JPH0711874B2 - Magneto-optical signal detector - Google Patents

Description

The present invention relates to a magneto-optical signal detecting device for a magneto-optical recording / reproducing device.

[Conventional technology]

Conventional magneto-optical recording / reproducing apparatuses are classified into a reflective type that uses force-rotation angle for reading and a transmissive type that uses Faraday rotation for reading. A conventional reflective type is described in MAG-84-70, Material of the Institute of Electrical Engineers of Japan, Magnetics Research Group. The structure of the optical head is shown in FIG. Here, a differential detection system surrounded by broken lines will be described. The light whose polarization plane is rotated after being reflected by the magneto-optical disk 106 first passes through the half-wave plate 100, and the polarization plane is rotated by 90 °.

Next, the polarized beam splitter 101 splits the transmitted light and the reflected light. At this time, at the same time, it passed through an analyzer having an incident polarization plane and a transmission axis angle of ± 45 °. The branched reflected light is focused by the lens 102 and enters the photodiode 103. Similarly, the transmitted light also enters the photodiode 105 via the lens 104. A signal can be detected by taking the difference between the outputs of the two photodiodes by means of a differential amplifier. Since this differential detection method can remove common-mode noise such as laser noise and increase the S / N of the reproduced signal, it is often used in magneto-optical heads.

As a transparent conventional example, the Proceedings, of,
PROCEE DINGS OF SPIE
382, pages 240-244 (1983). Figure 10 shows the schematic diagram of the optical head. Magneto-optical disk
The light transmitted through 107 passes through the analyzer 108 and reaches the four-division photodiode 109. This 4-division photo diode 109
Is composed of four photo diodes which are divided into four in parallel, whereby focusing and tracking are performed, and an RF signal (magneto-optical signal) is also obtained at the same time. However, differential detection is not performed in this example.

In this example, the light source side and the light receiving side are integrally driven for focusing and tracking.

Further, as a transmission type optical head, there is one having a structure recently invented by the present inventor as shown in FIG. 11 (Japanese Patent Application No. 60-25012).
8, Japanese Patent Application Sho 60-250127, both filed on November 8, 1985,
It is not known). This is a method of performing tracking and focusing with reflected light and detecting an RF signal from transmitted light. Tracking and focusing are performed by the two-dimensional actuator 116 of the objective lens, the beam splitter 111, the knife edge 112, and the four-division photodiode 113. RF
The signal is detected by the analyzer 114 and the photodiode 115. Compared to the example in Fig. 10, the advantage of this example is that the tracking and track access are performed in two stages, the coarse actuator and the fine actuator, so the tracking accuracy is improved and the access time is shortened. is there.

[Problems to be solved by the invention]

In the reflection type optical head, the differential detection method is often used as shown in FIG. 9, but for this reason, a half-wave plate, a polarization beam splitter, two lenses, and two photodiodes are required. As a result, there is a drawback that the entire optical head is large, heavy and expensive.

So far, there has been no case where the differential detection method is used in the transmission type optical head. The transmission type optical head tends to be large and heavy because parts are arranged above and below the magneto-optical disk. Therefore, when the differential detection system shown by the broken line in FIG. 9 is arranged on the transmission side, there is a drawback that it is considerably large, heavy and expensive.

When the optical head becomes large, it becomes an obstacle to miniaturization of the optical disk device. When it becomes heavy, high speed access becomes difficult.

Therefore, the present invention solves such a problem, and an object of the present invention is to provide a magneto-optical head which is small in size, light in weight, and low in cost at the same time as obtaining the performance equivalent to that of the differential detection method. .

[Means for solving problems]

The magneto-optical signal detecting device of the present invention is a magneto-optical recording / reproducing device in which the polarization plane of the incident linearly polarized light is rotated by reflecting or transmitting the magneto-optical recording medium, and the rotation of the polarization plane is used as an information signal. a) A photodetector for detecting the rotation of the plane of polarization is divided into 2n on a plane by n linear dividing lines (where n is an integer of 1 or more. Further, 2n divided photodetectors are used. In the counterclockwise direction from the photodetector at any position in the above, the photodetectors are a ₁ , a ₂ , a ₃ , ..., A ₂ n), b) Of the n linear dividing lines One of them is oriented in the track vertical direction, and c) the polarization plane and the transmission axis of the incident linearly polarized light are immediately before the photodetectors a ₁ , a ₃ , a ₅ , ..., A ₂ n _-1. analyzer with an angle phi _a is disposed, d) the photodetector _{a 2, a 4, a 6} , ···, and the polarization plane of the incident linearly polarized light immediately before a ₂ n transmission There is arranged an analyzer angled φ _B, e) said angle phi _A and the angle phi _B is set differently, f) the photodetector _{a 1, a 3, a 5} , ···, a The output sum P _A of ₂ n _-1 is taken, the output sum P _B of the photodetectors a ₂ , a ₄ , a ₆ , ..., a ₂ n is taken, and the output sum P _A and the output sum P _A are taken. It is characterized by having a differential amplifier that takes the difference of _B.

