Comparison of the Performances of NRZ and RZ WDM Systems with Long Amplifier Spacing and Dispersion Compensation

Abstract

The performances of NRZ and RZ in nonlinear WDM systems are compared by means of numerical simulation. Self-phase modulation, cross-phase modulation, group velocity dispersion, stimulated Raman scattering and other effects are included in our numerical model. The numerical results show that the performance of NRZ in the nonlinear WDM with dispersion compensation is better than that of RZ. The full dispersion compensation does not well improve the performance of RZ transmission in nonlinear WDM.

Optimization of Channel Spacing in WDM Transmission Systems with Dispersion Compensated Links in the Presence of Fiber Nonlinearities

“…Following the procedure described in the papers [5][6], the power of new optical waves of frequencies f ijk = f i + f j -f k generated through the FWM nonlinear interaction of three channels f i , f j and f k at the end of a dispersion compensated section can be derived as (1) where P i , P j and P k are the input light powers with frequencies f i , f j and f k , r is the fiber refractive index, l the wavelength, c the light velocity in vacuum, c the thirdorder nonlinear electric susceptibility (6 · 10 -14 m 3 W -1 ), d ijk is the degeneracy factor that takes a value of 3 (for i = j) or 6 (for i ≠ j), A e1 is the effective cross-sectional area of fiber with length L 1 and attenuation coefficient a 1 to be compensated, A e2 is the effective cross-sectional area of dispersion compensating fiber with length L 2 and attenuation coefficient a 2 , and h ijk the FWM factor defined by (2) where the phase mismatch of the first fiber Db (1) ijk and that of the second fiber Db (2) ijk can be expressed in terms of dispersion and frequency differences as follows where D (m) is the fiber dispersion, dD (m) /dl is the dispersion slope and f 0 (m) (m = 1, 2) is the optical frequency that corresponds to a zero-dispersion wavelength of a corresponding fiber segment. In a WDM system with N wavelengths channels with equal channel spacing, the total FWM power generated at the frequency f n at the end of M-th dispersion compensated section, in the worst case, assuming that the input power per channel is constant P i (0) = P 0 , l = 1, 2,…, N can be written as follows (4) where b = 1024p 6 c 2 /(r 4 l 2 c 2 A e1 A e2 ), and M = L/(L 1 + L 2 ) (with L being the total transmission distance) is the number of dispersion compensated links, that is the number of amplifiers.…”

“…Wavelength division multiplexing (WDM) can both significantly enhance transmission capacity and provide more flexibility in optical network design [1][2][3][4]. In longhaul high-speed transmission systems dispersion compensation must be employed, so that the optical link is composed of sections with two fiber segments of different dispersions and also an erbium-doped fiber amplifier (EDFA).…”

“…In longhaul high-speed transmission systems dispersion compensation must be employed, so that the optical link is composed of sections with two fiber segments of different dispersions and also an erbium-doped fiber amplifier (EDFA). In order to exactly investigate the performance of WDM systems in the presence of fiber nonlinearities the numerical simulations, based on solving of the nonlinear Schrödinger equation (NLSE), were employed in the most of present papers ( [1] for example). In order to exactly investigate the performance of WDM systems in the presence of fiber nonlinearities the numerical simulations, based on solving of the nonlinear Schrödinger equation (NLSE), were employed in the most of present papers ( [1] for example).…”