JPH07105548A - Optical head and optical information device using the same - Google Patents

Abstract

PURPOSE:To lessen the intrusion of a track crossing signal into a focus error signal to be caused by the aberration of the optical system of the optical head which reproduces information signals to an optical information recording medium or records and reproduces the signals to and from the medium. CONSTITUTION:The luminous flux reflected from a disk and separated to a servo detecting optical system by a first beam splitter is separated by a second beam splitter 9 to two luminous fluxes. Astigmatism (a circular cylindrical lens 10 rotates +45 deg. and a circular cylindrical lens 13 rotates -45 deg.) is applied to these luminous fluxes in such a manner that the directions of the astigmatism attain 90 deg. with each other. The luminous fluxes are then respectively introduced to photodetectors 11, 14 and the signals obtd. from the two photodetectors are subtracted to detect a focus error signal 111.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for reproducing or recording information signals on an optical information recording medium, and an optical information apparatus using the same, and more particularly to a focus error signal by an astigmatism method. The present invention relates to an optical head that reduces mixing of track crossing signals into an optical head, and an optical information device using the same.

[0002]

2. Description of the Related Art FIG. 15 is a configuration diagram showing a configuration of a detection optical system of a conventional optical head for detecting a focus error signal by the astigmatism method.

In FIG. 15, a divergent light beam emitted from a semiconductor laser (not shown), which is an example of a laser element for emitting a laser light beam, becomes a parallel light beam 100 by a collimator lens (not shown), and the first beam is emitted. Splitter 3
Then, the objective lens 4 irradiates the recording surface on which the track 5a of the optical disc 5 which is an optical information recording medium is formed.

The reflected light 101 from the optical disk 5 passes through the objective lens 4 and is reflected by the first beam splitter 3,
Guided to the detection optics. Then, after the reflected light is converged by the detection lens 6, astigmatism is given through the cylindrical lens 7 and enters the photodetector 8. The photodetector 8 has four light receiving regions 8a, 8b, 8c, 8d as shown in FIG. 16, and the spot 102 incident on the photodetector 8 is obtained according to the distance between the objective lens 4 and the disc 5. Focus error detection is performed by an astigmatism method for detecting a change in shape (for example, a substantially circular shape when focused, an elliptical shape when defocused).

However, in this configuration, in FIG.
When the spot on the optical disc 5 moves from the center (just track) of the information track 5a of the optical disc 5 to the inner and outer circumferences (off track), the spot is focused on the disc.
As shown in FIG. 7, a focus error signal occurs (this is called mixing of the track crossing signal into the focus error signal,
Hereinafter, there is a problem that a normal focus error signal cannot be obtained as a result of AF leak).

On the other hand, in 1987 (1987)
Autumn, Proceedings of 48th Annual Meeting of the Japan Society of Applied Physics (1
7p-ZP-2) "Countermeasures for reducing groove crossing signal mixed in focus error signal", two light receiving areas (two light receiving areas arranged in the track orthogonal direction) at the outputs of the four light receiving areas of the photodetector 8 ( 8a and 8b, and 8c and 8d) have the same sum of outputs (8a + 8b = 8c + 8d)
A method has been proposed in which the above problem is solved in a circuit manner by forming a focus error signal after gain correction as described above.

[0007]

By the way, the cause of the AF leakage is considered to be the positional deviation of the photodetector and the aberration of the optical system. It was possible to reduce only the AF leakage due to the position shift. Therefore, it is not possible to reduce the AF leakage due to other causes (such as aberration of the optical system).

FIG. 18 schematically shows a change in the intensity of a reflected light beam with respect to off-track when an aberration of an optical system, which is one of the causes of AF leakage, particularly an aberration in an optical system from a semiconductor laser to an optical disk occurs. FIG.
In FIG. 18, the black portion indicates that the light intensity is high.
As can be seen from FIG. 18, when the optical system has an aberration, the intensity of the reflected light flux is orthogonal to the direction 200a (the track direction in the image of the information track 5a of the optical disc 5 when the image is projected) and the direction thereof. Since it is also asymmetric with respect to the direction 200b, AF leakage occurs as a result.
Therefore, regarding the AF leakage due to the aberration of the optical system,
Like the optical head in the previously proposed example, the reflected light beam 10
It is said that there is no AF leakage reduction effect in a configuration in which 1 (which is performed at the spot 102 on the photodetector 8 in the proposed example, but the effect is the same) is divided into two in the track orthogonal direction 200b and the two outputs are equal to each other. There were challenges.

The object of the present invention is to solve the above-mentioned problems of the prior art and to reduce the mixture of the track crossing signal (AF leakage) into the focus error signal due to the aberration of the optical system. It is to provide an optical head.

[0010]

The above object is to separate the reflected light from the optical disk, which is guided to the detection optical system by the first beam splitter, into two light beams by the second beam splitter, and to separate the respective optical paths. The astigmatism generating means for giving astigmatism to the reflected light beam from the recording surface and the photodetector are provided therein, and the direction of the astigmatism generated by the astigmatism generating means provided in the two optical paths. Are approximately 90 degrees relative to each other and the focus error signal is obtained using the outputs of the two photodetectors.

