JPH03192528A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To prevent an S/N of a regenerative signal from deteriorating due to an effect of double refractivity of a resin substrate by dividing a light receiv ing surface of a photodetector into at least three areas and generating a regener ative information signal from a detecting signal of a middle area out of the areas on the light receiving surface of the photodetector. CONSTITUTION:Output signals Aa-Ac and Ba-Bc corresponding to the areas 11Aa, 11Ab, 11Ac and 11Ba, 11Bb, 11Bc of the light receiving surfaces of the photodetectors 10A and 10B are current/voltage-converted by amplifier groups 13, and are afterward processed of calculation by a calculation circuit 14 to generate the regenerative information signal S3, a focus error signal S1 and a tracking error signal S2. That is, the regenerative information signal is obtained by calculating the sum total of the output signals of the photodetectors 10A and 10B; [Aa+(Ab+Ac)]+[Ba+(Bb+Bc)], and the focus error signal is obtained by calculating [Aa-(Ab+Ac)]-[Ba-(Ba+Bc)], while the tracking signal by (Ab+Bb)-(Ac+Bc).

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention is directed to optically recording information on an optical information recording medium such as an optical disk, and optically recording recorded information. The present invention relates to an optical information recording/reproducing device for reproducing information, and more particularly to a detecting device for a reproduced information signal.

(Prior Art) In an information recording and reproducing device using an information recording medium that can optically record and reproduce information, such as an optical disk (including a magneto-optical disk), an optical head generates a servo error signal (a focus error signal, a tracking error signal, etc.). The information signal is reproduced by generating a signal (such as a signal) or detecting a pit string.

Servo error signals are generally generated by using a photodetector whose light-receiving surface is divided into a plurality of regions, and by performing arithmetic processing on the output signals from each region.

As a focus error detection method, for example, so-called 3-split light detection is used in which the light-receiving surface is divided into three strip-shaped areas before and after the focal plane of the condensing lens of the light-receiving optical system that receives reflected light from the recording medium. A beam size differential method is known in which the size of the reflected light beam incident on each photodetector is differentially changed by arranging the detectors respectively.

When using this method, the detection signals from the center area of the light receiving surface of the two 3-split photodetectors placed before and after the focal plane of the condensing lens of the light receiving optical system are defined as Aa and Ba, and the detection signals from both sides of the light receiving surface are defined as Aa and Ba. The detection signals from Ab, Bb and Ac, Be
Then, the focus error is [Aa - (Ab+Ac) ]
-[Ba-(Bb+Bc)] is generated by the calculation process.

On the other hand, the reproduced information signal is the sum of the output signals from all the light-receiving surface areas of the two 3-split photodetectors, that is, [Aa+ (Ab+Ac) ] + [Ba+ (Bb
+Bc) ] is generated by performing the calculation process.

Further, these two three-part photodetectors are arranged in a relative relationship such that the divided strip-shaped areas are orthogonal to the direction of pit rows (track direction) on the recording medium.

This is because when tracking control is performed by moving the focusing lens for focusing the light beam onto the recording medium in a direction perpendicular to the track, or by changing the incident angle of the light beam incident on the focusing lens using an oscillating mirror, This is to prevent the focus error signal from being offset due to movement of the light beam on the light receiving surface of the photodetector. Details of these effects are described in, for example, the 29th Micro-Optics Study Group "Optical Disk Pickup with SAW Light Polarization Deflector Element". However, as mentioned above, the photodetector is installed at a position far from the focal plane of the condensing lens of the light receiving optical system.
This position is an area close to the Fourier transform plane for the bits recorded on the recording medium. That is, on the light-receiving surface of the photodetector, the direction of the track projected image is the spatial frequency axis of the recorded bit, with the center of the incident light beam being zero.

In the three-part photodetector, the light-receiving surface is divided into three short areas with a light-insensitive area (hereinafter referred to as a light-insensitive area) in between. If the 3-split photodetector is arranged as described above, when considering an axis parallel to the tracks on the recording medium, the light-free area on the light-receiving surface of the 3-split photodetector will be perpendicular to this axis. exists. Therefore, a light-insensitive area exists in a part of the frequency axis, which is the spatial axis of the recorded bits on the light-receiving surface of the photodetector, and this becomes a factor in deteriorating the frequency characteristics of the reproduced information signal.

This problem will be explained in more detail. Figure 11 (a) (b
) (c) shows the relationship between the information bit on the recording medium, the reproduced signal waveform obtained by irradiating the information bit with a reproducing light beam and detecting the reflected light, and the waveform obtained by differentiating the reproduced signal waveform.

