<title>Optical interference in few-mode fibers: effect of temporal and spatial coherence</title>

The role played by optical interference in determining the mutual coherence function of an optical field propagating in few-mode fiber waveguides is examined under different conditions of the source coherence. By using the classical coherence formalism and guided-mode field representation, the mutual coherence function of the optical field guided in weakly-guiding fiber waveguides excited by stationary, cross- spectrally pure source is given in terms of the exciting coefficients, the source degree of coherence and guided-mode parameters that take also into account the first-order as well as the second-order modal dispersion. In particular, the optical interference is examined by evaluating the intensity distribution at the exit face and in the far- field of few-mode fiber waveguide as well as by evaluating the modulus of spatial and temporal coherence of an optical field at its output.115