WO2005086141A2 - Optical device for recording and reproducing - Google Patents

Optical device for recording and reproducing Download PDF

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Publication number
WO2005086141A2
WO2005086141A2 PCT/IB2005/000515 IB2005000515W WO2005086141A2 WO 2005086141 A2 WO2005086141 A2 WO 2005086141A2 IB 2005000515 W IB2005000515 W IB 2005000515W WO 2005086141 A2 WO2005086141 A2 WO 2005086141A2
Authority
WO
WIPO (PCT)
Prior art keywords
optical scanning
scanning device
beam shaper
radiation beam
collimation system
Prior art date
Application number
PCT/IB2005/000515
Other languages
French (fr)
Other versions
WO2005086141A3 (en
Inventor
Joris Vrehen
Petrus Jutte
Bernardus Hendriks
Peter Coops
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2005086141A2 publication Critical patent/WO2005086141A2/en
Publication of WO2005086141A3 publication Critical patent/WO2005086141A3/en

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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
    • G11B7/1398—Means for shaping the cross-section of the beam, e.g. into circular or elliptical cross-section
    • 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
    • G11B7/1353—Diffractive elements, e.g. holograms or gratings
    • 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
    • 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
    • G11B7/1372—Lenses
    • G11B7/1378—Separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders
    • 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
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0006—Recording, reproducing or erasing systems characterised by the structure or type of the carrier adapted for scanning different types of carrier, e.g. CD & DVD
    • 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 relates to an optical scanning device comprising means for compensating for spherical aberration.
  • the present invention is particularly relevant for an optical disc apparatus for recording to and reading from an optical disc, e.g. a CD, a DVD and/or a Blu-Ray Disc (BD) recorder and player.
  • an optical disc e.g. a CD, a DVD and/or a Blu-Ray Disc (BD) recorder and player.
  • laser diodes conventionally used in optical scanning devices emit a radiation beam which angular aperture in a given plane is smaller than the angular aperture in a plane perpendicular to this given plane.
  • the radiation beam thus has an elliptical intensity profile cross-section in the far field.
  • a round intensity profile cross section is preferred on an information carrier scanned by such an optical scanning device.
  • a beam shaper is required, which transforms the elliptical radiation beam into a round radiation beam.
  • a BD player from Nikkei described in "Nikkei Electronics 2003.5.12", page 127, comprises a beam shaper and means for compensating for spherical aberration.
  • the beam shaper is a prismatic beam shaper, and the means for compensating for spherical aberration comprise a telescope.
  • Fig. 1 shows such an optical scanning device.
  • This optical scanning device comprises a radiation source 101 for producing a radiation beam 102, a collimator lens 103, a prismatic beam shaper 104, a beam splitter 105, a telescope 106, an objective lens 107, a servo lens 108, detecting means 109, measuring means 110, and a controller 111.
  • This optical device is intended for scanning an information carrier 100. During a scanning operation, which may be a writing operation or a reading operation, the information carrier 100 is scanned by the radiation beam 102 produced by the radiation source 101.
  • the collimator lens 103 and the objective lens 107 focus the radiation beam 102 on an information layer of the information earner 100.
  • a focus error signal may be detected, corresponding to an error of positioning of the radiation beam 102 on the information layer. This focus error signal may be used for correcting the axial position of the objective lens 107, so as to compensate for a focus error of the radiation beam 102.
  • a signal is sent to the controller 111, which drives an actuator in order to move the objective lens 107 axially.
  • the focus error signal and the data written on the information layer are detected by the detecting means 109.
  • the prismatic beam shaper 104 transforms the elliptical intensity profile cross-section into a round intensity profile cross section. Such a prismatic beam shaper is well known to those skilled in the art.
  • the telescope 106 can change the vergence of the beam entering the objective lens 107.
  • a change in vergence of the beam entering the objective lens 107 will introduce a wavefront aberration in the radiation beam 102 while passing the objective lens 107, in order to compensate for spherical aberration due, for example, to a variation of the cover layer thickness of the information carrier 100.
  • the telescope 106 can transform the radiation beam 102 into a slightly converging or diverging beam, which compensates for the spherical aberration.
  • the optical scanning device comprises means for moving one of the two elements of the telescope 106.
  • the position of the moving element of the telescope 106 is determined in such a way that the spherical aberration is compensated.
