The occurrence of multiple solitary optical waves, called dark photovoltaic spatial solitons, has now been described in a theoretical model using the beam propagation method. Yuhong Zhang, a physicist from the Xi’an Institute of Optics and Precision Mechanics of the Chinese Academy of Sciences, and his colleagues performed the first numerical simulation of the formation and evolution of one-dimensional multiple dark solitons inside a photorefractive crystal. Dark solitons are generated in photorefractive crystals, which respond to an incoming light beam by decreasing their refractive index as optical intensity increases, which causes the incoming beam to defocus. This effect is known as nonlinear self-defocusing. In their experiment, the scientists showed that it was possible to create multiple dark solitons by expanding the width of the dark notch, which in previous studies was not given any special function. Depending on the initial beam phase, the solitons appeared in either odd or even numbers. The researchers also confirmed previous findings that showed that when multiple solitons are generated, the separation between them becomes smaller. The solitons become progressively wider and less visible the farther away they are from the main dark notch entry location, they concluded. Because the shape of dark solitons remains unaffected by the crystal in which they travel, they induce waveguides, which can be used to reconfigure optical beams by splitting them, among other applications. The study appeared online March 15 in European Physical Journal D. For more information, visit: www.opt.ac.cn