The wave propagation in symmetric, nonlinear, integrated-optical Y junctions is investigated with consideration of the nonlinear polarization coupling. The propagation of the field in the waveguide structure is described by a coupled pair of nonlinear two-dimensional wave equations, which are solved numerically by the beam-propagation method. The nonlinear Y junction is analyzed with respect to its application for all-optical modulation of a strong pump wave by a weak control beam. It is shown that sensitive continuous amplitude-to-amplitude modulation as well as phase-to-amplitude modulation is possible. This operation is stable with respect to the total powers in each output waveguide, despite the nonlinear-polarization coupling that, for example, is caused by a polarization error of the input field. Further, the results indicate that the conditions for a polarization-maintaining operation can be obtained from the known closed-form solutions for nonlinear polarization coupling in birefringent optical fibers.
© 1997 Optical Society of America
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