JP2000268434A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the residual of the wobbling signal contained in a reproducing signal by turning the optical axis of a magneto-optical analyzer around an incident optical axis so as to secure the balance between the noise levels included in the normal light and the abnormal light. SOLUTION: The light beam that is reflected on a disk 5 and has its polarizing surface turned by a magneto-optical signal is made incident on a polarizing beam splitter 4 via an objective lens 8 and a rising mirror 7. Then the light beam transmitted through the splitter 4 is separated into a normal light component, an abnormal light component and a synthetic component by a magneto- optical analyzer 9 and then received by a light receiving device 6. An RF signal, i.e., a reproducing signal is obtained by securing the difference between the normal and abnormal light components. Then the optical axis of the analyzer 9 is turned so as to secure the balance as much as possible between the noise levels included in the normal and abnormal light components. As a result, the noise level that is included in the RF signal obtained by the said difference can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical head for recording and reproducing information by projecting a light spot on an information track on a magneto-optical disk.

[0002]

2. Description of the Related Art In a conventional optical head for recording and reproducing information recorded on a magneto-optical disk including a magneto-optical signal such as MO and MD, the MO is an optical head described in the ISO standard as shown in FIG. 8), the major axis direction of the elliptical spot 40 on the disk is the direction of the information track 41, or as shown in FIG.
A method has been proposed in which the setting is made so as to be perpendicular to.

In the case of CDs and MDs, a method of setting the direction of the major axis of the elliptical spot 40 on the disk and the direction of the information track 41 at right angles is used as an optical head described in the standard.

[0004] Also, due to recent demands for miniaturization and weight reduction, an optical head for recording and reproducing a magneto-optical signal has been developed, and a finite optical system, that is, using a magneto-optical separation element in divergent light, Products that detect phenomena have begun to be released.

FIG. 9A is a configuration diagram showing an example of a conventional optical head for recording and reproducing a magneto-optical signal. In the example of FIG. 9A, the divergence of a light beam emitted from a light source 21 such as a semiconductor laser device is reduced by a convex lens 22, and the main beam (for generating a focus error, light After being separated into two sub-beams (for a tracking error signal) and two sub-beams (for a tracking error signal), they enter a polarizing beam splitter 24 as P-wave light, are reflected by a confronting mirror 25, are converged by an objective lens 26, and are converged by an objective lens 26
Incident on. At this time, the major axis direction and the polarization plane of the elliptical spot on the disk 27 are perpendicularly incident on the information track as shown in FIG. 8B, and are written on the perpendicular magnetization film in the information track at the time of reproduction. Rotation of the plane of polarization occurs corresponding to the magnetization direction for the information.

The reflected light from the magneto-optical disk 27 containing the information of the magneto-optical signal is collected again by the objective lens 26, reflected by the rising mirror 25, reflected by the polarization beam splitter 24 toward the light receiving element 30, After being separated by a magneto-optical analyzer 28 such as a three-beam Wollaston prism into ordinary light, extraordinary light (for magneto-optical reproduction signal), and a composite component of ordinary light component and extraordinary light component (for focus error signal), a focus error signal is obtained. The light enters the light receiving element 30 via the anamorphic lens 29 to generate astigmatism for detection.

[0007] The light beam incident on the light receiving element 30 is converted into an electric signal, and the magneto-optical signal information is extracted by taking the difference between the ordinary light component and the extraordinary light component.
Focus error control is performed by obtaining an astigmatism signal from a composite component of the ordinary light component and the extraordinary light component. The tracking error control is performed by comparing the intensities of the two sub beams separated by the diffraction grating.

FIG. 9B is a block diagram showing an example of a reproducing optical head such as a CD which does not handle a magneto-optical signal. In this head, the order of the light beams emitted from the light source 31 is reversed, but the main beam (for the focus error signal and the reproduction signal) and the two sub-beams (for the tracking error signal) are also formed by the diffraction grating 32 as described above. Then, the light passes through a convex lens 33, is reflected by a flat beam splitter 34 in this example, is reflected by a rising mirror 35, is focused through an objective lens 36, and is incident on an optical disk 37. The upper pit receives intensity modulation according to the information. At this time, the major axis direction of the elliptical spot on the optical disk 37 is incident at an angle according to the set polarization direction of the semiconductor laser.

