Optical head comprising a diffraction grating for directing two or more diffracted beams to optical detectors

An optical head device for use in combination with an optical source for generating a coherent beam along a main optical axis and with an optical recording medium, said optical head device comprising a focussing lens for focussing an input beam on said optical recording medium along a lens axis of said focussing lens and responsive to an optical beam reflected from said optical recording medium for producing an output beam along said lens axis, and a diffraction grating having a plurality of grating regions responsive to said coherent beam for producing a zeroth-order diffracted beam as said input beam and responsive to said output beam for directing a plurality of sidewards diffracted beams to an optical detector assembly along a plurality of side optical axes, said diffraction grating having substantially no dependency on p-polarized and s-polarized beams and substantially no focal power, wherein said grating regions consist of first through fourth grating regions for directing first through fourth diffracted beams to said optical detector assembly as said sidewards diffracted beams, said first and said second grating regions being on both sides of a grating line which passes through said main optical axis, said third grating regions being in a predetermined area of said first grating region to be surrounded by said first grating region, said fourth grating region being in a predetermined area of said second grating region to be surrounded by said second grating region.

An optical head device for use in combination with an optical source for generating a coherent beam along a main optical axis and an optical recording medium, said optical head device including a focussing lens for focussing an input beam on said optical recording medium along a lens axis of said focusing lens and responsive to an optical beam reflected from said optical recording medium for producing an output beam along said lens axis, wherein the improvement comprises a diffraction grating having a plurality of grating regions responsive to said coherent beam for producing a zeroth-order diffracted beam as said input beam and responsive to said output beam for directing a plurality of sidewards diffracted beams to an optical detector assembly along a plurality of side optical axes, said diffraction grating having substantially no polarization dependency, wherein said grating regions consist of first through grating regions for directing first through fourth diffracted beams to said optical detector assembly as said sidewards diffracted beams, said first and said second grating regions being on both sides of a grating line which passes through said main optical axis, said third grating region being in a predetermined area of said first grating region to be surrounded by said first grating region, said fourth grating region being in a predetermined area of said second grating region to be surrounded by said second grating region, and wherein said optical detector assembly is disposed on one side of said main optical axis and is partitioned into first through fourth individual optical detectors and first and second additional optical detectors, a set of said first and said second individual optical detectors and another set of said third and said fourth individual optical detectors being partitioned by main partition line which lies on a plane including said main optical axis and said grating line, a set of said first and said fourth individual optical detectors and another set of said second and said third individual optical detectors being patitioned by an auxiliary partition line which is perpendicular to said plane, said first and said second additional optical detectors being positioned along said auxiliary partition line on both sides of said first through said fourth individual optical detectors, said first grating region being for directing said first diffracted beam to at least one of said first and said fourth individual optical detectors, said second grating region being for directing said second diffracted beam to at least one of said second and said third individual optical detectors, said third and said fourth grating regions being for directing said third and said fourth diffracted beams to said first and said second additional optical detectors, respectively.

An optical head device for use in combination with an optical source for generating a coherent beam along a main optical axis and an optical recording medium, said optical head device including a focussing lens for focussing an input beam on said optical recording medium along a lens axis of said focussing lens and responsive to an optical beam reflected from said optical recording medium for producing an output beam along said lens axis, wherein the improvement comprises a diffraction grating having a plurality of grating regions responsive to said coherent beam for producing a zeroth-order diffracted beam as said input beam and responsive to said output beam for directing a plurality of sidewards diffracted beams to an optical detector assembly along a plurality of side optical axes, wherein said grating regions consist of first through fourth grating regions for directing first through fourth diffracted beams to said optical detector assembly as said sidewards diffracted beams, said first and said second grating regions being on both sides of a grating line which passes through said main optical axis, each of said third and said fourth grating regions being bisected by said grating line to be partly surrounded by said first grating region and partly by said second grating region, said third and said fourth grating regions being on both sides of a grating center at which said grating line passes through said main optical axis.

A holographic grating for use in an optical head device comprising an optical source for generating a coherent beam along a main optical axis substantially perpendicular passing through said holographic grating and a four-patitioned optical detector and first and second additional optical detectors on both sides of said four-partitioned optical detector, said four-partitioned and said first and said second additional optical detectors having a common light receiving surface directed to said holographic grating, the light receiving surface of said four-partitioned optical detector beam partition by a main partition line intersecting said main optical axis and an auxiliary partition line which is orthogonal to said main partition line, said four-partitioned optical detector having first and second main points on said main partition line on different sides of said auxiliary partition line, said first and said second additional optical detectors having first and second additional points on a plane defined by said main optical axis and a predetermined one of said main and said auxiliary partition lines, said holographic grating comprising first through fourth grating regions which have slits along interference fringes between spherical wave fronts of the coherent beam generated by said optical source and spherical wave fronts of another coherent beam emitted from said first and said second main points and from said first and said second additional points, respectively.