Based on anisotropic diffraction of photorefractive LiNbO<sub>3</sub> crystal, we theoretically discuss an optical WDM scheme implemented by a single volume grating. Using only one grating recorded by two He-Ne laser beams at a specific wavenumber, we can realize wavelength
demultiplexing around telecommunication wavelength. The possible wavelength range suitable for WDM is discussed, which is in the range from 1081nm to 1217nm. Our theoretical scheme can be used in the design of a practical WDM.