency of the incident signal, but also on the local beam intensity at any point inside the amplifier []. To understand how optical amplification works, the mutual or reciprocal action of electromagnetic radiation with matter must be understood [6]. Optical amplification uses the principle of stimulated emission same as used in a laser. Optical amplifiers can be divided into two basic classes: optical fiber amplifiers (OFAs) and semiconductor optical amplifiers (SOAs) [1]. An amplifier can boost the (average) power of a laser output to higher levels. It can generate extremely high peak powers, particularly in ultra short pulses, if the stored energy is extracted within a short time. It can amplify weak signals before photo detection, and thus reduce the detection noise, unless the added amplifier noise is large. In long fiber-optic links for optical fiber communications, the optical power level has to be raised between long sections of fiber before the information is lost in the noise. The combination of an erbium-doped fiber amplifier (EDFA) and a fiber Raman amplifier (FRA or RA) is called a hybrid amplifier (HA), the Raman-EDFA. Hybrid amplifier provides high power gain. Raman amplifier is better because it provides distributed amplification within the fiber. Distributed amplification uses the transmission fiber as the gain medium by multiplexing a pump wavelength and signal wavelength. It increases the length of spans between the amplifiers and regeneration sites. So this provides amplification over wider and different regions [7]. Hybrid Raman/erbiumdoped fiber amplifiers (HFAs) are an advance technology for future. Hybrid Raman/erbium doped fiber amplifiers are designed to maximize the long-haul transmission distance [8]. II. Model and Equations Analysis The evolution of the input signal power (P s ) and the input pump power (P p ) propagating along the single mode optical fiber in watt; can be quantitatively described by different equations called propagation equations. The rate of change of signal and pump power with the distance z, can be expressed as mentioned in [9]: dpp s Lp Pp gre ff Ps Pp (1) dz p dps s LsPs gre ff Ps Pp (2) dz p

177 Where λ s and λ p are the signal and pump wavelengths in µm respectively, z is the distance in km from z= to z=l, Ls and Lp are the linear attenuation coefficient of the signal and pump power in the optical fiber in km -1 respectively. Equation ( 1) can be solved when both sides of the equation are integrated. When using forward pumping, the pump power can be expressed as the following expression []: P z P exp z (3) PF pof Lp where P PoF is the input pump power in the forward direction in watt at z=. If the values of P P are substituted in differential Eq. 2, and is integrated from z= to z=l for the signal power in the forward, then the result mathematical equation can be written as mentioned in []: g R P S z Pso exp P L z po eff Ls (4) Aeff where P so and P po denotes to the input signal and pump power respectively. This means that P po = P pof in case of forward pump and P po =P pob in case of backward pump, and L eff, is the effective length in km, over which the nonlinearities still holds or stimulated Raman scattering (SRS) occurs in the fiber and is defined as [11]: 1exp Lp z Leff () Lp Recently, there have been many efforts to utilize fiber Raman amplifier (FRA) in long -distance, high capacity WDM systems. The net gain [12] is one of the most significant parameters of the FRA. It describes the signal power increase in the end of the transmission span and presents the ratio between the amplifier accumulated gain and the signal loss. It can be simply described by the expression: PS Gnet, (6) PS () The intensity of the stimulated scattered light grows exponentially once the incident pump power exceeds a certain threshold value. The threshold pump power P th is defined as the incident power at which half of the pump power is transferred to the Stokes field at the output end of a fiber of length L. The threshold pump power satisfies the condition [13]: 16 Pth, (7) L g eff Re ff For standard silica cable fiber, the transmitted signal bandwidth per transmitted channel can be given by [14]:.4848 BW. sig, (8) N ch z Where N ch is the number of transmitted channels, τ is the total pulse broadening after distance z which is given by [1]: D z, (9) Where D is the total dispersion coefficient in fiber link media in ps/nm.km, and Δλ is the spectral linewidth of the optical source. This is mainly because FRA can improve the optical signal to noise ratio (OSNR) and reduce the impacts of fiber nonlinearities [16], that is the OSNR of the system after amplification can be: OSNR db PS log, () 2 h c BW. Sig. Where h is the Planck's constant (6.2 x -34 J.sec), P S (z) is the transmitted signal power after z distance, c is the speed of light (3x 8 m/sec), λ is the operating signal wavelength in μm, and B.W sig is the transmitted signal bandwidth. According to modified Shannon theorem, the maximum bit rate per optical channel for supported number of users, or the maximum capacity of the channel for maximum subscribers is given by [17]: B BW. log 2 1 OSNR, (11) Sh sig Based on MATLAB curve fitting program, the relationship between the signal quality factor (Q) with both number of transmitted channels (N ch ) and effective length L eff in km and transmitted signal power after distance z can be expressed as the following formula: 12.4 2.78 187. Q 28.6 P 2 2 3 3 S N ch Leff N ch Leff N ch L,dB(12) eff Then the bit error rate (BER) can be expressed as a function of Q in the following formula [18]: 2 Q BER.exp,. (13) Q 8 III. Results and Performance Analysis The optical FRAs have been modeled and have been parametrically investigated in different fiber cable medias such as true wave reach fiber, non return to zero dispersion shifted fiber (), and single mode fiber () with employing different multiplexing techniques namely ultra wide wavelength division multiplexing (UW-WDM) based on the coupled differential equations of first order, and also based on the set of the assumed of affecting operating parameters on the system model. In fact, the employed software computed the variables under the following operating parameters as shown in Table 1. Table 1. Proposed operating parameters for performance.4 W -.38 W - signature of Raman amplifiers [3,, 12, 18]. Operating Symbol Value and unit parameter Operating signal λ s 1.3 μm wavelength Operating pump λ p 1.28 μm wavelength Input signal wavelength P So dbm Input pump power P po 3 dbm Forward pump r f. ratio Signal attenuation α s.2 db/km Pump attenuation α p.3 db/km Spectral linewidth Δλ.1 nm of optical source UW-WDM N ch(uw- channels channels WDM) Transmission distance z z, km 4 Types of fiber cable media True wave reach fiber Effective area A eff μm 2 72 μm 2 8 μm 2 Raman gain g Reff.6 W - efficiency 1 km -1 1 km -1 1 km -1 Dispersion coefficient D 2 ps/nm.km 2 ps/nm.km 16 ps/nm.km

178 Then the set of the series of the following figures are shown below as the following can be obtained: i) Fig. (1, 2) have assured that transmitted signal power and pump power decrease with increasing transmission distance. It is observed that true wave reach fiber has presented transmitted signal and pump powers with compared other transmission mediums. ii)fig. (3, 4) have assured that signal gain and threshold pump power decrease with increasing transmission distance. It is observed that true wave reach fiber has presented transmitted signal gain and threshold pump power with compared other transmission mediums. iii) Fig. has indicated that transmitted signal bandwidth decreases with increasing transmission distance. It is theoretically found that single mode fiber medium has presented the highest transmitted signal bandwidth with compared to other transmission fiber mediums. Transmitted signal power, Ps, dbm 14 12 8 6 4 2 Fig. 1. Variations of transmitted signal power against variations of transmission distance at the assumed set of the operating parameters. Pump power, Pp, dbm 3 27. 2 22. 2 17. 1 12. 7. 2. Fig. 2. Variations of pump power against variations of transmission distance at the assumed set of the operating parameters.

179 4 3 Signal gain, G db 3 2 2 1 Threshold pump power, Pth dbm Fig. 3. Signal gain in relation to transmission distance at the assumed set of the operating parameters. 4. 4 3. 3 2. 2 1. 1. Fig. 4. Threshold pump power in relation to transmission distance at the assumed set of the operating parameters. Transmitted signal bandwidth, BWsig., GHz 9 8 7 6 4 3 2 Fig.. Transmitted signal bandwidth in relation to transmission distance at the assumed set of the operating parameters.

18 Optical signal to noise ratio, OSNR, db 3 3 2 2 1 Fig. 6. Optical signal to noise ratio in relation to transmission distance at the assumed set of the operating parameters. Shannon transmission bit rate, BSh, Tb/s 9 8 7 6 4 3 2 Fig. 7. Shannon transmission bit rate in relation to transmission distance at the assumed set of the operating parameters. Signal transmission quality, Q, db 4 3 3 2 2 1 Fig. 8. Signal transmission quality in relation to transmission distance at the assumed set of the operating parameters.

