JP4114673B2 - Optical information recording / reproducing apparatus - Google Patents

Description

  The present invention relates to a laser module for optical information processing for recording and reading information recorded on an optical recording medium such as an optical disk or a magneto-optical disk using a laser beam, and more particularly, a plurality of combinations such as a combination of DVD and CD. TECHNICAL FIELD The present invention relates to a laser module that handles the wavelengths of light, an optical head using the same, and an optical information recording / reproducing apparatus.

  In recent years, a DVD (Digital Versatile Disc) having a recording density seven times that of a CD is rapidly spreading in the form of a two-wavelength compatible drive that can also use a conventional CD. The optical head used in this drive has compatibility with both DVD and CD, and each has a CD, DVD dedicated laser module, collimating lens, and objective lens, increasing the number of parts and complicating optical adjustment, resulting in increased costs. It is.

  On the other hand, the development of a 410 nm wavelength blue laser has been activated and is expected to be put to practical use in the near future. Therefore, in the future, it will be necessary to consider a three-wavelength compatible optical head that is compatible with CDs and DVDs and is also compatible with blue lasers. However, assembling parts corresponding to each of the three wavelengths will no longer reduce the size of the device. It is difficult to reduce the thickness, and the complexity of optical adjustment is expected to cause a significant cost increase.

  For example, Japanese Patent Application Laid-Open No. 10-21577 discloses two to three semiconductor laser chips, a silicon substrate having a micromirror and a light receiving element. An example of affixing and modularizing is disclosed.

JP-A-10-21577

  However, when two semiconductor laser chips are arranged, if one chip is aligned with the optical axis, the other chip is off the optical axis, so it is necessary to provide means for correcting coma aberration. When three laser chips are integrated on a silicon substrate having a light receiving element, it is necessary to correct the coma aberration of the two laser beams off the optical axis, but there is a burden on the polarization diffraction grating and the focus lens. It becomes large and it becomes difficult to put it into practical use as an optical head. In addition, the area of the silicon substrate having the three laser chips and the light receiving elements corresponding to the respective light sources is increased, which hinders downsizing and cost reduction of the laser module.

  For example, FIG. 4 shows a state of silicon in which three laser chips each having a 0.25 mm chip width are arranged. The width of the recess (hereinafter referred to as the sink portion) on the substrate on which the chip is placed is as large as 1.1 mm, and further, if the light receiving elements for focusing and tracking corresponding to each laser are arranged on both sides of the sink portion, The width of the Si substrate is about 3.9 mm, and the number of Si substrates that can be taken from the Si wafer is reduced and the cost is increased. On the other hand, adhering three laser chips close together in one Si substrate is extremely difficult because the material of the 410 nm wavelength semiconductor laser is GaN and the material of the DVD or CD laser is different from GaAs. Become.

A laser diode composed of a laser light source of wavelength C, a laser light source of wavelength B, a laser light source of wavelength A, a micromirror that reflects and rises light emitted from the laser light sources of wavelengths A and B, wavelengths A, B, and A laser module comprising a C light receiving element; a beam splitter that transmits light emitted from the laser light source having the wavelength C; and a beam splitter that reflects light emitted from the laser light source having the wavelength B and the laser light source having the wavelength A; Discrimination means for discriminating the information recording medium type;
  Selection means for selecting one of the three laser light sources, the three wavelengths have a relationship of A> B> C, and the laser module includes light receiving elements of wavelengths A, B, and C. The light receiving elements of the wavelengths A and B are arranged on both sides of the laser light sources, and the light receiving elements of the wavelengths B and C are arranged at symmetrical positions with respect to the apparent light emission point of the micromirror. The laser diode and the laser module are arranged so that the optical axis of the light emitted from the laser light source of B and the optical axis of the light emitted from the laser light source of the wavelength C are matched by the beam splitter, and the discrimination of the discrimination means The optical information recording / reproducing apparatus selects one of the laser light sources by the selection means based on the result.

  According to the present invention, it is possible to simplify the assembly of the apparatus, reduce the cost of individual components, and reduce the size and price of the optical head.

  1 and 2 show a first configuration example of an embodiment of an optical head according to the present invention. FIG. 1 shows a DVD-ROM, RAM (650 nm wavelength) or CD, CD-R (780 nm wavelength). FIG. 2 shows the optical path during reproduction or recording / reproduction of a high-density DVD (410 nm wavelength).

