The main subject of this contribution is the all-optical control over thestate of polarization (SOP) of light, understood as the control over the SOP ofa signal beam by the SOP of a pump beam. We will show how the possibility ofsuch control arises naturally from a vectorial study of pump-probe Ramaninteractions in optical fibers. Most studies on the Raman effect in opticalfibers assume a scalar model, which is only valid for high-PMD fibers (here,PMD stands for the polarization-mode dispersion). Modern technology enablesmanufacturing of low-PMD fibers, the description of which requires a fullvectorial model. Within this model we gain full control over the SOP of thesignal beam. In particular we show how the signal SOP is pulled towards andtrapped by the pump SOP. The isotropic symmetry of the fiber is broken by thepresence of the polarized pump. This trapping effect is used in experiments forthe design of new nonlinear optical devices named Raman polarizers. Along withthe property of improved signal amplification, these devices transform anarbitrary input SOP of the signal beam into one and the same SOP towards theoutput end. This output SOP is fully controlled by the SOP of the pump beam. Weoverview the sate-of-the-art of the subject and introduce the notion of an"ideal Raman polarizer".
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