JPH07105587A - Magneto-optical disk device - Google Patents

Abstract

PURPOSE:To reproduce a signal having no noise by eliminating effectively a signal incorporated in a read out signal and indicating a tracking state in a magneto-optical device. CONSTITUTION:The reflected beam of a magneto-optical disk 17 is collimated with an objective lens 15 and transmitted through a beam splitter 13 and made incident on a beam splitter 19. One part of the light beam is reflected at the reflection-transmission plane 19a of the beam splitter 19 to be guided to a tracking signal detecting optical system and a focusing signal detecting optical system. A beam transmitted the beam splitter 19 is rotated with a halfwave plate 21 in a polarization direction. A P-polarized light component is transmitted and an S-polarized light component is reflected by a beam splitter 23 and they are converted to electric signals respectively at MO sensors 25, 27 to be taken out as signals S25, S27. The difference of (S25-S27) is used as an MO signal (a read out signal). A light beam reflected at the beam splitter 19 is divided with a beam splitter 35 to be guided to a quadripartite sensor 37. The obtained 45 deg. umbalance signal Q is subtracted from the MO signal by being multiplied by an adequate coefficient (k). By such a constitution, the MO signal having no crosstalk is obtained.

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.

[0002]

2. Description of the Related Art In a magneto-optical (MO) disk device, data recorded on a magneto-optical disk is read as follows using a laser beam. That is, the reading light (laser beam) is irradiated toward the recording track of the magneto-optical disk, the reading light (return light) reflected by the recording track is received by the photosensor, and the polarized light is rotated according to the magnetism of the recording track surface. By detecting the change in state, the binary signal recorded on the magneto-optical disk is read. In the reading optical system in such a conventional magneto-optical disk device, a signal indicating a tracking state is mixed with the MO signal obtained from the return light reflected by the magneto-optical disk, that is, crosstalk occurs. Therefore, there has been a demand for a means for reliably reducing this crosstalk with a simple structure.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to effectively remove a signal indicative of a tracking state which is mixed in a read signal in a magneto-optical disk device to enable reproduction of a noise-free signal.

[Outline of the Invention]

The present invention has been made based on a new analysis. The reflected light reflected by the recording track of the magneto-optical disk is split into at least two by a beam splitter, and each branched light is received by a sensor. Is a magneto-optical disk device that detects a recording signal based on the detection signals of at least two sensors, and a branching unit that further branches the reflected light; and a split sensor that receives the split light and splits the split light. It is characterized in that it is provided with a detection means for detecting a recording signal from a signal obtained by multiplying a predetermined difference signal of a plurality of output signals of the sensor by a predetermined coefficient, and a detection signal of each sensor. According to a third aspect of the present invention, the reflected light reflected by the recording track of the magneto-optical disc is split into at least two by a beam splitter, and each branched light is received by a sensor, and detected by at least two sensors. A magneto-optical disk device for detecting a recording signal on the basis of a signal, wherein each sensor comprises one divided sensor extending in a direction corresponding to the track direction of the magneto-optical disk, and a magneto-optical disk positioned on both sides thereof. Each of the above-mentioned divided sensors is composed of four divided sensors divided by orthogonal axes corresponding to the diametrical direction of the disk and the track direction orthogonal thereto, and a predetermined difference signal of the output signals of the divided sensors is multiplied by a predetermined coefficient. The present invention is characterized in that a detection means for detecting a recording signal from the detection signal of the sensor is provided. Furthermore, the present invention according to claim 4 splits the reflected light reflected by the recording track of the magneto-optical disk into at least two, and receives each branched light by a sensor,
A magneto-optical disk device for detecting a recording signal based on detection signals of at least two sensors, characterized in that a predetermined diagonal portion of a light receiving portion of the sensor is shielded by a predetermined amount.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to illustrated embodiments. FIG. 1 is an optical path diagram showing an embodiment of an optical system of a reproducing system of a magneto-optical disk device to which the present invention is applied. The parallel beam emitted from the light source 11 such as a semiconductor laser is
The beam is reflected by the beam splitter 13, and is focused by the objective lens 15 at the center position (between the inner and outer guide grooves 17g) of the recording track 18 of the magneto-optical (MO) disk 17 and reflected there. The return light reflected by the magneto-optical disk 17 travels backward in the optical path, is focused in parallel by the objective lens 15, passes through the first beam splitter 13, and enters the second beam splitter 19. A part of the return light that has entered the second beam splitter 19 has its reflection / transmission surface 19a.
It is reflected by and is guided to a track signal detection optical system and a focus signal detection optical system (not shown).

