Nonlinear unidirectional coupler in photorefractive medium with diffusion nonlinearity

We consider switching characteristics of the nonlinear unidirectional coupl er embedded in the photorefractive medium with purely diffusion nonlinearit y, Transmission characteristics for both two- and three-waveguide couplers are presented. It is shown that the part of energy transmitted into the sec ond waveguide in two-waveguide coupler monotonically decreases with increas e of input energy, i.e. no threshold energy value exists. It is also shown that due to the specific character of diffusion nonlinearity transmission c haracteristics of the three-waveguide coupler strongly depends on the relat ive disposition of the input waveguide. (C) 2001 Elsevier Science B.V. All rights reserved.