Gap solitons in a nonlinear quadratic negative index cavity
  By integrating the full Maxwell's equations we predict the existence of gap solitons in a quadratic, Fabry-Perot negative index cavity. An intense, fundamental pump pulse shifts the band structure that forms when magnetic and electric plasma frequencies are different so that a weak, second harmonic pulse initially tuned inside the gap is almost entirely transmitted. The process is due cascading, which occurs far from phase matching conditions, and causes pulse compression. A nonlinear polarization spawns a dark soliton, while a nonlinear magnetization produces a bright soliton. 
Michael Scalora, Domenico de Ceglia, Giuseppe D'Aguanno, Nadia   Mattiucci, Neset Akozbek, Marco Centini, Mark Bloemer