On the other hand, the reflected beam transmitted through the second beam splitter 19 has its polarization direction rotated by the λ / 2 plate, the P polarized component is transmitted by the polarizing beam splitter 23, and the S polarized component is reflected. First and second MO sensor 2
It is incident on 5, 27. The incident reflected beams are converted into electric signals by the first and second MO sensors 25 and 27, respectively, and extracted as signals S25 and S27. And
The difference (S25-S27) between the electric signals S25 and S27 is used as the MO signal (readout signal).

Prior to the description of the present invention, the principles underlying the present invention and the terms used in the present specification will be briefly described. As shown in FIG. 8, consider a situation in which light is incident on a transparent glass plate having an antireflection coating on its surface at a predetermined angle. When the incident angle of the incident light increases, the reflectance of the S polarized component becomes higher than the reflectance of the P polarized component. Therefore, of the incident light, the P-polarized light component that is directly transmitted through the antireflection coating and the glass plate is larger than the S-polarized light component. However, the light that is multiple-reflected at the interface between the antireflection coating, the glass plate, and the air and passes through the glass plate has more S-polarized light component due to the difference in reflectance. This is
The S-polarized component has more detour components, that is, S
This means that the polarization component has a longer optical path length and the phase is delayed. This phenomenon indicates that birefringence is generated between the P-polarized component and the S-polarized component. In the present specification, this phenomenon is hereinafter referred to as "structural birefringence".

Considering the state where the image height is 0 in the optical system,
Light passing through the optical axis is vertically incident, and no birefringence occurs.
However, since the light passing through the periphery of the optical system has an incident angle,
Birefringence occurs with the axis of birefringence in the direction of the incident surface or in the direction orthogonal thereto. Therefore, it is understood that the optical system has a radial or concentric birefringence distribution, and this structural birefringence is unavoidable.

Further, when the antireflection coating is not applied, since multiple reflection does not occur, an optical path difference and a phase difference do not occur between the transmitted P polarized component and S polarized component, but the transmittance between the P polarized component and the S polarized component. Is different. In the present specification, this phenomenon is hereinafter referred to as "structural dichroism". This structural dichroism is also structural birefringence in a broad sense.

"Analysis of the Present Invention" Next, the analysis of the present invention will be described with reference to the model shown in FIG. This model shows the peripheral structure of the objective lens 15 and the magneto-optical disk 17 of the optical system shown in FIG. 1, in which the laser beam is focused on the magneto-optical disk 17 by the objective lens 15 and reflected to the objective. Return to lens 15.
In FIG. 12, the points P _{1 to} P ₄ have the following relationship with a plane orthogonal to the optical axis with the optical axis as the origin. P _1: 45 ° when viewed from the origin O, + 1 as viewed from the center of the primary light 135 ° P _2: -45 ° as viewed from the origin O, and viewed from the center of the + 1-order light -135 ° P _3: the origin O Seen 135 °, seen from the center of + 1st order light 45 ° P ₄ : Seen from the origin O −135 °, seen from the center of + 1st order light −45 °

Then, the following conditions are set in the illustrated model. (i) The pupil 15p of the objective lens 15 and the magneto-optical disk 17
Fourier analysis is established with the surface of the. (ii) The magneto-optical disk 17 is regarded as a one-dimensional phase type diffraction grating. Further, the shape is symmetric, that is, the structure is not blazed in one direction. This means that the + n-order light and the −n-order light have the same diffraction efficiency. When light is incident on the center of the recording track 18 of the magneto-optical disk 17, the phase difference between the + n-order light and the −n-order light becomes equal. (iii) Actually, the diffracted light of ± 2nd order or more hardly returns to the pupil 15p. Therefore, ± 1st order light and 0
Only the next light should be handled. (iv) Consider the returning light at the points P _{1 to} P ₄ . (v) The incident light intensity distribution is constant. The return light passing through the points P _{1 to} P ₄ is detected by the sensors 25, 27.
Is incident on each of the four equally divided regions 1 to 4.