In Japanese Patent Publication No. 5-8499, the angle θ of the major axis of the elliptical spot 40 with respect to the direction of the information track 41 is set to about 45 degrees, as shown in FIG. Japanese Patent Publication No. 5-22977 discloses an example in which the angle is 30 degrees.

The reflected light from the optical disk 37 containing the reproduction information is collected again by the objective lens 36, reflected by the rising mirror 35 and incident on the flat beam splitter 34, where the light is non-parallel. By arranging the optical axis at an angle in the light beam, astigmatism for a focus error signal is generated during this passage. Thereafter, the light enters the light receiving element 38 and is converted into an electric signal of a tracking error signal and a focus error signal in the same manner as described above. at the same time,
The intensity modulation of the main beam by the pits on the information track is converted into an electric signal, and a reproduced signal is obtained.

[0011]

However, FIG.
In the conventional optical head for magneto-optical signals shown in FIG. 1A, first, an anamorphic lens 29 must be used to obtain a focus error signal, and the number of components is increased. Second, since the major axis direction of the elliptical spot on the disk is perpendicular to the information track, the resolution of the reproduced signal is increased, but there is a problem that crosstalk from an adjacent track is liable to occur.

On the other hand, like an optical head for a CD which does not handle a magneto-optical signal as shown in FIG. 9 (B), a flat plate which also has an action of generating astigmatism for generating a focus error signal. When the beam splitter 34 is used, the number of components is small, the cost is low, and the entire optical head can be made small. In addition, the major axis direction of the elliptical spot on the disk can be set to a direction advantageous for the resolution of the reproduction signal and the crosstalk. That is, if the major axis direction of the elliptical spot is set to be oblique to the information track direction, the length of the elliptical spot in the information track direction will be shorter than when the major axis direction of the elliptical spot is set to the information track direction. The resolution can be shortened, so that a decrease in resolution can be prevented. Also, if the major axis direction of the elliptical spot is set to be oblique to the information track direction, compared to the case where the major axis direction of the elliptical spot is set perpendicular to the information track direction, the elliptical spot in the information track direction will be compared. The length can be shortened, and crosstalk can be reduced.

It is conceivable to apply the optical head which does not handle the magneto-optical signal of FIG. 9B having such an advantage to the optical head for the magneto-optical signal of FIG. 9A. However, in an optical head for recording / reproducing a magneto-optical signal, a reproducing signal is obtained by rotating a polarization plane of a light beam by a small angle by an information magnetic signal on the magneto-optical disk. It is necessary to input a light beam, and the beam splitter 34 shown in FIG. 9B is considered from the apparent increase of the rotation of the polarization plane, the necessity of improving the efficiency, and the C / N plane of the magneto-optical signal. It is often practiced to use a polarizing beam splitter to guide a linearly polarized light beam onto a magneto-optical disk. FIG.
The configuration of the optical head of (B) is applied to an optical head for recording and reproducing a magneto-optical signal, and as a beam splitting means on a flat plate,
When a polarizing beam splitter is used, the light beam is reflected as S-polarized light by the polarizing beam splitter, and impinges obliquely (for example, at 45 degrees) on an information track on the magneto-optical disk.

In the case where astigmatism is generated by the flat beam splitter 34, in FIG. 9B, when the left-right direction of the drawing is the X direction and the vertical direction of the drawing is the Y direction, the light beam is flat. When passing through the beam splitter, beam deformation due to astigmatism occurs in the X and Y directions.
When astigmatism is used as a focus error signal, as is well known, in order to prevent a control error with respect to the swinging direction of the beam on the disk, the direction of the dividing line of the four-divided light receiving element is used. One must be parallel.
As a result, the direction in which astigmatism occurs must be ± 45 degrees with respect to the information tracks on the disk.

That is, the arrangement of the optical system using the plate-shaped beam splitter 34 which also has the function of causing astigmatism is subject to restrictions in optical design, and is reflected by the beam splitter accordingly, and The S-polarized light guided on the disk is obliquely incident on the information track on the magneto-optical disk.

By the way, when reproducing a magneto-optical signal,
As described in the conventional example of FIG. 9A, the magneto-optical signal information is extracted by taking the difference between the ordinary light component and the extraordinary light component. If the polarization plane is non-parallel and non-perpendicular to the information track, the frequency component of the guide groove is asymmetrically mixed into the ordinary light component and the extraordinary light component separated by the analyzer, and the difference between the ordinary light component and the extraordinary component It becomes noise with respect to the reproduced signal obtained by the movement, and deteriorates the characteristics. Here, the frequency component of the guide groove is a constant frequency (about 22.05 kHz in MD) for generating an address signal on the magneto-optical disk.
z), which is a wobble signal and a magneto-optical signal (about 200 kHz).
z to 720 kHz).

