50 GB read only memory disc with dual layer structure

Recently, a Blu-ray Disc (BD) has been proposed as a rewritable optical disc, in which HDTV digital data can be recorded for two hours or more. It has a capacity of about 25 GB with a size of 120 mm in diameter. It employs a blue laser of 405 nm wavelength and an objective lens with an NA of 0.85 to reproduce through a transparent substrate which is about 0.1 mm-thick. We conducted experiments to study a read only memory (ROM) disc with the same capacity as BD. Then, we confirmed the feasibility of the dual layer ROM disc with density equivalent to 50 GB capacity, which can be read from one side. We report the experimental results on recording of the master and the results of the evaluations.