JP3491641B2 - Magneto-optical disk device and method of reproducing magneto-optical disk - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk device and a reproducing method for a magneto-optical disk, and more particularly to a magneto-optical disk which is tracked by forming a groove.

[0002]

2. Description of the Related Art Conventionally, in this type of magneto-optical disk device, tracking control can be performed with a groove formed on the magneto-optical disk as a reference, and the Kerr effect can be utilized to reproduce thermomagnetically recorded information. It is like this.

That is, the magneto-optical disk device emits a light beam of a predetermined polarization plane of a laser element such as a built-in semiconductor laser in an optical pickup, and collects the light beam by a predetermined objective lens to record information on the magneto-optical disk. Irradiate the recording surface. As a result, the magneto-optical disk device obtains reflected light whose polarization plane changes according to the direction of the magnetic pole at the light beam irradiation position due to the Kerr effect.

This magneto-optical disk device receives the reflected light obtained from the magneto-optical disk through an objective lens to convert the reflected light into parallel rays, separates the parallel rays from the light beam, and further polarizes them. For example, it is separated into an S-polarized component and a P-polarized component via the beam splitter. As a result, the magneto-optical disk device separates the reflected light of the magneto-optical disk into the S-polarized light component and the P-polarized light component whose light amount changes complementarily according to the change of the polarization plane, and then separates the S-polarized light component and the P-polarized light component. Light is received by each light receiving element.

This light receiving element is formed by dividing the light receiving surface in the radial direction of the magneto-optical disk (that is, in the direction orthogonal to the extending direction of the groove) so that the output current from each light receiving surface can be output. It has become. That is, in the magneto-optical disk, when the irradiation position of the light beam is displaced from the center of the groove in the radial direction, the light amount distribution of the reflected light changes correspondingly in the radial direction of the magneto-optical disk.

As a result, the magneto-optical disk device detects the difference signal between the light-receiving surfaces of the respective light-receiving elements in the radial direction of the magneto-optical disk to change the light quantity distribution of the reflected light in the radial direction of the magneto-optical disk. To detect. As a result, a tracking error signal whose signal level changes according to the tracking error amount is detected, and tracking control is performed based on this tracking error signal.

Further, in the magneto-optical disk device, after adding output signals on the light receiving surfaces of the respective light receiving elements and then subtracting the output signals between the light receiving elements, the signal level changes according to the change of the polarization plane. To detect the playback signal.
As a result, it is possible to detect a reproduction signal whose signal level changes according to the direction of the magnetic pole at the light beam irradiation position and reproduce the recorded information.

[0008]

By the way, in the magneto-optical disk device of this type, if the structure of the optical pickup can be simplified, the overall shape can be reduced accordingly.
Also, the optical pickup drive system and the like can be simplified. Specifically, in the conventional optical pickup, the light beam and the reflected light are converted into parallel light rays and separated, and further separated into S-polarized light component and P-polarized light component.
As shown in, if this separation process is performed in converging light,
It is considered that the overall configuration can be simplified.

That is, the optical pickup 1 reflects the light beam L1 (in this case, S-polarized light) having a predetermined polarization plane emitted from the laser diode 2 on the reflection surface 3 of the beam splitter 3.
It is reflected by a and guided to the objective lens 4, and is condensed on the magneto-optical disk 5 by this objective lens 4. Further optical pickup 1
Receives the reflected light of this light beam by the objective lens 4 and transmits it through the beam splitter 3 while holding it as a convergent light beam,
The polarized light is rotated by 45 ° with the half-wave plate 6, and then the prism 7
Incident on.

Here, the prism 7 is formed by laminating a first prism 8 having a parallelogram shape and a triangular prism 9 having a right-angled triangular cross section, and the PBS is attached to the laminating surface.
A film M1 is formed, and a total reflection mirror M2 is formed on the slope parallel to the bonding surface. As a result, the optical pickup 1 makes the reflected light incident on the PBS film M1 and separates it into transmitted light and reflected light, thereby separating the reflected light into, for example, a P-polarized component and an S-polarized component.

