JP3452944B2 - Optical disk drive - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for detecting an error when writing and reading information with a laser beam.

An optical disk device automatically controls a beam spot having a diameter of about 1 μm condensed by an objective lens in both the focusing direction and the tracking direction. The rotating disk causes surface wobbling in a direction perpendicular to the disk surface. The focus direction control is to move the objective lens in the optical axis direction so that the beam spot is always on the recording film by following the surface wobbling. Further, the disc is provided with a guide groove (pre-groove) in advance. The control of the tracking direction is to move the objective lens or the like so that the beam spot follows the predetermined guide groove. The error signal detection for controlling both is an important part that affects the reliability of the device,
A compact and low cost method is required.

[0003]

2. Description of the Related Art FIG. 5 is a diagram for explaining a conventional optical disk device. FIG. 5A is a block diagram and FIG.
(B) is an explanatory view of a compound prism.

In the optical disk device 11 of FIG. 5A, the divergent light emitted from the semiconductor laser 12 is converted into parallel light by the collimator lens 13. After passing through the beam splitter 14, it is reflected in the direction of the objective lens by the reflection mirror 15 and is focused by the objective lens 16 on the disk 17 into a beam spot having a diameter of about 1 μm.

The reflected light from the disk 17 returns to the original path and is reflected by the beam splitter 14 downward in the figure.
Further, the beam splitter 18 splits the light into two, one of which is reflected to the right side in the drawing, and the photodetector 21 detects the magneto-optical signal and the address signal via the Wollaston prism 19 and the condenser lens 20. Further, the light transmitted through the beam splitter 18 is narrowed down by the condenser lens 22 and is split into two by the beam splitter 23.

The reflected light to the right side in the figure is received by the photodetector 24 divided into two (A, B), and a tracking error signal is obtained by the push-pull method. In addition, the beam splitter 23
The light transmitted through the composite prism 25 is divided into four (A
D) is focused on the photodetector 26 and a focus error detection signal is obtained by the Foucault method (or the double knife edge method). That is, the focus error detection is performed by the Foucault method, and the tracking error detection is performed by the push-pull method.

As shown in FIG. 5 (B), the compound prism 25 has two emission surfaces 25a and 25b, and the reflected light from the disk 17 is divided into two and each light is divided into four ( The light is detected by the photodetectors 26 of A to D).

6 to 8 are diagrams for explaining the Foucault method of FIG. 5, and FIG. 9 is a graph of the output characteristics of FIGS. 6 to 8. FIGS. 6A and 6B show a case where the objective lens 16 is close to the disc 17, and the objective lens 16 is divided into four parts (A to
The beam pattern on the photodetector 26 in D) is as shown in FIG. Focus error signal FES (Focus Error Signal) for each of the outputs A to D of the photodetector 26.
Is calculated as (A + C)-(B + D), FES>
It becomes 0.

Similarly, FIGS. 7A and 7B show the case where the disk 17 is at the focal position of the objective lens 16, and the focus error signal FES is FES = 0. Further, FIGS. 8A and 8B show the case where the disk 17 is away from the objective lens 16, and the focus error signal FES
Is FES <0.

As shown in FIG. 9, these output signals form an S-shaped curve, and the focus direction is automatically controlled using this signal.

By detecting the focus error by using the Foucault method as described above, the disturbance signal generated when the beam spot crosses the guide groove is less mixed into the focus error signal, and the disc error from the disk 17 is reduced. Even if the reflected light undergoes an optical axis shift, since the photodetector 26 is placed in the vicinity of the focal point, no abnormal offset is generated in the focus error signal.

Next, FIGS. 10 to 12 are views for explaining the push-pull method of FIG. FIG. 10 (A)-
In (C), the beam spot has a guide groove 17 on the disk 17.
When it is shifted to the right in the figure from a, the intensity distribution of the reflected light from the disk 17 becomes unbalanced, and the left side in the figure becomes stronger. Therefore, the tracking error signal TES (Tracking Error Sig) from the photodetector 24 divided into two (A, B) is used.
nal), TES = (AB)
ES> 0.

Similarly, FIGS. 11A to 11C show the case where the beam spot is at the center of the guide groove 17a of the disk 17, and the intensity distribution of the reflected light from the disk 17 is uniform. Therefore, the tracking error signal TES is (A
-B) = 0. Further, FIGS. 12A to 12C show the case where the beam spot is displaced to the left of the guide groove 17a in the figure, and the intensity distribution of the reflected light is stronger on the left side of the figure, and the tracking error signal TES becomes TES <. It becomes 0.

