Modulational instability for normal dispersion

The observation of modulational instability of optical waves in the normal dispersion region has been accomplished through the copropagation of two nonlinearly coupled, orthogonally polarized visible waves in a strongly birefringent optical fiber. Intensity autocorrelations exhibit 1/4 3.5-THz oscillations on both waves, and each wave spectrum develops a single shifted frequency sideband. The results agree well with an analysis of coupled nonlinear Schrödinger equations. © 1990 The American Physical Society.