JPH0580051B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a disk inclination suitable for use in a disk device that reads out a series of optical transitions formed on a disk with an optical head and reproduces a video signal or an audio signal. The present invention relates to a correction device.

BACKGROUND TECHNOLOGY AND PROBLEMS The surface of a disk cannot be perfectly flat when viewed microscopically, and skew exists there. and,
When the normal direction of the signal plane and the optical axis of the optical head are misaligned due to skew, coma aberration occurs. When this skew is in the radial direction of the disk,
The laser spot spans multiple adjacent tracks, causing crosstalk. Furthermore, the radial resolution (cutoff frequency) of the disk deteriorates, making the servo system unstable.

Generally, the allowable skew angle is proportional to λ/(NA) ³ . Here, λ is the wavelength of the laser beam, and NA is the numerical aperture of the objective lens. As a light source for optical heads
When a He-Ne laser tube is used, its wavelength λ is as small as 632.8 nm, so even if sufficient resolution is maintained, the NA of the objective lens can be kept as small as 0.4, which reduces the allowable angle of skew. Can be made large. This is possible in terms of crosstalk and servo system stability.

Incidentally, in recent years, it has been desired to use a semiconductor laser instead of a He--Ne laser tube in order to make optical heads smaller, lighter, and less expensive.
However, in this semiconductor laser, the wavelength λ is
Since it is long at 780nm (±20nm), the NA of the objective lens must be 0.5 to make it equivalent to a He-Ne laser tube.
It must be made a big deal. As a result, the allowable skew angle is 1/2 (approximately (0.4/0.5) ³ ), which is inconvenient in terms of crosstalk and servo system stability.When using a semiconductor laser, it is important to suppress skew. It is.

OBJECTS OF THE INVENTION An object of the present invention is to provide a tilt correction device for a disk device that detects skew in the radial direction of a disk and controls the disk device based on this to eliminate the skew.

SUMMARY OF THE INVENTION In the present invention, first and second focus detections are performed at different first and second positions in the radial direction of the disk, respectively. After focusing at the first position based on the first focus detection, radial skew is corrected based on the second focus detection. According to the present invention, radial skew can be eliminated, and as a result, crosstalk caused by coma aberration and instability of the servo system can be avoided.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 mainly shows the optical system 1 of this embodiment. This optical system 1 detects the presence or absence of pits formed on the disk 2 based on, for example, the phase (interference) of laser light. As is well known, in this optical system 1, it is necessary for the laser beam to connect a beam spot on a series (track) of pits. Therefore, tracking servo and focus servo are performed in this example as well. In this example, in addition, the skew of the disk 2 with respect to the optical system 1 is detected and the skew is corrected.

In FIG. 1, a diffraction grating 4, a polarization beam splitter 5, a collimator lens 6, a 1/4λ plate 7, and an objective lens 8 are arranged in this order on the optical path from the semiconductor laser 3 to the disk 2. Laser light from the semiconductor laser 3 enters the signal surface of the disk 2 along this optical path.

The diffraction grating 4 is for separating the laser beam into one main beam and four auxiliary beams. The main light is arranged to connect the spots to the pit row, as shown by a in FIG. 2. This main light is used to read the presence or absence of pits and reproduce the RF signal. In this case, for example, the optical path at the depth of the pit is set to λ/4 so that the light reflected at the pit and the light reflected around it interfere and become dark. Therefore, the presence or absence of pits is detected as the brightness of the light. This main light is also used for focus servo. This point will be discussed later.

Two of the auxiliary lights connect the spots so as to be lined up substantially along the track, as shown by b and c in FIG. These spots b and c are slightly shifted in the direction in which the tracks are lined up, and by keeping these shifts constant, the main light spot a can accurately track the pit row. Such tracking servo is performed, for example, by driving a lens holder (not shown) of the objective lens 8 in the left-right direction in the figure.

The remaining two auxiliary lights, as shown by d and e in FIG. 2, connect spots separated from the main light spot a in the track alignment direction. These two auxiliary lights are for detecting radial skew, as will be understood later.

