JPH05274733A - Magneto-optical information reproducing device - Google Patents

Abstract

PURPOSE:To miniaturize an optical head and to reduce its weight by making light generated by a magneto-optical effect of a magneto-optical recording medium interfere with light generated by being diffracted with curved surfaces of an objective lens and detecting a light quantity distribution change. CONSTITUTION:When a linearly polarized light beam from a semiconductor laser 19 is incident upon a curvature surface of the objective lens 23, since a reflectance on vertical polarization to this light beam is tremendously different, a plane of polarization is rotated, and a diffracted image is obtained. A 1/2 wavelength plate 1 is provided between the lens 23 and a polarization beam splitter 22. A polarization beam splitter 2 is used as specified as a transmissivity of 100% and a reflectance of 0% for a P-polarization component, and a transmissivity of 0% and a reflenctance of 100% for an S-polarization component. Then, by making the light generated by the magneto-optical effect of the magneto-optical disk 24 interfere with the light generated by being diffracted with the curved surfaces of the lens 23 and detecting a light quantity distribution change, the optical head can be simplified in constitution, and a domain edge is optically and directly detected, so that irrespective of the size of a domain and a light spot, a domain edge position can accurately be 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 information reproducing apparatus for reproducing recorded information on a magneto-optical recording medium.

[0002]

2. Description of the Related Art In recent years, a magneto-optical information recording / reproducing apparatus using a magneto-optical disk as a recording medium is portable.
There are great expectations for its large storage capacity and its ability to be erased and rewritten. FIG. 15 is a block diagram showing an optical system of the conventional magneto-optical information recording / reproducing apparatus. In FIG. 15, reference numeral 19 denotes a semiconductor laser which is a recording / reproducing light source. A divergent light beam emitted from this semiconductor laser 19 is collimated by a collimator lens 20 and is corrected to a parallel light beam having a circular cross section by a beam shaping prism 21. It Here, the parallel light flux is a linearly polarized light flux (hereinafter, referred to as P-polarized light) having a polarization direction parallel to the paper surface. The P-polarized light beam enters the polarization beam splitter 22. The characteristics of the polarization beam splitter 22 are:
For example, the transmittance of P-polarized light is 60%, the reflectance is 40%, the transmittance of light of linearly polarized light (hereinafter referred to as S-polarized light) having a polarization direction perpendicular to the polarization direction of P-polarized light is 0%, and the reflectance is Is 100%. The P-polarized light flux transmitted through the polarization beam splitter 22 is condensed by the objective lens 23, and a light spot is formed on the magnetic layer of the magneto-optical disk 24.
An external magnetic field is applied from the magnetic head 25 to the light spot irradiating section, and information magnetic domains are recorded on the magnetic layer.

The reflected light from the magneto-optical disk 24 is returned to the polarization beam splitter 22 via the objective lens 23, where a part of the reflected light is separated and introduced to the reproducing optical system. In the reproduction optical system, the separated light beam is further separated by the polarization beam splitter 26 separately prepared. As the characteristics of the polarization beam splitter 26, for example, the transmittance of P-polarized light is 20%, the reflectance is 80%, the transmittance of S-polarized light is 0%, and the reflectance is 100%. One of the light beams separated by the polarization beam splitter 26 is guided to the reproduction optical system 27, and a reproduction signal is generated as described later. The other light flux is guided to the half prism 36 via the condenser lens 35, and is divided into two here, one to the photodetector 37 and the other to the photodetector 39 via the knife edge 38. Be guided. Then, these control optical systems generate servo error signals for light beam auto-tracking control and auto-focusing control.

The reproduction optical system 27 changes the polarization direction of the light beam to 45.
Composed of a half-wave plate 28 for rotating the beam, a condenser lens 29 for condensing the light beam, a polarization beam splitter 30, and photodetectors 31 and 32 for detecting the light beams separated by the polarization beam splitter 30, respectively. Has been done.
As the characteristics of the polarization beam splitter 30, the transmittance of P-polarized light is 100%, the reflectance is 0%, and the transmittance of S-polarized light is 0%.
%, The reflectance is 100%. The signals detected by the photodetectors 31 and 32 are differentially detected by the differential amplifier 33 to generate the reproduction signal 34. Here, in the magneto-optical recording medium, information is recorded by the difference in the direction of perpendicular magnetization, and the recording method includes an optical modulation method and a magnetic field modulation method. The optical modulation method is a method of irradiating a laser beam modulated according to recording information while applying a constant external magnetic field to a recording medium. The magnetic field modulation method is a method in which a recording medium is irradiated with a laser beam having a constant intensity and an external magnetic field modulated according to recording information is applied.

