JPH06187687A - Light pickup - Google Patents

Abstract

PURPOSE:To obtain the sufficient effect of a noise reduction by providing two photodetectors in a light pickup in which a recording/reproducing/erasing is performed by irradiating a magneto-optical disk with light and detecting the reflected light from the disk, and making gains of a first stage amplifiers connectted to respective elements imbalance. CONSTITUTION:The magneto-optical signal detecting system of the light pickup is provided with two photodetectors for magnetro-optical detection, i.e., a focuss detecting photodetector and a track detecting photodetector, photoelectric conversion magnifications of those elements are not made to be the same but made to be imbalance. To be concrete, noises having the same phase are made to be imbalance by changing the light quantities of photodetectors at the time of a reproduction and the generating quantities of shot-noise are also made different from each other. Thus, in a recording system in which a recording duty is less than 50%, the gain of a first stage amplifier connected to a photodetector having larger quantity of an incident light in an erasing state is lowered. For this purpose, the feedback resistance RA in the first stage amplifier 13 for the focuss detection is made greater than the feedback resistance RB in the first stage amplifier 14 for track detection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for a magneto-optical information recording / reproducing apparatus.

[0002]

2. Description of the Related Art Conventionally, magneto-optical information recording / reproducing in which information is recorded / reproduced / erased by projecting light on a magneto-optical disk on which information is magnetically recorded and detecting reflected light from the magneto-optical disk. The device is known. In such a magneto-optical information recording / reproducing apparatus, for example, the polarization plane of the light reflected from the magneto-optical disk is incident on the polarization plane of the polarization beam splitter at an azimuth of 45 °, and is split into two light fluxes.
Signal detection is performed by a so-called differential method, in which the two light fluxes are respectively received by corresponding light receiving elements and a magneto-optical signal is detected by the output difference of the light receiving elements (Japanese Patent Laid-Open No. 59-59).
-168951 publication).

The prior art will be described below with reference to the drawings. FIG. 10 is a schematic configuration diagram showing an example of an optical pickup of a magneto-optical information recording / reproducing apparatus. In FIG. 10, the light emitted from the semiconductor laser (LD) 1 is collimated by the collimator lens (CL) 2, transmitted through the beam splitter (BS) 3, reflected by the deflection prism (DP) 4, and the objective lens. Upon entering the (OL) 5, a spot having a diameter of about 1 μm is formed on the recording surface of a magneto-optical disc (hereinafter referred to as a disc) 6, and the spot records, reproduces, and erases information on the disc 6.

The light reflected by the disk 6 is transmitted again through the objective lens 5 to be collimated, reflected by the deflecting prism 4 and reflected by the beam splitter 3, and separated from the light on the outward path. The deflection surface of the light reflected by the beam splitter 3 is λ /
It is rotated by 45 ° by the two plates 7, and is split into P-polarized light and S-polarized light by the polarization beam splitter (PBS) 9. Then, the light transmitted through the polarization beam splitter 9 is
Astigmatism is generated by the cylindrical lens (CYL) 10 and is incident on the focus detection light receiving element (FoPD) 11. Here, the focus detection method is a known astigmatism method (the description is omitted). In addition, the light reflected by the polarization beam splitter 9 receives the track detection light receiving element (T
It is incident on the rPD) 12. Here, the track detection method is a known push-pull method (the description is omitted). The focus signal and tracking signal detected by these FoPD 11 and TrPD 12 are fed back to an objective lens actuator (not shown) via a known focus servo circuit and tracking servo circuit, and the objective lens 5 focuses and tracks the disc groove. Do. Magneto-optical reproduction (data) signal (MO signal)
Is obtained as a differential signal between the total output of FoPD 11 and the total output of TrPD 12. The pre-pit signal is obtained as the sum output of either FoPD11 or TrPD12 or the sum output of both. still,
Reference numerals 13 and 14 in the figure denote first-stage amplifiers for amplifying the output signals of the FoPD 11 and TrPD 12, and 15 denotes the FoPD 11 and
A differential amplifier for obtaining the difference between the output signals of the TrPD 12 and a magnetic head 17 for recording / erasing.