[0011]

In the present invention, the reflected light beam from the optical disk is the first
Is separated by the second beam splitter and guided to the detection optical system, and further separated into two light beams by the second beam splitter. FIG. 2 shows optical systems for passing the light beams (reflected light beam 103, transmitted light beam 105) separated by the second beam splitter. The reflected light beam 103, which is a parallel light beam separated by the second beam splitter, is made into convergent light 104 by the detection lens 9 and enters the cylindrical lens 10 which is the first astigmatism generation means. This cylindrical lens 10 is X
Incident optical axis 104a with respect to the direction 200b (the direction orthogonal to the track direction in the image of the information track of the optical disc when the image is projected on the cylindrical lens 10).
It is provided by rotating +45 degrees around it. Therefore, the convergent light 104 is incident on the first photodetector 11 after being given astigmatism for the focus error detection by the cylindrical lens 10.

On the other hand, the transmitted light beam 105, which is a parallel light beam separated by the second beam splitter, is made into convergent light 106 by the detection lens 12 having the same performance as the detection lens 9, and is second astigmatism generation means. It enters the cylindrical lens 13. This cylindrical lens 13 is the same lens as the cylindrical lens 10, and the X-axis direction is relative to the direction 200b (the direction orthogonal to the track direction in the image when the image of the information track of the optical disc is projected on the cylindrical lens 13). It is provided by rotating -45 degrees around the incident optical axis 104a. Therefore, the convergent light 106 is incident on the second photodetector 14 after being given astigmatism for detecting the focus error by the cylindrical lens 13.

Here, if the direction 210 of astigmatism is defined as the direction in which there is no lens action in the cylindrical lenses 10 and 13 (in FIG. 2, it is the X-axis direction and the focus is on the rear side), the convergent light 104 Astigmatism direction 210 and convergent light 10
The astigmatism directions 210 of 6 have a relationship of having an angle difference of 90 degrees with each other (in FIG. 2, the astigmatism directions 210 depend on the reflected light beams 104 and 106.
It is rotated 45 degrees in the opposite direction with respect to 0b).

Next, the astigmatism-provided light beam 104,
A method in which 106 enters the first and second photodetectors 11 and 14 respectively and a focus error signal is obtained from the outputs thereof will be described with reference to FIGS. 3 and 4.

FIG. 3 is a configuration diagram showing the configuration of the photodetectors 11 and 14, and FIG. 4 is a waveform diagram showing changes in the signals 108 and 110 of FIG. In FIG. 3, the light beam 104 given astigmatism enters the first photodetector 11 and enters into the four-division light receiving region 1
Spots 107 are formed on 1a, 11b, 11c and 11d. Here, the difference signal 108 obtained by subtracting the sum signal of the outputs of the light receiving areas 11a and 11c and the sum signal of the outputs of the light receiving areas 11b and 11d changes the shape of the spot 107 according to the distance between the objective lens and the disc ( For example, a substantially circular shape 107a when focused, and elliptical shapes 107b and 107 when defocused.
Therefore, as shown in FIG. 4A, an S-shaped signal is generated with respect to the defocus amount. In FIGS. 3 and 4, the case where the disc is far from the in-focus position at the time of defocus is referred to as out-focus, and the case where it is close is referred to as in-focus. The AF leakage of the signal 108 is as shown in FIG.

On the other hand, in FIG. 3, the light beam 106 having astigmatism is incident on the second photodetector 14 and spots 10 are formed on the four-divided light receiving regions 14a, 14b, 14c and 14d.
9 is formed. Here, the difference signal 110 obtained by subtracting the sum signal of the outputs of the light receiving regions 14a and 14c and the sum signal of the outputs of the light receiving regions 14b and 14d changes the shape of the spot 109 according to the distance between the objective lens and the disc ( For example, a substantially circular shape 109a when focused, and an elliptical shape 109 when defocused.
b, 109c), as shown in FIG. 4C, an S-shaped signal which is opposite to the signal 108 with respect to the defocus amount but has the same magnitude. However, at this time, the AF of the signal 110
The leakage is the same output as the signal 108 shown in FIG. 4B, as shown in FIG.

Therefore, the signal obtained by subtracting the signal 108 and the signal 110 becomes the focus error signal 111 in which the AF leakage is canceled and which is twice the output of the signals 108 and 110.

As described above, the optical head of the present invention can obtain a good focus error signal in which mixing of track crossing signals is reduced.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical head of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a structural diagram showing the structure of an optical head as a first embodiment of the present invention. In FIG. 1, the divergent light flux 99 emitted from the semiconductor laser 1 which is the light source is
The collimator lens 2 forms a parallel light flux 100. The parallel light flux 100, after passing through the first beam splitter 3,
The optical disk 5 is illuminated by the objective lens 4.

The reflected light 101 from the optical disk 5 passes through the objective lens 4, is reflected by the beam splitter 3, enters the second beam splitter 9, and is reflected light 103 and transmitted light 10.
It is divided into 5 minutes.

The parallel light beam 103 reflected by the second beam splitter 9 is converted into a convergent light beam 104 by the lens 9 as shown in FIG. 2, and the X-axis direction is rotated +45 degrees around the incident optical axis with respect to the direction 200b. Cylindrical lens 10 provided as
After being given astigmatism for focus error detection,
It is incident on the photodetector 11. Then, in the photodetector 11, according to the calculation shown in FIG. 3, when the spot on the optical disk has a defocus amount of zero (at the time of focusing), the output is almost zero, and a signal is generated when defocusing, a so-called S-shaped signal. Signal 108 is obtained.

