Analysis of the signal polarization evolution with pump power in a fibre optical parametric amplifier

In this paper, we analyse the evolution with pump power of the FOPA output signal polarization and discuss its implications. The FOPA comprises a typical configuration, in which signal and pump are semiconductor lasers. It can be theoretically shown that both cross-phase modulation (XPM) and parametric amplification can cause the signal polarization change with pump power. It is important to note that, if two orthogonally polarized signals are inserted into the FOPA, any source of birefringence will maintain their orthogonality while the parametric gain will tend to make their polarization parallel