Abstract— Intensity induced random varying birefringence leads to nonlinear polarization mode dispersion (PMD) in addition to linear PMD. In this article we investigate the effect of nonlinear PMD on a sideband channels with respect to centre wavelength. It is shown that if three or more channels are launched in the fibre such that the two sideband signals are aligned along the fast and the slow axis respectively, the nonlinear PMD due to change in power of the centre wavelength will affect the two signals differently. The effect will depend on how the State of polarization (SOP) of the centre wavelength are oriented with respect to the fibre axis. Generally we noticed that the sideband signals are little affect with nonlinear PMD if the centre wavelength power is coupled equally into the fibre axes. It was also shown that the nonlinear and linear PMD can be compensated for the effective PMD for each channel by tracking the SOPs of the sideband signals and applying the feedforward technique. The worst channel signal Degree of polarization (DOP) improved by more than 100%. Index Terms — Nonlinear PMD, Linear PMD, compensation and Multichannel I. INTRODUCTION As bit rates per channel increases up to 40 Gb/s or beyond and the transmission distance increases, the linear polarization mode dispersion (PMD) and nonlinearities are gradually becoming a major factor limiting the performance of optical transmission system. In order to cancel fibre PMD in multi-channel system, several optical and electrical PMD compensation (PMDC) techniques have been proposed [1]. In a Subcarrier-Multiplexing, electrical equalization is not effective as it is based on cancelling intersymbol interference and therefore does not recover a PMD-faded RF tone. Optical PMD compensation using RF signal power as feedback control signal is not effective because it is affected by nonlinearities [2, 3]. The feedforward PMDCs have shown advantages over feedback PMDCs. It is the purpose of this paper to demonstrate a DOP based PMD compensator using feedforward double sideband (DSB) method. We also show that nonlinear polarization rotation due to change in input power of the sidebands can also be cancelled PMDC. II. THEORETICAL BACKGROUND The evolution of a polarized field of a continous wave signal in a birefringent fibre, in the presence of the mode coupling can be expressed as follows [4] (29 1 ψ σ σ - σ σ - 1 σ σ 2 1 iω - ψ iω - ψ θ ψ θ 2 Π θ ψ 3 ψ 3 θ z                   + + + = ∂ 2 Π θ α βσ Ψ represents the complex transverse electric fields at the position z. The first term accounts for linear birefringence with β being the birefringence, ω is the optical frequency and σ θ is the birefringence axis in the θ direction. The second term accounts for nonlinear birefringence with eff 2 3cA P n = α and 2 2 2 2 ψ - 2 1 2 1 3 E E E E + = σ . P is the total light power, A eff is the effective mode area, c is the speed of light and n 2 is the nonlinear refractive index. If we assume that the birefringence is very small, like in a spool. The equation (1) changes to ( 2 )ψ σ σ ψ iω - ψ 3 ψ 3 θ z α σ + = ∂ β Since β<<α, the output polarization are power dependent. When β is small, the nonlinear birefringence causes the SOPs to slowly rotate along the σ 3 axis. As the birefringence strength tends to zero, the length scale over which the field remains correlated along a fixed set of axes increases. We expect that the SOPs will be preserved over this length scale, but because of the increasing nonlinear birefringence the beat length is reduced and the SOPs are randomly scattered along the S 3 axis, hence the signal is depolarized. When β > α and θ σ is fixed or minimally vary to the first order, from (1) the terms 3 ψ 3 σ σ and σ σ 2 Π θ ψ + + 2 Π θ cancel each other. Thus (1) can be expressed as follows (29 3 ψ σ σ 2 1 iω - σ σ 2 iω ψ i ω - ψ θ ψ θ θ ψ θ θ z       - = + = ∂ α β α βσ Compensation for Polarization Mode Dispersion in Multi-Channel System. David W. Waswa 1 , Vitalis Musara 2 , Lorinda Wu 2 and Andrew W. R. Leitch 2 Department of Physics 1 , Moi University, P.O Box 1125, Eldoret, 30100, Kenya Tel: +254 053- 2063101, +254 722 984 904 Fax: +254 053 43047/2063257 Department of Physics 2 , Nelson Mandela Metropolitan University, P.O Box 77000, Port Elizabeth, 6031, South Africa Tel: +27 41 504 2141, Fax: +27 41 504 2573 E-mail contact: dwaswa2000@yahoo.com or david.waswa@mu.ac.ke