It is assumed that the interval between the two information pits in FIG. 11(a) is the narrowest interval conceivable for the modulation method. Figure 11 (
When specifying the bit position from the reproduced signal waveform in b), the pit position is often the zero-crossing point of the differential waveform shown in FIG. 11(e) obtained by differentiating the reproduced signal waveform.

How accurately the pit position can be detected from the reproduced signal waveform depends on how large the slope of the differential waveform is at the zero-crossing point. In other words, the larger the second differential coefficient in the bit part of the reproduced signal waveform, the better the detected bit position accuracy. For this reason, the reproduced signal waveform is as shown in Figure 11 (
In a case similar to the SIN function as in a), the closest resolution (i/I) is often used as an evaluation parameter of the reproduced signal waveform.

Generally, the closest resolution increases as the distance between two information pits increases for the same bit size, so it is important to increase this value as much as possible under the condition that the distance between two information pits is the narrowest. On the other hand, if the lower limit of the allowable closest resolution is determined, the higher the closest resolution is, the smaller the bit pitch in the track direction will be, which will lead to higher recording density. However,
In a conventional photodetector arrangement, a light-insensitive area of the photodetector and
The area where the reflected light is affected by the diffraction of the bits in the track direction is located. Therefore, there is a region on the light receiving surface where information pits cannot be detected, leading to a decrease in the frequency characteristics (closest resolution) of the reproduced information signal.
Bit position detection accuracy deteriorates.

Furthermore, in the conventional arrangement of photodetectors, the amplitude of the reproduced information signal decreases significantly when it is off-track (when reproduced with the optical beam deviated in the cross-track direction). For this reason, in optical discs using the sample servo method, in which data areas for recording information signals and servo areas containing clock bits for extracting clock signals are arranged alternately on the track, the accuracy of clock bit detection during access is low. descend.

On the other hand, in the case of magneto-optical disks, the differential detection method that generates a reproduced information signal by taking the difference between the outputs of two photodetectors is used to cancel out the noise caused by fluctuations in the reflectance of the disk and the noise of the laser that is the light source. I can do it. Polycarbonate resin substrates, which are generally widely used as substrates for magneto-optical disks, tend to have increased birefringence due to molecular orientation and residual strain during injection molding. The birefringence of a polycarbonate resin substrate is larger in the vertical direction than in the in-plane direction, and incident light at the periphery of the focused beam, where the angle of incidence on the substrate is large, is strongly influenced by birefringence.

For this reason, when generating a reproduced information signal by taking the difference between the total outputs of conventional photodetectors, the low frequency noise that cannot be canceled out by the differential detection method becomes large, and the S of the reproduced information signal increases.
/N decreases.

(Problems to be Solved by the Invention) As described above, in the conventional optical head incorporating a beam size differential type detection system, focus error occurs due to movement of the light beam on the light receiving surface of the photodetector by tracking control. 3 in the direction that no offset occurs in the detection characteristics.
Because a split photodetector is installed, the frequency characteristics (closest resolution) of the reproduced information signal may deteriorate due to the influence of the light-insensitive area on the light-receiving surface of the photodetector, the accuracy of bit position detection may decrease, or the device may turn off. There is a problem in that the accuracy of clock bit detection during access is reduced due to a decrease in the amplitude of the reproduced signal during tracking.

Furthermore, since the sum of the detection signals from each part of the light-receiving surface of the 3-split photodetector is used as the reproduced information signal, the amplifier system that receives the detection signals from both end regions and the center region of the light-receiving surface has characteristics such as group delay. If there is a mismatch, there is a problem that the closest resolution of the reproduced signal decreases and the bit position accuracy decreases.

In addition, especially in the case of a recording/reproducing device using a magneto-optical disk, in the past, the S/S/
There was a problem in that it caused N deterioration.

It is an object of the present invention to prevent the frequency characteristics and bit position detection accuracy of the reproduced information signal from deteriorating due to the influence of the light-insensitive area on the light-receiving surface of the photodetector, and to reduce the decrease in the amplitude of the reproduced signal when off-track. An object of the present invention is to provide an optical information recording and reproducing device that can detect a lock bit with high precision when accessing.

Another object of the present invention is to provide an optical information recording/reproducing apparatus that can prevent S/N deterioration of a reproduced information signal due to the influence of birefringence of a resin substrate when applied to a magneto-optical disk.