In this way, the beam spot is guided by the guide groove 17
If the output is shifted to the left or right with respect to a, the output also changes to positive or negative depending on each, so the output (AB) of the photodetector 24 divided into two (A, B) is used as the tracking error signal. is there.

[0015]

However, as described above, in order to establish the Foucault method and the push-pull method at the same time, the beam splitter 23 must split the light in two orthogonal directions. It is necessary to secure a space for 23 and the photodetector 24, and it is difficult to reduce the number of parts.

Although the number of components can be reduced by the astigmatism method which is normally used for focus error detection instead of the Foucault method, the astigmatism method has a large beam diameter and is easily affected by disturbance. Therefore, there is a problem of low reliability.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide an optical disk device which improves the reliability of error detection and is small in size and low in cost.

[0018]

SUMMARY OF THE INVENTION The above-mentioned problem is to irradiate a disc with light emitted from a light source, detect an information signal, a focus error and a tracking error by the reflected light from the disc, and control the focus and the tracking. In the device, light splitting means for splitting the reflected light from the disc into first to fourth lights in substantially the same direction,
Receiving the first and second lights split by the light splitting means to detect a focus error signal based on the Foucault method ,
Third and fourth up the tracking error signal by receiving light
A light detection unit for detecting light based on the Shook method, and the light splitting means is located at the center and has a third emission surface and a fourth emission surface which intersect each other and have ridge lines. , The third and fourth
Angle of improving who exit surface extends above ridge line forming chevron portions intersect, are located on one side, less than the third and the third in the same direction as the exit surface of the exit surface Located on the other side in the extending direction of the ridgeline of the chevron portion and inclined in the same direction as the fourth emission surface and at an angle smaller than the fourth emission surface. the second possess an exit surface, made of a composite prism having a central ridge lines of the chevron portions, the composite prism, the third
And the third and fourth light beams are emitted from the fourth and fourth emission surfaces, respectively.
And from the first and second emission surfaces, respectively,
This is solved by adopting a configuration in which the first and second lights are arranged to be emitted .

[0019]

As described above, the reflected light from the disk is split into the first to fourth light beams in substantially the same direction by the light splitting means, and the light detecting portion receives the first and second light beams and focuses them. An error is detected and the third and fourth lights are received to detect a tracking error.

That is, in obtaining the focus error signal and the tracking error signal, it is not necessary to bend the optical path by 90 degrees by the beam splitter and divide it into two directions.

As a result, the beam splitter and the photodetector installed in the 90 ° direction can be omitted, and the size and cost can be reduced. Further, since the focus error signal is obtained by the Foucault method using the first and second lights, it is possible to reduce the beam diameter on the photodetector, the influence of disturbance is reduced, and the error detection It is possible to improve reliability.

[0022]

FIG. 1 is a block diagram of the first embodiment of the present invention. In the optical disc device 31 of FIG. 1, emitted light (divergent light) from a semiconductor laser 32 (which may be a He—Ne laser) which is a light source is converted into parallel light by a collimator lens 33. After passing through the beam splitter 34, the collimated light is reflected by the reflection mirror 35 toward the objective lens, and is focused by the objective lens 36 on the magneto-optical disk 37 into a beam spot having a diameter of about 1 μm.

The reflected light from the disk 37 returns to the original path and is reflected by the beam splitter 34 downward in the drawing.
Further, the beam splitter 38 splits the light into two, one of which is reflected to the right side in the figure, and the photodetector 41 detects the magneto-optical signal (information signal) via the Wollaston prism 39 and the condenser lens 40. . Further, the light transmitted through the beam splitter 38 is focused by the condenser lens 42.
The above structure is similar to that of FIG.

The reflected light focused by the condenser lens 42 is first reflected by a compound prism 43 (described later) which is a light splitting means.
~ The fourth light 44a ~ 44d is divided into four, the light detection unit 45
Is received by. The photodetector 45 is configured to detect the first and second lights 44.
a first light receiving portion (45a) divided into four (A to D) for receiving a and 44b, a second light receiving portion E (45b) for receiving the third light 44c, and a fourth light 44d. The third light receiving portion F (45c) that receives light is formed on one plane (may be separated from each other) (see FIG. 2C).