On the other hand, the parallel light beam 105 transmitted through the second beam splitter 9 is, as shown in FIG.
Is a convergent light beam 106, and the X-axis direction is rotated by -45 degrees around the incident optical axis with respect to the direction 200b (rotated in the opposite direction to the cylindrical lens 10). After being given astigmatism, the photodetector 1
It is incident on 4. Then, in the photodetector 14, the signal 110 obtained by the calculation shown in FIG.
As shown in (d), the signal is an S-shaped signal that is the opposite of the signal 108 and the AF leakage is the same.

Thus, the signal 10 obtained from the photodetector 11
By subtracting 8 and the signal 110 obtained from the photodetector 14, it is possible to obtain a good focus error signal 111 in which AF leakage is canceled.

In the description of the present embodiment, the directions of rotation of the cylindrical lenses 10 and 13, the configuration of the photodetectors 11 and 14 and the method of detecting the signals 108 and 110 in the photodetectors 11 and 14 are as described above. Since it is the same as that described using FIG. 2, FIG. 3, and FIG.

Further, in this embodiment, the detection lens 9,
Although the light beams 12 reflected by the second beam splitter 9, that is, the light beams 103 and 105 are provided independently of each other, the present invention is not limited to this, and the light beams incident on the second beam splitter 9 (in the present embodiment, the light beams 101) may be provided with one lens, and the detection lens 9 and the detection lens 12 may be combined.

In the present embodiment, the cylindrical lens is used as the astigmatism generating means, but the invention is not limited to this. Another specific example of the astigmatism generation means will be described with reference to FIG.

In the lens 15 shown in FIG. 5, the entrance surface 15a and the exit surface 15b are cylindrical surfaces having different curvatures, and the direction of the lens action of each cylindrical surface (in FIG. 5, the entrance surface 15a is the X-axis direction, The incident surface 15b is orthogonal to the Y-axis direction. By using this lens 15, the detection lens 9 (detection lens 12) and the cylindrical lens 10 (cylindrical lens 13) shown in FIG. 2 can be replaced by one lens.

That is, in this specific example, as shown in FIG. 5, a parallel light beam 10 reflected by the second beam splitter 9 is used.
3, the lens 15 is moved in the X-axis direction 200b.
In contrast, the lens 15 is arranged so as to rotate by +45 degrees around the incident optical axis, and the lens 15 is rotated by -45 degrees around the incident optical axis with respect to the direction 200b in the X-axis direction in the parallel light beam 105 transmitted through the beam splitter 9. To arrange.

As a result, the detection lens 9 (detection lens 1
2) and the cylindrical lens 10 (cylindrical lens 13) are used, the signal 108 and the signal 110 obtained from the photodetector 11 and the photodetector 14 are subtracted to obtain the AF
Good focus error signal 111 with offset leakage
Can be obtained.

Further, as another specific example of the astigmatism generating means, the same effect can be obtained by using a toric lens in which the entrance surface 15a of the lens 15 is not a cylindrical surface but a spherical surface.

By the way, in addition to the focus error detection in the optical head, the tracking error detection and the optical disc 5 are performed.
It is necessary to detect the information signal. However, since these detections are essentially unrelated to the present invention, in the optical head of this embodiment, the description and description of the tracking error detection component, the information detection component, etc. are omitted.

Next, the optical head of the present invention including the tracking error detection will be described. FIG. 6 shows the second aspect of the present invention.
2 is a configuration diagram showing a configuration of an optical head as an example of FIG. In FIG. 6, the same symbols as those in FIG. 1 indicate the same parts.

The divergent light beam 99 emitted from the semiconductor laser 1 which is the light source becomes a parallel light beam 100 by the collimator lens 2. After passing through the first beam splitter 3, the parallel light flux 100 is irradiated onto the optical disc 5 by the objective lens 4.

The reflected light 101 from the optical disk 5 is reflected by the first beam splitter 3 via the objective lens 4 and is incident on a prism of an isosceles triangular prism (hereinafter referred to as a roof prism) 16 which is a light beam separating means. .

FIG. 7 shows the positional relationship between the shape of the roof prism 16 and the parallel light flux 101. 7, (a) is a front view of the roof prism 16 viewed from the direction A in FIG. 6,
FIG. 7B is a side view seen from the direction B in FIG. 6. As shown in FIG. 7, in the roof-type prism 16, the ridgeline 16a has a luminous flux of 1
01 is perpendicular to the optical axis 101a, and the direction of the ridge line 16a coincides with the direction 150 (the track direction in the image of the information track 5a of the optical disc 5 when the image is projected on the roof prism 16). Of the light beams 101, only a semicircular light beam 101b divided into two in a direction 151 orthogonal to the direction 150 is arranged. Therefore, of the light flux 101b incident on the roof-type prism 16, a semicircular light flux 101b is emitted from the light exit surfaces 16b and 16c.
Of the roof prism 16 is deflected in two directions (light fluxes 112a, 1a).
12b).

Then, the luminous fluxes 112a and 112b which are incident on the roof type prism 16 and are deflected, and the semicircular luminous flux 101c of the luminous flux 101 which is not incident on the roof type prism 16.
Respectively enter the second beam splitter 9 and are split into reflected light 113 and transmitted light 114. That is, the luminous flux 11
2a is reflected light 113a, transmitted light 114a, and luminous flux 112b
Is divided into reflected light 113b and transmitted light 114b, and the light flux 101c is divided into reflected light 113c and transmitted light 114c.