[Structure of the Invention] (Means for Solving the Problems) The present invention guides a light beam emitted from a light source to an optical information recording medium by a first optical system, and directs reflected light from the recording medium to the first optical information recording medium. A light-insensitive area is separated from the middle of the optical system and taken out by a second optical system, and is placed in the spatial frequency region (for example, at least one of the front and rear sides of the image plane) of information recorded on the recording medium. In an optical information recording/reproducing device, the light is guided to a photodetector having a light-receiving surface divided into a plurality of areas with a light-insensitive area in between. They are characterized by being arranged so that they are almost parallel to each other.

A photodetector typically has a light receiving surface divided into at least three regions. A reproduction information signal is generated from the detection signal of the central region of the light-receiving surface among the outputs of the photodetector.

Furthermore, in a more preferable embodiment when a magneto-optical recording medium is used as the optical information recording medium, insensitive areas are provided respectively in front and behind the image formation plane of the information recorded on the magneto-optical recording medium. A first and second photodetector having a light-receiving surface divided into at least three areas in between is arranged under the same conditions as above, and these first and second photodetectors are arranged under the same conditions as above.
The reproduction information signal is generated by taking the difference between the detection signals of the central region of the light receiving surface of the photodetector.

(Function) If the photodetector that detects reflected light from the recording medium is configured and arranged as described above, the spatial frequency axis of information (bits or magnetic domains) along the track direction on the recording medium and the photodetector coincides with the direction of the light-free region, and there is no light-free region that is an undetectable region with respect to the spatial frequency.

Therefore, the frequency characteristics of the reproduced information signal are improved, and the accuracy of bit detection is also improved.

In addition, generating a reproduction information signal using a detection signal from the central region of the light-receiving surface of a photodetector is useful in areas where the degree of temporal change in the intensity distribution of the light beam is large (locations that are often affected by bit diffraction). Since the reproduction information signal is a detection signal that reflects only the detection signal, only the high spatial frequency components of the bits on the recording medium that are incident on the photodetector are detected. This increases the closest resolution of the reproduced signal, further improving the bit position detection accuracy, and in other words, increasing the recording density. At the same time, the drop in the amplitude of the reproduced signal during off-track is reduced, and the accuracy of clock bit detection during access on a sample servo type optical disk is improved.

Furthermore, if photodetectors are placed in the same way in front and behind the image formation plane of the information recorded on the recording medium, and the difference between the detection signals in the center area of each light-receiving surface is taken as the reproduced information signal, In the case of a magneto-optical recording medium in which birefringence of a resin substrate is a problem, S/N deterioration of reproduced information signals due to birefringence is reduced.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a main part including an optical head (optical system) of an optical information recording/reproducing apparatus according to a first embodiment of the present invention. A light beam emitted from a semiconductor laser 1, which is a light source, is turned into a parallel beam by a collimator lens 2, and then by a beam shaping prism 3, the light beam with an anisotropic intensity distribution is transformed into a light beam with an isotropic intensity distribution. The beam is converted and enters the first beam splitter 4. The light beam transmitted through the beam splitter 4 is reflected by a reflecting mirror 5, guided to a focusing lens 6, and is irradiated as a minute light spot onto the recording surface of an optical disk 7, which is an optical information recording medium. The collimator lens 2, beam shaping prism 3, beam splitter 4, reflecting mirror 5, and focusing lens 6 constitute a first optical system for guiding the light beam to the optical disk 7.

The light reflected by the optical disk 7 passes through the focusing lens 6 and the reflecting mirror 5 in the opposite direction to the incident light, and is reflected by the first beam splitter 4. The light beam reflected by the beam splitter 4 becomes a condensed beam by a condensing lens 8, and without being converged, it is divided into two beams by a second beam splitter 9, which are sent to the first and second photodetectors 10A and IOB, respectively. incident. Beam splitter 4. The condensing lens 8 and the beam splitter 9 separate and extract the reflected light from the optical disk 7 from the middle of the first optical system, and the photodetectors 10A, I
It constitutes a second optical system for guiding the light to the OB. Here, the photodetector 10A is placed behind the focal point of the condensing lens 8, and the photodetector 10B is placed in front of the focal point of the condensing lens 8.

In addition, the light-receiving surfaces of the photodetectors 10A and IOB have three regions 11A a in a short lI) shape, as shown in an enlarged view in FIG.
, LIA b, IIA c and IIB a, lLB
b, llB and c. Area I
A a, 11A b.