A description will now be given of the degradation of the reproduced signal when the plane of polarization of the light beam is non-perpendicular and non-parallel to the information track. FIG. 10 shows a case where, as shown in FIG. 8C, the major axis direction of the elliptical spot, that is, the direction of the light beam deflection surface and the information track direction are non-perpendicular and non-parallel (θ = 45 degrees). It shows the detrack characteristic, that is, the level of the wobble signal with respect to the deviation (horizontal axis) of the spot 41 on the disk from the information track 41. In FIG. 10, a represents the level of the wobble signal in the ordinary light separated by the magneto-optical analyzer 28, b represents the level of the wobble signal in the extraordinary light, and c represents the difference between the ordinary light and the extraordinary light in the RF signal. This is the residual of the remaining wobble signal.

FIG. 11 shows a case where the polarization plane of the light beam on the disk is parallel or perpendicular to the information track as shown in FIG. 8 (A) or FIG. 8 (B) (θ = 0). Shows the fluctuation of the wobble signal level with respect to the detrack of the frequency component of the guide groove in the ordinary light component (curve d), the extraordinary light component (curve e), and the RF signal (curve f), respectively. .

As shown in FIGS. 10 and 11, when the plane of polarization of the light beam on the disk is non-parallel and non-perpendicular to the information track 41, the guide in the ordinary light component and the extraordinary light component is used. Since the frequency component of the groove becomes asymmetric, the frequency component of the guide groove in the reproduction signal obtained by the difference between the ordinary light component and the extraordinary light component becomes large, and becomes noise with respect to the reproduction signal, and the reproduction is accordingly performed. The signal quality also degrades.

As described above, according to the conventional configuration, in order to prevent the deterioration of the reproduction signal, the direction of the polarization plane of the light beam on the magneto-optical disk is restricted. It is not easy to take measures such as using a plate-shaped polarizing beam splitter having the function of providing the optical system, and there is a problem that the degree of freedom in designing an optical system such as component selection and arrangement is low.

The present invention has been made in view of the above-mentioned problems of the prior art,
An object of the present invention is to provide a magneto-optical recording / reproducing head which can increase the degree of freedom in selecting and arranging components of an optical system without deteriorating a magneto-optical reproducing signal and which can be reduced in size and cost. .

[0022]

According to a first aspect of the present invention, there is provided an optical head comprising: a light source for generating a light beam having a polarization plane; and a light beam emitted from the light source is applied to a magneto-optical disk including an information track comprising a guide groove. An optical head comprising: an optical unit for guiding the light beam; a condensing unit for converging the light beam on the magneto-optical disk; and a magneto-optical analyzer for separating the light beam from the magneto-optical disk into ordinary light and extraordinary light. The directions of the polarization planes of the information tracks on the magneto-optical disk and the light beam incident on the magneto-optical disk are non-parallel and non-perpendicular, and the optical axis of the magneto-optical analyzer is centered on the incident optical axis. The noise is rotated so as to balance the noise levels included in the ordinary light and the extraordinary light.

As described above, according to the present invention, the noise component included in the difference between the ordinary light and the extraordinary light is reduced by rotating the magneto-optical analyzer, and the frequency of the guide groove mixed asymmetrically into the ordinary light and the extraordinary light is reduced. The component can be adjusted so as not to cause noise at the time of differential operation, and the reproduction signal characteristics can be improved even if the direction of the polarization plane is not parallel or non-perpendicular to the information track. Therefore, the degree of freedom in selecting and arranging the components of the optical system can be increased, and the size and cost can be reduced.

According to a second aspect of the present invention, in the optical head according to the first aspect, the magneto-optical analyzer has a mechanism for adjusting a rotation angle about the incident optical axis.

As described above, by providing a mechanism for adjusting the rotation angle of the magneto-optical analyzer, an optimum angle adjustment can be performed.

According to a third aspect of the present invention, in the optical head according to the first or second aspect, a flat plate beam splitter for generating astigmatism for giving a focus signal is provided as the beam splitter.