The parallel light beams 113a, 113b and 113c reflected by the second beam splitter 9 are converged by the lens 9 (convergent light beam 113a is a convergent light beam 115a, parallel light beam 113b is a convergent light beam 115b, and parallel light beam 113c is a convergent light beam 115c). ), And the astigmatism for focus error detection is given by the cylindrical lens 10 provided by rotating the X-axis direction by +45 degrees around the incident optical axis with respect to the direction 200b, and then, is applied to each photodetector 17. A signal 117 which is incident and used for focus error detection and a tracking error signal 118 are obtained.

On the other hand, the parallel light beams 114a, 114b, 114c which have passed through the second beam splitter 9 are reflected by the lens 12
Convergent beam 114 (parallel beam 114a is converged beam 116)
a, the parallel light flux 114b is the convergent light flux 116b, and the parallel light flux 1 is
14c is a convergent light beam 116c), and the X-axis direction is the direction 2
00b, a cylindrical lens 13 rotated by −45 degrees around the incident optical axis (rotated in the opposite direction to the cylindrical lens 10).
After being given astigmatism for focus error detection,
A signal 119 that enters the photodetector 18 and is used for detecting a focus error is obtained.

Next, a method of detecting the signal 117 and the tracking error signal 118 using the photodetector 17 and a method of detecting the signal 119 using the photodetector 18 will be described in detail with reference to FIG.

In FIG. 8, the convergent light beams 115a, 115b, and 115c, which are given astigmatism by the cylindrical lens 10, enter the first photodetector 17, respectively. That is, the light beam 115a has a spot 124a in the light receiving region 17e, the light beam 115b has a spot 124b in the light receiving region 17f, and the light beam 115c (a semicircular light beam 101c of the light beam 101 which does not enter the roof prism 16) is a central four-divided light receiving region. Spots 124c on 17a, 17b, 17c and 17d
(The spot shape at the time of focusing is substantially semicircular) is formed. Here, the difference signal 117 obtained by subtracting the sum signal of the outputs of the light receiving areas 17a and 17c and the sum signal of the outputs of the light receiving areas 17b and 17d changes the shape of the spot 124c according to the distance between the objective lens and the disc. Therefore, FIG. 4 (a)
Similar to the signal 108 indicated by, the S-shaped signal (the signal level is half) with respect to the defocus amount. At this time, the AF leakage with respect to the off-track amount of the signal 117 is similar to the signal 108 shown in FIG. 4B (the signal level is about half). Further, the tracking error signal 118 is obtained by the push-pull method that detects the difference in the diffracted light when the reading spot deviates from the information track 5a by subtracting the output of the light receiving area 17e and the output of the light receiving area 17f.

On the other hand, the convergent light beams 116a, 116b, and 116c, which are given astigmatism by the cylindrical lens 13, enter the second photodetector 18, respectively. That is, the light flux 116a
Is a spot 125a on the light receiving area 18e and a light beam 116b
Is a spot 125b on the light receiving area 18f and a light beam 116c.
(A semi-circular light flux 101c of the light flux 101 which does not enter the roof-type prism 16) is a central four-division light receiving region 18a,
Spots 125c (the spot shape at the time of focusing is a semicircle) are formed on 18b, 18c, and 18d, respectively. Here, the difference signal 119 obtained by subtracting the sum signal of the outputs of the light receiving regions 18a and 18c and the sum signal of the outputs of the light receiving regions 18b and 18d changes the shape of the spot 125a according to the distance between the objective lens and the disc. Therefore, as with the signal 110 shown in FIG. 4C, the signal 1 with respect to the defocus amount is
This is an S-shaped signal that is the opposite of 17 and has the same magnitude. However, at this time, the AF leakage with respect to the off-track amount of the signal 119 becomes the same output as the signal 117.

Therefore, the signal obtained by subtracting the signal 117 and the signal 119 becomes the focus error signal 126 in which the AF leak is canceled and which is twice the output of the signals 117 and 119. Further, by subtracting the output of the light receiving area 18e from the output of the light receiving area 18f, it is possible to obtain the tracking error signal by the push-pull method similarly to the tracking error signal 118 described above. It may also be obtained from two photodetectors 17, 18.

As described above, in the optical head of this embodiment, it is possible to obtain a good focus error signal in which the mixing of the tracking error signal and the track crossing signal is reduced.

In this embodiment, the push-pull method is used for detecting the tracking error, but the present invention is not limited to this. For example, the three-spot method which is widely used in the optical head for compact discs may be used. . In this case, the roof prism 16 is removed and replaced by 3
The diffraction grating used for the spot method may be arranged in the optical path from the semiconductor laser 1 to the first beam splitter 3. The detailed description is omitted here because it is essentially unrelated to the present invention.

Next, an optical head as a third embodiment of the present invention will be described. FIG. 9 is a configuration diagram showing a configuration of an optical head as a third embodiment of the present invention. In addition,
9, the same reference numerals as those in FIG. 1 indicate the same parts.

In FIG. 9, a semiconductor laser 1 which is a light source
The divergent light flux 99 emitted from the collimator lens 2 becomes a parallel light flux 100. The parallel light flux 100 is the first
After passing through the beam splitter 3, the objective lens 4 illuminates the optical disc 5.