By the way, when a magneto-optical medium on which information is recorded due to the difference in the direction of magnetization is irradiated with linearly polarized light,
The polarization direction of the reflected light rotates clockwise or counterclockwise depending on the direction of magnetization. For example, the polarization direction of linearly polarized light incident on the magneto-optical recording medium as shown in FIG. 16, a coordinate axis P direction, the light reflected against the downward magnetization R ₊ rotated + theta _k, reflected light for the upward magnetization - [theta] _K Rotation R
_- to be. Therefore, when the analyzer is placed in the direction as shown in FIG. 16, the light transmitted through the analyzer is A, R with respect to R _+.
- to B next, when this is detected by the photodetector, it is possible to obtain information as a difference in light intensity. In the example of FIG. 15, the polarization beam splitter 30 serves as an analyzer, and one of the separated light beams is detected in the direction of +45 degrees from the P axis and the other light beam is detected in the direction of −45 degrees from the P axis. Become a photon. That is, since the signal components obtained by the photodetectors 31 and 32 have opposite phases, it is possible to obtain a reproduced signal with reduced noise by differentially detecting individual signals. Also,
Recently, in order to increase the storage capacity, the inter-mark recording method in which the center position of the information pit has a meaning is shifting to the mark length recording method in which the information pit length has a meaning. In this mark length recording method, after the position of the information pit is optically detected by the optical head, the signal is electrically processed to detect the edge portion of the information pit.

[0006]

However, since the polarization rotation angle θ _{k of} the conventional magneto-optical recording medium is very small at ˜1 degree, the information can be obtained by using only the light in the S-axis direction shown in FIG. Was difficult to reproduce. Therefore, conventionally, information is reproduced by causing the light in the P-axis direction and the light in the S-axis direction to interfere with each other using the polarization beam splitter 30 as shown in FIG. Therefore, in such a reproducing system, there are problems that the number of partial points of the optical head increases, the structure becomes complicated and the size becomes large. Further, in the mark length recording method, it is necessary to detect the edge portion of the domain, but in the above-mentioned conventional example, the edge portion is not optically detected directly, and therefore the size of the domain becomes about the light spot. Then, the detection position of the edge portion is shifted, which causes a problem that information cannot be accurately detected.

The present invention has been made to solve the above problems, and its purpose is to reduce the number of constituent parts of an optical head and to accurately detect the edge position of an information pit. It is to provide a magnetic information reproducing device.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical information reproducing apparatus which irradiates a magneto-optical recording medium with a light beam and reproduces recorded information on the recording medium from its reflected light.
Light generated by the magneto-optical effect of the magneto-optical recording medium,
Recorded information is reproduced by causing light generated by diffracting on a curved surface of a lens for narrowing a light beam applied to the recording medium into a minute light spot and detecting the light with a photodetector. And a magneto-optical information reproducing device.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a magneto-optical information reproducing apparatus of the present invention. In FIG. 1, components having the same functions as those of the conventional device shown in FIG. 15 are designated by the same reference numerals, and detailed description thereof will be omitted in this embodiment. In FIG. 1, the NA of the objective lens 23 is 0.
About 55, which has a large curvature surface is used. The semiconductor laser 19 is formed on the curvature surface of the objective lens 23.
When a linearly polarized light beam from is incident, the reflectance for polarized light perpendicular to this light is remarkably different, so the polarization plane rotates and only the polarized light perpendicular to the polarization plane of the incident light is observed. A diffraction image like a leaf clover can be obtained. The light flux of the semiconductor laser 19 is linearly polarized light (P-polarized light) having a polarization direction parallel to the paper surface as in the conventional case. Between the objective lens 23 and the polarization beam splitter 22, 1
A half wave plate 1 is provided. Reference numeral 2 is a polarization beam splitter, in which the transmittance of the P-polarized component is 10
0%, a reflectance of 0%, an S-polarized component transmittance of 0%, and a reflectance of 100% are used. Further, 3 is a condenser lens, 4 is a two-division photodetector, and 5 is a differential amplifier.
The two-division photodetector 4 is arranged so that the division line is orthogonal to the information track of the magneto-optical disk 24. Other configurations are the same as those of the conventional device shown in FIG. Also,
A magnetic field modulation method is used for the information recording method, a knife edge method is used for the autofocus control method in the control optical system, and a push-pull method is used for the autotracking control method.

Next, the operation of this embodiment will be described. First,
The function of the half-wave plate 1 will be described with reference to FIG.
2 (a-1), (a-2) and (a-3) show the behavior of the incident polarization component, and FIGS. 2 (b-1), (b-2) and (b-
3C shows the behavior of the polarization component perpendicular to the incident polarization component generated according to the information on the magneto-optical disk 24, and FIG.
1), (c-2), and (c-3) show the behavior of the polarized light component perpendicular to the incident polarized light component generated by diffraction on the curved surface of the objective lens 23. 2 (a-1), (b-1), (c)
2 (a-2), (b-2), and (c-2) show reflected light before it enters the half-wave plate 1, and FIG. 2 (a-3), (b-3), (c-
3) shows the reflected light that has passed through the half-wave plate 1. Further, in the figure, P is the P polarization direction, S is S
The polarization direction is shown, and the dotted line shows the direction of the optical axis of the half-wave plate 1. Here, it is arranged so as to form an angle of 22.5 degrees with the P polarization direction.