As described above, when the flat beam splitter is used as the light beam splitting means, the light beam splitting means can be realized with a cheaper and simpler structure than the angular beam splitter. In addition, since astigmatism is generated by the flat beam splitter, an anamorphic lens that generates astigmatism is not required.

[0028]

FIG. 1 is a structural view showing an embodiment of an optical head for magneto-optical recording and reproduction according to the present invention, and FIG. 2 is a perspective view thereof. 1 and 2, reference numeral 1 denotes a semiconductor laser device provided as a light source, and 2 denotes a light beam emitted from the semiconductor laser device 1 as a main beam (for a focus error signal and for a magneto-optical signal) and a sub beam (for a tracking error signal). (For signal). Reference numeral 3 denotes a convex lens for reducing the divergence of the light beam emitted from the diffraction grating 2. Reference numeral 4 denotes a polarization beam splitter that reflects the light beam emitted from the convex lens 3 toward the magneto-optical disk 5 and transmits the reflected light from the magneto-optical disk 5 toward the light receiving device 6. Reference numeral 7 denotes a rising mirror for reflecting the light beam from the polarizing beam splitter 4 so as to be incident on the magneto-optical disk 5 at a right angle. Reference numeral 8 denotes an objective lens. Reference numeral 9 denotes an ordinary light component, an extraordinary light component, and an extraordinary light component. This is a magneto-optical analyzer that separates a light component into a combined component.

In this head, the semiconductor laser device 1
Is split by the diffraction grating 2 into the main beam and the sub-beam, and the divergence is reduced by the convex lens 3 to be incident on the flat polarizing beam splitter 4. In the polarization beam splitter 4, the incident light beam is substantially reflected as an S-wave, reflected by the rising mirror 7, condensed by the objective lens 8, and irradiated perpendicularly to the disk 5 as an elliptical spot on the disk 5. The light beam whose polarization plane is rotated by the magneto-optical signal and reflected by the disk 5 is incident on the polarization beam splitter 4 via the objective lens 8 and the rising mirror 7, and the light beam transmitted therethrough is converted into a magneto-optical analyzer. At 9, an ordinary light component, an extraordinary light component, and a composite component thereof are separated and received by the light receiving device 6. Light receiving device 6
The components received at are input to an arithmetic circuit (not shown) to obtain a difference between the ordinary light component and the extraordinary light component, thereby obtaining an RF signal as a reproduction signal. Further, the combined component is used as a focus control signal.

As shown in FIG. 1, the center axis 10a of the spindle motor 10 for rotating the disk 5 and the objective lens 8
(I.e., a direction perpendicular to the direction of the information track 41 formed by a groove) connecting the central axis 8a of the optical axis 12a, and the optical axis 12 that passes through the polarizing beam splitter 4 and reaches the passive device 6.
Let ψ be the angle formed by = 90 ° −θ =
The components are arranged such that 90 ° −45 ° = 45 °. Therefore, the direction of the elliptical spot in this case is 45 degrees shown in FIG. 8C. That is, FIG.
The inclination angle θ of the elliptical spot 40 with respect to the information track 41 shown in (C) is 90 = ψ with respect to the component arrangement angle ψ shown in FIG.

The center axis 8a of the objective lens 8 fluctuates during operation of the optical head. The center axis 8a is the center of the fluctuation, that is, the center axis determined by design. As described above, in the polarization beam splitter 4, the light beam is substantially S
Since the light beam is set to be reflected as a wave, it is desirable that the polarization plane of the light beam emitted from the light source 1 be parallel to the S wave reflected by the polarization beam splitter 4 from the viewpoint of efficiency. That is, in FIG. 1, it is desirable to set the direction perpendicular to the paper surface.

In the present invention, by rotating the optical axis of the magneto-optical analyzer 9, the noise levels contained in the ordinary light component and the extraordinary light component are made as equal as possible, whereby the RF obtained by the differential is obtained. This is to reduce the noise level included in the signal.

Next, the magneto-optical analyzer 9 used in the present invention.
An example disclosed in Japanese Patent Application Laid-Open No. 10-90518 will be described with reference to FIGS. FIG. 3 is a perspective view of the magneto-optical analyzer 9.
First crystal body 51, second crystal body 52, third crystal body 5
3 are joined. Each of these crystals 51 to 53 is a parallel plate made of an optically anisotropic material exhibiting birefringence. Although lithium niobate is used as the crystals 51 to 53, an optically anisotropic material such as calcite, rutile, and quartz may be used.

