A fundamental study on the capability of a crossing of two optical wave guides basedon dark-spatial solitons to act as a controllable optical beam splitter is presented in this work. It is based on the fact that the guided beam is diffracted at the wave guide crossing by an effective phase screen formed by the soliton collision profile. It was found that when the two dark solitons are immersed into the same finite bright background, the energy of a guided beam can be split into the desired optical channel according to the collision angle. On the other hand, when each dark soliton is immersed into its own bright background, the corresponding optical junction can not operate. This is because the finite width of the backgrounds acts as a low-pass filter over the diffracted beam, and because the onset of the cross-phase modulation instability effect occurs for small enough collision angles.