  We develop a self-consistent method to study the optical response of metallic
gratings with nonlinear media embedded within their subwavelength slits. An
optical Kerr nonlinearity is considered. Due to the large E-fields associated
with the excitation of the transmission resonances appearing in this type of
structures, moderate incoming fluxes result in drastic changes in the
transmission spectra. Importantly, optical bistability is obtained for certain
ranges of both flux and wavelength.
