WO2004093063A2 - Systeme optique - Google Patents

Systeme optique Download PDF

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Publication number
WO2004093063A2
WO2004093063A2 PCT/IB2004/050453 IB2004050453W WO2004093063A2 WO 2004093063 A2 WO2004093063 A2 WO 2004093063A2 IB 2004050453 W IB2004050453 W IB 2004050453W WO 2004093063 A2 WO2004093063 A2 WO 2004093063A2
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WO
WIPO (PCT)
Prior art keywords
radiation beam
optical
optical system
mode
information layer
Prior art date
Application number
PCT/IB2004/050453
Other languages
English (en)
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WO2004093063A3 (fr
Inventor
Jorrit E. De Vries
Bernardus H. W. Hendriks
Original Assignee
Koninklijke Philips Electronics N.V.
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Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2004093063A2 publication Critical patent/WO2004093063A2/fr
Publication of WO2004093063A3 publication Critical patent/WO2004093063A3/fr

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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
    • G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
    • G11B7/1367—Stepped phase plates
    • 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
    • G11B7/13922—Means for controlling the beam wavefront, e.g. for correction of aberration passive
    • 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

Definitions

  • the present invention relates to an optical system, particularly to an optical system for scanning optical record carriers of different types, and to a compensator for use within such an optical system.
  • an optical record carrier such as a compact disc (CD) or a digital versatile disc (DVD).
  • An increase in the density of information which can be stored on such an optical disc can be achieved by decreasing the size of a focal spot of a radiation beam which is used to scan the information layer of the optical disc.
  • Such a decrease in spot size can be achieved by using a shorter wavelength and a higher numerical aperture (NA) of the radiation beam.
  • NA numerical aperture
  • Increased resolution however tends to reduce tolerances which apply to optical elements within the optical system. These reduced tolerances cause the focal spot of the radiation beam for scanning the optical disc to be more susceptible to degradation in quality.
  • Optical systems are commonly designed to be compatible with different types of optical disc, for example both a CD and a DVD.
  • a separate radiation beam with an appropriate and different wavelength for scanning each type of disc is used.
  • Each radiation beam is generally directed along a common portion of an optical path within the system along which lies optical elements for focusing the radiation beam to a focal spot on the optical disc.
  • optical elements for example an objective lens, as it is needed to ensure that the radiation beam being used to scan the type of optical disc is focused to a spot of sufficient quality on the optical disc.
  • This problem is caused in part by the different wavelength and numerical aperture of the radiation beam for scanning each type of disc, but also to a difference between an information layer depth of a transparent cover layer of a first and a second type of optical disc through which the radiation beam passes.
  • This cover layer modifies the radiation beam passing through the cover layer. This modification is considered when designing the precise specifications of the objective lens so that a wavefront deviation is introduced into the radiation beam which compensates the modification by the cover layer and ensures that the focal spot achieved is of the highest quality. In the case of a CD and a DVD, the thickness of this cover layer is approximately 1.2mm and 0.6mm respectively.
  • An optical system of this type generally comprises a collimator lens for modifying the vergence of the radiation beam scanning the optical disc and an objective lens for focusing the radiation beam to the focal spot on the optical disc.
  • the optical system is designed for use at a standard operating temperature and the precise specifications of the optical elements including the collimator and the objective lens are determined based upon this standard temperature.
  • a non-periodic phase structure has a phase structure comprising annular areas forming a non-periodic pattern of optical paths of different lengths.
  • An NPS commonly introduces a wavefront deviation to a radiation beam passing through the NPS and may be used to modify or correct a wavefront deviation of a radiation beam by introducing a further wavefront deviation.
  • Patent application EP-A-0865037 describes an objective lens of an optical head for scanning optical discs with different thicknesses of cover layer.
