All-optical information conversion in Rb vapor based on the spatial cross-phase modulation.

Abstract

All-optical information conversion, conveying optical signals without electro-optical transformation, plays a vital role in the all-optical devices and optical communication. We achieve the all-optical information conversion in Rb vapor by utilizing the spatial cross-phase modulation. The refractive index of atomic medium is spatially modulated by the strong switch laser beam, which makes it as a nonlinear focusing lens for the weak signal laser beam. As a result, the far-field diffraction ring patterns of the signal laser beam interacted with atoms can effectively carry the nonlinear phase shift information of the switch laser beam. The channel numbers, channel capacities and channel storage densities of information transmission from switch laser beam to signal laser beam are investigated in the terms of switch laser intensity and vapor temperature. Finally, a special "sxu" alphabetic string, encoded by ASCII code, is introduced to verify this all-optical information conversion scheme. This work paves the way for studying optical information processing and all-optical networking with atomic ensembles.