The above-mentioned diffraction grating 4 is, for example, cross-shaped,
Zero-order diffracted light is used as the main light, and first-order diffracted light is used as the auxiliary light.

The laser light incident on the disk 2 is reflected and returns to the beam splitter 5 along the same optical path. During this time, the laser beam passes through the 1/4 λ plate 7 twice in a round trip, and as a result, an optical path difference of λ/2 occurs between the linearly polarized lights in both principal axis directions, and as a result, the polarization plane of the returned light is 90°. can only be rotated. Therefore,
The returned light is reflected by the beam splitter 5 and is then made incident on the detector 11 via the concave lens (spherical surface) 9 and the cylindrical lens 10.

Five light receiving paths 12, 13, 14, 15, and 16 are formed in the detector 11, as shown in FIG. The light receiving sections 12, 13, 14, 15, and 16 correspond to the main light and auxiliary light spots a to e, respectively. The light receiving sections 13 and 14 are composed of a single light receiving element. It is unnecessary to explain that a tracking error is detected from these light reception outputs and tracking servo is performed.

On the other hand, the light receiving sections 12, 15, and 16 are each composed of four light receiving elements A, B, C, and D (see FIG. 5). Of these, the light receiving element A of the light receiving section 12
An RF signal is formed from the sum of all received light outputs of ~D.
At the same time, the fifth light-receiving element A to D of this light-receiving section 12
The output is taken as shown and focus detection is performed as will be understood below. The light receiving outputs of the light receiving elements A to D of the other light receiving sections 15 and 16 are also taken out as shown in FIG. 5, and focus detection is performed on both of them.

Focus detection by the light receiving section 12 is used for focus servo, that is, to connect the crossover point of the main light to the signal surface of the disk 2, thereby improving resolution (cutoff frequency).

Focus detection of the other light receiving sections 15 and 16 is used for radial skew correction. That is, the disk 2 is driven so that the focus is on two different points in the radial direction of the disk 2, thereby eliminating the skew. In this case, if the light receiving section 12 for focus servo is also used for skew correction, one of the light receiving sections 15 and 16 can be omitted.

The so-called astigmatism method is adopted for the above focus detection. That is, cylindrical lens 1
The laser beam that has passed through 0 has astigmatism, and therefore, the horizontal plane ray bundle crosses over more across the cylindrical lens 10 than the vertical plane ray bundle, and as a result, each The spot shape at that position is as shown in FIG. As for the spot shape, the spot position is cylindrical lens 10.
As you move away from the ellipse, it changes from a vertically long ellipse to a perfect circle, and then to a horizontally long ellipse.

In the astigmatism method, when the crossover point of the laser beam is on the signal surface of the disk 2, the light receiving section 12,
Make sure that the spots 15 and 16 are shaped like perfect circles. In this way, when the disk 2 moves away from the semiconductor laser 3, that is, when the distance of the object point (crossover point) becomes long, the image point distance becomes small, and therefore both plane ray bundles are The crossover will occur to the left of the position shown in Figure 1. Therefore, the spot shape on the light receiving portions 12, 15, 16 becomes an ellipse that is elongated in the horizontal direction. Conversely, when the disk 2 approaches the semiconductor laser 3, the light receiving sections 12, 15, 16
The shape of the spot on the top is an ellipse that is long in the vertical direction.

The above changes in spot shape are shown in Figure 5 A, B, and C.
It is detected as shown in . In this case, when the disk 2 is too close, an output of +V is obtained, and when it is in focus, an output of 0 is obtained. Also, when the disk 2 is too far away, an output of -V is obtained.
There is no need to explain these matters.

In such a configuration, the inclination of the disk 2 is controlled based on the light receiving sections 15 and 16 for radial skew correction so that the focus is achieved at the positions of spots d and e. This eliminates the radial skew of the disk 2 with respect to the optical system 1. Therefore, comatic aberration is eliminated, crosstalk between adjacent tracks can be suppressed, and the stability of the servo system can be improved. Such an effect is particularly effective in the case of the semiconductor laser 3 having a long λ. Of course, even with a normal He--Ne laser, etc., there is a margin for increasing the NA, resulting in advantages such as being able to improve the resolution.