The diffracted light is analyzed as follows. First, the parameters are defined as follows. a: Amplitude of 0th-order light b: Amplitude of ± 1st-order light P: Phase of ± 1st-order light with respect to 0th-order light when light is incident on the center of the groove (recording track) of the magneto-optical disk x: Magneto-optical disk Top light incident position (center is origin (0)
Is normalized to ± π on the "ridge"). Further, the wavefront aberration at point P ₁ is W ₁ , the birefringence Jones matrix is M ₁ , the wavefront aberration at point P ₂ is W ₂ , and the birefringence Jones is Matrix is M ₂ , point P ₃
Is W ₃ , the birefringence Jones matrix is M ₃ , the wavefront aberration at the point P ₄ is W ₄ , the birefringence Jones matrix is M ₄ , and the Jones vector of the incident light is the I vector (hereinafter, the Jones vector “I , "I _n " represents a vector). far.

Letting the light returning to the point P ₁ be an O ₁ vector (hereinafter, returning lights “O” and “O _n ” represent a vector), the returning light O ₁ is the point P at the time of incidence (i). ₄ [W ₄ , M
0] -order light passing through ₄ ] undergoes birefringence of M ₁ , and (ii) + _1st- order light passing through point P ₂ [W ₂ , M ₂ ] at the time of incidence receives birefringence of M ₁ . Therefore, the return light O ₁ is expressed by the following formula 1.

## EQU1 ## O ₁ = M ₁ ae ^iW4 M ₄ I + M ₁ be ^{i (W2 + P + x)} M ₂ I = {ae ^iW4 M ₁ M ₄ + be ^{i (W2 + P + x)} M ₁ M ₂ } I

When the returning light returning to the point P ₂ is O ₂ , the returning light O ₂ is the point P ₃ [W ₃ , M ₃ ] at the time of incidence (i).
The 0th-order light passing through undergoes birefringence of M ₂ and (ii) is incident at point P
_The + _1st order light passing through ₁ [W ₁ , M ₁ ] undergoes birefringence of M ₂ . Therefore, the return light O ₂ is given by the following equation.

[ ^Equation 2] O ₂ = {ae ^iW3 M ₂ M ₃ + be ^{i (W1 + P + x)} M ₂ M ₁ } I

Assuming that the light returning to the point P ₃ is O ₃ , the returning light O ₃ has a birefringence of M _{3 when} the 0th order light passing through the point P ₂ [W ₂ , M ₂ ] at the time of incidence (i). When receiving, (ii) incident point P ₄ [W
_The −first-order light passing through ₄ , M ₄ ] undergoes birefringence of M ₃ . Therefore, the return light O ₃ is expressed by the following equation.

[ ^Equation 3] O ₃ = {ae ^iW2 M ₃ M ₂ + be ^{i (W4 + Px)} M ₃ M ₄ } I

When the return light returning to the point P ₄ is O ₄ , the return light O ₄ is the point P ₁ [W ₁ , M ₁ ] at the time of incidence (i).
The 0th-order light passing through undergoes birefringence of M ₄ and (ii) is incident at point P
_The −1st order light passing through ₃ [W ₃ , M ₃ ] undergoes birefringence of M ₄ . Therefore, the return light O ₄ is given by the following equation.

[ ^Equation 4] O ₄ = {ae ^iW1 M ₄ M ₁ + be ^{i (W3 + Px)} M ₄ M ₃ } I

Due to the structural birefringence, the pupil 1 of the objective lens 15
It is assumed that a birefringence distribution occurs on the 5p plane. in this case,
The birefringence axes are arranged radially or concentrically, and the pupil 1
The Jones matrix M at the polar coordinate position (r, θ) on 5p is as follows.

[Equation 5]

If Δ (r) = δ in P ₁ (r, θ),
It can be expressed as in Equation 6.

[Equation 6] P ₂ (r, −θ) can be expressed as in Equation 7.

[Equation 7] P ₃ (r, π−θ) can be expressed as in Equation 8.

[Equation 8] P ₄ (r, π + θ) can be expressed as in Equation 9.