11A c and areas 11B a, llB b
, 11B c are band-shaped insensitive regions 12A ab, 12A be and 12B ab forming parting lines.
, 12B be are provided. And these non-photosensitive areas 12Aab.

12A be and 12B ab, 12B be,
Photodetector 10A.

Track 15 on the optical disk 7 projected onto 10B (
The photodetectors 10A and IOB are arranged parallel to the projected image of the bit string).

Photodetector 10A, each light receiving surface area 11A a, IIA b, IIA c, and IIB a of IOB.
,llB b.

Output signals Aa, Ab, Ac and Ba corresponding to 11Bc.

After Bb and Be are subjected to current-to-voltage conversion in the amplifier group 13, they are subjected to arithmetic processing in the arithmetic circuit 14, thereby generating a reproduction information signal, a focus error signal and a tracking error signal necessary for controlling the optical head. be done. Specifically, for example, the reproduced information signal is the sum of the output signals of the photodetector 10A and IOB [Aa+(Ab+AC)] + [Ba
+ (Bb+Bc) 3, and the focus error signal is [Aa-(Ab+^c)] - [Ba
-(Bb+Bc), the tracking error signal is (Ab
+Bb) -(Ac+Bc).

In addition, recent disk drive devices have improved accessibility, which was inferior to magnetic disk drive devices, by increasing the rigidity of the carriage, which is an access movement member, and by separating the optical system of the optical head and reducing the weight of the carriage. Measures are being taken to improve the characteristics of the access mechanism system, and high-speed access is now being achieved. By improving the characteristics of the access mechanism system, the control range that must be followed by the fine access mechanism (lens actuator, swing mirror, etc.) during tracking control becomes significantly narrower. Therefore, it is no longer necessary to limit the arrangement and configuration of the multi-division photodetector by focusing on the movement of the light beam on the photodetector by tracking control as seen in the prior art.

This point will be explained in more detail with reference to FIG.

FIG. 3 shows an example of the configuration of an optical information recording/reproducing apparatus in which the characteristics of the access mechanism system are improved. The optical system of the optical head shown in Fig. 1 is separated between the beam splitter 4 and the reflecting mirror 5, and only the reflecting mirror 5 and focusing lens 6 are mounted on the carriage, and the optical system before the beam splitter 4 is accessible. It is configured to be placed at the rear of the mechanical system.

The transfer characteristics of the access mechanism system configured in this way are expressed as
As shown in the figure. From this transfer characteristic, it can be easily inferred that the control band is 1 kHz or more. In addition, with respect to the suppression of the eccentricity component of the optical disk required for the tracking control system, for example, when the eccentricity of the optical disk is 50 μm, the degree of suppression in the access mechanism system is 40 dB or more, which is the amount that must be covered by the precision access mechanism. is a minute amount of about 1 μm, and the amount is so minute that the movement of the light beam on the photodetector surface due to tracking control is almost nonexistent.

Focusing on the fact that there is no need to limit the arrangement and configuration of the photodetector in response to the movement of the light beam on the photodetector due to tracking control, as described above, the photodetector 10A
, the IOB is arranged, and the spatial frequency axis of the information pit along the track direction on the optical disk 7 and the photodetector 10A,
When the directions of the light-insensitive regions 12A ab, 12A be and 12B ab, 12B be of the IOB are matched, there is no light-insensitive region that is an undetectable region with respect to the spatial frequency, so that the frequency characteristics of the reproduced information signal are good. Therefore, the accuracy of pit detection is also increased, and the reliability of the recording/reproducing device is generally improved.

FIG. 5 shows a second embodiment of the present invention, and the configuration of the arithmetic circuit 14 is different from the previous embodiment. That is, in this embodiment, the photodetector 10A, the central region 11A of the light receiving surface of the IOB,
Output signal Aa corresponding to 11B a.

A reproduction information signal is generated by taking the sum Aa+Ba of Ba. Note that, according to the present embodiment, it has become clear from the simulation results by the present inventor that the closest resolution of the reproduced information signal is further improved. The simulation was performed using the optical system model shown in FIG. 1 and a pit-shaped model shown in FIG. 6. Photodetector 10A, IO
The configuration and arrangement of B is exactly the same as in the previous example, and the temporal change in the light intensity distribution on the light receiving surface was determined using diffraction theory. When the photodetector 10A and the IOB are installed at equal positions in front and behind the focal point of the condenser lens 9, the photodetector 10A.

