Polarization effects on Brillouin gain in single-mode fibers

Stimulated Brillouin scattering is one of the most important nonlinear effects in single-mode fibers. Brillouin gain depends on the polarization states of pump and Stokes fields. Stolen1 has demonstrated that the Brillouin threshold optical power in fibers is higher by a factor of 2 with scrambled polarization states than with maintained linear polarization states. However, little attention has been paid to the Brillouin gain in single-mode fibers where the polarization state is not maintained and not completely scrambled. We investigated the polarization dependence of the Brillouin gain in an ordinary single-mode fiber. The Brillouin gain measured for a 5-km single-mode fiber showed a G [1 + Kcos(2θ + ϕ)] dependence, where G is the Brillouin gain with scrambled polarization states, θ is the incident polarization direction angle of the pump or Stokes (probe) fields relative to an arbitrarily fixed azimuth in the fiber cross section, and K and ϕ are constants. The value of K reached as high as 0.31. The Brillouin gain distribution along the single-mode fiber is also presented.