JPH0836762A - Optical disk apparatus - Google Patents

Abstract

PURPOSE:To obtain an optical disk apparatus having a focus error detector in which the change of a reflected light quantity or an optical axis due to the state of an optical disk recording surface scarcely influences a focus error signal. CONSTITUTION:The optical disk apparatus comprises an optical system 21 for casting a laser beam at a rotating recording medium 22, a beam splitter 25 for separating the reflected light beam from the medium into first and second convergent light beams, first and second photodetectors 13, 14 disposed on the optical paths of the first and secod light beams, and a circuit for generating a focus error signal corresponding to the difference of the outputs of the photodetectors. The photodetectors are disposed on the paths in the positional relationship in which the amplitude changes of light receiving images due to the lights upon the deviation of the focuses occurs in reverse directions to form focus error signals from the outputs of second and third areas 16a-16d to obtain a tracking control signal for allowing the positions which is irradiated with the laser beam, from the output of the spit areas 16e-16h to follow up the track of the medium.

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,
More specifically, the present invention relates to a light beam application device, such as a video disc, an audio disc, or a digital optical disc device, which needs to follow the focal position of irradiation light according to the position variation of a reflecting surface.

[0002]

2. Description of the Related Art In an optical disk apparatus for irradiating a laser beam on the surface of a rotary recording medium to optically record or reproduce information, an objective lens of an optical pickup in accordance with a vertical movement occurring on a rotating optical disk. Is required to control the information recording surface so that the information recording surface is always within the depth of focus of the laser spot. The automatic focus servo system includes, for example, a voice coil type servo motor for moving the objective lens up and down, a focus error detection unit, and a servo amplifier for operating the servo motor according to the detected focus error. However, among these elements, the focus error detection unit is particularly important, and when applied to an optical disc device, the reflected light caused by a pregroup forming an information pit or a track formed on the information recording surface, etc. It is desirable that the change does not affect the focus error signal. In addition, for correct focus control, even if a deviation occurs in the optical axis of the reflected light from the information recording surface due to, for example, displacement of the optical system, the device configuration does not affect the focus error signal. Is desired.

Conventionally, various types of apparatus configurations for detecting a focus error have been proposed.
One is to focus the reflected light from the information recording surface (reflective surface) with a lens and place a knife edge at the focusing point so that only a part of the reflected light reaches the photodetector behind the knife edge. (For example, the magazine "Nikkei Electronics"
(November 21, 1983 issue, p. 202). According to this method, when a cylindrical lens is arranged between the focusing lens and the knife edge, it is possible to obtain a semi-circular optical image that rotates according to the amount of defocus on the photodetector, and it is divided into two. A highly accurate focus error signal can be obtained by taking the differential output of the photodetector.

[0004]

However, in the above method, since the focus error signal depends on the relative positional relationship between the knife edge and the focused light, the position change of the knife edge due to thermal expansion or the reflection of the knife edge occurs. There is a problem that the deviation of the optical axis of light affects the focus error signal.

Another method is, for example, Japanese Patent Laid-Open No. 59-59.
As described in JP-A-77637, an optical element that separates a central portion and a peripheral portion of a light beam in different directions is provided on an optical path that focuses reflected light, and these separated light beams are received by different photodetectors. However, a method is known in which a focus error signal is obtained from the output difference. However, since the manner in which the light quantity changes due to the information pits and tracks described above differs between the central part and the peripheral part of the reflected light, this method has a problem that an error signal contains a noise component.

It is an object of the present invention to provide an optical disk device provided with a focus error detection device in which a change in the amount of reflected light or a change in the optical axis due to the state of the above-described reflecting surface does not easily affect the focus error signal.