181 Signal bit error rate, BERx -12 9 8 7 6 4 3 2 1 Fig. 9. Signal bit error rate in relation to transmission distance at the assumed set of the operating parameters. iv) Fig. 6 has indicated that optical signal to noise ratio increases with increasing transmission distance. It is theoretically found that true wave reach fiber medium has presented the highest optical signal to noise ratio with compared to other transmission fiber mediums. v) Fig. 7 has assured that Shannon transmission bit rate decreases with increasing transmission distance. It is observed that single mode fiber has presented the highest transmitted signal bit rate with compared other transmission mediums. vi) Fig. 8 has indicated that signal transmission quality decreases with increasing transmission distance. It is theoretically found that true wave reach fiber medium has presented the highest signal transmission quality with compared to other transmission fiber mediums. vii) Fig. 9 has indicated that signal transmission bit rate increases with increasing transmission distance. It is theoretically found that true wave reach fiber medium has presented the lowest signal transmission bit rate with compared to other transmission fiber mediums. IV. Conclusions In a summary, the model has been investigated forward pumping based fiber optical Raman amplifiers in different optical fiber transmission medium systems over wide range of the affecting parameters. It is observed that transmitted signal power, pump power and its threshold value, signal gain, optical signal to noise ratio, transmitted signal bandwidth, signal transmission quality and transmission bit rates decrease with increasing transmission distance. As well as true wave reach fiber has presented the highest systems transmission performance compared to other transmission fiber mediums under the same operating of conditions. REFERENCES [1] Ahmed Nabih Zaki Rashed, Abd El-Naser A. Mohammed, Mohamed M. E. El-Halawany, and Mohamoud M. Eid Optical Add Drop Multiplexers with UW-DWDM Technique in Metro Optical Access Communication Networks, Nonlinear Optics and Quantum Optics, Vol. 44, No. 1, pp. 2 39, 212. [2] Ahmed Nabih Zaki Rashed, Abd El-Naser A. Mohammed, Mohamed M. E. El-Halawany, and Mohammed S. F. Tabour High Transmission Performance of Radio over Fiber Systems over Traditional Optical Fiber Communication Systems Using Different Coding Formats for Long Haul Applications, Nonlinear Optics and Quantum Optics, Vol. 44, No. 1, pp. 41 63, 212. [3] Ch. Headley, G. Agrawal, Raman Amplification in Fiber Optical Communication Systems, Elsevier, 29. [4] M. Islam, Raman Amplifiers for Telecommunications and Physical Principles, Springer, 24. [] L. Binh, T. Lhuynh, S. Sargent, A. Kirpalani, Fiber Raman Amplification in Ultra-high Speed Ultra-long Haul Transmission: Gain Profile, Noises and Transmission Performance, Technical Report MECSE-1-27, CTIE, Monash University, 27. [6] H. B. Sharma1,T. Gulati, and B. Rawat, Evaluation of Optical Amplifiers, International Journal of Engineering Research and Applications (IJERA), Vol. 2, No. 1, pp. pp.663-667, 212. [7] Q. Hen, J. Ning, H. Zhang, and Z. Chen, Novel Shooting Algorithm for Highly Efficient Analysis of Fiber Raman Amplifiers, IEEE J. Lightwave Technol., Vol. 24, No. 4, pp. 1946-192, 26. [8] Abd El-Naser A. Mohammed, Abd El-Fattah Saad, Ahmed Nabih Zaki Rashed, and Hazem Hageen Low Performance Characteristics of Optical Laser Diode Sources Based on NRZ Coding Formats under Thermal Irradiated Environments, International Journal of Computer Science and Telecommunications (IJCST), Vol. 2, No. 2, pp. 2-3, 211. [9] M. N. Islam, Raman Amplifiers for Telecommunications, IEEE J. of Select. Topics in Quantum Electron., Vol. 8, No. 3, pp. 48 9, 28. [] A. Galtarossa, L. Palmieri, M. Santagiustina, and L. Ursini, Polarized Backward Raman Amplification in Randomly Birefringent Fibers, J. Lightwave Technol., Vol. 24, No. 3, pp. 4 463, 29. [11] Abd El Naser A. Mohammed, Osama S. Fragallah, Ahmed Nabih Zaki Rashed, and Mohamed El-Abyad, New Trends of Multiplexing Techniques Based Submarine

