JP3668096B2 - Optical pickup device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup device that reads signals from two types of recording media using laser beams generated from two types of laser elements having different laser wavelengths.
[0002]
[Prior art]
The optical pickup device includes a laser diode that emits a laser beam having a wavelength suitable for the recording density of a CD (Compact Disc) and a laser diode that emits a laser beam having a wavelength suitable for the recording density of a DVD (Digital Versatile Disc). Two types of laser light sources with different wavelengths are prepared, and the light source to be used is switched according to the recording density of the disk from which signals are read, so that a single optical pickup supports CDs and DVDs with different recording densities. There is.
[0003]
By the way, in CD and DVD, the thickness of the transparent substrate to the signal recording surface is greatly different from about 1: 2. Therefore, an optical pickup device compatible with CD and DVD requires objective lenses having different NA (numerical aperture) so as to have optical characteristics adapted to each disk.
[0004]
In order to use an objective lens of NA corresponding to each of CD reproduction and DVD reproduction, when achieved by a single objective lens, the laser beam incident on the objective lens is limited according to the laser wavelength of the laser light source used. This is achieved by switching the diameter of the aperture stop. To switch the diameter of the aperture stop, a wavelength selection filter is used, or an aperture stop having a different aperture diameter is mechanically or switched by a liquid crystal shutter. .
[0005]
In addition, as a method of using a single objective lens so that an objective lens of NA corresponding to each of CD reproduction and DVD reproduction is substantially used, it is also realized by using an objective lens having two focal points. Is done.
[0006]
[Problems to be solved by the invention]
By the way, in the optical pickup device corresponding to the above-described CD reproduction and DVD reproduction, light in which a CD light receiving unit used for CD reproduction and a DVD light receiving unit used for DVD reproduction are formed independently on the same semiconductor substrate. It was configured using a detector.
[0007]
Since the optical detector needs to output a main signal and various signals used for focus control and tracking control respectively for CD and DVD, light formed by the CD light receiving unit and the DVD light receiving unit independently. When the detector is used, the number of output terminals of the photodetector increases, and handling becomes complicated.
[0008]
Further, in an optical pickup device having a configuration in which a CD laser element and a DVD laser element are independently arranged, a CD light receiving unit and a DVD light receiving unit are made by matching the optical axes of laser beams emitted from the respective laser elements. However, in the case of an optical pickup device using a two-wavelength laser unit in which a laser element for CD and a laser element for DVD are housed in the same package, the laser elements are arranged side by side. Therefore, the optical axis of the laser beam emitted from each laser element is shifted, and it is difficult to share the CD light receiving unit and the DVD light receiving unit in the photodetector.
[0009]
[Means for Solving the Problems]
The present invention provides a photodetector that receives both a laser beam emitted from a first laser element and modulated by a first recording medium and a laser beam emitted from a second laser element and modulated by a second recording medium. And a wavelength selective diffraction grating disposed in front of the photodetector, adopting the same focus control system for the first recording medium and the second recording medium, and the first laser element and the second laser A laser beam of one wavelength emitted from the element is diffracted by the wavelength selective diffraction grating, and a laser beam of the other wavelength emitted from the first laser element and the second laser element is produced by the wavelength selective diffraction grating. In order to receive the laser beam having a wavelength that is not diffracted and not diffracted, a main light receiving portion is provided in the photodetector, and the first light receiving portion is provided from the main light receiving portion. A sub-light-receiving unit is provided at a position approximately twice as long as the interval between the laser element and the second laser element, and a laser beam having a wavelength diffracted by the wavelength-selective diffraction grating; An RF of a recording medium that is received by the sub light receiving unit and read by a laser beam having a wavelength that is diffracted by the wavelength selective diffraction grating by adding the light receiving output obtained from the sub light receiving unit to the light receiving output obtained from the main light receiving unit. It is configured to obtain a signal.
[0010]
【Example】
FIG. 1 is an optical layout diagram of an optical pickup device showing an embodiment of the present invention.
[0011]
The optical pickup device shown in FIG. 1 is configured to be able to read CD and DVD signals.
[0012]
Reference numeral 1 denotes a first laser element 2 for emitting a laser beam having a wavelength suitable for DVD, for example, 650 nm, on the same semiconductor substrate, and a second laser element for emitting a laser beam having a wavelength suitable for CD, for example, 780 nm. 3 is a two-wavelength laser unit in which the first laser element 2 and the second laser element 3 are housed in the same package.
[0013]
The laser beams emitted from the first laser element 2 and the second laser element 3 of the two-wavelength laser unit 1 are oblique through the diffraction grating 4 having an effective diffraction action with respect to the laser wavelength of the second laser element 3. The optical axis is bent by the surface of the parallel flat plate type half mirror 5 arranged on the surface, and then the light is made parallel light by the collimator lens 6, then incident on the objective lens 7, and converged by the objective lens 7. The signal recording surface of the disk D is irradiated.
