Spatial Solutions in Photorefractive Media,
CALIFORNIA INST OF TECH PASADENA
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Light solitons in space spatial soliton have been under an intensive theoretical and experimental research in the last three decades. The solitons evolve from nonlinear changes in the refractive index of the material, due to the light intensity distribution. When the modulation of the index confines the light beam in such a way that diffraction is compensated for exactly, the beam becomes self-trapped, and is called a spatial soliton. The nonlinear effects, which are responsible to soliton formation, are in general Kerr-like effects, causing local index changes proportional to the local light power. The index changes needed for spatial solitons require high power densities, and often exceed 1MWattsq.cm. We present here a new type of solitons in space, generated by the photorefractive PR effect in the medium. The solitonic waveform modulates the refractive index due to the PR effect, compensates for the diffraction exactly, and causes the light beam to propagate with no spatial change. This specific index modulation is introduced by interference gratings between the pairs of the spatial components which compose the light beam, that are translated into phase gratings by the PR effect. Since the efficiency of this effect is independent of absolute light intensity, our solitons can be generated even at very moderate light power densities. Moreover, the same solitonic waveform can propagate unchanged in the medium, at very high or very low light intensities.