Tracking and focus actuator for a holographic optical head

Claims

What is claimed is:

1. An actuator for focus and tracking movements of an objective lens relative to a fixed laser and photodetector in an optical head, comprising:

an optical element for receiving a laser beam from said laser along a first path and reflecting said laser beam at an angle along a second path to said objective lens;

a tube holding said optical element and a leaf spring coupling said objective lens to said tube, thereby allowing movement of said objective lens relative to said optical element along said second path while restricting movement in directions orthogonal to said second path;

first means for moving said tube along said first path for tracking movements;

second means for moving said objective lens relative to said optical element for focusing movements;

a flag coupled to said tube and supporting a mask with a variable gradient for transmitting varying amounts of light depending upon position;

a light source disposed on one side of said mask; and

a photo sensor disposed on a second side of said mask.

2. An actuator for focus and tracking movements of an objective lens relative to a fixed laser and photodetector in an optical head, comprising:

an optical element for receiving a laser beam from said laser along a first path and reflecting said laser beam at an angle along a second path to said objective lens;

a tube holding said optical element and a leaf spring coupling said objective lens to said tube, thereby allowing movement of said objective lens relative to said optical element along said second path while restricting movement in directions orthogonal to said second path;

first means for moving said tube along said first path for tracking movements;

second means for moving said objective lens relative to said optical element for focusing movements; and

a pair of leaf springs coupling said tube to a support structure for said laser and detector for allowing movement along said first path and restricting movement in directions orthogonal to said first path.

3. An apparatus, comprising:

a support structure;

an optical head mounted on said support structure, said optical head having a laser and a photodetector;

an objective lens;

an optical element for receiving a laser beam from said laser along a first path and reflecting said laser beam at an angle along a second path to said objective lens;

means, coupled to said support structure, for coupling said objective lens and said optical element together allowing movement of said objective lens relative to said optical element along said second path while restricting movement between said objective lens and said optical element in directions orthogonal to said second path;

a motor, having at least one electrically conducting coil, for moving the combination of said optical element and said means for coupling linearly along said first path for tracking movements, said laser beam travelling along said first path through said coil of said motor; and

means for moving said objective lens relative to said optical element for focusing movements.

4. The apparatus of claim 3 wherein said angle is 90.degree..

5. The apparatus of claim 3 wherein said means for coupling comprises a tube holding said optical element and a leaf spring coupling said objective lens to said tube.

6. The apparatus of claim 5 wherein said second means for moving comprises a coil coupled to said leaf spring and at least one magnet for interacting with said coil.

7. The apparatus of claim 5 wherein said first means for moving comprises a coil coupled to said leaf spring and said tube and at least one magnet for interacting with said coil.

8. The apparatus of claim 3 wherein said optical element is a mirrored prism.

9. The apparatus of claim 3 further comprising:

a diffraction grating disposed between said laser and said optical element to produce a diffracted beam from a reflected beam of said laser beam off a medium, said diffracted beam having an optical axis inclined relative to an optical axis of said reflected beam, said diffraction grating being patterned to produce a spacial variation in said diffracted beam responsive to variations in the focus of said laser beam on said medium; and

said photodetector being configured for detecting said spacial variation in said diffracted beam, said photodetector being positioned to intercept said diffracted beam.

10. The apparatus of claim 3 wherein said optical head is a magneto-optical head for reading information recorded on a reflective medium, comprising:

a laser pen for directing said laser beam having a first polarization to said optical element, said laser pen including a diffraction grating for producing a diffracted beam from a reflected beam of said laser beam off said medium for focus error detection;

a polarization beam-splitter mounted between said diffraction grating and said optical element for reflecting substantially all of a first component of said reflected beam having a second polarization orthogonal to said first polarization of said laser beam; and

second photodetector means for detecting said reflected component.

11. The apparatus of claim 3 wherein said optical head is a magneto-optical head for reading information recorded on a reflective medium, comprising:

a laser pen for directing said laser beam to said optical element, said laser pen including a diffraction grating for producing a diffracted beam from a reflected beam of said laser beam off said medium for focus error detection;

a polarization beam-splitter mounted between said diffraction grating and said optical element for reflecting a substantial portion of a component of said reflected beam having a polarization orthogonal to said laser beam, transmitting to said diffraction grating a portion of a component of said reflected beam having the same polarization as said laser beam and reflecting a portion of said second component;

a second diffraction grating for producing a plurality of different beams from said reflected components;

second and third photodetectors for detecting beams from said second diffraction grating; and

first and second depolarizes mounted between said second diffraction grating and said first and second photodetectors, respectively, said first polarizer transmitting light of a second polarization oriented approximately 45.degree. with respect to said first polarization and said second polarizer transmitting light of a third polarization oriented approximately 90.degree. with respect to said second polarization.

