JPH035924A - Track deviation detection device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a device for detecting track deviation of an optical head used in an optical information processing device such as an optical disk device, an optical card device, or an optical tape device. be.

[Conventional technology]

Conventionally, track deviation detection devices for optical disk devices and the like have been developed using a three-spot method using a diffraction grating.
9-58637) is known.

In a three-spot type track deviation detection device using a diffraction grating, two sub-spots for detecting track deviation are provided 17η behind the main spot, and by tilting the diffraction grating.

The sub spot is shifted left and right from the main spot. The amount of deviation of the sub-spot in the left-right direction is approximately one-fourth of the track interval. Here, the forward direction is the direction in which the spot moves along the track, and the left-right direction is the direction perpendicular to the track direction.

In this track deviation detection device, when the amount of reflected light from one of the two sub-spots increases due to the tracking deviation of the main spot, the amount of reflected light from the other sub-spot decreases. Therefore, by detecting the amount of reflected light from the two sub-spots with two photodetectors and obtaining a difference signal between the outputs thereof, a track deviation detection signal can be obtained.

[Problem to be solved by the invention]

However, when a conventional three-spot type track deviation detection device using a diffraction grating is used in a recordable optical disk device, for example, as discussed in Japanese Patent Application Laid-Open No. 63-44322, There is a problem in that an offset occurs in the track deviation detection signal during recording. this is,
When information bits are recorded on the h rack using the main spot, the front sub-spot is not affected by the information pits recorded at the main spot, while the amount of reflected light from the rear sub-spot is recorded at the main spot. This is because the output of the two photodetectors is unbalanced due to the influence of the information pits.

Furthermore, if a conventional three-spot type track deviation detection device using a diffraction grating is used in a separate optical head, and the diffraction grating, photodetector, etc. are placed in a fixed optical system, for example, As discussed in Japanese Patent No. 298725, the movement of the moving optical system causes lateral deviation, that is, optical axis deviation, due to precision of mechanical parts, assembly errors, etc.
The amount of vignetting of the two sub-spots by the focus lens is different. Therefore, an imbalance occurs in the amounts of reflected light of the two sub-spots, resulting in a difference in the outputs of the two photodetectors and an offset in the track deviation detection signal.

In this way, when the influence of recorded information bits occurs, or when the two sub-spots are vignetted by different amounts by the focus lens.

When a difference occurs in the outputs of the two photodetectors due to effects other than track deviation, an offset occurs in the track deviation detection signal.

This invention was made to solve the above-mentioned problem, and even when a difference occurs between the outputs of two photodetectors due to effects other than track deviation, an offset does not occur in the trunk deviation detection signal. It is an object of the present invention to provide a 1-rack deviation detection device that can accurately detect 1-rack deviation.

[Means to solve the problem]

In order to achieve this object, the present invention includes a light source, a diffraction grating that splits the beam emitted from the light source into a main beam and two sub-beams, and a diffraction grating that divides the main beam and the sub-beam into a main spot on an information recording medium. an optical focusing means for converging the sub-spots into two sub-spots; two photodetectors for respectively receiving the two sub-reflected beams reflected by the information recording medium of the sub-spots; and two photodetectors for receiving two output signals of the photodetectors. A track deviation detection device having a differential calculation means for outputting a difference signal, the rotation vibration means for rotationally vibrating the diffraction grating; a polarity reversing means for reversing the polarity of the difference signal in either case of rotation, and a signal of the differential calculation means and a signal of the polarity reversing means are selected in accordance with the rotational vibration of the diffraction grating. A selection means is provided.

In this case, the diffraction grating, the rotary vibration means, and the photodetector are provided in a fixed optical system, and the optical focusing means is provided in a movable optical system movable in a direction perpendicular to the track of the information recording medium. may be provided.

Further, the distance between the sub spot and the main spot in the direction perpendicular to the track is 4 of the distance between the tracks.
A signal holding means may be provided for holding the signal of the selection means when the signal becomes approximately equal to an odd multiple of 1/1.

