JP2005302120A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an optical pickup device capable of handling at least three kinds of recording media different in recording density with simplified configuration using a two-wavelength laser unit and a single objective lens. <P>SOLUTION: A laser beam of a first wavelength for a first laser unit 1 is made to be reflected by a filter side 12a of a prism 12 and led to a collimator lens 13. A laser beam of second wavelength of the first laser unit 1 and a laser beam of a third wavelength of a second laser unit 4 are made to transmit the filter face 12a and made to be reflected by a first reflective face 12b of the prism 12 and a second reflective face 12c, and led to the collimator lens 13. Each of the laser beams of the second wavelength and the third wavelength is made to be incident in an objective lens 15 by an infinite optical system and the laser beam of the first wavelength is made to be incident in the objective lens 15 by a finite optical system. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention includes a first laser unit that emits at least two types of laser beams having different laser wavelengths, and a first laser unit that emits a laser beam having a laser wavelength different from any of the laser beams emitted by the laser unit. The present invention relates to an optical pickup device that includes two laser units and corresponds to a signal recording medium of at least three recording formats having different recording densities.

  In a signal recording medium such as an optical disc in which signal reproduction and / or signal recording is optically performed using a laser beam, a new method in which the recording density of a high density DVD (Digital Versatile Disc), Blu-ray Disc, etc. is improved Has been proposed.

  In a disk drive compatible with such a new high-density recording medium, an existing CD (Compact Disc) and DVD can be played back and / or recorded. In order to support high-density DVD (tentative name: HD-DVD) and Blu-ray Disc high recording density media, it is necessary to have a configuration that emits laser light having a wavelength suitable for various disks. Incurs complications.

By the way, an optical pickup device using a two-wavelength laser unit capable of selectively generating two types of laser beams having different wavelengths by housing two types of laser elements in the same package is known. (See Patent Document 1)
Therefore, when designing an optical pickup device adapted to CD, DVD, and a new high-density recording medium, it is conceivable to use a two-wavelength laser unit in order to simplify the optical system.
JP 2000-121176 A

  By the way, in CD and DVD, the thickness of the transparent substrate to the signal recording surface is 1.1 mm and 0.6 mm, respectively, which is greatly different from about 1: 2, and the thickness of the transparent substrate to the signal recording surface is HD−. In the case of DVD, it is 0.6 mm, and in the case of Blu-ray Disc, it is 0.1 mm.

  In addition, the wavelength of the suitable laser light is 765 nm to 805 nm of infrared wavelength for CD, 635 nm / 645 nm to 675 nm of red wavelength for DVD, and 400 nm to 420 nm of blue violet (blue) wavelength for HD-DVD and Blu-ray Disc. It has become.

  Due to these points, the signal recording density, the recording method, and the like, the optical pickup device requires an objective lens having a different NA (numerical aperture) so as to have optical characteristics adapted to each disk. This NA is 0.45 for CD, 0.6 for DVD, 0.65 for HD-DVD, and 0.85 for Blu-ray Disc.

Also, in various types of discs, the optical magnification may differ greatly due to the difference in the required optical characteristics of the light spot. CD, DVD, and a new type high recording density medium (HD-DVD or Blu-ray) can be obtained with a single objective lens. -RayDisc), in order to make the objective lens have optical characteristics such as a predetermined NA, magnification, and spherical aberration correction for each type of disk, especially for the purpose of correcting aberrations during CD recording / reproduction. Employs a finite system in which laser light of a suitable wavelength is incident as diffuse light at a predetermined angle, and adopts an infinite system in which laser light of a suitable wavelength is incident as parallel light during recording and playback of DVDs and new high-density recording media. Products to be proposed.

  In an optical pickup device using such an objective lens, if a two-wavelength laser unit that emits each laser beam having a wavelength suitable for a CD and a DVD is employed, each laser emission point that emits each laser beam is determined. Since the positional relationship is fixed, the distance to the objective lens cannot be changed by changing the position of each of the laser emission points. It has been difficult to make the laser light having a wavelength suitable for the DVD parallel light while making the diffused light at a predetermined angle.

  In addition, it is necessary to design the optical system in consideration of this point because it is necessary to adopt a configuration in which a laser beam having a wavelength suitable for the new high-density recording medium is incident on the objective lens as parallel light. It has not been possible to provide a simple optical pickup device that satisfies the above condition.

  In addition, in order to receive each laser beam suitable for each of the three types of recording systems of the optical pickup device by a single photodetector, a beam splitter is arranged on a common optical path of all the laser beams. In the optical pickup device in which a plurality of laser units are used to adapt to a plurality of recording methods, a beam for arranging each laser unit in a separate optical path is arranged on the optical path separated by Because it requires a splitter or has an optical system for selectively using laser light of each wavelength, the optical layout designed simply means that the amount of light loss of each laser light guided to the photodetector is reduced. It becomes a problem.

