MATCHED PULSE-PROPAGATION IN A 3-LEVEL SYSTEM

The Backlund transformation for the three-level coupled Schrodinger-Ma xwell equation is presented in the matrix potential formalism. By appl ying the Backlund transformation to a constant-electric-fieId backgrou nd, we obtain a general solution for matched pulses (a pair of solitar y waves) that can emit or absorb a light velocity solitary pulse but o therwise propagate with their shapes invariant. In the special case, t his, solution describes a steady-state pulse without emission or absor ption, and becomes the matched pulse solution-recently obtained by Hio e and Grobe [Phys. Rev. Lett. 73, 2559 (1994)]. A nonlinear superposit ion rule is derived from the Backlund transformation and used for the explicit construction of two solitons as well as non-Abelian breathers . Various features of these solutions are addressed. In particular, we analyze in detail the scattering of ''binary solitons,'' a specific p air of different wavelength solitons, one of which moves with the velo city of light. Unlike the usual case of soliton: scattering, the broad er soliton changes its si,on after the scattering, thus exhibiting a b inary behavior. Surprisingly,;the light velocity soliton receives a ti me advance through the scattering, thereby moving faster than Light, w hich, however, does not violate causality.