JPH08249669A - Method and apparatus for correcting astigmatic difference of optical head - Google Patents

Abstract

PURPOSE: To obtain a method for correcting an astigmatic difference of an optical head and an apparatus for easily adjusting an astigmatic difference, whereby the rotation of a glass plate inserted slant-wise to an optical beam between a laser and a collimator lens for the correction of the astigmatic difference can be easily adjusted. CONSTITUTION: A glass plate 33 is inserted between a semiconductor laser 31 and a collimator lens 32 so as to correct an astigmatic difference. The glass plate 33 is rotated by a lever 41. Laser beams are reflected at a spherical mirror of a spherical mirror unit 38 through a complex prism 34 and an objective lens 35, and made incident on an interference fringe observation part 39. The interference fringes are caught by a built-in camera and projected to a monitor television 42. The astigmatic difference is corrected by adjusting the lever 41 as indicated by 44 so as to uniform the interference fringes on the whole screen. The correction of the astigmatic difference can be confirmed also by a multisplit sensor in the observation part 39.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an astigmatic difference correction method for an optical head and a correction method for correcting the astigmatic difference of an optical head used when writing, reading or erasing information on an optical disk or the like. For equipment.

[0002]

2. Description of the Related Art Conventionally, in the optical system of a general optical head,
No device for correcting the astigmatic difference of the semiconductor laser is installed. Therefore, there is a phenomenon in which the position of the focus offset when the tracking error signal of the optical head is the maximum and the position of the maximum focus offset of the reproduction signal of the optical disc are different. When the tracking error signal is maximum, the tracking servo operation is stable, but when the RF (high frequency) signal deteriorates, good signal reproduction cannot be performed. Further, if the focus offset is set to maximize the RF signal, the tracking operation becomes unstable.

Therefore, in the conventional optical head, the stability of servo control for tracking is prioritized, and the carrier / noise ratio (CNR) in the reproduced signal is set.
We are making adjustments at the expense of. As a result, sufficient high density recording cannot be performed. This will be described below with reference to the drawings.

FIG. 6 shows the carrier / noise ratio and the level characteristic of the tracking error signal when the focus offset is deviated. In the figure, the horizontal axis represents the focus offset, and the vertical axis represents the carrier / noise ratio (CNR) and tracking error signal (TE) level, which represent the CNR characteristic 11 and the tracking error signal level characteristic 12, respectively. ing. As can be understood from this figure, the difference between the focus offset point 14 in the best state of the CNR characteristic 11 and the focus offset point 15 in the best state of the tracking error signal is
It becomes 0.9 μm. This means that the set positions of the focus offsets in the focus servo of the convergent beam waist in the tangential direction and radial direction of the disc in the light beam that converges on the disc (not shown) are deviated by 0.9 μm.

Therefore, it has been proposed to correct the astigmatic difference of the semiconductor laser in order to enable high density recording.

FIG. 7 shows an example of a magneto-optical head in which the astigmatic difference is corrected. The light beam emitted from the semiconductor laser 21 is a glass plate 22 for astigmatic difference correction.
To reach the collimator lens 23, where it is collimated into a parallel beam and enters the compound prism 24. The compound prism 24 has a configuration including two beam splitters 25 and 26 and a 45-degree mirror 27. The light beam that has passed through the two beam splitters 25 and 26 and is reflected by the 45-degree mirror 27 enters the objective lens 28 and converges on a disk surface (not shown).

In the magneto-optical head, the optical components existing on the outward path from the semiconductor laser 21 to the objective lens 28 cause the astigmatic difference. Here, it is examined whether or not only the semiconductor laser 21 is the cause of the astigmatic difference in the conventional magneto-optical head having no glass plate 22 for correcting the astigmatic difference.

The focal length of the collimator lens 23 is 12.
The focal length of the objective lens 28 is 4.1 mm. Then, 0.9 μm as the focus offset difference of the convergent beam to the disk shown in FIG. 6 corresponds to 9 μm as the astigmatic difference of the semiconductor laser 21. This is because it is determined by the square of the ratio of the focal length of the collimator lens 23 and the focal length of the objective lens 28. It is numerically too large that the semiconductor laser 21 itself has an astigmatic difference of 9 μm, and therefore the compound prism 24 and the objective lens 28 themselves also have an astigmatic difference, as shown in FIG. I understand.