[0007]

In order to achieve the above-mentioned object, an optical disk apparatus of the present invention comprises an optical system for irradiating a rotating recording medium with laser light, and a first and a second optical system for reflecting light from the recording medium. Means for splitting into two focused lights, first and second photodetectors arranged on the optical paths of the first and second focused lights, respectively, and at least outputs of the two photodetectors. It consists of a circuit that generates a focus error signal according to the difference,
The respective photodetectors are arranged on the respective optical paths in such a positional relationship that changes in the size of the received image due to the focused light due to defocusing appear in mutually opposite directions, and each photodetector receives the central portion of the received image. An area, and second and third areas which are located on both sides of the first area and which receive the edges of the received light image and are separated from each other. The first area is divided into two, and the circuit is The focus error signal is generated from the outputs of the second and third areas, and the tracking control signal for causing the irradiation position of the laser beam to follow the track of the rotating recording medium is output from the output of the first area divided into two. It is characterized by occurring.

The positional relationship of the above photodetectors is, for example,
The first photodetector is arranged behind the focal point of the first focused light,
Filled by placing a second photodetector in front of the focal point of the second focused light.

[0009]

In the present invention, when the light reflecting surface is out of the focus position, the light receiving image is enlarged by one of the two photodetectors and is reduced by the other, so that the light receiving surface of each photodetector is received. Of the first area for receiving light in the central portion of the second area, and second and third regions located on both sides of the area for receiving the edge portions of the received light image.
If the peripheral portion of the received light image is subjected to photoelectric conversion by the second and third regions, it is divided into the region and the second and third regions out of the total amount of light on the side where the received light image is enlarged. The ratio of the amount of light emitted is increased and the output is increased. On the contrary, in the photodetector on the side where the received light image is reduced, the ratio of the photodetector to be contained in the first region is increased, so that the outputs from the second and third regions are decreased. Therefore, the focus error signal can be obtained by taking the difference between the outputs from the second and third regions of the two photodetectors. In this case, even when the amount of reflected light changes due to the unevenness of the reflecting surface, these noise components appear in the two focused lights at the same time, and in addition, they appear in the central portion,
The influence on the focus error signal can be eliminated by obtaining the focus error signal from the outputs of the second and third regions that receive the edge portion of the received light image.

Further, the tracking control signal can be detected from the output of the first area obtained by dividing each photodetector into two parts, and the photodetector for focus error detection can also be used for the track deviation detection.

[0011]

EXAMPLES The details of the present invention will be described below with reference to examples. First, the principle of focus position detection used in the present invention will be described.

FIG. 1 is a diagram showing the principle of focus position detection used in the present invention. Reference numeral 1 is a reflecting surface at the focus position.
Reference numeral 1'indicates a state in which the reflecting surface is displaced in the direction away from the focus position, and reference numerals 2, 2'indicate the reflected light at each of the above positions. 3 is a focusing lens for focusing the reflected light 2 on the point P ₁ , 10 is a beam splitter of, for example, a half mirror type inserted between the focusing lens 3 and the focusing point P _1, and is focused by the focusing lens 3. The reflected light 2 thus split is bisected by the beam splitter 10, and goes straight 2A and split 2B.
Are convergent points P _{1 at} positions equidistant from the bifurcation surface 10 ′.
And P ₂ are formed.

In the present invention, two photodetectors 13 and 14 are used, and one photodetector 13 has a predetermined distance w from the focal point P _2.
Is arranged at a position close to the beam splitter, and the other photodetector is arranged at a position away from the focal point P ₁ by a distance w so that the beam splitter output light is received at each position.

As shown in FIG. 2D, the photodetectors 13 and 14 have a structure in which an effective light-receiving surface 16 is left in the central portion and the periphery thereof is shielded by a mask 15, which is basically the same. A shape is used. When the reflecting surface 1 is aligned with the focus position, the two focused lights 2A and 2B at the position equidistant from the focusing points P ₁ and P ₂ have the same cross-sectional area, and the photodetectors 13 and 14 are the same. 2B, a light receiving image (light spot) having the same area is formed, as shown by hatching in FIG. 2B, and the ratio of the light receiving amount of the light receiving surface 16 to the total incident light amount is equal to each other. Therefore, in the beam splitter 10, the straight light 2
If A and the branched light 2B are branched with the same light intensity, the outputs of the two photodetectors 13 and 14 at the time of focusing are equal to each other.

