• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:

    公开号:NL1008739A1
    申请号:NL1008739
    申请日:1998-03-27
    公开日:1998-09-29
    发明作者:Jang-Hoon Yoo；Chul-Woo Lee
    申请人:Samsung Electronics Co Ltd；
    IPC主号:
    专利说明:

    Title: Optical pick-up compatible with a digital versatile disc and a recordable compact disc using a holographic ring lens.
    Background of the invention
    The invention relates to an optical pick-up device compatible with a digital video disc (DVD: digital video disk) and a recordable compact disc (CD-R: recordable compact disk), and more particularly to an optical pick-up device which can record and read compatible information on a digital video disc (DVD) and a recordable compact disc (CD-R) respectively using a holographic lens.
    An optical pick-up device serves to record and read information such as high density video, audio or data, and recording media therefor are a disc, a card or a tape. Of these, the disc type is mainly used. Recently, a laser disc (LD), a compact disc (CD) and a digital video disc (DVD) have been developed in the field of optical disc devices. Such an optical disc comprises a plastic or glass medium of a certain thickness along an axial direction in which light enters and a signal recording surface on which information is recorded and placed on the plastic or glass medium.
    So far, a high density optical disc array increases the numerical aperture of an objective lens to increase a recording density and uses a short wavelength light source of 635 nm or 650 nm. Therefore, the high-density optical disc system can record or read signals from a digital video disc and can also read signals from a CD. However, to be compatible with a recent type of CD, i.e. a recordable CD (CD-R), light having a wavelength of 780 nm must be used, due to the recording characteristic of the CD-R recording medium. As a result, the use of light beam wavelengths of 780 nm and 650 nm in a single optical pickup becomes very important for the compatibility of the DVD and the CD-R. A conventional optical pickup compatible with the DVD and the CD-R will now be described below with reference to Fig. 1.
    Fig. 1 shows an optical pick-up using two laser light-emitting diodes as the light source for a DVD and a CD-R and a single objective lens. The optical pickup of Fig. 1 uses laser light with a wavelength of 635 nm when reproducing a DVD and uses laser light with a wavelength of 780 nm when recording and reproducing a CD-R.
    Light with a wavelength of 635 nm emitted from a first laser light source 11 falls on a first collimation lens 12, in which the light is shown continuously. The first collimation lens 12 allows the incident light beam to be a parallel light beam. The light beam passing through the first collimation lens 12 is reflected by a beam splitter 13 and then goes to an interference filter prism 14.
    Light with a wavelength of 780 nm emitted from a second laser light source 21 passes through a second collimation lens 22, a beam splitter 23 and a converging lens 24 and then passes to the interfere filter prism 14, in which the light is shown streaked. Here, the light beam with a wavelength of 780 nm is converged by the interference filter prism 14. An optical system with such a structure is called a "finite optical system". The interference filter prism 14 fully transmits the light beam with a wavelength of 635 nm reflected by the beam splitter 13 and fully reflects the light beam with a wavelength of 780 nm which is converged by the converging lens 24. As a result, the light beam falls from the first laser light source 11 on a quarter-wavelength wafer 15 in the form of a parallel beam through the collimation lens 12, while the light beam from the second laser light source 21 is incident on the quarter-wavelength wafer 15 in the form of a diverging beam through the converging lens 24 and the interference filter prism 14. The light transmitted from the quarter-wavelength plate 15 passes through a variable aperture 16 with a thin film structure and then incident on an objective lens 17.
    The light beam with a wavelength of 635 nm emitted by the first laser light source 11 is focused by the objective lens 17 on an information recording surface in the DVD 8 with a thickness of 0.6 mm. Therefore, the light reflected from the information recording surface of the DVD 8 contains information recorded on the information recording surface. The reflected light is transferred through the beam splitter 13 and then falls on a photo detector 19 for detecting optical information.
    If the finite optical system as described above is not used, when the 780 nm wavelength light beam emitted from the second laser light source 21 is focused on an information recording surface in the CD-R 25 having a thickness of 1.2 mm using the objective lens 17 described above, a spherical aberration is generated due to a difference in thickness between the DVD 18 and the CD-R 25. The spherical aberration is due to the distance between the information recording surface of the CD- R 25 and the objective lens 17 is larger than that between the information recording surface of the DVD 18 and the objective lens 17 along the optical axis. To reduce such spherical aberration, construction of a finite optical system including the converging lens 24 is required. Using the variable aperture 16 which will be described later with reference to Fig. 2, the 780 nm wavelength light beam forms an optimized beam spot on the information recording surface of the CD-R 25. The wavelength 780 nm wavelength is reflected by CD-R 25 is reflected by the beam splitter 23 and then detected in the photo detector 26.