Actually, the astigmatic difference of the optical head is generated not only by the semiconductor laser 21, but also by the compound prism 24 and the objective lens 28 which are composed of the beam splitters 25, 26 and the 45-degree mirror 27. It is also caused by deterioration of the flatness of the entrance surface and the exit surface of the composite prism 24.

Therefore, in Japanese Unexamined Patent Publication No. 6-144282, as shown in FIG. 7, a glass plate 22 for astigmatic difference correction is obliquely inserted into a light beam between a semiconductor laser 21 and a collimator lens 23. ing. Then, this is rotated about the optical axis to correct the astigmatic difference.

Now, let the thickness of this glass plate 22 having a refractive index n be t, and the inclination with respect to the optical axis be θ. The astigmatic difference correction value ΔZ ₀ by the glass plate 22 is expressed by the following equation (1). Further, when the glass plate 22 is rotated around the optical axis by the rotation angle φ with respect to the correction value of the astigmatic difference, the astigmatic difference correction value ΔZ at this time is expressed by the equation (2). Become.

[0012]

[Equation 1]

[0013]

In an optical head designed for high density recording and high transfer rate, it is important to stabilize tracking servo and obtain a good RF signal. Therefore, a correction method and apparatus for correcting the astigmatic difference as shown in FIG. 7 have been proposed. However, the proposed optical head uses the compound prism 24. The composite prism 24 is made of a glass material and is generally fixed to an aluminum base with an adhesive. This fixing causes mechanical deformation, resulting in deterioration of the flatness of the incident surface and the exit surface. Therefore, it is necessary to finely rotate the glass plate 22 about the optical axis for adjustment, but there was no method for confirming that the astigmatic difference was corrected at the adjustment stage.
For this reason, it is necessary to repeat the adjustment after confirming it using the optical head, and there is a problem that the adjustment work is time-consuming.

Therefore, an object of the present invention is to correct the astigmatic difference of the optical head, which facilitates the rotation adjustment of the glass plate for correcting the astigmatic difference inserted obliquely with respect to the light beam between the laser and the collimator lens. A method and an apparatus for easily adjusting astigmatic difference are provided.

[0015]

According to the first aspect of the invention, the laser beam output from the laser forming the optical head is inclined with respect to the optical axis before entering the collimator lens, and the optical axis is centered. As a result, the transparent astigmatic difference correction plate having a predetermined shape is rotatably rotated, and the laser beam emitted from the objective lens of the optical head is returned to the objective lens by the reflection of the predetermined reflecting means. In the optical head at the turning position, the interference fringes due to the interference of both the laser beams obtained by combining the obtained laser beam and the laser beam before reaching the objective lens become a predetermined pattern. A feature of the astigmatic difference correction method of the optical head is that the rotation of the astigmatic difference correction plate is stopped to end the correction of the astigmatic difference.

That is, according to the first aspect of the invention, the astigmatic difference correction plate composed of a glass plate or a cylindrical lens is rotated between the laser and the collimator lens obliquely with respect to the optical axis and about the optical axis. A reflecting means such as a spherical mirror is arranged on the exit side of the objective lens of the freely arranged optical head, the laser beam emitted from the objective lens is returned to the objective lens, the laser beam passing through this and this objective lens The laser beam extracted by some means is made to interfere with each other before it is incident on. Then, by observing with the observing means, the astigmatic difference correction plate is rotated to a rotation position where the interference fringes become a predetermined pattern such that the interference fringes become parallel stripes with a constant pitch, and the astigmatic difference is corrected. To finish. As described above, according to the present invention, since the astigmatic difference is corrected while checking the pattern of the interference fringes,
Even an unskilled person can quickly and surely perform the astigmatic adjustment work.

