JPH02105357A - Magneto-optical disk device - Google Patents

Abstract

PURPOSE:To obtain a compact and light-weight magneto-optical disk device by using a 1st and 2nd photodetectors having a dividing line parallel to the track direction of a disk in one of both photodetectors to detect the P an S polarized components of the light which is reflected from or transmitted through the disk and travels in the same direction. CONSTITUTION:The reflected light received from a magneto-optical disk 24 is separated into the P and S polarized components by a polarized beam splitter 27. Then the S polarized component is reflected by a reflecting surface 27a and travels in the same direction as the P polarized component. The P polarized component is detected by a photodetector 28 which is set at a position closer to the optical axis by a distance (x) against a focus 26a of a converging lens 26 and has a dividing line 28a set parallel to the track direction of the disk 24. While the S polarized component is detected by a photodetector 29 which is set at a position further away from the optical axis by the distance (x) against the focus 26a. In such a constitution, a compact and light-weight magneto-optical disk device is obtained.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a magneto-optical disk device that records and reproduces information using magneto-optical effects such as the magnetic Kerr effect and the Faraday effect, and in particular to a magneto-optical disk device that records and reproduces information using magneto-optical effects such as the magnetic Kerr effect and the Faraday effect. The present invention relates to a method for detecting track error signals and magneto-optical signals.

(Prior Art) Generally, in a magneto-optical disk device, information recording,
When performing reproduction, a light beam from a light source such as a laser is directed onto the magneto-optical disk by the optical system of the optical head.
．． It is necessary to always be able to irradiate a minute spot with a diameter of about 1μ. At this time, as the magneto-optical disk rotates, vibration occurs in a direction perpendicular to the rotation direction, that is, a direction perpendicular to the disk surface (focus direction), or eccentricity occurs in the radial direction. Therefore, in order to correct these two deviations, focus control (also called focus servo) that makes the light spot follow the movement of the surface runout, and tracking control (tracking) that makes the light spot follow the movement of eccentricity. (also called servo).

Conventionally, this type of magneto-optical disk device has been published in Japanese Patent Application Laid-Open No. 59-168951, and ■ Kazuo Terada, "Key Points of Optical Pickup System Design", [6] (1982-1).
0-31>Japan Industrial Technology Center, P, 151-173
There was something written in. The configuration will be explained below using figures.

FIG. 2 is a diagram showing an example of the configuration of a conventional magneto-optical disk device described in the above-mentioned document (2).

This magneto-optical disk device includes a recording optical system and a reproducing optical system, of which the recording optical system is omitted from the drawing and only the reproducing optical system is shown. In the magneto-optical disk 1- which has a perpendicular magnetization film as a recording layer, information is recorded by reversing the magnetization direction of the perpendicular magnetization film using a recording optical system (not shown). To reproduce information, linearly polarized light is irradiated onto the perpendicularly magnetized film-1 using a reproduction optical system, and the transmitted or reflected light rotates to the left or right depending on the magnetization direction, which is the so-called Faraday effect or magnetic Kerr effect. This is used to read magneto-optical signals.

That is, in the reproduction optical system, the light emitted from the semiconductor laser 2 is made into a parallel beam by the lens 3, split into three beams by the diffraction grating 4, and then reflected toward the magneto-optical disk 1 by the half mirror etc. The light is focused by the objective lens 6 onto the magneto-optical disk], -1-. One shoulder of the reflected light from the magneto-optical disk 1 rotates by ±Δθ in accordance with the magnetization direction of the perpendicularly magnetized film on the magneto-optical disk 1.

This reflected light passes through the objective lens 6 and the half mirror 5 again, and after the plane of polarization is rotated by a predetermined angle θ by the optical rotator 7,
By means of a polarizing beam splitter 9 through an intermediate lens 8,
P-polarized light component parallel to the incident plane and S1 perpendicular to the incident plane
The light is separated into the polarized light component. The P-polarized light component is transmitted from the three photodetecting elements 11a, llb, and llc for photo/electrical conversion via the cylindrical lens (as the structure is described in detail in 2) mentioned above. The light of the S@ light component is further input to a photodetector 12 for photo/electrical conversion.

