JPH07121931A - Optical head and optical disk apparatus - Google Patents

Abstract

PURPOSE:To optically detect the edge position of a magneto-optical domain without arranging a detector on a condensing part and without being affected by fine uneven parts on a disk. CONSTITUTION:Linearly polarized light from a semiconductor laser 1 is condensed on an optical disk 5 via a lens 2, a beam splitter 3 and a lens 4. Reflected light is reflected by the beam splitter 3, and the clockwise circularly polarized light component and the counterclockwise circularly polarized light component of the linearly polarized light are converted into orthogonal linearly polarized light through a quarter-wave plate 11. The polarized light is separated by a polarization beam splitter 6, and optical outputs in regions divided so as to be arranged in the signal recording direction of the optical disk 5 are detected by two-split detectors 8, 9. A difference signal is found by differential amplifiers 10a, 10b, a difference between a clockwise component and a counterclockwise component is found further by a differential amplifier 10c, and the edge signal of a magneto-optical domain in which the influence of uneven parts on the disk has been offset is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk device or other optical disk device.

[0002]

2. Description of the Related Art Conventionally, in a magneto-optical disk device,
A magneto-optical disk with a ferromagnetic material magnetized in one direction above or below is irradiated with laser light, and the heat causes the temperature of the ferromagnetic material at the spot irradiation location to rise above the Curie temperature, and a magnetic field is applied to it. Information is recorded in the domain formed by reversing the magnetization of the spot irradiation portion.
In reproducing this information, linearly polarized light is focused on the domain, and the polarization rotation is optically detected by utilizing the fact that the polarization direction rotates due to the direction of magnetization by the magnetic Kerr effect. However, this method has a problem that the signal level is low because the car rotation angle is small. For this reason, when differential processing is performed on the read signal in order to perform mark edge reproduction, which has been used for improving the recording density of magneto-optical disks in recent years, noise increases, and aberration of the optical system and adjustment accuracy of the device are increased. It was a cause of tightening the allowable value such as.

On the other hand, a method of optically differentiating the read electric signal instead of differentiating the electric signal from the beginning is disclosed in, for example, the 1994 Autumn Applied Physics Society Academic Lecture Proceedings 950, 18a. -Proposed in T-8, 9, 10. This optical system is shown in FIG. The reflected light from the disk 5 is split into orthogonal linearly polarized lights of approximately equal light quantity through a polarization beam splitter 6, and separate photodetectors 8 and
Focus on 9. The photodetectors are separated from each other in the information recording direction on the medium (8a, b, 9a, b), and when the light spot is on the boundary of the recording domain on the recording medium, the detectors 8, 9a, a, The light incident on b is subjected to Kerr rotation in the opposite direction due to the magnetizations that are reversed, and the output becomes the axial projection components of 8 and 9 in FIG. Therefore, the edge signal of the domain can be detected by arithmetically processing these outputs as shown in FIG.

As a second conventional example, the optical system shown in FIG. 3 is an optical data storage.
Is shown in. Here, the light that has passed through the beam splitter from the semiconductor laser 1 passes through the λ / 4 plate 11 and is condensed on the optical disc 5 as circularly polarized light. The magnetic Kerr effect described above is generally known as the effect of rotating the polarization direction of linearly polarized light in a magnetic field, but if the linearly polarized light is separated into right-handed circularly polarized light and left-handed circularly polarized light, Can also be regarded as an effect that a phase difference in the opposite direction is generated between the clockwise circularly polarized light and the counterclockwise circularly polarized light. Therefore, when right-handed or left-handed circularly polarized light is incident on the magneto-optical disk as shown in FIG. 4, the phases of the reflected lights are shifted in opposite directions depending on the magnetization direction of the domain. Therefore, the light incident on the magneto-optical domain causes a phase shift depending on the domain, and it is observed as if the domain region has a convex shape or a concave shape, and the light intensity changes due to the light interference effect. However, in reality, the phase shift due to the magneto-optical domain is very small, and it is difficult to detect the overall intensity shift with high accuracy. Therefore, FIG.
As described above, due to the effect of the phase shift at the boundary of the domain, the traveling direction of light is tilted, and the intensity distribution of reflected light is shifted on the lens surface. Detect from output.

[0005]

In the first conventional example described above, the photodetector needs to be placed at the focal point of the lenses 7a and 7b, and the adjustment accuracy is strict. However, there is a problem that the deterioration becomes large.

