JPH06101153B2 - Signal detector for magneto-optical disk - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk device, and more particularly to a magneto-optical disk device having a small and inexpensive optical head.

[Background of the Invention]

The optical head of the conventional magneto-optical disc device is, for example, as shown in Fig. 9 on page 17 of the Technical Report of the Institute of Electrical Communication, CPM83-53, an information reproducing optical system and a defocus detecting optical system and a track deviation detecting optical system. The system was separated. This will be described with reference to FIG. The laser light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and the laser spot 5 is focused on the disk 4 surface by the focusing lens 3. The above-mentioned Technical Report of the Institute of Electrical Communication of Japan, CPM 83-53, 17
In the description example of FIG. 9 on the page, a triangular prism for shaping the beam intensity distribution and a mirror for bending the optical axis are described, but they are omitted because they are not related to the present invention. Disk 4
The reflected light from is again collimated by the focusing lens 3, reflected by the beam splitter 6, and part of it passes through the beam splitter 7 and is composed of a focusing lens 8, a cylindrical lens 9 and a four-division photodetector. To the optical system for detecting the focus shift and the track shift detection. On the other hand, the light reflected by the beam splitter 7 is guided to an information reproducing optical system including a half-wave plate 11, a focusing lens 12, a polarization beam splitter 13, and photodetectors 14 and 15. FIG. 7 is a diagram for explaining the principle of information reproduction. The horizontal axis 16 indicates the P polarization direction with respect to the reflecting surface of the polarized beam splitter 13 in FIG. 6, and the vertical axis 17
Indicates the polarization direction. There is a magnetic film on the surface of the disk 4, and information is recorded by reversing the magnetization direction in the magnetic film. Laser spot 5 on this magnetic film
Is irradiated, the polarization direction of the reflected light is rotated by about 0.5 degree due to the reversal of the magnetization direction due to the magneto-optical effect (Kerr effect).
The magneto-optical disk device reproduces information by detecting the minute rotation of the polarization direction. FIG. 7 (a) shows the polarization direction of light before entering the half-wave plate of FIG. 6, and the spot 5 is irradiated on the magnetic film of the disk 4 where information is not recorded. The direction of deflection of light in the case of the presence is shown by an arrow 18. When the spot 5 moves to a portion where information is recorded, the deflection direction of the light rotates as shown by an arrow 19. FIG. 7 (b) shows the deflection direction of the light passing through the half-wave plate 11. By rotating and adjusting the half-wave plate, the state in the deflection direction can be rotated by about 45 degrees.
And the direction of arrow 19 is rotated about 45 degrees compared to (a).
Since the polarized beam splitter has a property of transmitting P-polarized light shown by the horizontal axis 16 and reflecting S-polarized light shown by the vertical axis 17,
When the spot 5 is present on the magnetic film portion where no information is recorded, of the polarized light indicated by the arrow 18, the amount of light indicated by the arrow 20 is transmitted through the polarized beam splitter 13 and received by the photodetector 14,
The amount of light indicated by the arrow 21 is reflected by the polarized beam splitter 13 and received by the photodetector 15. On the other hand, when the spot 5 is present on the magnetic film portion on which information is recorded, the light quantity indicated by the arrow 22 of the polarized light indicated by the arrow 19 is received by the photodetector 14, and the arrow 23
The light amount indicated by is received by the photodetector 15. Therefore, depending on the presence or absence of information recording, the photodetector 14 decreases by the amount of light indicated by the arrow 24, and the photodetector 15 increases by the amount of light indicated by the arrow 25, so the difference between the outputs of the photodetectors 14 and 15. An information reproduction signal can be obtained by taking When the avalanche photodiode is used for the photodetectors 14 and 15, the focusing lens 12 is used for the purpose of focusing the light flux on the light receiving surface because the light receiving surface is small. It is arranged at the focal point of light by the focusing lens 12.

However, as shown in the above example, in the conventional optical head, the information reproducing optical system and the focus deviation detection and the track deviation detection optical system are separated, so the optical head becomes large, and the number of parts is large and expensive. There was a problem.

[Object of the Invention]

It is an object of the present invention to provide a magneto-optical disk device having a compact and inexpensive optical head.

[Outline of idea]

