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WO2004029949A2 - Dispositif de balayage optique - Google Patents

Dispositif de balayage optique Download PDF

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Publication number
WO2004029949A2
WO2004029949A2 PCT/IB2003/004032 IB0304032W WO2004029949A2 WO 2004029949 A2 WO2004029949 A2 WO 2004029949A2 IB 0304032 W IB0304032 W IB 0304032W WO 2004029949 A2 WO2004029949 A2 WO 2004029949A2
Authority
WO
WIPO (PCT)
Prior art keywords
scanning device
optical scanning
optical
profile
polarisation
Prior art date
Application number
PCT/IB2003/004032
Other languages
English (en)
Other versions
WO2004029949A3 (fr
Inventor
Sjoerd Stallinga
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.
Priority to AU2003263438A priority Critical patent/AU2003263438A1/en
Publication of WO2004029949A2 publication Critical patent/WO2004029949A2/fr
Publication of WO2004029949A3 publication Critical patent/WO2004029949A3/fr

Links

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
    • G11B7/1365—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
    • G11B7/1374—Objective lenses
    • 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
    • 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
    • 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
    • G11B2007/13727—Compound lenses, i.e. two or more lenses co-operating to perform a function, e.g. compound objective lens including a solid immersion lens, positive and negative lenses either bonded together or with adjustable spacing

