Three-dimensional patterned media for ultrahigh-density optical memory

We report a recording medium in which a three-dimensional nanoscale structure can be photofabricated for multilayered optical memory using a two-photon process. By fabricating the structures in the medium, we can control the shape of recorded bits and, in effect, their spatial frequency distribution. We succeeded in recording bits with a $0.5μm$ interval in any particular plane and $2.0μm$ interval between successive layers. Thus, storage density of $2.0Tbits∕cm3$ is achieved.