We observed experimentally one-dimensional even-number sequence of dark photovoltaic solitons in LiNbO3:Fe crystal
without additional background illumination with spatially incoherent beam that contains a dark stripe generated from an
amplitude jump in the center of the incoherent beam. In experiment, we found that the initial stripe width at the
entrance face of the crystal is a key parameter for generating an even-number sequence of dark incoherent photovoltaic
solitons. If the initial width of the dark stripe was small, only a Y-junction soliton pair was generated. As the initial
width of the dark stripe was creased to 20.1μm, the stripe can split into an even-number sequence of soliton structure.
The soliton pairs far away from the center had smaller width and less visibility. In addition, the separations between
adjacent dark stripes became slightly smaller than that of the Y-junction dark solitons. In particular, when the input
width in the entrance face of the crystal was 30.8μm, the diffractive beam in the output face of the crystal was no longer
expanding its outer boundary, but shrank its width.