[0014]
The objective lens 7 is configured such that the diameter of the aperture stop that restricts the incident laser beam depending on the laser wavelength can be switched, or can be configured by a bifocal lens so that the NA corresponding to each of CD reproduction and DVD reproduction can be achieved. It is made to act as a lens.
[0015]
The laser beam modulated and reflected by the signal recording surface of the disk D returns to the objective lens 7, returns to the half mirror 5 through the collimator lens 6, passes through the half mirror 5, and is astigmatism used for focus control. Is received by the photodetector 9 through the wavelength selective diffraction grating 8.
[0016]
The light receiving unit 13 for receiving the laser beams respectively emitted from the first laser element 2 and the second laser element 3 in the photodetector 9 is divided into four and arranged in a square shape as shown in FIG. The main light receiving region 10 for receiving the 0th-order light main beam composed of the A, B, C, and D light-receiving elements, and the E and F receiving ± 1st-order subbeams formed by the diffraction grating 4. Sub-light-receiving regions 11 and 12 made up of the respective light-receiving elements.
[0017]
Here, the wavelength selective diffraction grating 8 does not have an effective diffractive action for a laser beam having a wavelength emitted from the first laser element 2 suitable for a high-density DVD. Therefore, most of the laser beam having the wavelength emitted from the first laser element 2 goes straight without being diffracted by the wavelength selective diffraction grating 8.
[0018]
The position of the photodetector 9 is a laser beam received so that the laser beam emitted from the first laser element 2 is targeted and the main light receiving region 10 of the light receiving unit 13 is accurately irradiated with the laser beam. The optical axis direction of the beam and the direction orthogonal to the optical axis are adjusted and set.
[0019]
The wavelength selective diffraction grating 8 has an effect of effectively diffracting a laser beam having a wavelength emitted from the second laser element 3, and diffracts the laser beam so that the light receiving unit 13 of the photodetector 9 receives the laser beam. Have a role.
[0020]
Therefore, the laser beam having the wavelength emitted from the second laser element 3 is diffracted by the wavelength selective diffraction grating 8 and received by the light receiving unit 13 as shown in FIG. Light is received by the light receiving region 10, and each sub beam is received by the sub light receiving regions 11 and 12, respectively. In this case, the wavelength selective diffraction grating 8 is adjusted in a direction orthogonal to the optical axis of the laser beam, and the light receiving position of the laser beam having the wavelength emitted from the second laser element 3 is an appropriate position in the main light receiving region 10. It is adjusted to become.
[0021]
The light receiving unit 13 of the photodetector 9 adjusted in position as described above is used for both CD reproduction and DVD reproduction.
[0022]
Here, in the optical pickup device shown in the present embodiment, the astigmatism method is used for focus control and the three-beam method is used for tracking control in CD reproduction, and each light receiving element A, B, Light receiving outputs corresponding to various signals used for RF signal generation and focus control are derived from C and D, and used for tracking control from the light receiving elements E and F of the sub light receiving regions 11 and 12. The received light output corresponding to the received signal is derived.
[0023]
On the other hand, in the optical pickup apparatus shown in this embodiment, the astigmatism method is used for focus control and the DPD method is used for tracking control in DVD reproduction, and each light receiving element A, B, C, From D, received light outputs corresponding to various signals used for RF signal reproduction, focus control and tracking control are derived.
[0024]
FIG. 4 shows a photodetector having a light receiving unit of a different form from the photodetector shown in FIG. 2, and the photodetector shown in FIG. 4 has the optical arrangement shown in FIG. 1 instead of the photodetector shown in FIG. Applied to optical pickup device.
[0025]
The photodetector shown in FIG. 4 includes a main light receiving region 14 in which the light receiving elements A, B, C, and D are arranged in a square shape and sub light receiving regions that are arranged on both sides of the main light receiving region 14. A main light receiving portion 17 similar to that shown in FIG. 2 is formed, and a sub light receiving portion 18 formed side by side with the main light receiving portion 17 on the same semiconductor substrate on which the main light receiving portion 17 is formed. Is formed.
[0026]
The interval L between the main light receiving unit 17 and the sub light receiving unit 18 is the interval between the light emitting points of the first laser element 2 and the second laser element 3, that is, the first laser element 2 and the second laser element 3. Is set to approximately twice the interval at which the symbols are arranged.
[0027]
As with the case of using the photodetector of FIG. 2, the installation position of the photodetector 9 is the main light receiving region of the main light receiving unit 17 for the laser beam emitted from the first laser element 2. 14 is adjusted and set in the optical axis direction of the received laser beam and the direction orthogonal to the optical axis so that the laser beam 14 is accurately irradiated.