    The thin film type variable aperture 16 of Fig. 1, as shown in Fig. 2, has a structure that can selectively transmit the light beams incident on the areas whose numerical aperture (NA) is less than or equal at 0.6 and coincides with the diameter of the objective lens 17. The variable aperture 16 is divided into two regions based on the numerical aperture (NA) of 0.45 with respect to an optical axis. Of the two regions, a first region 1 transmits both beams of light with a wavelength of 635 nm and a wavelength of 780 nm. A second region 2 transmits the light beam with a wavelength of 635 nm in total and reflects the light beam with a wavelength of 780 nm in total. Area 1 is an area whose numerical aperture is less than or equal to 0.45 and area 2 is an outer area of area 1 in which a thin dielectric film is coated. The area 1 consists of a thin quartz (SiOs) film to remove any optical aberration generated by the dielectric coated thin film area 2.
    Using the variable aperture 16, the light having a wavelength of 780 nm transmitted through the region 1 with an NA of 0.45 or lower forms a beam spot suitable for the CD-R 25 on its information recording surface. Therefore, the optical pickup of Figure 1 uses an optimal beam spot when a disc mode changes from the DVD 18 to the CD-R 25. Therefore, the optical pickup of Figure 1 is compatible for use with the CD-R.
    However, the optical pickup of FIG. 1 as described above must form a "finite optical system" with respect to the light having a wavelength of 780 nm to remove any spherical aberration produced when compatible DVD changes with a CD-R. Also, because of the thin optical film, that is, the thin dielectric film formed in the region 2 of the variable aperture 16 with an NA of 0.45 or higher, an optical path difference is produced between the light transmitted by the region 1 with an NA of 0.45 or lower and the light transmitted through the region 2 with an NA of 0.45 or higher. To counteract this difference, it is necessary to form a thin optical film in the area 1. For this reason, a quartz coating is formed in the area 1, and a thin multi-layer film is formed in the area 2. However, such a manufacturing process is not only complicated but also adjusting the thickness of the thin film must be done accurately in units of "μηη". It is therefore difficult to accomplish this in mass production of the optical pick-up.
    Summary of the invention
    It is therefore an object of the present invention to provide an optical pick-up device compatible with a digital video disc (DVD) and a recordable compact disc (CD-R) by adopting an infinite optical system and using a holographic lens to remove a spherical aberration generated due to a difference in thickness between optical discs.
    To accomplish this object of the present invention, there is provided an optical pick-up device that is compatible with at least two types of optical recording media, using light beams of respective different wavelengths for recording and reading information, the optical pick-up device includes: two laser light sources to emit beams of different wavelengths, respectively, a> holographic lens comprising a holographic ring, to transmit a plurality of light beams emitted by the laser light sources in an inner region of the ring, and refracting a specific light beam from the light beams emitted from the laser light sources in an outer region of the area, an objective lens to focus the light beams passing through the holographic ring lens on the respective information recording surfaces of the two types of optical recording media, optical elements om optis traces of the light beams reflected by changing the information recording surfaces of the optical recording media, and two photo detectors to detect separate optical information from the light beams incident from the optical elements.
    Brief description of the drawings
    Preferred embodiments will now be described with reference to the drawings, in which: Fig. 1 is a view showing the construction of a conventional optical pickup; FIG. 2 is a view for explaining the structure of a conventional variable aperture shown in FIG. 1; Fig. 3 is a view showing an optical system of an optical pick-up according to the present invention; Fig. 4A is a view showing a positional relationship between a holographic ring lens and an objective lens according to the present invention; and Fig. 4B is a view showing the flat surface of a holographic ring lens; Fig. 5A is a view showing the flat surface of a holographic ring lens; and FIG. 5B is a graphical view showing part of the area of FIG. 5A that has been enlarged; Fig. 6 is a graphical view showing the transmission efficiency according to the groove depth of a holographic ring lens with respect to two wavelengths; and FIG. 7 is a view showing that a holographic ring lens and an objective lens are integrally incorporated.
    Detailed description of the preferred embodiments ^
    Preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings.