Here, the incident light before entering the half-wave plate 1 is P-polarized light as shown in FIG.
At this time, as shown in FIGS. 2B-1 and 2C-1, S-polarized light has not yet occurred. As for the reflected light reflected by the magneto-optical disk 24 and before entering the half-wave plate 1 through the objective lens 23, the polarization plane of the incident polarization component is 1/2 as shown in FIG. By passing through the two-wave plate 1 once, it rotates 45 degrees. On the magneto-optical disk 24, the light is polarized in a direction forming an angle of 45 degrees with respect to the track direction. In addition, due to the magneto-optical effect (Kerr effect or Faraday effect) of the magneto-optical disk 24, FIG.
2), light having a polarization component perpendicular to the polarization direction of the light in FIG. 2A-2 is generated. Further, as the light of FIG. 2 (a-2) reciprocates through the objective lens 23, a polarization component perpendicular to the polarization direction of the light of FIG. 2 (a-2) is also generated as shown in FIG. 2 (c-2). Light is generated. Then, when each reflected light passes through the half-wave plate 1, the incident polarization component is
As shown in -3), the light returns to P-polarized light, and the light generated by the magneto-optical effect and the light generated by the curved surface of the objective lens 23 become S-polarized light. The relationship between these light intensities is (incident polarization component)> (light generated on the curved surface of the objective lens 23)> (light generated by the magneto-optical effect).

P-polarized light reflected by the magneto-optical disk 24, S
The respective reflected light beams of the polarized light are polarized beam splitter 2
It is separated into a reproduction optical system by 2 and enters the polarization beam splitter 2. The characteristics of the polarization beam splitter 2 are that the transmittance of P-polarized light is 100%, the reflectance is 0%, and S is S, as described above.
Since the transmittance of polarized light is 0% and the reflectance is 100%, the reflected light beam is separated into a P-polarized light beam and an S-polarized light beam. P
The polarized light beam passes through the polarization beam splitter 2 as it is, and a focus error signal and a tracking error signal for autofocus and autotracking control are generated by the control optical system as in the conventional case. On the other hand, the S-polarized light beam is reflected by the polarization beam splitter 2 and enters the two-split photodetector 4 via the condenser lens 3. Then, the reproduction signal 6 is generated by being detected by the respective photodetection surfaces 4-1 and 4-2 of the two-division photodetector 4 and differentially detecting the respective detection signals by the differential amplifier 5. Here, the dividing line of the two-divided photodetector 4 is provided in the direction orthogonal to the information track of the magneto-optical disk 24 as described above.
The light incident on the two-division photodetector 4 is the S-polarized light beam generated by the magneto-optical effect among the light beams shown in FIG.
It is an S-polarized light beam generated on the curved surface of the objective lens 23.

As is clear from FIG. 16, the S-polarized light beam generated by the magneto-optical effect is S _{+ with} respect to the upward magnetization.
Light flux of S ₋ with respect to the downward magnetization, and the phase difference between them is π. In other words, when the boundary (edge portion) of upward magnetization and downward magnetization enters the light spot,
Diffraction of light similar to a pit having a depth of λ / 4 (λ is the wavelength of light) occurs. This will be described later in detail. The S-polarized light flux generated on the curved surface of the objective lens 23 is as follows. In FIG. 3, an arrow A indicates the direction of the information track, and FIG. 3A shows the distribution of S ₊ light generated by the magneto-optical effect on the downward magnetization.
(C) shows the distribution of the diffracted light of S polarization generated on the curved surface of the objective lens 23 in the case where the half-wave plate 1 is not provided in the optical head shown in FIG. As will be described later, if it is left as it is, the overlapping with the diffracted light generated by the magneto-optical effect is poor, and only a DC component is obtained. Therefore, by providing the half-wave plate 1, it is possible to change the distribution of the diffracted light of S polarization generated on the curved surface of the objective lens 23 as shown in FIG. In the four-leaf distribution shown in FIG. 3B, the phases of the lights of the leaves facing each other are the same, and the phase difference of the lights of the adjacent leaves is π. The light in FIG. 3 (b) is
The light enters the two-divided photodetector 4 regardless of the direction of magnetization on the magneto-optical disk 24. FIG. 4 shows the amplitude of light in the cross section taken along the line BB 'in FIG. In this embodiment, this FIG.
The light flux generated on the curved surface of the objective lens 23 in (b) is caused to interfere with the light flux generated by the magneto-optical effect, and the resulting change in the light amount distribution is detected to reproduce the information.

