JPH1196583A - Astigmatic difference correcting method and correcting device for optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a correcting method and a correcting device capable of performing the correcting of an astigmatic difference in an optical head easily and with high accuracy. SOLUTION: An astigmatic difference detecting device 200 having a condensing lens 202 and a quadripartite photosensor 203 is arranged on the optical axis of an optical head 100 projecting a light beam to an optical disk. An astigmatic difference is detected from the beam waist position of the light beam in the radial direction and the tangential direction of the optical disk by the sensor 203. Moreover, the astigmatic difference of the light beam is made adjustable by arranging the inclined glass plate 107 inclined with respect to the optical axis on the optical axis of the light beam and rotatingly positioning the inclined glass plate 107 around the optical axis. Then, the asigmatic difference is corrected by performing the adjusting of the astigmatic difference by the inclined glass plate 107 so that the astigmatic difference detected by the astigmatic difference detecting device 220 becomes minimum.

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 writing and reading information to and from an optical disk such as a phase change optical disk and a magneto-optical disk compatible with high-density recording, and more particularly to correction of astigmatic difference in a light beam. It relates to a method and a correction device.

[0002]

2. Description of the Related Art In an optical head of this type, a laser beam emitted from a semiconductor laser is used as a light beam, and this light beam is focused on an optical disk to write and read information. However, this light beam has an astigmatic difference in that the optical axis position of the beam waist at which the diameter of the light beam becomes smallest differs in the radial direction (y-axis direction) of the optical disk and in the tangential direction (x direction) of the optical disk. This astigmatism has an unfavorable effect on the CNR (carrier / noise ratio) and tracking in the optical head. For this reason, conventionally, various techniques for correcting the astigmatic difference of the optical head have been proposed. For example, as for Japanese Patent No. 2605636, a light transmitting glass that is inclined with respect to the optical axis is inserted between the semiconductor laser of the optical head and the collimator lens, and this light transmitting glass is centered on the optical axis. There has been proposed a technique in which a beam waist position of a light beam on a side along an inclined surface is changed by rotating the beam waist and the position is adjusted to a beam waist on a side orthogonal to the light beam. In addition to this, JP-A-8-1
No. 47747, the collimator lens is inclined with respect to the optical axis, JP-A-7-105562 applies a mechanical stress to the collimator lens, and JP-A-1-270285 discloses a semiconductor. Some oblique glasses are fixedly arranged between a laser and an objective lens.

However, these conventional techniques can correct astigmatism, but cannot detect and correct the astigmatism occurring in an actual optical head. I have. Therefore, it is necessary to measure this astigmatic difference. For example, FIG.
(A) is an apparatus for measuring the astigmatic difference in the conventional optical head, and the measured optical head 300 is moved in the optical axis direction (z
The optical head is mounted on a Z-axis stage 301 movable in the optical axis and an XY stage 302 movable in the optical disk radial direction (y axis) and the optical disk tangential direction (x axis), and the numerical aperture of the optical head (= 0.8) Opposite to the objective lens 303, the thickness is 0.
Numerical aperture (0.9) through 6 mm cover glass 305
Is disposed, and the measurement objective lens 304 captures the light emitted from the optical head 300,
The optical path is gained by the 45 ° mirrors 306 and 307, and once converged, the light is condensed on the two-dimensional CCD sensor 309 again by the relay lens 308. Then, the optical head 30
0 is minutely moved in the optical axis direction by the Z-axis stage 301, and the center light brightness e ^-2 (13.5%) within the focal depth of the converged beam in the two-dimensional CCD sensor 309 at that time.
Is measured for the X axis and the Y axis. The result is as shown in FIG. 6B. The Z-axis position of the beam waist in the optical disk radial direction (y extraction) and the optical disk tangential direction (x pong) are different, and this difference can be measured as astigmatic difference. . In addition, as this measuring device, reference: Shinichi Katsura: “Optical Pickup Checker” Optics, 2
3,2, pp. 104-105 (1994-02).

[0004]

However, in this type of conventional astigmatic difference measuring device, the astigmatic difference is obtained by measuring the optical head independently, and the astigmatic difference is calculated as x based on the measurement result.
It is possible to correct the position in the axial direction and the y-axis direction. However, since this type of measuring device is configured as an independent device, it cannot be used in a state where it is actually installed as an optical head for an optical disk. It is difficult to measure the astigmatic difference and correct the astigmatic difference based on the measurement result.
Further, the above-described measuring device has a problem that an expensive objective lens having a large numerical aperture is required, a plurality of mirrors and relay lenses are required, the number of components is large, and the entire device is expensive.

An object of the present invention is to detect an astigmatic difference in an optical head set to be capable of writing and reading information on and from an optical disk, and to correct the astigmatic difference based on the detection result. It is an object of the present invention to provide a correction method and a correction device for astigmatic difference that enable the above.