[Equation 9]

From the above,

[Equation 10] α ² −β ² = c ⁴ e ₁ ² + s ⁴ e ₂ ² + 2c ² s ² e ₁ e ₂ −c ² s ² (e ₁ ² −
2e ₁ e ₂ ＋ e ₂ ² ) ＝ c ² e ₁ ² (c ² −s ² ) ＋ s ² e ₂ ² (s ² −c ² ) ＋ 4c ² s ² e ₁ e ₂ ＝ (c ² −s ² ) ( c ² e ₁ ² −s ² e ₂ ² ) + 4c ² s ² γ ² −β ² = s ⁴ e ₁ ² + c ⁴ e ₂ ² + 2c ² s ² e ₁ e ₂ −c ² s ² (e ₁ ² −
2e ₁ e ₂ ＋ e ₂ ² ) ＝ s ² e ₁ ² (s ² −c ² ) ＋ c ² e ₂ ² (c ² −s ² ) ＋ 4c ² s ² e ₁ e ₂ ＝ (s ² −c ² ) ( s ² e ₁ ² −c ² e ₂ ² ) + 4c ² s ² β (α−γ) = cs (e ₁ −e ₂ ) (c ² e ₁ + s ² e ₂ −s ² e ₁ −c ² e ₂ ) ＝ cs (e ₁ −e ₂ ) {e ₁ (c ² −s ² ) ＋ e ₂ (s ² −c ² )} ＝ cs (c ² −s ² ) (e ₁ −e ₂ ) ²

[0020]

[Equation 11]

[Equation 12]

[Equation 13]

The relationship between the Jones matrices M _{1 to} M ₄ is as follows.

[Equation 14] M ₃ M ₂ = M ₂ M ₂

[Equation 15] M ₃ M ₄ = M ₂ M ₁

[Equation 16] M ₄ M ₁ = M ₁ M ₁

[Expression 17] M ₄ M ₃ = M ₁ M ₂

[0022]

[Equation 18]

[Formula 19]

[Equation 20]

[Equation 21]

Here, if θ = 45 ° as shown in FIG. 9,

[Equation 22]

[Equation 23]

[Equation 24]

[Equation 25]

Equations 22 to 25 and equations 14 to 17 above
Due to the relation of the equations, the equations 1 to 4 are as follows.

[Equation 26]

[Equation 27]

[Equation 28]

[Equation 29]

The above can be summarized as shown in Formula 30.

[Equation 30]

Here, the relationship between n, m and l is as follows. nm l 1 4 2 2 3 1 1 3 2 4 4 1 3

In order to obtain the MO signal, the polarization plane is rotated by 45 ° by the optical rotator or the λ / 2 plate.
_n45 is _expressed by the following Expression 31.

[Equation 31]

Next, the relationship between the return beams (return light) received by the sensors 25 and 27 and the signals output from the sensors 25 and 27 will be described. The intensities in the x and y directions of the expression 31 are as shown in the following expressions 32 and 33.

[Equation 32]

[Expression 33]

Therefore, the differential signal can be expressed by the equation (34).

[Equation 34]

Here, the plus / minus sign before the coefficient 2ab is up when n = 1, 4, and down when n = 2, 3. Therefore, the signals input to the sensors 25 and 27 are as in Expression 35.

[Equation 35]

"Position Sensor Signal" The signal I _n in the sensor obtained by dividing the MO sensor into four equal parts on the orthogonal axis can be analyzed as follows. First, the above equation (30) can be transformed into equation (36).

[Equation 36]

The light intensity (sensor signal) I _n is given by
It can be expressed like an expression.

[Equation 37]

Therefore, the sensor signal I _{1 of} each divided sensor
~ I ₄ is given by the following equation.

(38) I ₁ = a ² + b ² + 2ab cos δcos (W ₄ -W ₂ -Px)

I ₂ = a ² + b ² + 2ab cos δcos (W ₃ -W ₁ -Px)

(40) I ₃ = a ² + b ² + 2ab cos δcos (W ₂ -W ₄ -P + x)

(41) I ₄ = a ² + b ² + 2ab cosδcos (W ₁ -W ₃ -P + x)

"Tracking signal" The tracking signal T obtained by the push-pull method is obtained by the equation (42).

T = I ₁ + I ₂ −I ₃ −I ₄ Here, since the sensor signals I _{1 to} I ₄ are expressed by the equations 38 to 41, if these are substituted into the equation 42, the tracking signal T Is expressed by the following equation.