The output of the photodetection element 11b is a focus error signal Ef
used as. The output of the photodetector element 11b and the output of the photodetector 12 are differentially amplified by a differential amplifier 13 and output as a magneto-optical signal So.

Further, the outputs of the two photodetecting elements 11a and llc are differentially amplified by a differential amplifier 14 and output as a track error signal Et. These focus error signal Ef and track error signal Et are processed by a focus servo circuit and a track servo circuit (not shown) to perform focus servo and track servo.

In this type of magneto-optical disk device, the servo error signal detection system and the magneto-optical signal detection system are integrated, so the optical system is simpler than in a device where the rain detection system is provided independently. This has the advantage that the number of parts is small and costs can be reduced.

(Problem to be Solved by the Invention) However, in the apparatus with the above configuration, in order to detect the focus error signal Ef and the l/rack error signal Et, the cylindrical lens 10 and the three photodetecting elements]
However, the cylindrical lens 10 is relatively expensive because the horizontal arrangement is complicated, and three photodetector elements 11a are used.
.

], ], b, llc, the photodetector element 1 ], a,, 1 ]f+, 1. ], c arrangement adjustment etc. are complicated. Therefore, from the point of view of shortening access time, which is one of the biggest challenges in magneto-optical disk drives, it is not technically satisfactory in terms of making the optical head smaller and lighter, and moreover, it is not completely satisfactory from the viewpoint of reducing the size and weight of the optical head. I am not satisfied with this point either.

The present invention solves the problems that the prior art had, such as small size,
It is an object of the present invention to provide a magneto-optical disk device that solves the problem that weight reduction and cost reduction are not fully satisfactory.

(Means for Solving the Problems) In order to solve the above problems, in the invention of claim 1, reflected light or transmitted light from a magneto-optical disk is incident on a polarizing beam splitter with a polarization plane of approximately 45 degrees through a converging lens. In a magneto-optical disk device that detects a focus error signal, a track error signal, and a magneto-optical signal based on the P-polarized component and S-polarized component light separated by the polarized beam splitter, the polarized beam splitter The light emitted from the lens is separated into P-polarized light component and S-polarized light component, and the S-polarized light component is reflected and emitted in the same direction as the P-polarized light component.

Furthermore, a first photodetector is provided at a position a certain distance closer to the optical axis direction than the focal point of the convergent lens, and a second photodetector is provided at a position a certain distance away from the focal point of the convergent lens in the optical axis direction. A photodetector is provided. The first photodetector has a first light-receiving surface smaller than the cross-sectional area of the P-polarized light component, and the second photodetector has an area equal to the first light-receiving surface and the sl It has a second light-receiving surface smaller than the cross-sectional area of the light component. And the above-mentioned 1. At least one of the second photodetectors is constituted by a two-part photodetector having a dividing line, and the dividing line is arranged parallel to the track direction of the magneto-optical disk. In addition, 1. Both of the second photodetectors may be composed of two-split photodetectors.

In the invention of claim 2, in claim 1, two of the first or second photodetectors are configured of the two-split photodetector.
a first differential amplifier that amplifies an output difference and outputs a track error signal; a second differential amplifier that amplifies an output difference between the first and second photodetectors; and a second differential amplifier that amplifies an output difference and outputs a track error signal. There is also a filter that separates the frequency of the output of the amplifier and filters out the focus error signal and the magneto-optical signal.

According to a third aspect of the invention, in the first or second aspect, the first and second photodetectors are integrated.

(Function) According to the first aspect of the invention, since the magneto-optical disk device is configured as described above, the polarizing beam splitter emits the S-polarized light component and the P-polarized light component in the same direction. The first photodetector directly receives the P-polarized light from the polarizing beam splitter and converts it into an electrical signal, and the second photodetector directly receives the S-polarized light from the polarizing beam splitter. It receives light and converts it into an electrical signal. A focus error signal and a magneto-optical signal can be detected from the difference in output between the first and second photodetectors. Furthermore, a photodetector configured with a two-split photodetector enables detection of a tracking error signal from the difference between the two outputs.

This makes it possible to reduce the number of parts and simplify the structure.

In the invention according to claim 2, the first differential amplifier functions to output a month/rack error signal, the second differential amplifier and filter function to output a focus error signal and a magneto-optical signal, and the signal detection circuit has a configuration. We aim to simplify and make it more accurate.

