Apparatus and method employing fast polarization modulation to reduce effects of polarization hole burning and polarization dependent loss

摘要

The effects of polarization dependent hole burning and polarization dependent loss are reduced by modulating the state of polarization (SOP) of an optical signal being launched into an optical transmission path periodically between first and second states of polarization of at least one pair of orthogonal states of polarization. Preferably, the SOP is modulated at a rate that is substantially higher than 1/ts , where ts is the anistropic saturation time of the optical amplifier. Ideally, the state of polarization of the launched optical signal should be modulated such that it traces a complete great circle on the Poincare' sphere. In addition, the effects of polarization dependent loss are further reduced by controllably selecting the particular great circle being traced on the Poincare' sphere. In one example, the particular great circle being traced is selected such that a predetermined parameter, for example, the signal to noise ratio, of the optical information signal being received at the remote end of the optical transmission network is maintained at a prescribed value, e.g., a maximum value. In an embodiment of the invention, the great circle is traced at a uniform speed such that the launched optical signal spends equal time intervals in both states of any pair of orthogonal states of polarization on the selected great circle on the Poincare' sphere.