JP5653140B2 - Optical pickup device - Google Patents

Description

  The present invention relates to an optical pickup apparatus for optically recording / reproducing information signals.

  In recent years, optical disks have been widely used as recording media for information signals such as video data, audio data, and computer data.

  Optical discs include a CD (Compact Disc) that uses a light beam with a wavelength of about 785 nm, a DVD (Digital Versatile Disc) that uses a light beam with a wavelength of about 660 nm that achieves higher density recording than a CD, and the like.

  In addition, an optical pickup device is used to record an information signal on the above-described optical disk such as CD or DVD, or to reproduce an information signal recorded on the optical disk.

  In a conventional optical pickup device, a diffraction element and a polarization beam splitter are sequentially arranged from the light source side between the light source and the objective lens. The diffractive element transmits the laser beam emitted from the light source and separates it into three beams consisting of a main beam (0th order light) and a pair of sub beams (+ 1st order light and −1st order light) (Patent Document 1). reference).

  In such an optical pickup device, a diffractive element made of glass has been mainly used. However, the use of a diffractive element made of resin is increasing in order to reduce the overall weight and reduce the manufacturing cost.

  Here, recently, research and development of a high-density optical disk system for recording / reproducing information signals using a blue-violet semiconductor laser having a wavelength of about 400 nm is rapidly progressing. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called BD (Blu-ray Disc (registered trademark)), for an optical disc having a diameter of 12 cm which is the same size as a DVD, It is possible to record 25 GB of information per layer.

JP 2010-67333 A

  However, in a high-density optical disk system such as a BD, the energy of a blue-violet semiconductor laser when recording an information signal is large. Therefore, if a laser beam is transmitted through a resin-made diffraction element, the diffraction element is deteriorated (cloudy). End up). When the diffractive element deteriorates, the transmittance of the diffractive element decreases, and the accuracy of recording / reproducing information signals on the optical disc decreases.

  The present invention has been made in view of the above points, and uses a resin-made diffractive element in a high-density optical disk system using a laser beam having a large energy, and the accuracy of recording / reproducing information signals on the optical disk. An object of the present invention is to provide an optical pickup device capable of maintaining the above.

  The optical pickup device of the present invention has a light source that emits laser light of a predetermined wavelength, and a grating surface that periodically repeats unevenness, and reflects the laser light emitted from the light source on the grating surface to generate a main beam. A diffraction grating that separates the main beam and the sub beam into parallel light, a collimating lens that converts the main beam and the sub beam into parallel light, and the main beam and the sub beam output from the collimating lens are optical discs. The objective lens which condenses the light and a photodetector which receives the return light from the optical disk output from the objective lens are adopted.

  According to the present invention, the laser light emitted from the light source can be reflected on the grating surface of the diffractive element, so that even if the diffractive element becomes cloudy, the amount of laser light reaching the optical disk does not decrease. Therefore, it is possible to use a resin diffractive element in a high-density optical disk system that uses a laser beam having a large energy and to maintain the accuracy of recording / reproducing information signals on the optical disk.

The figure which shows the structure of the optical pick-up apparatus which concerns on Embodiment 1 of this invention. The figure which shows the structure of the optical pick-up apparatus which concerns on Embodiment 2 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
[Configuration of optical pickup device]
FIG. 1 is a diagram showing a configuration of an optical pickup device according to Embodiment 1 of the present invention. As shown in FIG. 1, the optical pickup device 1 of the present embodiment includes a light source 11, a diffraction element 12, a polarization beam splitter 13, a collimator lens 14, a quarter wavelength plate 15, and a rising mirror 16. And an objective lens 17, a cylindrical lens 18, and a photodetector 19.

  The light source 11 is made of, for example, a semiconductor laser and emits laser light having a predetermined wavelength. The wavelength of the laser light emitted from the light source 11 is appropriately selected depending on which type of optical disk the optical pickup device 1 records / reproduces information. When the optical pickup device 1 corresponds to, for example, BD, the light source 11 emits a blue-violet semiconductor laser.