In the third aspect of the invention, the first and second photodetectors are integrally configured, thereby making the device more compact and lightweight.

Therefore, the above problem can be solved.

(Embodiment) FIG. 1 is a schematic configuration diagram of a magneto-optical disk device showing an embodiment of the present invention, and FIG. 3 is a configuration diagram of its signal detection circuit.

In the magneto-optical disk device shown in Fig. 1, the recording optical system is
L is omitted and only the reproduction optical system is shown. This reproduction optical system has a light source 20 such as a semiconductor laser, and a collimator lens 21. A reflective magneto-optical disk 24 is provided via a beam splitter 22 for light separation and an objective lens 23 for convergence.

In the reflection optical path of the beam splitter 22, a /2 wavelength plate 25 for rotating the plane of polarization by approximately 45 degrees, a converging lens 26 for converging light having a focal point 26a, and a polarizing beam splitter 27 are provided.

The polarizing beam splitter 27 splits the incident light into a P polarized component and an S polarized component.
It has a structure in which the light of the S polarization component is separated into the += direction component, and the light of the S polarization component is reflected in the same direction as the light of the P polarization component by the reflecting surface 27a, and then emitted.

A first photodetector 28 is provided on the P polarization component output side of the polarization beam splitter 27, and two second photodetectors are provided on the S polarization component output side.

1st. The second photodetectors 28 and 29 convert light into electricity, have, for example, a circular light-receiving surface, and are composed of photodiodes or the like. The first photodetector 28 is placed at a distance X closer to the convergent lens side from the focal point 26a of the converging lens 26, whereas the second photodetector 29 is placed closer to the focal point 26a of the converging lens 26 by a distance X. It is placed at a position separated by a distance X. Furthermore, the first. The circular light-receiving surfaces of the second photodetectors 28 and 29 have the same diameter, and
Moreover, the receiving diameter is set to be smaller than the outer diameter of the incident light at the arrangement position shown in FIG.

As shown in FIG. Second photodetector 28.29
Among them, for example, the first photodetector 28 has a light receiving section 28b-11 divided into two by a dividing line 28a.

8 consisting of a two-split photodetector with 28b-2
The dividing line 28a is arranged parallel to the track direction in order to detect the deviation of the magneto-optical disk 24 from the track. Light receiving section 2 of first photodetector 28
8b-1 and 28b-2 are connected to the (+) and (-) input terminals of the first differential amplifier 32 via amplifiers 30 and 31, respectively, and the output terminals of the differential amplifier 32. The configuration is such that the track error signal Et is output. Further, the second photodetector 29 is connected to (-) input terminals of the second differential amplifier 33, and its (+) input terminals are commonly connected to the output side of the amplifier 30.31. . A frequency separation filter 34 is connected to the output terminal of the second differential amplifier 33, and the filter 34 outputs a focus error signal Ef and a magneto-optical signal So.

Next, the operation will be explained.

The light emitted from the light source 20 is made into a parallel beam by the lens 2], passes through the beam splitter 22, is converged by the objective lens 23, and is irradiated onto the magneto-optical disk 24.

The plane of polarization of the reflected light from the magneto-optical disk 24 rotates by ±Δθ according to the magnetization direction of the perpendicular magnetization film on the magneto-optical disk 24. This reflected light is separated from the outgoing light by a beam splitter 22, the polarization plane of the linearly polarized light is rotated approximately 45 degrees by a 1/'2 wavelength plate 25, and then converged by a converging lens 26. The light converged by the converging lens 26 is
The polarizing beam splitter 27 separates the light into P-polarized light that is parallel to the incident plane and the S-polarized light that is perpendicular to the incident plane, and the S-polarized light is further split into P-polarized light at the reflective surface 27a. After being reflected in the same direction, the P-polarized light component enters the first photodetector 28, and the S-polarized light component enters the second photodetector 29, respectively.