According to the second aspect of the invention, (a) a laser, (b) a collimator lens for collimating a laser beam emitted from the laser, and (c) an arrangement for converging the collimated light at a predetermined position. And a transparent astigmatic difference correction plate of a predetermined shape, which is disposed between the laser and the collimator lens and is tiltable with respect to the optical axis and rotatable about the optical axis. ) Adjusting means for rotating the astigmatic difference correction plate about the optical axis by a desired angle;
Reflecting means arranged on the exit side of the objective lens to return the emitted laser beam to the objective lens side, and (g) laser beam reflected by the reflecting means and passing through the objective lens again and reaching the objective lens via the collimator lens. The astigmatic difference correction device of the optical head is provided with a combining means for combining the laser beam before the generation with each other to generate interference, and (h) an observing means for observing the interference fringes generated by the combining means.

That is, according to the second aspect of the invention, a transparent astigmatic difference correction having a predetermined shape is disposed between the laser and the collimator lens in a state of being inclined with respect to the optical axis and rotatable about the optical axis. The boards are arranged. Then, a reflecting means for returning the laser beam emitted to the exit side of the objective lens to the objective lens side is arranged, and reaches the objective lens via the collimator lens and the laser beam reflected by the reflecting means and passing through the objective lens again. An interference fringe is generated by combining with the preceding laser beam, and the rotational position of the astigmatic difference correction plate is determined while observing the interference fringe. As described above, in the present invention, the pattern of the interference fringes can be confirmed by the observing means, so that the astigmatic difference adjustment operation can be performed quickly and reliably.

According to the third aspect of the invention, (a) a laser, (b) a collimator lens for collimating the laser beam output from the laser, and (c) an arrangement for converging the collimated light at a predetermined position. And a transparent astigmatic difference correction plate of a predetermined shape, which is disposed between the laser and the collimator lens and is tiltable with respect to the optical axis and rotatable about the optical axis. ) An adjusting lever for rotating the astigmatism correction plate by a desired angle about the optical axis,
(F) A spherical mirror that is arranged on the exit side of the objective lens and returns the emitted laser beam to this objective lens side;
A half mirror that causes interference by combining the laser beam reflected by the spherical mirror and passing through the objective lens again and the laser beam before reaching the objective lens through the collimator lens; and (h) This half mirror An astigmatic difference correction device of the optical head is equipped with an observation means for observing interference fringes.

That is, according to the third aspect of the invention, a transparent astigmatic difference correction having a predetermined shape is arranged between the laser and the collimator lens in a state of being inclined with respect to the optical axis and rotatable about the optical axis. The boards are arranged. Then, a spherical mirror that returns the laser beam emitted to the exit side of the objective lens to the objective lens side is arranged, and reaches the objective lens via the collimator lens and the laser beam reflected by the spherical mirror and passing through the objective lens again. The preceding laser beam is combined with a half mirror to generate an interference fringe, and the observing means observes the interference fringe to determine the rotational position of the astigmatic difference correction plate by the adjusting lever. As described above, in the present invention, the pattern of the interference fringes can be confirmed by the observing means, so that the astigmatic difference adjustment operation can be performed quickly and reliably.

According to the fourth aspect of the invention, the astigmatic difference correction plate is a glass plate. In addition, claim 5
The described invention is characterized in that the astigmatic difference correction plate is a cylindrical lens.

Further, in the invention according to claim 6, the observing means is a television camera which captures the interference fringes as a visible image,
It is characterized in that it is composed of a monitor television connected to the television camera for displaying interference fringes and a multi-division optical sensor for capturing the pattern of the same interference fringes as a difference in light intensity of a plurality of regions. Of course, the television camera and the multi-segment photo sensor may include either one. In addition to the television camera, the present invention can be applied to a device that can quickly visualize interference fringes, such as an electronic camera.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows an appearance of an astigmatic difference correction device for an optical head according to an embodiment of the present invention. The astigmatic difference correction device includes a semiconductor laser 31, a collimator lens 32 for making a laser beam emitted from the semiconductor laser parallel light, an astigmatic difference correction glass plate 33 disposed between these, and a collimator. The optical head 37 is provided with a biaxial actuator 36 to which a compound prism 34 and an objective lens 35 for entering parallel light emitted from the lens 32 are attached. Then, a spherical mirror unit 38 is provided on the focal plane side of the objective lens 35 in the optical head 37.
Is arranged as a jig so that the interference fringe observation section 39 is rotatably arranged on the opposite side.