Here, the optical pickup 1 totally reflects the reflected light of the PBS film M1 by the total reflection mirror M2 to emit the reflected light of the PBS film M1 in the same direction as the transmitted light. In this case, the optical pickup 1 once collects the reflected light of the PBS film M1 inside the prism 7 so that the P-polarized light component and the S-polarized light component emitted from the prism 7 have almost equal beam diameters. After that, the light is emitted in the state of divergent light flux, and the transmitted light of the PBS film M1 is emitted in the state of convergent light.

Further, in the optical pickup 1, the light receiving element 10 is arranged on the exit surface of the prism 7, and the light receiving element 10 is arranged.
As shown in FIG. 9, the first and second P polarized components separated by the PBS film M1 can be received respectively.
And second light receiving surfaces I and J are formed. As a result, in the magneto-optical disk device to which the optical pickup 1 is applied, by detecting the difference signal between the light receiving surfaces I and J, a signal is generated according to the direction of the magnetic pole formed at the focus position of the light beam on the disk 5. It is possible to obtain a reproduction signal whose level changes, and thus it is possible to reproduce recorded information by utilizing the Kerr effect.

By the way, in this type of magneto-optical disk 5, a predetermined address signal is frequency-modulated to form a track wobble signal, and the groove is provided so as to meander based on the track wobble signal. .
Thereby, the meandering of the groove can be detected to detect the position information of the light beam irradiation position. When the beam splitter 3 is arranged in the convergent light flux to separate the reflected light from the light beam like the optical pickup 1 with respect to the groove formed so as to meander, this track wobble signal is mixed in the reproduction signal. There is a problem,
As a result, the SN ratio of the reproduction signal deteriorates, and thus there is a drawback that the recorded information cannot be reproduced correctly.

The present invention has been made in view of the above problems, and it is possible to reduce mixing of track wobble signals into reproduced signals with a simple configuration in which output signals of light receiving elements are added and subtracted. An object of the present invention is to provide a magneto-optical disk device and a magneto-optical disk reproducing method.

[0015]

According to the invention of claim 1 , the above object is to irradiate a magneto-optical disk with a light beam,
In a magneto-optical disk device that receives the reflected light and reproduces recorded information magnetically recorded on the magneto-optical disk, an irradiation optical system that emits the light beam and irradiates the magneto-optical disk, and receives the reflected light. And then converge the reflected light
A separation optical system that separates into a first polarization component and a second polarization component in the state of a light flux, and first and second separation light systems that receive the reflected light separated into the first polarization component and the second polarization component, respectively. And a signal processing circuit for processing the output signal of the light receiving element, and the light receiving surface of the first light receiving element has first and second light receiving surfaces in the radial direction of the magneto-optical disk. And a light receiving surface of the second light receiving element is divided into third and fourth light receiving surfaces corresponding to the first and second light receiving surfaces of the first light receiving element, and The reflected light of the second polarization component corresponding to the reflected light of the first polarization component received by the first and second light receiving surfaces is received, and the signal processing circuit includes the first and fourth light receiving surfaces. Subtracting the output signal of the above to generate a first subtraction signal, and The output signal of the surface is subjected to subtraction processing to generate a second subtraction signal, the first and second subtraction signals are added at a predetermined addition ratio to output a reproduction signal, and the addition ratio is the reproduction signal. By the magneto-optical disk device selected to suppress the track wobble signal mixed in the signal,
To be achieved.

The above object is, in the invention of claim 2 ,
In a reproducing method of a magneto-optical disk, which irradiates a magneto-optical disk with a light beam and receives the reflected light to detect a reproduction signal of the magneto-optical disk, the reflected light is received and the reflected light is converted into a converged light beam. In the state, it is separated into a first polarized component and a second polarized component, and the reflected light separated into the first polarized component and the second polarized component is received by the first and second light receiving elements, respectively, and The output signal of the light receiving element is processed by a signal processing circuit to output the reproduction signal, and the light receiving surface of the first light receiving element is divided into first and second light receiving surfaces in the radial direction of the magneto-optical disk. Has been done, the second above
The light receiving surface of the light receiving element of
And a second polarized light which is divided into third and fourth light receiving surfaces corresponding to the second and second light receiving surfaces and which corresponds to reflected light of the first polarization component received by the first and second light receiving surfaces. The reflected light of each component is received, and the signal processing circuit subtracts the output signals of the first and fourth light receiving surfaces to generate a first subtracted signal, and the second and third light receiving surfaces. Output signal is subtracted to generate a second subtraction signal, the first and second subtraction signals are added at a predetermined addition ratio to output a reproduction signal, and the addition ratio is the reproduction signal. This is achieved by the reproducing method of the magneto-optical disk selected so as to suppress the track wobble signal mixed in with.

