Abstract
Parametric gain associated with discrete modulational instability due to the second order nonlinearity chi(2)(-2omega;omega,omega) was investigated experimentally in periodically poled lithium niobate arrays of weakly coupled channel waveguides for conditions of both positive and negative phase-mismatch for second harmonic generation.
Highlights
Parametric gain associated with discrete modulational instability due to the second order nonlinearity χ(2)(-2ω;ω,ω) was investigated experimentally in periodically poled lithium niobate arrays of weakly coupled channel waveguides for conditions of both positive and negative phase-mismatch for second harmonic generation
The most fundamental consequence of propagating high intensity, plane waves beams in bulk optically nonlinear media is that filamentation due to any amplitude or phase noise present on the beam occurs for media with an effective self-focusing nonlinearity but not in media with negative nonlinearities [1,2]
Such phenomena have been observed in a variety of continuous nonlinear optical media, the behavior having many universal properties because diffraction has only one sign in continuous media [3,4,5]
Summary
The most fundamental consequence of propagating high intensity, plane waves beams in bulk optically nonlinear media is that filamentation due to any amplitude or phase noise present on the beam occurs for media with an effective self-focusing nonlinearity but not in media with negative (defocusing) nonlinearities [1,2] Such phenomena have been observed in a variety of continuous nonlinear optical media, the behavior having many universal properties because diffraction has only one sign in continuous media [3,4,5]. Discrete quadratic solitons associated with second harmonic generation (SHG) have been observed in arrays of periodically poled lithium niobate waveguides [8] In those arrays, can the sign of diffraction for the fundamental beam be changed by varying the propagation direction (ky) across the array, and the sign of the effective focusing or defocusing nonlinearity by varying the phase-mismatch condition for the parametric interaction [13]. We demonstrate for normal incidence onto quadratically nonlinear waveguide arrays the existence of parametric gain associated with modulational instability for self-focusing nonlinearities, and its absence in the defocusing case
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