A more detailed description will be given with reference to FIG. Figure 5
(A) is a diagram showing recorded magnetic domains and reproducing light spots, 7 is an information track, and 8 is a domain recorded by a magnetic field modulation method. The recording method may be an optical modulation method. Further, in this embodiment, the magnetization of the magneto-optical disk 24 is all initialized downward at the time of initialization, so that the magnetization of the recorded domain 8 is upward. The light spot 9 is A as shown by 10, 11, 12, and 13 on the information track 7 on which such a domain 8 is recorded.
Scan in the direction. FIG. 5B is a diagram showing the distribution of light on the two-division photodetector 4 at each position of the light spot of FIG. 5A. At the positions of the light spots 9 and 13, since the magnetizations in the light spots are all downward, the diffraction of light does not occur and the distribution on the two-division photodetector 4 becomes circular as shown by 14 and 18. .. Further, at the positions of the light spots 10 and 12, since the arc-shaped boundary between the upward magnetization and the downward magnetization, that is, the edge of the domain 8 is located in the light spots, the light is diffracted in the direction parallel to the information track 7, As shown by 15 and 17, the distribution is divided in the lateral direction, and the phase difference between the left and right lights is π. However, in 15 and 17, the left and right phases are reversed. Further, at the position of the light spot 11, since the downward magnetization is slightly present at the upper and lower positions in the light spot, the light is slightly diffracted in the direction orthogonal to the track, and the distribution extends slightly upward and downward as indicated by 16. Becomes The phase of light at this time has a difference of π as compared with 14 and 18.

FIG. 5C is a diagram showing the light on each of the two-divided photodetectors 4 shown in FIG. 5B as an amplitude distribution in the BB ′ cross section, and the light spots 9, 11, and 13. At the position of, the intensity distribution of light is symmetrical. At the positions of the light spots 10 and 12 located at the edge of the domain 8, the light intensity distribution is asymmetrical. Further, FIG. 5D is a diagram showing a light intensity distribution as a result of causing the distribution shown in FIG. 5C and the distribution shown in FIG. 4 to interfere with each other. Similar to FIG. 5C, the intensity distribution is bilaterally symmetrical at the positions of the light spots 9, 11, 13 and bilaterally asymmetrical at the positions of the light spots 10, 12 at the edge of the domain 8. FIG. 5E is a diagram showing a reproduction signal obtained by differentially detecting the output signals of the respective photodetection surfaces 4-1 and 4-2 of the above-mentioned two-division photodetector 4 with the differential amplifier 5. is there. At the positions of the light spots 9, 11 and 13, since the intensity distribution in the BB ′ cross section of the two-divided photodetector 4 is bilaterally symmetrical as described above, when differential detection is performed by the differential amplifier 5,
As shown in FIG. 5E, the output signal becomes 0, and the reproduced signal does not appear. On the other hand, at the positions of the light spots 10 and 12 where the edge of the domain 8 is located, the intensity distribution is asymmetrical, so that the reproduced signal having a peak in the positive or negative direction as shown in FIG. Can be obtained. Therefore, the edge position of the domain 8 can be detected by detecting the positive and negative peak positions of this reproduction signal.

As described above, in this embodiment, the light generated by the magneto-optical effect of the magneto-optical disk 24 and the light diffracted by the curved surface of the objective lens 23 are caused to interfere with each other, and the change in the light amount distribution is detected. By doing so, the polarization beam splitter, which was conventionally required to interfere the P-axis and S-axis light, becomes unnecessary, and the structure of the spectroscopic head can be simplified. In addition, in order to directly detect the edge of the domain directly, regardless of the size of the domain and the light spot,
The edge position of the domain can be accurately detected.

FIG. 6 is a block diagram showing another embodiment of the present invention. In the present embodiment, the dividing line of the two-divided photodetector 4 is provided in parallel with the information track of the magneto-optical disk 24, and the detection signals of the respective photodetectors of the two-divided photodetector 4 are differentiated. A reproduction signal can be generated by the detection. The half-wave plate 1 shown in the embodiment of FIG. 1 is not used. The other structure is the same as that of the embodiment of FIG. The light flux of the semiconductor laser 19 is similarly linearly polarized light (P-polarized light) having a polarization direction parallel to the paper surface, and this light flux passes through a collimator lens 20, a beam shaping prism 21, a polarization beam splitter 22, and an objective lens 23. The magneto-optical disk 1 is irradiated. The objective lens 23 has an NA of about 0.55 and has a large curvature surface, as in the above-described embodiment. Then, the incident light flux of P-polarized light is focused into a minute light spot by the objective lens 23 and is applied to the magneto-optical disk 24. At this time, the polarization direction of the P polarized light is
It is parallel or perpendicular to the 4th track. When a light beam is incident on the magneto-optical disk 24, S-polarized light which is a component perpendicular to P-polarized light is generated due to the magneto-optical effect (Kerr effect or Faraday effect) of the disk. The light beam incident on the magneto-optical disk 24 is reflected by the medium surface, passes through the objective lens 23 again, and becomes a parallel light beam. This parallel light flux includes S-polarized light generated by the curved surface of the objective lens 23 in addition to S-polarized light generated by the magneto-optical disk 24.

