JP2001307369A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the conventional problems of increased number of output terminals in a photodetector and the incident complication in the handling, which are due to the light receiver independently provided in the photodetector in accordance with each recording medium, in the case of an optical pickup device made adaptive to two different kinds of recording mediums. SOLUTION: A laser beam of one wavelength emitted from a first and second laser elements is diffracted by a wavelength selective diffraction grating; a laser beam of the other wavelength emitted from the first and second laser elements is not diffracted by the wavelength selective diffraction grating; but each of these laser beams from the first and second laser elements is designed to be received by the same light receiver of the photodetector. Thus, the same light receiver is shared in the reproduction of two different kinds of recording mediums.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for reading signals from two types of recording media using laser beams generated from two types of laser elements having different laser wavelengths.

[0002]

2. Description of the Related Art As an optical pickup device, a CD (Co)
laser diode and DVD (Digital Versa) that emit a laser beam with a wavelength suitable for the recording density of mpact Discs.
Prepare two types of laser light sources with different wavelengths from the laser diode that emits a laser beam with a wavelength suitable for the recording density of the tile disc), and switch the light source to be used according to the recording density of the disc for signal reading The recording density varies with a single optical pickup.
D and DVD are available.

Incidentally, the thickness of the transparent substrate up to the signal recording surface differs greatly between CD and DVD, which is approximately 1: 2. Therefore, an optical pickup device compatible with CD and DVD requires an objective lens having a different numerical aperture (NA) so as to have optical characteristics adapted to each disk.

In order to use an objective lens having a NA corresponding to each of CD reproduction and DVD reproduction, when a single objective lens is used, a laser beam incident on the objective lens according to the laser wavelength of the laser light source used. This is achieved by switching the diameter of the aperture stop that restricts the aperture stop, by using a wavelength selection filter to switch the diameter of this aperture stop, by mechanically switching the aperture stop with a different aperture diameter, or by switching with a liquid crystal shutter. Achieved.

Further, as a method of using a single objective lens to substantially use an objective lens of NA corresponding to CD reproduction and DVD reproduction, an objective lens having two focal points is used. It is also realized by things.

[0006]

By the way, the aforementioned CD
In an optical pickup device compatible with reproduction and DVD reproduction, a CD light receiving unit and a DVD generally used for CD reproduction are used.
A DVD light receiving unit used for reproduction is configured using a photodetector formed independently on the same semiconductor substrate.

Since it is necessary to output a main signal and various signals used for focus control and tracking control from CD and DVD from the photodetector, respectively,
When a photodetector in which the D light receiving unit and the DVD light receiving unit are formed independently is used, the number of output terminals of the photodetector increases, and the handling becomes complicated.

In an optical pickup device having a configuration in which a laser element for CD and a laser element for DVD are arranged independently, an optical axis of a laser beam emitted from each laser element is made coincident with a CD light receiving section. DV
It can easily be shared with the D light receiving unit,
Pickup device using a two-wavelength laser unit in which the laser element for DVD and the laser element for DVD are housed in the same package, the laser elements emitted from each laser element are arranged because the laser elements are arranged side by side. Since the optical axis is shifted, it has been difficult to share a CD light receiving unit and a DVD light receiving unit in the photodetector.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to 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. The same focus control method is adopted for the first recording medium and the second recording medium. A laser beam of one wavelength emitted from the first laser element and the second laser 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. The laser beams emitted from the first laser element and the second laser element are not diffracted by the wavelength-selective diffraction grating, and the laser beams emitted from the first laser element and the second laser element are sent to the same light receiving portion of the photodetector. And so as to be received.

[0010]

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

The optical pickup device shown in FIG. 1 has a configuration capable of reading a signal from a CD and a DVD.

Reference numeral 1 denotes a first light emitting a laser beam having a wavelength suitable for DVD, for example, 650 nm, on the same semiconductor substrate.
A laser element 2 is installed, and a second light emitting a laser beam having a wavelength suitable for a CD, for example, 780 nm.
A two-wavelength laser unit in which a laser element 3 is installed and the first laser element 2 and the second laser element 3 are housed in the same package.