[Effect]

In this track deviation detection device, a rotational vibration means for rotationally vibrating a diffraction grating and a diffraction grating detect a difference in either case when the diffraction grating rotates to the right or to the left with approximately the center position of the rotational vibration as a boundary. This is because polarity inversion means for inverting the polarity of the signal and selection means for selecting the difference signal and the signal of the polarity inversion means in accordance with the rotational vibration of the diffraction grating are provided.

Even when a difference occurs in the outputs of the two photodetectors due to effects other than track deviation, this effect can be removed.

Furthermore, if the diffraction grating, the rotational vibration means, and the photodetector are provided in a fixed optical system, and the optical focusing means is provided in a movable optical system that is movable in a direction perpendicular to the track of the information recording medium,
The weight of the moving optical system can be reduced.

Further, a signal holding means is provided for holding a signal of the selection means when the distance between the sub spot and the main spot in a direction perpendicular to 1 to 100 mm is approximately equal to an odd multiple of 1/4 of the track distance. For example, a large track deviation detection signal can be obtained.

(Embodiment) FIG. 1 is a diagram showing an optical head section of an optical disk device having a track deviation detection device according to an embodiment of the present invention, and FIG.
The figure is a perspective view showing the rotary vibration mechanism used in the track deviation detection device shown in FIG. 1, FIG. 4 is an enlarged view showing the information recording surface of the disk of the optical disk device shown in FIG. 1, and FIG. This figure shows a photodetector used in the track deviation detection device shown in FIG. 1. In the figure, 1 is a semiconductor laser, and the wavelength λ of the laser beam emitted from the semiconductor laser 1 is 0.78 μm. 2 is a collimating lens that converts the laser beam emitted from the semiconductor laser 1 into a parallel beam; 3 is a diffraction grating that separates the parallel beam into a main beam 4c and two sub-beams 4a and 4b; the grating spacing p of the diffraction grating 3 is 128 μm; and sub-beams 4a, 4
The third-order diffraction angle θ of b is O from the relationship psinθ=λ.
=0.35 degree. 5 is a polarizing beam splitter, 6 is a quarter wavelength plate, 7 is a galvano mirror 175 is a deflection means for the galvano mirror 7, and the deflection means 75 rotates the galvano mirror 7 by electromagnetic force. 9 is a disk, 8 is a focus lens, and the focal length f of the focus lens 8 is 3.
It is 3mm. 83 is a focus lens driving means that drives the focus lens 8 in a direction perpendicular to the disk 9 using electromagnetic force, 10c is a main spot focused on the information recording surface of the disk 9, and 10a and lob are on the information recording surface of the disk 9. Main spot 10 with focused sub-spots
The distance d between C and the sub-spot 10a and fob is d =
From the relationship f tan O, d=20 μm.

11 is a convex lens; 12 is a cylindrical lens that imparts astigmatism to the reflected beam of the main spot 10c; 13 is a six-divided photodetector; and 13a, 13b, and 13c are photodetection elements of the six-divided photodetector 13.

20 is a rotational vibration mechanism that rotationally vibrates the diffraction grating 3;
For example, it is configured as shown in FIG.

In the figure, reference numeral 21 denotes a diffraction grating holder of the rotary vibration mechanism 20, and the diffraction grating 3 is attached to the diffraction grating holder 21. 25 is a pin which connects the diffraction grating holder 21. is pin 25
It is rotatable in the direction shown by arrow 26 around . 22 is a permanent magnet attached to the diffraction grating holder 21; 23 is a yoke; 24 is a coil wound around the yoke 23; 27 is a soft rubber provided between the permanent magnet 22 and the yoke 23; The maximum rotation angle φ of the diffraction grating 3 is ±1.15 degrees.