[0006]

An astigmatic difference correcting apparatus according to the present invention is arranged on an optical axis of an optical head for projecting a light beam onto an optical disk, and is adapted to detect the radial and tangential light beams of the optical disk. Means for detecting the astigmatic difference from the beam waist position, and means for correcting the astigmatic difference of the light beam, which is disposed on the optical path of the light beam. The means for detecting the astigmatic difference includes a four-division optical sensor arranged on the optical axis of the light beam, and a condenser lens for condensing the light beam on the four-division optical sensor. The astigmatic difference is calculated from the beam waist in the radial direction and the tangential direction of the optical disk obtained from the light receiving output of each light receiving element of the split optical sensor. Further, the means for correcting the astigmatic difference is made of glass which is arranged on the optical axis of the light beam, is inclined with respect to the optical axis, and is rotated around the optical axis.

Further, the astigmatism correction method of the present invention corrects the astigmatism of the light beam so as to minimize the astigmatism while detecting the astigmatism of the light beam projected on the optical disk. It is characterized by doing. In this case, the above 4
It is preferable that one of the split optical sensor and the condensing lens is wobbled in the optical axis direction, and the correction by the astigmatic difference correcting means is performed so that the astigmatic difference detected at that time is minimized.

[0008]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic perspective view showing a schematic configuration of an embodiment of the present invention. A light beam composed of laser light emitted from a semiconductor laser 101 provided in the optical head 100 is converted into parallel light by a collimator lens 102, and a wedge prism 103 for beam shaping, a polarizing beam splitter 104, a 45 ° mirror 105, After passing through the 波長 wavelength plate 106, it is incident on an objective lens (not shown). Then, the light is condensed by the objective lens and projected on the recording surface of an optical disk (not shown). Note that information reading, tracking adjustment, focusing adjustment, and the like are performed based on the light reflected from the optical disk, but the description of the operation is omitted here. In such an optical head, an inclined glass slope 107 whose plane is inclined with respect to the optical axis is disposed between the semiconductor laser 101 and the collimator lens 102, and the inclined glass plate 107 is aligned with the optical axis. By adjusting the rotational position around the optical axis around the center, it is possible to adjust the astigmatic difference in the light beam condensed by the objective lens by the same mechanism as in the above-described conventional technology. Note that, as in this embodiment, the wedge prism 103 and the polarization beam splitter 10
When the 4, 45 ° mirror 105 and the 波長 wavelength plate 106 are formed as a composite prism 108 integrated with each other, mechanical deformation occurs due to optical precision of each optical portion and distortion due to adhesion, and as a result, this composite Although the astigmatic difference is also generated by the prism 108 itself, the astigmatic difference can be corrected.

Here, the optical head 100 does not have the above-mentioned objective lens, and an astigmatic difference detection device 200 is arranged on the optical axis of the emitted light beam instead. The astigmatic difference detection device 200 includes a Gaussian inverse correction filter 201, a condenser lens 202, and a four-division optical sensor 203. The Gaussian inverse correction filter 201 uses the Gaussian inverse correction filter 201 because the light beam emitted from the semiconductor laser 101 and converted into a collimated light of a parallel light beam by the collimator lens 102 has a Gaussian light intensity distribution. By performing the inverse correction, the collimated light is equivalently e.
The light intensity distribution is made uniform to ^-2 , and the detection of astigmatism by the four-divided optical sensor 203 can be performed with high accuracy as described later. FIG. 2 is a diagram showing this state, and FIG. 2B shows the light transmittance characteristics of the Gaussian inverse correction filter 201 with respect to the light intensity distribution of the collimated light in FIG.

The condensing lens 202 is for condensing the light beam on the four-divided optical sensor 203, and has an aperture equal to or larger than that of the objective lens originally provided in the optical head 100. Preferably, a number of lenses are used. Further, the four-division optical sensor 203
Is composed of four light receiving elements A, B, C, and D arranged in a grid, as shown in FIG. 3A, and the light condensing position of the condensing lens 202, usually the recording surface of the optical disc. Is arranged at a position equivalent to. Further, in the four-division optical sensor 203, two orthogonal division lines 204 and 205 that divide the light into the light receiving elements A to D are separated from the optical disk in the radial direction (y-axis) and the tangential direction (x-axis). It is set in a state of being inclined by 45 ° around the axis. For this reason,
When the collimated light condensed by the condenser lens 202 has an astigmatic difference in the x-axis direction and the y-axis direction, the position of the four-division optical sensor 203 changes along the optical axis. The light receiving pattern is changed by the beam waist in each axial direction. That is, as shown in FIG.
If the beam waist in the x-axis direction is closer to the light source than the beam waist in the y-axis direction, the light receiving pattern becomes flatter in the x-axis direction on the light source side than the middle position between the two beam waists, and the y-axis is on the opposite side. The light receiving pattern becomes flat. Therefore, symmetrical light receiving patterns can be received by the light receiving elements A and C and B and D at the point symmetric positions, but the light receiving amount differs between adjacent light receiving elements depending on the optical axis position of the four-divided optical sensor. .

