| 摘要 |
<p>An optical head device (201) is provided with a light source (1), an objective lens group (13), a two-dimension actuator (15), spherical aberration adding means (9, 10, 16), a hologram element (17) for splitting an optical beam from an optical disc (14) into a plurality of split beams, and a photodetector (22), which includes at least one light receiving part composed of a plurality of divided light receiving areas and outputs an electric signal corresponding to a light quantity of the split beam entered each of the plurality of divided light receiving areas or an electric signal corresponding to a combination of the light quantities of the split beams entered the plurality of divided light receiving areas. The plurality of split beams split by the hologram element (17) include one circular luminous flux (U1) and at least two annular luminous fluxes (U2, U3).</p> |
