US 5,850,380 A · Photomagnetic head apparatus

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 recording tracks is smaller than the numerical aperture in the radial direction.

Claims14

Dependent claims

A photomagnetic head apparatus, comprising:

a beam splitting assembly which splits a laser beam reflected by concentric recording tracks of a rotated photomagnetic recording disc into three bundles of rays having different polarization directions in a plane which lies in a radial direction of said recording tracks, one of said three bundles of rays being for a servo-signal light and the remaining two bundles of rays being for data signal lights;
a defocusing diffraction element which splits said servo-signal light into at least two bundles of rays in a direction corresponding to a tangential direction of said recording tracks, substantially perpendicular to a splitting direction of said beam splitting assembly and which provides at least two split lights with a predetermined amount of one of a positive defocus and a negative defocus in an optical axis direction;
and
a pair of servo-signal light receiving elements which receive said split beams of said servo-signal light produced by said defocusing diffraction element,
wherein said defocusing diffraction element is made of a non-circular element with a numerical aperture corresponding to said tangential direction of said recording tracks being smaller than a numerical aperture corresponding to said radial direction of said recording tracks to reduce detection of off-axis servo-signal light.

2 more elements

A photomagnetic head apparatus, comprising:

a beam splitting assembly which splits a laser beam reflected by concentric recording tracks of a rotated photomagnetic recording disc into three bundles of rays having different polarization directions in a plane which lies in a radial direction of said recording tracks, one of said three bundles of rays being for a servo-signal light and the remaining two bundles of rays being for data signal lights;
a non-circular defocusing diffraction element which splits said servo-signal light into a least two bundles of rays in a direction corresponding to a tangential direction of said recording tracks, substantially perpendicular to a splitting direction of said beam splitting assembly and which provides at least two split lights with a predetermined amount of one of a positive defocus and a negative defocus in an optical axis direction, said defocusing diffraction element defining a substantially circular shape together with a linear diffraction element;
a pair of servo-signal light receiving elements which receive said split beams of said servo-signal light produced by said defocusing diffraction element;
data signal light receiving elements which receive said data signal lights;
and
a condenser lens which gathers said servo-signal light and said data signal light onto said servo-signal light receiving elements and said data signal light receiving elements,
wherein said servo-signal light receiving elements and said data signal light receiving elements are arranged such that light transmitted through and split by said linear diffraction element is received by said data signal light receiving elements without being made incident upon said servo-signal light receiving elements, a detection of off-axis servo-signal light being reduced by having a numerical aperture in said non-circular diffraction element corresponding to said tangential direction of said recording tracks being smaller than a numerical aperture in said non-circular diffraction element corresponding to said radial direction of said recording tracks.

4 more elements

Dependencies are inferred from the claim text.

Photomagnetic head apparatus

Life of this patent

Photomagnetic head apparatus

Life of this patent

Abstract

Claims14