  • a radiation beam having a different wavelength is used to scan each optical disc with a different cover layer thickness.
  • a NPS is attached to a surface of the objective lens and is arranged to reduce a spherical aberration of a first radiation beam when scanning a disc of a first type, for example a CD.
  • a second type of optical disc is being scanned, for example a DVD
  • a second radiation beam does not have a spherical aberration and the NPS is arranged to have no effect on the radiation beam.
  • International patent application WO 01/48745 describes an optical head for scanning one type of optical record carrier.
  • Patent application EP-A-1143429 describes an objective lens of an optical system for scanning two different types of optical disc, for example a CD and a DVD, using radiation beams of different wavelengths.
  • a first surface of the lens has a first NPS. This first NPS produces a phase difference in the radiation beam used when scanning the first type of optical disc and improves an aberration of the radiation beam.
  • a second side of the objective lens has a second NPS. This produces a phase difference in the different radiation beam used when scanning the second type of optical disc and improves an aberration of this radiation beam.
  • Both International patent application WO 02/29798 and International patent application WO 02/39440 describe an optical device for scanning optical record carriers of a first and a second type with a first and a second radiation beam respectively. Each radiation beam has a different numerical aperture. Both devices include a NPS which does not affect the first radiation beam but introduces a spherical aberration into the second radiation beam. This introduced spherical aberration is for compensating a spherical aberration resulting when scanning through a difference in a cover layer thickness of the first and second optical record carriers. Summary of the Invention.
  • an optical system having a first mode for scanning a first optical record carrier of a first type and having an information layer at a first information layer depth, and a second mode for scanning a second optical record carrier of a second, different, type having an information layer at a second, different, information layer depth, said optical system having a parameter which is variable, the optical system comprising: a) a radiation source system for generating a first radiation beam in the first mode and a second, different, radiation beam in the second mode; b) one or more optical elements for focusing either the first radiation beam to a spot on the information layer of the first record carrier in the first mode, or the second radiation beam to a spot on the information layer of the second record carrier in the second mode; and c) a compensator having a phase structure comprising annular areas forming a non-periodic pattern of optical paths of different lengths, wherein said compensator is arranged to compensate a first wavefront deviation introduced during scanning of the information layer of the first
  • a compensator for use in an optical system having a first mode for scanning an information layer of a first optical record carrier of a first type, and a second mode for scanning a second, different, optical record carrier of a second, different, type, said optical system having a parameter which is variable, the optical system comprising: a) a radiation source system for generating a first radiation beam in the first mode and a second, different, radiation beam in the second mode; and b) one or more optical elements for focusing either the first radiation beam to a spot on the information layer of the first record carrier in the first mode, or the second radiation beam to a spot on the information layer of the second record carrier in the second mode, the compensator having a phase structure comprising annular areas forming a non-periodic pattern of optical paths of different lengths, wherein said compensator is arranged to compensate a first wavefront deviation introduced during scanning of the information layer of the first optical record carrier with said first radiation beam in the first mode, character
  • the phase structure of the compensator of the present invention compensates the first wavefront deviation, generally comprising a spherical aberration, of the first radiation beam.
  • the first wavefront deviation is introduced to the first radiation beam during scanning of an optical disc of the first type having a first information layer depth, for example a CD, when an optical element of the system, for example an objective lens, with specifications for scanning an optical record carrier of the second type, for example a DVD, with the second radiation beam, is used.