The reflected light 101 from the optical disk 5 passes through the objective lens 4 and is reflected by the first beam splitter 3.
The light enters the second beam splitter 9 and is divided into reflected light 103 and transmitted light 105.

The parallel light beam 103 reflected by the second beam splitter 9 is made into a convergent light beam 104 by the lens 9 as shown in FIG. 2, and the X axis direction is rotated +45 degrees around the incident optical axis with respect to the direction 200b. Cylindrical lens 10 provided as
After being given astigmatism for focus error detection,
When the spot on the disc enters the photodetector 11 and the defocus amount is zero (at the time of focusing), the output is almost zero, and a signal is generated when defocusing, so-called S-shaped signal 108 is obtained.

On the other hand, the parallel light beam 105 that has passed through the beam splitter 9 is converted into a convergent light beam 127 by the lens 21 and enters the photodetector 22 to obtain a tracking error signal 132 and a signal 129 used for focus error detection.

Next, a method of detecting the signal 108, the tracking error signal 132, and the signal 129 using the photodetector 11 and the photodetector 22 will be described in detail with reference to FIG.

In FIG. 10, the convergent light beam 104 given astigmatism by the cylindrical lens 10 is incident on the four-divided light receiving regions 11a, 11b, 11c, 11d of the first photodetector 11 and the spot 107 (focused) is obtained. (The spot shape at the time is a semi-circle)
To form. Here, the sum signal of the outputs of the light receiving regions 11a and 11c, and the sum signal of the outputs of the light receiving regions 11b and 11d,
4 is subtracted from the difference signal 108, the shape of the spot 107 changes according to the distance between the objective lens and the disk.
As shown in (a), it becomes an S-shaped signal with respect to the defocus amount. At this time, the AF leakage with respect to the off-track amount of the signal 108 is as shown in FIG.

On the other hand, the convergent light beam 12 that has passed through the lens 21
Reference numeral 7 denotes the four-division light receiving areas 22a, 22 of the second photodetector 22.
It is incident on b, 22c and 22d to form a spot 128. Here, the difference signal 132 obtained by subtracting the sum signal 140 obtained by adding the outputs of the light receiving areas 22a and 22b and the sum signal 141 obtained by adding the outputs of the light receiving areas 22c and 22d has a read spot deviated from the information track 5a. The tracking error signal 132 is obtained by the push-pull method for detecting the difference in diffracted light at the time. Further, the light receiving areas 22b and 22
The difference signal 129 obtained by subtracting the sum signal 142 obtained by adding the output of d and the sum signal 143 obtained by adding the outputs of the light receiving regions 22a and 22c is the same as the signal 108 shown in FIG.
F leaks.

Therefore, by subtracting the signal 108 and the signal 129, a good focus error signal 130 with reduced AF leakage can be obtained (however, in the present embodiment, the signal 108 and the signal 129 are defocused). Since the AF leaks are slightly different from each other, the effect of reducing the AF leaks by subtracting the signal 108 and the signal 129 is slightly reduced).

As described above, the optical head of this embodiment can obtain a good focus error signal with reduced AF leakage.

In each of the above embodiments, it is desirable that the light utilization rate of the second beam splitter 9 be substantially equal to the reflectance and the transmittance. However, when the reflectance and the transmittance are different in the actual optical head, the gain adjustment may be performed in a circuit so that the light amounts detected by the two photodetectors are equal to each other.

In the optical head of each of the above embodiments, the information signal on the optical disk can be detected by using the light beam incident on the photodetector. Further, in order to detect the information signal of the magneto-optical disk, for example, the second beam splitter 9 is used as an analyzer (for example, a polarization beam splitter) for detecting polarized light, and the first beam splitter 3 and its analyzer are used. This can be detected by differentially detecting the outputs of the two photodetectors with a configuration of a differential detection system in which a half-wave plate is provided in the luminous flux (luminous flux 101).

Next, the optical head of the present invention for reducing the AF leakage by using the polarization converting means will be described.
FIG. 11 is a constitutional view showing the constitution of an optical head as a fourth embodiment of the present invention. In FIG. 11, the same symbols as those in FIG. 1 indicate the same parts.

In FIG. 11, the divergent light beam 99 emitted from the semiconductor laser 1 which is a linearly polarized light source becomes a parallel light beam 100 by the collimator lens 2. Parallel light flux 10
0 enters the half-wave plate 23 which is the polarization conversion means.

FIG. 12 shows the half-wave plate 23 and the parallel light flux 10.
The positional relationship with 0 is shown. FIG. 12 is a front view seen from the direction A in FIG. As shown in FIG. 12, the half-wave plate 2
3 is divided into four in a direction 131 (a track direction in the image of the information track 5a of the optical disc 5 when the image of the information track 5a is projected on the half-wave plate 23) of the light flux 100 and a direction 132 orthogonal to the direction. Is arranged so that only the luminous flux 100b is applied. Here, the half-wave plate 23 is arranged so as to rotate the polarization direction 160 of the incident light beam 100 by 90 degrees (the polarization direction 161 in FIG. 12).