The invention according to claim 1 is common to the beam splitter that guides the laser light emitted from the laser emission points of the first laser unit and the second laser unit arranged on separate optical paths onto the common optical path, and the beam splitter. A wavelength-selective filter surface that is disposed in front of the objective lens on the optical path and reflects the laser beam having the first laser wavelength is formed, and each of the second and third laser wavelengths that pass through the filter surface is formed. The first reflecting surface that reflects the laser light and the second and third laser wavelengths reflected by the first reflecting surface are reflected so as to be guided on the same optical path as the laser light reflected by the filter surface. A prism having a second reflecting surface; a collimator lens that collimates the laser beams having the second and third laser wavelengths that have passed through the prism; In addition, each laser beam having the third laser wavelength is incident as parallel light, and is focused on each recording medium suitable for each laser beam having the second and third laser wavelengths. And an objective lens for condensing the light onto a recording medium suitable for the laser light having the first laser wavelength by entering light at a predetermined divergence angle. As a result, the laser beam of the first laser wavelength of the first laser unit is reflected by the filter surface of the prism and guided to the collimator lens, and the laser beam of the second laser wavelength of the first laser unit and the second laser unit Laser light having a third laser wavelength is transmitted through the filter surface of the prism, reflected by the first reflecting surface and the second reflecting surface of the prism, and then guided to a collimator lens. The optical path length from the light emitting point to the collimator lens is made shorter than the optical path length from the laser light emitting point to the collimator lens in each laser light of the second and third laser wavelengths, and each laser light having the second and third laser wavelengths. Is incident on the objective lens in an infinite system and the first laser wavelength It is to be incident on the objective lens with a laser beam in a finite system.

  According to the present invention, the first laser unit that emits the laser beams having the first and second laser wavelengths respectively suitable for the recording media having different recording densities, and the first laser unit in addition to the first laser unit. And a second laser unit that emits a laser beam having a third laser wavelength different from the second laser wavelength, and each laser beam of each laser wavelength of the first laser unit is divided into a finite system and an infinite system. The optical pickup device can be incident on the objective lens and laser light of the third laser wavelength can be incident on the objective lens in an infinite system, and an optical pickup device corresponding to at least three types of recording media having different recording densities can be used. This can be achieved with a simple configuration using a unit and a single objective lens.

  In addition, the first laser unit and the second laser unit are arranged in separate optical paths using a dichroic prism, and the polarization direction of each laser beam emitted by the first laser unit and the second on the common optical path guided by the dichroic prism. Since the polarization direction of the laser light emitted by the laser unit is set to the same direction, each of the first, second, and third laser wavelengths on the optical path where the dichroic prism is arranged and the optical path branched. A photodetector that receives the laser beam can be disposed, and the laser beam can be guided to a common photodetector while suppressing loss of light amount.

  FIG. 1 is an optical layout diagram showing an optical system of an optical pickup device showing an embodiment of the present invention.

  The optical pickup device shown in FIG. 1 has a configuration corresponding to CD, DVD, and HD-DVD.

  The first laser unit 1 includes a first laser emission point 2 that emits a laser beam having an infrared wavelength band of 765 nm to 805 nm suitable for CD, for example, 780 nm, and a red wavelength band of 645 nm suitable for DVD on the same semiconductor substrate. Consists of a laser diode having a 675 nm wavelength, for example, a second laser emission point 3 that emits a laser beam of 650 nm, and emits two wavelengths of laser light suitable for CD recording / reproduction and DVD recording / reproduction with a single laser unit. It is supposed to be.

  The second laser unit 4 includes a laser diode having a laser emission point 5 that emits a laser beam having a wavelength of 400 nm to 420 nm, for example, 405 nm, suitable for HD-DVD.

  Each laser beam emitted from the first laser emission point 2 and the second laser emission point 3 of the first laser unit 1 is diffracted by the diffraction grating 6 to form ± first-order diffracted light used for tracking control, Thereafter, the polarization direction is adjusted by the half-wave plate 7 and supplied to the dichroic prism 8 from the transmission direction of the filter surface 8 a of the dichroic prism 8.

  On the other hand, the laser light emitted from the laser emission point 5 of the second laser unit 4 is diffracted by the diffraction grating 9 so as to form ± first-order diffracted light used for tracking control, and thereafter, by the half-wave plate 10. The polarization direction is adjusted and supplied to the dichroic prism 8 from the reflection direction of the filter surface 8a of the dichroic prism 8.

The dichroic prism 8 plays a role of arranging the first laser unit 1 and the second laser unit 4 in separate optical paths, and the filter surface 8a of the dichroic prism 8 has a laser beam of 650 nm and 780 nm as shown in FIG. A reflection / transmission coat having a wavelength selectivity that ensures a transmittance of 90% or more and a transmittance of 405 nm laser light of less than 10%, that is, a reflectance of 90% or more is applied.

