Two-wave mixing and slow-light effects in liquid crystal light-valves

Abstract

Two-wave mixing experiments performed in a liquid crystal light-valve leads to optical amplification in the Raman-Nath regime of diffraction. By exploiting the dispersion properties associated with the two-wave mixing gain, we demonstrate slow and fast light effects, with the output signal pulse either delayed or anticipated with respect to the input light field. Group velocity as slow as a 0.2 mm/s are obtained, and a large tunability of the group delay is achieved thanks to the ability of controlling the liquid crystal nonlinear response through the main experimental parameters. A theoretical model based on the Kerr-like response of the liquid crystal light-valve accounts for the experimental results and allows us to calculate the group delays for the different output orders. We show that the large group delay obtained in the slow light regime can be exploited to enhance the spectral sensitivity of a Mach-Zehnder interferometer and, on the other side, the narrow frequency bandwidth of the two-wave mixing gain can be used to realize an adaptive holographic system that achieves picometer detection.