The glass plate 33 arranged in the optical head 37
Is adjusted by moving the adjustment lever 41 having a shape in which the "?" Mark is inverted and displaying the measurement result of the interference fringe observation unit 39 on the monitor television 42.

That is, an adjusting window is opened in the cylinder portion (not shown) of the laser pen 43 to which the semiconductor laser 31 is attached, and the tip end of the adjusting lever 41 is at the glass plate 33.
Is in contact with the rotation adjusting shaft for gripping the cylinder at two points corresponding to the radius of curvature of the mounted cylindrical member 33A. Therefore, when the other end of the adjusting lever 41 is rotated in the direction of the arrow 44, the cylindrical member 33A to which the glass plate 33 is attached rotates in the direction of the arrow 45.

FIG. 2 shows the inside of this astigmatic difference correction device by cutting along the optical axis. The semiconductor laser 31 is emitted, passes through the glass plate 33, and collimator lens 32
The laser beam collimated by the laser beam sequentially passes through two beam splitters 51 and 52 in the compound prism 34, is reflected by a 45-degree mirror 53, and is deflected by 90 degrees in its path. Then, the light passes through the objective lens 35 attached to the biaxial actuator 36 and is reflected by the spherical mirror 54 in the spherical mirror unit 38.

This reflected laser beam enters the compound prism 34 through the objective lens 35, is reflected by the 45-degree mirror 53, and then is reflected by the beam splitter 52.
Is reflected by. The reflected laser beam enters the interference fringe observation unit 39.

The interference fringe observation section 39 includes a half mirror 56.
And an eight-division optical sensor 57 for detecting the laser beam reflected by it, and a CCD camera 58 for visualizing the laser beam transmitted through the half mirror 56. The interference fringe observation unit 39 is a half mirror 56.
It is rotatably arranged with respect to the optical head 37 with the laser beam incident on the optical axis as the central axis.

By the way, a part of the laser beam incident on the compound prism 34 from the collimator lens 32 is reflected by the beam splitter 52 and a part of it is reflected by the side surface 61 of the compound prism 34. A part of the reflected laser beam further passes through the beam splitter 52 and enters the interference fringe observation unit 39. That is, the laser beam entering the interference fringe observation section 39 is a combination of the laser beam once reflected by the spherical mirror 54 and the laser beam before the reflection.
Therefore, the CCD camera 58 displays the interference fringes resulting from this on the monitor television 42 (not shown), and the 8-division optical sensor 57 obtains an electric signal corresponding to the pattern of the interference fringes.

FIG. 3 shows various interference fringe patterns displayed on a monitor television. (A) to (d) of the figure show the respective cases where the astigmatic difference occurs, and (e) of the figure shows the state where the astigmatic difference does not occur or the astigmatic difference is corrected. Shows the monitor screen. In this figure (e), the intervals of the interference fringes are almost constant.

When the parallel laser beam is converged by the objective lens 35, it becomes an elliptical convergent beam depending on the direction in which the astigmatic difference occurs. As a result, the interference fringes are as shown in FIGS. Depending on whether the major axis of the ellipse in the elliptical converging beam exists at 0 degree, 90 degrees, 45 degrees, or 135 degrees, the interference fringes are densely generated on the left half and the right half of the screen as shown in these figures. , "C", or the opposite "C".

With the astigmatic difference of only the semiconductor laser 31, the interference fringes as shown in FIG. If the compound prism 34 and the objective lens 35 have an astigmatic difference, their directions are not constant. Therefore, the interference fringes are displayed on the monitor television 42 to determine the azimuth of the interference fringes, and the interference fringe observation unit 39 is rotated to adjust the rotation to the position of 0 degree, 90 degrees, 45 degrees or 135 degrees. .
Then, the interference fringes at this time are detected by the 8-division optical sensor 57 to move the adjustment lever 41, and the glass plate 33 is rotationally adjusted about the optical axis.

