| 摘要 |
PROBLEM TO BE SOLVED: To achieve high density by using three-dimensional recording and reproducing method. SOLUTION: A three-dimensional recording and reproducing device having a recording medium 4 accumulating plural recording layers 1 on a substrate 3 and an optical system focuses light on each of the plural recording layers 1 from the side of the substrate 3, and records or reproduces information three- dimensionally, satisfies the expression, λ/4<=(1/8NB)(1/NB2-1)NAF4Δd. In the expression, λ is a wavelength of the light, NB is a refractive index of the substrate 3, NAF is a numerical aperture of a focusing lens 8, and Δd is a range of the positions in the direction of the optical axis where the recording layers exist and the light should be focused on. Thus, high density recording/ reproducing of data is achieved with a high reliability by focusing a light spot on each layer of a multi-film structured disk. |
