JPH01211328A - Optical head device - Google Patents

Abstract

PURPOSE:To easily adjust positions of a photodetector, etc., and a diffraction grating by detecting relation between projecting light and a track in accordance with the variation of the light quantity of a light spot formed on the light receiving surface of the photodetector by using the reflecting light of an optical beam. CONSTITUTION:The light oscillated from a semiconductor laser 11 is projected on a diffraction grating 12 and converged to a track of an optical disk in a focused state through a convergent lens 13. The reflecting light of the converged light is projected on a photodetector 21 after it is diffracted by the grating 12. When the optical disk 50 is brought nearer to and separated farther from an optical head device 10, the light spot formed on the light receiving surface of the photodetector 21 concentrically increases or decreases against the light spot formed by the light projected in a focused state and focus error signals are obtained. Moreover, since each light receiving surface of the photodetector 21 is divided by dividing lines which are parallel to the track direction of the disk 50, the optical intensity distribution of the light spot 20 becomes asymmetrical about the center line in the track direction and tracking error signals are obtained, when the projecting light is deviated. Therefore, positions of the photodetector and the diffraction grating can be easily adjusted.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an optical disc and a digital disc.

The present invention relates to an optical head device for reproducing information recorded on a recording medium such as a video disc.

(Prior Art) In a recording medium such as an optical disk, information is recorded on strip-shaped tracks. Information on such a recording medium is reproduced by an optical head device that uses lens light or the like that can be easily focused on a minute spot.

The optical head device is moved along a track of a recording medium while projecting light onto the track, and reproduces information based on light reflected from the track.

As shown in FIG. 8, a conventional optical head device 30 is shown.

For example, a semiconductor laser light source 31 is provided, and light is projected from the light source 31 onto a diffraction grating 32, and the 0th order diffracted light of the diffraction grating 32 is focused on a track of the optical disk 50 by a converging lens 33. Converged. The light converged on the track of the optical disc 50 is reflected by the track of the optical disc 50, and the reflected light is.

The light is projected onto the diffraction grating 32 through a converging lens 33.

The first-order diffracted light by the diffraction grating 32 is used, in addition to the reproduction signal, to detect the focal shift and tracking error of the light converged on the track of the optical disk 50.

The first-order diffracted light by the diffraction grating 32 is projected onto a pair of two-split photodetectors 34 and 35 arranged on the sides of the light source 31.

The diffraction grating 32 may be one, for example, as shown in FIG.

The optical disc 50 is divided into two areas 32a and 32b by a line 32c parallel to the track direction (direction indicated by arrow A in FIG. A grating composed of parallel lines having different periods is formed.

The two-split photodetectors 34 and 35 are arranged side by side in the track direction on the side of the light source 31, and the light-receiving surfaces 34a, 34b and 35a, 35b of each photodetector 34 and 35 correspond to one diffraction grating 32. It is divided by a dividing line parallel to the dividing line 32c. When the light projected from the light source 31 is focused on the track of the optical disk 50, the first-order diffracted light by the diffraction grating in one area 31a is transmitted to the light receiving surfaces 34a and 34b of one photodetector 34. The photodetector 34 is arranged at a predetermined position so as to be focused on the dividing line. Similarly, in the other photodetector 35, the first-order diffracted light by the diffraction grating in the other region 32b is transmitted to its light-receiving surface 3.
It is arranged so as to converge in a focused state on the dividing line between 5a and 35b.

In such an optical head device 30, based on the detection results of each of the photodetectors 34 and 35, a focus shift of light projected onto a track of the optical disk 50 and a tracking error are detected.

