Statistics of polarization dependant gain in Raman fiber amplifiers due to PMD

Abstract

Summary form only given. With the recent availability of high power pump lasers, Raman amplification has become feasible for commercial DWDM fiber-optic communication systems. Raman fiber amplifiers are highly attractive for their low equivalent noise figure and wideband gain. However, the Raman gain coefficient is polarization sensitive and can be up to 10 times higher when the signal and pump polarization states are parallel rather than perpendicular. Previous studies of this polarization dependent gain (PDG) investigate its relationship with the polarization mode dispersion (PMD) of the fiber, and the degree of the polarization (DOP) of the pump laser. These studies show that when the average PMD of the fiber becomes high enough, or if the pump DOP is very low, then the PDG becomes negligible. But these studies do not investigate the statistical behavior of the polarization dependant gain. There are two ways of characterizing polarization sensitivity in Raman amplifiers. One is to measure the PDG at a given point in time, which is determined by varying either the pump or signal polarization and recording the difference between the maximum and minimum gains. Alternatively, one can monitor how the instantaneous gain varies over time due to both PMD induced variations and changes to the signal's input state of polarization (SOP). In the paper we investigate the statistical characteristics of both of these parameters theoretically and experimentally.