The present invention comprises a light source, a detection system, and an optical system for irradiating the information recording medium with light from the light source as a light spot, and guiding reflected light from the information recording medium to the detection system, In order to separate the output light of the focusing lens, the focusing lens, and the output light of the focusing lens into the first focusing light and the second focusing light, the detection system sequentially arranges the wavelength plate on the output optical path from the optical system. A beam splitter, a first photodetector arranged on the optical path of the first focused light, and a second photodetector arranged on the optical path of the second focused light,
The first photodetector is located in front of the focal point of the first focused light, the second photodetector is located behind the focal point of the second focused light, and the first and second The defocus signal and the information reproduction signal are obtained from the output of the photodetector.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. The laser beam emitted from the semiconductor laser 1 is collimated by the collimator lens 2, reflected by the mirror 30, and the laser spot 5 is imaged on the surface of the disk 5 by the focusing lens 3. The reflected light from the disc is collimated again by the focusing lens 3 and reflected by the beam splitter 6,
A part of it is further reflected by the beam splitter 7, and the half-wave plate 11, the focusing lens 32, and the polarization beam splitter 13 are reflected.
And the defocusing detection and information reproducing optical system including the two photodetectors 35 and 36. First, the principle of defocus detection will be described. By rotating and adjusting the half-wave plate 11,
The polarization direction of the incident light of the polarization beam splitter 13 can be rotated about 45 degrees with respect to the S polarization direction or the P polarization direction of the reflection film of the polarization beam splitter 13, and the amount of light can be changed by the polarization beam splitter 13. Can be separated almost equally.
In a focused state where the spot 5 is on the disk 4 surface, a photodetector 35 is arranged between the position of one focusing point 33 by the focusing lens 32 and the polarized beam splitter 13 and the position of the other focusing point 34. A photodetector 36 is arranged in the direction opposite to the polarized beam splitter 13. The distance between the focusing point 33 and the photodetector 35 and the distance between the focusing point 34 and the photodetector 36 are substantially equal. The shaded portions 36a, 36b, and 36c in FIG.
Shows the shape of the divided light receiving element of, and the shaded portions 35a and 35b in (b)
Reference numeral 35c indicates the shape of the split light receiving element of the photodetector 35. Yen 37 and 38
Indicate the shape of the light beam on the light receiving surfaces of the photodetectors 35 and 36, respectively, and have substantially the same size in the above-mentioned focused state.
When the disc 4 approaches the focusing lens 3, the focusing point 34 approaches the photodetector 36, so that the light flux 38 on the light receiving surface becomes small as shown in FIG. 7C, and the focusing point 33 is separated from the photodetector 35. Therefore, the light flux 37 on the light receiving surface becomes large as shown in (d). On the contrary, when the disk 4 is displaced in the direction away from the focusing lens 3, the luminous flux 38 increases and the luminous flux 37 decreases as shown in (e) and (f). Therefore, split light receiving element
The defocus detection signal can be obtained by subtracting the sum of the outputs of 36a and 36b and the output of the divided light receiving elements 35a and 35b. Further, the defocus detection signal can also be obtained by subtracting the outputs of the divided light receiving elements 36C and 35C.

Next, the information reproduction signal can be obtained by subtracting the sum of the divided light receiving elements 36a, 36b and 36c and the sum of the divided light receiving elements 35a, 35b and 35c. The half-wave plate 11, the polarization beam splitter 13 and the two photodetectors shown in this embodiment are used.
The reproducing principle in the information reproducing system using 35 and 36 has been described in detail in the above-mentioned conventional example, and therefore will be omitted here.

Since there is a common part in the calculation of the outputs of the respective divided light-receiving elements in order to obtain the defocus signal and the information reproduction signal, there is a possibility that the signals interfere with each other. However, the fluctuation frequency of the defocus signal is several hundred Hz because the disk rotation speed is several tens Hz, whereas the frequency of the information reproduction signal is several mega Hz because the information recording interval is several μm. In this case, there is no problem because they can be sufficiently separated by using a filter circuit or the like.

The photodetector 39 is for detecting the deviation between the track on the disk surface and the spot 5. For example, the oblique lines 39a and 3 in FIG.
It has divided light receiving elements indicated by 9b and 39c. Since the principle of detecting the track shift is described in detail in Japanese Patent Laid-Open No. 58-56236, the description thereof will be omitted. The luminous flux patterns on the light receiving surface of the photodetector 39 are the O-order diffracted light 40a and the ± 1st-order diffracted lights 40b and 40c.
Interfere with each other, and the light intensity in the interference regions 40ab and 40ac changes due to the track shift.
A track shift detection signal is obtained by subtracting the outputs of the light receiving elements 39a and 39b placed in ab and 40ac.

The electromagnet 31 is for generating an external magnetic field applied to the magnetic film of the disk 4 in order to record and erase information. Further, the optical head composed of the above-mentioned optical elements, the electromagnet 31, and the disk 4 are movably mounted in, for example, a moving table, and are positioned at a desired track position by a feed motor such as a liner motor. The tracking control is performed by using, for example, a deflecting mirror as the mirror 30, and driving the deflecting mirror by a tracking signal detected from the output of the photodetector 39. On the other hand, in the automatic focus control, for example, an actuator such as a voice coil is provided around the squeezing lens 3, and the actuator is driven by the defocus detection signal detected from the outputs of the photodetectors 35 and 36, and the squeezing lens 3 It is performed by moving in the optical axis direction. Even if the actuator provided in the aperture lens 3 is a two-dimensional actuator that can also move in the radial direction of the disk and this actuator is driven by a tracking signal and a defocus detection signal, tracking control and automatic focus control can be performed. Good.