  • the optical scanning device may comprise means for measuring the spherical aberration, such as those described in Applicant's US 6,229,600.
  • the amount of spherical aberration to be compensated may be calibrated in the optical scanning device, depending on, for example, the type of information carrier that is scanned.
  • a drawback is that the use of a telescope renders such an optical scanning device bulky.
  • an optical scanning device comprising a beam shaper and means for compensating for spherical aberration, which optical scanning device is compact.
  • the invention proposes an optical scanning device comprising a radiation source for producing a radiation beam, a collimation system, means for changing said collimation system so as to change the vergence of said radiation beam, and a beam shaper placed between said radiation source and said collimation system in such a way that the radiation beam beyond the beam shaper is divergent.
  • the radiation beam beyond the beam shaper has a numerical aperture greater than 0.02
  • the means for compensating for spherical aberration comprise a collimation system and means for changing said collimation system, in order to obtain a slightly diverging or converging beam on the objective lens when spherical aberration compensation is needed.
  • this optical scanning device is more compact than the optical scanning device of the prior art, which comprises a bulky telescope.
  • the use of a changing collimation system is not possible.
  • a diverging or converging radiation beam would enter the prismatic beam shaper 104. This would result in a large amount of astigmatic aberrations in the radiation beam.
  • a changing collimation system is used and the beam shaper is placed before the changing collimation system in the optical path.
  • the beam shaper is chosen in such a way that it can be placed in the diverging radiation beam generated by the radiation source without creating any astigmatic aberration.
  • the radiation beam beyond the beam shaper has a numerical aperture greater than 0.02, which means that a diverging beam passes through said beam shaper, and not a parallel beam as is the case in the prior art.
  • the beam shaper includes a pre-collimation function such that the numerical aperture of the radiation beam before the beam shaper is greater than the numerical aperture of the radiation beam beyond the beam shaper.
  • a lens type beam shaper is for example suitable for such an application.
  • Such a lens type beam shaper is known from, for example, Applicant's EP 0 605923, published July 13, 1994, and patent application US 2002/0166952, by Tanaka et al., published Nov. 14, 2002.
  • the optical scanning device described in US 2002/0166952 comprises a radiation source, a collimator and a lens type beam shaper between the radiation source and the collimator.
  • the optical scanning device does not comprise any means for moving the collimator, because no spherical aberration compensation is required.
  • the technical field of US 2002/0166952 thus completely differs from the one of the present invention, which deals with spherical aberration compensation.
  • Other examples of beam shapers suitable for such an application are described in the detailed description.
  • An example of collimation system that can be changed in order to change the vergence of the radiation beam is a moving collimator.
  • Other examples of collimation systems suitable for such an application are described in the detailed description.
  • the changing means are controlled by a signal indicating which information layer is scanned between at least two information layers of the information carrier. This allows automatically compensating for spherical aberration when jumping from one layer to another layer of the information carrier.
  • the changing means are controlled by a signal indicating which type of information earner is scanned between at least two types of information canier. This allows automatically compensating for spherical aberration when changing the type of information scanned, thus allowing the optical scanning device to be compatible with different types of information carrier.
  • FIG. 1 shows an optical scanning device in accordance with the prior art
  • FIG. 2 shows an optical scanning device in accordance with the invention.
  • FIG. 2 An optical scanning device in accordance with the invention is depicted in Fig. 2.
  • the optical scanning device of Fig. 2 comprises a beam shaper 201 and a changing collimation system
  • the radiation beam 102 produced by the radiation source 101, has an elliptical intensity profile cross section in the far field.
  • the beam shaper 201 is designed in such a way that a substantially circular intensity profile cross section of the radiation beam 102 is obtained when the diverging radiation beam 102 passes through the beam shaper 201.
  • the beam shaper 201 is a lens type beam shaper, which realizes different angular magnifications in two different planes.
  • the beam shaper 201 is placed in the diverging radiation beam 102, i.e. between the radiation source 101 and the changing collimation system 202.