For example, when the optical disk 50 moves toward or away from the converging lens 33, the first-order diffracted light by the gratings in each region 32a and 32b in the nine diffraction grating 32 moves in a direction perpendicular to the dividing line 32c of the nine diffraction grating 32. do. As a result, the amount of light captured by each light receiving surface 34a, 34b and 35a, 35b of each photodetector 34 and 35 fluctuates, and the amount of light captured by each light receiving surface 34a, 34b of one photodetector 34 varies. , the other photodetector 34
Based on the difference in the amount of light between the light receiving surfaces 34a and 34b,
A change in the distance between the optical disk 50 and the converging lens 33 is detected. Further, when the convergence position of the light projected onto the optical disc 50 is the center position in the width direction of the track, the entire scene captured by each of the light receiving surfaces 34a and 34b of the photodetector 34 and each of the light detectors 35 The total amount of light captured by the light-receiving surfaces 35a and 35b is equal, but if the light convergence position on the track shifts in the left-right direction with respect to the track direction,
The total amount of light captured by each of the light receiving surfaces 34a and 34b of the photodetector 34 and each of the light receiving surfaces 35a and 3 of the photodetector 35
A difference occurs in the total amount of light captured by 5b, and a tracking error signal is detected based on the difference (so-called push-pull method).

(Problems to be Solved by the Invention) In such a conventional optical head device 30, the light projected from the light source 31 and transmitted through the diffraction grating 32 is transmitted when the optical head device 30 is at an appropriate position with respect to the optical disk 50. , the positions of the light source 31 and the converging lens 33 are determined so that the light source 31 and the converging lens 33 converge on the optical disk 50 in a focused state. The reflected light that is focused on the optical disk 50 is focused by the single diffraction grating 32 onto the light receiving surface of each of the photodetectors 34 and 35. For this reason, the light source 31. The positions of each photodetector 34, 35, etc. are as follows.

Must be determined precisely. However, if these are placed out of position.

The first-order diffracted light of the diffraction grating 32 is transmitted to each of the photodetectors 34 and 3.
The light does not converge in a focused state on the light receiving surface of No. 5, and a so-called focus offset occurs. In order to eliminate this focus offset, the nine diffraction gratings 32 are translated or rotated relative to the optical disk 50.

It is necessary to adjust so that while the light is converged on the optical disk 50, the first-order diffracted light of the reflected light by the diffraction grating 32 is focused on the light receiving surfaces of the photodetectors 34 and 35.

However, since the light spots formed on the light-receiving surfaces of the photodetectors 34 and 35 are usually minute, ranging from several μm to more than ten-odd μm, the diffraction grating 32 is adjusted to It is not easy to focus the light on the

The present invention solves the above conventional problems, and its purpose is to adjust the position of a light source, a photodetector, etc.

It is an object of the present invention to provide an optical head device in which adjustment of a diffraction grating, etc. can be easily performed.

(Means for Solving the Problems) The present invention is an optical head device that projects light onto a recording medium having a track on which predetermined data is recorded and reproduces data based on the light intensity of the reflected light. a light source that projects light toward the tracks of the medium; a lens system that focuses the projected light of the light source onto the tracks of the recording medium;
a diffraction grating that diffracts light reflected from the tracks of the recording medium;

In order to form a light spot of a predetermined area on the light receiving surface by the light that is focused on the track of the recording medium and diffracted by the diffraction grating, the light is moved to a position different from the focused position of the light. with a photodetector installed.

and detecting the relationship between the track of the recording medium and the light projected onto the track based on the change in the light intensity of the light spot on the light receiving surface of the photodetector, The above objective is achieved.

(Example) The present invention will be described below with reference to Examples.

As shown in FIG. 1, an optical head device 10 of the present invention has a semiconductor laser 11 as a light source.
The light oscillated from the 9-diffraction grating 12 is projected onto the 9-diffraction grating 12, and the 0th-order diffracted light of the diffraction grating 12 is focused on the track of the optical disc 50 by the converging lens 13. Note that the converging lens 13 may be a lens system including a collimating lens and a condensing lens. The reflected light converged on the track of the optical disk 50 is diffracted by the first diffraction grating 12, and the first-order diffraction light is projected onto a photodetector 21 disposed on the side of the semiconductor laser 11.

The photodetector 21 is arranged in front of the focal position of the first-order diffracted light so that the first-order diffracted light of the diffraction grating 12 forms a circular or elliptical light spot having a predetermined area on its light receiving surface. It is set up.