The light intensity distribution on the light receiving surface of 10B is approximately equal.

Next, the light intensity distribution is integrated over the area of the light receiving surface,
This is the temporal instantaneous value of the reproduced information signal.

As a result of this simulation, it was found that due to the influence of pit diffraction, there was a large change in light intensity near the pit (track) projected image in the central region of the light receiving surface of the photodetector 10A, IOB. Therefore, if the reproduction information signal is an output signal that corresponds only to the central areas 11A and 11B a of the light receiving part where the light intensity changes are large as in this embodiment, the light intensity change can be detected sensitively, and as a result, the light intensity change can be detected sensitively. The closest resolution of the reproduced information signal is improved.

FIG. 7 shows a comparison of the closest resolution with respect to the disk radius of the reproduced information signal according to this embodiment and the prior art. Note that a change in the disk radius corresponds to a change in the pitch of the two pits. Also, 8th r! 4 shows a comparison of the closest resolution with respect to the bit length of the reproduced information signal between this embodiment and the prior art.

For example, disk radius 24IIIm1 pit length 0.85
.mu.m and a pit pitch of 1.41 .mu.m, the closest resolution is improved by 11% compared to the conventional level, and the radial position equivalent to the conventional level of closest resolution is 20i+g.

In other words, the recording density in the track direction is 2 compared to the conventional technology.
0% higher.

Furthermore, FIG. 9 shows the amplitude reduction characteristic when off-track, with the reproduced signal amplitude when there is no track deviation being 100%. It can be seen that the amplitude decrease is smaller for the same amount of off-track compared to the prior art. This is extremely useful especially when high pit position detection accuracy is required, such as clock reproduction by clock pit detection performed during access on a sample servo type optical disk.

FIG. 10 shows a third embodiment of the present invention, in which the arithmetic circuit 14
In the center area 1 of the photodetector + OA and IOB light-receiving surface
Difference A between output signals Aa and Ba corresponding to 1Aa and 11Ba
A reproduction information signal is generated by taking a-Ba. As in the case of FIG. 5, the tracking error signal generation system is omitted.

This embodiment is particularly effective when a magneto-optical disk drive device is used. When applied to a magneto-optical disk drive device, a photodetector 10A installed in the spatial frequency region of a mark (magnetic domain) on the magneto-optical disk corresponding to a bit in the case of an optical disk, a band-shaped light-insensitive area on the light receiving surface of the IOB. 12A ab, 12A be and 12B ab
, 12Bbe coincide with the spatial frequency axis of the mark on the magneto-optical disk, it is possible to improve the frequency characteristics of the reproduced information signal as in the first embodiment, and also to improve the resin of the magneto-optical disk. S/N deterioration of the reproduced information signal due to birefringence of the substrate is suppressed.

Signal S/N deterioration due to birefringence of the substrate occurs at the periphery of the beam where the angle of incidence of the beam on the substrate is large, that is, on the photodetector, in the central light receiving plane area 11Aa.

11Ba, both sides of the light-receiving surface area 11A b, lIA
c.

The output signals corresponding to 11B b and IIB c are larger.

From this, the photodetector 10A is used as in this embodiment.

10B, and the center area 11A of the light receiving surface a
, IIB a, if the output signal A a, B aO difference Aa-Ba is generated as a reproduction information signal, birefringence can be reduced compared to simple differential detection performed in conventional magneto-optical disk drives. S/ of reproduced information signal due to influence
N deterioration can be extremely reduced.

In the above embodiment, the beam size differential method was used as an example of the focus error detection method, but the same applies to other known focus error detection systems using a ball-type photodetector or a multi-segment photodetector. A similar effect can be obtained by using the following configuration. However, as in the case where a 4-split photodetector detects focus errors using astigmatism caused by a cylindrical lens, an axis that passes through the center of the light beam incident on the photodetector and is perpendicular to the projected image of the track. It has no effect if the light-receiving surface is divided.

That is, as in the present invention, the light-insensitive area of the light-receiving surface of the photodetector is approximately parallel to the projected image of the track.
A photodetector may be placed.

[Effects of the Invention] According to the present invention, the frequency characteristics and bit detection accuracy of the reproduced information signal are basically improved, and by generating the reproduced information signal using only the detection signal in the central area of the light receiving surface,
The closest resolution of the reproduced information signal is increased, the bit position detection accuracy is further improved, and it is expected that the recording density will be improved.

