Engineering competing nonlinearities

Weak modulation of a quasi-phase-matching (QPM) grating opens possibilities for engineering both the average quadratic nonlinearity and the incoherent average cubic nonlinearity induced by QPM. The relative strength of the av erage quadratic and effective (intrinsic plus induced) cubic nonlinearity i s studied for LiNbO3. We show how the induced average cubic nonlinearity ca n be engineered to dominate the intrinsic material cubic nonlinearity and h ow doing so will allow the intensity at which the quadratic and cubic nonli nearities balance and thus compete to be decreased to a few gigawatts per s quare centimeter. (C) 1999 Optical Society of America OCIS codes: 070.4340. 050.2770, 060.4080, 190.5530.