In FIG. 1, when used as a DVD-ROM or RAM, the laser light emitted from the semiconductor laser chip 11 having a wavelength of 650 nm in the laser module 1 is reflected by the beam splitter 3 and collimated by the collimator lens 4. Then, the light is focused on the recording surface of the 0.6 mm thick optical disk 8 of the DVD by the focus lens 6.
When used as a CD or CD-R, the laser light emitted from the semiconductor laser chip 12 having a wavelength of 780 nm in the laser module 1 is reflected by the beam splitter 3 and adjusted into parallel rays by the collimator lens 4. The light is condensed on the optical disk 9 having a thickness of 1.2 mm of the CD by the focus lens 6.
Here, the correction of the focus position due to the difference in thickness between the DVD and the CD is performed by a focus lens, and when the light is focused on the optical disk 8 having a thickness of 0.6 mm of the DVD, the primary side rope is minimized. The optical disk 9 of 1.2 mm thickness of CD-R is corrected so that only the inner peripheral light is used.
On the other hand, correction of coma aberration that occurs because the 780 nm laser chip 12 is disposed outside the optical axis is also supported by making the focus lens 6 aspherical. Reflected light from the optical discs 8 and 9 enters the collimator lens 4 as first-order diffracted light 14 by the polarization diffraction grating 5 through the focus lens 6, reflects by the beam splitter 3, and then receives the light-receiving element substrate in the laser module 1. Enter 15. In each light receiving element, the reflected light of the optical disks 8 and 9 is converted into an electrical signal and output.

  On the other hand, FIG. 2 shows the optical path of a high-density DVD (410 nm wavelength). In the laser diode 2, the laser light emitted from the semiconductor laser chip 13 having a wavelength of 410 nm passes through the beam splitter 3, is collimated by the collimator lens 4, and is optical disc for high density DVD by the original focus lens 7. 10 is condensed. Then, the reflected light from the optical disk 10 enters the collimator lens 4 through the focus lens 7 as the first-order diffracted light 14 by the polarization diffraction grating 5, is reflected by the beam splitter 3, and is received in the laser module 1. The light receiving element on the element substrate 15 enters, is converted into an electrical signal, and is output.

FIG. 3 shows an embodiment of the light receiving element substrate 15 on which the laser chips 11 and 12 are mounted. In the light receiving element substrate, a focus error and a tracking error are independently detected for three wavelengths of 410 nm, 650 nm, and 780 nm, and focusing is performed by a knife edge method and tracking is performed by a differential phase detection method.
The left side of the laser chip portion of the light receiving element substrate 15 is a light receiving element for tracking and signal detection, and has the configurations of 16 (a), 17 (a), and 18 (a) for wavelengths of 410 nm, 650 nm, and 780 nm. The right side of the laser chip portion of the light receiving element substrate 15 is a light receiving element for focus detection, and the configurations of 16 (b), 17 (b), and 18 (b) for wavelengths of 410 nm, 650 nm, and 780 nm. I take the.

  The 650-nm wavelength laser chip 11 and the 780-nm wavelength laser chip 12 have a junction-down structure with the emitting part down, and are attached to the recess (sink part) of the light-receiving element substrate 15 in order to ensure heat dissipation. The emitted light of each laser is reflected by the micromirror 19 using the concave slope and rises vertically from the light receiving element substrate 15. The rising point of the laser beam on the micromirror 19 is called “apparent light emission point”.

  The distance between the apparent light emission point 20 of the 650 nm wavelength laser beam and the focus detection light receiving element portion 17 (a) or the tracking and signal detection light receiving element 17 (b) of 650 nm wavelength is represented by R650, and the wavelength is 780 nm. The distance from the apparent light emitting point 21 to the focus detection light receiving element portion 18 (a) having a wavelength of 780 nm or the tracking and signal detection light receiving element 18 (b) is represented by R780. 5, the laser wavelength λ, the focal length Fc of the collimator lens 4, and the following relational expression (1).

R = (Fc · λ) / p ---- (1)
Where Fc is the focal length of the collimator lens, λ is the semiconductor laser wavelength, and p is the polarization grating pitch.

