Slow and Fast Light in Liquid Crystal Light Valves

We show that fast and slow light results from multiple scatterings in a liquid crystal light valve, where nondegenerate two-wave mixing occurs in the Raman-Nath regime of optical diffraction. The large nonlinear response and dispersive characteristics of the liquid crystals allow us to obtain group velocities as slow as less than $0.2\mathrm{mm}/\mathrm{s}$, which is attractive for the realization of ultrahigh precision interferometers and metrology measurements.

Figure 1

Schematic setup for fast and slow light operation: the input pulse $I_{\mathrm{in}}$ is coupled with a cw pump beam $I_p$; at the output the pulse is split into several diffraction orders showing different advance or delay. An image (a) is imposed on the input pulse and (b) is delayed on the $I_1$ pulse.

Figure 2

Theoretical variation of the two-wave mixing (a) gain $G_m$ and (b) phase shift ${\phi }_m$ as a function of the frequency (${\omega }_m-{\omega }_p$) for each diffracted order $m$.

Figure 3

Experimental time dependencies of the output pulse taken on the (a) $m=0$ [gray (red) line] and (b) $m=-2$ [gray (blue) line] diffraction order of the input pulse (black line), showing (a) fast and (b) slow light behavior. For each pulse, the intensity is normalized to its peak value.

Figure 4

(a) Maximum delay time $\Delta t_{\max }^m$ versus the order $m$ of the output for ${\tau }_g=95\mathrm{ms}$; red dots are numerical points, black squares are experimental data. (b) Group velocity $v_g$ vs $\delta /2\pi$ for $m=0$ [gray (red)] and $m=-2$ (black); lines are theoretical, squares are experimental points.