THEORY OF CONTINUOUS-WAVE BEAM PROPAGATION IN NON-LINEAR OPTICAL-WAVEGUIDES

The paraxial approximation is used to calculate the propagation characteristics of cw beams possessing Gaussian spatial profiles in nonlinear optical waveguides. For powers below the critical power for self-focusing in a homogeneous medium, it is found that the waveguide effect dominates, i. e. , the beam becomes trapped and the spot size varies sinusoidally. Above the critical power, the propagation is dominated by nonlinearity; the beam becomes unstable and displays self-focusing analogous to that in a homogeneous medium. Mode mixing is defined in terms of the nonlinearity-induced mixing of the initially excited modes at the guide face, and explicit expressions are obtained for the mode mixing for special cases.