R.V. Kutluyarov - Ph.D. (Eng.), Senior Research Scientist, Ufa State Aviation Technical University A.K. Sultanov - Dr.Sc. (Eng.), Professor, Ufa State Aviation Technical University V.K. Bagmanov - Dr.Sc. (Eng.), Professor, Ufa State Aviation Technical University

Polarization scrambling is a useful tool for avoiding of multiple errors related to polarization-dependent gain in erbium amplifiers and polarization-dependent loss in fiber optic communications. It was shown in recent articles that polarization scrambling may be effectively used for mitigating penalties related to undesirable polarization effects as PMD and for monitoring of such effects. We show that fast polarization scrambling at transmitting end of the fiber link may be used for mitigating penalties related to Kerr-nonlinearities. Fast polarization scrambling efficiency was defined by simulation. We have simulated propagation of two 40Gbps WDM signals by numerical solving system of coupled nonlinear Schrödinger equations. For solving equations we have used split-step Fourier-method and coarse-step method. Model that we used includes chromatic dispersion, fiber loss, Kerr-nonlinearities and random birefringence. Simulated link includes five spans, consisting of non-zero dispersion shifting fiber, dispersion compensating fiber and erbium amplifier. Receiver consists of pass-band optical filter and square-law detector. To model polarization scrambler we used rotating linear birefringent wave plate. Frequency of rotation is assumed as scrambling frequency. We have investigated efficiency of the scrambler consisting of the only half-wave plate. This kind of scrambler rotates Stokes vector of the signal through the Poincare sphere equator. For scrambling frequency range 1 - 60 000 kHz we have found out the local maximum of Q-factor improvement function. Optimum scrambling frequency is 32,5 MHz. Q-factor improvement is 0,9 - 1,1 dB at this frequency. Scrambler, consisting of the concatenation of the quarter-wave plate, half-wave plate and other quarter-wave plate is more complex and more effective because it rotates Stokes vector on the whole Poincare sphere. Each of the three wave plates has its own rotation frequency. Simulation shows that this kind of scrambler providing for better signal improvement than the only half-wave plate. Timing jitter due to polarization scrambling is the main factor limiting its employment in fiber optics. The origin of jitter is that signal polarization moving between birefringent axis of the fiber. Therefore polarization scrambling may be used only for links with small total PMD.

 

1. Menyuk C.R., Marks B.S.Interaction of Polarization Mode Dispersion and Nonlinearity in Optical Fiber Transmission Systems // Journal of Lightwave Technology. 2006. V. 24. № 7. P. 2806-2826.
2. Ibragimov E., Menyuk C.R., Kath W.L. PMD-induced reduction of nonlinear penalties in terrestrial optical fiber transmission // Proc. OFC. 2000. Paper WL3. P. 195-197.
3. Marcuse D., Menyuk C.R., Wai P.K.A. Application of the Manakov-PMD equation to studies of signal propagation in optical fibers with randomly varying birefringence // Journal of Lightwave Technology. 1997. V. 15. № 9. P. 1735-1746.
4. Kogelnik H., Jopson R.M., Nelson L.E. Polarization-Mode Dispersion // Optical Fiber Telecommunications, IVB. Systems and Impairments. San Diego. CA: Academic. 2002. P. 725-861.
5. Karlsson M., Sunnerud H. Effects of Nonlinearities on PMD-Induced System Impairments // Journal of Lightwave Technology. 2006. V. 24. № 11. P. 4127-4137.
6. Bergano N.S., Mazurczyk V.J., Davidson C.R. Polarization scrambling improves SNR performance in a chain of EDFAs // Proc. of Optical Fiber Commun. Conference. ThR2. San Jose. California. 1994.
7. Fukada Y., Imai T., Mamoru A. BER fluctuation suppression in optical in-line amplifier systems using polarization scrambling technique // Electron. Lett. 1994. V.30. № 5. P. 432-433.
8. Naito T., Terahara T., Shimojoh N., Tanaka T., Chikama T., Suyama M.PDL-induced noise reduction in long-haul transmission system using synchronous polarization scrambling // Proc. of European Conference on Optical Commun. Madrid. Spain. 1998. P. 683-684.
9. Park K. J., Kim H., Lee J.H., Youn C.J., Shin S.K., Chung Y.C. Polarization-mode dispersion monitoring technique based on polarization scrambling // Electron. Lett. 2002. V. 38. № 2. P. 83-85.
10. Yan L.-S., Yu Q., Willner A.E. Demonstration of in-line monitoring and compensation of polarization-dependent loss for multiple channels // IEEE Photonics Technol. Lett. 2002. V. 14. № 6. P. 864-866.
11. Wedding B., Haslach C.N.Enhanced PMD mitigation by polarization scrambling and forward error correction // Optical Fiber Communication Conference and International Conference on Quantum Information. 2001 OSA Technical Digest Series. 2001. Paper WAA1.
12. Liu X. All-Channel PMD Mitigation Using Distributed Fast Polarization Scrambling in WDM Systems with FEC // Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference. OSA Technical Digest Series. 2007. Paper OMH4.
13. Klekamp A., Werner D., Bülow H. Study of Different 40Gbit/s FECs Regarding PMD Mitigation Efficiency by Fast Polarization Scrambling // Optical Fiber Communication Conference/National Fiber Optic Engineers Conference, OSA Technical Digest (CD). 2008. Paper JWA54.
14. Park K.J., Lee J.H., Chung Y.C. Optimization of polarization-scrambling frequency in lightwave systems // Optical Engineering. 2008. V. 47. № 3. P. 035005.
15. Agrawal, G.P. Nonlinear Fiber Optics, 4 ed. San Diego. CA: Academic. 2007. 529 p.
16. Sultanov A.K., Bagmanov V.K.; Kutluyarov R.; Zaynullin A. WDM signal impairments due to the cross-modulation in the case of nonlinear transmission in the presence of PMD // Proc. SPIE 8787. Optical Technologies for Telecommunications 2012. P. 878704-1 - 878704-6.
17. Kumar A., Ghatak A. Polarization of light with applications in optical fibers // SPIE Tutorial texts in optical engineering. 2011. V. TT90.