[Work]

The principle of the present invention will be described below with reference to the drawings. FIG. 1 shows a conceptual diagram of a magneto-optical signal detecting device of the present invention when n = 1. Reference numeral 1 is a laser beam reflected or transmitted through the magneto-optical recording medium, and 2 is its plane of polarization. Since the rotation angle due to the magneto-optical recording medium is minute (1 ° or less), the polarization plane 2
Is substantially coincident with the plane of polarization of the incident linearly polarized light incident on the medium. 3 is the track tangential direction, 4 is the track vertical direction,
In this figure, the direction is as shown. here,
The track tangential direction and the track vertical direction will be described with reference to FIG. 2 by taking an optical disk as an example. Reference numeral 12 is an optical disk, and 13 is a guide groove or a recorded pit row. At this time, 14 is the track tangential direction, and 15 is the track vertical direction. In optical cards and the like, the track is a straight line, but it can be considered in the same way. Return to FIG. The analyzers 9 and 10 are respectively arranged immediately before the photodetectors a ₁ (6) and a ₂ (7) of the two-divided photodetector 5 which is divided in a plane, and the transmission axes (indicated by diagonal lines). There are different angles _A and _B. In this figure, _A is a positive angle and _B is a negative angle. Therefore, the differential amplifier
When the difference between the photodetectors a ₁ and a ₂ is calculated by 11, common mode noise such as laser noise is removed, and therefore, performance equivalent to that of the conventional differential detection method can be obtained. That is, a signal with a high S / N ratio can be obtained. On the other hand, unlike the conventional differential detection method shown by the broken line in FIG. 9, it does not require a half-wave plate, a beam splitter, and two photodetectors, each of which is an individual lens, so that the size, weight and cost are reduced. This is extremely advantageous.

Next, the reason why the straight line dividing line 8 faces the direction perpendicular to the track will be described below by taking an optical disk as an example. At present, the magneto-optical disk, which is becoming the mainstream, is provided with a guide groove with a track pitch of 1.6 μm, a groove width of 0.8 μm and a groove depth of 700 Å. It is done by law. There are other three-beam methods and the like as the tracking method, and any of them has a so-called "tracking fluctuation" or "tracking accuracy". Therefore, in order to prevent the influence of the tracking accuracy from appearing in the detection of the RF signal, the straight dividing line 8 is oriented in the track vertical direction 4. This is shown in FIG.
The explanation will be made more easily with reference to (b) and (c). 16 is a guide groove on the disk, 17a, 17b, 17c are laser spots focused on the disk, 18 is a photodetector, and 19a, 19b, 19c are light intensity distributions on the photodetector. When the laser spot is at the center of the guide groove, a light intensity distribution having a peak at the position corresponding to the center of the guide groove on the photodetector is obtained. However, if the laser spot shifts to the left or right with respect to the center of the guide groove, the light intensity distribution on the photodetector also shifts to the left or right. Therefore, if the photodetector is divided along the dividing line in the tangential direction of the track, the amount of light incident on each of the divided photodetectors (the amount of light before passing through the analyzer) will fluctuate, so the difference signal The "wandering of tracking" is mixed in. If you divide the track vertically,
This has no effect. As a result, it is possible to achieve the same performance as the conventional differential detection method in which the beam splitter splits the beam into two and then the difference is obtained, and a signal with a high S / N ratio is obtained.

