Patent ID: 8228574

Claim:
A holographic data storage medium comprising: a substrate; a cover layer; and a holographic recording layer disposed between the substrate and the cover layer; wherein the holographic recording layer comprises: a layer discrimination region comprising a plurality of reflection layers separated to each other in a depth direction of the holographic recording layer; and a data recording region being separated from the layer discrimination region; data is recorded by interference fringes produced by a first beam interfering with a second beam at different depths in the data recording region so that a plurality of data layers formed of the interference fringes are arranged in a depthwise direction of the holographic recording layer; a height of each of the data layers in a depth direction of the holographic recording layer is equal to a height of an associated one of the reflection layers in the depth direction of the holographic recording layer; and before data is recorded, the data layers do not exist physically in the data recording region.