As shown in FIG. 2, the diffraction grating 12 has a grating formed of concentric circles or circular arcs having a center on the side where the photodetector 21 is disposed in the track direction indicated by arrow A.

The light-receiving surface of the photodetector 21 is divided into four parts in a direction perpendicular to the track direction of the optical disc 50, and the two central light-receiving surfaces A1 and B2 are divided into two outer light-receiving surfaces a1 and a.
The width direction dimension perpendicular to the track direction is shorter than that of No. 2. The photodetector 21 is.

The optical spot 20 of the first-order diffracted light reflected by the optical disk 50 and diffracted by the 9-diffraction grating 12 satisfies the quadratic equations (1) and (2), and each light receiving surface aI+ at + b
j+b! Its position and output are adjusted so that it is projected with an amount of light equal to .

P bj + P b□=P, l+P,! ...(
1) P□+P=P-t+Pbt (2) where Po: amount of light projected onto the light-receiving surface a, P! = Amount of light projected onto the light receiving surface a2 Pbl: Amount of light projected onto the light receiving surface Pbz: Amount of light projected onto the light receiving surface b2 In the optical head device 10 having such a configuration, the amount of light projected onto the optical disk 50 is An optical focus error signal and a tracking error signal are obtained as follows.

If the optical disc 50 has a predetermined distance from the optical head device 10, the light projected onto the optical disc 50 will be focused on the optical disc 50, and the reflected light will be reflected by the photodetector 21. A light spot of a predetermined area is formed on the light receiving surface.

On the other hand, when the optical disk 50 approaches or moves away from the optical head device 10.

The light projected onto the optical disc 50 is not focused on the optical disc 50, and the reflected light causes the light to be detected by the photodetector 2.
A light spot 20 is formed on the light receiving surface of 1.

The light spot formed on the light receiving surface of the photodetector 21 by the light projected onto the optical disk 50 in a focused state increases or decreases concentrically. the result.

The amount of light captured by the light spot 20 on each of the outer light receiving surfaces at and a2 of the photodetector 21.

Difference between each light receiving surface in the center and the amount of light captured by b2 ((P-++Paz) (Pb++Pbz)
) gives a focus error signal.

Further, the tracking error signal is obtained as follows. In this embodiment, each light-receiving surface of the photodetector 21 is divided by dividing lines parallel to the track direction of the optical disc 50, so that the light projected onto the optical disc 50 is If the light spot 20 is converged at a position shifted in the left-right direction perpendicular to the center line, the light intensity distribution of the light spot 20 formed on the light-receiving surface of the photodetector 21 becomes asymmetrical with respect to the center line in the track direction. Therefore, by using the push-pull method, the difference between the amount of light captured by the light receiving surfaces a, , and of the photodetector 21 and the amount of light captured by the light receiving surfaces a2 and b2 ((P, t + Pb +) - (P, z + Pbz)
).

Or the difference in the amount of light captured by the outer light-receiving surfaces a1 and a2 (P-+P-t), or the difference in the amount of light captured by the center light-receiving surfaces b1 and b2 (Pb, -Pb).
The tracking error signal F is obtained by 2).

Note that the reproduced signal is obtained by the total light amount of the light spot 20 formed on the light receiving surface of the photodetector 21.

The focus error signal F= ((P, I+P, □) (Pb++Pbz
)) Distance d between the optical disk 50 and the converging lens 13
The relationship between the two is shown in the graph of FIG.

Another embodiment of the invention is shown in FIG. In this embodiment, the light projected from the semiconductor laser 11, which is a light source, is separated into a 0th order beam (main beam) and ±1st order diffracted light (sub beams) by a first diffraction grating 15. The light is applied to the converging lens 13 via the second diffraction grating 16, and is focused on the track of the optical disk 50 by the converging lens 13. As shown in FIG. 5, the first diffraction grating 15 on the light source 11 side has a grating that is inclined by several degrees to several degrees from the orthogonal direction with respect to the track direction A. The second diffraction grating 16 is.