  Therefore, each laser beam emitted from the first laser unit 1 passes through the filter surface 8a of the dichroic prism 8 and enters the polarization beam splitter 11, while the laser beam emitted from the second laser unit 4 is dichroic. The light is reflected from the filter surface 8 a of the prism 8 and is incident on the polarization beam splitter 11.

  Here, the laser light emitted from the first laser unit 1 and the laser light emitted from the second laser unit 4 are polarized by the polarization beam splitter 11 by the half-wave plate 7 and the half-wave plate 10, respectively. The filter surface 11a is set to be p-polarized light so as to pass through the polarization filter surface 11a. In addition, by setting the direction of the rotation direction of the first laser unit 1 and the second laser unit 4, each laser beam emitted from the first laser unit 1 and the laser beam emitted from the second laser unit 4 are polarized beams. It is possible to set the polarization filter surface 11a of the splitter 11 to p-polarized light. In this case, the half-wave plate 7 and the half-wave plate 10 can be omitted.

  The laser light emitted from the first laser unit 1 and the laser light emitted from the second laser unit 4 that have passed through the polarizing filter surface 11 a of the polarizing beam splitter 11 are incident on the optical path length adjusting prism 12.

  The optical path length adjusting prism 12 has a shape in which a right-angled isosceles triangle portion and a trapezoidal portion are joined, and the joining surface is a filter surface 12a to which a wavelength selective coating is applied. As shown in FIG. 3, the filter surface 12a has a transmittance of 780 nm laser light of less than 10%, that is, a reflectance of 90% or more and a transmittance of 405 nm to 650 nm laser light of 90% or more. Wavelength selectivity.

  Therefore, the 780 nm CD laser light emitted from the first laser emission point 2 of the first laser unit 1 is reflected by the filter surface 12a of the optical path length adjusting prism 12, and after the optical axis is raised, the collimator The light enters the lens 13.

  On the other hand, the 650 nm DVD laser light emitted from the second laser emission point 3 of the first laser unit 1 and the 405 nm HD-DVD laser light emitted from the laser emission point 5 of the second laser unit 5 are: When passing through the filter surface 12 a of the optical path length adjusting prism 12, reflected by the first inner surface 12 b and the second inner surface 12 c constituted by the mirror surfaces of the optical path length adjusting prism 12, and entering the optical path length adjusting prism 12, respectively. After the direction of the optical axis and 90 degrees are changed, the light passes again through the filter surface 12a of the optical path length adjusting prism 12 and enters the collimator lens 13.

  Here, the laser light reflected by the filter surface 12a of the optical path length adjusting prism 12 is set to have a shorter optical path length than the laser light transmitted through the filter surface 12a. When the HD-DVD laser beam is set to be converted into parallel light, the CD laser beam has its diffusion angle narrowed by the collimator lens 13 but passes through the collimator lens 13 as diffuse light.

  The laser light that has passed through the collimator lens 13 is ¼ wavelength polarized by the ¼ wavelength plate 14, then enters the objective lens 15, is converged by the objective lens 15, and is applied to the disk D.

  That is, the laser beam for CD and the laser beam for DVD emitted from the first laser emission point 2 and the second laser emission point 3 of the first laser unit 1 and the laser emission point 5 of the second laser unit 4 are emitted. The HD-DVD laser light is incident on a single objective lens 15, converged by the objective lens 15, and applied to the disk D.

  A diffraction grating (not shown) is formed on the incident surface of the objective lens 15, and the objective lens 15 is adapted to a CD emitted from the first laser emission point 2 of the first laser unit 1 by the diffraction grating. The desired characteristics are exhibited so that a laser beam having a wavelength is incident in a predetermined area at a predetermined divergence angle to obtain an NA and aberration-corrected laser spot suitable for CD recording and reproduction. Laser light having a wavelength suitable for DVD emitted from the second laser emission point 3 of the first laser unit 1 and laser light having a wavelength suitable for HD-DVD emitted from the laser emission point 5 of the second laser unit 4 By entering parallel light in a predetermined area, NA and aberration-corrected laser spots suitable for DVD and HD-DVD recording / reproduction can be obtained. Desired characteristics can be exhibited so.

  In this way, the laser beam for CD and the laser beam for DVD emitted from the first laser emission point 2 and the second laser emission point 3 of the first laser unit 1 and the laser emission point 5 of the second laser unit 4 are emitted. The laser beam for HD-DVD is converged corresponding to various disks by a single objective lens 15.

  The laser light modulated and reflected by the disk D returns to the objective lens 15 and returns to the polarization beam splitter 11 via the optical path that has come.