FIG. 4A is an explanatory diagram for explaining a polarization separation distance in an optically anisotropic material, and shows one surface of a parallel plate (crystal 50) having a thickness t made of an optically anisotropic material. 3 shows a light beam 80 perpendicularly incident from the light source, and an ordinary light beam 80a and an extraordinary light beam 80b emitted from the other surface after being polarized and separated. Here, d in the figure indicates a polarization separation distance in a plane including the optical axis 60 of the crystal 50 of the optically anisotropic material and the optical axis of the light beam 80. Α is an angle between the optical axis 60 of the crystal 50 and the optical axis of the light beam 80. The separation distance d between the ordinary ray 80a and the extraordinary ray 80b depends on the thickness t of the crystal 50, the refractive index felt by the ordinary ray, the refractive index felt by the extraordinary ray, and the angle α.

The direction of the optical axis in FIG. 3 will be described with reference to FIG. As shown in FIG. 4A, the direction of the optical axis is such that the X axis and the Y axis are in a plane parallel to the incident surface 71, and the Z axis is the normal direction of the incident surface 71. (0 degree <α <80 degrees) and an angle β (0 ° ≦ β ≦ 180 degrees in a counterclockwise direction) between the projection 60a of the optical axis on the XY plane and the X axis.

In FIG. 3, the angle β between the projection 60a of the optical axis 60 on the XY plane of the first crystal body 51 and the X axis,
Similarly, β of the second crystal 52 is β1, and the third crystal 53
Let β be β2, these angles and the optical axis 6
The angle α between 0 and the Z axis is set as follows. The direction of the optical axis 61 of the first crystal body 51 (α, β) = (4
5 °, O °) Direction (α, β1) of optical axis 62 of second crystal body 52 =
(45 °, 45 °) The direction (α, β2) of the optical axis 63 of the third crystal body 53 =
(45 °, 135 °) FIGS. 5 and 6 are views showing a process in which a light beam incident on the magneto-optical analyzer 9 is separated into three light beams. FIG. 5 is a perspective view showing a polarization separation process, and FIG. 6 is a view showing the respective surfaces ((A) of the incident surface 71 and (B) of the first crystal body 51 and the second crystal body 52) of the magneto-optical analyzer 9. The joining surface 72, (C) shows the joining surface 73 between the second crystal body 52 and the third crystal body 53, and (D) shows the polarization separation on the emission surface 74).

In FIG. 6A, reference numeral 91 denotes the direction of linearly polarized light of the light beam (indicated by 81 in FIG. 5) incident on the magneto-optical analyzer 9, and δ (counterclockwise, 0 ° ≦ δ ≦ 18
0 °) is the angle between the direction of the linear polarization plane of the light beam and the optical axis 61a of the first crystal body 51. Β1 is the optical axis 61a of the first crystal 51 and the second crystal 52
Represents the angle between the optical axis 62a and the optical axis 62a, and β2 represents the optical axis 61a of the first crystal body 51 and the optical axis 63 of the third crystal body 53.
The angle formed with a is shown, and β2 = β1 + 90 °.

FIG. 6B shows the polarization separation at the joint surface 72 between the first crystal body 51 and the second crystal body 52 in FIG.
As shown in this figure, the light beam that travels through the first crystal body 51 and reaches the bonding surface 72 has a polarization plane of the first crystal body 51.
Extraordinary ray 9 parallel to ordinary ray 92 perpendicular to optical axis 61a
3 is separated along the optical axis 61a.

That is, the light beam incident from P11 in FIG. 5 is separated into an ordinary ray and an extraordinary ray in the first crystal body 51.
The ordinary ray goes straight and reaches P21 on the joining surface 72, and the extraordinary ray refracts and reaches P22 on the joining surface 72. Therefore, the light is split into two light beams at the bonding surface 72.

FIG. 6C shows the polarization separation at the junction 73 between the first crystal body 51 and the second crystal body 53 in FIG.
As shown in this figure, of the light beam that has traveled into the second crystal body 52 and has reached the bonding surface 73, the light beam that has traveled as an ordinary ray in the first crystal body 51 has a polarization plane The light beam that has been separated into an ordinary ray 94 and an extraordinary ray 95 perpendicular to the optical axis 62a of the second crystal body 52 and has traveled through the first crystal body 51 as an extraordinary ray 93 has a polarization plane of the second crystal body 52. Along the optical axis 62a into an extraordinary ray 97 parallel to the ordinary ray 96 perpendicular to the optical axis 62a.