  The diffractive element 12 has a grating surface 12a that repeats unevenness periodically, reflects / diffracts the laser light emitted from the light source 11, and produces a main beam (0th order light) and a pair of sub beams (+ 1st order light and -1st order light). Thus, the reason why the laser light emitted from the light source 11 is separated into three beams is to enable servo control. Note that a reflective coat may be applied to the surface of the lattice surface 12a.

  The polarization beam splitter 13 is an optical path separation unit that separates the optical path of the forward laser light (laser light that has passed through the diffraction element 12) and the optical path of the backward laser light (return light reflected by the optical disc 30). Specifically, the polarization beam splitter 13 transmits the laser light (zero order light and ± first order light) from the diffraction element 12. The polarization beam splitter 13 reflects the return light reflected by the optical disc 30 in the direction of the photodetector 19. The polarization beam splitter 13 functions as an optical isolator in cooperation with the quarter-wave plate 15.

  The collimating lens 14 adjusts and emits laser light (zero order light and ± first order light) that is diffused light that has passed through the polarization beam splitter 13 so as to become parallel light. The collimating lens 14 adjusts the return light (parallel light) reflected by the optical disc 30 so as to be convergent light and emits the light.

  The quarter wavelength plate 15 converts the laser light (linearly polarized light) that has passed through the collimating lens 14 into circularly polarized light. The quarter wavelength plate 15 converts the return light (circularly polarized light) reflected by the optical disk 30 into linearly polarized light. The polarization direction at this time is a direction rotated by 90 ° with respect to the deflection direction of the laser light (linearly polarized light) emitted from the light source 11.

  The rising mirror 16 reflects the laser beam that has passed through the quarter-wave plate 15 and sets its traveling direction to a direction orthogonal to the disk surface of the optical disk 30. The rising mirror 16 reflects the return light reflected by the optical disk 30 and sets the traveling direction to a direction orthogonal to the quarter-wave plate 15.

  The objective lens 17 focuses the laser beam reflected by the rising mirror 16 on the information recording layer of the optical disc 30. FIG. 1 shows a case where the optical disc 30 is a two-layer optical disc, and the objective lens 17 condenses the incident laser light on the L0 layer or the L1 layer. The objective lens 17 converts return light (diffused light) reflected by the optical disc 30 into parallel light.

  The cylindrical lens 18 outputs the return light reflected by the polarization beam splitter 13 to the photodetector 19 in order to keep the distance between the optical disk 30 and the objective lens 17 normal.

  The photodetector 19 is a PD (Photo Detector), for example, and receives the return light that has passed through the cylindrical lens 18 and converts the received optical information into an electrical signal. The light receiving surface 19 a of the photodetector 19 has a main detector that receives the return light from the optical disc 30 of the main beam and a sub-detector that receives the return light of the sub beam from the optical disc 30.

[Optical path of laser light]
The laser light emitted from the light source 11 is reflected by the diffraction element 12 and separated into three beams consisting of a main beam (0th order light) and a pair of sub beams (+ 1st order light and −1st order light). Laser light (0th order light and ± 1st order light) reflected by the diffraction element 12 passes through the polarization beam splitter 13 and is converted into parallel light by the collimating lens 14. The laser light that has passed through the collimating lens 14 is reflected by the quarter-wave plate 15 so that the polarization direction is rotated by 90 ° and the rising mirror 16 changes its traveling direction by 90 °. The laser light reflected by the rising mirror 16 is converted into focused light by the objective lens 17 and condensed on the disk surface of the optical disk 30.

  The return light reflected by the optical disk 30 is converted into parallel light by the objective lens 17 and reflected by the rising mirror 16 so that the traveling direction is changed by 90 °. The return light reflected by the rising mirror 16 is rotated by 90 ° in the polarization direction in the quarter-wave plate 15 and converted into focused light by the collimator lens 14. The return light that has passed through the collimating lens 14 is reflected by the polarization beam splitter 13, passes through the cylindrical lens 18, and is condensed on the light receiving surface 19 a of the photodetector 19.