Next, FIG. 2 shows a diagram for explaining the compound prism of FIG. 2A is a perspective view of the composite prism 43, FIG. 2B is a view showing the exit surface of the composite prism 43, and FIG. 2C is for explaining the light reception of the photodetector 45. FIG.

2A and 2B, the exit surface of the compound prism 43 is the first light 44 of the reflected light flux.
The first emission surface 43a that emits a is formed with a right inclination in the drawing, and the second emission surface 43b that emits the second light 44b is formed with a left inclination in the drawing. Also, the third and fourth lights 44
c and 44d, and third and fourth emission surfaces 43c and 4
3d is formed in a mountain shape.

The first emission surface 43a is the third emission surface 43.
It is inclined in the same direction as c and the inclination angle α ₁ is smaller than the inclination surface α ₃ of the third emission surface 43c.

The second emission surface 43b is the fourth emission surface 43.
It is inclined in the same direction as d, and the inclination angle α ₂ is smaller than the inclination surface α ₄ of the fourth emission surface 43d.

Then, in FIG. 2C, the first light 44 of the reflected light flux emitted from the first emission surface 43a.
The light “a” is received by the areas A and D of the first light receiving unit 45 a of the light detection unit 45. The second light 44b emitted from the second emission surface 43b is received by the B and C regions of the first light receiving portion 45a. As a result, as described with reference to FIGS. 4 to 7, the calculation of (A + C)-(B + D) is performed by the Foucault method to detect the focus error signal.

Of the reflected light flux, the third emission surface 43
The third light 44c emitted from c is received by the second light receiving portion 45b (E region) of the light detection portion 45, and the fourth light 44d emitted from the fourth emission surface 43d is the third light 44c. The light is received by the light receiving unit 45c (F region). As a result, FIGS.
As described in FIG. 12, the push-pull method (E-
F) is calculated and the tracking error signal is detected.

As described above, compared with FIG. 5A, even if the Foucault method is used for focus detection and the push-pull method is used for tracking error signal detection, it is not necessary to divide the optical path into two parts by using a beam splitter or the like. Therefore, the volume occupied by the entire optical system can be reduced. Moreover, since the number of beam splitters and the number of photodetectors can be reduced from one to two, the number of parts can be reduced, and the cost can be reduced. Furthermore, compared with the case where the astigmatism method is used for focus error signal detection, the beam diameter on the photodetector can be reduced,
It is possible to prevent the influence of disturbance and improve reliability.

When the photodetector 45 is adjusted so that a predetermined focus error signal can be detected, the third light 44c and the fourth light 44d are automatically received by the light receiver 45d (E area) and the light receiver 45c ( Since the structure can be made to enter the F region), there is also an advantage that the adjustment for detecting the track error signal becomes unnecessary.

FIG. 3 shows an optical disk device 31A according to a second embodiment of the present invention.

In the figure, parts corresponding to those shown in FIG. 1 are designated by the same reference numerals, and their description will be omitted.

The optical disk device 31A is provided with a composite prism-Wollaston prism integrated component 50 in place of the composite prism 43 shown in FIG. 1, and the beam splitter 3 shown in FIG.
5, the Wollaston prism 39, the condenser lens 40, and the photodetector 41 are deleted.

The laser light emitted from the semiconductor laser 32 is focused on the disk 37. The reflected light from the disk 37 returns to the original path, is reflected downward by the beam splitter 34, proceeds without being branched thereafter, and is focused by the condenser lens 42.

Reflected light beam 49 narrowed down by the condenser lens 42
Is split into first to sixth lights 51a to 51f by a component 50 (described later) which is a light splitting means, and the photodetector 45 is split.
The light is received by A.

The photo-detecting section 45A has a first and a second light 51.
a first light receiving portion 45Aa divided into four (A to D) for receiving a and 51b, a second light receiving portion 45Ab _-1 (E ₁ region) for receiving the third light 51c, and a fourth light The third light receiving portion 45Ab _-2 (E ₂ region) for receiving 51d and the fifth light 5
Fourth light receiving portion 45Ac _-1 (F ₁ area) for receiving 1e
And a fifth light receiving portion 45Ac _-2 for receiving the sixth light 51f.
The (F ₂ region) is formed on one plane (see FIG. 4C). Next, the component 50 will be described.

As shown in FIG. 4 (B) and FIG. 4 (C), the component 50 is formed on the back surface of the compound prism 43 shown in FIG.
This is a structure in which the Wollaston prism 52 shown in FIG.