  • An example of such a beam shaper, which can be placed in a diverging beam without generating any coma and astigmatism, is known from EP 0 605923, which describes a lens type beam shaper having a cylindrical entrance surface and a toroidal exit surface.
  • Another example is known from US 2002/0166952, which describes a lens type beam shaper whose both surfaces are toric surfaces.
  • a lens type beam shaper can always be placed in a diverging radiation beam without generating any coma and astigmatism.
  • Another example of beam shaper that can be used in accordance with the invention is an absorption type beam shaper.
  • Such an absorption type beam shaper is known from non- published patent application PCT/IB2003/006157 (applicant's reference PHNL021484), filed under priority of patent application EP 02293260.2.
  • An absorption type beam shaper can be placed in a diverging radiation beam without generating any coma and astigmatism.
  • a further example is a diffractive type beam shaper.
  • Such a diffraction type beam shaper is known from non-published patent application EP 04300065.2 (applicant's reference PHFR040018).
  • a diffraction type beam shaper can be placed in a diverging radiation beam without generating any coma and astigmatism.
  • the radiation beam 102 with a circular intensity profile cross section, subsequently reaches the collimation system 202.
  • the collimation system 202 is a moving collimator.
  • the collimation system 202 may also comprise additional optical elements in order to ensure complete collimation of the radiation beam.
  • the moving collimator 202 transforms the diverging radiation beam 102 into a parallel radiation beam 102, which is then focused on an information layer of the information carrier 100, by means of the objective lens 107.
  • the moving collimator transforms the diverging radiation beam 102 into a slightly converging radiation beam 102.
  • the moving collimator transforms the diverging radiation beam 102 into a slightly diverging radiation beam 102.
  • the optical scanning device in accordance with the invention is used for scanning three different types of information carrier, such as a CD, a DVD and a BD.
  • a CD, a DVD and a BD have different cover layer thicknesses, typically 1.2 millimetres, 0.6 millimetres and 0.1 millimetres respectively. Different amount of spherical aberration are thus generated.
  • the objective lens 107 is designed in such a way that it focuses a parallel radiation beam 102 into the information layer of a DVD without spherical aberration.
  • the moving collimator 202 is placed in a position, where a slightly converging beam is generated. The position of the moving collimator is determined in such a way that the spherical aberration due to the difference in cover layer thicknesses is compensated.
  • the moving collimator 202 When a CD is scanned, the moving collimator 202 is placed in a position, where a slightly diverging beam is generated.
  • the position of the moving collimator 202 may be calibrated, depending on the type of information can ⁇ er scanned.
  • a signal indicating the type of information carrier scanned is sent to the means for moving the collimator, not shown in Fig. 2, which place the moving collimator 102 in the calibrated position.
  • the optical scanning device comprises means for measuring the spherical aberration, and a control loop is used for placing the moving collimator 202 in such a way that the spherical aberration is compensated.
  • the optical scanning device in accordance with the invention is used for scamiing an information carrier comprising a first, a second and a third information layer, the first information layer being closer to the objective lens than the second, which is closer than the third.
  • the objective lens 107 is designed in such a way that it focuses a parallel radiation beam 102 into the second information layer without spherical aberration.
  • the moving collimator 202 is placed in a position, where a slightly converging beam is generated.
  • the moving collimator 202 is placed in a position, where a slightly diverging beam is generated.
  • the position of the moving collimator 202 may be calibrated, depending on the information layer scanned.
  • a signal indicating which information layer is scanned may be sent to the means for moving the collimator, which place the moving collimator 102 in the calibrated position.
  • a collimation system comprising a liquid crystal cell or an electrowettmg cell.
  • the electrowetting cell of patent application WO2003069380 may be used as a changing collimation system.
  • the transparent front element and/or the transparent back element of the electrowetting cell have to be made aspherical such that the electrowetting cell can transform the diverging radiation beam into a parallel radiation beam.
  • the electrowetting cell is used in a collimation system together with other optical elements that ensure collimation of the diverging radiation beam.
  • the electrowetting cell can be changed such that the vergence of the radiation beam beyond the electrowetting cell is modified.
  • the shape of the meniscus is modified by application of a potential difference between the two electrodes of the electrowetting cell, as described in WO2003069380.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Facsimile Scanning Arrangements (AREA)
  • Optical Head (AREA)