In this structure, when the reflecting surface 1 is deviated to the position 1 ', due to defocus, the broken line 2A',
As shown in 2B ', the focal point of the two focused light is moved to the front side than the position P _1, P ₂ of the focal point. Therefore, FIG.
As shown in (A), the photodetector 13 has a light spot 6 '.
Is reduced and most of the incident light is narrowed down to the light receiving surface 16, and the light receiving surface 16 receives a part of the expanded light spot on the other photodetector 14. In this case, the output of the photodetector 13 becomes larger than the output of the photodetector 14,
The difference between the output signals of the two photodetectors has a value according to the amount of defocus. In this configuration, when the reflecting surface is deviated from the position of 1 toward the lens 3, the light spot on the photodetector 13 is expanded and the light on the photodetector 14 is expanded, as shown in FIG. As the spot is narrowed down, the detector output relationship is reversed. Therefore, the differential output V of the two photodetectors 13 and 14 becomes an S-shaped characteristic curve as shown in FIG. 3 with respect to the defocus amount δ, and this is used to configure an automatic focusing servo system. be able to.

In the above-mentioned focus position detection, when an optical disk having, for example, a pre-group type information track is applied as the reflecting surface 1, the two photodetectors 1 described above are used.
First-order diffracted light appears on the light spots 3 and 14 as shown by 11a and 11b in FIG. If the light spot position on the optical disc deviates from the track, the first-order diffracted light 11a,
Although the intensity of 11b changes, if the defocus is small, the intensity change appears equally in the two photodetectors 13 and 14, so that they can be canceled by taking the differential output, and the focus error detection signal Little impact.

FIG. 5 shows an example of performing both focus position detection and track position detection. Here, the photodetectors 13, 14
The respective effective light-receiving surfaces of the
a and 11b are divided into two in the separating direction, and 16a and 16
The light detection signals A, B, C, and D can be taken out independently from the four light receiving surfaces b, 16c, and 16d. When independent outputs are taken out from the four light receiving surfaces in this way, as shown in FIG. 6, the focus error detection signal AF
Is obtained by (A + B)-(C + D), and the track position detection signal TR can be obtained by (AB) + (CD). Further, by adding all the outputs, the information signal on the track can be obtained. When the effective light receiving surface of the photodetector is divided into a plurality of regions in this way, the track position detection signal TR may use only one photodetector.

FIG. 7 is an explanatory view when the optical axis of the reflected light is deviated from the detectors 13 and 14 in the example of the focus position detection shown in FIG. Such a state occurs, for example, when the lens follows the eccentricity of the track of the optical disk, and also occurs when the position of the optical component is shifted due to a change in temperature or a change with time. Assuming that the position of the light spot moves on the reflecting surface 1 by ε as shown in FIG. 7A and the lens 3 also moves by ε in the same direction, as shown in FIG. The light spot 6 on the containers 13 and 14 moves by ε to the position 6 ′ shown by the broken line.
Even if there is such a movement of the light receiving spot 6, if the intensity distribution of the light spot 6 is uniform, the photodetectors 13, 1
There is no change in the output of No. 4 and no error occurs in the focus error signal. Further, even if the intensity distribution of the light spot 6 on the photodetector is not uniform, the movement of the light spot 6 appears equally to the two detectors, so that the error generated in the focus error signal obtained by the differential output is extremely small. small.

FIG. 8 is a photodetector 13, 1 in the case where the above-mentioned optical axis shift of the reflected light occurs in the state where the track position is detected using the split type photodetector shown in FIG.
It is explanatory drawing about the light spot on 4. In this case, since the positions of the light receiving surfaces 16a, 16b, 16c, 16d and the first-order diffracted lights 11a, 11b are deviated, the outputs are significantly reduced at 16b and 16c where the boundaries of the first-order diffracted lights are located. However, the amount of decrease in output is almost equal between 16b and 16c, and if this value is p, the track position detection signal is {A- (B-p)} + {(C-p) -D} = (A-
B) + (C−D), and p is canceled out. That is, it can be seen that there is no influence of the change in the optical axis on the track position detection signal, and the error is extremely small even if it is assumed.