The operation of the rotary vibration mechanism 20 will be explained using FIGS. 4 and 5. In FIG. 4, reference numeral 41 indicates a plurality of track grooves provided on the information recording surface of the disk 9.
The interval (track pitch) is 1.6 μm. In FIG. 5, 50c is a main detection beam that is a reflected beam of the main spot 10c, and 50a and 50b are subspora l"lOa.

The photodetecting elements 13a, 13b, 13c are the sub-detection beams which are the reflected beams of tab, and the sub-detection beams 50a, 5
0b, the light intensity of the main detection beam 50c is detected. 1st
40 in the figure is an oscillator that outputs a signal 61 as shown in FIG. When the signal 61 is applied, the diffraction grating 3 rotates and oscillates in the direction of the arrow 26 about the pin 25, and the sub-spots 10a and 10b rotate and oscillate in the directions of arrows 42 and 43 about the main spot 10c.

Returning to FIG. 1, 63 is a zero level that outputs a signal 64 (FIG. 6(b)) which becomes a positive level when the signal 61 is higher than the zero level 62 and becomes a zero level when it is lower than the zero level 62. It is a comparator. 51 is a photodetecting element 13a
Let A be the output signal of the photodetector 13b, and B be the output signal of the photodetecting element 13b, a differential amplifier performs the calculation of A-B, 65 is an inverting circuit connected to the differential amplifier 51, and 66 is the differential amplifier 51.
output signal A-B of the differential amplifier 51 and output signal B-A of the inverting circuit 65 are input, and if the signal 64 is at a positive level, the output signal A-B of the differential amplifier 51 is selected, and if the signal 64 is at zero level, the output signal B-A of the inverting circuit 65 is selected.
This is a switch for selecting output signal B-A of No. 5. 68 differentiates the signal 61 which is the output of the oscillator 40 and obtains the result shown in FIG.
c) A differentiation circuit that outputs the signal 69 shown in FIG. 7, 71 is the signal 6
9 is at zero level 70, the pulse signal 72 (Fig. 6(b)
)), and 73 is a hold circuit that holds the signal level of the output signal 67 of the switch 66 by the pulse signal 72 until the next pulse signal 72 comes, and the output signal of the hold circuit 1 & 67, that is, the track deviation detection signal. 74 is input to the deflection means 75 of the galvanometer mirror 7. Reference numeral 80 adds the output signals of the elements arranged diagonally to the four-split photodetection element 13c, calculates the defocus detection signal 82 from the difference signal of the two added outputs, and calculates the defocus detection signal 82 from the sum signal of the two added output signals. , a calculation circuit 80 calculates an information signal 81 according to the recorded information, and the defocus detection signal 81 is applied to a focus lens driving means 83. 84 is a variable gain amplifier that amplifies the output signal of the detection element 13b, and the variable gain amplifier 84 changes the amplification factor depending on the magnitude of the signal 61 from the oscillator 40.
A recording confirmation signal 85 of constant amplitude is output.

In this track deviation detection device, a semiconductor laser 1
The laser beam emitted from the is converted into a parallel beam by collimator 1 to lens 2, and the parallel beam is separated into a main beam 4c and two sub-beams 4a and 4b by a diffraction grating 3, and the main beam 4c and sub-beams 4a and 4b are polarized beams. The light passes through the splitter 5/4 wavelength plate 6, is reflected by the galvanometer mirror 7, and is focused by the focus lens 8 onto the information recording surface of the disk 9 as a main spot 10c and sub spots 10a and 10b. Main spot l
The beam reflected by the disk 9 at sub-spots oc, loa, and 10b is turned into a parallel beam by the focus lens 8, and
It passes through the half-wave plate 6, is reflected by the polarizing beam splitter 5, becomes a convergent beam with astigmatism by the convex lens 11 and the cylindrical lens 12, and the main detection beam 50c is received by the 4-split photodetector element 13c. The information signal 81 is calculated by the calculation circuit 80, and the detection beams 50a, b
is received by the sub-photodetecting elements 13a and 13b.