  In this embodiment, Fc = 20 mm, p = 14 μm, R = 929 μm at the wavelength of 650 nm, and R = 1114 μm at the wavelength of 780 nm. The 410 nm wavelength emission point coincides with the 650 nm wavelength emission point 20, R = 586 μm, and the width of the light receiving element substrate 15 falls within 2.5 mm.

  In order to compare the size of the light receiving element substrate 15, FIG. 4 shows a configuration example of the light receiving element substrate when three laser chips are arranged. The width of the light receiving element substrate 22 is required to be 3.9 mm, the area of the light receiving element substrate is increased by 50% or more, and material removal from the wafer is greatly reduced, resulting in an increase in cost. In addition, the two laser beams of the 780 nm wavelength laser chip 11 and the 410 nm wavelength laser chip 13 are disposed off the optical axis, and correction of the recoma aberration is necessary. However, it is no longer possible to cope with only the aspherical focus lens. Become. Further, considering the technical difficulty of arranging and sticking the three chips with high accuracy and the strictness of the performance yield after mounting each semiconductor laser chip on the Si substrate, the cost merit of this embodiment is extremely large.

  In the above configuration example, the laser module 1 includes two semiconductor laser chips having a wavelength of 780 nm and a wavelength of 650 nm. If lasers having a wavelength of 780 nm and a wavelength of 650 nm are accommodated in one semiconductor laser chip, the Si substrate of the laser chip is used. Assembly is easy, and further cost merit is obtained.

On the other hand, it is possible to mount two semiconductor laser chips of 780 nm wavelength and 650 nm wavelength on the laser diode, or to mount the 410 nm wavelength laser chip on the laser module by mounting the two-wavelength semiconductor laser chip.
The optical information recording apparatus as a whole has a discriminating means for CDs, DVDs, and high-density DVD discs, and the laser light source selection means is used to select lasers having wavelengths of 780 nm, 650 nm, and 410 nm according to the discrimination results. The information is recorded by emitting an optimal light source.

  Next, FIG. 5 and FIG. 6 show a second configuration example of the embodiment of the optical head of the present invention, and a CD-R such as a DVD-ROM and a CD-R or a DVD-RAM and a CD-R. This is a preferred embodiment for efficiently using the power of the laser chip when handling two wavelengths with recording.

When used as a DVD-ROM or RAM, as shown in FIG. 5, the laser light emitted from the semiconductor laser chip 11 having a wavelength of 650 nm in the laser module 23 is reflected by the beam splitter 26 and applied to the collimator lens 4. Then, the light beam is adjusted to parallel rays, and is focused on the recording surface of the DVD optical disk 8 having a thickness of 0.6 mm by the focus lens 27.
On the other hand, when used as a CD-R, as shown in FIG. 6, the laser light emitted from the 780 nm wavelength semiconductor laser chip 25 for CD-R of the laser diode 24 passes through the beam splitter 26 and is collimated by the collimator lens 4. The light is adjusted to parallel rays and focused on the optical disk 9 having a thickness of 1.2 mm of CD by the focus lens 27.
As described above, the correction of the focus position due to the difference in thickness between the DVD and the CD can be made by making the focus lens 27 aspherical, but the CD-R is designed to use only the inner peripheral light. It becomes difficult to secure a sufficient amount of light for CD-R recording on the optical disk 9. For this reason, as a means for obtaining the amount of light necessary for CD-R recording, a beam shaping prism 28 is disposed between the CD-R laser diode 24 and the beam splitter 26 to round the CD-R laser light. The use efficiency of laser light is increased. For example, an elliptical light beam having a full width at half maximum of 10 ° or 30 ° emitted from the semiconductor laser is corrected. Compared with the method in which the optical output of the CD-R laser diode 16 is set to high power, this method reduces the high-temperature use conditions and improves the reliability, and improves the laser performance yield and thermal conductivity due to the high power. Cost increase factors such as the adoption of an excellent heat sink can be suppressed.

  Reflected light from the optical disk 8 or 9 enters the polarization diffraction grating 29 through the focus lens 27, enters the collimator lens 4 as first-order diffracted light, is reflected by the beam splitter 26, and is provided in the laser module 23. The light receiving element substrate 30 is entered. And in each light-receiving part of a light receiving element, it converts into an electrical signal and outputs it.

