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The ability to delay short light pulses is a promising solution for all-optical telecommunications, but suffers from a large distortion of the delayed pulse as a consequence of the high material dispersion. In this Letter, we demonstrate the possibility to all-optically control the group delay in a photorefractive (PR) crystal by the use of the two-wave mixing (TWM) effect in the pulse regime at room temperature. Most importantly, we show that a proper choice of the pump pulse width in the TWM process enables us to slow down shorter or longer signal pulses without distortion. The technique is demonstrated both at visible (638 nm) and infrared (1064 nm) wavelengths and for slowed-down pulses with durations ranging from 10 ns up to 30 ms, hence confirming its broad applicability.

We demonstrate self-pumped optical phase conjugation in Te-doped Sn2P2S6, a semiconducting ferroelectric crystal, using a 1.06 microm wavelength cw Nd:YAG laser. The photorefractive gain of this crystal has been increased to Gamma = (3.9+/- 0.4) cm-1 by Te doping. We observed self-pumped optical phase conjugation in a ring cavity scheme with phase conjugate reflectivities of more than 40 percent and a very fast phase conjugate rise time below 100ms at a light intensity of 20 W/cm2. This is more than two orders of magnitude faster than in any other photorefractive crystal, as e.g. in Rh-doped BaTiO3.