The sub photodetecting elements 13a and 13b output output signals A and B. Since an AC voltage (signal 61) is applied to the coil 24 from the first oscillator 40, the first diffraction grating 3 rotates and oscillates in the direction shown by the arrow 26 around the pin 25, so that the sub-spots 10a and 10b are centered around the main spot 10c. It rotates and vibrates to the position shown by arrows 42 and 43. in this case,
The maximum rotation angle of the sub-spots 10a and 10b is the diffraction grating 3.
It is ±1.15 degrees, which is the same as the maximum rotation angle φ of
The deviation in direction is determined by the relationship t = d sinφ,
t=0.4 μm, which is one quarter of the track pitch of 1.6 μIn. By the way, sub spot 10a.

The amount of reflected light from the sub-spots 10a, 10b is minimum when the centers of the sub-spots 10a, 10b are located on the track groove 4, and is maximum when the centers of the sub-spots 10a, 10b are located at the center between the tracking grooves 41.

Therefore, when the sub-spots 10a and 10b rotate to the position shown in FIG. It changes like a curve 200a in FIG. 7(b), and the relationship between the center position of the main spot 10c and the output signal B changes like a curve 5200b in FIG. 7(c). Here, due to the influence of the information pits 45, the amount of reflected light of the sub-spot 10b is lower than the amount of light reflected from the sub-spot 10b when there is no information pit 45 (
(two-dot chain line). Therefore, the differential amplifier 51
The output signal A-B becomes as shown by the curve 201 in the seventh section (d). On the other hand, Subspora! -10a and 10b are the 8th
When the main spot 10c is rotated to the position shown in FIG. 8(a), the relationship between the center position of the main spot 10c and the output signal A is as shown in FIG.
The relationship between the center position of the main spot loc and the output signal B changes as shown in the curve 202b in FIG. 8(c). here,
Due to the influence of the information pits 45, the amount of reflected light from the sub-spot 10b is reduced compared to the case without the information pits 45 (double-dashed line). Therefore, the output signal B-A of the inverting circuit 65 becomes as shown by the curve 203 in FIG. 8(d). In this way, the curve 201 and the curve 203 have the same polarity in the track deviation direction. Then, the signal 64 is output from the zero level comparator 63, and the switch 66 selects the output signal A-B of the differential amplifier 51 and the output signal r-3-A of the inverting circuit 65 in accordance with the signal 64. As shown in the lower part of FIG. 6(b), the signal 61 is higher than the zero level 62,
When the sub-spots 10a, 10b rotate to the positions shown in FIG. 7(a), the output signal 67 of the switch 66 becomes A.
-Becomes B. Conversely, when the signal 61 is lower than the zero level 62 and the sub-spots 10a and iob rotate to the positions shown in FIG. 8(a), the output signal 67 of the switch 66 becomes B-A. Further, the signal 61 is differentiated by a differentiating circuit 68, a pulse signal 72 is output from a zero level pulser 71, and a hold circuit 73 holds the signal level of the output signal 67 until the next pulse signal 72 comes. Therefore, the output signal 67 when the absolute value of the signal 61 is maximum, that is, the subspora l-10a, 10b and the main spot 1
The signal level of the output signal 67 at which the deviation t in the X-axis 44 direction from 0c becomes maximum is held until the next pulse arrives. Therefore, the output signal A-B and the output signal 13-A are substantially added, and the track position deviation signal 74 becomes a curve 204 shown in FIG. In this way, even if the amount of reflected light from the rear sub-spot lob is reduced due to the influence of the information pit 45, this influence can be removed, so that no offset occurs in the track deviation detection signal, and it can be accurately detected. Track deviation can be detected. Since the track deviation detection signal 74 is input to the deflection means 75 of the galvanometer mirror 7, the main spot 10c can be positioned at the center of the track. Further, since the arithmetic circuit 80 calculates the defocus detection signal 81 and applies the defocus detection signal 81 to the focus lens swelling means 83, defocus can be prevented. Furthermore, since the variable gain amplifier 84 amplifies the output signal B of the detection element 13b in accordance with the signal 61, it is possible to output a recording confirmation signal 85 with a constant amplitude, so that recording confirmation can be performed reliably.

