  We study the light transmission in two-dimensional photonic crystal
waveguides with embedded nonlinear defects. First, we derive the effective
discrete equations with long-range interaction for describing the waveguide
modes, and demonstrate that they provide a highly accurate generalization of
the familiar tight-binding models which are employed, e.g., for the study of
the coupled-resonator optical waveguides. Using these equations, we investigate
the properties of straight waveguides and waveguide bends with embedded
nonlinear defects and demonstrate the possibility of the nonlinearity-induced
bistable transmission. Additionally, we study localized modes in the waveguide
bends and (linear and nonlinear) transmission of the bent waveguides and
emphasize the role of evanescent modes in these phenomena.
