  We propose a new concept to generate efficient one-third harmonic light from
an unseeded third harmonic process in optical fibers. Our concept is based on
the dynamic constant (Hamiltonian) of the nonlinear third harmonic generation
in optical fibers and includes a periodic array of nonlinear fibers and phase
compensation elements. We test our concept with a simulation of the nonlinear
interaction between the fundamental and third harmonic modes of a realistic
optical fiber, demonstrating high-efficiency one-third harmonic generation. Our
work opens a new approach to achieving the so far elusive one-third harmonic
generation in optical fibers.
