Abstract
Over the past decade, photorefractive materials have become a key tool in the study of optical spatial solitons, by enabling experiments with very low optical power, and allowing for self-trapping in both transverse dimensions.1 Photorefractives are candidates for exciting soliton applications, such as light-induced reconfigurable directional couplers,2 beam splitters,3 waveguide switching devices,4 and a tunable waveguides for nonlinear frequency conversion.5 Unfortunately, the formation time of solitons in most photorefractives is long (at low intensities), being inversely proportional to the mobility, which is low (~1 cm2/Vsec) in oxides. In principle, photorefractive semiconductors (GaAs, InP), having a high mobility, could offer formation 1000 times faster than other photorefractives, but these have tiny electrooptic coefficients so narrow solitons would mean applying very large bias fields. Yet narrow solitons were observed in InP:Fe at moderate fields (~5 kV/cm).6 This is because in InP:Fe, a unique resonance mechanism occurs when the thermal excitation of electrons is comparable to the optical hole excitation. At a particular resonance intensity, both charge carriers are drastically depleted in the illuminated regions, leading to a dramatic decrease in conductivity, resulting in a 15-fold enhancement of the space charge field in this region. The resonance effiect in InP was first observed in two-wave-mixing,7 and recently the theory was formulated for solitons as well.
© 2002 Optical Society of America
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