12. The apparatus of claim 3 wherein said optical head is a magneto-optical head for reading information recorded on a reflective medium, comprising:

said laser;

a diffraction grating disposed between said laser and said optical element to produce a diffracted beam from a reflected beam of said laser beam off said medium, said diffracted beam having an optical axis inclined relative to an optical axis of said reflected beam, said diffraction grating being patterned to produce a spacial variation in said diffracted beam responsive to variations in the focus of said laser beam on said medium;

said first-mentioned photodetector being configured for detecting said spacial variation in said diffracted beam, said first photodetector being positioned to intercept said diffracted beam;

a polarization beam-splitting mounted between said diffraction grating and said optical element for reflecting substantially all of a component of said reflected beam having a polarization orthogonal to said laser beam; and

a second photodetector for detecting said reflected component.

13. An actuator for focus and tracking movements of an objective lens relative to a fixed laser and photodetector in an optical head, comprising:

an optical element for reflecting a laser beam at an angle;

a first wire coil coupled to said optical element so that said laser beam passes through the center of said wire coil on a first side of said optical element;

a second coil positioned on a second side of said optical element and coupled to said objective lens so that said laser beam, after being reflected by said angle, passes through a center of said second coil and said objective lens;

first resilient means for supporting said first wire coil and said optical element, allowing movement along a first path of said laser beam on said first side of said optical element;

second resilient means for coupling said second coil and said objective lens to said first coil, allowing movement along a second path of said laser beam on said second side of said optical element;

a first permanent magnet positioned to interact with said first coil to cause movement of said first coil along said first path; and

a second permanent magnet positioned to interact with said second coil to cause movement of said second coil along said second path.

14. An actuator for focus and tracking movements of an objective lens relative to a fixed laser and photodetector in an optical head, comprising:

a mirrored prism for reflecting a laser beam received on a first path from said laser at a right angle along a second path to said objective lens;

a tube supporting said mirrored prism and having an opening adjacent said prism for allowing said laser beam on said second path to pass, said tube having a first open end for receiving said laser beam on said first path;

first and second leaf springs coupled to said tube for supporting said tube;

third and fourth leaf springs coupled to said objective lens and to each other at a first end;

a first, tracking coil coupled to said first end of said tube and a second end of said third and fourth leaf springs;

a first magnet for interacting with said first, tracking coil for moving said tube, prism, third and fourth leaf springs and objective lens parallel to said first path;

a second, focusing coil coupled to one of said third and fourth leaf springs; and

a second magnet for interacting with said second, focusing coil for producing relative movement of said objective lens with respect to said prism parallel to said second path.

15. The actuator of claim 14 further comprising a plurality of additional tracking coils coupled to said focusing coil and positioned to interact with said second magnet to move said tube in a direction parallel to said first path in cooperation with said first tracking coil.

16. An apparatus comprising:

an objective lens;

an optical head having a laser and photodetector;

an optical element for reflecting a laser beam at an angle;

a first wire coil coupled to said optical element so that said laser beam passes through the center of said wire coil on a first side of said optical element;

a second coil positioned on a second side of said optical element and coupled to said objective lens so that said laser beam, after being reflected by said angle, passes through a center of said second coil and said objective lens;

first resilient means for supporting said first wire coil and said optical element, allowing movement along a first path of said laser beam on said first side of said optical element;

second resilient means for coupling said second coil and said objective lens to said first coil, allowing movement along a second path of said laser beam on said second side of said optical element while restricting movement between said objective lens and said optical element in directions orthogonal to said second path;

a first permanent magnet positioned to interact with said first coil to cause movement of said first coil along said first path; and

a second permanent magnet positioned to interact with said second coil to cause movement of said second coil along said second path.

17. An actuator for focus and tracking movements of an objective lens relative to a fixed laser and photodetector in an optical head, comprising:

a mirrored prism for reflecting a laser beam received on a first path from said laser at a right angle along a second path to said objective lens;

a tube supporting said mirrored prism and having an opening adjacent said prism for allowing said laser beam on said second path to pass, said tube having a first open end for receiving said laser beam on said first path;

first and second leaf springs coupled to said tube for supporting said tube;

third and fourth leaf springs coupled to said objective lens and to each other at a first end allowing movement of said objective lens along said second path while restricting movement between said objective lens and said optical element in directions orthogonal to said second path;

a first, tracking coil coupled to said first end of said tube and a second end of said third and fourth leaf springs;

a first magnet for interacting with said first, tracking coil for moving said tube, prism, third and fourth leaf springs and objective lens parallel to said first path;

a second, focusing coil coupled to one of said third and fourth leaf springs; and

a second magnet for interacting with said second, focusing coil for producing relative movement of said objective lens with respect to said prism parallel to said second path.

18. The actuator of claim 17 further comprising a plurality of additional tracking coils coupled to said focusing coil and positioned to interact with said second magnet to move said tube in a direction parallel to said first path in cooperation with said first tracking coil.