The phase is different from that of the first diffraction grating 15 by 90 degrees.

Two, for example, three photodetectors 2 are placed on the side of the semiconductor laser 11.
2, 23, and 24 are arranged in parallel in a direction inclined from several degrees to more than ten degrees with respect to the track direction. Each photodetector 22゜23, 24
is diffracted by the first diffraction grating 15, and the optical disc 5
from each focal position of the three light beams reflected at 0 and then diffracted at the second diffraction grating 16.

They are each provided at the rear, and a light spot having a predetermined area is formed on each detection surface.

The three light beams diffracted by the first diffraction grating 15 are
The light is reflected by the optical disk 50, diffracted by the second diffraction grating 16, and projected onto the light receiving surfaces of the corresponding photodetectors 22, 23, 24, respectively. The central photodetector 23 has
The main beam diffracted by the first diffraction grating 15 is projected into a spot having a predetermined area.

Each of the other photodetectors 22 and 24 includes a first diffraction grating 1
The sub beams diffracted at 5 are projected in the form of spots each having a predetermined area. As a result, each photodetector 22
．． On the light receiving surfaces 23 and 24, circular or elliptical light spots 20b and 20c of a predetermined area are provided.

20d are formed respectively.

The central photodetector 23 has a light receiving surface X++7+x2 divided into three by a line segment parallel to the center line of one diffraction grating 16. The remaining two photodetectors 22 and 2 arranged on the outside
4 each have one square light-receiving surface ZI+ZZ.

Each light receiving surface XI r V+ X of the central photodetector 23
2, there is an optical spora (20c) formed by the reflected light of the light beam projected onto the optical disk 50 in a focused state.

The position and output of the photodetector 23 are adjusted so that the following equations (3) and (4) are satisfied and the same amount of light is captured on each light receiving surface.

Py=PXI+PX□...(3) P XI = P xt...(4) However, P
81: Amount of light captured by the light-receiving surface X, Px! : Amount of light captured by light-receiving surface X2 Py : Amount of light captured by light-receiving surface y
A focus error signal and a tracking error signal of the light projected onto 0 are obtained as follows.

When the optical disk 50 approaches or separates from the optical head device 10, the optical spora (20c) formed on the central photodetector 23 by the main beam moves the optical disk 5 in a focused state.
The light spot formed by the main beam projected onto the photodetector 23 increases or decreases concentrically. Therefore, a focus error signal is obtained from the difference ((pxt+PX□)-P,) between the amount of light captured by the outer light-receiving surfaces X1 and x2 of the photodetector 23 and the amount of light captured by the central light-receiving surface y.

FIG. 6 shows focus error signals obtained by the optical head devices of the two embodiments.

Further, the tracking error signal is a tracking error signal obtained by the conventional three-beam method based on the light intensity of the respective optical spots 20b and 20d formed by the sub beams projected onto the photodetectors 22 and 24 disposed on the outside. is detected in the same way as the detection of .

The photodetectors 22 and 24 are arranged in parallel in the track direction, and each photodetector 22 and 24 receives ±1st order diffracted light (sub beam) projected from the light source 11 and transmitted by the first diffraction grating 15 onto the optical disc 50. It is projected after being reflected. When the main beam projected onto the optical disc 50 in a focused state is on the track, the light intensity of the optical spots 20b and 20d formed by each sub-beam is equal, but each sub-beam is on the track. When the position shifts in the horizontal direction perpendicular to the track direction, the light intensity of each light spot captured by each photodetector 22 and 24 changes, and the difference in light intensity (P
,, -P, □) (where, P21 is the amount of light captured by the light receiving surface z of the photodetector 22, and Px2 is the light receiving surface 2 of the photodetector 24
! A tracking error signal is obtained based on the amount of light captured by

