A holographic storage layer includes a reflective structure and photosensitive units. The reflective structure is a grid-shaped structure and includes cavities. The photosensitive units are disposed in the cavities, in which each of the photosensitive units is surrounded by the reflective structure. First openings and second openings are defined by the reflective structure, and the photosensitive units are exposed by the first openings and the second openings respectively.