OPTICAL DISC DEVICE

摘要

A hologram (4) is divided into n areas (Ak) by lines perpendicular to the optical axis. An optical sensor (7) is divided into at least two areas (A, A'). An optical disc has signal surfaces. A light reflected from a first signal surface (6a) turns to a light (a) falling on a hologram (4) and a light reflected from a second signal surface (6b) turns to a light (a') also falling on the hologram (4). First-order diffracted lights (ak, ak') having a common diffraction optical axis are produced from the lights (a, a') and projected onto the optical sensor (7). The distributions of the first-order diffracted lights (ak, ak') on the optical sensor (7) is nearly inverted with respect to the intersecting point of the diffraction optical axis and the sensing surface. The first-order diffracted light (ak) is almost included in the area (A), and the first-order diffracted light (ak') is almost included in the area (A').