[Embodiment 1] FIG. 4 is a configuration diagram of a reflection type optical head using a magneto-optical signal detecting device (when n = 1) according to the present invention. The optical system will be briefly described. The light emitted from the semiconductor laser 23 is collimated by the collimator lens 24 and collimated into a beam shaping prism.
Make a perfect circle at 25, transmit the beam splitter 26,
The light is reflected in the direction perpendicular to the paper surface by 27, and is condensed on the magneto-optical disk 29 by the objective lens 28. Magneto-optical disk 29
The reflected light from the light source follows the reverse path, is reflected by the beam splitter 26, and enters the beam splitter 30. The transmitted light of the beam splitter 30 is a lens 31 and a cylindrical lens 32.
Then, the light enters the 4-division PIN photo diode 33. The push-pull method is used for tracking, and the astigmatism method is used for focusing. The lower half of the reflected light of the beam splitter 30 is transmitted through the polaroid film 20, the upper half is transmitted through the polaroid film 21, and is detected by the two-divided PIN photodiode 22. Here, a polarizing film was used as the analyzer. Polaroid film is a well-known polarizing film and has a trade name. Polaroid film 2
The transmission axis angles of 0 and 21 were set to ± 45 ° with respect to the incident polarization plane direction. Normally, it is set within the range of 0 <1 _A 1.1 _B 1 ≦ 45 °, but if it is set to ± 45 °, there is an advantage that the accuracy of the set angle may be loose.

The arrow in FIG. 4 indicates the polarization plane direction of the linearly polarized light. However, the minute rotation angle due to the magneto-optical recording medium is ignored. From this figure, it can be seen that the plane of polarization incident on the magneto-optical disk 29 is oriented in the track tangential direction of the disk. Therefore, the straight dividing line of the two-divided PIN photodiode is oriented in the direction perpendicular to the paper surface.

In this embodiment, a signal having a high S / N ratio equivalent to that of the conventional differential detection method can be obtained. In addition, compared with the conventional differential detection method,
Since a wavelength plate, a polarized beam splitter, two lenses, and two separate photodetectors are not required, it is possible to realize a significantly smaller size, lighter weight, and lower cost.

[Embodiment 2] FIG. 5 is an embodiment in which a magneto-optical signal detecting device (when n = 1) according to the present invention is applied to the transmission type optical head recently invented by the present inventors. In this embodiment, a two-divided PIN photodiode is arranged on the transmission side of the conventional example shown in FIG. 11, and like the first embodiment, the straight dividing line is oriented in the track vertical direction. In this embodiment, the push-pull method is used for tracking, and the knife edge method is used for focusing.

In this embodiment, even if the laser spot completely follows the center of the guide groove, there is a track shift from the perspective of the two-divided PIN photodiode on the transmission side due to lens shift. However, this effect can also be eliminated because the straight dividing line 36 faces the track vertical direction.

In this embodiment, even if the magneto-optical signal detection device according to the present invention is applied, the size, weight, and cost are almost unchanged, and the S / N
The ratio can be improved. Note that the knife edge, the lens, and the four-division photodiode in this embodiment are actually arranged on the side perpendicular to the plane of the drawing, and it should be added that the optical head is thinner than that in this figure.

[Third Embodiment] In the first and second embodiments, n = 1, that is, in the case of two divisions, but in the case of two divisions, it is easily affected by defects such as dust and scratches on the surface of the magneto-optical recording medium, and reading is performed. The reason why an error easily occurs will be described with reference to FIG. Suppose that the track runs from right to left on the drawing as seen from the two-division photodetector 5, and there is a defect on the track. The reflected light diffracted by the defect first enters the analyzer 9 and the photodetector a ₁ (6) immediately thereafter, and then the analyzer 10 and the photodetector a ₂ (7) immediately thereafter.
Incident on. Therefore, when the difference between the outputs of the two photodetectors is calculated, the influence of defects appears in the reproduced signal. However, it is not affected by the defect only when the straight dividing line 8 is located at the center of the defect. Therefore, in the present embodiment, n = 2, that is, four divisions are used to reduce reading errors due to defects.

