Trapping polarization of light in nonlinear optical fibers: An ideal Raman polarizer

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 of asignal beam by the SOP of a pump beam. We will show how the possibility of suchcontrol arises naturally from a vectorial study of pump-probe Raman interactionsin optical fibers. Most studies on the Raman effect in optical fibers assume a scalarmodel, which is only valid for high-PMD fibers (here, PMD stands for thepolarization-mode dispersion). Modern technology enables manufacturing of low-PMD fibers, the description of which requires a full vectorial model. Within thismodel we gain full control over the SOP of the signal beam. In particular we showhow the signal SOP is pulled towards and trapped by the pump SOP. The isotropicsymmetry of the fiber is broken by the presence of the polarized pump. Thistrapping effect is used in experiments for the design of new nonlinear opticaldevices named Raman polarizers. Along with the property of improved signalamplification, these devices transform an arbitrary input SOP of the signal beaminto one and the same SOP towards the output end. This output SOP is fullycontrolled by the SOP of the pump beam. We overview the state-of-the-art of thesubject and introduce the notion of an ‘‘ideal Raman polarizer."