FIG. 7 shows an embodiment of the light receiving element substrate 30 on which the laser chip 11 is mounted. The collimator lens has a focal length of 20 mm and a polarization diffraction grating pitch of 20 μm. From the above equation (1), R = 660 μm at the wavelength of 650 nm, R = 780 μm at the wavelength of 780 nm, and the width of the Si substrate 27 is 1.0 mm. It can be reduced to an area of 1/2 or less of the case where two laser chips are mounted, and the cost can be reduced.
In this embodiment, DVD-ROM and RAM have been described by taking a wavelength of 650 nm, a CD and CD-R as a wavelength of 780 nm, and a high-density DVD as an example of a wavelength of 410 nm, but a wavelength of 650 nm, 780 nm, and 410 nm. It is apparent that the present invention can be applied to numerical values such as 650 ± 10 nm, 780 ± 10 nm, and 400 ± 10 nm, respectively.

As described above in detail, according to the present embodiment, in an optical head for recording or reproducing optical information recording media having two different wavelengths, the assembly of the apparatus and the cost reduction of individual parts can be realized, and the temperature can be reduced. The present invention provides an optical head that is strong against changes and has improved reliability by reducing the number of components, and contributes to downsizing and cost reduction of an optical head that records or reproduces optical information recording media of three different wavelengths.

The figure which shows the structural example of the optical head which has the 3 wavelength light source of this invention. The figure which shows the structural example of the optical head which has the 3 wavelength light source of this invention. The figure which shows one Example of the laser module in FIG. 1, FIG. The figure which shows an example of the laser module when 3 wavelength light sources are arranged The figure which shows the structural example of the optical head which has the 2 wavelength light source of this invention. The figure which shows the structural example of the optical head which has the 2 wavelength light source of this invention. The figure which shows one Example of the laser module in FIG. 5, FIG.

Explanation of symbols

1. Laser module, 2. Laser diode, 3. Beam splitter, 4. Collimator lens, 5. Polarization diffraction grating, 6. Focus lens, 7. 7. Focus lens for high density DVD 8. optical disc for DVD, CD optical disc, 10. 13. optical disc for high density DVD, 11.650 nm wavelength laser chip, 12.780 nm wavelength laser chip, 13.410 nm wavelength laser chip, 15. First-order diffracted light, Light receiving element substrate, 16 (a) 410 nm wavelength focus detection light receiving element, 16 (b) 410 nm wavelength tracking and signal detection light receiving element, 17 (a) 650 nm wavelength focus detection light receiving element, 17 (b) 650 nm tracking and signal 18. Light receiving element for detection, 18 (a) 780 nm wavelength focus light receiving element, 18 (b) 780 nm tracking and signal light receiving element, 21. Micromirror, apparent emission point of 20.650 nm wavelength laser, 21.780 nm wavelength laser apparent emission point, Light receiving element substrate, 23. Laser module, 24. Laser diode, 25. 25. Semiconductor laser chip for CD-R Beam splitter, 27. Focus lens, 28. Beam shaping prism, 29. Polarization diffraction grating, 30. Light receiving element substrate.

Claims (2)

A laser diode comprising a laser light source of wavelength C;
A laser module comprising a laser light source having a wavelength B, a laser light source having a wavelength A, a micromirror that reflects and raises light emitted from the laser light sources having the wavelengths A and B, and a light receiving element having wavelengths A, B, and C;
A beam splitter that transmits light emitted from the laser light source having the wavelength C, and that reflects light emitted from the laser light source having the wavelength B and the laser light source having the wavelength A;
A discriminating means for discriminating an optical information recording medium type;
Selecting means for selecting any of the three laser light sources,
The three wavelengths have a relationship of A>B> C,
In the laser module, light receiving elements of wavelengths A, B and C are arranged on both sides of the laser light sources of wavelengths A and B, and the light receiving elements of wavelengths B and C are only over the wavelength B of the micromirror. It is arranged at a symmetrical position around the light emitting point of
The laser diode and the laser module are arranged so that the optical axis of the light emitted from the laser light source of the wavelength B and the optical axis of the light emitted from the laser light source of the wavelength C are matched by the beam splitter,
An optical information recording / reproducing apparatus that selects one of the laser light sources by the selection unit based on a determination result of the determination unit. The wavelength A is 780 ± 10 nm,
The wavelength B is 650 ± 10 nm,
The wavelength C is 410 ± 10 nm,
The optical information recording and reproducing apparatus according to claim 1 Symbol placement is.

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