Abstract

The invention relates to an optical scanning device comprising a radiation source (101) for producing a radiation beam (102), and a collimation system (202). The optical scanning device comprises means for changing the collimation system so as to change the vergence of the radiation beam. It also comprises a beam shaper (201) placed between the radiation source and the collimation system in such a way that the radiation beam beyond the beam shaper is divergent.

Description

Optical device for recording and reproducing
FIELD OF THE INVENTION The present invention relates to an optical scanning device comprising means for compensating for spherical aberration. The present invention is particularly relevant for an optical disc apparatus for recording to and reading from an optical disc, e.g. a CD, a DVD and/or a Blu-Ray Disc (BD) recorder and player.
BACKGROUND OF THE INVENTION Many optical scanning devices require means for compensating for spherical aberration. Actually, information carriers are often scanned by an optical scanning device through a transparent layer protecting an information layer. A small variation of the thickness of the transparent layer causes a substantial change in the spherical aberration incurred by a high-numerical aperture radiation beam passing through the transparent layer. Spherical aberration compensation is also needed for scam ing a multilayer information carrier, because the spacer layer between two layers generates spherical aberration when jumping from one layer to the other. Spherical aberration compensation is also needed for scanning different types of information carrier having different cover layer thicknesses. Moreover, laser diodes conventionally used in optical scanning devices emit a radiation beam which angular aperture in a given plane is smaller than the angular aperture in a plane perpendicular to this given plane. The radiation beam thus has an elliptical intensity profile cross-section in the far field. However, a round intensity profile cross section is preferred on an information carrier scanned by such an optical scanning device. As a consequence, a beam shaper is required, which transforms the elliptical radiation beam into a round radiation beam. A BD player from Nikkei, described in "Nikkei Electronics 2003.5.12", page 127, comprises a beam shaper and means for compensating for spherical aberration. The beam shaper is a prismatic beam shaper, and the means for compensating for spherical aberration comprise a telescope. Fig. 1 shows such an optical scanning device. This optical scanning device comprises a radiation source 101 for producing a radiation beam 102, a collimator lens 103, a prismatic beam shaper 104, a beam splitter 105, a telescope 106, an objective lens 107, a servo lens 108, detecting means 109, measuring means 110, and a controller 111. This optical device is intended for scanning an information carrier 100. During a scanning operation, which may be a writing operation or a reading operation, the information carrier 100 is scanned by the radiation beam 102 produced by the radiation source 101. The collimator lens 103 and the objective lens 107 focus the radiation beam 102 on an information layer of the information earner 100. A focus error signal may be detected, corresponding to an error of positioning of the radiation beam 102 on the information layer. This focus error signal may be used for correcting the axial position of the objective lens 107, so as to compensate for a focus error of the radiation beam 102. A signal is sent to the controller 111, which drives an actuator in order to move the objective lens 107 axially. The focus error signal and the data written on the information layer are detected by the detecting means 109. The prismatic beam shaper 104 transforms the elliptical intensity profile cross-section into a round intensity profile cross section. Such a prismatic beam shaper is well known to those skilled in the art. The telescope 106 can change the vergence of the beam entering the objective lens 107. A change in vergence of the beam entering the objective lens 107 will introduce a wavefront aberration in the radiation beam 102 while passing the objective lens 107, in order to compensate for spherical aberration due, for example, to a variation of the cover layer thickness of the information carrier 100. To this end, the telescope 106 can transform the radiation beam 102 into a slightly converging or diverging beam, which compensates for the spherical aberration. The optical scanning device comprises means for moving one of the two elements of the telescope 106. Depending on the amount of spherical aberration to be compensated, the position of the moving element of the telescope 106 is determined in such a way that the spherical aberration is compensated. The optical scanning device may comprise means for measuring the spherical aberration, such as those described in Applicant's US 6,229,600. Alternatively, the amount of spherical aberration to be compensated may be calibrated in the optical scanning device, depending on, for example, the type of information carrier that is scanned. A drawback is that the use of a telescope renders such an optical scanning device bulky.
SUMMARY OF THE INVENTION It is an object of the invention to provide an optical scanning device comprising a beam shaper and means for compensating for spherical aberration, which optical scanning device is compact. To this end, the invention proposes an optical scanning device comprising a radiation source for producing a radiation beam, a collimation system, means for changing said collimation system so as to change the vergence of said radiation beam, and a beam shaper placed between said radiation source and said collimation system in such a way that the radiation beam beyond the beam shaper is divergent. Preferably, the radiation beam beyond the beam shaper has a numerical aperture greater than 0.02 According to the invention, the means for compensating for spherical aberration comprise a collimation system and means for changing said collimation system, in order to obtain a slightly diverging or converging beam on the objective lens when spherical aberration compensation is needed. As a consequence, this optical scanning device is more compact than the optical scanning device of the prior art, which comprises a bulky telescope. In the optical scanning device of the prior art, the use of a changing collimation system is not possible. Actually, if the collimator 103 of Fig. 1 were moved in order to generate a diverging or converging radiation beam, a diverging or converging radiation beam would enter the prismatic beam shaper 104. This would result in a large amount of astigmatic aberrations in the radiation beam. According to the invention, a changing collimation system is used and the beam shaper is placed before the changing collimation system in the optical path. The beam shaper is chosen in such a way that it can be placed in the diverging radiation beam generated by the radiation source without creating any astigmatic aberration. Preferably the radiation beam beyond the beam shaper has a numerical aperture greater than 0.02, which means that a diverging beam passes through said beam shaper, and not a parallel beam as is the case in the prior art. This will be true even if the beam shaper includes a pre-collimation function such that the numerical aperture of the radiation beam before the beam shaper is greater than the numerical aperture of the radiation beam beyond the beam shaper. A lens type beam shaper is for example suitable for such an application. Such a lens type beam shaper is known from, for example, Applicant's EP 0 605923, published July 13, 1994, and patent application US 2002/0166952, by Tanaka et al., published Nov. 14, 2002. It should be noted that the optical scanning device described in US 2002/0166952 comprises a radiation source, a collimator and a lens type beam shaper between the radiation source and the collimator. However, the optical scanning device does not comprise any means for moving the collimator, because no spherical aberration compensation is required. The technical field of US 2002/0166952 thus completely differs from the one of the present invention, which deals