A method for preparing cascaded bulk holographic raster DWDM device features that the holographic record medium is divided into different space subregions for recording 1-4 bulk holographic rasters in each subregion, the vector directions of all bulk rastors have a 45 deg of included angle relative to the end face, when raster is recorded by short wavelength, the plane of writing-in beam is perpendicular to the plane of I/O beams, the output channels for all wavelengthes are parallel for highest diffraction efficiency, the diffraction efficiency and wavelength selectivity are optimized, the crosstalking between channels is suppressed, and the service life of raster is elongated by thermal or optical fixing. |