    Fig. 3 shows an optical pickup optical system according to a preferred embodiment of the present invention. Referring to Fig. 3, the optical pickup device comprises two laser light sources 31 and 39 for emitting light beams of different wavelengths, respectively, two holographic beam splitters 32 and 40 for changing the optical path of the light beams reflected by information recording surfaces of optical disks, a beam splitter 33 for transmitting or reflecting the incident light beam totally according to the wavelength of the light, a collimation lens 34 which serves to make the incident light beam a parallel light beam, a holographic ring lens 35 to refract the incident light beam according to its wavelength and an objective lens 36 for focusing the light beams on the respective information recording surfaces of the optical disks 37 and 41. Two photo detectors 38 and 42 detecting the light beams reflected by the respective information registration suggestion faces of the optical disks 37 and 41 and the laser light sources 31 and 39 are integrally incorporated in a single module to form units 30 and 43. The operation of the optical pickup constructed according to the above will be described below, with a DVD and a CD-R described as optical recording media.
    When recording and reading information on a DVD, a 650 nm wavelength light beam emitted from the first laser light source 31 first strikes the holographic beam splitter 32, where the light is shown as a solid line. The incident light beam passes through the holographic beam splitter 32 and continues to the beam splitter 33. When recording and reading information at a CD-R, a light beam with a wavelength of 780 nm emitted by the second laser light source 39 is incident on the holographic beam splitter 40, in which the light is shown as a dashed line. The incident light beam passes through the holographic beam splitter 40 and continues to the beam splitter 33.
    The beam splitter 33 transmits the incident light beam with a wavelength of 650 nm in total and reflects the incident light beam with a wavelength of 780 nm in total. The total transmitted or reflected light beam passes to the holographic ring lens 35 in the form of a parallel beam through the collimation lens 34.
    The holographic ring lens 35 selectively breaks the incident light beam according to its wavelength to prevent spherical aberration from being generated with respect to the light beams focused on the information recording surfaces of the optical disks 37 and 41.
    Fig. 4A is a view showing the positional relationship between the holographic ring lens 35 and objective lens 36. As shown in Fig. 4A, objective lens 36 is divided into regions A and B. The region A which is closer to the optical axis has little effect on spherical aberration and the region B further from the optical axis has a large effect on spherical aberration. Also, the objective lens 36 is best suited for a thin thickness disc such as a DVD. Therefore, when a DVD is exchanged with a thick disc such as CD-R to operate the optical pickup, the holographic ring lens 35 is required.
    If the holographic ring lens 35 is not used in recording and reading information on the CD-R, the spherical aberration in the beam spot formed on the information recording surface of the disc becomes large, the size being more than 1.7 µ. In general, the size of the beam spot formed on the information recording surface of the CD-R is 1.4 μτπ. The holographic ring lens 35 refracts the light beam passing through the area B of the objective lens 36 and prevents the generation of spherical aberration for which a hologram indicated by dots in Fig. 4B is located between the outer boundary of the area A and the area B. Therefore, the light beam incident on the holographic ring lens 35 and passes through the region A of the objective lens 36 through the objective lens 36 without any diffraction through the holographic ring lens 35, and is then directly focused on the disc. The light beam incident on the holographic ring lens 35 and passing through the area B of the objective lens 36 is refracted by the holographic ring lens 35 and then continues on to the objective lens 36. The refracted light beam passing through the objective lens 36 makes the size of the beam spot it is focused on the disk smaller and no spherical aberration is generated. A focal surface of the disk on which the refracted light beam passing through region B must coincide with an optimized surface of the disc on which the beam of light passing through region A is focused. Using the holographic annular lens 35, the working distance from the surface of the objective lens 36 to the information recording surfaces of the discs becomes shorter in the CD-R 41 than in the DVD 37.