  • phase structure of the compensator is optimised to compensate the second wavefront deviation, comprising a spherical aberration, of the second radiation beam at a given value of a parameter of the system.
  • the second wavefront deviation is introduced to the second radiation beam by a deviation in the parameter of the optical system, for example a deviation in temperature.
  • the phase structure of the compensator comprises an inner structure and an outer structure, wherein the inner structure is arranged to compensate said first wavefront deviation and the outer structure is arranged to compensate said second wavefront deviation.
  • the compensator of the optical system for compensating both the first wavefront deviation and the second wavefront deviation is relatively compact and inexpensive to manufacture.
  • said inner and outer structures are both arranged on a single surface of one of said optical elements.
  • a manufacture process, for example an injection moulding process, of the compensator is relatively simple, efficient and inexpensive.
  • Figure 1 shows schematically an optical system according to an embodiment of the present invention for scanning an optical record carrier of a first and a second type.
  • Figure 2 shows graphically a side profile of a phase structure of a compensator of the optical system in accordance with an embodiment of the present invention.
  • Figure 3 shows graphically a wavefront deviation introduced to a radiation beam by an optical element of the optical system in accordance with an embodiment of the present invention.
  • Figure 4 shows graphically a wavefront deviation having been at least partly compensated by controlling a focal position of an optical element of the optical system in accordance with an embodiment of the present invention.
  • Figure 5 shows graphically the at least partly compensated wavefront deviation of Figure 4 now with a compensation of a temperature of the optical system in accordance with an embodiment of the present invention.
  • Figure 1 shows schematically an optical system having a first mode and a second, different, mode for scanning an optical record carrier of a first and a second, different type, respectively.
  • the first optical record carrier is a compact disc (CD)
  • the second optical record carrier is a digital versatile disc (DVD).
  • the position of the DVD, although not shown directly, is indicated in outline in Figure 1.
  • Both the CD and the DVD optical discs to be scanned by the optical system include at least one information layer 2, 3.
  • Information may be stored in the information layer or layers of the optical disc in the form of optically detectable marks arranged in substantially parallel, concentric or spiral tracks. The marks may be in any optically readable form, for example in the form of pits or areas with a reflection coefficient different from their surroundings.
  • Each optical disc has a transparent cover layer arranged parallel the information layer 2, 3 such that an upper surface of the cover layer lies in contact with the information layer 2, 3 and a lower surface of the cover layer, substantially parallel the upper surface, is an outer surface of the optical disc.
  • a thickness of the transparent layer between said upper and lower surface is an information layer depth.
  • the CD has a first information layer depth 4 of approximately 1.2mm which is greater than a second information layer depth 5 of the DVD of approximately 0.6mm.
  • Optical elements of the optical system are held in a rigid housing which is formed of moulded aluminium or suchlike.
  • the first or second optical record carrier to be scanned is located in a planar scanning area adjacent to the optical system, mounted on a motorised rotating bearing in an optical scanning device including the optical system, whereby the disc is moved relative to the optical system during scanning.
  • the optical system includes two optical branches for scanning optical discs with radiation beams of two different wavelengths.
  • a first radiation beam 7 for scanning a first optical record carrier is of a first wavelength ⁇ i within the range of approximately 775-795nm and preferably approximately 785nm with the system in the second mode.
  • a second radiation beam 8 for scanning a second optical record carrier is of a second wavelength ⁇ 2 within the range of approximately 645nm- 665nm and preferably approximately 650nm.
  • the second wavelength ⁇ 2 is substantially different to the first wavelength ⁇ i by at least lOnm and in this embodiment by approximately 135nm.
  • a first optical branch includes a first radiation source 6, for example a semiconductor laser of a radiation source system, operating at a predetermined wavelength, in this example the first wavelength ⁇ i, which produces the first radiation beam 7.