In this manner, the optical head device of the second aspect of the present invention obtains a focus error signal of the light beam projected onto the optical disk by capturing changes in the size of the light spot projected onto the detection surface of the photodetector. The shape of the light-receiving surface of the photodetector is not limited to that of the above-described embodiment, but may be, for example, the shape shown in FIG. 7. The photodetector 25 shown in FIG. 7(a) has a square light receiving surface 25a.
It is a two-part type in which a square light-receiving surface 25b is arranged concentrically in the center of the light receiving surface. Then, each light receiving surface 25a and 2
The size of 5b, the position of photodetector 25, etc. are determined. The photodetector 26 shown in FIG. 7(b) has a light receiving surface 26a, 26-b divided into three parts in a direction perpendicular to the track direction A,
26c, and a light spot 20e is formed such that the amount of light received by the central light receiving surface 26b is equal to the amount of light received by each of the outer light receiving surfaces 26a and 26c.

The photodetector 27 shown in FIG.
It has two light receiving surfaces 27a and 27b. In such a photodetector 27, for example, the light intensity of the light spot 20c formed on each light receiving surface 27a and 27b by the reflected light of a light beam projected in a focused state onto the optical disk 50 is and 27b may be different.

In this case as well, a focus error signal is obtained based on the change in the amount of light received by each of the light receiving surfaces 27a and 27b. The photodetector 28 shown in FIG. 7(d) is.

A circular light receiving surface 28 is provided at the center of the square light receiving surface 28a.
b is provided. 2 on each light receiving surface 28a and 28b.
The light intensity of the light spot 20e formed by the reflected light of the light beam projected onto the optical disk 50 in a focused state is made equal on each light receiving surface 28a and 28b.

In an optical head device having any of the photodetectors shown in FIGS. 7(a) to (d), in order to obtain a tracking error signal, it is necessary to align the light receiving surface of each photodetector with
What is necessary is to detect a change in the amount of light captured by each divided light receiving surface. Alternatively, in the case of a 3-beam system, such as the optical head device shown in FIGS. 4 and 5, a photodetector is placed on each side of the photodetector used to detect the focus error. A tracking error signal can also be obtained by detecting a change in the amount of light captured by both of the sensors.

(Effects of the Invention) As described above, the optical head device of the present invention causes the reflected light of the light beam projected to be focused on the track of a recording medium such as an optical disk to a predetermined position on the light receiving surface of the photodetector. A light spot having an area of Therefore, the light spot formed on the light-receiving surface of the photodetector is large, and adjustment of the position adjustment two diffraction gratings of the photodetector etc. can be easily performed.

4. Figure 1 is a schematic diagram showing an example of the optical head device of the present invention, Figure 2 is a plan view showing the relationship between the grating pattern of the diffraction grating and the light receiving surface of the photodetector, and Figure 2 is a schematic diagram showing an example of the optical head device of the present invention. Fig. 3 is a graph showing the detection results of the focus error signal by the optical head device, Fig. 4 is a schematic diagram of an optical head device according to another embodiment of the present invention, and Fig. 5 is a grating pattern of the diffraction grating and light detection. Figure 6 is a graph showing the detection results of the focus error signal by the optical head device, and Figures 7 (a) to (d) are examples of the light-receiving surface of the detector. FIG. 8 is a schematic view of a conventional optical head device, and FIG. 9 is a plan view showing the relationship between the grating pattern of the diffraction grating and the detection surface of the photodetector.

10... Optical head device, 11... Light source, 12.1
5.16...Diffraction grating, 13...Converging lens, 2
1.22.23.24...Photodetector.

that's all

Claims (1)

[Scope of Claims] 1. An optical head device that projects light onto a recording medium having a track on which predetermined data is recorded and reproduces data based on the light intensity of the reflected light, which is directed toward the track of the recording medium. a light source that projects light; a lens system that focuses the projected light of the light source onto a track of a recording medium; a diffraction grating that diffracts the light reflected from the track of the recording medium; and the recording medium. In order to form a light spot of a predetermined area on the light receiving surface by the light that is focused on the track and diffracted by the diffraction grating, the light is disposed at a different position from the focused position of the light. a photodetector, and detecting a relationship between a track of the recording medium and the light projected onto the track based on a change in light intensity of a light spot on a light receiving surface of the photodetector. Characteristic optical head device.