Abstract

The intensity pattern created by the collision of two bright (dark) solitons can be considered as a nonlinear X-junction. In a self-focussing (self-defocussing) medium, this induces changes of refractive index, thus setting up a linear X-junction as well. It is possible to use this induced X-junction as a linear device. It can be much smaller than present X-junctions. The X-junction can be made in a photo-induced medium where the refractive index is changed permanently. This can be done because the exact solutions for the intensity distribution are known. We find a linear relation between the transmission ratio of the bright soliton coupler and the squire of the tangent of the angle between the two solitons. In the case of zero angle, this X-junction is a one-beat-length device in the sense that 100% of the energy goes to the left output if initially only the left input is excited. The coupler created by two dark solitons is a half-beat device. A linear coupler exploiting exact solutions has no loss, and is thus an ideal coupler in this respect at a given wavelength. The length of interaction for this coupler is the shortest possible and is thus optimal.

© 1993 Optical Society of America