[0005]

Next, the drawbacks of the above-mentioned prior art will be described below. Conventionally, Fo before differential of MO signal
For the PD output and the TrPD output, a λ / 2 plate 7 is adjusted so that the respective outputs are equal using a disk without magnetization. Here, when the disc reflected light is P-polarized light as shown in FIG. 11A, the polarization plane of the PBS 9 generally coincides with the disc reflected light. At this time, the optical axis of the λ / 2 plate 7 is set to be 22.5 ° with respect to the polarization plane of the PBS 9, as shown in FIG. 11 (b). As a result, as shown in FIG. 11C, the angle formed by the polarization plane of the disc reflected light and the polarization plane of the PBS 9 is 45 °. When this light is reflected and transmitted through the PBS 9, as shown in FIG. 11D, the light amount (X) incident on the TrPD 12 and the FoPD
The light amounts (Y) incident on 11 are equal. FoPD11
When the amounts of light incident on the TrPD 12 are equal to each other, the in-phase noise of the MO signal as a differential signal is minimum, and a reproduction signal with a good carrier-to-noise ratio (C / N ratio) is obtained.

However, the magneto-optical disk is entirely made of a magnetic material, and the recording / reproducing area is magnetized in a recorded or erased state (the directions of magnetization are opposite in recording and erasing). Therefore, when the laser light of the optical pickup enters the disk 6 and is reflected, the polarization plane of the laser light is rotated by ± θk depending on the magnetization direction. For example, when the disk 6 is in the recording state, the polarization plane rotates by θk in the direction shown in FIG. 12A, and as a result, the amount of light incident on the TrPD 12 and the amount of light incident on the FoPD 11 are unbalanced. Here, when the amount of light incident on each light receiving element is obtained, if the amplitude of the disc reflected light is K,
The amount A of light incident on the FoPD 11 is A = (K · cos (45 ° −θk)) ² , and the amount B of light incident on the TrPD 12 is B = (K · cos (45 ° + θk)) ² . When the disc is in the erased state, the polarization plane rotates by θk in the direction shown in FIG.
The amount C of light incident on D11 is C = (K · cos (45 ° + θk)) ² , and the amount D of light incident on TrPD12 is D = (K · cos (45 ° −θk)) ² The output of the element reverses. That is, when the magneto-optical disk is actually reproduced, the outputs of the respective light receiving elements before the differential are always unbalanced, the magnitude of the common mode noise is different, and the common mode noise remains. Further, in the case of a recording method (1-7, 2-7 modulation, etc.) in which the duty of the recording and erasing states is less than 50%, the average incident light amount to each light receiving element becomes unbalanced, and the shot noise must be either The number of photo detectors increases

Here, FIG. 13 shows (a) FoPD output for the recording state (recording: W, erasing: E) of the disc,
(B) TrPD output and (c) MO signal output are shown.
The signal modulation method was 2-7 modulation. As shown in FIG. 13, the fluctuation of the light amount (in-phase noise) is larger when the amount of light incident on the light receiving element is larger, and the in-phase noise remains in the MO signal. Further, when the levels of the maximum value V _A and the minimum value V _B of the FoPD output and the TrPD output are matched, it is normally Fo
Average output V _C and V _D of PD output and TrPD output is TrP
D is larger and the amount of shot noise generated is P when erased.
The larger the D output, the larger.

The present invention has been made in view of the above points, and the total noise is minimized by balancing the in-phase noise and the shot noise in the actual use state.
An object of the present invention is to provide an optical pickup capable of obtaining a reproduction signal having a high / N ratio.

[0009]

In order to achieve the above object, the invention of claim 1 projects light onto a magneto-optical disk on which information is magnetically recorded and detects reflected light from the magneto-optical disk. An optical pickup of a magneto-optical information recording / reproducing apparatus for recording / reproducing / erasing information by means of a method of detecting the information, which is a differential method for obtaining a difference between outputs of two light receiving elements, and a recording method having a recording duty of 50. In an optical pickup which is a magneto-optical recording / reproducing method of less than%, the gain of the first-stage amplifier connected to each of the two light-receiving elements is unbalanced. In addition, claim 2
In the above invention, in the above optical pickup, the gain of the first-stage amplifier in which the amount of light incident on the light receiving element is large when the magneto-optical disk is in the erased state is set to be smaller than that of the other amplifier.