(43) T = a ² + b ² + 2ab cos δcos (W ₄ -W ₂ -Px) + a ² + b ²
+ 2abcosδcos (W ₃ -W ₁ -Px) -a ² -b ² -2abcosδcos (W ₂ -W ₄ -P +
x) -a ² -b ² -2ab cosδcos (W ₁ -W ₃ -P + x) = 2abcosδ (cos (W ₄ -W ₂ ) cos (P + x) + sin (W ₄ -W ₂ ) sin (P + x) + c
os (W ₃ -W ₁ ) cos (P + x) + sin (W ₃ -W ₁ ) sin (P + x) -cos (W ₂ -W ₄ ) cos
(Px) -sin (W ₂ -W ₄ ) sin (Px) -cos (W ₁ -W ₄ ) cos (Px) -sin (W _{1
-W 3) sin (Px)}} = 2abcosδ [cos (W 4 -W 2) {cos (P + x) -cos (Px)} + sin (W 4 -
W ₂ ) {sin (P + x) + sin (Px)} + cos (W ₃ -W ₁ ) {cos (P + x) -cos (P-
x)} + sin (W ₃ -W ₁ ) {sin (P + x) + sin (Px)}] = 2abcosδ [-2sinPsinx {cos (W ₄ -W ₂ ) + cos (W ₃ -W ₁ )} + 2sinP
cosx {sin (W ₄ -W ₂ ) + sin (W ₃ -W ₁ )}] = -4abcosδsinP [sin {cos (W ₄ -W ₂ ) + cos (W ₃ -W ₁ )}-cosx {s
in (W ₄ -W ₂ ) + sin (W ₃ -W ₁ )}]

"Focus signal F" (signal input to the focus sensor) When the focus signal F is obtained by the astigmatism method, the focus signal F can be expressed by the following equation.

F = I ₁ + I ₂ −I ₃ + I ₄

By substituting the equations 38 to 41 into the equation 44, the focus signal F can be expressed by the following equation.

F = a ² -b ² + 2ab cos δcos (W ₄ -W ₂ -Px) -a ² -b
² -2abcosδcos (W ₃ -W ₁ -Px) -a ² -b ² -2abcosδcos (W ₂ -W ₄ -P
+ x) + a ² + b ² + 2ab cosδcos (W ₁ -W ₃ -P + x) = 2abcosδ (cos (W ₄ -W ₂ ) cos (P + x) + sin (W ₄ -W ₂ ) sin ( P + x) -c
os (W ₃ -W ₁ ) cos (P + x) -sin (W ₃ -W ₁ ) sin (P + x) -cos (W ₂ -W ₄ ) cos
(Px) -sin (W ₂ -W ₄ ) sin (Px) + cos (W ₁ -W ₃ ) cos (Px) + sin (W _{1
-W 3) sin (Px)}} = 2abcosδ [cos (W 4 -W 2) {cos (P + x) -cos (Px)} + sin (W 4 -
W ₂ ) {sin (P + x) + sin (Px)}-cos (W ₃ -W ₁ ) {cos (P + x) -cos (P-
x)}-sin (W ₃ -W ₁ ) {sin (P + x) + sin (Px)}] = 2abcosδ [-2sinPsinx {cos (W ₄ -W ₂ ) -cos (W ₃ -W ₁ )} + 2sinP
cosx {sin (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}] = -4abcosδsinP [sin {cos (W ₄ -W ₂ ) -cos (W ₃ -W ₁ )}-cosx {s
in (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}]

"Upper / lower unbalanced signal U" Although not actually used, the upper / lower unbalanced signal U can be defined by the following equation.

U = I ₁ −I ₂ + I ₃ −I ₄ Substituting the formulas 38 to 41 into I _{1 to} I ₄ of this formula,
The vertical unbalance signal U can be expressed by the following equation.

