Two-dimensional random access scanner for optical disks

Abstract

A system and a method for optical access of the surface of an optical disk (or another moving media information storage device) with a very short seek time is presented. The system uses two-dimensional deflection of a light (typically laser) beam. The beam reaches a stationary lenslet array, where, at a particular moment, it intercepts a single lenslet. The lenslet focuses the beam to a spot on the information storage surface of the disk. For reading information, the beam is reflected through the lenslet. Taking advantage of the "cat-eye" retro-reflection principle, only one detector (or very few detectors) is needed. Since only one spot at the surface is illuminated at any given moment, this spot gets most of the laser's light, allowing sufficient power concentration when needed for writing information on the disk.

I claim: 
     
       1. A method of directing an optical beam from an optical beam source to a selected storage location spot on the surface of a moving optical storage medium, comprising: interposing a static two-dimensional array of image focussing elements adjacent to the surface between the surface and the optical beam source; and   steering the optical beam from the source to a selected single one of said image focussing elements in the two-dimensional array to focus the optical beam to a single selected storage location spot on the surface.   
     
     
       2. A method in accordance with claim 1, wherein the storage location spot to which the optical beam is focussed has a size in the order of magnitude of the light wavelength of the optical beam. 
     
     
       3. The method according to claim 1, wherein the optical storage medium is a rotatable optical data disk. 
     
     
       4. The method according to claim 1, wherein said static two-dimensional array of image focussing elements is an array of refractive lenslets. 
     
     
       5. The method according to claim 1, wherein said static two-dimensional array of image focussing elements is an array of diffractive lenses. 
     
     
       6. The method according to claim 1, further comprising interposing an apertured mask between the array of image focussing elements and the optical beam source to prevent the optical beam from reaching two image focussing elements at the same time. 
     
     
       7. The method according to claim 1, further including the step of reflecting the optical beam from the focussed spot via an image focussing element to a static detector assembly. 
     
     
       8. The method according to claim 7, wherein the reflected optical beam is reflected via a beam splitter to the static detector assembly. 
     
     
       9. The method according to claim 7, further including introducing some astigmatism into the optical beam reflected from the selected image focussing element and using said introduced astigmatism for detecting and correcting focussing errors. 
     
     
       10. The method according to claim 1, further including providing a lens adjacent the image focussing elements between the image focussing elements and the optical beam source to produce a virtual image of the optical beam close to the image focussing elements. 
     
     
       11. The method according to claim 1, further including disposing a planar optical member over the array of image focussing elements, wherein said steering step comprises steering the optical beam into an edge of the planar optical member. 
     
     
       12. The method according to claim 1, further including passing said optical beam through a grating before the optical beam reaches said static array of image focussing elements to split the beam into a zero order straddled by two weaker-orders, and using said two weaker orders for detecting and correcting tracking errors. 
     
     
       13. Apparatus for directing an optical beam from an optical beam source to a selected storage location spot on the surface of a moving optical storage medium, comprising: a static two-dimensional array of image focussing elements located adjacent to the surface between the surface and the optical beam source; and   means for steering the optical beam from the source to a selected single one of said image focussing elements in said two-dimensional array to focus the optical beam to a single selected storage location spot on the surface.   
     
     
       14. An apparatus in accordance with claim 13, wherein the storage location spot to which the optical beam is focussed has a size in the order of magnitude of the light wavelength of the optical beam. 
     
     
       15. The apparatus according to claim 13, wherein the optical storage medium is a rotatable optical disk, and further including a holder for the rotatable optical disk. 
     
     
       16. The apparatus according to claim 13, wherein said static two-dimensional array of image focussing elements is an array of refractive lenslets. 
     
     
       17. The apparatus according to claim 13, wherein said static two-dimensional array of image focussing elements is an array of diffractive lenses in the form of a hologram. 
     
     
       18. The apparatus according to claim 13, further including an apertured mask interposed between said two-dimensional array of image focussing elements and the optical beam source, which mask prevents the optical beam from reaching two image focussing elements at the same time. 
     
     
       19. The apparatus according to claim 13, further including means for detecting the optical beam after reflection from a focussed spot via one of said image focussing element. 
     
     
       20. The apparatus according to claim 19, further including a beam splitter located to pass the optical beam from the optical beam source to the array of image focussing elements, and to reflect the optical beam reflected from the selected image focussing element to said means for detecting. 
     
     
       21. The apparatus according to claim 20, further including a lens between said beam splitter and said means for detecting, said lens designed to introduce some astigmatism into the beam, and a control system for detecting and correcting focussing of the beam in response to the output of said lens. 
     
     
       22. The apparatus according to claim 13, further including a negative lens adjacent to the image focussing elements between said elements and the optical beam source, said negative lens being designed to produce a virtual image of the optical beam close to the image focussing elements. 
     
     
       23. The apparatus according to claim 13, further including a planar optical member overlying the array of image focussing elements, said means for steering steering the optical beam into an edge of said planar optical member. 
     
     
       24. The apparatus according to claim 23, wherein said planar optical member is a slab having one surface which is slanted with respect to an opposed surface to thereby produce multiple-reflections of the optical beam steered into the edge of said planar optical member at decreasing angles to the normal of said opposed surface until the optical beam exits from said member at a selected location thereof to a selected one of said image focussing elements. 
     
     
       25. The apparatus according to claim 23, wherein said planar optical member includes a holographic layer on the side thereof opposite to that facing said image focussing elements, to reflect the light to a selected one of said image focussing elements. 
     
     
       26. The apparatus according to claim 13, further including a grating located upstream of said static array of image focussing elements to split the beam into a zero order straddled by two weaker±orders, and a control system for detecting and correcting tracking errors in response to said two weaker orders. 
     
     
       27. In a method for reading from and writing to selected storage location spots on an optical storage medium using a focussed optical beam the improvement wherein the optical beam is directed from an optical beam source to a selected storage location spot on the optical storage medium by steps comprising: interposing a static two-dimensional array of image focussing elements adjacent to the optical storage medium, between the optical storage medium and the optical beam source; and   steering the optical beam from the optical beam source to a selected single one of said image focussing elements in the two-dimensional array to focus the optical beam to a single selected storage location spot on the optical storage medium.