That is, in FIG. 5, the light beam that has reached P21 is separated into an ordinary ray and an extraordinary ray in the second crystal body 52, and the ordinary ray travels straight and reaches P31 on the bonding surface 73.
The extraordinary ray is refracted and reaches P32 on the joint surface 73. The light beam that has reached P22 is separated into an ordinary ray and an extraordinary ray in the second crystal body 52.
3 to P33, the extraordinary ray is refracted and
Reach 34. Therefore, the light is split into four light beams at the bonding surface 72.

FIG. 6D shows the polarization separation at the emission surface 74 of FIG. In the magneto-optical analyzer of this example, β2
= Β1 + 90 °, the light beam that has traveled in the second crystal 52 as an ordinary ray travels in the third crystal 53 as an extraordinary ray. Therefore, the ordinary ray 9 of the joint surface 73
4 is an extraordinary ray 94 ′ at the exit surface 94,
Extraordinary ray 95 becomes an ordinary ray 95 ′ at the exit surface 94,
The ordinary ray 96 of the joining surface 73 is changed to the extraordinary ray 9 at the exit surface 95.
6 ′, and the extraordinary ray 97 of the joint surface 73 is
Becomes an ordinary ray 97 '.

That is, in FIG. 5, the light beam (ordinary ray 94 in FIG. 6C) that has reached P31 is refracted at the joint surface 73, travels through the third crystal 53 as an extraordinary ray, and exits. The light beam that reaches P41 on the surface 74 and reaches P32 (the extraordinary ray 95 in FIG. 6C) travels as an ordinary ray in the third crystal body 53 and reaches P42 on the emission surface 74,
Light beam reaching P33 (ordinary ray 96 in FIG. 6C)
Are refracted at the bonding surface 73, travel as extraordinary rays in the third crystal body 53, reach P42 on the emission surface 74, and P34
The light beam (the extraordinary ray 97 in FIG. 6 (C)) that has reached the point (A) travels through the third crystal body 53 as an ordinary ray and reaches P43 on the emission surface 74. Here, the light beam that has reached P32 (the extraordinary ray 95 in FIG. 6C) and the light beam that has reached P33 (the ordinary ray 96 in FIG. 6C) both exit from P42 on the exit surface 74. Therefore, the light beams emitted from the magneto-optical analyzer are three light beams emitted from P41, P42, and P43, and are 82, 83, and 84. Of these, the light beam 82 corresponds to an ordinary ray that travels straight through the first crystal body 51, the light beam 84 corresponds to an extraordinary ray in the first crystal body 51, and the light beam 83 corresponds to a composite component thereof. .

In order for the light beam reaching P32 and the light beam reaching P33 to both exit from P42 on the exit surface 74, the polarization separation distance in the first crystal body 51 must be d1, and the second The polarization separation distance d2 in the crystal 52,
The polarization separation distance d3 in the third crystal body 53 needs to satisfy the following expression.

D1 = d2 + d3 That is, when a triangle having three sides d1, d2, and d3 is considered, the angle between the side d1 and the side d2 is β1
Then, the angle between the side d2 and the side d3 becomes a right-angled right triangle. Note that the light beam P41 emitted from the magneto-optical analyzer,
The separation distance between P42 and the separation distance between P42 and P43 are equal to d1.

The first, second, and third crystal bodies 51, 5
Considering the polarization separation at 2, 53 as a vector,
Vector d1 shown in polarization separation in first crystal body 51
(Displacement from P21 to P22), a vector d2 (P31 to P32) indicating polarization separation in the second crystal body 52
) And a vector d3 (displacement from P33 to P32) indicating polarization separation in the third crystal body 53 satisfies the following expression. (Vector d1) + (vector d3) = (vector d
2) Here, the separation ratio a: c of the light beams emitted from P41 and P43 is obtained by a: c = sin ² δ: cos ² δ. This separation ratio (a: c) changes according to the rotation of the plane of polarization of the light beam (change in δ). Therefore, when used in an optical head, rotation of the polarization plane can be detected by detecting a change in the separation ratio (a: c) of the light beam.

If the separation ratio of the light beams emitted from P41 and P42 is a: b, the separation ratio a: b is determined by the angle β1. Therefore, by changing β1, the separation ratio between the light beam for signal reproduction (P41, P43) and the light beam for focus control (P42) when used in an optical pickup device can be adjusted.