Since the second conventional example utilizes the effect that the magneto-optical domain is observed as minute unevenness, the same applies when the disk has no domain and actually has minute unevenness. There is a problem that the signal of is detected.

However, in the first conventional example, since the signals due to the unevenness of the disk are generated symmetrically in the detectors 8 and 9, they are canceled by the differential amplifier 10c. Therefore, the problem of the second conventional example does not occur. Further, in the second conventional example, the detector 8 is not arranged at the converging point.
No problem occurs in the conventional example.

In view of the above problems, it is an object of the present invention to optically detect the edge position of a magneto-optical domain which is not affected by the unevenness of the disk without disposing the detector on the focal point. is there.

[0009]

In order to solve the above problems, a semiconductor laser emitting linearly polarized light, a lens, an optical recording medium for concentrating the linearly polarized light from the semiconductor laser by the lens, and the optical recording medium A beam splitter that splits the light reflected by the recording medium, a splitting unit that splits the right-handed circularly polarized light component and the left-handed circularly polarized light component of the light split by the beam splitter, and the right and left-handed circularly polarized light At least 2 in the signal recording direction of the optical recording medium.
At least an optical head is composed of a photodetector that detects the light intensity of each of the divided regions. Further, an optical disk device for reproducing a recording signal of an optical recording medium is constructed by using this optical head.

[0010]

As shown in FIG. 5, the intensity distributions of the right-handed circularly polarized light component and the left-handed circularly polarized light component of the linearly polarized light reflected by the optical recording medium are shifted in opposite directions on the lens surface. Therefore, after detecting the deviation of these light intensities for each of the right-handed circularly polarized light and the left-handed circularly polarized light by a photodetector which is divided into two in the signal recording direction of the optical recording medium, the difference is obtained, and thereby the minuteness of the disc is reduced. The edge position of the magneto-optical domain can be detected by canceling the signal due to the unevenness.

[0011]

EXAMPLE FIG. 6 shows an example of the present invention. The linearly polarized light from the semiconductor laser 1 is collimated by the lens 2, transmitted through the beam splitter 3, and focused on the optical disc 5 by the lens 4. The reflected light passes through the lens 4 again, is reflected by the beam splitter 3, and passes through the λ / 4 plate 11 to be circularly polarized light. Further, this enters the polarization beam splitter 6 and separates orthogonal linearly polarized light components. Here, the axis direction of the polarization beam splitter 6 is aligned with the fast axis and the slow axis of the λ / 4 plate 11 at 45 °.

FIG. 7 shows how the right-handed circularly polarized light component and the left-handed circularly polarized light component of linearly polarized light are separated by such a method. Although the light reflected by the disk 5 is linearly polarized light, it can be considered that the linearly polarized light is a combination of right-handed circularly polarized light and left-handed circularly polarized light with equal amplitude. On the other hand, the λ / 4 plate 11 has a property of converting linearly polarized light that is incident at an angle of 45 ° to the orthogonal fast axis and slow axis into circularly polarized light. It becomes linearly polarized light in a direction forming 45 ° with respect to the phase axis. However, with right-handed circularly polarized light and left-handed circularly polarized light,
It becomes linearly polarized light which is orthogonal to each other. When this is incident on the polarization beam splitter 6 as shown in the figure, the right-handed circularly polarized light component and the left-handed circularly polarized light component of the original linearly polarized light can be separated.

After separating the right-handed circularly polarized light and the left-handed circularly polarized light in this way, the optical output for each area divided by the two-division detectors 8 and 9 in FIG. If detected, the intensity shift occurring at the edge of the magneto-optical domain can be detected as already described in FIG. At this time, in the magneto-optical domain, with right-handed circularly polarized light and left-handed circularly polarized light,
Since the shift directions are opposite and the same direction is obtained at the boundary of the unevenness of the disk, after the differential signals are obtained by the differential amplifiers 10a and 10b, the difference between the clockwise component and the counterclockwise component is further obtained by the differential amplifier 10c. As a result, it is possible to detect the edge signal of the magneto-optical domain that cancels the influence of the unevenness of the disk.

This state will be described with reference to FIG. The left side of the figure is the boundary of the magneto-optical domain, and the right side is the boundary of the irregularities.
The respective outputs of the two-divided photodetector of FIG. 7 and the final differential output when the light spot crosses these boundaries are shown. At the edge of the magneto-optical domain, the intensity distribution shifts in the opposite directions on the right-hand side and the left-hand side, so the final output appears, while on the uneven surface, the phase shift direction on the disk is the same for both clockwise and counterclockwise rotation. Therefore, the intensity deviation directions are the same, and the final output is canceled by the differential detection.