This embodiment is shown in FIG. Reference numeral 43 denotes a 4-division photodetector, which is divided by two straight division lines 48 and 49. The straight line dividing line 49 faces the track vertical direction, and the straight line dividing line 48 faces the track tangential direction. Reference numerals 44, 45, 46 and 47 denote photodetectors a ₁ , a ₂ , a ₃ and a ₄ , respectively. Immediately before the photodetectors a ₁ and a ₃ , analyzers 50 and 51 having a transmission axis angle A are arranged.
Immediately before ₂ and a ₄ , analyzers 53 and 52 having a transmission axis angle B are arranged. In addition, the two straight dividing lines 48, 49 are the analyzers 50, 51, 5
It is arranged so as to overlap with the junction of 2,53. Photo detector
The difference between the sum of outputs of a ₁ and a _{3 and} the sum of outputs of the photodetectors a ₂ and a ₄ is taken by the differential amplifier 54 to obtain a reproduction signal. Photodetector a ₁ , a
Output I of the _2, a _3, outputs A1 of a _4, A2, A3, A4 to the differential amplifier 54, I = (A1 + A3) - (A2 + A4) ·· (1) = (A1-A2) + ( A3-A4)-(2) = (A1-A4) + (A3-A2)-(3). Since the first and second terms on the right side of the equation (2) are the difference between the photodetectors on both sides divided by the straight line dividing line 49 in the vertical direction of the track, they are not affected by the tracking accuracy (fluctuation). .

Next, if the line is divided by a straight line in the track tangential direction, it is difficult to be affected by defects.
Will be described. 55 is a guide groove, 56a, 56b and 56c are laser spots focused on the recording medium, and 57 is a defect on the guide groove. a1-a, a2-a, a3-a, a4-a shows an optical detector _{a 1, a 2, a 3} , a light intensity distribution on a ₄ in the case of (a). Below, −b, −
The same applies to the case of c. Looking at the light intensity distributions of (a), (b), and (c), in any case, the output difference between the photodetectors a ₁ and a ₄ , a ₂
If the output difference between a and a ₃ is taken, the difference becomes minute and the influence of the defect does not appear in the output I. In this embodiment, as shown in equation (3),
This operation is being performed. Therefore, it is not easily affected by the defect on the guide groove.

The magneto-optical signal detection device of the present embodiment, as in the first and second embodiments,
By applying it to reflective optical heads and transmissive optical heads, it is possible to reduce the size, weight and cost of optical heads.
A reproduced signal with a high S / N ratio equivalent to that of a conventional differential detector can be obtained. Furthermore, it is less susceptible to defects on the surface of the recording medium,
This has the effect of reducing read errors. Since the magneto-optical signal detecting device reduces reading errors, the requirement for defects on the substrate and the recording medium does not become too strict, which is advantageous for cost reduction of the recording medium.

Fourth Embodiment In the first, second and third embodiments, the case where n = 1,2 has been shown.
In these examples, the C / N ratio may be slightly lower than that of the conventional differential detection method due to the influence of fine irregularities on the substrate of the optical recording medium. A glass substrate with a guide groove directly formed on the surface by the dry etching method is less affected by fine unevenness (hereinafter abbreviated as substrate noise), but a low-cost resin substrate with a guide groove made by injection molding causes substrate noise. It will be slightly larger.

Therefore, in order to remove the influence of the substrate noise, n = 4, that is, eight divisions are used, but this is the embodiment.

This embodiment is shown in FIG. Reference numeral 62 denotes an 8-division photodetector, and the straight division lines 63 'and 64' are directed in the track tangential direction 60 and the track vertical direction 61, respectively. 63,64,65,66,67,6
8,69,70 are photodetectors a ₁ , a ₂ , a ₃ , a ₄ , a ₅ , a ₆ , a ₇ , a ₈
Is. Immediately before the photodetectors a ₁ , a ₃ , a ₅ , a ₇ the transmission axis angle _A
Analyzers 71, 73, 75, 77 of the photodetectors a ₂ , a ₄ , a ₆ , a ₈
An analyzer 72, 74, 76, 78 having a transmission axis angle _B is arranged immediately before. The diagonal lines in the analyzer indicate the transmission axis direction.
Output sum P _{A of} photodetectors a ₁ , a ₃ a ₅ , and a ₇ and photodetectors a ₂ , a ₄ , a ₆ and a ₈
The difference between the output sum P _B of the differential amplifier 79 connexion, RF signal is obtained.

Since the number of divisions of the photodetector is larger than in the case of Examples 1, 2, and 3, it is possible to remove the influence up to higher spatial frequency components with respect to the unevenness of the substrate, and the C / N ratio is There is almost no difference compared to the case where the conventional differential detection method is used.

The magneto-optical signal detection device of the present embodiment, as in the first and second embodiments,
By applying it to reflective optical heads and transmissive optical heads, it is possible to reduce the size, weight and cost of optical heads.
The S / N ratio is almost the same as the conventional differential detection method. Further, since the number of divisions is larger than those in Examples 1, 2, and 3, the influence of defects on the recording medium surface is extremely small.