182 Optical Transmission Links for High Transmission Capacity Computing Network Systems, Canadian Journal on Science and Engineering Mathematics, Vol. 3, No. 3, pp. 112-126, 212. [12] X. Liu, J. Chen, C. Lu, and X. Zhou, Optimizing Gain Profile and Noise Performance for Distributed Fiber Raman Amplifiers, Opt. Express, Vol. 12, No. 24, pp. 63 666, 211. [13] G. P. Agrawal, Fiber Optical Communication Systems, New York, John Wiley and Sons, 2. [14] I. Mandelbaum, M. Bolshtyansky, Raman Amplifier Model in Single Mode Optical Fiber, IEEE Photon. Technol. Lett., Vol. 1, No. 12, pp. 174 176, 29. [1] Abd El Naser A. Mohamed, Ahmed Nabih Zaki Rashed, and Amina El-Nabawy, The Effects of the Bad Weather on the Transmission and Performance Efficiency of Optical Wireless Communication Systems, Canadian Journal on Electrical ad Electronics Engineering, Vol. 3, No,, pp. 29-224, May 212. [16] S. Hu, H. Zhang and Y. Guo, Stiffness Analysis in the Numerical Solution of Raman Amplifier Propagation Equations, Opt. Exp., Vol. 12, No. 2, pp. 166-1664, 2. [17] S. Kumar, and H. Singh, Transmission Performance 64 Gb/s WDM System Based on Optical Hybrid Amplifiers Using RZ- Soliton Modulation Format at Different Transmission Distance, IOSR Journal of Engineering, Vol. 2, No. 7, pp. 7-12, July 212. [18] Ahmed Nabih Zaki Rashed, Abd El Naser A. Mohamed, Sakr A. S. Hanafy, and Amira I. M. Bendary Electrooptic Polymer Modulators Performance Improvement With Pulse Code Modulation Scheme in Modern Optical Communication Networks, International Journal of Computer Science and Telecommunications (IJCST), Vol. 2, No. 6, pp. 3-39, 211. systems, advanced optical communication networks, wireless optical access networks, analog communication systems, optical filters and Sensors, digital communication systems, optoelectronics devices, and advanced material science, network management systems, multimedia data base, network security, encryption and optical access computing systems. As well as he is editorial board member in high academic scientific International research Journals. Moreover he is a reviewer member and editorial board member in high impact scientific research international journals in the field of electronics, electrical communication systems, optoelectronics, information technology and advanced optical communication systems and networks. His personal electronic mail ID (E - mail:ahmed_733@yahoo.com). His published paper under the title "High reliability optical interconnections for short range applications in high speed optical communication systems" has achieved most popular download articles in Optics and Laser Technology Journal, Elsevier Publisher in year 213. Author s Profile Dr. Ahmed Nabih Zaki Rashed was born in Menouf city, Menoufia State, Egypt country in 23 July, 1976. Received the B.Sc., M.Sc., and Ph.D. scientific degrees in the Electronics and Electrical Communications Engineering Department from Faculty of Electronic Engineering, Menoufia University in 1999, 2, and 2 respectively. Currently, his job carrier is a scientific lecturer in Electronics and Electrical Communications Engineering Department, Faculty of Electronic Engineering, Menoufia university, Menouf. Postal Menouf city code: 3291, EGYPT. His scientific master science thesis has focused on polymer fibers in optical access communication systems. Moreover his scientific Ph. D. thesis has focused on recent applications in linear or nonlinear passive or active in optical networks. His interesting research mainly focuses on transmission capacity, a data rate product and long transmission distances of passive and active optical communication networks, wireless communication, radio over fiber communication systems, and optical network security and management. He has published many high scientific research papers in high quality and technical international journals in the field of advanced communication systems, optoelectronic devices, and passive optical access communication networks. His areas of interest and experience in optical communication