Preferably, the separation optical system of the first invention is configured to separate the reflected light into the first polarized light component and the second polarized light component in a converged light flux state.

Further, preferably, the reflected light of the second invention is configured to be separated into the first polarized component and the second polarized component in the state of a convergent light flux.

In the present invention, the first polarized light component corresponds to, for example, the S polarized light component of the embodiment, and the second polarized light component corresponds to the P polarized light component.

[0020]

According to the above-mentioned configuration of the magneto-optical disk device,
By suppressing the track wobble signal in the processing of the reproduction signal, the noise of the reproduction signal can be removed accordingly.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings. The examples described below are
Since it is a preferred specific example of the present invention, various technically preferable limitations are attached, but the scope of the present invention is, unless otherwise stated to limit the present invention, in the following description.
It is not limited to these modes.

FIG. 1 is a perspective view showing an embodiment of a magneto-optical disk device according to the present invention. In the figure, in the structure of the magneto-optical disk device 20, the parts denoted by the same reference numerals as those of the magneto-optical disk device 1 described in FIG. 8 have the same structure, and thus the duplicated description will be omitted. Further, in the figure, an optical system such as a laser diode has the same configuration as that of the magneto-optical disk device 1, and therefore the description thereof will be omitted.

In this magneto-optical disk device 20, the light-receiving surfaces of the light-receiving elements I and J have two light-receiving surfaces Ia and Ia, respectively.
It is divided into b, Ja and Jb. Each of the light receiving surfaces Ia,
The output currents output from Ib, Ja, and Jb are current-voltage converted by the signal processing circuit 21 and then subjected to addition / subtraction processing, whereby the focus error signal FE, the tracking error signal TE, and the reproduction signal RF are detected. In this embodiment, the light receiving elements I and J are formed, for example, on one semiconductor substrate and arranged so as to be in close contact with the prism 7.

Here, the inventors of the present invention have studied in detail the phenomenon in which the track wobble signal is mixed with the reproduction signal, and as a result, in the light beam L1 emitted from the laser diode 2 as described above with reference to FIG. Is a linearly polarized light of S polarization (symbol P1 in FIG. 8), is reflected by the magneto-optical disk 5 and is polarized by a predetermined angle θk (symbol P2 in FIG. 8), and then passes through the beam splitter 3. It was found that the track wobble signal is mixed in the reproduction signal in the conventional magneto-optical disk device due to the polarized light.

That is, in this case, the magneto-optical disk device 1
With the beam splitter 3 arranged in the reflected light flux that is a convergent light flux, the incident angle of the reflected light on the reflecting surface of the beam splitter 3 changes according to the incident position. As a result, the transmitted light of the beam splitter 3 rotates in different directions of polarization in each region of the grooved diffracted light forming the transmitted light and by the same angle (represented by an angle α in FIG. 8). As a result, it was found that in the magneto-optical disk device 1 described above with reference to FIG. 8, the track wobble signal is mixed in the reproduction signal. In FIG. 1, this situation is indicated by the symbol P4 and the polarization direction is indicated by the arrow.

That is, as shown in FIG. 2, in the reflected light (return light) L1 of the magneto-optical disk 5, diffracted light from the groove forms a central portion and a region of only the 0th-order light in the extending direction of the groove. And the 0th order light and 1 on both sides
It can be considered that a region where the second-order diffracted light overlaps is formed.

The zero-order light amplitude in this region of zero-order light is E
Let 0 be the amplitude of the 1st-order diffracted light, and E be the phase difference between the 0th-order light and the 1st-order diffracted light.