  Since the laser beam returned to the polarization beam splitter 11 passes through the quarter wavelength plate 14 twice in the forward path and the return path to the disk D, the polarization direction of the laser beam returned to the polarization beam splitter 11 is 1 /. Two wavelengths are rotated. Therefore, the laser beam that has been p-polarized in the forward path to the disk D becomes s-polarized light and enters the polarization beam splitter 11. Therefore, the laser beam returned to the polarization beam splitter 11 is reflected by the polarization filter surface 11a, generates a focus error component of the laser beam irradiated to the disk D, and passes through a servo lens 16 that performs focus adjustment. To the photodetector 17.

  The photodetector 17 includes a CD light receiving unit (not shown) used for CD recording / reproduction, a DVD light receiving unit (not shown) used for DVD recording / reproduction, and an HD-DVD light receiving used for HD-DVD recording / reproduction. (Not shown) are formed, the laser beam for CD is received in each light receiving region of the CD light receiving unit, the laser beam for DVD is received in each light receiving region of the DVD light receiving unit, and is for HD-DVD Laser light is received by each light receiving region of the HD-DVD light receiving unit.

  Therefore, recording signals for various discs are obtained, and control signals used for focusing control and tracking control corresponding to the various discs are obtained.

  The optical arrangement shown in FIG. 1 is used, and the first laser unit 1 and the second laser unit 4 are arranged in separate optical paths using the dichroic prism 8, and light is emitted from the first laser unit 1 incident on the polarization beam splitter 11. The polarization direction of each laser beam and the polarization direction of the laser beam emitted by the second laser unit 4 are set to be the same direction, whereby the optical path in which the photodetector 17 is arranged is changed to the first laser unit 1 and The second laser unit 4 can be separated from the optical path in which the second laser unit 4 is disposed. In this case, since it is the polarization beam splitter 11, the light loss is suppressed and each laser beam is received by the photodetector 17.

It is an optical arrangement | positioning figure which shows the optical system of the optical pick-up apparatus which shows one Example of this invention. 6 is a characteristic diagram showing transmission characteristics of a filter surface 8a of the dichroic prism 8. FIG. 6 is a characteristic diagram showing transmission characteristics of a filter surface 12a of the optical path length adjusting prism 12. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st laser unit 2 1st laser emission point 3 2nd laser emission point 4 2nd laser unit 5 Laser emission point 6 Diffraction grating 8 Dichroic prism 11 Polarizing beam splitter 12 Optical path length adjustment prism 12a Filter surface 12b First reflection surface 12c Second reflecting surface 13 Collimator lens 14 1/4 wavelength plate 15 Objective lens 17 Photodetector

Claims (3)

A second laser unit having a first laser unit having laser emission points of different first and second laser wavelengths and having a laser emission point of a third laser wavelength different from the first and second laser wavelengths; An optical pickup device comprising a laser unit, wherein each of the first, second, and third laser wavelengths is selectively incident on a single objective lens to correspond to various recording media. A beam splitter for guiding laser light emitted from each laser emission point of the first laser unit and the second laser unit disposed on the path onto the common optical path, and disposed before the objective lens on the common optical path by the beam splitter. A wavelength-selective filter surface that reflects the laser light of the first laser wavelength is formed, and the second and second filter surfaces that pass through the filter surface are formed. On the same optical path as the laser beam reflected by the filter surface, the first reflection surface that reflects each laser beam having the laser wavelength and the second and third laser wavelengths reflected by the first reflection surface. A prism having a second reflecting surface that reflects to lead to the laser beam, a collimator lens that collimates the laser beams having the second and third laser wavelengths that have passed through the prism, and each of the second and third laser wavelengths. The laser beam is incident as parallel light and condensed on each recording medium suitable for the respective laser beams of the second and third laser wavelengths, and the laser beam of the first laser wavelength is incident at a predetermined divergence angle. And an objective lens for focusing on a recording medium suitable for the laser beam having the first laser wavelength. 2. The optical pickup device according to claim 1, wherein the laser beam emitted from the laser emission point of the second laser unit has a shorter wavelength than each laser beam emitted from each laser emission point of the first laser unit. The beam splitter reflects the laser beam emitted from one of the first laser unit and the second laser unit, and reflects the laser beam emitted from the other laser unit of the first laser unit and the second laser unit. A dichroic prism having a wavelength selective filter characteristic to be transmitted, and a polarization direction of each laser beam emitted by the first laser unit and a laser beam emitted by the second laser unit on a common optical path guided by the dichroic prism. The polarization direction is set to the same direction, a quarter wavelength plate is disposed on a common optical path guided by the dichroic prism, and a polarization beam splitter is disposed between the quarter wavelength plate and the dichroic prism. This The photodetector for receiving each laser beam of the first, second and third laser wavelengths is disposed on an optical path branched from an optical path where the dichroic prism is disposed by a polarizing beam splitter. 1. The optical pickup device according to 1.

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