FIG. 9 shows another configuration example of the photodetectors 13 and 14. In this example, a band-shaped mask 15 is provided at the center of the photodetectors 13 and 14 so as to divide the light-receiving surface into upper and lower parts. The light spot 6 is divided into two light receiving surfaces 16a and 16
b, and the outputs of 16c and 16d are substantially in the same position at the time of focusing. The output of each light-receiving surface 16a-16d is A,
Assuming B, C, and D, the focus error detection signal is (A + B)-
The error signal output V obtained by (C + D) with respect to the movement δ of the focal position has the characteristic shown in FIG.

FIG. 11 shows, in portions corresponding to the mask 15 of the photodetectors 13 and 14 in the configuration example of FIG. 9 described above, light-receiving surfaces 16e and 16f divided into two for track position detection.
And 16g and 16h are respectively arranged. 16
When the outputs e to 16h are E to H, the track position detection signal TR becomes (EF) + (GH). Compared with the configuration example shown in FIG. 8, the light receiving surface 16a for focus error detection
Since the light amounts of the first-order diffracted lights 11a and 11b received by 16d can be reduced, the error amount included in the focus error detection signal due to the first-order diffracted light becomes smaller than that in the configuration example of FIG. . In the above-described structure in which the light receiving surface is vertically divided into two, as shown by 6 ′ in FIG. 12, when the light spot on the photodetector is vertically displaced due to the optical axis deviation of the reflected light, the photodetector 13, The 14 outputs (A + B) and (C + D) each slightly change.
However, since this change amount also appears in the two photodetectors 13 and 14, if the value is q, the focus position detection signal is (A + B-q)-(C + D-q) = (A + B)-(C
+ D) and they cancel each other out. With respect to the tracking position detection signal, the influence of the light beam shift is the same as that of the previous configuration example.

FIG. 13 shows an example in which the photodetector structure shown in FIG. 5 is used in an optical disk device. Reference numeral 17 denotes a light beam generator including a laser diode and an optical system for converting the laser light into a parallel light beam. A parallel light beam 18 emitted from the device 17 is a polarization beam splitter 19, a quarter wave plate 20, and an objective. The lens 21 focuses on the information track 23 formed on the optical disk 22. The light reflected from the optical disk 22 is polarized beam splitter 1
The light passes through 9 and is guided to the focus error detection device described in FIG. In this example, the photodetectors 13 and 14 having the shape shown in FIG. 5 are used, and a track position detection signal is also obtained at the same time. When the outputs of the light receiving surfaces 16a, 16b, 16c, 16d are A, B, C, D, the focus error detection signal AF,
The track position detection signal TR and the information signal SI are respectively

[0023]

## EQU1 ## AF = (A + B)-(C + D)

[0024]

[Equation 2] TR = (A−B) + (C−D)

[0025]

(3) SI = (A + B) + (C + D) Lens 2 depending on signals AF and TR
By moving 1 in the directions of arrows 24 and 25, autofocus and autotracking are achieved.

FIG. 14 shows an embodiment of the optical disk device according to the present invention. 14, the same elements as those of the configuration example of FIG. 13 are designated by the same reference numerals. In the present embodiment, a quarter wavelength plate 24 is arranged between the polarization beam splitter 19 and the lens 3 and the beam splitter 12
A polarization beam splitter 25 is used instead of the. When the polarization beam splitter 25 is used, the ratio of the straight light 2A and the branched light 2B can be adjusted by changing the mounting angle of the quarter-wave plate 24, and the two light detectors 13 and 14 can be input. Adjustment work for making the amount of light to be equal becomes easier. However, this light amount adjustment can be compensated for by adjusting the gain of an amplifier inserted in the output circuit of each detector. In the present embodiment, the photodetectors 13 and 14 of the type shown in FIG. 11 are used. In this case, the focus error detection signal AF, the track position detection signal TR, and the information signal SI are the photodetector 13 respectively. Light receiving surfaces 16a, 16
b, 16c, 16d, light receiving surfaces 16e, 1 of the photodetector 14
The outputs of 6f, 16g, and 16h are A, B, C, and
D, E, F, G, H

[0027]

## EQU4 ## AF = (A + B)-(C + D)

[0028]

[Equation 5] TR = (FE) + (HG)

[0029]