Next, a specific circuit configuration for radial skew correction will be explained with reference to FIG. In this example, as described above, the light receiving section 12 for focus servo is also used for radial skew. In addition, in Fig. 6, the reference numeral 1 of the light receiving section is
2, 15 and the symbols A, B, C, and D of the light receiving elements are combined to represent all the corresponding light receiving elements.

In FIG. 6, the outputs of the light receiving elements 12A and 12C of the light receiving section 12 for focus servo are amplified by amplifiers 17 and 18, respectively, and then added by an adder 19, and then the non-inverting inputs of two differential amplifiers. Supplied at the end. On the other hand, the outputs of the other light-receiving elements 12B and 12D of this light-receiving section 12 are amplified by amplifiers 21 and 22, respectively, and then added by an adder 23, and then supplied to the inverting input terminals of two differential amplifiers. . In this case, a focus servo error signal is obtained as the output of the differential amplifier 20, and this error signal is supplied to the focus servo system. This error signal is also supplied to a comparator 24, where it is compared with a reference signal Ref corresponding to a predetermined tolerance range. When the focus is reached to a certain extent at the position of spot a, a detection output is supplied to the switching circuit 25, and the switching circuit 25 is turned on.

On the other hand, the same amplifiers 26, 27, 28, 2 as described above are also used for the light receiving elements 15A, 15B, 15C, and 15D of the light receiving section 15 for radial skew correction.
9, adders 30 and 31, and a differential amplifier 32 are provided. The error signal from the differential amplifier 32 is supplied to the radial skew correction system via the switching circuit 25.

In this example, focus servo is first performed based on the error signal of the differential amplifier 20. Then, after the focus servo is performed or after the error signal becomes small to some extent, the switching circuit 25 is turned on and radial skew correction is performed. That is, this time the other differential amplifier 32
The inclination of the disk 2 is varied based on the error signal, thereby correcting the radial skew.

Effects of the Invention According to the present invention, the focus is matched at two different positions in the radial direction of the disk, thereby eliminating radial skew. Therefore, crosstalk caused by coma aberration and instability of the servo system can be avoided.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of this explanation as a whole, FIG. 2 is a rear view showing the arrangement of spots on the signal surface of the disk 2 shown in FIG. 1, and FIG. 3 is a diagram showing the detector 11 shown in FIG. 4 and 5 are diagrams for explaining the example in FIG. 1, and FIG.
FIG. 1 is a block diagram showing a specific example of a circuit configuration for radial skew correction in the example shown in FIG. 1 is an optical system, 2 is a disk, 3 is a semiconductor laser, 4 is a diffraction grating, 10 is a cylindrical lens, 11 is a detector, 12 is a light receiving part for focus servo, 15 and 16 are light receiving parts for radial skew correction It is.

Claims (1)

[Claims] 1. Disk tilt correction for correcting the radial tilt of the disk so that the optical axis of an optical head for optically reading symbols recorded on the disk is perpendicular to the signal surface of the disk. In the apparatus, a first beam of light irradiated onto a track of the disk returns from the disk, and a first
a first light receiving section that performs focus detection; a focus control means that performs focus control based on a focus detection output from the first light receiving section; and a focus control means that performs focus control based on a focus detection output from the first light receiving section; a second light receiving section that performs second focus detection by receiving return light from the disk of a second light beam irradiated to positions spaced apart in the direction in which the tracks of the disk are arranged; a tilt control means for controlling the tilt of the disk based on a second focus detection output from the first light receiving section; a switching circuit for switching on/off of tilt control in the tilt control means; and a focus detection output from the first light receiving section. and switching control means for controlling the switching circuit based on the detection output, and when the switching control means detects that the focus detection output from the first light receiving section has become equal to or less than a predetermined error amount. . A disk tilt correction device, characterized in that the switching circuit is turned on to start tilt control by the tilt control means.