Abstract: An optical recording medium includes recording layers and intermediate layers. The recording layers include a diffraction grating that has a predetermined grating pitch and is obtained by alternately laminating first layers and second layers being transparent and having slightly different refractive indexes. The intermediate layers are transparent and have a larger thickness than that of the recording layers. In the optical recording medium, the recording layers and the intermediate layers are alternately laminated.

Abstract: A disc-shaped optical data recording medium has a signal recording layer for reading and/or writing data using light, and a 10 ?m to 200 ?m thick transparent protective layer disposed over the signal recording layer. The optical data recording medium includes a protrusion projecting from a surface of the transparent protective layer on a light-incidence surface side to which light is emitted to the signal recording layer. The protrusion is disposed in an area between a center hole and a clamping area where the optical data recording medium is held when reading and/or writing data in the signal recording layer.

Abstract: According to one embodiment, letting Vf be a maximum voltage value level within the range of a frequency 60 to 170 times the rotational speed of a stamper and Vave be the average sum signal voltage value of a data recording portion in the sum signal of a voltage signal when the data recording portion is irradiated with a laser having a wavelength of 450 nm or less and an NA of 0.6 or more, whether Vf and Vave meet Vf/Vave<7.7×10?4 . . . (1) is determined.