  • the first branch further includes a beam splitter 9 for reflecting a returning first radiation beam 7 towards a detector system 10, and a collimator lens 11 for producing a more collimated beam.
  • a dichroic beam splitter 12 reflects the collimated first radiation beam 7 towards the first optical record carrier along a common optical path portion between the dichroic beam splitter 12 and the first optical record carrier.
  • the common optical path portion is shared by both the first and the second radiation beams 7, 8 of the optical system. In this embodiment the common optical path portion is coincident with an optical axis OA.
  • the first radiation beam 7, having been reflected by the dichroic beam splitter 12 is focused by an objective lens 14, the beam having a numerical aperture (NA) of approximately 0.5, and compensated by a compensator 16 to a first focal spot 17 on the information layer 2 of the first optical record carrier.
  • the first radiation beam 7 is reflected by the information layer 2 of the first optical record carrier and follows a return path which includes travelling along the common optical path portion.
  • the dichroic beam splitter 12 reflects the returning first radiation beam 7 to the beam splitter 9 which reflects it towards a photodiode detector array arranged in the detector system 10, where data, focus error and tracking error signals are detected.
  • the objective lens 14 is driven by servo signals derived from the focus error signal to maintain the focused state of the first focal spot 17 on the first optical record carrier and from the tracking error signal to maintain alignment with a track on the first optical record carrier being scanned.
  • a second optical branch includes a second radiation source 18, for example a semiconductor laser of the radiation source system, operating at a predetermined wavelength, in this example the second wavelength ⁇ 2 , which produces the second radiation beam 8.
  • the second branch further includes a beam splitter 20 for reflecting a returning second radiation beam 8 towards a detector system 18, and a collimator lens 24 for producing a collimated beam.
  • the collimated second radiation beam 8 is transmitted substantially fully by the dichroic mirror 12. Travelling along the common optical path, the second radiation beam 8 is focused by the objective lens 14, the beam having a numerical aperture (NA) of approximately 0.65, and compensated by the compensator 16 to a second focal spot 26 on the information layer 3 of the second optical record carrier.
  • NA numerical aperture
  • the second radiation beam 8 is reflected by the information layer 3 of the second optical record carrier and follows a return path which includes travelling along the common optical path portion.
  • the beam splitter 20 reflects it towards a photodiode detector array arranged in the detector system 22, where data, focus error and tracking error signals are detected.
  • the objective lens 14 is driven by servo signals derived from the focus error signal to maintain the focused state of the second focal spot 26 on the second optical record carrier and from the tracking error signal to maintain alignment with a track on the second optical record carrier being scanned.
  • the objective lens 14 has a numerical aperture (NA) of between approximately 0.55 and 0.75 and preferably approximately 0.65 and a focal length (f) of between approximately 2.65mm and 2.85mm and preferably approximately 2.75mm.
  • the lens is made of COC (Cyclo Olefinic Copolymer). Specifications of the objective lens 14 are determined at a design temperature T 0 of the optical system of between approximately 10°C and 30°C and preferably approximately 20 °C At this design temperature To of approximately 20°C and where the objective lens 14 is focusing the first radiation beam 7 of the first wavelength ⁇ i of approximately 785nm the objective lens 14 has a refractive index (n) of approximately 1.537.
  • the objective lens 14 has a refractive index (n) of approximately 1.5312, 1.5310 and 1.5309 when the second wavelength ⁇ 2 of the second radiation beam 8 being focused is approximately 650nm, 655nm and 660nm respectively.
  • a first wavefront deviation Wi comprising a spherical aberration is introduced into the first radiation beam 7.
  • This first wavefront deviation Wi is introduced by a difference between the first information layer depth 4 and the second information layer depth 5.
  • the second information layer depth 5 introduces a cover layer wavefront deviation comprising a spherical aberration.
  • Specifications of the objective lens 14 are designed such that a compensatory wavefront deviation comprising a spherical aberration is introduced into the second radiation beam 8 which compensates the cover layer wavefront deviation introduced by the second information layer depth 5. Consequently the second focal spot 26 of the second radiation beam 8 on the information layer 3 has substantially no wavefront deviation and is of a high quality.