According to a third aspect of the invention, magneto-optical information for recording / reproducing / erasing information by projecting light on a magneto-optical disk on which information is magnetically recorded and detecting reflected light from the magneto-optical disk. In an optical pickup of a recording / reproducing apparatus, the information detecting method is a differential method that takes a difference between outputs of two light receiving elements, and the recording method is a magneto-optical recording / reproducing method with a recording duty of less than 50%. ,
The gain of the differential amplifier that takes the difference between the outputs of the two light receiving elements is unbalanced. According to a fourth aspect of the present invention, in the above optical pickup, the gain of the differential amplifier, which has a larger amount of light incident on the light receiving element when the magneto-optical disk is in the erased state, is smaller than the other gain. . According to a fifth aspect of the present invention, in the optical pickup according to the first or third aspect, the amplifier gain of one light receiving element output is made variable, and a magneto-optical disk recorded at a recording duty of less than 50% is used. It is characterized in that the amplifier is adjusted so that the average output after the movement becomes substantially zero.

The invention of claim 6 records / reproduces / erases information by projecting light onto a magneto-optical disk on which information is magnetically recorded and detecting reflected light from the magneto-optical disk. In an optical pickup of a recording / reproducing apparatus, the information detecting method is a differential method that takes a difference between outputs of two light receiving elements, and the recording method is a magneto-optical recording / reproducing method with a recording duty of less than 50%. ,
It is characterized in that the amounts of light incident on the two light receiving elements for detecting information at the time of reproducing the magneto-optical signal are unbalanced. Further, the invention of claim 7 is characterized in that, in the above-mentioned optical pickup, the amount of light which is incident on the light receiving element when the magneto-optical disk is in an erased state is increased.

According to an eighth aspect of the invention, in the optical pickup according to the sixth and seventh aspects, a magneto-optical disk recorded with a recording duty of less than 50% is used, and the amount of light incident on two light receiving elements for information detection is The feature is that the amount of light is adjusted to be substantially equal. According to the invention of claim 9, in the optical pickup of claim 8, the method of adjusting the amount of light incident on the two light receiving elements for detecting information is performed by rotating a λ / 2 plate. In addition, claim 10
In the optical pickup according to the present invention, the method of adjusting the amount of light incident on the two light receiving elements for information detection is performed by rotating the polarization beam splitter.

According to an eleventh aspect of the present invention, in the optical pickup according to the sixth and seventh aspects, when the magneto-optical disk is in the erased state, the amount of light incident on the light receiving element is decreased before the light receiving element having the larger light amount. It is characterized by having a filter. The invention of claim 12 is characterized in that, in the optical pickup of claim 8 or claim 11, the transmittance of the filter is changed so that the amounts of light incident on the two light receiving elements are substantially equal.

[0014]

As described above with reference to FIG. 13, the fluctuation of the light quantity (in-phase noise) in the optical pickup is larger when the quantity of light incident on the light receiving element is larger.
If there is an imbalance in the average amount of light incident on the two light receiving elements, in-phase noise remains in the magneto-optical signal (MO signal). Therefore, in the recording method in which the duty of the recording portion is less than 50%, the amplifier (first stage amplifier, differential amplifier) connected to the two light receiving elements for detecting the magneto-optical signal as in the invention of claims 1 to 5 is used. When the detection gain is unbalanced and the amount of received light at the time of erasing, that is, the detection gain of the amplifier that increases the output of the light receiving element is decreased, the total common mode noise rejection ratio is increased, and the noise reduction effect improves the C / N ratio. . Further, in the example shown in FIG. 13, the average light amount of the outputs of the two light receiving elements for detecting the magneto-optical signal, that is, the outputs of the focus detecting light receiving element (FoPD) and the track detecting light receiving element (TrPD) is TrPD. And the amount of shot noise generated becomes larger as the output of the light receiving element at the time of erasing becomes larger. Therefore, also with respect to shot noise, noise can be reduced by lowering the detection gain of the amplifier for which the light-receiving element output during erasing is larger.