[0028]
Further, the wavelength selective diffraction grating 8 is configured so that a laser beam having a wavelength emitted from the second laser element 3 is diffracted by the wavelength selective diffraction grating 8 and accurately irradiated to the main light receiving unit 17. Adjustment is made in a direction orthogonal to the optical axis.
[0029]
By the way, when the laser beam having the wavelength emitted from the second laser element 3 is diffracted by the wavelength selective diffraction grating 8, one of the ± first-order diffracted lights is directed to the main light receiving unit 17 as shown in FIG. The other diffracted light of the ± first-order light travels symmetrically with respect to the laser beam and the optical axis toward the main light receiving unit 17. Here, the interval at which the main light receiving unit 17 and the sub light receiving unit 18 are arranged is set to be approximately twice the interval at which the first laser element 2 and the second laser element 3 are arranged. By adjusting the diffracted light of the diffracted laser beam so as to be received by the main light receiving unit 17, the other diffracted light is simultaneously received by the sub light receiving unit 18.
[0030]
Accordingly, a laser beam having a wavelength emitted from the second laser element 3 is received by the sub light receiving unit 18 during CD reproduction, and the light receiving output of the sub light receiving unit 18 is used as each light receiving element A in the main light receiving region 14 of the main light receiving unit 17. , B, C, and D, the RF signal is efficiently output by adding to the sum of the received light outputs.
[0031]
The wavelength-selective diffraction grating 8 reduces the leakage component of the laser beam that travels straight without being diffracted by the wavelength-selective diffraction grating 8 in the laser beam having the wavelength emitted from the second laser element 3, thereby reducing the main light receiving unit. 17 and the sub light receiving unit 18 are designed so that the light amounts of the ± first-order laser beams received by the sub light receiving unit 18 are increased.
[0032]
FIG. 6 shows a photodetector having a light receiving unit of a different form from the photodetector shown in FIG. 4. The photodetector shown in FIG. 6 has the optical arrangement shown in FIG. 1 instead of the photodetector shown in FIG. Applied to optical pickup device.
[0033]
The photodetector shown in FIG. 6 has a main light receiving portion 19 and a sub light receiving portion 20 formed on the same semiconductor substrate in the same manner as the photodetector shown in FIG. 4, and is interposed between the main light receiving portion 19 and the sub light receiving portion 20. A second sub light receiving unit 21 is formed.
[0034]
The main light receiving unit 19, the sub light receiving unit 20, and the second sub light receiving unit 21 are arranged at an equal interval l, and the interval l is the interval between the light emitting points of the first laser element 2 and the second laser element 3. They are set the same.
[0035]
As in the case of using the photodetector of FIG. 2, the installation position of the photodetector 9 is a laser beam emitted from the first laser element 2 as a target, and the laser beam is a main light receiving region of the main light receiving unit 19. It is adjusted and set in the optical axis direction of the received laser beam and the direction orthogonal to the optical axis so as to be irradiated accurately.
[0036]
When the installation position of the light detector 9 is set in this way, the second sub-element is set at the same interval between the light emitting points of the first laser element 2 and the second laser element 3 as shown in FIG. The light receiving unit 21 receives the leakage component of the laser beam which is straightly traveled without being diffracted by the wavelength selective diffraction grating 8 in the laser beam having the wavelength emitted from the second laser element 3.
[0037]
The wavelength-selective diffraction grating 8 is a laser beam light so that a laser beam having a wavelength emitted from the second laser element 3 is diffracted by the wavelength-selective diffraction grating 8 and accurately irradiated to the main light receiving unit. The laser beam of ± primary light is adjusted in the direction orthogonal to the axis, and is received by the main light receiving unit 19 and the sub light receiving unit 20, respectively.
[0038]
Therefore, the RF signal is obtained by adding the respective light receiving outputs of the sub light receiving unit 20 and the second sub light receiving unit 21 to the sum of the respective light receiving outputs obtained from the light receiving elements A, B, C, D of the main light receiving unit 17 during CD reproduction. Is output efficiently.
[0039]
When the photodetector shown in FIGS. 4 and 6 is used, the sub light receiving unit 18 or the sub light receiving unit 20 and the second sub light receiving unit 21 are formed. Since the second sub light receiving unit 21 is used only for obtaining an RF signal, the sub light receiving unit 18, the sub light receiving unit 20, and the second sub light receiving unit 21 can be configured by a single light receiving element, respectively, for CD reproduction. The number of light receiving elements is reduced and the number of output terminals of the photodetector can be reduced as compared with the case where the photodetector is formed independently of the CD light receiving unit used and the DVD light receiving unit used for DVD reproduction.
[0040]
【The invention's effect】
As described above, the present invention diffracts a laser beam of one wavelength using a wavelength selective diffraction grating, and sets the light in accordance with the laser beam of the other wavelength that is not diffracted by the wavelength selective diffraction grating. Since the light receiving unit on the detector is shared, various signals necessary for reproducing the first recording medium and the second recording medium can be obtained by reducing the number of output terminals of the photodetector.