[0028]

[Equation 1]

As shown in, when p is a detrack amount standardized by the track pitch, the amplitude d1 of the light wave in the region where the 0th-order light and the 1st-order diffracted light overlap is

[0030]

[Equation 2]

## EQU3 ## The amplitude d0 of the light wave in the region containing only zero-order light is

[0032]

[Equation 3]

It can be expressed by Here, Δp represents the detrack amount, and Tp represents the track pitch. Note that, in this arithmetic processing, the relational expressions are described only for the regions of the 0th-order light and the 1st-order diffracted light on the right side in FIG. 2 and the 0th-order light and the 1st-order diffracted light on the left side of FIG. The description of the relational expression is omitted for the area.

For this reflected light, the magneto-optical disk device 2
In 0, the transmitted light of the half-wave plate 6 is separated by the PBS film M1 and is received by the light receiving elements I and J. As a result, as shown in FIG. 3, the I-axis and the J-axis represented by an angle of 45 degrees with respect to the S-polarized light of the light beam L1 with reference to the polarization plane of the light beam L1 emitted from the laser diode. The reflected light is received with the reference. In this case, it is assumed that θk represents the rotation angle due to the Kerr effect, and the reflected light is polarized by the beam splitter 3 by the uniform polarization rotation angle α.

Accordingly, the amplitude of the light wave incident on the light receiving element is the region where the 0th-order light and the 1st-order diffracted light overlap,

[0036]

[Equation 4]

Can be expressed by

[0038]

[Equation 5]

It can be represented by

Here, the light quantity Ipo with respect to the amplitude Iamp of the light wave
wer is the following formula

[0041]

[Equation 6]

As can be expressed by, by substituting the equations 2 and 3 into the equations 4 and 5, and then substituting into the equation 6, the light amount Ipower1 in the region where the 0th-order light and the 1st-order diffracted light overlap is expressed by the following equation.

[0043]

[Equation 7]

Can be expressed by

[0045]

[Equation 8]

It can be represented by

On the other hand, as shown in FIG. 4, in the light receiving elements I and J, a region where the 0th-order light and the 1st-order diffracted light overlap each other and a region where only the 0th-order light is formed. In this embodiment, the light receiving surfaces Ia, Ib, J of the light receiving elements I and J are used.
Since a and Jb are formed by being divided in the radial direction of the magneto-optical disk, a region where 0th-order light and −first-order diffracted light overlap and a region where only 0th-order light overlaps, or a region where 0th-order light and + 1st-order diffracted light overlap and A light receiving surface Ia corresponding to a region of only 0th order light,
Ib, Ja, and Jb will receive light.

Thereby, the light receiving surfaces Ia, Ib, Ja, Jb
If the light amounts of the light receiving surfaces Ia, Ib, Ja, Jb are represented using the symbols Ia, Ib, Ja, Jb assigned to

[0049]

[Equation 9]

[0050]

[Equation 10]

[0051]

[Equation 11]

[0052]

[Equation 12]

It can be represented by Here, when the reproduction signal is detected by the configuration described above with reference to FIG. 8, the reproduction signal RF
Where MO is

[0054]

[Equation 13]

Since this can be expressed by
~ Substituting the relational expression of Expression 12 into the following expression

[0056]

[Equation 14]

It can be represented by

Here, in the second term on the right side of the equation (14), p
Is the detrack amount, the signal level of the reproduction signal RF fluctuates according to the detrack amount P when the incident light of the light receiving element is accompanied by the polarization rotation angle α, and the reproduction signal RF is tracked. It can be seen that the wobble signal is mixed. When there is no wobble in the groove, P = 0 in the equation (14) and the reproduction signal MO is

[0059]

[Equation 15]

It can be seen that the track wobble signal is also mixed in the reproduction signal RF.

By the way, a predetermined constant k is set for the equation (13), and the following equation is obtained.

[0062]

[Equation 16]

By setting the relational expression of, and substituting the relational expressions of the equations 9 to 12 into this relational expression, the following equation is obtained.

[0064]

## EQU17 ## MO = θk (1 + k) {2E0 ² + 4E1E
0 · cos [φ] cos [2πp]} − 2 {(1 + 2
α) -k (1-2α)} · E0E1 · sin (φ] si
n [2πp]

The relational expression of can be obtained.