Further, instead of unbalanced the detection gains of the amplifiers connected to the two light receiving elements, it is preferable that the amplifier gains are unbalanced.
As in the inventions of ˜12, the amount of light incident on the two light receiving elements for detecting the magneto-optical signal is unbalanced, and the amount of light on the side where the amount of incident light on the light receiving element becomes large when the magneto-optical disk is in the erased state If it is decreased, the total common mode noise removal ratio is increased, and the C / N ratio is improved due to the noise reduction effect.
Also, with respect to shot noise, noise reduction can be achieved by reducing the light amount of the incident light amount on the light receiving element during erasing.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. [Embodiment 1] FIG. 1 is a schematic diagram of a magneto-optical signal (MO signal) detection system of an optical pickup according to an embodiment of the present invention. The configuration of the optical system of the optical pickup is the same as in FIG. In this embodiment, 2 for MO signal detection is used.
Two light receiving elements, that is, the light receiving elements for focus detection (F
In this example, the photoelectric conversion magnifications of the oPD) and the track detection light receiving element (TrPD) are not the same but are unbalanced. As described above, the light amounts of the light receiving elements for detecting the two MO signals at the time of signal reproduction are different, so that the in-phase noise is unbalanced and the shot noise is also generated in different amounts. Therefore, in the recording method in which the recording duty is less than 50%, the gain of the first-stage amplifier connected to the light receiving element having the larger incident light amount in the erased state is reduced.
More specifically, in the case of the optical pickup shown in FIG. 10, since the amount of incident light in the erased state is large on the TrPD side, the first stage amplifier 13 connected to the FoPD side of the MO signal detection system shown in FIG. The feedback resistor R _A is made larger than the feedback resistor R _B of the first stage amplifier 14 connected to the TrPD side (R _A
> R _B), lower the gain of the first-stage amplifier 14 of TrPD side. That lowers the gain of the first-stage amplifier 14 of TrPD side, as shown in FIG. 2, the average output V _C and T of FoPD
By making the average output V _D 'of the rPD substantially equal, it is possible to reduce the residual common mode noise and shot noise.

[Embodiment 2] FIG. 3 shows a magneto-optical signal (MO) of an optical pickup according to an embodiment of the present invention.
It is a schematic diagram of a (signal) detection system. In the present embodiment, the gains of the first-stage amplifiers 13 and 14 are the same, and the gain of the differential amplifier 15 that takes the difference between the outputs of the two light-receiving elements is unbalanced. That is, the feedback resistors R _C and R _D of the differential amplifier 15 are set to R _C ≠ R _D , and the gains on the FoPD side and the TrPD side are unbalanced. In the present embodiment as well, the amplifier gain on the side to which the light receiving element (TrPD) whose incident light amount becomes larger in the erased state is connected is lowered (R _C > R _D ) as in the first embodiment. Then, as shown in FIG.
By adjusting the gains on the FoPD side and the TrPD side so that the average output V _{C of} PD and the average output V _D ′ of TrPD are substantially equal to each other, residual common-mode noise and shot noise can be reduced.

In the first and second embodiments, as a method for actually minimizing the in-phase noise and the shot noise, a recording method with a recording duty of less than 50% as shown in FIG. 4 (for example, 1-7, 2). The media (adjustment disk) randomly recorded by -7 modulation or the like is reproduced, and the light-receiving element output for information detection, that is, the average output of FoPD and TrPD is made substantially equal (the average output after differential is Alternatively, the amplifier gain of the first-stage amplifier or the differential amplifier may be adjusted so that the noise level is minimized (claim 5). Since the unbalance amount is determined by the reproduction signal modulation degree of the optical system, the Kerr rotation angle of the medium, and the detection circuit system, it may be a constant value for the same model. Further, as shown in FIG. 5, the gain of the first stage amplifier 14 on the side of the light receiving element (TrPD) where the amount of incident light in the erased state is large is made variable (the feedback resistor R _E is made a variable resistor), and the signal is checked. However, you may adjust so that noise may become the minimum.

[Third Embodiment] In the first and second embodiments, two light receiving elements for MO signal detection, that is, a focus detecting light receiving element (FoPD) and a track detecting light receiving element (TrP) are used.
This is an example in which the photoelectric conversion magnifications in D) are not the same but are unbalanced. However, instead of unbalanced the detection gains of the amplifiers connected to the two light receiving elements, as in the invention of claim 6, Even if the amounts of light incident on the two light receiving elements for detecting the magneto-optical signal are unbalanced, the same effect can be obtained, and residual common-mode noise and shot noise can be reduced. That is, as in the seventh aspect of the invention, if the amount of light that increases the amount of light incident on the light receiving element when the magneto-optical disk is in the erased state is decreased, the total common-mode noise removal ratio is increased, and the noise reduction effect is achieved. The C / N ratio is improved.