Therefore, the luminous flux 1 that has passed through the half-wave plate 23
33 denotes a light beam 133b that is linearly polarized light with a polarization direction 161.
(The light flux 100b of the light flux 100 that has passed through the half-wave plate 23) and the light flux 133a that is linearly polarized light in the same polarization direction 160 as the light flux 100 (the light flux of the light flux 100 that does not pass through the half-wave plate 23). 100a) is a light beam having two different polarization states. This light beam 133 is generated by the first beam splitter 24 (the beam splitter 24 of this embodiment).
Is non-polarized and has a light utilization factor whose reflectance and transmittance are almost equal. ), The traveling direction is changed by the reflection mirror 35, and the disc rotation system 2 is changed by the objective lens 4.
The optical disc 5 mounted on the optical disc 6 (spindle motor or the like) is irradiated.

The reflected light beam 134 from the optical disk 5 passes through the objective lens 4 and is reflected by the first beam splitter 24, which is a light beam separating means shown in FIG.
It is incident on 6.

FIG. 13 shows a roof prism 16 and a parallel light beam 1.
The positional relationship with 34 is shown. FIG. 13 is a front view seen from the direction B in FIG. As shown in FIG. 13, in the roof prism 16, the direction of the ridge line 16a coincides with the direction 150 (the track direction in the image of the information track 5a of the optical disc 5 when the image is projected on the roof prism 16). Further, of the light flux 134, only the semicircular light flux 134b divided into two in the direction 151 orthogonal to the direction 150 is arranged to be applied. Therefore, the semicircular light flux 134b of the light flux 134 incident on the roof prism 16 is deflected in two directions by the roof prism 16 (136a, 13a).
6b).

The light beams 136a and 136b deflected by the roof prism 16 and the semicircular light beam 134c of the light beam 134 which does not enter the roof prism 16 are converged by the lens 9 (convergent light beam 136a is converged light beam). 137a, the parallel light beam 136b is the convergent light beam 137
b, the parallel light flux 134c is a convergent light flux 137c), and X
After the astigmatism for focus error detection is given by the cylindrical lens 10 provided by rotating the axial direction by +45 degrees around the incident optical axis with respect to the direction 200b, the photodetector 25 is provided.
Then, a focus error signal 138 and a tracking error signal 139 are obtained.

Next, a method of detecting the focus error signal 138 and the tracking error signal 139 using the photodetector 25 will be described in detail with reference to FIG.

In FIG. 14, the convergent light beams 137a, 137b, 137c to which astigmatism has been given by the cylindrical lens 10 are shown.
Respectively enter the photodetectors 25. That is, the luminous flux 1
37a forms a spot 140a on the light receiving area 25e and a light beam 1
37b forms a spot 140b in the light receiving area 25f and a light beam 1
37 c (a semicircular light flux 134 c of the light flux 134 that does not enter the roof-type prism 16) is a central four-division light receiving area 2
Spots 140c (the spot shape at the time of focusing is a semi-circle) are formed on 5a, 25b, 25c, and 25d, respectively.
Here, the focus error signal 138 is obtained by subtracting the sum signal of the outputs of the light receiving regions 24a and 24c and the sum signal of the outputs of the light receiving regions 24b and 24d.

The light flux used to obtain the focus error signal 138 is only the light flux 134c of the reflected light flux 134 from the disk 5. This light flux 134c is included in the light flux 133 entering the objective lens 4 in the direction 132 (the image of the information track 5a of the optical disk 5 is the half-wave plate 23).
Corresponds to a substantially semi-circular light beam (including a light beam 133b whose polarization direction is rotated 90 degrees by the ½ wavelength plate 23) divided in two when projected onto the image (direction orthogonal to the track direction in the image) To do. Here, the substantially semi-circular light flux has a direction 131 (the image of the information track 5a of the optical disk 5 is 1 /
Light flux 1 that is linearly polarized light in the polarization direction 161 in the track direction in the image when projected onto the two-wave plate 23
33b and a light flux which is a linearly polarized light having a polarization direction 160 orthogonal thereto is split into two. Therefore, the above-mentioned luminous flux 1
Similarly to the substantially semicircular light beam 34c, the light beam 34c is split into a light beam which is a linearly polarized light beam having a predetermined polarization direction and a light beam which is a linearly polarized light beam having a polarization direction orthogonal to the light beam.

By the way, the reading spot is the disk 5
Mixing of the track crossing signal into the focus error signal, which occurs when crossing over, that is, AF leakage, in other words, the change in the diffracted light when the reading spot deviates from the information track 5a leaks into the focus error signal. That's what it means. Here, the change of the diffracted light is caused by the interference effect of the diffracted light (for example, the 0th-order diffracted light and the + 1st-order diffracted light or the 0th-order diffracted light and the -1st-order diffracted light interfere with each other). However, for example, when the polarization directions of the 0th-order diffracted light and the + 1st-order diffracted light (or the 0th-order diffracted light and the -1st-order diffracted light) are orthogonal to each other, interference does not occur, so that the diffracted light does not change. .

That is, the above-mentioned light beam 134c is divided into two, that is, a light beam which is a linearly polarized light beam in a predetermined polarization direction and a light beam which is a linearly polarized light beam in a polarization direction orthogonal thereto, and the diffracted light beams hardly interfere with each other. The change in the diffracted light when the reading spot deviates from the information track 5a is reduced. Therefore, the focus error signal 13
In FIG. 8, the leak of the change of the diffracted light into the focus error signal generated when the reading spot traverses the disk 5, that is, the AF leak does not occur.