Since the first photodetector 28 is composed of a two-split photodetector, changes in the intensity distribution of the diffraction pattern due to the groups (c+roove) forming the tracks of the magneto-optical disk 24 are reflected in the light receiving section 281)- 1°28b-2, and two electrical signals corresponding to changes in the intensity distribution are output. After the two electrical signals are amplified by each amplifier 30.31, they are supplied to the (+) and (-) input terminals of the first differential amplifier 32, and the output of the amplifier 330.31. The sum is (+
) input terminals. The first differential amplifier 32 has two
In order to amplify the difference in human power, a track error signal Et is output from the output terminal of the differential amplifier 32.

On the other hand, the second photodetector 29 converts the light of the S polarization component into an electric one.
3 and supplies the electrical signal to (-) input terminals of the second differential amplifier 33. The second differential amplifier 33 calculates the difference between the output sum of the amplifiers 30 and 31 and the output of the second photodetector 29, and amplifies the difference between the sum of the outputs of the amplifiers 30 and 31 and the output of the second photodetector 29.
1\Give. The filter 34 performs frequency separation on the output of the second differential amplifier 33, and outputs the focus error signals 1'' and f in the low frequency band, as well as the magneto-optical signal So in the high frequency band.

Here, in focus error detection, the objective lens 2
3 and the magneto-optical disk 24 are in focus, the reflected light from the magneto-optical disk 24 is transmitted to the first and second photodetectors 28.
．． 29 receives the same amount of light, so the potential of the focus error signal Ef becomes zero. When the magneto-optical disk 24 moves away from the in-focus position, the reflected light from the magneto-optical disk 24 passes through the objective lens 23 and becomes convergent light.
The focal length of the photodetector 26a becomes shorter and its focal point 26a approaches the first photodetector 28. Therefore, the amount of light received by the first photodetector 28 increases, and the output of that photodetector 28 increases. Conversely, the second photodetector 29 is located at the focal point 26 of the converging lens 26.
Since the distance is further away from a, the amount of light received decreases and the output becomes smaller. Therefore, the focus error signal Ef obtained from the second differential amplifier 33 and filter 34
The potential increases, for example, in the (+) direction.

On the other hand, when the magneto-optical disk 24 approaches the in-focus position, the amount of light received by the first photodetector 28 decreases and its output becomes smaller, while the amount of light received by the second photodetector 29 increases. Since the output becomes larger, the focus error signal Ef
The potential of increases in the (=) lateral direction.

Focus error signal Ef obtained as described above
The track error signal Et is processed by a focus servo circuit and a track servo circuit (not shown) to perform focus servo and track servo. Further, the magneto-optical signal So output from the filter 34 is processed by a signal processing circuit (not shown) and output as a readout data.

The magneto-optical disk device of this embodiment has the following advantages.

(a) Since the first photodetector 28 directly receives the P-polarized light component separated by the polarizing beam splitter 27, the relatively expensive device required in the conventional device shown in FIG. The cylindrical lens 10 becomes unnecessary, and
The structure of the first photodetector 28 can be simplified. Therefore,
It is possible to reduce the number of parts, simplify the structure, and thereby make the device smaller, lighter, and lower in cost.

(b) The first and second photodetectors 28 and 29 have the same diameter of their circular light-receiving surfaces, so the photodetection sensitivities are the same, and by taking the difference in their re-outputs, highly accurate focus errors can be achieved. A signal Ef is obtained. Furthermore, since the first and second photodetectors 28 and 29 are installed at positions where the receiving diameter is smaller than the outer diameter of the incident light, the magneto-optical disk 24 may run out in the focus direction. Also, 1st.
Since the incident light is always incident on the entire light receiving surface of the second photodetector 28, 29, and the photodetection sensitivity is constant, the detection accuracy of the focus error signal Ef is further improved.

(c) P emitted from the polarizing beam splitter 27
Since the polarized light component and the S-polarized light component are in the same direction, it becomes possible to arrange the first and second photodetectors 28, 29 on the same plane, for example, and easily form an integrated structure. 1st
When the second photodetector is integrated, one photodetector can receive light of P polarization component and S polarization component, thereby reducing the weight of the movable part, which is an essential part of high-speed access. It is possible to further improve miniaturization.

Note that the present invention is not limited to the illustrated embodiment, and various modifications are possible. Examples of such modifications include the following.