More specifically, in this embodiment, M
This is an example in which the amounts of incident light on the two light receiving elements for O signal detection, that is, the focus detection light receiving element (FoPD) and the track detection light receiving element (TrPD) are not the same but are unbalanced. As mentioned earlier, 2 during signal reproduction
Since the light amounts of the two light receiving elements for detecting the MO signal are different, imbalance occurs in the noise of the same phase, and the generation amount of the shot noise is also different. Therefore, the recording duty is 50%
In the recording method of less than 1, the incident light amount of the light receiving element having the larger incident light amount in the erased state is decreased. By doing so, as shown in FIG.
The average output V _C and TrPD average output V _D 'and can substantially equal that of the residual phase noise, it is possible to reduce the shot noise. It should be noted that when the amount of incident light is reduced, the carrier (signal) is also reduced, but the noise reduction effect is greater than the carrier reduction, and the C / N ratio is improved in total.

As a method for actually minimizing the in-phase noise and the shot noise, a recording method with a recording duty of less than 50% as shown in FIG. 4 (for example, 1-7, 2-
The medium (adjustment disk) randomly recorded by 7 modulation or the like is reproduced, and the incident light amount on the TrPD is adjusted so that the light-receiving element output for information detection, that is, the average output of FoPD and TrPD becomes substantially equal ( Claim 8).

As means for realizing the actual imbalance of the light quantity, in the optical system of the optical pickup shown in FIG.
As shown in FIG. 6, the optical axis of the λ / 2 plate 7 is set so as to deviate from the conventional 22.5 ° with respect to the polarization plane of the PBS 9 (FIG. 6 (b)). The rotation amount of 7 is adjusted to reduce the light amount on the TrPD 12 side (the one in which the output of the light receiving element becomes large during erasing in the past) (FIG. 6C).
(D)). Then, if the optical axis of the λ / 2 plate 7 is adjusted so that the FoPD output V _A and the TrPD output V _F at the time of erasing become substantially equal (FIG. 6 (f)), the MO signal becomes as shown in FIG. , S / N ratio and C / N ratio can be improved (claim 9).

[Embodiment 4] As another means for realizing the light quantity imbalance, as shown in FIG. 8, the PBS 9 itself is rotationally adjusted except for the λ / 2 plate of the optical system of the optical pickup. . That is, the polarization plane of the PBS 9 is set to be offset from 45 ° with respect to the polarization plane of the disc reflected light. Also in this case, FoPD output V _A and Tr at the time of erasing
If the polarization plane of the PBS 9 is adjusted so that the PD outputs V _F become substantially equal, the MO signal becomes as shown in FIG.
The ratio and the C / N ratio can be improved (claim 10).

[Embodiment 5] As yet another method of realizing the light quantity imbalance, as shown in FIG. 9, the light receiving element of the optical system of the optical pickup whose output of the light receiving element becomes large at the time of erasing, that is, A filter 16 for reducing the light amount is inserted on the TrPD 12 side (claim 11). In this case, since the filter 16 reduces the amount of light incident on the TrPD 12 to the whole, the average output of the TrPD 12 decreases,
The MO signal is the same as in FIG. As a method for actually minimizing the in-phase noise and the shot noise, random recording is performed by a recording method (for example, 1-7, 2-7 modulation, etc.) with a recording duty of less than 50% as shown in FIG. The medium (adjustment disc) is reproduced, and the transmittance of the filter 16 is adjusted so that the light-receiving element output for information detection, that is, the average output of the FoPD 11 and TrPD 12 is substantially equal, and the amount of light incident on the TrPD 12 is adjusted. Item 1
2).

[0025]

As described above, in the optical pickups according to the first and third aspects, the optical pickup for detecting information (MO signal) is used.
Residual common-mode noise and shot noise caused by the imbalance of the amount of light incident on two light-receiving elements can be reduced by adjusting the gain of the circuit system amplifier (first stage amplifier or differential amplifier) to an unbalanced level, and the effect of noise is small. Signal reproduction becomes possible. Further, in the optical pickups according to claims 2 and 4, since the gain of the amplifier connected to the light receiving element having the larger incident light amount when the magneto-optical disk is in the erased state is lowered, shot noise can be effectively reduced, In addition, residual common-mode noise is also reduced, and signal reproduction that is less affected by noise is possible. Further, in the optical pickup according to the fifth aspect, since the noise can be minimized by adjusting the amplifier gain for each model, a sufficient noise reduction effect can be obtained even if there are variations in the light amount and the circuit.