The reflected light beam from the magneto-optical disk 24 is reflected by the polarization beam splitter 22 and guided to the polarization beam splitter 2. The characteristics of the polarization beam splitter 2 are that the transmittance of P-polarized light is 100%, the reflectance is 0%, the transmittance of S-polarized light is 0%, and the reflectance is 100%. As a result, the P-polarized light beam passes through the polarization beam splitter 2 and is guided to the control optical system, and the S-polarized light beam is reflected and guided to the condenser lens 3 side of the reproducing optical system. The control optical system generates error signals for autofocus and autotracking control. The S-polarized light flux guided to the condenser lens 3 is detected by each photodetector of the two-division photodetector 4, and the detection signal of each photodetector is differentially detected by the differential amplifier 5. As a result, the reproduction signal 6 is generated. Two
The dividing line of the divided photodetector 4 is provided parallel to the track of the magneto-optical disk 24 as described above.
The light incident on is the S-polarized light flux generated by the magneto-optical effect and the S-polarized light flux generated on the curved surface of the objective lens 23. As described above, the S-polarized light flux generated by the magneto-optical effect is the S ₊ light flux with respect to the upward magnetization and the S ₋ light flux with respect to the downward magnetization. ) Enters, diffraction of light similar to a pit having a depth of λ / 4 (λ is the wavelength of light) occurs.

The S-polarized light flux generated on the curved surface of the objective lens 23 is as follows. In FIG. 7, reference numerals 4-1 and 4-2 indicate the detection surfaces of the photodetectors of the two-division photodetector 4, and the arrow A indicates the direction of the track. Also,
FIG. 7A shows the distribution of S ₊ light generated by the magneto-optical effect on the downward magnetization, and FIG. 7B shows the distribution of S-polarized diffracted light generated on the curved surface of the objective lens 23. Figure 7
In (b), the distribution is four-leaf, and the phases of the light of the leaves facing each other are the same, and the phase difference of the light of the adjacent leaves is π. That is, the phases of the lights of the leaves that face each other in the detection surfaces 4-1 and 4-2 are the same, and the phase difference between the leaves that are adjacent to each other in the detection surfaces 4-1 and 4-2 is π. Moreover, this FIG.
The light distribution of (b) appears on the two-divided photodetector 4 regardless of the direction of magnetization on the magneto-optical disk 24. FIG. 8 is a diagram showing the amplitude of light in the cross section taken along the line BB ′ and the line CC ′ of FIG. 7B. FIG. 8 (a) shows the amplitude on the line BB ', and FIG. 8 (b) shows the amplitude on the line CC', which are as shown in the figure due to the phase relationship of the above-mentioned four-lobed leaves. Amplitude. In this embodiment, the light flux generated by the magneto-optical effect shown in FIG. 7A is caused to interfere with the curved surface of the objective lens 23 shown in FIG. 7B, and the resulting change in the light amount distribution is detected. To reproduce the information.

Information reproduction will be further described with reference to FIG. FIG. 9A is a diagram showing a reproducing light spot and magnetic domains.
Is an information track, and 8 is a domain recorded by the magnetic field modulation method. The recording method may be an optical modulation method. Further, the magnetizations of the magneto-optical disk 24 are all initialized downward, so that the magnetization of the domain 8 is upward. The light spot 9 scans in the A direction on the information track 7 on which the domain 8 is recorded as shown by 10, 11, 12, and 13. FIG. 9B is a diagram showing the distribution on the two-division photodetector 4 of the S-polarized light generated by the magneto-optical effect at each position of the light spot of FIG. 9A. 4-1 and 4-2
Indicates each detection surface of the two-divided photodetector 4. At the positions of the light spots 9 and 13, since the magnetizations in the light spots are all downward, the diffraction of light does not occur and the distribution on the two-division photodetector 4 becomes circular. At the positions of the light spots 10 and 12, the edge of the domain 8 is located in the light spot and the upward magnetization and the downward magnetization are mixed, so that the light is diffracted in the direction parallel to the track 7 and the two-divided photodetector 4 In the above, the light is distributed to the left and right as shown in the figure. The phase difference between the left and right lights at this time is π, but the phase difference between the left and right lights is reversed at the positions of the light spots 10 and 13. Also, the light spot 11
At the position of, since the magnetization in the light spot is almost upward, the light is not diffracted, and the light distribution is as shown in the figure. The phase of the light at this time has a difference of π from the phase at the positions of the light spots 9 and 10.

FIG. 9C is a diagram showing the amplitude of light in the cross section taken along the line DD 'of FIG. 9B at the position of each light spot. 9 (d) and 9 (e) are respectively shown in FIG.
FIG. 9D is a diagram showing a light intensity distribution as a result of causing the light distribution shown in FIG. 7B and the light distribution shown in FIG. 7B to interfere on the two-division photodetector 4. Is the intensity distribution along the line BB ', and FIG. 9 (e) is the intensity distribution along the line CC'.
At the positions of the light spots 9, 11, and 13 shown in FIG.
Looking at the distribution of (e), the left and right distributions are asymmetrical on the two-division photodetector 4, but the light amounts on the detection surfaces 4-1 and 4-2 are the same. Further, the left and right distributions are symmetrical at the positions of the light spots 10 and 12 where the edges of the domain 8 are located, but a light amount difference occurs between the detection surfaces 4-1 and 4-2. As a result, when the detection signals of the detection surfaces 4-1 and 4-2 are differentially detected by the differential amplifier 5, the light amounts are the same on the detection surfaces 4-1 and 4-2 as shown in FIG. 9F. The reproduced signal does not appear at the positions of the light spots 9, 11 and 12, and the reproduced signal having a peak in the positive or negative direction appears only at the positions of the light spots 10 and 12 where the light amounts differ. Therefore,
By detecting the positive and negative peak positions of this playback signal,
The edges of domain 8 can be detected. As described above, also in the present embodiment, the configuration of the optical head can be simplified and the edge position of the domain can be accurately detected as in the embodiment of FIG.

