  We report on a scheme which might make it practically possible to engineer
the effective competing nonlinearities that on average govern the light
propagation in quasi-phase-matching (QPM) gratings. Modulation of the QPM
period with a second longer period, introduces an extra degree of freedom,
which can be used to engineer the effective quadratic and induced cubic
nonlinearity. However, in contrast to former work here we use a simple
phase-reversal grating for the modulation, which is practically realizable and
has already been fabricated. Furthermore, we develop the theory for arbitrary
relative lengths of the two periods and we consider the effect on solitons and
the bandwidth for their generation. We derive an expression for the bandwidth
of multicolor soliton generation in two-period QPM samples and we predict and
confirm numerically that the bandwidth is broader in the two-period QPM sample
than in homogeneous structures.
