Isotropic polarization modulational instability and domain walls in spun fibers

By means of a very low birefringence spun fiber, we investigate experimentally the phenomenon of polarization modulational instability in the conditions of effective isotropy of the Kerr medium. By showing that birefringence in spun fibers can be negligibly small as compared to nonlinear effects, our results open up new prospects in the development of applied nonlinear fiber optics. This aspect is illustrated through the generation of polarization domain walls whose interest for optical fiber data transmissions has been recently discussed.