In this paper, we analyze the radiated, reflected, and transmitted power due to an abrupt step discontinuity in a multimode optical waveguide by a numerical technique without any physical approximations other than neglecting the evanescent radiation modes. The amount of power loss depends primarily on the number of modes the portion of the waveguide on each side can support. The range of thickness mismatch for which reasonably low loss occurs depends on the wavelength. The technique can be used to analyze step discontinuities of symmetric or asymmetric, single or multimode optical slab waveguides with arbitrary cross section accurately.
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