FIG. 4 shows the arrangement of the sensor elements in the 8-division optical sensor. The 8-division optical sensor 57 has a structure in which eight sensor elements A to H are arranged in pairs of two, as shown in this figure.

FIG. 5 shows the waveform response due to the movement of the interference fringes by the sensor elements that are a pair of various interference fringes and the 8-segment photosensor. For example, when the interference fringes appear evenly as shown in FIG. 6A, the outputs of the sensor elements A-B, C-D, EF, and GH have the same phase, and the interference fringes are dense. The amplitude of the waveform in the generated sensor elements CD is large.

In the case of (b) or (c) in the figure, since the interference fringes are in the shape of "C" or in the opposite direction of "C", the phase shifts and the interference fringes The amplitude of the waveform is small at the point where is rough.

Therefore, when the astigmatic difference is corrected by using the eight-division optical sensor 57, the output waveforms of the sensor elements AB, CD, EF, and GH that form a pair are determined. The rotation adjustment of the glass plate 33 may be performed so that they have the same phase and have the same crest value. When the correction of the astigmatic difference is completed by the rotation adjustment of the glass plate 33, the spherical mirror unit 38 as a jig is removed, the interference fringe observation section 39 and the adjustment lever 41 are also removed, and this optical head is used for writing or reading an optical disk. Will be used for.

In the embodiment described above, the semiconductor laser 31
Although the astigmatic difference correction device for the optical head using the above is shown, it is obvious that the invention can be applied to other lasers, for example, a helium-neon gas laser. Further, in the embodiment, the laser beam is reflected by the spherical mirror 54 to generate interference fringes with other laser beams, but in addition to this, an interferometer in which a plane mirror is combined is used to monitor the interference fringes. You may

Further, in the embodiment, the astigmatic difference is corrected by using the 8-division optical sensor 57, but generally, the same correction can be performed by using the multi-division sensor. The state of arrangement of the sensor elements is not limited to that of the embodiment.

Further, although the glass plate is used for the correction of the astigmatic difference in the embodiment, a cylindrical lens may be arranged instead of this to perform the correction.

[0041]

As described above, according to the first aspect of the invention, the pattern of the interference fringes is observed by the observing means while rotating the astigmatism correction plate made of a glass plate or a cylindrical lens, The correction of the astigmatic difference is completed at the rotational position where the pattern becomes a predetermined pattern such that parallel stripes having a constant pitch are formed. Thus, claim 1
In the invention described, the astigmatic difference is corrected while checking the pattern of the interference fringes, so that even an unskilled person can quickly and surely perform the astigmatic adjustment operation for correcting the entire optical system. . Therefore, the focus offset and the offset in the tracking error signal best match exactly, and the tracking servo control can be sufficiently performed, and the optical head can perform good recording and reproduction.

Further, according to the inventions of claims 2 to 6, a glass plate or a cylinder disposed between the laser and the collimator lens in a state inclined with respect to the optical axis and rotatable about the optical axis. A transparent astigmatic difference correction plate such as a lens is arranged, and a reflecting means such as a spherical mirror for returning the laser beam emitted to the exit side of the objective lens to the objective lens side is arranged. The laser beam that has passed through the lens again and the laser beam that has not passed through the collimator lens and before reaching the objective lens are combined to generate interference fringes. I am trying to decide.

Therefore, in these inventions, only by temporarily adding predetermined means such as reflecting means and observing means to the optical head to be adjusted, even an unskilled person can confirm the pattern of the interference fringes. The position of the astigmatic difference correction plate for correcting the entire optical system can be set quickly and accurately. Therefore, the focus offset and the offset in the tracking error signal best match exactly, and the tracking servo control can be sufficiently performed, and the optical head can perform good recording and reproduction.