[Effect of this embodiment]
As described above, according to the present embodiment, the laser beam emitted from the light source 11 can be reflected on the grating surface 12a of the diffractive element 12, so that even if the diffractive element 12 becomes cloudy, it reaches the optical disk. The amount of laser light to be emitted does not decrease. Therefore, it is possible to use a resin diffractive element in a high-density optical disk system that uses a laser beam having a large energy and to maintain the accuracy of recording / reproducing information signals on the optical disk.

  Moreover, according to this Embodiment, since the position of the light source 11 and the photodetector 19 can be closely approached, the holder holding the light source 11 and the photodetector 19 can be formed integrally.

  In the present embodiment, the case where the rising mirror 16 changes the traveling direction of the laser beam to a direction orthogonal to the disk surface of the optical disc 30 has been described. However, the present invention is not limited to this, and the rising mirror 16 It can also be used for an optical pickup device of no type.

(Embodiment 2)
[Configuration of optical pickup device]
FIG. 2 is a diagram showing a configuration of an optical pickup device according to Embodiment 2 of the present invention. In FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and detailed description thereof is omitted.

  Compared with the optical pickup device 1 shown in FIG. 1, the optical pickup device 2 shown in FIG. 2 has a configuration in which the diffraction element 12 and the rising mirror 16 are deleted and a rising mirror 21 with a diffraction function is added.

  The rising mirror 21 with a diffraction function has both the function of the diffraction element 12 and the function of the rising mirror 16. That is, the rising mirror 21 with a diffraction function has a grating surface 21a that periodically repeats unevenness, reflects / diffracts the laser light that has passed through the quarter-wave plate 15, and is paired with the main beam (0th-order light). Are divided into three beams consisting of + 1st order light and −1st order light, and the traveling direction thereof is set to a direction orthogonal to the disk surface of the optical disk 30. Note that a reflective coat may be applied to the surface of the lattice surface 21a.

  Further, the rising mirror 21 with a diffraction function reflects the return light reflected by the optical disc 30 and sets its traveling direction to a direction orthogonal to the quarter-wave plate 15.

[Effect of this embodiment]
As described above, according to the present embodiment, since the laser light emitted from the light source 11 can be reflected on the grating surface 21a of the rising mirror 21 with a diffraction function, the rising mirror 21 with a diffraction function is clouded. Even if this is done, the amount of laser light reaching the optical disk 30 does not decrease. Therefore, it is possible to use a resin diffractive element in a high-density optical disk system using a laser beam having a large energy and to maintain the accuracy of recording / reproducing information signals on the optical disk 30.

  Furthermore, according to the present embodiment, the rising mirror 21 with a diffraction function has both the function of the diffraction element 12 and the function of the rising mirror 16, so that the number of parts can be reduced.

  The optical pickup device according to the present invention can be widely used in electronic devices such as personal computers.

DESCRIPTION OF SYMBOLS 1, 2 Optical pick-up apparatus 11 Light source 12 Diffraction element 13 Polarizing beam splitter 14 Collimating lens 15 1/4 wavelength plate 16 Rising mirror 17 Objective lens 18 Cylindrical lens 19 Photo detector 21 Rising mirror with diffraction function 30 Optical disk

Claims (1)

A light source that emits laser light having a wavelength of 405 nm;
A resin-made diffraction grating having a grating surface that repeats irregularities periodically, and that reflects the laser beam emitted from the light source on the grating surface and separates it into three beams consisting of a main beam and a pair of sub beams. When,
A collimating lens for converting the main beam and the sub beam into parallel light;
An objective lens for condensing the main beam and the sub beam output from the collimating lens on an optical disc;
A photodetector for receiving the return light from the optical disk output from the objective lens;
An optical pickup device comprising:

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