All-optical switching in most guided-wave devices relies on light-induced changes in the refractive index, whereas absorptive changes degrade the switching responses.1 We investigate a new class of purely absorptive nonlinear device where switching of ultrashort pulses is based on coherent effects. This permits a favorable combination of enhanced nonlinearity and ultrafast response.2 Consider, for example, a dual channel nonlinear directional coupler (NLDC) with two-level absorber resonant impurities. The guiding properties of the NLDC are described in terms of coupled modes of the linear host material, whereas the nonlinear polarization is due to the doping centers. When the input pulse is coupled to one of the two NLDC ports, the nonlinear coupling is described by the extended sine-Gordon (SG) equations

© 1990 Optical Society of America

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