with spherical aberration compensation. Other examples of beam shapers suitable for such an application are described in the detailed description. An example of collimation system that can be changed in order to change the vergence of the radiation beam is a moving collimator. Other examples of collimation systems suitable for such an application are described in the detailed description. Advantageously, the changing means are controlled by a signal indicating which information layer is scanned between at least two information layers of the information carrier. This allows automatically compensating for spherical aberration when jumping from one layer to another layer of the information carrier. Preferably, the changing means are controlled by a signal indicating which type of information earner is scanned between at least two types of information canier. This allows automatically compensating for spherical aberration when changing the type of information scanned, thus allowing the optical scanning device to be compatible with different types of information carrier. These and other aspects of the invention will be apparent from and will be elucidated with reference to the embodiments described hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which:
- Fig. 1 shows an optical scanning device in accordance with the prior art;
- Fig. 2 shows an optical scanning device in accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION An optical scanning device in accordance with the invention is depicted in Fig. 2.
Numbers that are identical to numbers of Fig. 1 stand for the same elements. The optical scanning device of Fig. 2 comprises a beam shaper 201 and a changing collimation system
202. The radiation beam 102, produced by the radiation source 101, has an elliptical intensity profile cross section in the far field. The beam shaper 201 is designed in such a way that a substantially circular intensity profile cross section of the radiation beam 102 is obtained when the diverging radiation beam 102 passes through the beam shaper 201. In Fig.
2, the beam shaper 201 is a lens type beam shaper, which realizes different angular magnifications in two different planes. The beam shaper 201 is placed in the diverging radiation beam 102, i.e. between the radiation source 101 and the changing collimation system 202. An example of such a beam shaper, which can be placed in a diverging beam without generating any coma and astigmatism, is known from EP 0 605923, which describes a lens type beam shaper having a cylindrical entrance surface and a toroidal exit surface. Another example is known from US 2002/0166952, which describes a lens type beam shaper whose both surfaces are toric surfaces. Whatever the type of entrance and exit surfaces, a lens type beam shaper can always be placed in a diverging radiation beam without generating any coma and astigmatism. Another example of beam shaper that can be used in accordance with the invention is an absorption type beam shaper. Such an absorption type beam shaper is known from non- published patent application PCT/IB2003/006157 (applicant's reference PHNL021484), filed under priority of patent application EP 02293260.2. An absorption type beam shaper can be placed in a diverging radiation beam without generating any coma and astigmatism. A further example is a diffractive type beam shaper. Such a diffraction type beam shaper is known from non-published patent application EP 04300065.2 (applicant's reference PHFR040018). A diffraction type beam shaper can be placed in a diverging radiation beam without generating any coma and astigmatism. The radiation beam 102, with a circular intensity profile cross section, subsequently reaches the collimation system 202. In Fig. 2, the collimation system 202 is a moving collimator. The collimation system 202 may also comprise additional optical elements in order to ensure complete collimation of the radiation beam. In a first position, the moving collimator 202 transforms the diverging radiation beam 102 into a parallel radiation beam 102, which is then focused on an information layer of the information carrier 100, by means of the objective lens 107. In a second position, the moving collimator transforms the diverging radiation beam 102 into a slightly converging radiation beam 102. In a third position, the moving collimator transforms the diverging radiation beam 102 into a slightly diverging radiation beam 102. In the example described below, the optical scanning device in accordance with the invention is used for scanning three different types of information carrier, such as a CD, a DVD and a BD. A CD, a DVD and a BD have different cover layer thicknesses, typically 1.2 millimetres, 0.6 millimetres and 0.1 millimetres respectively. Different amount of spherical aberration are thus generated. The objective lens 107 is designed in such a way that it focuses a parallel radiation beam 102 into the information layer of a DVD without spherical aberration. When a BD is scanned, the moving collimator 202 is placed in a position, where a slightly converging beam is generated. The position of the moving collimator is determined in such a way that the spherical aberration due to the difference in cover layer thicknesses is compensated. When a CD is scanned, the moving collimator 202 is placed in a position, where a slightly diverging beam is generated. The position of the moving collimator 202 may be calibrated, depending on the type of information canϊer scanned. In this case, a signal indicating the type of information carrier scanned is sent to the means for moving the collimator, not shown in Fig. 2, which place the moving collimator 102 in the calibrated position. Alternatively, the optical scanning device comprises means for measuring the spherical aberration, and a control loop is used for placing the moving collimator 202 in such a way that the spherical aberration is compensated. In the following example, the optical scanning device in accordance with the invention is used for scamiing an information carrier comprising a first, a second and a third information layer, the first information layer being closer to the objective lens than the second, which is closer than the third. The objective lens 107 is designed in such a way that it focuses a parallel radiation beam 102 into the second information layer without spherical aberration. When the first information layer is scanned, the moving collimator 202 is placed in a position, where a slightly converging beam is generated. When the third information layer is scanned, the moving collimator 202 is placed in a position, where a slightly diverging beam is generated. The position of the moving collimator 202 may be calibrated, depending on the information layer scanned. In this case, a signal indicating which information layer is scanned may be sent to the means for moving the collimator, which place the moving collimator 102 in the calibrated position. Another example of collimation system that can be changed in order to change the vergence of the radiation beam is a collimation system comprising a liquid crystal cell or an electrowettmg cell. For example, the electrowetting cell of patent application WO2003069380 may be used as a changing collimation system. To this end, the transparent front element and/or the transparent back element of the electrowetting cell have to be made aspherical such that the electrowetting cell can transform the diverging radiation beam into a parallel radiation beam. Alternatively, the electrowetting cell is used in a collimation system together with other optical elements that ensure collimation of the diverging radiation beam. The electrowetting cell can be changed such that the vergence of the radiation beam beyond the electrowetting cell is modified. To this end, the shape of the meniscus is modified by application of a potential difference between the two electrodes of the electrowetting cell, as described in WO2003069380. Any reference sign in the following claims should not be construed as limiting the claim. It will be obvious that the use of the verb "to comprise" and its conjugations does not exclude the presence of any other elements besides those defined in any claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