  • the first wavefront deviation Wi of the first radiation beam 7 results.
  • This first wavefront deviation Wi leads to a decrease in the quality of the first focal spot 17.
  • the compensator 16 comprises a transparent plate, a surface of which is a phase structure which is rotationally symmetrical about the optical axis OA.
  • a second surface of the transparent plate and on an opposite side to the phase structure is attached in this embodiment to a first surface of the objective lens 14 such that the phase structure faces the cover layer of the first or second optical record carrier.
  • the phase structure has a plurality of annular areas arranged about the optical axis OA and is a non-periodic phase structure (NPS). Each annular area is a ring with a height h from the surface of the phase structure of the transparent plate, and a beginning normalised radial coordinate p b and an ending radial normalised coordinate p e from the optical axis OA.
  • the beginning normalised radial coordinate pb and the ending normalised radial coordinate p e describe an annular width and position of each ring.
  • Each individual height h of one of the rings is an optical path with a different length.
  • a side profile 28 of the phase structure of the compensator 16 is shown graphically in figure 2 and has a non-periodic stepped pattern.
  • the side profile 28 of the NPS is a plot of the individual heights h of the rings on a first axis 30 as a function of their beginning normalised radial coordinate pb and ending normalised radial coordinate p e from the optical axis OA on a second axis 32.
  • the NPS of the compensator 16 has an inner structure 34 and an outer structure 36.
  • the inner and outer structures 34, 36 include annular zones in the form of a series of the individual rings of different heights.
  • the inner structure 34 preferably has a beginning and an ending normalised radial coordinate p b, p e of approximately 0 and above 0.5, in this embodiment 0 and 0.769, respectively.
  • the outer structure 36 preferably has a beginning and an ending normalised radial coordinate pb, p e of above 0.5 and approximately 1, in this embodiment 0.769 and 1, respectively.
  • a boundary 37 between the inner and the outer structures 34, 36 is marked by a change between a first sequence of decreasing heights of adjacent rings of the inner structure 34 and a second, different, sequence of decreasing heights of adjacent rings of the outer structure 36.
  • the height of the ring of the inner structure 34 adjacent the boundary 37 is less than the height of the ring of the outer structure 36 adjacent the boundary 37.
  • the boundary 37 is at a numerical aperture (NA) of between 0.4 and 0.6, preferably approximately 0.5.
  • NPS of the compensator 16 is arranged to approximately compensate the first wavefront deviation Wi introduced into the first radiation beam 7 by the difference between the first and the second information layer depths 4, 5.
  • the approximate compensation in this embodiment is such that a root mean square optical path difference (RMS OPD) of the first radiation beam 7 is reduced to below 70m ⁇ and more preferably below approximately 45m ⁇ , for example 40m ⁇ .
  • RMS OPD root mean square optical path difference
  • Table 1 gives approximate data of the heights h and the beginning and the ending normalised radial coordinates pb, p e of each of the individual rings of the inner structure 34.
  • a height of a ring of the inner structure 34 having a negative value indicates that the ring is a depression of the surface of the compensator 16 having the NPS.
  • a unit height ho is determined to introduce a phase shift of approximately 2 ⁇ to the second wavelength ⁇ 2 during scanning in the second mode and at the design temperature To of approximately 20°C
  • Equation 1 is used to calculate the unit height ho, wherein n is the refractive index of the material from which the ring of the NPS is formed.
  • n is the refractive index of the material from which the ring of the NPS is formed.
  • the unit height ho has a value approximately between the range 1.18-1.28 ⁇ m and preferably approximately 1.23 ⁇ m.
  • Table 1 gives approximate data of the radial coordinates and the heights of the rings of the inner structure 34:
  • the first radiation beam 7 travelling along the optical axis OA having passed through the objective lens 14 enters the compensator 16 at the surface attached to the objective lens 14.
  • the first radiation beam 7 is modified by the optical paths of different lengths of the inner structure 34. Consequently the first radiation beam 7 emerging from the surface of the compensator 16 having the NPS has a compensatory wavefront deviation comprising a spherical aberration.