The direction (α, β) of the optical axis 61 of the first crystal 51 is set to (−45 °, O °), and the other crystal 5
Even if the directions of the optical axes 62 and 63 of 2, 53 are the same as described above, similar results can be obtained.

Using such a magneto-optical analyzer 9, the optical axes 61 and 62 are rotated about the optical axis (the Z axis).
By rotating 63, the ordinary light component (light beam P4
1) and the amount of the wobble signal mixed in the extraordinary light component (corresponding to the light beam P43), and the balance is reduced to reduce the residual of the wobble signal in the RF signal due to the differential.

The perspective view of FIG. 7A and the sectional view of FIG. 7B show an example of a mechanism for adjusting the rotation angle of the magneto-optical analyzer 9. The mounting member 14 is rotatably fitted in a cylindrical holder 15, and is fixed to the mounting member 14.
The adjusting member 16 provided on the holder 15 is projected from the groove 17 provided on the holder 15, and the magneto-optical analyzer 9 is rotated about the optical axis Z by the adjusting member 16. The shaft is rotated.

Here, as shown in FIG. 8B, when the major axis direction of the elliptical spot 40, that is, the direction of the polarization plane and the direction of the information track 41 are 45 degrees, a mirror without a wobble signal and a magneto-optical signal is provided. The normal light when the magneto-optical analyzer 9 is rotated several degrees and the abnormal light when the intensity of the ordinary light and the extraordinary light become equal when the focus servo is applied to the disk having The level of the wobble signal for each detrack amount of light is shown by curves g and h in FIG. 12, and the level of the wobble signal in the RF signal is shown by a curve i.

FIG. 13 summarizes the residuals of the wobble signal in the RF signals of FIGS. 10 and 12, and shows the jitter (fluctuation in the time of the electric signal) before and after rotating the magneto-optical analyzer 9 several times. Are shown in comparison. As shown in FIG. 13, due to the rotation of the magneto-optical analyzer 9, the residual of the wobble signal in the RF signal becomes asymmetric before and after the rotation (c) for the positive and negative detracks with respect to the detrack. In the latter case (i), the shape becomes symmetrical, and the detrack margin is expanded. As a result, the jitter (k) characteristic after rotation becomes better than the jitter (j) before rotation, and the detrack margin of jitter can be expanded.

FIG. 14 is a diagram showing the relationship between the rotation angle of the magneto-optical analyzer 9 and the jitter in one experimental example. In this case, if the rotation angle exceeds 0 ° and is 7 ° or less,
The jitter characteristic can be improved from the rotation angle of 0 degree, and the rotation angle is more preferably set to about 2 degrees to 5 degrees, and still more preferably set to 3 degrees to 4 degrees.

The rotation of the magneto-optical analyzer 9 is not limited to that having the rotation angle adjusting mechanism shown in FIG.
A configuration in which the rotation angle is fixed to a preset rotation angle can also be adopted.
As a configuration for fixing at the set angle, the housing of the magneto-optical analyzer 9 is fixed to the inclined mounting surface of the optical head, or the optical axis of the magneto-optical analyzer is pressed against the housing. It is possible to adopt a configuration such as inclining with respect to a plane.

As shown in FIGS. 1 and 2, when the flat beam splitter 4 is used, it is much cheaper (about 1/3 or less) than the cube type beam splitter, and furthermore, the astigmatism for giving a focus signal is provided. Since an aberration can be generated, an anamorphic lens is not required, and the cost of the entire system can be significantly reduced.

In the present invention, not only the parallel plate element shown in FIGS. 3 to 6 but also a three-beam Wollaston prism can be used as the magneto-optical analyzer 9.

[0057]

According to the first aspect, the information tracks on the magneto-optical disk and the plane of polarization of the light beam incident on the magneto-optical disk are non-parallel and non-perpendicular, and the optical axis of the magneto-optical analyzer is Since the rotation is performed about the incident optical axis so that the noise levels included in the ordinary light and the extraordinary light are balanced, the residual of the wobble signal in the reproduced signal can be reduced. As a result, jitter,
Reproduction signal characteristics such as a block error rate can be improved. Even if the plane of polarization is not parallel or non-perpendicular to the information track, good signal characteristics can be obtained.
The degree of freedom in selecting and arranging optical components can be increased,
The optical head can be reduced in size and cost.