In the embodiment shown in FIG. 1, the track deviation detection signal is obtained by the dedicated photodetector 39, but the diffraction interference pattern due to the track is the light beam 37 and the light beam 38 in FIGS. 2 (a) and 2 (b). Also occurs. Therefore, the light receiving element 35 in the center of the photodetectors 35 and 36
Since a split light receiving element is formed symmetrically in the interference region of the 0th-order diffracted light and the ± 1st-order diffracted light in c and 36c, and the track shift signal can be obtained by subtracting the outputs thereof, the beam splitter The photodetector 39 can be eliminated.

FIG. 4 is a diagram showing another embodiment of the present invention in which the embodiment shown in FIG. 1 is improved based on the above idea. Photo detector
Reference numeral 51 denotes a divided light receiving element indicated by shaded portions 51a, 51b, 51c, 51d and 51e in FIG. 5 (a), and the photodetector 52 is shown in FIG. 5 (b).
The divided light receiving elements indicated by the shaded portions 52a, 52b, 52c, 52d, and 52e. The operation of the other configuration in FIG. 4 is the same as that in FIG. 3, and therefore the description is omitted. The focus shift detection signal can be obtained by subtracting the sum of the divided light receiving elements 51a and 51c and the sum of 52a and 52b. Divided light receiving element 51d placed in the interference region between 53c or 54b and 54c
And output of 51e or subtraction of outputs of 52d and 52e or addition of two subtraction results. The information reproduction signal can be obtained by subtracting the total output of the photodetector 51 and the total output of the photodetector 52.

The tracking control and the automatic focusing control can be performed in the same manner as the embodiment shown in FIG.

The optical head according to the present embodiment described above is not limited to the information reproduction by the magneto-optical effect described above, but the photo detector of FIG.
By adding the total output of 35 and the total output of the photodetector 36, or by adding the total output of the photodetector 52 and the total output of the photodetector 53 in FIG. It goes without saying that the information recorded by the can be reproduced.

〔The invention's effect〕

According to the present invention, the number of optical components constituting the optical head can be reduced, the optical head can be made compact and lightweight, and an inexpensive optical head can be obtained.

[Brief description of drawings]

FIGS. 1, 2 and 3 are views for explaining an embodiment of the optical head of the magneto-optical disk device according to the present invention, and FIGS. 4 and 5 are other embodiments of the optical head according to the present invention. 6 is a diagram showing an example of the structure of a conventional magneto-optical disc optical head, and FIG. 7 is a diagram showing the principle of information reproduction by the magneto-optical effect. 1 ... Semiconductor laser, 3 ... Focusing lens, 4 ... Disk, 11 ... Half wave plate, 32 ... Focusing lens, 13 ... Polarized beam splitter, 35, 36, 52, 53 ... Photodetector.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takeshi Maeda 1-280 Higashi Koigakubo, Kokubunji, Tokyo 1-280, Central Research Laboratory, Hitachi, Ltd. (72) Yoshito Tsunoda 1-280 Higashi Koigakubo, Kokubunji, Tokyo Hitachi Ltd. Central Research Laboratory (72) Inventor Toshimitsu Kaku 1-280 Higashi Koigakubo, Kokubunji, Tokyo Hitachi Central Research Laboratory (72) Inventor Tsuyoshi Kato 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Hitachi Central Research Institute ( 56) References JP 49-126323 (JP, A) JP 60-43234 (JP, A) Radio Science, February 1985 (1985-2-1) Japan Broadcast Publishing Association, P. 99 ~ 103

Claims (3)

[Claims] 1. A light source, a detection system, and an optical system for irradiating the information recording medium with light from the light source as a light spot and guiding reflected light from the information recording medium to the detection system. The detection system splits the output light of the focusing lens and the output light of the focusing lens into a first focused light and a second focused light, which are sequentially arranged on the output optical path from the optical system. A polarizing beam splitter, a first photodetector divided into three parts arranged on the optical path of the first focused light, and three light detectors arranged on the optical path of the second focused light. A second photodetector divided into parts,
The first photodetector is located in front of the focal point of the first focused light, the second photodetector is located behind the focal point of the second focused light, and the first and second Of the first photodetector has the same shape as the light-receiving surface of the first photodetector, and includes the first part and the second and third parts sandwiching the first part, and the second part of the first and second photodetectors.
And a defocus signal is obtained by subtracting the sum signals of the outputs obtained from the third part, and the magneto-optical information reproduction signal is obtained by subtracting the signals obtained from all the parts. Signal detector for magneto-optical disk. 2. The distance between the first photodetector and the focal point of the first focused light is equal to the distance between the second photodetector and the focal point of the second focused light. A signal detecting device for a magneto-optical disk according to claim 1. 3. The magneto-optical device according to claim 1 or 2, wherein the optical system has means for separating a light beam for detecting a track shift signal from the output light. Signal detection device for discs.