Experimental Observation of Discrete Modulational Instability

We report the first experimental observation of modulation instability in a discrete optical nonlinear array.

Figure 1

Experimental setup.

Figure 2

MI gain coefficient $\mathrm{Im}(k_z)$ versus power $P_0$ and spatial frequency $\theta$ for (a) $Q=0$ and (b) $Q=0.3\pi$ and $C=1{\mathrm{mm}}^{-1}$, $\gamma =5{\mathrm{m}}^{-1}{\mathrm{W}}^{-1}$. The thick, solid line indicates the threshold power below which the gain is zero for a given phase shift $\theta$; the dashed line shows the location of the maximum MI gain for a given power $P_0$.

Figure 3

Observed output intensity distribution versus phase difference $Q$ for 6, 72, and 193 W.

Figure 4

Dependence of the amplified seed wave at the output on spatial frequency $\theta$ and power $P_0$. (a) shows the experimental data and (b)  the theoretical prediction. The inset of (a) shows the output spatial intensity distribution at 120 W input pump power at the peak of the gain curve.