1 An optical scanning device comprising a radiation source (101) for producing a radiation beam (102), a collimation system (202), means for changing said collimation system so as to change the vergence of said radiation beam, and a beam shaper (201) placed between said radiation source and said collimation system in such a way that the radiation beam beyond the beam shaper is divergent.
2 An optical scanning device as claimed in claim 1, wherein the beam shaper is placed in such a way that the radiation beam beyond the beam shaper has a numerical aperture greater than 0.02.
3 An optical scanning device as claimed in claim 1, wherein the beam shaper is a lens type beam shaper.
4 An optical scanning device as claimed in claim 1, wherein the beam shaper is a diffractive type beam shaper. 5 An optical scanning device as claimed in claim 1, wherein the beam shaper is an absorption type beam shaper.
6 An optical scanning device as claimed in claim 1, wherein the collimation system comprises a moving collimator.
7 An optical scanning device as claimed in claim 1, wherein the collimation system comprises an electrowetting cell.
8 An optical scanning device as claimed in claim 1, wherein the collimation system comprises a liquid crystal cell.
9 An optical scanning device as claimed in claim 1, for scanning an information carrier comprising at least two information layers, said changing means being controlled by a signal indicating which infom ation layer is scanned.
10 An optical scanning device as claimed in claim 1, for scamiing at least two types of information carrier, said changing means being controlled by a signal indicating which type of information carrier is scanned.
PCT/IB2005/000515 2004-02-26 2005-02-21 Optical device for recording and reproducing WO2005086141A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP04300097 2004-02-26
EP04300097.5 2004-02-26