FIG. 10 is a block diagram showing still another embodiment of the present invention. This embodiment is an example in which a 4-divided photodetector is used as the photodetector so that a reproduction signal can be obtained regardless of whether the pit position recording system or the pit edge recording system is used. In FIG. 10, reference numeral 50 designates a four-division photodetector for detecting the reflected light from the magneto-optical disk 24.
Reference numerals 1 and 52 are addition amplifiers for adding detection signals on the detection surfaces of the four-division photodetector 50 at the diagonal positions, and 53 is differential detection of the output signals of the addition amplifiers 51 and 52 to determine the pit position. It is a differential amplifier for generating a reproduction signal of information by a recording method. Further, 54 and 55 are addition amplifiers for adding the detection signals of the detection surfaces which are adjacent to each other in the direction parallel to the tracks of the four-division photodetector 50, and 56 differentially detects the output signals of the addition amplifiers 54 and 55. This is a differential amplifier for reproducing information by the pit edge recording method. Other configurations are the same as those of the embodiment shown in FIG. Further, in the present embodiment, as in the previous embodiments, the information recording method is the magnetic field modulation method, the focus control is the knife edge method, and the tracking control is the push-pull method. Further, the light flux of the semiconductor laser 19 is linearly polarized light (P polarized light) having a polarization direction parallel to the paper surface.

The detection surface of the four-division photodetector 50 is divided into four in a cross shape, and one of the division lines of the four-division photodetector 50 is parallel to the track direction of the magneto-optical disk 24. , The other is arranged to be orthogonal. The light beams incident on the four-division photodetector 50 are the S-polarized light beam generated by the magneto-optical effect and the S-polarized light beam generated by the curved surface of the objective lens 23 as described above. The luminous flux of is similar to that described in the embodiment of FIGS. The S-polarized light flux generated on the curved surface of the objective lens 23 is basically the same as that of the embodiment of FIG. 6, but the detection surface of the photodetector is different,
FIG. 11 shows the detection surface of the four-division photodetector 50 and the light distribution on this detection surface. In FIG. 11, 50-1 to 50-4
Are the detection surfaces divided by the four-division photodetector 50, and the arrow A indicates the direction of the track. 11A shows the distribution of S ₊ light generated by the magneto-optical effect on the downward magnetization, and FIG. 11B shows the distribution of S-polarized diffracted light generated on the curved surface of the objective lens 23. In the four-leaf light distribution shown in FIG. 11B, the light phases of the leaves facing each other are the same, and the phase difference of the light of the adjacent leaves is π. In addition, the four-leaf light shown in FIG.
It is distributed on the four-division photodetector 50 regardless of the direction of magnetization of No. 4. The amplitudes of the light on the lines BB 'and CC' in FIG. 11B are as shown in FIGS. 8A and 8B. In the present embodiment, information is reproduced by causing the light flux generated on the curved surface of the objective lens 23 shown in FIG. 11B to interfere with the light flux generated by the magneto-optical effect and detecting the resulting change in the light amount distribution. It is a thing.

A more detailed description will be given with reference to FIG. Figure 1
2 (a) is a diagram showing a reproducing light spot and magnetic domains.
Is an information track, and 8 is a domain recorded by the magnetic field modulation method. Of course, a light modulation method may be used. The magnetizations of the magneto-optical disk 24 are all initialized downward, so that the domain 8 has an upward magnetization. The light spot 9 is A on the information track 7 as indicated by 10, 11, 12, and 13.
Scan in the direction. FIG. 12B is a diagram showing the distribution on the 4-division photodetector 50 of the S-polarized light generated by the magneto-optical effect at each position of the light spot of FIG. 12A. The light distribution is the same as that of the embodiment of FIG. 6 described above (see FIG. 9). That is, the light spots 9 and 1
At the position of 3, all the magnetization in the light spot is downward, so that light diffraction does not occur and the distribution on the two-division photodetector 50 is circular. At the positions of the light spots 10 and 12, since the edge of the domain 8 is located within the light spot,
Light is diffracted in the direction parallel to the track 7, and the light distribution is divided into left and right as shown in the figure. At the position of the light spot 11,
Since the inside of the light spot is almost upwardly magnetized, there is almost no light diffraction and the distribution is as shown in the figure.