(i> In FIG. 3, instead of the first photodetector 28, the two second photodetectors may be configured with a two-split photodetector. In this case, the second photodetector If the dividing line of the detector 29 is arranged parallel to the track direction and the difference between the two outputs of the two photodetectors is differentially amplified by a differential amplifier, the track error signal Et can be detected, and the same result as in the Jtic'\ embodiment can be obtained. Benefits can be obtained.

Also, both the first and second photodetectors 28.29
It may also be configured with a split photodetector. In this case, the dividing lines of each of the two-split photodetectors are arranged parallel to the track/reverse directions. If the difference between the sums of the outputs of the respective two-split child detectors in the same direction is determined using a differential amplifier, a highly accurate I/rack error signal E1. can be detected.

(ii) In FIG. 1, a reflective magneto-optical disk 24
However, a transmission type magneto-optical disk may also be used.

In this case, after the transmitted light of the transmission type magneto-optical disk is made into parallel light by a collimator lens, the light is sent to the 1/2 wavelength plate 2.
If the light is incident on the converging lens 26 side J\ through the lens 5, substantially the same operation and effect as in the embodiment described above can be obtained.

(iii> The reproducing optical system shown in FIG. 1 can also be used during recording.

(Effect of the invention) As explained in detail above, according to the invention of claim 1,
P-polarized light that is not emitted from the polarizing beam splitter is directly incident on a first photodetector, and S-polarized light that is in the same direction as the P-polarized light is incident on a second photodetector. Because of this configuration, it is possible to detect track error signals, focus error signals, and magneto-optical signals with high precision based on the outputs of the first and second photodetectors. This eliminates the need for a conventional cylindrical lens, and simplifies the structure of the first photodetector, reducing the number of parts and simplifying the structure, making the device smaller, lighter, and lower in cost. can be improved.

In the invention of claim 2, the first photodetector is formed by a two-split photodetector.
Alternatively, the I/Rack error signal can be detected by the difference between the two outputs of the second photodetector, and by further determining the output difference between the first and second photodetectors and performing frequency separation with a filter,
Since focus error signals and magneto-optical signals can be detected, a highly accurate signal detection circuit can be easily configured with a simple structure.

In the third aspect of the invention, since the first and second photodetectors are integrated, it is possible to further reduce the size and weight of the device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a magneto-optical disk device showing an embodiment of the present invention, FIG. 2 is a block diagram of a conventional magneto-optical disk device, and FIG. 3 is a block diagram of the signal detection circuit shown in FIG. 1. 20...Light source, 22...Beam splitter, 23...Objective lens, 24...Magneto-optical disk, 25...1/2 wavelength Board, 26・
...Convergent lens, 26 a...Focus, 2
7... Dimming beam splitter, 27a...
...Reflective surface, 28.29...1st. Second photodetector, 28a... Division line, 32.33...
...First and second differential amplifiers, 34...Filter.

Claims (1)

[Scope of Claims] 1. The reflected light or transmitted light from the magneto-optical disk is incident on a polarizing beam splitter with a polarization plane of approximately 45 degrees through a converging lens, and the P-polarized light component and the S-polarized light component are separated by the polarized light beam splitter. In the magneto-optical disk device that detects a focus error signal, a track error signal, and a magneto-optical signal based on the light of and is configured to reflect the S-polarized light component and emit it in the same direction as the P-polarized light component, and is arranged at a position a certain distance closer to the optical axis direction than the focal point of the convergent lens, and a first photodetector having a first light-receiving surface smaller than the cross-sectional area of the light of the polarized component; A second beam having an area equal to the light-receiving surface and smaller than the cross-sectional area of the S-polarized light component.
a second photodetector having a light-receiving surface, at least one of the first and second photodetectors is a two-split photodetector having a dividing line, and the dividing line is connected to the magneto-optical disk. 1. A magneto-optical disk device characterized in that the disk is arranged parallel to the track direction. 2. In the magneto-optical disk device according to claim 1, a first difference outputs a track error signal by amplifying the difference between two outputs of the first or second photodetector constituted by the two-split photodetector. a dynamic amplifier; a second differential amplifier that amplifies the difference in output between the first and second photodetectors; and a focus error signal and a magneto-optical signal by frequency-separating the output of the second differential amplifier. A magneto-optical disk device equipped with a filter that outputs . 3. The magneto-optical disk device according to claim 1 or 2, wherein the first and second photodetectors are integrated.