U = a ² + b ² + 2ab cos δcos (W ₄ -W ₂ -Px) -a ² -b
² -2abcosδcos (W ₃ -W ₁ -Px) + a ² + b ² + 2abcosδcos (W ₂ -W ₄ -P
+ x) -a ² -b ² -2ab cosδcos (W ₁ -W ₃ -P + x) = 2abcosδ (cos (W ₄ -W ₂ ) cos (P + x) + sin (W ₄ -W ₂ ) sin ( P + x) -c
os (W ₃ -W ₁ ) cos (P + x) -sin (W ₃ -W ₁ ) sin (P + x) + cos (W ₂ -W ₄ ) cos
(Px) + sin (W ₂ -W ₄ ) sin (Px) -cos (W ₁ -W ₃ ) cos (Px) -sin (W _{1
-W 3) sin (Px)}} = 2abcosδ [cos (W 4 -W 2) {cos (P + x) + cos (Px)} + sin (W 4 -
W ₂ ) {sin (P + x) -sin (Px)}-cos (W ₃ -W ₁ ) {cos (P + x) + cos (P-
x)}-sin (W ₃ -W ₁ ) {sin (P + x) -sin (Px)}] = 2abcosδ [2cosPcosx {cos (W ₄ -W ₂ ) -cos (W ₃ -W ₁ )}- 2cosPs
inx {sin (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}] = 4abcosδcosP [cosx {cos (W ₄ -W ₂ ) -cos (W ₃ -W ₁ )} + sinx {si
n (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}]

"Classification by Aberration" Relatively low-order aberrations are
It can be classified into the following four types depending on the symmetry. When the ξ and η axes are set as shown in FIG. 9, the aberrations have the following relationships. (i) It is an even function for both ξ and η axes, and spherical aberration, astigmatism 1 (0 ° direction astigmatism), defocus, etc. (ii) Even function for ξ axis, for η axis Is an odd function,
Frame 2 (Y-axis direction frame), Y-tilt, etc. (iii) Odd-axis odd function and η-axis even function, frame 1 (X-axis direction frame), X-tilt etc. (iv) It is an odd function for both ξ and η axes,
5 ° direction ass) etc.

The wavefront aberration W has the following relationship due to "symmetry of even function with respect to both ξ and η axes" symmetry.

[Expression 48] W ₁ = W ₂ = W ₃ = W ₄ = W Therefore, the expression 43 regarding the tracking signal T, the expression 45 regarding the focus signal F, the expression 47 regarding the upper and lower unbalance signals U, and the MO signal M Number 3
According to the formula 5, the tracking signal T _ee and the focus signal F
_ee , upper and lower unbalance signals U _ee , and MO signal M
_ee is given by the following equation.

[Equation 49] T _ee = -8ab cos δ sinP sinx

[ _Equation 50] F _ee = 0

[ _Equation 51] U _ee = 0

M _ee = 0 As described above, when there are even function aberrations on both ξ and η axes, only the tracking signal T is generated, and the focus (noise) signal F and the vertical unbalance signal U are generated. , MO (noise) signal M is not generated.

"Aberration of even function with respect to ξ axis and odd function with respect to η axis" Due to symmetry, the wavefront aberration W has the following relationship.

[Equation 53] W ₁ = -W ₂ = W ₃ = -W ₄ = W Here, the equation 43 regarding the tracking signal T, the equation 45 regarding the focus signal F, and the vertical unbalance signal U
According to the equation 47 regarding the MO signal M and the equation 35 regarding the MO signal M, the tracking signal T _e0 , the focus signal F _e0 ,
The upper and lower unbalanced signals U _e0 and the MO signal M _e0 are given by the following equations.

[Equation 54] T _e0 = -8ab cosδ sinP sinx

F _e0 = 0

( _Equation 56) U _e0 = 0

As described above, M _e0 = 0, an even function with respect to the ξ axis,
When there is an odd function aberration with respect to the η axis, only the tracking signal T is generated as in the case of the even function.

The wavefront aberration W has the following relationship due to the symmetry "abnormal function with respect to ξ axis and even function with respect to η axis".

[Equation 58] W ₁ = W ₂ = -W ₃ = -W ₄ = W where, the equation 43 relating to the tracking signal T, the equation 45 relating to the focus signal F, and the vertical imbalance signal U
Equation 47 regarding the MO signal M and Equation 35 regarding the MO signal M, the tracking signal T _0e , the focus signal F _0e ,
The vertical unbalanced signal U _0e and the MO signal M _0e are expressed by the following equations.

[Equation 59] T _0e = -8ab cosδ sinP sin (x + 2W)

(60) F _0e = 0

[ _Equation 61] U _0e = 0

[ _Equation 62] M _0e = 0 As described above, the tracking signal T _0e
A phase shift of 2 W occurs. However, the focus (noise) signal F _0e , the vertical imbalance (noise) signal U _0e , and the MO (noise) signal M _0e are not generated.