Therefore, the respective light receiving amounts VA, VB, VC,... At the respective light receiving elements A, B, C, D of the four-split optical sensor.
The astigmatic difference AS is defined by the following relational expression based on the output of VD. AS = (VA + VC)-(VB + VD) Therefore, when the astigmatic difference AS is measured while moving the four-division optical sensor 203 in the optical axis direction, FIG.
The following characteristics are obtained. The position on the optical axis when the AS value is 0 is a position where the beam waists in the x-axis direction and the y-axis direction have the same diameter.

At the time of actual correction, the astigmatic difference AS is measured while wobbling for repeatedly reciprocating the four-divided optical sensor 203 in the optical axis direction, and at this time, the inclined glass plate 107 is moved around the optical axis. Rotate to. As a result, the maximum amplitude value of the AS value is changed as shown in FIGS. 4A and 4B, so that the rotation position of the inclined glass plate 107 is set to a position where the maximum amplitude value becomes minimum. Thus, the astigmatic difference can be minimized. In this state, by setting the optical head so that the recording surface of the optical disk is located at the optical axis position where the AS value is 0, it is possible to configure an optical head with astigmatic difference corrected. .

Here, as shown in FIG. 5, the four-division optical sensor 203 has a circular dead area 20 having a diameter smaller than the diameter of the condensed beam at a center position including the respective light receiving elements A to D.
6 may be provided. By providing this dead area, the absolute value of the light receiving output at each of the light receiving elements A to D can be reduced,
By performing the above relational expression with a small absolute value, the astigmatic difference AS can be finely detected, and the correction accuracy can be improved. The Gaussian inverse correction filter 20
1 may be arranged at the position of the condensed light beam after the condenser lens 202. In this case, the Gaussian inverse correction filter can be arranged at any position on the optical axis, and the size can be reduced. Becomes

In the present invention, the method for directly adjusting the astigmatic difference is not limited to the above-mentioned oblique glass, but a method for inclining a collimator lens as described in the prior art with respect to the optical axis, Other methods can be used as long as they can be incorporated in an optical head, such as those that apply mechanical stress to a collimator lens. Further, in the above-described embodiment, when detecting and correcting the astigmatic difference, the focusing is performed using the focusing lens provided in the astigmatic difference detecting device, but the objective lens provided in the optical head is used. Is also possible.

[0015]

As described above, the present invention comprises means for detecting the astigmatic difference of the light beam of the optical head and means for correcting the astigmatic difference of the light beam. By correcting the astigmatism of the light beam while detecting the astigmatism of the beam, the correction device can be realized with a simple configuration, and the correction operation can be easily performed. The effect of accurately correcting the astigmatic difference of the optical head can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an astigmatic difference correcting apparatus according to the present invention.

FIG. 2 is a diagram illustrating a light intensity distribution of a light beam and transmission characteristics of a Gaussian inverse correction filter.

FIG. 3 is a diagram for explaining a four-divided optical sensor and its detection operation.

FIG. 4 is a diagram for explaining an embodiment of a method for correcting astigmatism.

FIG. 5 is a diagram illustrating another configuration example of the four-division optical sensor.

FIG. 6 is a diagram for explaining a conventional astigmatic difference measuring apparatus and its measuring method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 optical head 101 semiconductor laser 102 collimator lens 103 wedge prism 104 polarizing beam splitter 105 45 ° mirror 106 quarter-wave plate 107 inclined glass plate 200 astigmatic difference detector 201 Gaussian inverse correction filter 202 condensing lens 203 four-division optical sensor 206 Dead Zone

Claims (6)

[Claims] 1. A method for correcting an astigmatic difference of an optical head for projecting a light beam onto an optical disk, wherein the astigmatic difference of the light beam is detected while detecting the astigmatic difference of the light beam. And correcting the astigmatic difference of the optical head. Means for detecting an astigmatic difference from a beam waist position of a light beam in a radial direction and a tangential direction of the optical disk, the means being arranged on an optical axis of an optical head for projecting a light beam onto the optical disk; Means for correcting the astigmatism of the light beam disposed on the optical path of the light beam. 3. A means for detecting the astigmatic difference, comprising: a four-division optical sensor arranged on the optical axis of the light beam;
And a condensing lens for condensing the light beam on the divided optical sensor. The astigmatic difference is obtained from the radial and tangential beam waist of the optical disk obtained from the light receiving output of each light receiving element of the four-divided optical sensor. Claim 2 to calculate
3. The optical head astigmatism correction device according to claim 1. 4. The means for correcting the astigmatic difference is made of glass disposed on the optical axis of the light beam, inclined with respect to the optical axis, and rotated around the optical axis. 4. An apparatus for correcting astigmatic difference of an optical head according to claim 2 or 3. 5. The optical head according to claim 2, further comprising a Gaussian inverse correction filter on the optical path of the light beam, for inversely correcting the light intensity of the Gaussian distribution to obtain a uniform light intensity distribution. Astigmatic difference correction device 6. The astigmatic difference correcting device according to claim 2, wherein one of the four-division optical sensor or the condensing lens is wobbled in the optical axis direction, and the astigmatic difference detected at that time is determined. A method for correcting astigmatic difference of an optical head, wherein the correction is performed by the astigmatic difference correcting means so as to minimize the difference.