The Wollaston prism 52 has a structure in which two triangular prisms cut out from quartz are bonded together,
It has a size corresponding to the central chevron portion of the compound prism 43.

The Wollaston prism 52 is arranged over the entire width of the chevron portion of the compound prism 43 directly behind the chevron portion 43e at the center, and the laser beam
The chevron portion 43e is separated in the direction in which the ridgeline 43e extends.

That is, the Wollaston prism 52 is located at a position immediately before the compound prism 43 in the optical path of the reflected light 49.

Next, the splitting of light and the detection of signals by the component 50 having the above structure will be described.

Of the reflected light flux 49 which is emitted from the condenser lens 42 and is incident on the component 50, the light 49 _-1 which is directly incident on the composite prism 43 through the portion above the Wollaston prism 52 in FIG. 4B. Is refracted at the first emission surface 43a and emitted as the first light 51a from the first emission surface 43a.

As shown in FIG. 4C, the first light 51a is emitted from A of the first light receiving portion 45Aa of the light detecting portion 45A.
The light is received in the D area.

Of the reflected light beam 49 shown in FIG.
In (B), the light 49 _-2 that has directly entered the composite prism 43 through the portion below the Wollaston prism 52 is refracted by the second emission surface 43b and then emitted from the second emission surface 43b to the second side. Of the light 51b.

This second light 51b is, as shown in FIG. 4C, B of the first light receiving portion 45Aa of the light detecting portion 45A,
Light is received in the C region.

Areas A, B, of the first light receiving portion 45Aa
As described with reference to FIGS. 6 to 9, based on the outputs from C and D, the (A + C)-(B + D) operation is performed by the Fuco method to detect the focus error signal.

Of the above-mentioned reflected light beam 49, FIG.
(B) Light 49 _-3 toward the Wollaston prism 52 in the middle
Enters the Wollaston prism 52, where FIG.
As shown in (A) and (B), it is separated into a p-wave 55 and an s-wave 56.

The p-wave 55 is deflected by the angle β toward the first emission surface 43a side with respect to the extension line 57 of the light 49 _-3 .

Contrary to the p-wave 55, the s-wave 56 is the light 4
The angle β is deflected toward the second exit surface 43b side with respect to the extension line 57 of 9 _-3 .

The p-wave 55 and the s-wave 56 exit the Wollaston prism 52 and enter the composite prism 43.

The angle β is small, and the p wave 55 and the s wave 5 are
6 propagates in the mountain portion 43e of the composite prism 43, reaches both the third emission surface 43c and the fourth emission surface 43d, and is refracted and emitted there.

Looking at the third emission surface 43c, the p-wave 55 is emitted as the third light 51c in FIG. 4C, which is the second light receiving portion 45Ab _-1 (E ₁ region). Irradiate.

The s-wave 56 is the fourth light 51 in FIG.
It is emitted as d, and this is emitted from the third light receiving portion 45Ab.
Irradiate _-2 (E ₂ area). In FIG. 4C, the fifth light 5
1e, and the fourth light receiving portion 45Ac
_-1 (F ₁ area) is irradiated.

The s-wave 56 is the sixth light 51 in FIG.
It is emitted as f and this is the fifth light receiving portion 45Ac _-2 (F
₂ areas).

The second to sixth light receiving portions 45Ab _-1 to 45-4
Based on the output from 5Ac _-2 (regions E _{1 to} F ₂ ),
The tracking error signal is detected by performing the calculation of (E ₁ + E ₂ ) − (F ₁ + F ₂ ).

Further, a magneto-optical signal can be obtained by performing the calculation of (E ₁ + F ₁ )-(E ₂ + F ₂ ).

Further, the address signal is obtained by performing the calculation of (E ₁ + E ₂ + F ₁ + F ₂ ).

As can be seen from the above, according to the present embodiment, all the signals (focus error signal, tracking error signal, It is possible to detect magneto-optical signals and address signals.

Comparing the configuration of FIG. 3 with the configuration of FIG.
In FIG. 1, since there is no optical path extending laterally from the beam splitter 38, the space occupied by the optical system is reduced and the number of parts is reduced.

Therefore, the optical disk device 31 of the second embodiment.
A is smaller in size and lower in cost than the optical disk device 31 of the first embodiment.

In addition, when the photodetector 45A is adjusted so that a predetermined focus error signal can be detected, it is automatically adjusted to the third value.
Light 51c to sixth light 51f from the light receiving portion 45Ab-
1 (E ₁ region) and the light receiving part 45Ac-2 (F ₂ region) can be automatically made incident on the structure, so that there is no need to make adjustments for detecting the track error signal and the magneto-optical signal. is there.