  • Each optical path of a different length introduces a phase shift into the first radiation beam 7.
  • the different phase shifts introduced by the different rings of the inner structure 34 together form the compensatory wavefront deviation.
  • the compensatory wavefront deviation comprising a spherical aberration is arranged to compensate the first wavefront deviation Wi, thus reducing the spherical aberration of the first radiation beam 7.
  • the heights of the rings of the inner structure 34 of the NPS are determined to introduce the desired phase shifts into the first radiation beam 7. Additionally the heights of the rings of the inner structure 34 are arranged to introduce a phase shift of an integral multiple of 2 ⁇ into the second radiation beam 8 such that no substantial wavefront deviation is introduced into the second radiation beam 8 when a second optical record carrier is being scanned at least during scanning at the design temperature To. During scanning of the first optical record carrier, because of the smaller NA being used, substantially none of the first radiation beam 7 which is focused to the first 17 focal spot passes from the outer structure 36 of the NPS. Additionally any variation of the first wavelength ⁇ i due to a manufacture process of the radiation source system lies substantially within the tolerances of the detector system 10.
  • specifications of the objective lens 14 and the compensator 16 are determined at a design temperature To of approximately 20°C.
  • To the objective lens 14 introduces a spherical aberration into the second radiation beam 8 when scanning the second optical record carrier to compensate the cover layer wavefront deviation introduced by the second information layer depth 5.
  • a temperature of the optical system and therefore of the objective lens 14 deviates from the design temperature To, a change in a refractive index n of the objective lens 14 occurs. Additionally a change in a shape and a dimension of the objective lens 14 occurs.
  • ⁇ 2 With this deviation in temperature a variation of the first and second wavelengths ⁇ i, ⁇ 2 occurs also.
  • To the second wavelength ⁇ 2 is approximately 650 nm and at a temperature of the optical system of approximately 80°C the second wavelength ⁇ 2 is approximately 660nm.
  • This wavelength variation with temperature is approximately 0.2 nmIC 1 .
  • the change of the objective lens 14 with the deviation in temperature cause an additional wavefront deviation comprising a spherical aberration to be introduced into the first or second radiation beam 7, 8 when scanning a first or second optical record carrier respectively.
  • the amount of spherical aberration introduced is proportional to the deviation in temperature. Since the additional wavefront deviation is not required for the compensation of the first wavefront deviation Wi of the first radiation beam 7 or the cover spherical aberration of the second radiation beam 8, the additional wavefront deviation introduced by the first or second information layer depth 4, 5 reduces the quality of the first or second focal spot 17, 26.
  • the introduced additional wavefront deviation comprising a spherical aberration is a second wavefront deviation W 2 .
  • the RMS OPD of this second wavefront deviation W 2 is approximately 88m ⁇ .
  • Figure 3 shows graphically a cross section of the second wavefront deviation W 2 plotted on a third axis 38 as a function of the normalised radial coordinate p on a fourth axis 40.
  • a second plot line 44 shows the second wavefront deviation W with the temperature being approximately 50°C and the second wavelength ⁇ 2 being approximately 655nm.
  • a third plot line 46 shows the second wavefront deviation W 2 with the temperature being approximately 80°C and the second wavelength ⁇ 2 being approximately 660nm.
  • the second wavefront deviation W 2 illustrated by the third plot line 46 has a greater spherical aberration than that of the first and the second plot lines 42, 44.
  • an area of the second wavefront deviation W 2 of the second radiation beam 8 having a numerical aperture (NA) between approximately 0 and 0.5 is at least partly compensated by adjusting a focal position along the optical axis OA of the objective lens 14 using the servo signals from the focus error signal.
  • This focal position is adjusted to minimise an RMS OPD of the second radiation beam 8 and at a temperature of 80°C this focal position is a focus offset of between approximately - 0.5 and -1.5 ⁇ m and more preferably approximately -l.O ⁇ m from a focal position of the objective lens 14 when scanning the second optical record carrier at the design temperature To.
  • Figure 4 shows graphically a cross section of the second wavefront deviation W 2 with the objective lens 14 being at the focal offset of preferably approximately -l.O ⁇ m.
