Spatial modulational instability in one-dimensional LiNbO/sub 3/ slab waveguides

Summary form only given. There has always been a close link in optically nonlinear media between solitons and high power beam break-up, i.e., modulational instability (MI). The classical example are temporal solitons, and the break-up of CW beams into a periodic pattern of pulses in fibers. Similarly for spatial solitons which have a finite spatial extent, very wide beams break up into periodic filaments. Theory has predicted MI for planewave nonlinear eigenmodes consisting of fundamental (FW) and second harmonic (SH) waves. However, MI occurs with only FW injection in SHG and was observed with quasione-dimensional (Q1D) input. A wide elliptical beam incident into a doubling medium broke up into a line of periodic two-dimensional quadratic solitons. There the excess energy was shed transverse to the line allowing the formation of solitons. The situation is different for the one-dimensional (1D) case in slab waveguides because the radiation is trapped in the plane of the waveguide and can only leak out after a long propagation distance. In the paper we report on spatial MI during SHG in LiNbO/sub 3/ slab waveguides.