According to a second aspect of the present invention, in the optical head according to the first aspect, since the magneto-optical analyzer has a mechanism for adjusting a rotation angle about the incident optical axis, an optimal angle adjustment can be performed. it can.

The optical head according to the third aspect has a flat plate beam splitter for generating astigmatism that gives a focus signal as the beam splitter according to the first or second aspect, so that the cost is lower than that of the angular beam splitter. The light beam splitting means can be realized with a simple configuration. In addition, since astigmatism is generated by the flat beam splitter, an anamorphic lens that generates astigmatism is not required, and a more inexpensive optical head can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical head for magneto-optical recording and reproduction according to the present invention.

FIG. 2 is a perspective view of the optical head of FIG.

FIG. 3 is a perspective view showing a configuration of an example of a magneto-optical analyzer used in the present invention.

4A is an explanatory diagram of an optical axis in an optically anisotropic crystal of the magneto-optical analyzer of FIG. 3, and FIG. 4B is an explanatory diagram illustrating a polarization separation distance.

FIG. 5 is a perspective view showing a polarization separation process in the magneto-optical analyzer of FIG.

FIG. 6 is an explanatory diagram for explaining the operation principle of the magneto-optical analyzer of FIG. 3;

FIG. 7A is a perspective view showing an example of a rotation adjusting mechanism of the magneto-optical analyzer according to the present invention, and FIG. 7B is a sectional view thereof.

FIGS. 8A, 8B, and 8C are explanatory diagrams showing states in which the angle formed by the elliptical spot with respect to the information track is parallel, perpendicular, and inclined.

9A is a configuration diagram illustrating an example of a conventional optical head for magneto-optical recording and reproduction, and FIG. 9B is a configuration diagram illustrating an example of a conventional optical head for CD.

FIG. 10 is a correlation diagram showing a wobble signal level for a detrack when an elliptical spot is inclined with respect to an information track.

FIG. 11 is a correlation diagram showing a wobble signal level for a detrack when an elliptical spot is parallel or perpendicular to an information track.

FIG. 12 is a correlation diagram showing a wobble signal level for a detrack when the elliptical spot is inclined with respect to the information track and the magneto-optical analyzer is rotated by a predetermined angle.

FIG. 13 is a detrack characteristic diagram comparing the characteristics of FIGS. 10 and 12, and showing the jitter characteristics in comparison with the present invention and the conventional example.

FIG. 14 is a diagram showing a change in jitter with respect to a rotation angle of a magneto-optical analyzer in the present invention.

[Explanation of symbols]

1: semiconductor laser device, 2: diffraction grating, 3: convex lens,
4: polarizing beam splitter, 5: magneto-optical disk, 6:
Light receiving device, 7: rising mirror, 8: objective lens, 9: magneto-optical analyzer, 10: spindle motor, 40: elliptical spot, 41: information track, 51 to 53: crystal, 60
To 63, 61a to 63a: optical axis, 71: incident surface, 7
2, 73: bonding surface, 73: emission surface, 80: light beam, 8
0a: ordinary ray, 80b: extraordinary ray, 81 to 84: light beam, 91: direction of polarization plane, 92, 94, 95 ', 96,
97 ': ordinary ray, 93, 94', 95, 96 ', 97:
Extraordinary ray

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Sayuri Terasaki 1-1-13 Nihonbashi, Chuo-ku, Tokyo T-D Corporation F-term (reference) BA01 BB05 EC06 JA09 JA24

Claims (3)

[Claims] A light source for generating a light beam having a plane of polarization; an optical means for guiding the light beam emitted from the light source to a magneto-optical disk including an information track comprising a guide groove; An optical head having a focusing means for converging on a disk, and a magneto-optical analyzer for separating a light beam from the magneto-optical disk into ordinary light and extraordinary light, comprising: an information track on the magneto-optical disk; The plane of polarization of the light beam incident on the disk is non-parallel, non-perpendicular, and the optical axis of the magneto-optical analyzer, with the incident optical axis as the center,
An optical head, wherein the optical head is rotated so that a noise level included in each of the ordinary light and the extraordinary light is balanced. 2. The optical head according to claim 1, wherein the magneto-optical analyzer has a mechanism for adjusting a rotation angle about the incident optical axis. 3. The optical head according to claim 1, further comprising a flat plate beam splitter that generates astigmatism that gives a focus signal, as the beam splitter.