  • the second wavefront deviation W 2 is plotted on the third axis 38 as a function of the normalised radial coordinate p on the fourth axis 40.
  • a fourth plot line 48 shows the second wavefront deviation W 2 with the temperature being approximately 80°C and the second wavelength ⁇ 2 being approximately 660nm.
  • An area of the second wavefront deviation W 2 of the second radiation beam 8 has a numerical aperture (NA) between approximately 0.5 and 0.65 and is approximately compensated by the outer structure 36 of the NPS of the compensator 16, the optical system being in the second mode.
  • NA numerical aperture
  • the approximate compensation in this embodiment is such that a RMS OPD of the second radiation beam 8 is reduced to below 70m ⁇ and more preferably below approximately 45m ⁇ , for example 30.6m ⁇ .
  • Table 2 gives approximate data of the heights h and the beginning and the ending normalised radial coordinates pb, p e of each of the individual rings of the outer structure 36. Each of these rings preferably has a height difference of approximately 3.7 ⁇ m from an adjacent ring of the outer structure 36.
  • the unit height ho of the rings of the outer structure 36 is approximately 1.23 ⁇ m and, in a similar manner to that described earlier, is determined to introduce a phase shift of approximately 2 ⁇ to the second wavelength ⁇ 2 during scanning in the second mode at the design temperature To.
  • Figure 5 shows graphically a cross section of the second wavefront deviation W 2 with the objective lens 14 being at the focal offset of preferably approximately -l.O ⁇ m and the area of the second radiation beam 8 having a NA of approximately between 0.5 and 0.65 being compensated by the outer structure 36.
  • the second wavefront deviation W 2 is plotted on the third axis 38 as a function of the normalised radial coordinate p on the fourth axis 40.
  • a fifth plot line 50 shows the second wavefront deviation W 2 for the area compensated by the outer structure 36.
  • the temperature is approximately 80°C and the second wavelength ⁇ 2 is approximately 660nm.
  • the inner and the outer structures 34, 36 and the boundary 37 are shown also.
  • Table 3 shows approximate values, for this embodiment of the present invention, of the RMS OPD of the second radiation beam 8 at different temperatures of the objective lens 14 and different values of the second wavelength ⁇ 2 .
  • the variation of the second wavelength ⁇ may be attributed not only to the deviation in temperature but also to a manufacture process of the radiation source system.
  • the optical system is arranged to scan different other types of optical record carrier from a CD or a DVD, for example a Blu-rayTM disc or a small form factor optical (SFFO) disc.
  • a CD or a DVD for example a Blu-rayTM disc or a small form factor optical (SFFO) disc.
  • SFFO small form factor optical
  • different radiation beams with different wavelengths are used which are appropriate for the type of optical record carrier being scanned.
  • an optical scanning system having greater than two modes is envisaged for scanning more than two types of optical record carrier whilst maintaining an insensitivity to a variation of a parameter of the system, for example a deviation in temperature.
  • optical record carriers with one information layer are scanned by the optical system. It is envisaged further that optical record carriers having multiple information layers are scanned.
  • the compensator of the described embodiment of the present invention is arranged to compensate a wavefront deviation of the radiation beam with a deviation in temperature. In further embodiments of the present invention it is envisaged that the compensator is arranged to compensate for a deviation in other variable parameters of the optical system.
  • variable parameters include a variation in the wavelength of the radiation beam occurring during a switching between a reading and writing power of the radiation beam; a tilting of the objective lens leading to a change in a field angle of the radiation beam entering the objective lens; a humidity of the surroundings of elements of the optical system; a polarisation of the radiation beam scanning the optical disc; and a tilt of the optical disc being scanned.
  • the described embodiment of the present invention has the compensator attached to a surface of the objective lens. It is further envisaged that the compensator is separate from the objective lens. Additionally it is envisaged that in an arrangement unlike that of the described embodiment, the NPS of the compensator is arranged on two surfaces of the transparent plate.
  • each zone may have curved surface characteristics. It is to be understood that any feature described above in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