Furthermore, by reducing the amplitude drop of the reproduced signal during off-track, the accuracy of clock bit detection during access in a sample servo type optical disk is improved, and stable clock reproduction is possible.

In addition, when the present invention is applied to a magneto-optical recording/reproducing device, the S/N of the reproduced information signal due to the influence of birefringence of the resin substrate
Deterioration can be effectively suppressed.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of the main parts including the optical system of an optical information recording/reproducing apparatus according to a first embodiment of the present invention, and FIG. 2 is for explaining the configuration and arrangement of a photodetector in the same embodiment. FIG. 3 is a diagram showing the configuration of the optical information recording/reproducing apparatus including the access mechanism system of the same embodiment, FIG. 4 is a diagram showing the transfer characteristics of the access mechanism system in FIG. 3, and FIG. is a configuration diagram of the main part of the second embodiment of the present invention, and FIG. 6 is a schematic diagram of the bit shape used in the simulation conducted for the same embodiment.
Figure 7 is a characteristic diagram showing the change in close-packed resolution with respect to the disk radius obtained in the same simulation, Figure 8 is a characteristic diagram showing the change in close-packed resolution with respect to the pit length obtained in the same simulation, and Figure 9 is A diagram showing the off-track characteristics of the reproduced signal obtained in the same simulation, Figure 10 is a configuration diagram of the main part of the third embodiment of the present invention, and Figure 11 is the bit on the optical disk and the detected reproduced signal It is a figure which shows a waveform and its differential waveform. 1... Semiconductor laser, 2... Collimator lens, 3
... Beam shaping prism, 4... Beam splitter, 5... Reflector, 6... Focusing lens, 7... Optical diffuser, 8... Focusing lens, 9... Beam splitter, ! OA, 10B--Photodetector, IOA a, I
OB a-- Central area of light-receiving surface, 11A b, 11A
c, IfB b, 11B c - regions on both sides of the light-receiving surface, 1
2A ab, 12A ac, 12B ab, 12
B ac--non-photosensitive area, 13... amplifier group, 14
... Arithmetic circuit, 15... Track.

Claims (3)

[Claims] (1) In an optical information recording and reproducing device that records and reproduces information along a predetermined track by irradiating a light beam onto an optical information recording medium, a light source and a light beam emitted from the light source are used to record and reproduce information along a predetermined track. a first optical system that guides the light to the recording medium; and a second optical system that separates and extracts the reflected light from the recording medium from the middle of the first optical system.
and a photodetector that is arranged in a spatial frequency region of information recorded on the recording medium and detects reflected light extracted by the second optical system, the photodetector An optical device having a light-receiving surface divided into a plurality of regions with a light-insensitive region in between, the light-insensitive region being arranged so as to be substantially parallel to the projected image of the track. Information recording and reproducing device. (2) An optical information recording and reproducing device that records and reproduces information along a predetermined track by irradiating a light beam onto an optical information recording medium, which includes a light source and a light beam emitted from the light source that records the information on the optical information recording medium. a first optical system that guides the light to the recording medium; a second optical system that separates and extracts reflected light from the recording medium from the middle of the first optical system; and imaging information recorded on the recording medium. a photodetector that is disposed at least one of the front and rear sides of the surface and detects the reflected light extracted by the second optical system; and a signal generator that generates a reproduction information signal from the output signal of the photodetector. means, the photodetector has a light-receiving surface divided into at least three regions with a light-insensitive region in between, and the light-insensitive region is substantially parallel to the projected image of the track. An optical information recording and reproducing apparatus, wherein the signal generating means generates a reproduced information signal from an output signal corresponding to a central region of a light receiving surface of the photodetector. (3) In an optical information recording and reproducing device that records and reproduces information along a predetermined track by irradiating a light beam onto a magneto-optical recording medium, a light source and a light beam emitted from the light source are transmitted to the recording medium. a first optical system that guides the reflected light from the recording medium, a second optical system that separates and takes out the reflected light from the first optical system, and an imaging surface for information recorded on the recording medium. first and second photodetectors that are arranged in front and behind the camera and detect the reflected light extracted by the second optical system; and output signals of the first and second photodetectors. signal generating means for generating a reproduction information signal, each of the first and second photodetectors having a light-receiving surface divided into at least three regions with a light-insensitive region in between; The area is arranged so as to be substantially parallel to the projected image of the track, and the signal generating means calculates the difference between output signals corresponding to central areas of the light receiving surfaces of the first and second photodetectors. An optical information recording/reproducing device characterized in that it generates a reproduction information signal.