Definitions

  • This invention relates to an optical scanning device for scanning an optical record carrier comprising an information layer, the device comprising: a radiation source system for generating a radiation beam; an objective lens arranged to converge the beam to a spot on an information layer; and a birefringent element arranged along an optical axis in the device between the radiation source system and the location of the optical record carrier, the birefringent element having a first aberration generating characteristic in a first polarisation mode and a second, different, aberration generating characteristic in a second, different, polarisation mode.
  • an optical scanning device for scanning an optical record carrier comprising an information layer
  • the device comprising: a radiation source system for generating a radiation beam; an objective lens arranged to converge the beam to a spot on an information layer; and a birefringent element arranged along an optical axis in the device between the radiation source system and the location of the optical record carrier, the birefringent element having a first aberration generating characteristic in a first polarisation mode and a second, different, aberration generating characteristic in a second, different, polarisation mode, the birefringent element including a birefringent material forming a surface having a first profile along a first plane, which is parallel to the optical axis, and a second profile along a second plane, which is parallel to the optical axis and is perpendicular to the first plane, characterised in that the first profile and the second profile are different.
  • the birefringent element By arranging the birefringent element to have a surface which has two different profiles in mutually perpendicular planes, each parallel to the optical axis, a selected amount of focusing power can be added to the radiation beam in a selected mode, for example the extraordinary mode, in a selected plane, which may for example be the plane containing the preferential axis of the uniaxially symmetric birefringent material.
  • the birefringent element comprises a first portion, which is formed from the birefringent material, and a second portion, which is formed of a different material, the portions being joined at the surface having the different profiles in the different planes.
  • the first and second portions are arranged to have refractive indices which are substantially matched in one of the first and second polarisation modes, preferably the ordinary polarisation mode.
  • the birefringent element When a birefringent element in accordance with the prior art publication WO- A-0124174 is used as described, the birefringent element generates astigmatism in the extraordinary mode which is proportional to the birefringence An, the thickness of the layer d and the square of the numerical aperture NA of the radiation beam incident on the birefringent layer:
  • ⁇ n is typically relatively small for birefringent materials (typically 0.05-0.15)
  • the amount of difference in the spherical aberration compensation generated in the two polarisation modes is relatively small.
  • the birefringent element by arranging the birefringent element to have an anamorphic power in the extraordinary mode, both the astigmatism can be compensated fully and the defocus difference between the two modes can be increased, thus providing more spherical aberration compensation difference between the two modes.
  • Figure 1 is a schematic illustration of components of an optical scanning device, arranged in accordance with an embodiment of the invention
  • Figure 2A is a cross section of a birefringent element in accordance with an embodiment of the invention, taken along plane A-A in Figure 2B;
  • Figure 2B is a cross section of a birefringent element in accordance with an embodiment of the invention, taken along plane B-B in Figure 2A.
  • an optical scanning device is arranged, in accordance with an embodiment of the invention, for scanning an optical record carrier 1.
  • the record carrier 1 is for example an optical disk as will be described, by way of example, below.
  • the optical disk 1 in this embodiment is a dual-layer disk comprising a first information layer 2 and a second information layer 3, each arranged behind the entrance face 5 of the disk, at different depths within the disk.
  • the first information layer 2 is a semi- transparent layer located behind a transparent cover layer providing the entrance face 5 of the disk
  • the second information layer 3 is a reflective layer spaced from the first information layer 2 by a transparent spacer layer.
  • the side of the second information layer 3 facing away from the entrance face 5 is protected from environmental influences by a protection layer which provides the rear face 4 of the disk.
  • Information may be stored in the first and second information layers 2, 3 of the optical disk in the form of optically detectable marks ananged in substantially parallel, concentric or spiral tracks, not indicated in Figure 1.
  • the marks may be in any optically readable form, e.g. in the form of pits, or areas with a reflection coefficient or a direction of magnetisation different from their surroundings, or a combination of these forms.
  • the disk 1 may be of a read-only type, a recordable (write once) type or a rewritable type, and the form of the marks takes a form consistent with the type of the disk 1.
  • the scanning device includes a radiation source 6, for example a semiconductor laser, emitting a diverging radiation beam 7 towards a collimator lens 9.
  • a beam splitter 8 for example a semi-transparent plate, transmits the radiation beam towards a compound objective lens 10.
  • the compound objective lens 10 includes a first, or back, lens element 12 and a second, or front, lens element 13, fixed at a mutual relative spacing by a rigid mounting 14.
  • Each of the lens elements 12, 13 is shown as a plano-convex lens, however other lens types such as convex-convex or convex-concave lenses may also be used.
  • the collimator lens 9 changes the diverging radiation beam 7 to a collimated beam 15.
  • collimated we intend to mean a substantially parallel beam, for which the compound objective lens has a transverse magnification substantially equal to zero.
  • the need for a collimated beam arises when optical elements in the collimated beam path are designed for use with an ideally collimated (parallel) beam.
  • a collimated beam is not necessary when the elements in the beam path are designed for use with a divergent or convergent beam.
  • the collimated beam preferably has a vergence resulting in an absolute magnification of the objective lens smaller than 0.02.
  • the first lens element 12 of the objective lens 10 transforms the collimated radiation beam 15 into a converging beam having an intermediate numerical aperture (NA), for example 0.55, and incident on the second lens element 13.
  • NA intermediate numerical aperture
  • the second lens element 13 changes the incident beam into a converging beam 17, having a relatively high NA, for example 0.85, which comes to a spot 18 on a selected one of the information layers, in the case shown in Figure 1, the information layer 3.
  • the objective lens 10 is indicated in Figure 1 as having two lens elements, it may comprise more elements, and may also comprise a hologram operating in transmission or reflection, or a grating for coupling radiation out of a waveguide carrying the radiation beam.
  • Radiation of the converging beam 17 reflected by the information layer 3 forms a diverging reflected beam 19, which returns on the optical path of the forward converging beam 17.
  • the two elements of objective lens transform the reflected beam 19 first to a less divergent beam, then to a substantially collimated reflected beam 21, and the beam splitter 8 separates the forward and reflected beams by reflecting at least part of the reflected beam 21 towards a condenser lens 11.
  • the condenser lens 11 transforms the incident beam into a convergent reflected beam 22 focused on detection system, generally indicated by a single element 22 although as is conventional in the art a plurality of detector elements are used.
  • the detection system 23 captures the radiation and converts it into electrical signals.
  • One of these signals is an information signal 24, the value of which represents the information read from the information layer 3.
  • Another signal is a focus enor signal 25, the value of which represents the axial difference in height between the focus position of the spot 18 and the information layer 3.
  • Another signal is a tracking enor signal 26, which represents a deviation from a track following position of the spot 18.
  • Each of the signals 25, 26 are input to a servo and spherical abenation compensation controller 27. Alternatively, a separate controller may be used for each of the signals 25, 26.
  • the focus enor signal 25 is used to generate a focus control signal 28 for a focus servo actuator 29, which controls the axial position of the mounting 14, thereby controlling the axial position of the objective lens 10 such that the axial position of the spot 18 coincides substantially with the plane of the information layer 3 being scanned.
  • the tracking enor signal 26 is used to generate a tracking control signal 30 for a tracking servo actuator (not shown), which controls the radial position of the mounting 14, thereby controlling the radial position of the objective lens 10 such that the radial position of the spot 18 coincides substantially with the track on the information layer 3 cunently being scanned.