On the other hand, of the reflected light flux 134 from the disk 5, the light flux 134b is the light flux 13 incident on the objective lens 4.
Direction 3 out of 3 (information track 5 of optical disk 5
When the image of a is projected on the half-wave plate 23, it is divided into two substantially semicircular light beams in the direction orthogonal to the track direction in the image (the half-wave plate 23 has a polarization direction of 90 degrees). It does not include the rotated light flux 133b). Here, the substantially semicircular light flux is a light flux that is linearly polarized in the polarization direction 160. Therefore, the above-mentioned luminous flux 134
Similarly to the substantially semicircular light flux, b is also a light flux that is linearly polarized light in a predetermined polarization direction. Therefore, when the diffracted light beams interfere with each other in the light flux 134b and the reading spot deviates from the information track 5a. The change of the diffracted light is occurring. The luminous flux 134b is divided in the direction 150 (the track direction in the image of the information track 5a of the optical disc 5 when the image of the information track 5a of the optical disc 5 is projected on the roof type prism 16) in the roof type prism 16 and is then deflected respectively to receive light. 25e and the light receiving area 25f. Therefore, the tracking error signal 139 is obtained by the push-pull method that detects the difference in the diffracted light when the reading spot deviates from the information track 5a by subtracting the output from the light receiving area 25e and the output from the light receiving area 125c.

As described above, according to the optical head of the present embodiment, a good focus error signal in which mixing of track crossing signals is reduced and a tracking error signal by the push-pull method can be collectively detected by one photodetector.

In the optical head of this embodiment, the reflecting mirror 35, the objective lens 4, and the objective lens 4 are used as objectives in two axes of the focus direction (Z axis in FIG. 11) and the track direction (Y axis in FIG. 11). Two-dimensional actuator 36 for driving the lens position, and carriage 3 for mounting them
7 (this optical system is referred to as the movable part optical system in FIG. 11) using the access mechanism (control system and the like is not shown) of the optical disc 5 (Y in FIG. 11).
It is a separate type optical head that moves from an inner peripheral position to an outer peripheral position on an axis) and fixes other optical parts and the like (this optical system is referred to as a fixed part optical system in FIG. 11). The optical information device equipped with this separate type optical head has the advantages that the access operation is stable and the access speed is fast because it uses a good focus error signal in which the mixing of track crossing signals is reduced.

Further, in the optical head of this embodiment,
In order to prevent the change of the diffracted light when the reading spot is deviated from the information track 5a in the reflected light from the disk 5, a part of the light emitted from the semiconductor laser 1 is polarized by the ½ wavelength plate 23. It was carried out by rotating the polarization direction by 90 degrees (the deviation of the diffracted light would occur if deviated from 90 degrees), but the present invention is not limited to this. It suffices to change the polarization state of a part of the light flux incident on the disk 5 from that of the other area, and the polarization conversion means is not limited to the ½ wavelength plate 23.

[0074]

According to the present invention, in an optical head for reproducing or recording / reproducing an information signal on / from an optical information recording medium, a track crossing signal is mixed in a focus error signal caused by an aberration of an optical system ( AF leakage) can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an optical head as a first embodiment of the present invention.

FIG. 2 is a perspective view showing an optical system that allows a light beam separated by a second beam splitter to pass therethrough.

FIG. 3 is a configuration diagram showing a configuration of photodetectors 11 and 14 of FIG.

FIG. 4 is a waveform diagram showing changes in signals 108 and 110 in FIG.

FIG. 5 is a perspective view showing another specific example of the astigmatism generation means.

FIG. 6 is a configuration diagram showing a configuration of an optical head as a second embodiment of the present invention.

FIG. 7 shows the shape of the roof prism 16 shown in FIG.
It is a block diagram which shows the positional relationship with 01.

FIG. 8 is a configuration diagram showing a configuration of photodetectors 17 and 18 of FIG.

FIG. 9 is a configuration diagram showing a configuration of an optical head as a third embodiment of the present invention.

10 is a configuration diagram showing a configuration of photodetectors 11 and 22 of FIG. 9. FIG.

FIG. 11 is a configuration diagram showing a configuration of an optical head as a fourth embodiment of the present invention.

12 is a configuration diagram showing a positional relationship between the shape of the half-wave plate 23 and the parallel light flux 100 of FIG.

13 is a configuration diagram showing a positional relationship between the shape of the roof prism 16 of FIG. 11 and a parallel light flux 134.

14 is a configuration diagram showing a configuration of a photodetector 25 of FIG.

FIG. 15 is a configuration diagram showing a configuration of a detection optical system of a conventional optical head.

16 is a configuration diagram showing a configuration of a photodetector 8 of FIG.

FIG. 17 is an explanatory diagram illustrating mixing of a track crossing signal into a focus error signal.

FIG. 18 is an explanatory diagram showing a change in reflected light flux when the spot on the disk is off-track when the optical head has an aberration.

[Explanation of symbols]

1 ... Semiconductor laser, 3 ... First beam splitter, 4 ...
Objective lens, 5 ... Optical disk, 9 ... 2 beam splitter, 9, 12 ... Detection lens, 10, 13 ... Cylindrical lens, 11, 14 ... Photodetector.