    Fig. 5A is a view showing the structure of the holographic ring lens 35. An area D where the hologram is contained in the holographic ring lens 35 shown in FIG. 5A corresponds to the numerical aperture of 0.3-0.5 which is it is believed suitable for the CD-R. In Fig. 5A, the symbol E indicates the diameter of the objective lens for a DVD whose numerical aperture (NA) is 0.6. Also, the holographic ring lens 35 used in the present invention can selectively set the numerical aperture (NA) of the objective lens according to the wavelengths of the light beam and does not require a separate aperture. The holographic ring lens 35 has the same function as in a conventional spherical lens that transmits a light beam in converging or diverging form. Furthermore, the holographic ring lens 35 has a negative optical power and uses a phase shift hologram. The optimized depth of the groove must be determined such that the holographic ring lens 35 selectively refracts the incident light beam according to its wavelength. The holographic ring lens 35 is constructed such that the 650 nm wavelength light beam has a transmitting efficiency close to 100% and the 780 nm wavelength light beam has a zero order transmitting efficiency with respect to the unbroken beam of light. For this, the phase variation due to the groove depth of the holographic ring lens 35 must be 360 ° with respect to the light with a wavelength of 650 nm. Since the phase variation is generated at 360 °, the holographic ring lens 35 transmits the light with a wavelength of 650 nm. The phase variation must take place by 180 ° with respect to the light with a wavelength of 780 nm, so that the light with a wavelength of 780 nm is completely refracted as first order light. As a result, holographic ring lens 35 is not designed to refract the light having a wavelength of 650 nm but to refract the light having a wavelength of 780 nm as first order light. An optimized surface groove depth d of the holographic ring lens 35 for the selective refraction of light beams with a wavelength of 650 nm and 780 nm is determined by the following equations (1) and (2):
    Here λ is the wavelength of 650 nm, λ 'the wavelength of 780 nm and n and n' indicate a refractive index (1.514520) for the wavelength of 650 nm and the refractive index (1.511183) for the wavelength of 780 nm respectively. In the above equations (1) and (2), if m = 3 and m '= 2, the depth d becomes approximately 3.8 μπκ
    Fig. 5B is a graphical view showing that the hologram area C shown in FIG. 5A is enlarged. A hologram has a groove with a constant depth by etching or it can be made by metal casting. Furthermore, the hologram can be formed step by step together with a ring pattern.
    Fig. 6 is a graphical view showing the zero-order transmission efficiency of the holographic annular lens 35 according to the wavelengths of the incident light. When the surface groove depth d is 3.8 μπι, the light with a wavelength of 650 nm is transmitted through the holographic ring lens 35 at 100% as shown by a solid line overlapped with the symbol "++", and the light with a wavelength of 780 nm transmitted through the holographic ring lens 35 at 0% as shown in a continuous line overlapped with a circle. The holographic ring lens 35 now refracts the light with a wavelength of 780 nm as the first order light, its diffraction efficiency being 40%.
    The 650 nm wavelength light incident on the holographic ring lens 35 having the above characteristics is completely transferred and then passes to the objective lens 36. The incident light beam passes through the objective lens 36 and forms a beam spot on the information recording surface of the DVD 37. The light beam reflected from the information recording surface of the DVD 37 is incident on the holographic ring lens 35. The holographic ring lens 35 changes the optical path of the incident light beam and directs the light beam to the photodetector 38. The 780 nm wavelength light incident on the holographic ring lens 35 is transferred in the area A and then goes to the objective lens 36 and is broken in the area B and goes to the objective lens 36 as shown in Fig. 4A. Therefore, the light beam passing through the objective lens 36 forms an optimized beam spot on the information recording surface of the CD-R 41. The light beam reflected from the information recording surface of the CD-R 41 is incident on the beam splitter 33 and is then reflected. The reflected light proceeds to holographic beam splitter 40 and then incident on the photo detector 42 by changing the optical path.
    The holographic ring lens 35 having the above functions can be fabricated in one piece with an objective lens via etching to a constant depth inward from one surface of the objective lens or metal mold. The one piece holographic ring lens has the same function as the holographic ring lens 35. FIG. 7 is a view showing that the holographic ring lens and the objective lens are included in one piece.
    As described above, the optical pickup device of the present invention is compatible with a DVD and a CD-R using a holographic ring lens to counteract spherical aberration that is generated when a disc is exchanged for a other disc of different thickness, in which the working distance is shorter in case of the CD-R. Also, the optical pick-up device provides advantages that include ease of construction of a holographic ring lens and good mass production.
    While only certain embodiments of the invention have been specifically described herein, it will be apparent to those skilled in the art that various modifications can be made without exceeding the scope and scope of the claims and the invention.
