Slow light in photorefractive phase-engineered index structures

The authors investigate all-optical tunable index structures, induced in photorefractive materials for the observation of room-temperature slow light. The potential of this technique lies in the possibility of reconfiguration in different spectral windows at low pump intensities and transmission properties comparable to fiber-based resonant delay-lines. Volume-holographic gratings offer low insertion loss and narrow bandwidth selectivity but are nearly insensitive to photo-induced damage in the NIR, thus making them suitable for telecom applications, e.g. WDM filters. The narrow spectral features of the thick volume gratings produce a steep slope in the dispersion which can be considered as the basis of all slow-light experiments. Investigations of increased group index of single band-stop configurations in photorefractive materials without gain have proven this concept.