FIG. 12C shows each DD 'of FIG. 12B.
The figure which showed the amplitude of the light in the cross section in a line, FIG.12 (d).
And (e) are the distribution of light shown in FIG. 11 (b) and FIG.
FIG. 12D is a diagram showing a light intensity distribution as a result of interference of the light distribution of FIG. 12B on the four-division photodetector 50, and FIG.
The intensity distribution along line B ', and FIG. 12 (e) is the intensity distribution along line CC'. The amplitude and intensity distribution of these lights are the same as in FIG. At the positions of the light spots 9 and 13,
The strengths of the detection surfaces 50-1 and 50-3 are the same as those of the other detection surfaces 50-.
It becomes larger than the strength of 2, 50-4. In this case, the detection surfaces 50-1 and 50-3 have the same strength, and the detection surfaces 50-2 and 50-4 also have the same strength. At the position of the light spot 11, on the contrary, the detection surfaces 50-2, 50-
4 becomes larger than the intensities of the detection surfaces 50-1 and 50-3, and the intensities of the detection surfaces 50-2 and 50-4 and the detection surfaces 50-1 and 50-3 at this time are the same. .. At the position of the light spot 10 where the left edge of the domain 8 is located, the intensities of the detection surfaces 50-1 and 50-2 are the same.
-3 and 50-4, the detection surfaces 50-1 and 50-2 and the detection surfaces 50-3 and 50-4 have the same strength. At the position of the light spot 12 where the left edge of the domain 8 is located, the intensity of the detection surfaces 50-3 and 50-4 is higher than the intensity of the detection surfaces 50-1 and 50-2, contrary to the above. .. Detection surface 5 at this time
0-3 and 50-4 and the detection surfaces 50-1 and 50-2 have the same intensity.

The detection signal of each detection surface of the four-division photodetector 50 is output to the summing amplifiers 51, 52 and 54, 55 as described with reference to FIG. Here, the detection signals of the detection surfaces 50-1 and 50-3 and the detection surfaces 50-2 and 50-4 of the diagonal positions are added by the addition amplifiers 51 and 52, respectively, and the obtained addition signals are differentiated. When differential detection is performed by the amplifier 53, a reproduction signal as shown in FIG. 12 (f) can be obtained. That is, a positive signal is obtained in the downward magnetization region and a negative signal is obtained in the upward magnetization region, and a reproduction signal corresponding to the pit position recording rising or falling at the edge of the domain 8 can be obtained. In addition, the detection surfaces 50-1 and 50-2 and the detection surfaces 50-3 and 5 that are adjacent to each other in the track direction.
The detection signals of 0-4 are added to the addition amplifiers 54 and 55, respectively.
When the differential signal is differentially detected by the differential amplifier 56, a reproduction signal as shown in FIG. 12G can be obtained. That is, a reproduced signal having a positive or negative peak is obtained at the edge of the domain 8, and a reproduced signal corresponding to pit edge recording can be obtained.

In this embodiment, the information reproducing apparatus capable of both pit position recording and pit edge recording is shown. However, when the recording medium is attached to the apparatus, the pit position recording is automatically performed according to the recording medium. It is desirable to select either the reproduction of pit edge recording or the reproduction of pit edge recording. Therefore, an example of this selection switching control device will be described. First, as shown in FIG. 13, a mark 61 indicating whether the disc is a pit position recording disc or a pit edge recording disc is added to the case 60 of the magneto-optical disc 24. The mark 61 is optically detected. For example, a disc for recording pit positions has a high reflectance and a disc for recording pit edges has a low reflectance. On the other hand, a light emitting diode 62 and an optical sensor 63 are provided on the device side so that when the disc is mounted in the device, the light emitting diode 62 projects light to the mark 61 and the reflected light is received by the optical sensor 63. Leave. Therefore, when the magneto-optical disk 24 is mounted on the apparatus, signal reproduction may be switched and controlled by the procedure shown in FIG. That is, mounting of the magneto-optical disk in the apparatus (step 1), investigation based on the detection signal of the mark 61 of the disk case 60 by the optical sensor 63 (step 2), and whether the disk is a pit position recording disk according to the result Discrimination as to whether the disc is an edge recording disc (step 3), reproduction selection corresponding to pit position recording based on the discrimination result (step 4), or reproduction selection corresponding to pit edge recording (step 5) may be performed. As described above, when the magneto-optical disk is mounted on the apparatus, it is possible to automatically select the signal reproduction corresponding to the disk recording method.

[0028]

As described above, the present invention has the following effects. (1) The light generated by the magneto-optical effect of the magneto-optical recording medium interferes with the light generated by diffraction on the curved surface of the objective lens,
By detecting the change in the light quantity distribution, the number of components of the optical head can be reduced, and the optical head can be made smaller, lighter and less expensive. (2) To solve the problem that the detection position of the edge of the pit shifts when the size of the pit becomes almost the same as that of the light spot in order to directly detect the edge of the recording pit optically. You can Therefore, the position of the pit edge can be accurately detected regardless of the size of the pit, and the reliability of the reproduction signal in the pit edge recording system can be significantly improved. (3) The light is detected by the four-division photodetector that is divided in the direction orthogonal to the information track and in the direction parallel to the information track, and a predetermined analog operation is performed using the detection signal of each photodetector. Information can be reproduced on any recording medium for pit position recording and pit edge recording.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a magneto-optical information reproducing apparatus of the present invention.