The laser beams respectively emitted from the first laser element 2 and the second laser element 3 of the two-wavelength laser unit 1 pass through a diffraction grating 4 having an effective diffraction effect on the laser wavelength of the second laser element 3. The optical axis is bent by the surface of a parallel plate type half mirror 5 which is arranged obliquely through the optical axis, and then is formed into a parallel light by a collimator lens 6, thereafter, is incident on an objective lens 7, and is incident on the objective lens 7. The light is converged and irradiated onto the signal recording surface of the disk D.

The objective lens 7 is designed so that the diameter of an aperture stop for restricting a laser beam incident on the basis of a laser wavelength can be switched, or a bifocal lens can be used for CD reproduction and DVD reproduction, respectively. It is configured to act as a lens with a corresponding NA.

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 via the collimator lens 6, passes through the half mirror 5, and is used for focus control. After the astigmatism is imparted, the light is received by the photodetector 9 via the wavelength-selective diffraction grating 8.

The light receiving section 13 of the photodetector 9 for receiving the laser beams respectively emitted from the first laser element 2 and the second laser element 3 is divided into four parts as shown in FIG. A, B, C, D arranged in a shape
The main light receiving area 10 for receiving the main beam of the zero-order light composed of the respective light receiving elements of
It is composed of sub-light receiving areas 11 and 12 composed of E and F light-receiving elements that receive each sub-beam of the primary light.

Here, the wavelength-selective diffraction grating 8 does not have an effective diffraction effect on a laser beam having a wavelength emitted from the first laser element 2 compatible with a DVD having a high density. Therefore, most of the laser beam having the wavelength emitted from the first laser element 2 travels straight without being diffracted by the wavelength-selective diffraction grating 8.

The position of the photodetector 9 is determined based on the laser beam emitted from the first laser element 2 and the laser beam is applied to the main light receiving area 1 of the light receiving section 13.
The laser beam is adjusted and set in the optical axis direction of the received laser beam and in the direction orthogonal to the optical axis so as to be accurately irradiated with zero.

The wavelength-selective diffraction grating 8 has a function of effectively diffracting a laser beam having a wavelength emitted from the second laser element 3 and causes the light-receiving section 13 of the photodetector 9 to receive the laser beam. It plays the role of diffracting as much as possible.

Therefore, as shown in FIG. 3, 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 section 13 so that the main beam is received. The beam is received by the main light receiving area 10, and each sub beam is respectively transmitted to the sub light receiving area 11,
12 is received. 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 adjusted to an appropriate position in the main light-receiving region 10. It is adjusted so that

The light receiving portion 13 of the photodetector 9 thus adjusted in position is used for both CD reproduction and DVD reproduction.

Here, the optical pickup device shown in this embodiment employs an astigmatism method for focus control and a three-beam method for tracking control in CD reproduction.
Each of the light receiving elements A, B, C, D in the main light receiving area 10
Light receiving outputs corresponding to various signals used for generation of the F signal and focus control are derived, and signals corresponding to signals used for tracking control from the light receiving elements E and F of the sub light receiving areas 11 and 12 are provided. The received light output is derived.

On the other hand, the optical pickup device shown in this embodiment employs the astigmatism method for focus control and the DPD method for tracking control in DVD reproduction, and the light receiving elements A and B in the main light receiving area 10. , C, D to RF
Light reception outputs corresponding to various signals used for signal reproduction, focus control, and tracking control are derived.

FIG. 4 shows a photodetector provided with a photodetector of another form different from the photodetector shown in FIG. 2. The photodetector shown in FIG. 4 is shown in FIG. 1 instead of the photodetector shown in FIG. It is applied to an optical pickup device having an optical arrangement.

The photodetector shown in FIG. 4 has a main light receiving area 14 in which the light receiving elements A, B, C, and D are arranged in a cross shape.
A main light receiving portion 17 similar to that shown in FIG. 2 is formed, and the same semiconductor substrate on which the main light receiving portion 17 is formed. A sub-light receiving portion 18 formed alongside the main light receiving portion 17 is formed thereon.

The distance L at which the main light receiving section 17 and the sub light receiving section 18 are arranged is determined by the first laser element 2.
The distance between the light-emitting points of the second laser element 3 and the light-emitting point of the second laser element 3, that is, the distance between the light-emitting points of the first laser element 2 and the second laser element 3 is approximately twice as large.

The installation position of the photodetector 9 is the same as the case of using the photodetector of FIG. The laser beam is adjusted and set in the optical axis direction and the direction orthogonal to the optical axis of the laser beam received so that the main light receiving area 14 is accurately irradiated.