In the optical pickups of claims 6 and 7, residual in-phase noise and shot noise can be reduced by adjusting the amounts of light incident on the two light receiving elements for detecting information (MO signals) to be unbalanced. It is possible to reproduce a signal that is less affected by. In the optical pickup of claim 8, since the light amount imbalance can be determined by the signal from the magneto-optical disk recorded by the same modulation method as that in use, noise can be reduced in substantially the same state as in actual use. .

In the optical pickup of claim 9, λ
Since the / 2 plate is rotated to adjust the optical axis, the imbalance of the light amount can be easily set to a desired value, so that the residual common-mode noise can be easily reduced (there is no reduction in signal). In the optical pickup of claim 10, since the unbalance of the light quantity can be easily set to a desired value by rotating the polarization beam splitter to adjust the polarization plane, the same effect as that of claim 9 can be obtained. , Λ / 2 plate is not required, the cost can be reduced. In the optical pickup according to claim 11, when a filter for reducing the light quantity is inserted in front of the light receiving element having a larger incident light quantity to the light receiving element when the magneto-optical disk is in the erased state, residual common-mode noise and Shot noise can be reduced and signal reproduction that is less affected by noise is possible. Claim 12
In the optical pickup of (1), the residual common-mode noise and the shot noise are the most in order to change the transmittance of the filter so that the amounts of light incident on the two light receiving elements when the magneto-optical disk is in the erased state are substantially equal. It can be adjusted to be small.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a magneto-optical signal detection circuit system of an optical pickup according to an embodiment of the present invention.

FIG. 2 is (a) FoPD output for recording / erasing state of a magneto-optical disk by the optical pickup of the present invention, (b).
It is a figure which shows an example of TrPD output and the (c) MO signal.

FIG. 3 is a schematic diagram of a magneto-optical signal detection circuit system of an optical pickup showing an embodiment of the invention as claimed in claims 3 and 4.

FIG. 4 is an explanatory diagram of a magneto-optical disk used for adjusting an amplifier gain or a light amount.

FIG. 5 is a schematic diagram of a magneto-optical signal detection circuit system of an optical pickup showing an embodiment of the invention as set forth in claim 5.

6A and 6B are explanatory views of the embodiment of claim 9, wherein FIG. 6A is a diagram showing disk reflected light with respect to the polarization plane of the polarization beam splitter, and FIG. 6B is a λ / 2 plate with respect to the polarization plane of the polarization beam splitter. Showing the optical axis of FIG. 2, (c) showing the polarization plane of the disc reflected light after passing through the λ / 2 plate with respect to the polarization plane of the polarization beam splitter, and (d) showing two light receiving elements separated by the polarization beam splitter. (FoPD, TrP
FIG. 6E is a diagram showing light incident on D), and FIG. 7E is two light receiving elements (FoPD, TrPD) when the disc is in a recording state.
FIG. 6F is a diagram showing incident light on the two light receiving elements (FoPD, TrPD) when the disc is in an erased state.

7 (a) FoPD output for recording / erasing state of a magneto-optical disk by the optical pickup of the present invention, (b).
It is a figure which shows another example of TrPD output and (c) MO signal.

FIG. 8 is a schematic configuration diagram of an optical pickup showing an embodiment of the invention as set forth in claim 10.

FIG. 9 is a schematic configuration diagram of an optical pickup showing an embodiment of the invention described in claim 11.

FIG. 10 is a schematic configuration diagram of an optical pickup showing an example of a conventional technique.

FIG. 11 is an explanatory diagram of a conventional technique, in which FIG.
The figure which shows the disc reflected light with respect to the polarization plane of the polarization beam splitter in the optical pickup shown in FIG. 6, (b) shows the optical axis of the λ / 2 plate with respect to the polarization plane of the polarization beam splitter, and (c) shows the polarization of the polarization beam splitter. The polarization plane of the disc reflected light after passing through the λ / 2 plate with respect to the plane,
FIG. 3D is a diagram showing light that is split by the polarization beam splitter and is incident on two light receiving elements (FoPD, TrPD).

12 is an explanatory diagram of a conventional technique, in which FIG.
The figure which shows the incident light to the two light receiving elements (FoPD, TrPD) when the disc is in the recording state in the optical pickup shown in (b) is the two light receiving elements (FoPD, TrPD) when the disc is in the erasing state. ) Is a diagram showing incident light on the light.