FIG. 10 is a diagram showing a part of a magneto-optical disk device having a track deviation detection device according to another embodiment of the present invention, and FIG. 11 is a diagram showing a photodetector used in the magneto-optical disk device shown in FIG. In FIG. 1, which is a diagram showing the device, 110 is a magneto-optical disk, 100 is a fixed optical system fixed to the magneto-optical disk device, and the fixed optical system 100 includes a semiconductor laser 1.
, collimating lens 2, diffraction grating 3, rotation vibration mechanism 20
, beam splitter 101, 1/2 wavelength plate 102, convex lens 103, compound deflection prism 104, photodetector 10
5 is installed.

122a, 122b, 123a, 123b, 124a~
124c and 1258 to 125c are photodetecting elements of the photodetector 105. The photodetecting element 122a is the sub-spot 10
The photodetecting element 1 receives the p-polarized detection beam 120a of
22b is the p-polarized detection beam 12 of the sub-spot 101)
0b is received. The photodetecting elements 124a to 124C receive the P-polarized detection beam 120c of the main spot 10c. The photodetecting element 123a receives the S-polarized detection beam 121a of the sub-spot 10a, and the photo-detecting element 123b receives the S-polarized detection beam 121b of the sub-spot 10b. Photodetecting elements 125d to 125c are main spot 1
The S polarization detection beam 121c of 0c is received. and,
The photodetectors P124a to 124c and 125a to 125c are installed at positions where the detection beam 120C and the detection beam 121C are equal in size when the magneto-optical disk 110 is exactly at the focal position.

108 is a moving optical system, 109 is a raising mirror 111 is a two-dimensional lens actuator, the focus lens 8 is attached to the two-dimensional lens actuator 111, and the raising mirror 109, the two-dimensional lens actuator 111, and the focus lens 8 are moved. It is installed in the optical system 108.

107 is a wheel of the moving optical system 108, 106 is a rail provided in the radial direction of the magneto-optical disk 110, and the moving optical system 108 runs on the rail 106.

In this track deviation detection device, a moving optical system 10
8 on the rail 106, the main spot loc and sub-spots 10a, 10b can be accessed at any position in the radial direction of the magneto-optical disk 110. In addition, the main spot 10c and sub-spots 10a and 10b reflected by the magneto-optical disk 110 are as follows:
The detection beam is turned into a parallel beam by the focus lens 8. This parallel beam is reflected by a beam splitter 101, and the linear polarization direction is changed into four directions by a half-wave plate 102.
The light is rotated by 5 degrees, converged by the convex lens 103, separated by the polarization separation film 104a of the composite deflection prism 104 into an S-polarized beam and a p-polarized beam, each having an approximately equal amount of light, and then received by the photodetector 105. . The output signals A and B are the sum of the output signals of the photodetecting element 122a and the photodetecting element 122b, or the photodetecting element 123a and the photodetecting element 123b, or the sum of the output signals of the photodetecting element 122a and the photodetecting element 123a and the photodetecting element 122b. It can be obtained from the sum of the output signals of the photodetecting elements 123b.

By inputting these output signals A and B to the differential amplifier 51 described in FIG. 1, a track deviation detection signal 74 can be obtained. Further, the moving optical system 108 is connected to the magneto-optical disk 11.
With a radial movement of 0.

Lateral displacement occurs due to the precision of mechanical parts and assembly errors. As a result, an imbalance occurs in the amount of vignetting of the two sub-spots 10a and 10b by the focus lens 8, resulting in a difference in the amount of light between the sub-spots loa and 10b.

