Nonreciprocal propagation of solitons in a chiral medium

The evolution of polarization of a light pulse in a system consisting of two-level atoms located on symmetric helices twisted into a bundle has been considered. The interaction of induced dipoles is taken into account by additional third order differential terms in Maxwell's equations in the nearest neighbor approximation. An integrable generalization of the reduced Maxwell-Bloch equations has been derived under the conditions of almost unidirectional propagation. The analysis of the solutions obtained has shown that the evolution of field pulses critically depends on the direction of their propagation or on the chirality of the medium.