In the theory of optical gap solitons, slowly-moving finite-amplitude
Lorentzian solutions are found to mediate the transition from bright to
coexistent dark-antidark solitary wave pairs when the laser frequency is
detuned out of the proper edge of a dynamical photonic bandgap. Catastrophe
theory is applied to give a geometrical description of this strongly
asymmetrical 'morphing' process.Comment: 6 pages, 3 figures, submitted to Phys. Rev.