Instead of the integrated component 50, the composite prism 50 and the Wollaston prism 52 are independent components, and the Wollaston prism 52 is spaced apart and opposed to the back surface of the composite prism 50 and is independent of the composite prism 50. It may be configured to be arranged in.

[0065]

As described above, according to the present invention of claim 1, the reflected light is divided into four by one compound prism , and these are detected by the photo-detecting section to obtain the focus error signal and the tracking error signal. By detecting, the reliability of error detection can be improved, and the size and cost can be reduced.

According to the second aspect of the invention, since the first to fourth light receiving portions are formed on one plane, the positional accuracy of each light receiving portion can be improved, and the first light receiving portion can be improved. It is possible to omit the adjustment for tracking error signal detection as compared with the case where the fourth light receiving portion is not formed on one plane.

[0067]

[0068]

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram for explaining the compound prism of FIG.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a view for explaining the composite prism-Wollaston prism integrated component of FIG. 3;

FIG. 5 is a diagram for explaining a conventional optical disc device.

FIG. 6 is a diagram for explaining the Foucault method of FIG. 5.

FIG. 7 is a diagram for explaining the Foucault method of FIG.

FIG. 8 is a diagram for explaining the Foucault method of FIG.

FIG. 9 is a graph of the output characteristics of FIGS.

FIG. 10 is a diagram for explaining the push-pull method of FIG.

FIG. 11 is a diagram for explaining the push-pull method of FIG.

12 is a diagram for explaining the push-pull method of FIG.

[Explanation of symbols]

31, 31A Optical disk device 32 Semiconductor laser 33 Collimator lenses 34, 38 Beam splitter 35 Reflecting mirror 36 Objective lens 37 Disk 39 Wollaston prisms 40, 42 Condensing lens 41 Photodetector 43 Compound prisms 43a to 43d First to fourth exit surface 43e chevron portion 43f ridge 44a~44d first to fourth light 45,45A light detector 45a~45c first to third light-receiving portion 45Aa first light receiving portion 45Ab _-1 second light receiving portion 45Ab _{- 2} 3rd light receiving portion 45Ac _-1 4th light receiving portion 45Ac _-2 5th light receiving portion 49 reflected light flux 49 _-1 , 49 _-2 , 49 _-3 light 50 composite prism-Wollaston prism integrated parts 51a to 51f 1st to 6th light 52 Wollaston prisms 53, 54 Crystal triangular prism 55 p-wave 56 s-wave 57 Extension line of light 49 _-3

Continuation of front page (56) Reference JP-A-3-137841 (JP, A) JP-A-1-144233 (JP, A) JP-A-1-241028 (JP, A) JP-A-2-121139 (JP , A) JP 62-298029 (JP, A) JP 62-295226 (JP, A) JP 62-243148 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) G11B 7/09-7/22 G11B 11/00-11/26

Claims (2)

(57) [Claims] 1. A disc is irradiated with light emitted from a light source,
In an optical disc device for detecting an information signal, a focus error and a tracking error by reflected light from the disc and controlling focus and tracking, the reflected light from the disc is converted into first to fourth light in substantially the same direction. A light splitting means for splitting, and the first and second lights split by the light splitting means are received to detect a focus error signal based on the Foucault method ,
Third and fourth up the tracking error signal by receiving light
The light splitting means detects the light based on the Shook method, and the light splitting means includes third and fourth emission surfaces having a chevron shape whose intersecting portions located at the center form a ridge, and improve Write, third and fourth output surface extends above ridge line forming chevron portions intersect, are located on one side, and the third outgoing in the same direction as the third emission surface Located on the other side in the extending direction of the ridgeline of the chevron portion in the same direction as the fourth emission surface and from the fourth emission surface. have a second exit surface which is inclined at a small angle, made of a composite prism having a central ridge lines of the chevron portions, the composite prism, respectively from the exit surface of the third and fourth people
The third and fourth lights are emitted, and the first and fourth lights are emitted.
The first and second lights are emitted from the second emission surface, respectively.
An optical disk device characterized in that it is arranged in such a manner. 2. The light detection unit receives a first light receiving unit divided into four for receiving the first and second lights and a third light and a fourth light on one plane. The optical disk device according to claim 1, wherein a second and a third light receiving portion are formed.