  Spectral method related to Lame equation with finite-gap potential is used to
study the optical cascading equations. These equations are known not to be
integrable by inverse scattering method. Due to "partial integrability" two-gap
solutions are obtained in terms of products of elliptic functions and are
classified in five different families related to eigenvalues of appropriate
spectral problem. In special cases, when periodic solutions reduce to localized
solitary waves, previously known phase-locked solutions are recovered, and
additional one solution is obtained. For vector nonlinear Schrodinger equation
n=3 we present exact solutions in a form of multicomponent cnoidal waves.