Here, paying attention to the second term on the right side of the equation (17), the constant k is given by

[0067]

[Equation 18]

In other words, the second term on the right side can be set to the value 0, and

[0069]

[Formula 19]

It is possible to obtain a reproduction signal RF (MO) represented by

Here, it is understood that the reproduction signal RF expressed by the equation (19) can reduce the mixing of the track wobble signal as compared with the reproduction signal RF expressed by the equation (14). Note that the term of cos [2πp] remains in the equation (19), but in reality, this value has a small change, and even in the magneto-optical disk device that processes the reflected light once by converting it into parallel rays, Due to the presence of this component, this c
The term of os [2πp] is almost negligible.

Therefore, in this embodiment, the magneto-optical disk device 20 uses the signal processing circuit 21 in the equation (17).
The addition / subtraction processing of the equation is executed, thereby reducing the mixing of the track wobble signal and detecting the reproduction signal RF.

Specifically, as shown in FIG. 5, in the signal processing circuit 21, the output currents of the respective light receiving surfaces Ia to Jb are converted into current and voltage through a current / voltage conversion circuit (not shown), and the result is obtained. The respective output voltages Ia to Jb are input to the operational amplifier circuits 23 and 24.

Here, the operational amplifier circuit 23 includes a feedback resistor 2
5, the output voltage Jb obtained from the light receiving surface Jb is input to the inverting input terminal via the input resistor 26, and the output voltage Ia obtained from the light receiving surface Ia is
It is input to the non-inverting input terminal via the input resistor 27 and the ground resistor 28. As a result, the operational amplifier circuit 23 executes the arithmetic process of the first term on the right side of the equation 16 and outputs the output signal represented by the relational expression (Ia-Jb).

On the other hand, the operational amplifier circuit 24 is formed of a differential amplifier circuit having a feedback resistor 29, and the output voltage Ib obtained from the light receiving surface Ib is input to the inverting input terminal via the input resistor 30. output voltage Ja obtained from the light receiving surface Ja
Is input to the non-inverting input terminal via the input resistor 31 and the grounding resistor 32. As a result, the operational amplifier circuit 24 outputs the output signal represented by the relational expression (Ib-Ja) in the second term on the right side of Expression 16.

The operational amplifier circuit 34 forms an inverting amplifier circuit together with the feedback resistor 35 formed of a semi-fixed resistor and the input resistor 36, and outputs the output signal of the operational amplifier circuit 24 with a gain determined by the feedback resistor 35 and the input resistor 36. The signal processing circuit 21 can adjust the resistance value of the feedback resistor 35 to adjust the constant k in the second term on the right-hand side of the equation (16).

The operational amplifier circuit 37 includes input resistors 38 and 3
9 and a feedback resistor 40, an inverting amplifier circuit having an addition circuit configuration is formed, whereby the output signals of the operational amplifier circuits 23 and 34 are added and output. Reproduction signal R represented by the relational expression
Output F. As a result, in the signal processing circuit 21, while adjusting the resistance value of the feedback resistor 35 while monitoring the reproduction signal RF with an oscilloscope or the like,
The signal level of the track wobble signal mixed in the reproduction signal can be suppressed by adjusting the gain of the operational amplifier circuit 34 to the constant k represented by the equation (8).

Incidentally, according to the experiment by the present inventors, as shown in FIG. 6, as compared with the reproduction signal RF (FIG. 6A) of the magneto-optical disk device 1 described with reference to FIG. In the reproduction signal RF (FIG. 6B) by the magneto-optical disk device 20 of the example, the signal level of the track wobble signal could be sufficiently suppressed.

In the above embodiment, the prism 7
Although the case where the reflected light is separated into the S-polarized light component and the P-polarized light component by using is described, the present invention is not limited to this, and the polarization beam splitter 52 formed by laminating the right-angle prisms 50 and 51 as shown in FIG. It can be widely applied to the case where the reflected light is separated into the S-polarized component and the P-polarized component by using. In this case, in the light receiving element J,
The magneto-optical disk device 20 described above with reference to FIG.
On the other hand, the relationship of the light receiving surface of the light receiving element J with respect to the light receiving element I is such that the light receiving surfaces Ja and Jb are interchanged.

Further, in the above-mentioned embodiment, the case where the track wobble signal mixed in the reproduced signal is suppressed when the beam splitter is arranged in the convergent light beam has been described, but the present invention is not limited to this. For example, when a polarization beam splitter is arranged in the converged light beam, and when the polarization of the light beam emitted from the laser diode also has a rotation, the same phenomenon as described above occurs, so that a track wobble is generated in the reproduced signal. By mixing signals, the present invention can be applied even in such a case to suppress the track wobble signal mixed in the reproduction signal.

