| 摘要 |
A difference is set equal to or smaller than 47 nm between first and second birefringent values of a substrate. The first birefringent value is measured for a single pass of an optical beam passing through the substrate of an attitude rotated, relative to a reference plane perpendicular to the optical beam, by 20 degrees around the tangent line tangent to the sequence of phase pits at the projection of the optical beam on the substrate. The second birefringent value is measured for a single pass of the optical beam passing through the substrate of an attitude rotated, relative to the reference plane, by 20 degrees around a straight line extending within a plane including the surface of the substrate in a direction perpendicular to the sequence of phase pits. Jitter can be suppressed in the readout data from phase pits and magnetization in a magnetic film over the phase pits.
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