Abstract: An optical device includes a waveguide and a film or layer of a material having highly nonlinear optical characteristics, in particular a semiconductor material. The film is located so close to the waveguide core that the evanescent field of light propagating along the waveguide extends up to the film. In this optical device, the large nonlinear properties of the material influence the optical characteristics of the waveguide. When positioned along a similar D-fiber, the device can be used as a fiber-based, nonlinear coupler controlled by a relatively weak light signal. The same device can be used as an element of a laser and in a number of various other applications.