  • a spherical abenation selection signal (not shown).
  • the spherical abenation selection signal represents the information layer cunently being scanned.
  • An unwanted spherical abenation represented by the spherical abenation selection which arises when the radiation beam has to be focused through a depth of the optical disk which is thicker or thinner than a thickness for which the objective lens is cunently adjusted, is compensated for by a spherical abenation compensation optical subsystem.
  • This subsystem includes an electro-optical device 16, located in the optical path between the collimator lens 9 and the front lens 12 of the objective lens.
  • the electro-optical device of the spherical abenation compensation optical subsystem is a Twisted Nematic (TN) liquid crystal cell 16.
  • the TN liquid crystal cell 16 is a planar cell, consisting of a liquid crystal layer interposed between two transparent planar plates having conductive transparent layers formed on the inner surfaces thereof, forming the electrodes of the TN liquid crystal cell 16.
  • the TN liquid crystal cell 16 is connected to a voltage source which is controlled by the spherical abenation control signal 31.
  • the surfaces of the electrodes adjacent the liquid crystal layer are coated with an alignment material.
  • the director at one side of the TN liquid crystal cell 16 aligns the liquid crystal molecules in an orientation which is perpendicular to the direction of orientation with which the direction on the other side of the liquid crystal cell aligns the liquid crystal molecules. Accordingly, a 90° twist is formed in the bulk of the liquid crystal layer, between the two sides of the TN liquid crystal cell, when in an off-state.
  • the voltage source switches the TN liquid crystal cell 16 into an on-state, in which the liquid crystal molecules are aligned substantially parallel to the optical axis.
  • the polarisation of the incident radiation is rotated through 90° when passing through the TN liquid crystal cell 16.
  • the TN liquid crystal cell 16 has no effect on the polarisation of the radiation passing through the cell 16.
  • the thickness of the liquid crystal layer in the TN liquid crystal cell 16 can be relatively thin, at 4-6 ⁇ m.
  • the response speed of the spherical abenation compensation optical subsystem is thus capable of being conespondingly fast, with the cell switching between on and off states within 10-50 ms.
  • the TN liquid crystal cell 16 is shown as a separate component in Figure 1, it should be mentioned that the cell 16 may be integrated with another component, for example the beam splitter 8.
  • a rotatable half-wave plate may be used instead of the TN liquid crystal cell.
  • the preferential axis of the half-wave plate is in the plane perpendicular to the optical axis and, in a first state, makes an angle of ⁇ 45 degrees with the linear polarization of the radiation beam 7 exiting the light source 6 or, in a second state, is parallel or perpendicular to the linear polarization of the radiation beam 7 exiting the light source 6.
  • the half-wave plate rotates the polarization of the passing radiation beam 15 by 90 degrees, whereas in the second state it does not alter the polarization of the passing radiation beam 15.
  • This anangement also involves an actuator for rotating the half- wave plate over the required angular range.
  • the spherical abenation compensation optical subsystem further includes a passive linear birefringent planar element 20, preferably located in the optical path between the back lens element 12 and the front lens element 13 where the beam has an intermediate numerical aperture, for example approximately 0.55. In this anangement the element 20 exhibits a relatively large spherical abenation compensating effect.
  • the birefringent may be integrated with the front lens element 12, by attachment to the rear surface thereof. Further, the birefringent element 20 may also be located between the front lens element 13 and the entrance face 5 of the optical disk 1.
  • the birefringent element 20 is illustrated in further detail in Figures 2A and 2B.
  • the element 20 includes a first portion 40 formed of a substantially homogeneous birefringent material, and a second portion 42.
  • the birefringent material of the first portion 40 may for example be formed of a cured liquid crystal material.
  • the second portion 42 is formed of a substantially homogeneous isotropic material with a refractive index equal to that of the birefringent material in the ordinary mode, n 0 .
  • the two portions are joined at an intermediate surface 44 having two different profiles in mutually orthogonal planes which are each parallel to the optical axis of the objective lens 10.
  • a first profile is illustrated in Figure 2A, which is a cross section through the plane A-A shown in Figure 2B.
  • this plane is parallel to the preferential axis of the birefringent material.
  • the profile of the surface 44 in this plane is substantially part circular, such that the surface has a cylindrical lens power in this plane.
  • a second profile is illustrated in Figure 2A, which is a cross section through the plane B-B shown in Figure 2 A.
  • the profile of the surface 44 in this plane is straight, such that the surface has no lens power in this plane. Note that the described profiles are maintained across the widths of the element 20, to provide a cylindrical lens surface shape.
  • the portions 40, 42 have plane parallel outer surfaces 46, 48.
  • the refractive index of the birefringent portion 40 is n 0 when the ordinary mode of the incident radiation is used, in which the polarisation is perpendicular to the preferential axis of the birefringent material, whereas the refractive index is n e when the extraordinary mode of the incident radiation is used, in which the polarisation is parallel to the preferential axis of the birefringent plate 40.
  • the element 20 acts as a birefringent plate, similar to the homogeneously birefringent plate of the prior art, and generates a selected amount of spherical abenation compensation.
  • the refractive index of the birefringent portion is n e
  • the element 20 has an anamorphic lens power which is ananged to make the astigmatism generated in the extraordinary mode zero and makes the defocus difference between the ordinary and extraordinary modes proportional to An (compared with the square of An in the prior art).
  • the birefringent element generates a selected amount of spherical abenation compensation which is substantially different from the amount generated in the ordinary mode.
  • the curvature of the circular profile can be calculated by paraxial raytracing, and the surface is defined by a curvature radius:
  • nj is the refractive index of the medium in front of entrance surface 46 of the element 20
  • d is the thickness of the birefringent layer 40 measured along the optical axis
  • v is the distance between the (intermediate) focal point of the beam entering the element and the front surface 46 of the element 20.
  • Switching the TN liquid crystal cell 16 thus creates a difference in the spherical abenation of the beam incident upon the optical disk, and therefore is useful improving resolution on the optical disk, thereby to read data pits or other markings on the optical disk more efficiently, even where two different depths of information layer are required to be read by the scanning device in a dual-layer optical disk 1.
  • the present invention allows for the reading of an optical disk of high capacity, using a relatively low wavelength radiation beam, for example a radiation beam of approximately 400nm wavelength, using a high numerical aperture beam at the optical disk, and without using a mechanical actuator to effect improved spherical abenation compensation, for varying depths of information layer in the optical disks being read.
  • the above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged.
  • the two orthogonal plane profiles are part circular and straight, respectively, other profiles are envisaged. Both profiles may be circular, with different radii of curvature, and one profile may be convex while the other is concave.
  • a variable spherical abenation is generated by a birefringent element of uniform thickness and having planar outer surfaces, the element may have at least one non-planar outer surface, for example a lens surface.
  • a TN liquid crystal cell is used to selectively rotate the polarisation of the incident radiation through 90°
  • similar (but less optimal in terms of complexity and the efficiency of the optical system) functionality could be provided by dispensing with the polarisation rotating element and instead using either a single radiation source emitting radiation at an orientation of 45° to the preferential axis and/or the beam splitter, or two separate radiation sources emitting orthogonally-polarised radiation at each of the required polarizations.
  • the required spherical abenation compensation can then be selected, in accordance with a selection control signal, for example by a switchable polarisation-selective filter at the detector.
  • the sources may be selectively energised in accordance with the selection control signal.
  • the birefringent element has been used for spherical abenation compensation
  • a similar component may be used as an anamorphic beamshaper with the additional property of being polarisation dependent.