In the above-mentioned first, second, third and fourth embodiments, the plane of polarization coincides with the track tangential direction, but it does not have to coincide with each other.

The magneto-optical signal detecting device of the present invention is closer to the performance of the conventional differential detection method as the number of divisions is increased, but practically, n = 1,2,3,4 is suitable. is there. From the viewpoint of performance, it is preferable that n ≧ 2.

〔The invention's effect〕

As described above, the use of the magneto-optical signal detecting device according to the present invention has the following effects.

Since one of the straight line dividing lines that divides the photodetector faces the direction perpendicular to the track, even if the light intensity distribution moves on the photodetector surface due to the lens shift caused by tracking fluctuation or tracking I do not receive it. As a result, the amplitude of the reproduction signal does not fluctuate, laser noise can be sufficiently removed, and a magneto-optical signal having a high S / N ratio can be reproduced.

Since the photodetector is divided into two or more and the output sum of every other photodetector is made differential, it is unlikely to be affected by defects on the surface of the recording medium and minute unevenness of the substrate. That is. As a result, the substrate and the recording medium do not have to be overly strict, and the cost of the magneto-optical recording medium can be reduced.

With a simple structure consisting of a split photodetector and an analyzer placed immediately before it, the magneto-optical head is small and lightweight,
The cost can be significantly reduced. The access time is shortened by making the optical head smaller and lighter, and the recording / reproducing apparatus itself can be made smaller and lighter. The cost of the optical head accounts for a large portion of the total cost of the apparatus, and the cost of the optical head can be reduced to reduce the cost of the apparatus itself.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and it goes without saying that many modifications are added. For example, the shape of the recording medium may be a card type instead of a disk type. Also,
The method of dividing the photodetector can also be divided at different angles according to the characteristics of the recording medium.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a magneto-optical signal detecting device (n = 1) of the present invention. FIG. 2 is an explanatory diagram of the track vertical direction and the track tangential direction. FIG. 3A is a light intensity distribution diagram on the photodetector when the laser spot is displaced to the left. FIG. 3B is a light intensity distribution diagram on the photodetector when the laser spot is at the center. FIG. 3C is a light intensity distribution diagram on the photodetector when the laser spot is displaced to the right. FIG. 4 is a configuration diagram of a reflection type optical head to which the magneto-optical signal detecting device according to the present invention is applied. FIG. 5 is a configuration diagram of a transmission type optical head to which the magneto-optical signal detecting device according to the present invention is applied. FIG. 6 is a block diagram of an embodiment of the magneto-optical signal detecting device (n = 2) of the present invention. FIG. 7A is a light intensity distribution diagram on the photodetector when there is a defect under the laser spot. FIG. 7B is a light intensity distribution diagram on the photodetector when there is a defect in the center of the laser spot. FIG. 7C is a light intensity distribution diagram on the photodetector when there is a defect on the laser spot. FIG. 8 is a block diagram of an embodiment of the magneto-optical signal detecting device (n = 4) of the present invention. FIG. 9 is a block diagram of a conventional reflection type optical head. FIG. 10 is a block diagram of a conventional transmission type optical head. FIG. 11 is a block diagram of a conventional transmission type optical head. 1 …… Laser light 2 …… Polarization plane 3 …… Truck tangential direction 4 …… Truck vertical direction 5 …… Divided photodetector 6 …… Photodetector a ₁ 7 …… Photodetector a ₂ 8 …… Straight line Split line 9 …… Analyzer 10 …… Analyzer 11 …… Differential amplifier 12 …… Optical disc 13 …… Guide groove 14 …… Track tangential direction 15 …… Track vertical direction 16 …… Guide groove 17a, 17b, 17c ...... Laser spot 18 …… Photodetector 19a, 19b, 19c …… Light intensity distribution 20,21 …… Polaroid film 22 …… 2-divided PIN photo diode 23 …… Semiconductor laser 24 …… Collimating lens 25 …… Beam shaping Prism 26 …… Beam splitter 27 …… Mirror 28 …… Objective lens 29 …… Optical magnetic disk 30 …… Beam splitter 31 …… Lens 32 …… Cylindrical lens 33 …… Four-division PIN photodiode 34 …… Poloride film 35 …… 2-division PIN photo diode 36 ... front view of a straight line dividing line 37 ...... 2 divided PIN photodiode. 38 …… Polarization plane 39 …… Laser light 40 …… Polarization plane 41 …… Truck tangential direction 42 …… Truck vertical direction 43 …… 4-division photodetector 44 …… Photodetector a ₁ 45 …… Photodetector a ₂ 46 …… Photodetector a ₃ 47 …… Photodetector a ₄ 48,49 …… Straight dividing line 50, 51, 52, 53 …… Analyzer 54 …… Differential amplifier 55 …… Guide groove 56a, 56b , 56c …… laser spot 57 …… defect a ₁ −a, a ₁ −b, a ₁ −c …… light intensity on the photodetector a ₁ at (a), (b), (c) distribution _{a 2 -a, a 2 -b,} a 2 -c ...... (a), (b), the light intensity distribution on the photodetector a ₂ when the _{(c) a 2 -a, a} 3 - _{b, a 3 -c ...... (a} ), (b), the light intensity distribution a ₄ -a on optical detector a ₃ when the _{(c), a 4 -b,} a 4 -c ...... ( Light intensity distribution on the photodetector a _{4 for} a), (b), and (c) 58 …… Laser light 59 …… Polarization plane 60 …… Track tangential direction 61 …… Track vertical direction 62 …… 8 Split light Detector 63 °, 64 ° …… Straight line 63 …… Photodetector a ₁ 64 …… 〃 a ₂ 65 …… 〃 a ₃ 66 …… 〃 a ₄ 67 …… Photodetector a ₅ 68 …… 〃 a ₆ 69 …… 〃 a ₇ 70 …… 〃 a ₈ 71,72,73,74,75,76,77,78 …… Analyzer 79 …… Differential amplifier 100 …… 1/2 wave plate 101 …… Polarized beam splitter 102,104 …… Lens 103,105 …… Photodiode 106,107 …… Optical magnetic disk 108 …… Analyzer 109 …… Qualit photo diode 110 …… Optical magnetic disk 111 …… Beam splitter 112 …… Knife edge 113 …… 4-division photo diode 114 …… analyzer 115 …… photo diode 116 …… two-dimensional objective lens actuator