[0042]
In particular, since a laser unit in which the first laser element and the second laser element are housed in the same package is used, light detection is performed with respect to laser beams of respective wavelengths emitted from the first laser element and the second laser element. When a laser beam of one wavelength is diffracted by a wavelength selective diffraction grating so as to share the main light receiving part of the detector, it proceeds in a line symmetry with respect to the one diffracted light of the laser beam toward the main light receiving part and the optical axis. The other diffracted light is generated, but the other diffracted light is received by the sub-light-receiving portion of the photodetector, so that the light-receiving output obtained from the main light-receiving portion is the light-receiving output obtained from the sub-light-receiving portion. By applying an output, an RF signal of a recording medium read by a laser beam having a wavelength diffracted by the wavelength selective diffraction grating can be efficiently obtained. In this case, since the sub-light-receiving part is provided at a position that is separated from the main light-receiving part by a distance that is approximately twice as long as the interval between the first laser element and the second laser element, the laser having a wavelength that is diffracted by the wavelength-selective diffraction grating. By adjusting the diffracted light of the beam so that it is received by the main light receiving portion, it is possible to adjust so that the other diffracted light is simultaneously received by the sub light receiving portion.
[0043]
Furthermore, since the second sub light receiving portion is formed between the main light receiving portion and the sub light receiving portion so as to receive the leakage component of the laser beam that goes straight without being diffracted by the wavelength selective diffraction grating, It is possible to output efficiently.
[Brief description of the drawings]
FIG. 1 is an optical arrangement diagram showing an optical system of an optical pickup device according to an embodiment of the present invention.
FIG. 2 is an explanatory view showing a light receiving pattern in the photodetector 9;
FIG. 3 is an explanatory diagram showing a traveling direction of a laser beam passing through a wavelength selective diffraction grating 8 when the photodetector shown in FIG. 2 is used.
FIG. 4 is an explanatory diagram showing a light receiving pattern in another photodetector different from the photodetector shown in FIG. 2;
5 is an explanatory diagram showing a traveling direction of a laser beam passing through a wavelength selective diffraction grating 8 when the photodetector shown in FIG. 4 is used.
6 is an explanatory view showing a light receiving pattern in another photodetector different from the photodetector shown in FIGS. 2 and 4. FIG.
7 is an explanatory diagram showing a traveling direction of a laser beam passing through a wavelength selective diffraction grating 8 when the photodetector shown in FIG. 6 is used.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 2 wavelength laser unit 2 1st laser element 3 2nd laser element 7 Objective lens 9 Photodetector 10, 13 Main light-receiving area (main light-receiving part)
11, 12, 14, 15 Sub light receiving area (main light receiving portion)
16, 18 Sub light receiving portion 17 Main light receiving portion 19 Second sub light receiving portion

Claims (2)

An optical pickup device using a laser unit in which a first laser element and a second laser element that emit laser beams having different laser wavelengths are contained in the same package, and is emitted from the first laser element and is used in a first recording medium. A photodetector for receiving both the modulated laser beam and the laser beam emitted from the second laser element and modulated by the second recording medium, and a wavelength selective diffraction grating disposed in front of the photodetector And adopting the same focus control method for the first recording medium and the second recording medium, and applying the wavelength selective diffraction to the laser beam of one wavelength emitted from the first laser element and the second laser element. While diffracting by the grating, the laser beam of the other wavelength emitted from the first laser element and the second laser element is the wave. Not diffracted by selective diffraction grating, provided with a main light receiving portion in the photodetector in order to receive the laser beam having a wavelength that does not diffraction, from the main light receiving portion of the first laser element and a second interval laser element are arranged A sub light receiving portion is provided at a position approximately twice as far away, and a laser beam having a wavelength diffracted by the wavelength selective diffraction grating is received by the main light receiving portion and the sub light receiving portion of a photodetector, and the main light receiving portion An RF signal of a recording medium that is read by a laser beam having a wavelength that is diffracted by the wavelength-selective diffraction grating is added to the light-receiving output obtained from the sub-light-receiving unit. Optical pickup device. A second sub-light-receiving unit that receives a non-diffracted leakage component of a laser beam having a wavelength diffracted by the wavelength-selective diffraction grating is provided in a photodetector between the main light-receiving unit and the sub-light-receiving unit. An RF signal of a recording medium read by a laser beam having a wavelength that is diffracted by the wavelength selective diffraction grating by adding the respective light receiving outputs respectively obtained from the sub light receiving unit and the second sub light receiving unit to the light receiving output obtained from The optical pickup device according to claim 1 , wherein the optical pickup device is configured to be obtained .

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