FIG. 2 is an explanatory diagram for explaining the function of a half-wave plate 1 used in the embodiment of FIG.

FIG. 3 is a diagram showing a distribution of light diffracted by the curved surface of the objective lens in the example of FIG.

FIG. 4 is a diagram showing the amplitude of light along line BB ′ in FIG.

5 is a diagram for explaining the information reproducing operation of the embodiment of FIG.

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

7 is a diagram showing the distribution of light diffracted by the curved surface of the objective lens of the embodiment of FIG.

FIG. 8 is a diagram showing the amplitude of light at the line BB ′ and the line CC ′ in FIG. 7.

FIG. 9 is a diagram for explaining the information reproducing operation of the embodiment of FIG.

FIG. 10 is a configuration diagram showing still another embodiment of the present invention.

11 is a diagram showing the distribution of light diffracted by the curved surface of the objective lens in the example of FIG.

FIG. 12 is a diagram for explaining the information reproducing operation of the embodiment of FIG.

FIG. 13 is a view showing a mark for discriminating a recording system added to a case of a magneto-optical disc and a sensor for detecting the mark.

FIG. 14 is a flowchart showing a procedure for switching control of signal reproduction corresponding to a pit position recording disc and a pit edge recording disc.

FIG. 15 is a configuration diagram showing an optical system of a conventional magneto-optical information recording / reproducing apparatus.

FIG. 16 is a diagram showing a polarization direction of linearly polarized light incident on the magneto-optical recording medium, a rotation state corresponding to the magnetization direction of the reflected light on the medium, and a change state thereof with respect to an analyzer.

[Explanation of symbols]

 1 1/2 Wave Plate 2 Polarizing Beam Splitter 3 Condensing Lens 4 Divided Photo Detector 5, 53, 56 Differential Amplifier 7 Information Track 8 Domain 9, 10, 11, 12, 13 Light Spot 19 Semiconductor Laser 23 Objective Lens 24 magneto-optical disk 25 magnetic head 50 four-division photodetector 51, 52, 54, 55 summing amplifier

Claims (7)

[Claims] 1. A magneto-optical information reproducing apparatus which irradiates a magneto-optical recording medium with a light beam and reproduces recorded information on the recording medium from the reflected light, and light generated by a magneto-optical effect of the magneto-optical recording medium, Recorded information is reproduced by causing light generated by diffracting on a curved surface of a lens for narrowing a light beam applied to the recording medium into a minute light spot and detecting the light with a photodetector. Magneto-optical information reproducing device. 2. A half-wave plate for rotating a polarization direction in an optical path of light incident on the magneto-optical recording medium by an angle of about 45 degrees with respect to an information track of the recording medium, and the recording. A polarization beam splitter for separating linearly polarized light having a polarization direction perpendicular to the polarization direction of the incident light from the reflected light of the medium is provided, and the separated light is directed in a direction orthogonal to the information track. 2. The magneto-optical information according to claim 1, wherein the information is reproduced by detecting with a two-divided photodetector divided into two and differentially detecting a detection signal of each detection surface of the photodetector. Playback device. 3. A polarization beam splitter for separating linearly polarized light having a polarization direction perpendicular to the polarization direction of the incident light from the reflected light of the magneto-optical recording medium is provided, and the separated light is used as the information. The information is reproduced by detecting with a two-division photodetector divided into two in the direction parallel to the track, and differentially detecting the detection signals of each detection surface of the photodetector. 1. A magneto-optical information reproducing device. 4. A polarization beam splitter for separating linearly polarized light having a polarization direction perpendicular to the polarization direction of the incident light from the reflected light of the magneto-optical recording medium is provided, and the separated light is used as the information. The pit position is detected by detecting with a four-division photodetector that is divided into four in the direction orthogonal to the track and in the direction parallel to it, and performing a predetermined analog operation using the detection signals of each detection surface of this photodetector. 2. The magneto-optical information reproducing apparatus according to claim 1, wherein signal reproduction corresponding to recording or pit edge recording is performed. 5. The information of the pit position recording is reproduced by adding the detection signals of the detection planes at the diagonal positions of the four-division photodetector and by differentially detecting the obtained addition signals. The magneto-optical information reproducing apparatus according to claim 4, wherein 6. The information of the pit edge recording is reproduced by adding the detection signals of the detection surfaces which are adjacent to each other in the information track direction of the four-division photodetector and differentially detecting the obtained addition signals. The magneto-optical information reproducing device according to claim 4, wherein 7. A means for detecting the medium identification information added to the magneto-optical recording medium to determine whether the medium is a pit edge recording medium or a pit position recording medium. 5. The magneto-optical information reproducing apparatus according to claim 4, wherein the magneto-optical information reproducing apparatus is provided, and signal reproduction corresponding to pit position recording or pit edge recording is selected according to a result of the determination.