13A and 13B are explanatory diagrams of a conventional technique, in which (a) FoPD output and (b) TrPD output for a recording / erasing state of the magneto-optical disk by the optical pickup shown in FIG.
(C) It is a figure which shows an example of MO signal.

[Explanation of symbols]

 1 ... Semiconductor laser (LD) 2 ... Collimating lens (CL) 3 ... Beam splitter (BS) 4 ... Deflection prism (DP) 5 ... Objective lens (OL) 6 ... Light Magnetic disk 7 ... λ / 2 plate 8 ... Condensing lens 9 ... Polarizing beam splitter (PBS) 10 ... Cylindrical lens (CYL) 11 ... Focus detection light receiving element (FoPD) 12. ..Track detection light receiving elements (TrPD) 13, 14 ... First stage amplifier 15 ... Differential amplifier 16 ... Filter 17 ... Magnetic head

Claims (12)

[Claims] 1. Light of a magneto-optical information recording / reproducing apparatus for recording / reproducing / erasing information by projecting light onto a magneto-optical disk on which information is magnetically recorded and detecting reflected light from the magneto-optical disk. In the optical pickup, which is a pickup, the information detection method is a differential method that takes a difference between outputs of two light receiving elements, and the recording method is a magneto-optical recording / reproducing method with a recording duty of less than 50%. An optical pickup characterized in that the gain of the first-stage amplifier connected to each element is unbalanced. 2. The optical pickup according to claim 1, wherein
An optical pickup characterized in that the gain of the first-stage amplifier, which has a larger amount of light incident on the light receiving element when the magneto-optical disk is in the erased state, is smaller than the gain of the other amplifier. 3. Light of a magneto-optical information recording / reproducing apparatus for recording / reproducing / erasing information by projecting light onto a magneto-optical disk on which information is magnetically recorded and detecting reflected light from the magneto-optical disk. In the optical pickup, which is a pickup, the information detection method is a differential method that takes a difference between outputs of two light receiving elements, and the recording method is a magneto-optical recording / reproducing method with a recording duty of less than 50%. An optical pickup having an unbalanced gain of a differential amplifier that takes a difference in element output. 4. The optical pickup according to claim 3,
An optical pickup characterized in that a gain of a differential amplifier whose incident light quantity to a light receiving element is large when the magneto-optical disk is in an erased state is made smaller than the gain of the other. 5. The optical pickup according to claim 1, wherein the amplifier gain of one light receiving element output is variable, and a magneto-optical disk recorded with a recording duty of less than 50% is used. An optical pickup characterized in that the amplifier is adjusted so that the average output becomes substantially zero. 6. Light of a magneto-optical information recording / reproducing apparatus for recording / reproducing / erasing information by projecting light on a magneto-optical disk on which information is magnetically recorded and detecting reflected light from the magneto-optical disk. In a pickup, the information detection method is a differential method that takes a difference between outputs of two light receiving elements, and the recording method is a magneto-optical recording / reproducing method with a recording duty of less than 50%. An optical pickup having an unbalanced amount of light incident on two light receiving elements for detecting information at the time. 7. The optical pickup according to claim 6,
An optical pickup characterized in that, when the magneto-optical disk is in an erased state, the amount of incident light on the light receiving element is increased, and the amount of incident light is decreased. 8. The optical pickup according to claim 6, wherein a magneto-optical disk recorded with a recording duty of less than 50% is used, and the amounts of light incident on the two light receiving elements for information detection are substantially equal. An optical pickup that is characterized by adjusting the amount of light. 9. The optical pickup according to claim 8,
An optical pickup characterized by rotating a λ / 2 plate as a method for adjusting the amount of light incident on two light receiving elements for information detection. 10. The optical pickup according to claim 8, wherein the method of adjusting the amount of light incident on the two light receiving elements for detecting information is performed by rotating a polarization beam splitter. 11. The optical pickup according to claim 6, further comprising a filter for reducing the light quantity in front of the light receiving element having a larger incident light quantity when the magneto-optical disk is in an erased state. An optical pickup characterized by that. 12. The optical pickup according to claim 8 or 11, wherein the transmittance of the filter is changed to make the incident light amounts to the two light receiving elements substantially equal.