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

Abstract

Cette invention concerne un dispositif de balayage optique permettant de balayer un support d'enregistrement optique (1) qui comprend une couche d'informations. Un élément biréfringent (20) est disposé le long d'un axe optique du dispositif entre la première et la seconde lentille d'un objectif composite (10). Cet élément biréfringent présente une première caractéristique génératrice d'aberrations dans un premier mode de polarisation, et une seconde caractéristique différente génératrice d'aberrations dans un second mode de polarisation. La surface de l'élément biréfringent présente un premier profil selon un premier plan qui est parallèle à l'axe optique, et un second profil différent selon un second plan qui est parallèle à l'axe optique et perpendiculaire au premier plan, ce qui procure la puissance d'une lentille anamorphique dans le mode de polarisation extraordinaire.
PCT/IB2003/004032 2002-09-27 2003-09-15 Dispositif de balayage optique WO2004029949A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003263438A AU2003263438A1 (en) 2002-09-27 2003-09-15 Optical scanning device

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
EP02078997.0 2002-09-27
EP02078997 2002-09-27
EP02079589 2002-11-01
EP02079589.4 2002-11-01
EP02080596 2002-12-30
EP02080596.6 2002-12-30

Publications (2)

Publication Number Publication Date
WO2004029949A2 true WO2004029949A2 (fr) 2004-04-08
WO2004029949A3 WO2004029949A3 (fr) 2004-07-15

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2003/004032 WO2004029949A2 (fr) 2002-09-27 2003-09-15 Dispositif de balayage optique

Country Status (2)

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AU (1) AU2003263438A1 (fr)
WO (1) WO2004029949A2 (fr)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5745465A (en) * 1997-01-23 1998-04-28 Industrial Technology Research Institute Digital video disc pick-up head system
WO2001024174A1 (fr) * 1999-09-30 2001-04-05 Koninklijke Philips Electronics N.V. Dispositif de balayage optique

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH09293268A (ja) * 1996-03-01 1997-11-11 Olympus Optical Co Ltd 光ピックアップ

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5745465A (en) * 1997-01-23 1998-04-28 Industrial Technology Research Institute Digital video disc pick-up head system
WO2001024174A1 (fr) * 1999-09-30 2001-04-05 Koninklijke Philips Electronics N.V. Dispositif de balayage optique

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 1998, no. 03, 27 February 1998 (1998-02-27) -& JP 09 293268 A (OLYMPUS OPTICAL CO LTD), 11 November 1997 (1997-11-11) *

Also Published As

Publication number Publication date
WO2004029949A3 (fr) 2004-07-15
AU2003263438A1 (en) 2004-04-19

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