  We present the first principle theory of the existence and stability of TE
and TM spatial solitons in a subwavelength periodic semiconductor-dielectric
structure. We have found that for the wavelength 1550nm and the interface
separation close to and less than 100nm the band structure of the linear TE and
TM waves becomes similar to the band structure of a homogeneous medium. The
properties of TE solitons change accordingly. However, the transverse profiles
of the TM solitons continue to reflect the subwavelength geometry of the
structure and develop dominant intensity peaks inside the low index dielectric
slots. Our stability analysis based on the linearized Maxwell equations
indicates that the nonlinear TM waves can be approximated as the evanescently
coupled modes of the slot waveguides with the low index dielectric core and the
high index semiconductor cladding. Transition to the regime where the slot
waveguides start to determine properties of TM waves is associated with the so
called Brewster condition.