In the above embodiment, the λ / 4 plate 11 and the polarization beam splitter 6 are used for separating the circularly polarized light, but it is also conceivable to use an optical rotatory medium as the separating means. Optical rotation is usually the property that the polarization direction of linearly polarized light is gradually rotated while it remains linearly polarized. In other words, it should be considered as a medium in which the right-handed circularly polarized light and the left-handed circularly polarized light have different refractive indices. You can also In principle, it is also possible to construct a left / right circularly polarized light separating prism using such a medium.

If a conventional push-pull signal is to be detected as the tracking deviation detection signal, the two-division detector may be a four-division photodetector which is also divided in the direction orthogonal to the information recording direction. The difference in intensity balance between the information recording direction and the orthogonal direction may be differentially detected in the same manner as described above. Or if it is a sample servo system,
If wobble pits are periodically provided on the disc beforehand, the tracking signal can be detected from the output difference.

For the defocus detection signal, for example, an astigmatism detection method can be used. Further, even if the two-division photodetector is used, it is possible to detect the defocus signal by using the effect of defocusing the spot due to the normal phase pit and the opposite direction depending on the defocus direction when defocus occurs. .

Further, according to the present method, only the magneto-optical signal is detected, but when the edge of the phase pit is detected using the present invention, only the output of the differential amplifier 10a is used in FIG. 6, for example. Signal detection is possible. At this time, the influence of the minute unevenness of the disk cannot be canceled, but since the depth of the phase pit is usually deeper than the minute unevenness of concern here, the signal-to-noise ratio is sufficiently high. Further, in this case, the magneto-optical signal cannot be detected because the signal amplitude becomes very weak, but it is possible to read whether to detect the magneto-optical signal or the phase pit signal when the disc is mounted. Sufficient support is possible by circuit-like switching.

[0019]

According to the present invention, it is possible to optically detect the edge position of the magneto-optical domain which is not affected by the unevenness of the disk without disposing the detector on the converging point. It is possible to realize a highly accurate magneto-optical signal detection that is easy to adjust.

[Brief description of drawings]

FIG. 1 is a block diagram of a conventional detection system.

FIG. 2 is a principle diagram of detection signal output in a conventional optical system.

FIG. 3 is a block diagram showing a second conventional example.

FIG. 4 is a principle diagram of phase shift depending on the direction of circularly polarized light and the direction of magnetization.

FIG. 5 is a principle diagram of a diffraction direction of circularly polarized light by an edge of a magneto-optical domain.

FIG. 6 is a block diagram showing an embodiment of the present invention.

FIG. 7 is a perspective view of a left-right circularly polarized light separating method according to the present invention.

FIG. 8 is an explanatory waveform diagram of a canceling effect of the influence of the disk unevenness in the present invention.

[Explanation of symbols]

1 ... Semiconductor laser, 2 ... Collimating lens, 3 ...
Beam splitter, 4 objective lens, 5 optical disc, 6 polarization beam splitter, 7 focusing lens,
8, 9 Photo detector, 10 Differential amplifier, 11 λ
/ 4 plate.

Claims (2)

[Claims] 1. A semiconductor laser that emits linearly polarized light, a lens that condenses the semiconductor laser, an optical recording medium on which the light from the lens is irradiated, and a light reflected by the optical recording medium are branched. A beam splitter, a branching unit for branching the right-handed circularly polarized light component and the left-handed circularly polarized light component of the light split by the beam splitter, and at least the right and left-handed circularly polarized light signal recording direction of the optical recording medium. And a photodetector for detecting the light intensity of each of the two divided regions. 2. A semiconductor laser that emits linearly polarized light, a lens that condenses the semiconductor laser, an optical recording medium on which the light from the lens is irradiated, and a light reflected by the optical recording medium are branched. A beam splitter, a branching unit for branching the right-handed circularly polarized light component and the left-handed circularly polarized light component of the light split by the beam splitter, and at least the right and left-handed circularly polarized light signal recording direction of the optical recording medium. A photodetector for detecting the light intensity of each of the two divided areas,
An optical disk device, which reproduces a recording signal of the optical recording medium based on an output signal of the photodetector.