The analytical solution for the interaction of three diffraction orders in
the Kerr medium is obtained by reducing the problem to the completely integ
rable Hamiltonian task. Intensities of all waves are periodic with propagat
ion length and linearly related, the amplitudes are quasi-periodic and expr
essed in elliptic functions. Symmetrical four-order interaction also admits
an analytical solution. (C) 2000 Optical Society of America.