Claims (4)

[Claims] 1. A magneto-optical recording / reproducing apparatus in which the plane of polarization of incident linearly polarized light is rotated by being reflected or transmitted through a magneto-optical recording medium, and the rotation of the plane of polarization is used as an information signal. The photodetector for detecting the rotation of is divided into 2n on the plane by n linear dividing lines (where n is an integer of 1 or more. Furthermore, the photodetector divided into 2n can be placed at any position. Photodetectors a ₁ , a ₂ , a ₃ , ..., A ₂ n are arranged counterclockwise from a photodetector.), B) One of the n linear dividing lines is perpendicular to the track. And c) the polarization plane of the incident linearly polarized light and the transmission axis form an angle φ _A immediately before the photodetectors a ₁ , a ₃ , a ₅ , ..., A ₂ n _-1. is the analyzer arrangement and, d) the photodetector _{a 2, a 4, a 6} , ···, a 2 n the plane of polarization of incident linearly polarized light transmission axis immediately before is an angle phi _B Analyzer is arranged, e) wherein the angle phi _A and the angle phi _B is differently set, f) an output sum of said photodetector _{a 1, a 3, a 5} , ···, a 2 n -1 P _A is taken, the output sum P _B of the photodetectors a ₂ , a ₄ , a ₆ , ..., a ₂ n is taken, and the difference between the output sum P _A and the output sum P _B is taken. A magneto-optical signal detecting device comprising an amplifier. 2. The magneto-optical signal according to claim 1, wherein the angles φ _A and φ _B satisfy the inequality: 0 <| φ _A |, | φ _B | ≦ 45 °. Detection device. 3. In the case of n = 2, one of the two straight line dividing lines faces the track vertical direction, and the other straight line dividing line faces the track tangential direction. The magneto-optical signal detecting device according to claim 1, wherein 4. A straight line that divides the photodetector a ₁ and the photodetector a ₈ and a straight line that divides the photodetector a ₂ and the photodetector a ₃ when n = 4. 2. The magneto-optical device according to claim 1, wherein, in the dividing line, one of the linear dividing lines faces the track vertical direction, and the other of the linear dividing lines faces the tangential direction of the track. Signal detection device.