However, the changes in the light intensity of the sub-spots 10a and 10b can be canceled using the rotary vibration mechanism 20 explained in detail in FIG. A detection signal 74 can be obtained. Therefore, tracking control is achieved by inputting the track deviation detection signal 74 to the two-dimensional lens actuator 111 and moving the focus lens 8 in the radial direction of the magneto-optical disk 110.
Ru. In addition, one diffraction grating 3, rotational vibration means 20. Since the photodetector 105 and the like are provided in the fixed optical system 100, the weight of the movable optical system 108 can be reduced, and high-speed access is possible. Further, when the magneto-optical disk 110 is exactly at the focal position, the detection beam 120G and the detection beam 121C are equal in size, and the photodetection element 1
The output signals of 24a, 124b and the photodetecting elements 125a, 125b are equal.

However, when the magneto-optical disk 110 approaches the focus lens 8, the detection beam 120c becomes larger and the detection beam 121c becomes smaller, so the output signals of the photodetecting elements 124a and 124b become larger, and the output signals of the photodetecting elements 125a and 124b become larger. The output signal of the photodetector element 125b becomes smaller. Conversely, when the magneto-optical disk 110 moves away from the focus lens 8, the detection beam 120C becomes smaller and the detection beam 121c becomes larger.
The output signal of the photodetection element 124b becomes small, and the output signals of the photodetection elements 125a and 125b become large. Therefore, the photodetecting element 124d and the photodetecting element 124b
The addition output signal of the photodetector element 125a and the photodetector element 1
A defocus detection signal is obtained from the differential signal of the addition output signal of 25b, and inputted to the two-dimensional lens actuator 111,
Automatic focus control is achieved by moving the focus lens 8 in the direction of the lens optical axis. Furthermore, in the magneto-optical disk device, information is recorded by reversing the direction of magnetization of the perpendicularly magnetized film of the magneto-optical disk 110, and the linear polarization direction of the detection beam reflected by the magneto-optical disk 110 is determined by the perpendicular magnetization. It rotates slightly depending on the direction of magnetization of the film. For this reason.

Polarized light component of the composite deflection prism 104 jllTyA104a
There is a slight difference in the amount of light between the S-polarized beam and the p-polarized beam separated by . Therefore, the photodetecting elements 124a~
A magneto-optical reproduction signal is obtained from a differential signal between the added signal of 124c and the added signals of photodetecting elements 125a to 125c.

In the above embodiment, the output signal 74 of the hold circuit 67 is input to the deflection means 75 of the galvanometer mirror 7, but the output signal 67 of the switch 66 may be input to the deflection means 75. Further, in the above-described embodiment, the diffraction grating 3 is vibrated in rotation by the rotary vibration mechanism 20, but a piezo element as shown in FIG. 3 may be used as a side of the one-rotation vibrator. That is, the four piezo elements 32 are attached to the fixed holder 31, the ends of the four sides of the diffraction grating 3 are attached to the four piezo elements 32 via the damping rubber 33, and the four piezo elements 32 are attached to the four piezo elements 32 as shown in FIG. When an AC voltage is applied by the oscillator 40, the diffraction grating 3 rotates and oscillates. Furthermore, in the above embodiment, the main spot 1
The distance between the main spot and the sub-spots 10a and 10b in the X-axis 44 direction was set to 1/4 of the distance between the track grooves 41, but the distance between the main spot and the sub-spots in the X-axis direction was set to 1/4 of the distance between the track grooves 41. If it is an odd multiple of 1/4, the phases of output signal A and output signal B will be shifted by 180 degrees, so the amplitude of difference signals A-B and B-A will be the largest, and the largest track deviation detection signal will be obtained. be able to. In addition, in the embodiment shown in FIG. 10 etc., the half wavelength plate 1
02 is attached, but the half-wave plate 102 can also be removed, and in this case, the composite deflection prism 104 is
In addition to fixing the angle rotated by 5 degrees, as shown in FIG.
2b, 124a, 124b.