[0081]

As described above, according to the present invention,
With a simple configuration in which the output signal of the light receiving element is simply added / subtracted, it is possible to reduce the mixing of the track wobble signal into the reproduced signal and obtain a reproduced signal with a low noise level.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a magneto-optical disk device according to the present invention.

FIG. 2 is a schematic diagram for explaining a light beam of the magneto-optical disk device of FIG.

FIG. 3 is a schematic diagram for explaining a principle of detecting a reproduction signal.

FIG. 4 is a schematic diagram illustrating a relationship between a light receiving element and reflected light.

FIG. 5 is a block diagram showing a signal processing circuit.

FIG. 6 is a signal waveform diagram showing a reproduced signal.

FIG. 7 is a perspective view showing a magneto-optical disk device according to another embodiment.

FIG. 8 is a schematic view showing a conventional magneto-optical disk device.

9 is a front view showing a light receiving element of the magneto-optical disk device of FIG.

[Explanation of symbols]

1,20 Magneto-optical disk device 2 Laser diode 3 beam splitter 4 Objective lens 5 magneto-optical disk 6 1/2 wave plate 7 prism 10, I, J light receiving element

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-5-258318 (JP, A) JP-A-4-263150 (JP, A) JP-A-5-266530 (JP, A) JP-A-6- 338090 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 11/10-11/105

Claims (2)

(57) [Claims] 1. A magneto-optical disk device for irradiating a magneto-optical disk with a light beam and receiving the reflected light to reproduce recorded information magnetically recorded on the magneto-optical disk. An irradiation optical system that irradiates a magnetic disk, a separation optical system that receives the reflected light and separates the reflected light into a first polarization component and a second polarization component in the state of a convergent light beam , It is provided with first and second light receiving elements for respectively receiving the reflected light separated into the first polarization component and the second polarization component, and a signal processing circuit for processing the output signal of the light receiving element. The light receiving surface of the first light receiving element is divided into first and second light receiving surfaces in the radial direction of the magneto-optical disk, and the light receiving surface of the second light receiving element is the same as that of the first light receiving element. Corresponding to the first and second light receiving surface Is divided into third and fourth light receiving surfaces, and receives reflected light of a second polarized component corresponding to reflected light of the first polarized component received by the first and second light receiving surfaces, and The signal processing circuit subtracts the output signals of the first and fourth light receiving surfaces to generate a first subtracted signal, and subtracts the output signals of the second and third light receiving surfaces to perform a second processing. Subtraction signal is generated, the first and second subtraction signals are added at a predetermined addition ratio to output a reproduction signal, and the addition ratio suppresses the track wobble signal mixed in the reproduction signal. A magneto-optical disk device characterized by being selected as follows. 2. A method of reproducing a magneto-optical disk, which comprises irradiating a magneto-optical disk with a light beam and receiving the reflected light to detect a reproduction signal of the magneto-optical disk, wherein the reflected light is received and the reflected light is received. Is separated into a first polarization component and a second polarization component in the state of a convergent light flux, and the reflected light separated into the first polarization component and the second polarization component is respectively separated into a first and a second polarization component. Light is received by the second light receiving element, the output signal of the light receiving element is processed by the signal processing circuit to output the reproduction signal, and the light receiving surface of the first light receiving element is the first in the radial direction of the magneto-optical disk. The light receiving surface of the second light receiving element corresponds to the first and second light receiving surfaces of the first light receiving element and is divided into third and fourth light receiving surfaces. The first light receiving surface is divided into the first and second light receiving surfaces. The reflected light of the second polarized light component corresponding to the reflected light of the polarized light component is received, and the signal processing circuit subtracts the output signals of the first and fourth light receiving surfaces to perform the first subtracted signal. Is generated, the output signals of the second and third light receiving surfaces are subjected to subtraction processing to generate a second subtraction signal, and the first and second subtraction signals are added at a predetermined addition ratio to obtain a reproduction signal. Is output and the addition ratio is selected so as to suppress the track wobble signal mixed in the reproduction signal.