Photomagnetic head apparatus
US5850380A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jul 10, 1997 |
| Grant date | Dec 15, 1998 |
| Priority date | — |
| Expiry date | Jul 10, 2017 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B7/0912
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A photomagnetic head apparatus includes a beam splitter which splits a laser beam, reflected by concentric recording tracks of a rotating photomagnetic recording disc, into three bundles of rays. The three bundles of rays have different polarization directions in a plane which lies in a radial direction of the recording tracks. One of the three bundles of rays is used as a servo-signal light, and the remaining two bundles of rays are used as data signal lights. A defocusing diffraction element splits at least the servo-signal light into a least two bundles of rays in a direction corresponding to the tangential direction of the recording tracks, substantially perpendicular to the split direction of the beam splitter and which provides at least two split lights with a predetermined amount of positive or negative defocus in an optical axis direction. A pair of servo-signal light receiving elements receive the split beams of the servo-signal light produced by the defocusing diffraction element. A data light receiving element receives the data signal lights. The defocusing diffraction element is made of a non-circular element whose numerical aperture in the tangential direction of the r…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.