Two-dimensional electromagnetically induced grating in coherent atomic medium

We propose a scheme for effectively creating a type of all optical device called electromagnetically induced two-dimensional grating by utilizing a four-level coherent atomic medium, which is coherently driven by two orthogonal standing-wave fields. With a far-off resonant trigger field, a spatially modulated cross-phase modulation takes place accompanied by vanishing absorption. The resulting phase grating can diffract the probe beam into high-order directions. When a resonant trigger field is applied on the atoms, the probe obtains gain without inversion due to the atomic coherence effect. And then a gain-phase grating is formed. The diffraction efficiency can be significantly improved compared with that of phase grating. The results show that the diffraction efficiencies attainable by the gratings strongly depend on the interaction length, coherent field intensity, probe field detuning and coherent field detuning. Therefore, the proposed gratings can be used as two-dimensional multi-channel beam splitter which have potential application in optical networking and communication.