Claims (10)

[Claims] 1. A laser element which emits a laser beam, and a laser beam which is emitted from the laser element and passes through a first beam splitter to be condensed to form a recording surface on which a track is formed in an optical information recording medium. An objective lens that irradiates a laser beam onto the recording surface and focuses the laser beam reflected on the recording surface, the laser beam focused by the objective lens, and the laser element and the optical information recording medium. And a second beam splitter for separating the laser light beam separated by the first beam splitter into a reflected light beam and a transmitted light beam, and a second beam splitter for separating the laser light beam separated by the first beam splitter. A first photodetector for receiving the reflected light flux (or the transmitted light flux) and converting it into a signal, and the transmission separated by the second beam splitter. In an optical head having at least a second photodetector that receives a light flux (or a reflected light flux) and converts it into a signal, in an optical path from the second beam splitter to the first photodetector, First astigmatism generating means for applying astigmatism to the reflected light beam (or transmitted light beam) separated by the second beam splitter is provided, and from the second beam splitter to the second photodetector An optical head, characterized in that a second astigmatism generating means for applying astigmatism to the transmitted light flux (or reflected light flux) separated by the second beam splitter is provided in the optical path of the above. 2. The optical head according to claim 1, wherein
An optical head, wherein a focus error signal is obtained from a signal obtained by conversion by the first photodetector and a signal obtained by conversion by the second photodetector. 3. The optical head according to claim 1, wherein the direction of the astigmatism given to the reflected light beam (or the transmitted light beam) by the first astigmatism generation means is the optical information recording medium. When the image of the track in is projected on the first astigmatism generating means, it is rotated about +45 degrees around the optical axis of the reflected light beam (or the transmitted light beam) with respect to the direction orthogonal to the track direction in the image. The direction of the astigmatism given to the transmitted light flux (or the reflected light flux) by the second astigmatism generation means is such that the image of the track on the optical information recording medium is the second astigmatism. An optical head which is a direction rotated by about −45 degrees around the optical axis of the reflected light flux (or transmitted light flux) with respect to the direction orthogonal to the track direction in the image when projected onto the generating means. De. 4. The optical head according to claim 1, 2, or 3, wherein the first beam splitter is connected to the second beam splitter.
When the image of the track on the optical information recording medium is projected with the laser light flux separated by the first beam splitter in the optical path to the beam splitter, the dividing line along the track direction in the image. The optical head is characterized in that a light beam splitting means for splitting is provided. 5. A laser element that emits a laser beam, and a recording surface on which an optical information recording medium has a track formed by condensing the laser beam emitted from the laser element and passing through a first beam splitter. An objective lens that irradiates a laser beam onto the recording surface and focuses the laser beam reflected on the recording surface, the laser beam focused by the objective lens, and the laser element and the optical information recording medium. And a second beam splitter for separating the laser light beam separated by the first beam splitter into a reflected light beam and a transmitted light beam, and a second beam splitter for separating the laser light beam separated by the first beam splitter. A first photodetector for receiving the reflected light beam (or the transmitted light beam) and converting it into a signal, and a light beam separated by the second beam splitter. In an optical head having at least a second photodetector that receives a light flux (or a reflected light flux) and converts it into a signal, in an optical path from the second beam splitter to the first photodetector, An astigmatism generating unit that applies astigmatism to the reflected light beam (or the transmitted light beam) separated by the second beam splitter is provided, and the first and second photodetectors are each a four-division light receiving region. A focus error signal is obtained from a signal obtained by conversion by the first photodetector and a signal obtained by conversion by the second photodetector, and the focus error signal is obtained by the second photodetector. An optical head characterized by obtaining a tracking error signal from a signal obtained by conversion. 6. A laser element which emits a laser beam, and a laser beam which is emitted from the laser element and passes through a beam splitter is condensed to emit light onto a recording surface on which a track is formed in an optical information recording medium. An objective lens for irradiating as a spot and condensing a laser light flux reflected on the recording surface, and an optical path connecting the laser light flux condensed by the objective lens with the laser element and the optical information recording medium. The beam splitter which is further separated, and the laser beam separated by the beam splitter are received,
An optical head having at least a photodetector for converting into a signal, and a polarization converting means for changing a polarization state of a part of a laser beam emitted from the laser element in an optical path from the laser element to the beam splitter. An optical head characterized by being provided with. 7. The optical head according to claim 6,
The polarization conversion means is composed of an optical rotator that rotates the polarization direction of the laser light flux by approximately 90 degrees, and the laser light flux emitted from the laser element is projected onto the polarization conversion means by an image of a track on the optical information recording medium. In the case of being divided by the dividing line along the track direction in the image, it is divided into approximately half, and one of the light fluxes obtained by the division is further divided by a dividing line along the direction orthogonal to the track direction. An optical head characterized by being divided into approximately half and arranged so as to pass only one light beam obtained by the division. 8. The optical head according to claim 6 or 7, wherein the polarization conversion means comprises a ½ wavelength plate. 9. The optical head according to claim 6, 7 or 8, wherein the laser light beam separated by the beam splitter is provided in the optical path from the beam splitter to the photodetector. 2. An optical head, characterized in that when a track image in is projected, a light beam splitting means is provided for splitting at a split line along the track direction in the image. 10. An information signal is reproduced by irradiating an optical information recording medium, a rotating system for rotating the optical information recording medium, and a laser beam as a light spot on a recording surface of the optical information recording medium. An optical information device comprising at least an optical head for recording and an access means for moving the optical head in an access direction of the optical information recording medium, wherein the optical head is the optical head. An optical information device using the optical head described in any one.