The wavelength-selective diffraction grating 8 is configured such that a laser beam of a wavelength emitted from the second laser element 3 is diffracted by the wavelength-selective diffraction grating 8 and
The laser beam is adjusted in a direction orthogonal to the optical axis of the laser beam so that the laser beam is accurately irradiated.

By the way, when a laser beam having a wavelength emitted from the second laser element 3 is diffracted by the wavelength-selective diffraction grating 8, one of the ± 1st-order diffracted lights becomes the main light receiving portion 17 as shown in FIG. , The other diffracted light of the ± 1st-order light travels line-symmetrically with respect to the optical axis with the laser beam heading to the main light receiving section 17. Here, the interval at which the main light receiving unit 17 and the sub light receiving unit 18 are arranged is substantially equal to the interval at which the first laser element 2 and the second laser element 3 are arranged.
Since it is set to twice, the diffracted light of the laser beam diffracted by the wavelength-selective diffraction grating 8 is
Is adjusted so that the other diffracted light is received by the sub light receiving unit 18 at the same time.

Accordingly, the laser beam of the wavelength emitted from the second laser element 3 is received by the sub light receiving portion 18 during CD reproduction, and the light output of the sub light receiving portion 18 is output to each of the main light receiving regions 14 of the main light receiving portion 17. Light receiving elements A, B,
An RF signal is output efficiently by adding it to the sum of the light receiving outputs obtained from C and D.

The wavelength-selective diffraction grating 8 reduces the leakage component of the laser beam having a wavelength emitted from the second laser element 3 which is not diffracted by the wavelength-selective diffraction grating 8 and travels straight. It is designed so that the amount of ± 1 order laser beams received by the main light receiving unit 17 and the sub light receiving unit 18 is increased.

FIG. 6 shows a photodetector provided with a light receiving section of a different form from the photodetector shown in FIG. 4. The photodetector shown in FIG. 6 is shown in FIG. 1 instead of the photodetector shown in FIG. It is applied to an optical pickup device having an optical arrangement.

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 as in the photodetector shown in FIG. The second sub-light receiving section 21 is formed between them.

The main light receiving section 19 and the sub light receiving section 2
0 and the second sub-light receiving unit 21 are arranged at equal intervals l,
The interval 1 is set to be equal to the interval between the light emitting points of the first laser element 2 and the second laser element 3.

The installation position of the photodetector 9 is the same as the case of using the photodetector of FIG. The laser beam is adjusted and set in the optical axis direction and the direction orthogonal to the optical axis of the laser beam received so that the main light receiving area is accurately irradiated.

When the installation position of the photodetector 9 is set in this manner, as shown in FIG. 7, since the intervals between the light emitting points of the first laser element 2 and the second laser element 3 are set to be the same, The second sub-light receiving portion 21 receives a leak component of a laser beam that travels straight without being diffracted by the wavelength-selective diffraction grating 8 in a laser beam having a wavelength emitted from the second laser element 3.

The wavelength-selective diffraction grating 8 is provided with a laser so that a laser beam of a wavelength emitted from the second laser element 3 is diffracted by the wavelength-selective diffraction grating 8 and accurately applied to the main light receiving portion. The laser beam of the ± 1st order is adjusted in a direction orthogonal to the optical axis of the beam and received by the main light receiving unit 19 and the sub light receiving unit 20, respectively.

Therefore, the respective light receiving outputs of the sub light receiving section 20 and the second sub light receiving section 21 are added to the sum of the respective light receiving outputs obtained from the light receiving elements A, B, C, D of the main light receiving section 17 during CD reproduction. As a result, an RF signal is output efficiently.

When the photodetector shown in FIGS. 4 and 6 is used, the sub light receiving section 18 or the sub light receiving section 20 and the second
Is formed, but the sub-light receiving unit 18, the sub-light receiving unit 20, and the second sub-light receiving unit 21 are used only for obtaining the RF signal. And the second sub-light receiving section 21 can be constituted by a single light receiving element, respectively, as compared with a case where a CD light receiving section used for CD reproduction and a DVD light receiving section used for DVD reproduction are independently formed with a photodetector. As a result, the number of light receiving elements can be reduced, and the number of output terminals of the photodetector can be reduced.

