Influence of the Polarization Mode Dispersion on Propagation of Ultrashort Optical Pulses in the Spun Light Guides with Very Weak Linear Birefringence and Random Inhomogeneities

Although the spun light guides were developed in early 1980s, their quantity production has started only a few years ago. At present, the spun light guides with both strong and weak natural (unperturbed) linear birefringence are produced. The former are used for creating sensors of various physical parameters, mainly, current and magnetic field. The latter are very promising for use in fiber communication lines, since they have a considerable advantage over the conventional telecommunication light guides. In this work, we consider the influence of the polarization mode dispersion due to random inhomogeneities in the single-mode fiber light guides (SMFLGs) on propagation of ultrashort optical pulses in the fiber communication lines, which are based on the SMFLGs with very weak linear birefringence and strong regular twisting (such SMFLGs are called telecommunication spun light guides). The dependences of evolution of the envelope function of the ultrashort optical pulses and their spectra on the length of a spun light guide with very weak linear birefringence and random inhomogeneities are obtained by the numerical-simulation method. It is shown that an increase in the pulse width is proportional to the SMFLG length rather than occurs as per the diffuse law, as it is the case in the absence of torsion. It is established that the pulse widening to a certain (rather long) length with increasing length of the spun light guide occurs much slower than that in the untwisted light guides and faster for very long lengths. It is also shown that the relative intensity of radiation which is pumped from one orthogonal polarization mode to another over the depolarization length of nonmonochromatic radiation in the telecommunication spun light guides is small compared with unity, whereas an opposite situation is observed in the conventional telecommunication light guides.