  We examine properties of an ultrashort laser pulse propagating through an
artificial Saturable Absorber based on Nonlinear Polarization Evolution device
which has been realized with Polarization Maintaining fibers only (PM NPE). We
study and compare in-line and Faraday Mirror geometries showing that the latter
is immune to errors in the PM NPE construction. Experimental results for the
transmission measurements of the PM NPE setup for different input linear
polarization angles and various input pulse powers are presented. We show that
PM NPE topology is of crucial importance for controlling the properties of the
output pulse as it rules the contribution of cross-phase modulation to an
overall nonlinear phase change. We also demonstrate an excellent agreement
between the numerical model and experimental results.
