  An envelope function approach is used to study the wave propagation in a
one-dimensional Photonic Crystal containing single negative layers. This
approach enables one to obtain the analytic expressions of the parameters of an
equivalent effective medium. From these parameters, it is seen that the
periodic structure appears to be an equivalent left-handed medium for the
envelope function. For the nonlinear wave propagation the phenomenon of
bistability and gap soliton formation near the edges of the zero-phi gap is
discussed.