[0040]

As described above, according to the present invention, a laser beam of one wavelength is diffracted by using a wavelength-selective diffraction grating so that the laser beam of the other wavelength is not diffracted by the wavelength-selective diffraction grating. Since the light receiving unit on the photodetector set in advance is shared, the number of output terminals of the photodetector can be reduced to obtain various signals necessary for reproducing the first recording medium and the second recording medium. I can do it.

In this case, the alignment between the laser beam of each wavelength and the light receiving section is performed by displacing the wavelength-selective diffraction grating in the direction orthogonal to the optical axis for the laser beam of one wavelength and the other wavelength. In the case of the laser beam, the installation position of the photodetector is adjusted, and the laser beam of each wavelength can be used independently.

Further, since the sub light receiving portion for receiving the laser beam having the wavelength to be diffracted by the wavelength selective diffraction grating is formed on the same semiconductor substrate as the main light receiving portion of the photodetector, the RF signal can be outputted efficiently. I can do it. In this case, since the interval at which the main light receiving unit and the sub light receiving unit are arranged is set to approximately twice the interval at which the first laser element and the second laser element are arranged, the laser beam diffracted by the wavelength-selective diffraction grating is set. By adjusting the diffracted light to be received by the main light receiving portion, it is possible to simultaneously adjust the other diffracted light so as to be received by the sub light receiving portion.

Further, a second sub-light-receiving portion is formed between the main light-receiving portion and the sub-light-receiving portion so as to receive a leak component of a laser beam which travels straight without being diffracted by the wavelength-selective diffraction grating. Therefore, it is possible to output more efficiently.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing a light receiving pattern in a 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 photo detector different from the photo detector 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.

FIG. 6 is an explanatory diagram showing a light receiving pattern in another photodetector different from the photodetectors 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 part) 16, 18 Sub light receiving section 17 Main light receiving section 19 Second sub light receiving section

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenji Nakamura 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. F-term (reference) 5D118 AA04 AA06 AA26 BA01 BB01 BF02 CD02 CD03 CD08 CF02 CF06 CG07 CG26 DA02 DB12 DC03 5D119 AA04 AA41 BA01 BB01 CA16 DA05 EA02 EA03 EC45 EC47 FA08 JA26 JA43 JC07 KA16 KA19 KA24 NA06

Claims (4)

[Claims] An optical pickup device for reading signals of different types of first recording medium and second recording medium using respective laser beams emitted from a first laser element and a second laser element having different laser wavelengths. A photodetector receiving both a laser beam emitted from the first laser element and modulated by the first recording medium and a laser beam emitted from the second laser element and modulated by the second recording medium; A wavelength-selective diffraction grating disposed in front of the photodetector, employing the same focus control method for the first recording medium and the second recording medium, and emitting light from the first laser element and the second laser element. The laser beam of one wavelength is diffracted by the wavelength selective diffraction grating, and the other is emitted from the first laser element and the second laser element. A laser beam having a wavelength is not diffracted by the wavelength-selective diffraction grating, and each laser beam emitted from the first laser element and the second laser element is received by the same light receiving portion of the photodetector. Optical pickup device. 2. The position of the photodetector is adjusted in accordance with the position on the photodetector of a laser beam having a wavelength not diffracted by the wavelength-selective diffraction grating, and the wavelength-selective diffraction grating is adjusted to the optical axis. 2. The optical pickup device according to claim 1, wherein a light receiving position on a photodetector of a laser beam having a wavelength diffracted by the wavelength-selective diffraction grating by being displaced in an orthogonal direction is adjusted. 3. An optical pickup device using a two-wavelength laser unit in which a first laser element and a second laser element are housed in the same package, wherein a wavelength that is not diffracted by the photodetector by the wavelength-selective diffraction grating. A main light receiving unit for receiving the laser beam of the, and a sub light receiving unit for receiving a laser beam of a wavelength to be diffracted by the wavelength selective diffraction grating is formed on the same semiconductor substrate of the photodetector, the main light receiving unit and 3. The optical pickup device according to claim 1, wherein an interval at which the sub-light receiving units are arranged is set approximately twice as large as an interval at which the first laser element and the second laser element are arranged. 4. The light receiving device according to claim 3, further comprising a third light receiving unit for receiving a laser beam having a wavelength to be diffracted by the wavelength selective diffraction grating, between the main light receiving unit and the sub light receiving unit. Optical pickup device.