Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
  • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
  • G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
  • G11B7/13925—Means for controlling the beam wavefront, e.g. for correction of aberration active, e.g. controlled by electrical or mechanical means
  • G11B7/13927—Means for controlling the beam wavefront, e.g. for correction of aberration active, e.g. controlled by electrical or mechanical means during transducing, e.g. to correct for variation of the spherical aberration due to disc tilt or irregularities in the cover layer thickness
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
  • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
  • G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
  • G11B7/1369—Active plates, e.g. liquid crystal panels or electrostrictive elements
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
  • G11B2007/0009—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage
  • G11B2007/0013—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage for carriers having multiple discrete layers

Definitions

• the present invention generally related to an optical reading device for writing /reading on/from multi-layer disks utilizing a light beam from a light source and provided with a device for controlling and correction of the wave front of phase shift of light beam which is produced by changing of thickness in the substrate of information layer.
• the thickness of substrate changes in transition from one informational layer to another during reading and due to technological deviations of substrate at disk fabrication.
• Magneto-optical and phase optical carriers such as optical and magneto-optical disks, magnetic disks and magnetic tapes are most popular carriers for digital information. Such carriers were used as information carriers for writing/reading by light beam from laser source. Recently, carriers using fluorescent layers for writing/reading of information were suggested in the related art. Thin film is distributed at the surface of a carrier with preliminary created profile forms a recording layer with a strong fluorescent action.
• Such optical carriers have exceptional optical properties like optical transparency and significant difference in wavelengths of laser write/excitement beam and reading fluorescent beam.
• Multi-layer fluorescent disk almost transparent for the laser beam allows developing disks with 10 and more layers.
• the allowable limit for inter-layer gap should be above 30 ⁇ m, which is necessary to keep the required level of cross-noise from different informational layers of the multi-layer disk. Therefore, only 3 layers of high-density record could be obtained without spherical aberration correction.
• the number of write/read layers on disk could be increased ten times or more by using a module for detection of the substrate thickness of the record layer and phase corrector for the lens spherical aberration. This solution allows a significant increase of the lens aperture, reduces the write/read wavelength and increases information density, and write/read 10 th informational layers on the disk.
• An additional problem for the high-density carrier is the focusing of the lens with a high numeric aperture.
• the design problem of an effective focus sensor having minimum cross-noise from neighbor layers is derived from decreasing focus deepness by inverse square of numeric lens aperture, and cross-interaction of neighbor layers on a focus sensor signal. Focusing sensors realizing algorithm of signal generation by phase methods e.g. synchronized detection, but not amplitude methods have certain advantages.
• Such a sensor construction could be realized with piezo-ceramic optical element that will produce a periodic phase difference for optical irradiation between central and peripheral lens zones with a property producing unfocusing on a carrier of light beam.
• a single piezo-ceramic element will allow a high-density multi-layer recording on optical carrier and provide an effective defocusing sensor that will not be sensitive to the amplitude cross-noise from the above and lower informational layers.
• an optical information reader for writing/reading of multi-layer optical disks utilizing light beam from the light source directed to optical carrier by the lens and receiving reflected or fluorescent light.
• the optical reader includes a device for receiving reflected fluorescent light and a detector of the disk writing/reading layer which determines the required value of compensation or correction of spherical aberration compared to the calculated one.
• the writing layer detector controls the reflected or fluorescent light signal obtained from information layer of the carrier.
• the optical reader also includes also a piezo-ceramic optical element located in a light beam that is directed from the light source to the carrier.
• This piezo-element has a phase difference between central and peripheral zones that depend on sign and value of voltage applied to it.
• An optical reader can determine a value and sign of optical aberration with high accuracy.
• the piezo-ceramic element reduces spherical aberrations to the accepted level at any writing layer and at any radial position of spot on record track. In such a way the average value of spherical aberration and its current value mediated by fluctuation of record layer thickness will be reduced.
• a piezo-ceramic device reduces aberrations by using the phase differences change between its central and peripheral zones as result of current change of record layer thickness.
• Fig. 1 is an electrostriction device for the spherical aberration correction. Electrodes are shown by numbers 1 ,2 and 3. Radius Ro» ho.
• Fig. 2 is an electrostriction device for the focus scanning. Electrodes are shown by numbers 1 ,2 and 3. Radius Ro ⁇ ho.
• Fig. 3 is a combined electrostriction device. Electrodes are shown by numbers 1 ,2,3 and 4.
• the present invention relates to the optical information reader for writing/reading of multi-layer optical disks utilizing the light beam from the light source directed to optical carrier by the lens and receiving reflected or fluorescent light from the optical carrier.
• the present invention comprises an optical reading device for reading, correction of spherical aberration and focusing that can maintains a minimum spherical aberration and a high accuracy lens focusing with high aperture during reading of multi-layer optical high-density disks.
• the optical reading device includes information reading means illuminating an optical disk with irradiated light beam via an objective lens and detecting a light reflected from the optical disk to read information, thickness record layer and defocusing detector, and an electrostriction device located in the path of a light beam passing from the light source and secured to the lens on moving part of the lens moving device for producing a phase difference between the central and peripheral parts when voltage is applied thereto.
• the present invention also comprises a device for controlling the lens spherical aberration invoked by deviation of informational layer thickness in comparison with calculation rating of the given lens.
• a device for controlling the lens spherical aberration invoked by deviation of informational layer thickness in comparison with calculation rating of the given lens are described US Patent No. 5513153 containing titanium or tin oxide and divided into central and peripheral compartments.
• the electrostriction devices in the '153 patent are incorporated herein in their entirety.
• Transparent electrodes are introduced in such medium.
• Light beam phase difference providing the lens focal point move or the convergence of light beams in the lens focus could be obtained by application of differential voltage to central and peripheral parts of the electrodes.
• Additional high frequency 'scanning' or phase difference formation for electrostriction device can be utilized for the detection of spherical aberration and focusing.
• ⁇ cf ⁇ r 4 + ⁇ 2 r 6 + ⁇ 3 r 8
• 2-coordinate actuator reducing the focusing error is sing as lens device control in focus direction.
• Electrostriction device used for the beam dephasing by formulas (1) or (2) can work as spherical aberration control device. It is necessary to reside the electrode system in such a way that phase gradient was achieving a necessary value.
• the dephasing at the spherical aberration correction will be up to 2-3 ⁇ in the range 0-100 Hz because of an electrostriction element is an executive mechanism if the phase difference due to base focusing signals less then O.l ⁇ at frequencies more 10 KHz.
• One central and one peripheral electrode is enough for the support of defocusing phase difference. At least 2 peripheral electrodes are necessary for spherical aberration phase difference to maintain bend of the function of phase difference at the maximum (minimum), which is not necessary for the defocusing phase difference.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Optical Head (AREA)
• Optical Recording Or Reproduction (AREA)

Applications Claiming Priority (3)

Publications (1)

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Cited By (1)

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• 2002
  • 2002-06-25 JP JP2003507811A patent/JP2005508559A/ja active Pending
  • 2002-06-25 CN CNA028161602A patent/CN101366085A/zh active Pending
  • 2002-06-25 EP EP02742281A patent/EP1579429A2/de not_active Withdrawn
  • 2002-06-25 WO PCT/US2002/019979 patent/WO2003001512A2/en not_active Ceased
  • 2002-06-25 AU AU2002315429A patent/AU2002315429A1/en not_active Abandoned

Non-Patent Citations (1)

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