Design of resonators using materials with negative refractive index
  By optimizing the design we show that inhomogeneous electromagnetic resonators with almost uniform field intensity and up to twice the energy density of conventional structures are possible by exploiting the properties of negative refractive index materials. materials. We demonstrate that using negative refractive index materials it is possible to make full width at half maximum (FWHM) of the transmission coefficient independent from cavity length L. 
Petra Schmidt, Ilya Grigorenko and A.F.J. Levi