Intensity-induced Rotation of the Polarization Ellipse in Low-birefringence, Single-mode Optical Fibres

An analysis is presented of the evolution of the electromagnetic field which propagates in a low-birefringence, single-mode fibre supporting two degenerate orthogonally polarized states in the presence of the interaction provided by the intensity-dependent part of the refractive index (the optical Kerr effect). This approach leads, in particular, to a generalization of the well-known ellipse-rotation method used to measure the magnitude and sign of the nonlinear refractive index coefficient in bulk media.