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  • Optical Head (AREA)

Abstract

L'invention porte sur un système optique doté d'un premier mode permettant de balayer un premier support d'enregistrement optique d'un premier type et pourvu d'un couche d'information (2) située à un premier niveau de couche d'information (4), et d'un deuxième mode permettant de balayer un deuxième support d'enregistrement optique d'un deuxième type, différent, pourvu d'une couche d'information située à un deuxième, différent niveau de couche d'information (5), ledit système optique comprenant un paramètre variable. Le système optique intègre les éléments suivants : un système à source de rayonnement (6 & 18) permettant de générer un premier faisceau de rayonnement (7) dans le premier mode et un deuxième faisceau de rayonnement différent (8) dans le deuxième mode ; un ou plusieurs éléments optiques permettant de concentrer le premier faisceau de rayonnement (7) sur un point de la couche d'information (2) du premier support d'enregistrement dans le premier mode, ou de concentrer le deuxième faisceau de rayonnement (8) sur un point (26) de la couche d'information du deuxième support d'enregistrement dans le deuxième mode ; et un compensateur (16) ayant une structure de phase comprenant des zones annulaires délimitant un tracé non périodique des trajets optiques de différentes longueurs. Le compensateur (16) est disposé de manière à pouvoir compenser une première déviation de front d'onde (W1) introduite lors du balayage de la couche d'information (2) du premier support d'enregistrement optique l'aide du premier faisceau de rayonnement (7) précité, dans le premier mode, et en outre disposé de manière à pouvoir compenser une deuxième déviation de front d'onde (W2) introduite dans le deuxième faisceau de rayonnement (8) lors d'une variation dudit paramètre du système optique dans le deuxième mode.
PCT/IB2004/050453 2003-04-17 2004-04-15 Systeme optique WO2004093063A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP03101063.0 2003-04-17
EP03101063 2003-04-17

Publications (2)

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WO2004093063A2 true WO2004093063A2 (fr) 2004-10-28
WO2004093063A3 WO2004093063A3 (fr) 2005-01-20

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006061755A3 (fr) * 2004-12-10 2008-04-17 Koninkl Philips Electronics Nv Compensateur optique utilise dans un dispositif de balayage optique

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000041173A1 (fr) * 1999-01-08 2000-07-13 Asahi Kogaku Kogyo Kabushiki Kaisha Capteur optique
WO2001026103A1 (fr) * 1999-10-06 2001-04-12 Sony Corporation Lentille d'objectif et capteur optique
US20010008512A1 (en) * 1999-12-28 2001-07-19 Asahi Kogaku Kogyo Kabushiki Kaisha Objective lens for optical pick-up
US20030048535A1 (en) * 2001-06-13 2003-03-13 Asahi Kogaku Kogyo Kabushiki Kaisha Objective lens for optical pick-up
US20030058776A1 (en) * 2001-04-12 2003-03-27 Konica Corporation Objective lens and optical pickup apparatus

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000041173A1 (fr) * 1999-01-08 2000-07-13 Asahi Kogaku Kogyo Kabushiki Kaisha Capteur optique
WO2001026103A1 (fr) * 1999-10-06 2001-04-12 Sony Corporation Lentille d'objectif et capteur optique
US20010008512A1 (en) * 1999-12-28 2001-07-19 Asahi Kogaku Kogyo Kabushiki Kaisha Objective lens for optical pick-up
US20030058776A1 (en) * 2001-04-12 2003-03-27 Konica Corporation Objective lens and optical pickup apparatus
US20030048535A1 (en) * 2001-06-13 2003-03-13 Asahi Kogaku Kogyo Kabushiki Kaisha Objective lens for optical pick-up

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
HENDRIKS B H W ET AL: "Application of nonperiodic phase structures in optical systems" APPLIED OPTICS, OPTICAL SOCIETY OF AMERICA,WASHINGTON, US, vol. 40, no. 35, 10 December 2001 (2001-12-10), pages 6548-6560, XP002264634 ISSN: 0003-6935 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006061755A3 (fr) * 2004-12-10 2008-04-17 Koninkl Philips Electronics Nv Compensateur optique utilise dans un dispositif de balayage optique

Also Published As

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