124c column and detection elements 123a, 123b, 125
The columns a, 125b, and 125c are shifted from each other.

〔Effect of the invention〕

As explained above, in the track deviation detection device according to the present invention, there is provided a rotational vibration means for rotationally vibrating the diffraction grating, and two cases in which the diffraction grating rotates to the right and to the left with approximately the center position of the rotational vibration as a boundary. Track misalignment is prevented by providing a polarity reversing means for reversing the polarity of the difference signal in either case, and a selection means for selecting the difference signal and the signal of the polarity reversal means according to the rotational vibration of the first diffraction grating. Even when a difference occurs in the output signals of the two photodetectors due to other influences, this influence can be removed, so that no offset occurs in the track deviation detection signal.

Furthermore, if the diffraction grating, the rotational vibration means, and the photodetector are provided in a fixed optical system, and the optical focusing means is provided in a movable optical system that is movable in a direction perpendicular to the track of the information recording medium,
Since the moving optical system can be made lightweight, high-speed access is possible.

Furthermore, if a signal holding means is provided for holding the signal of the selection means when the distance between the sub spot and the main spot in the direction perpendicular to the track becomes approximately equal to an odd multiple of one-fourth of the track distance, a large Since the track deviation detection signal can be obtained, the track deviation can be detected accurately.

As described above, the effects of this invention are remarkable.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an optical head portion of an optical disk device having a track deviation detection device according to the present invention, and FIG. 2 is a perspective view showing a rotary vibration mechanism used in the track deviation detection device shown in FIG. , FIG. 3 is a perspective view showing a rotary vibration mechanism used in another track deviation detection device, and FIG. 4 is an enlarged view showing the information recording surface of the disk of the optical disk device shown in FIG. 1. Fig. 5 is a diagram showing a photodetector used in the track deviation detection device shown in Fig. 1, and Figs. , FIG. 10 is a diagram showing a part of a magneto-optical disk device having another track deviation detection device according to the present invention, and FIG. 11 is a diagram showing a photodetector used in the magneto-optical disk device shown in FIG. FIG. 12 is a diagram showing a photodetector used in a magneto-optical disk device having another track deviation detection device according to the present invention. 1...Semiconductor laser 3...Diffraction grating 8...Focus lens 9...Disks 10a, 10b...Sub spot 10c...Main spot 13...Photodetector 20...Rotary vibration mechanism 40... Oscillator 51... Differential amplifier 65... Inversion circuit 66... Switch 73... Hold circuit lOO... Fixed optical system 105... Photodetector 108... Moving optical system 110・・・Magneto-optical disk

Claims (1)

[Claims] 1. A light source, a diffraction grating that divides the beam emitted from the light source into a main beam and two sub-beams, and a diffraction grating that divides the main beam and the sub-beam into a main spot and two sub-spots on an information recording medium. an optical focusing means for converging the sub-spots, two photodetectors each receiving the two sub-reflected beams reflected by the information recording medium at the sub-spots, and outputting a difference signal between the two output signals of the photodetectors. A track deviation detection device comprising: a differential calculation means for rotating the diffraction grating;
polarity inverting means for inverting the polarity of the difference signal when the diffraction grating rotates to the right or to the left with the approximate center position of the rotational vibration as a boundary;
A track deviation detection device comprising: a selection means for selecting a signal from the differential calculation means and a signal from the polarity inversion means in accordance with the rotational vibration of the diffraction grating. 2. The diffraction grating, the rotary vibration means, and the photodetector are provided in a fixed optical system, and the optical focusing means is provided in a movable optical system movable in a direction perpendicular to the track of the information recording medium. 2. A track deviation detection device according to claim 1, further comprising: a track deviation detection device. 3. Signal holding means for holding the signal of the selection means when the distance between the sub-spot and the main spot in the direction perpendicular to the track is approximately equal to an odd multiple of one-fourth of the distance between the tracks. 3. The track deviation detection device according to claim 1, further comprising: a.