## EQU6 ## SI = (A + B + E + F) + (C + D + G + H)

Although the present invention has been described above, in the present invention, the shape of the effective light-receiving surface of the photodetector can be modified in various ways other than the shape shown in the embodiment, and the light irradiated to the photodetector can be modified. The size of the spot may be changed according to the amount of defocus, and only a part of the spot may be reflected by the received light signal. Further, in the embodiment, the two photodetectors 13 and 14 are arranged at positions equidistant w from the focal point, but the positions may be adjusted according to the light amounts of the straight light 2A and the branched light 2B. Further, the positional relationship between the two photodetectors may be reversed so that the straight light 2A is received before the focusing point and the branched light 2B side receives the focused light.
Depending on the characteristics, the light receiving surfaces of the two light receiving elements may have different sizes.

[0031]

As is apparent from the above description, according to the present invention, the light from the reflecting surface to be focused is separated into two directions, and a light-receiving image (spot) generated by defocusing is formed on each optical path. The photodetectors are arranged in a positional relationship in which the size changes are opposite to each other, and the light receiving surface of each photodetector is located at the first region that receives the central portion of the received image, and on both sides of the first region. If the end portion is separated into the second and third regions separated from each other for receiving light, and only the peripheral portion of the received light image is subjected to photoelectric conversion by the second and third regions, the two photodetector The focus error signal can be obtained by taking the difference between the outputs from the second and third regions. In this case, even when the amount of reflected light changes due to the unevenness of the reflecting surface, these noise components appear in the two focused lights at the same time and appear in the center of the two focused lights. The influence on the focus error detection signal can be removed by obtaining the focus error signal from the outputs of the three regions.

Further, the tracking control signal can be detected from the output of the first area, which is divided into two, of each photodetector, and the focus error detection detector can also be used for track deviation detection.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining the principle of a focus error detection device.

FIG. 2 is a diagram for explaining a change in a received light image on a photodetector.

FIG. 3 is a diagram showing one characteristic of a focus error signal.

FIG. 4 is an explanatory diagram of a light-receiving image on a photodetector when first-order diffracted light is generated.

FIG. 5 is a diagram showing another configuration example of a photodetector.

FIG. 6 is a diagram showing an output signal circuit in the photodetector of FIG.

FIG. 7 is an operation explanatory diagram when an optical axis shift occurs in the configuration of FIG. 1;

8 is an explanatory diagram of a light-receiving image when an optical axis shift occurs in the photodetector of FIG.

FIG. 9 is a diagram showing still another configuration example of the photodetector.

10 is a waveform diagram of an output signal from the photodetector of FIG.

11 is a diagram showing a modification of the photodetector of FIG.

12 is an explanatory diagram of the operation of the photodetector of FIG.

FIG. 13 is a diagram showing an example of an optical disc device.

FIG. 14 is a diagram showing an embodiment of an optical disc device according to the present invention.

[Explanation of symbols]

 3 ... Focusing lens, 13 and 14 ... Photodetector, 6 ... Light receiving image, 15 ... Mask, 16 ... Effective light receiving surface, 17 ... Light beam generator, 21 ... Objective lens, 22 ... Optical disk.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masateru Watanabe 2880 Kozu, Odawara City, Kanagawa Prefecture Hitachi Ltd. Odawara Plant

Claims (1)

[Claims] 1. An optical system for irradiating a rotating recording medium with laser light, a means for separating reflected light from the recording medium into first and second focused light, and the first and second, respectively. Of the first and second photodetectors arranged on the optical path of the focused light, and a circuit for generating a focus error signal according to the difference between the outputs of at least the two photodetectors. The containers are arranged on the respective optical paths in a positional relationship in which the size change of the received light image due to the focused light due to defocusing appears in mutually opposite directions, and a first area for receiving the central portion of the received light image, A second region and a third region which are located on both sides of the first region and which receive the edges of the received light image and which are separated from each other, the first region is divided into two, and the circuit includes the second and third regions. The focus error signal is generated from the output of the three areas, and the focus error signal is output from the output of the first area divided into two. Optical disc apparatus characterized by the irradiation position of the laser beam generates a tracking control signal for follow a track of the recording medium to the rotation.