    权利要求:
    Claims (20)
    [1]
    Optical pick-up device compatible with at least two types of optical recording media using beams of respective different wavelengths for recording and reading information, characterized in that the optical pick-up device comprises: two laser light sources around light beams broadcast with different wavelengths respectively; a holographic lens that includes a holographic ring to fully transmit a number of light beams emitted by the laser light sources in an inner region of the ring and to refract a specific light beam from the light beams emitted by the laser light sources in an outer region of the respective area; an objective lens to focus the light beams passing through the holographic ring lens on the respective information recording surfaces of the two types of optical recording media; optical elements to change the optical paths of the light beams reflected from the information recording surfaces of the optical recording media; and two photo detectors to detect separate optical information from the light beams incident from the optical elements.
    [2]
    Optical pick-up device according to claim 1, characterized in that the holographic lens comprises a hologram composed of a flat part, in which the hologram is not arranged in an area of the objective lens closer to the optical axis but is located in an outer region further away from the optical axis.
    [3]
    Optical pick-up device according to claim 1, characterized in that the holographic lens is phase-shifted.
    [4]
    Optical pick-up device according to claim 2, characterized in that a focal surface in which the light beam passing through the region of the objective lens closer to the optical axis is focused on the optical recording medium coincides with a focal surface in which the light beam passing through the region further away from the optical axis is focused on the optical recording medium when displaying a relatively thick optical recording medium.
    [5]
    Optical pick-up device according to claim 1, characterized in that the holographic lens sets the numerical aperture (NA) of the objective lens according to the wavelength of the incident light.
    [6]
    Optical pick-up device according to claim 1, characterized in that the holographic lens does not break light of a relatively short wavelength and light of a relatively long wavelength according to the wavelengths of the incident light.
    [7]
    Optical pick-up device according to claim 1, characterized in that the holographic lens is optimized with respect to a thick optical recording medium.
    [8]
    Optical pick-up device according to claim 1, characterized in that the holographic lens has a negative optical power.
    [9]
    Optical pick-up device according to claim 1, characterized in that the holographic lens has the same function as a conventional spherical lens and transmits the light beam in converging or diverging form.
    [10]
    Optical pick-up device according to claim 1, characterized in that the hologram is etched to constant depth from the reference surface of a flat surface thereof or has a groove by metal casting.
    [11]
    Optical pick-up device according to claim 1, characterized in that the holographic ring is formed step by step.
    [12]
    Optical pick-up device according to claim 1, characterized in that the holographic lens is incorporated in one piece with the objective lens, the holographic ring lens being formed into a surface of the objective lens at a constant depth by etching or casting.
    [13]
    Optical pick-up device according to claim 12, characterized in that the holographic lens is incorporated in one piece with the objective lens and has the same function as the separate separated holographic lens.
    [14]
    Optical pick-up device according to claim 10, characterized in that the depth of the groove causes a phase variation according to the wavelength of the light emitted from the laser light sources.
    [15]
    Optical pick-up device according to claim 14, characterized in that the phase variation is produced by 360 ° with respect to a relatively short wavelength of the incident light beam and by 180 ° with respect to a relatively long wavelength of the incident light beam.
    [16]
    Optical pick-up device according to claim 15, characterized in that the holographic lens does not break an incident light beam when the 360 ° phase variation is generated, while the holographic lens breaks the incident light beam to reduce the spherical aberration of a beam spot is focused on the optical recording medium when the phase variation of 180 ° is produced.
    [17]
    Optical pick-up device according to claim 1, characterized in that the optical elements are arranged between the laser light sources and the holographic lens.
    [18]
    Optical pick-up device according to claim 1, characterized in that the optical elements are holographic photo detectors.
    [19]
    Optical pick-up device according to claim 1, characterized in that the two photodetectors and the corresponding laser light sources are integrally incorporated in a single unit.
    [20]
    Optical pick-up device according to claim 1, characterized in that the working distance becomes shorter in a relatively thick disc than in a relatively thin disc.
    类似技术:
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    法律状态:
    1998-12-01| AD1A| A request for search or an international type search has been filed|
    2000-08-01| RD2N| Patents in respect of which a decision has been taken or a report has been made (novelty report)|Effective date: 20000606 |
    2000-10-02| PD2B| A search report has been drawn up|
    2018-03-28| MK| Patent expired because of reaching the maximum lifetime of a patent|Effective date: 20180326 |
    优先权:
    申请号 | 申请日 | 专利标题
    KR1019970011297A|KR100209918B1|1997-03-28|1997-03-28|Optical pickup for cd-r and dvd using hologram ring lens|
    KR19970011297|1997-03-28|
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