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WO2005086141A2 true WO2005086141A2 (en) 2005-09-15
WO2005086141A3 WO2005086141A3 (en) 2006-03-23

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WO (1) WO2005086141A2 (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6108139A (en) * 1996-10-28 2000-08-22 Nec Corporation Optical head device and method of information reproduction using the same
US6418108B1 (en) * 1998-01-09 2002-07-09 Sony Corporation Optical head, recording and/or reproducing method and apparatus and method for detecting thickness
US20020166952A1 (en) * 2001-04-24 2002-11-14 Matsushita Electric Industrial Co., Ltd. Beam shaper, and semiconductor laser source device and optical head using the beam shaper
EP1441334A2 (en) * 2003-01-22 2004-07-28 Matsushita Electric Industrial Co., Ltd. Optical head, optical information recording/reproducing apparatus, computer, video recording/reproducing apparatus, server and car navigation system

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6108139A (en) * 1996-10-28 2000-08-22 Nec Corporation Optical head device and method of information reproduction using the same
US6418108B1 (en) * 1998-01-09 2002-07-09 Sony Corporation Optical head, recording and/or reproducing method and apparatus and method for detecting thickness
US20020166952A1 (en) * 2001-04-24 2002-11-14 Matsushita Electric Industrial Co., Ltd. Beam shaper, and semiconductor laser source device and optical head using the beam shaper
EP1441334A2 (en) * 2003-01-22 2004-07-28 Matsushita Electric Industrial Co., Ltd. Optical head, optical information recording/reproducing apparatus, computer, video recording/reproducing apparatus, server and car navigation system

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WO2005086141A3 (en) 2006-03-23

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