[Brief description of drawings]

FIG. 1 is a perspective view showing an appearance of an astigmatic difference correction device for an optical head according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state in which the inside of the astigmatic difference correction device shown in FIG. 1 is cut along the optical axis.

FIG. 3 is an explanatory diagram showing patterns of various interference fringes displayed on a monitor television.

FIG. 4 is a plan view showing the arrangement of each sensor element in the 8-division optical sensor of this embodiment.

FIG. 5 is an explanatory diagram showing a state of a waveform response due to movement of interference fringes by sensor elements forming a pair of various interference fringes and an 8-segment photosensor.

FIG. 6 is a characteristic diagram showing a carrier / noise ratio and a level characteristic of a tracking error signal when a focus offset is deviated.

FIG. 7 is a principle diagram showing an example of a conventional magneto-optical head in which astigmatism difference is corrected.

[Explanation of symbols]

 31 semiconductor laser 32 collimator lens 33 glass plate 34 composite prism 35 objective lens 38 spherical mirror unit 39 interference fringe observation section 41 adjustment lever 42 monitor television 51, 52 beam splitter 53 45 degree mirror 54 spherical mirror 56 half mirror 57 8 split light Sensor 58 CCD camera AH sensor element

Claims (6)

[Claims] 1. A transparent transparent glass having a predetermined shape, which is tilted with respect to the optical axis and is rotatable about the optical axis before the laser beam output from the laser constituting the optical head is incident on the collimator lens. The astigmatic difference correction plate is sequentially rotated, and the laser beam emitted from the objective lens of this optical head is returned to this objective lens by the reflection of a predetermined reflection means and the laser beam before reaching the objective lens. The rotation of the astigmatic difference correction plate in the optical head is stopped at the rotation position where the interference fringes due to the interference of the two laser beams obtained by combining the beams with each other form a predetermined pattern. Then, the astigmatic difference correction method for an optical head is characterized by terminating the correction of the astigmatic difference. 2. A laser, a collimator lens for collimating a laser beam output from the laser, an objective lens arranged for converging the collimated light to a predetermined position, and a light beam between the laser and the collimator lens. A transparent astigmatism correction plate of a predetermined shape which is tilted with respect to the axis and is rotatable about the optical axis, and the astigmatism correction plate is rotated about the optical axis by a desired angle. Adjusting means, a reflecting means arranged on the exit side of the objective lens for returning the emitted laser beam to the objective lens side, a laser beam reflected by the reflecting means and passing through the objective lens again, and the collimator lens. A combining means for combining the laser beam before reaching the objective lens to generate interference and an observing means for observing the interference fringes generated by the combining means. Astigmatism correction device for an optical head, characterized by Bei. 3. A laser, a collimator lens for collimating a laser beam output from the laser, an objective lens arranged for converging the collimated light to a predetermined position, and a light beam between the laser and the collimator lens. A transparent astigmatism correction plate of a predetermined shape which is tilted with respect to the axis and is rotatable about the optical axis, and the astigmatism correction plate is rotated about the optical axis by a desired angle. An adjusting lever, a spherical mirror arranged on the exit side of the objective lens to return the emitted laser beam to the objective lens side, a laser beam reflected by the spherical mirror and passing through the objective lens again, and the collimator lens Observe the half-mirror that combines the laser beam before reaching the objective lens through the interference to cause interference, and the interference fringes generated by this half-mirror Astigmatism correction device for an optical head, characterized by comprising a that observing means. 4. The astigmatic difference correction device for an optical head according to claim 2, wherein the astigmatic difference correction plate is a glass plate. 5. The astigmatic difference correction device for an optical head according to claim 2, wherein the astigmatic difference correction plate is a cylindrical lens. 6. The observing means comprises a television camera for capturing the interference fringes as a visible image, a monitor television connected to the television camera for displaying the interference fringes, and a pattern of the same interference fringes of light in a plurality of areas. 4. An astigmatic difference correction device for an optical head according to claim 2 or 3, which is configured by a multi-divisional optical sensor which is regarded as a difference in intensity.