"In the case of an odd function with respect to both the ξ-axis and the η-axis" Due to the symmetry, the relation of the wavefront aberration W is as follows.

[Expression 63] W ₁ = −W ₂ = −W ₃ = W ₄ = W Expression 43 regarding the tracking signal T, Expression 45 regarding the focus signal F, Expression 47 regarding the upper and lower unbalance signals U, and the MO signal M By the formula 35,
The tracking signal T ₀₀ , the focus signal F ₀₀ , the vertical imbalance signal U ₀₀ , and the MO signal M ₀₀ are given by the following equations.

[Equation 64] T ₀₀ = -8ab cosδ sinP cos2W sinx

[Equation 65] F ₀₀ = 8ab cosδ sinP sin2W cosx

[Equation 66] U ₀₀ = 8ab cosδ cosP sin2W sinx

(Equation 67) M ₀₀ = 8ab sinδ cosP sin2W cosx

From the above analysis, it can be seen that FT (focus / tracking) crosstalk occurs, and crosstalk between the upper and lower unbalance signals U and MO signals M and the tracking signal T also occurs. For example, when there is no structural birefringence in the optical system in which there is astigmatism in the 45 ° direction (astigmatism AS2), the MO signal M of the unmagnetized magneto-optical disk becomes zero. However, it can be seen that an offset signal is added to the MO signal M when structural birefringence occurs.

"Structural dichroism" The above is the analysis based on the structural birefringence, but the structural dichroism will be similarly analyzed below. The Jones matrix M of the dichroic element having the amplitude transmittances t ₁ and t ₂ can be expressed as follows.

[Equation 68]

Similar equations are obtained in the same manner as the equations 5 to 31.

[Equation 69]

[Equation 70]

[Equation 71] M ₂ M ₁ = (M ₁ M ₂ ) ^t

[Equation 72]

[Equation 73]

[Equation 74]

[Equation 75]

When θ = 45 °

[Equation 76]

[Equation 77]

[Equation 78]

[Equation 79]

Therefore,

[Equation 80]

[Equation 81]

[Equation 82]

[Equation 83]

[Equation 84]

[Equation 85]

The AC part of the equation (85) is t ₁ t ₂ (t ₁ ² + t ₂ ² )
When is replaced with 2cosδ, it is in agreement with the equation 37. Therefore,

(Equation 86) T = -2abt ₁ t ₂ (t ₁ ² + t ₂ ² ) sinP [sinx {cos (W ₄ -W
₂ ) + cos (W ₃ -W ₁ )}-cosx {sin (W ₄ -W ₂ ) + sin (W ₃ -W ₁ )}]

F = -2abt ₁ t ₂ (t ₁ ² + t ₂ ² ) sinP [sinx {cos (W ₄ -W
₂ ) -cos (W ₃ -W ₁ )}-cosx {sin (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}]

[Equation 88] U = 2abt ₁ t ₂ (t ₁ ² + t ₂ ² ) sinP [cosx {cos (W ₄ -W
₂ ) -cos (W ₃ -W ₁ )} + sinx {sin (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}]

On the other hand, in the MO signal system, the equation (84) is rotated by 45 °,

[Equation 89]

[Equation 90]

[Formula 91]

[Equation 92]

[0050]

I _1x = (1/2) {t ₂ ² acosW ₄ + t ₁ t ₂ bcos (W ₂ + P + x)} ² + (1/2) {t ₂ ²
asinW ₄ + t ₁ t ₂ bsin (W ₂ + P + x)} = (1/2) (t ₂ ⁴ a ² + t ₂ ² t ₁ ² b ² ) + t ₁ ³ t ₁ ab {cosW ₄ cos (W ₂ + P + x) + s
inW ₄ sin (W ₂ + P + x)} = (1/2) (t ₂ ⁴ a ² + t ₂ ² P ₁ ² b ² ) + t ₁ t ₂ ³ abcos (W ₄ -W ₂ -Px)

[Equation 94] I _1Y = (1/2) (t ₁ ⁴ a ² + t ₂ ² t ₁ ² b ² ) + t ₁ ³ t ₂ abcos (W ₄ -W ₂ -Px)

I _2x = (1/2) (t ₁ ⁴ a ² + t ₂ ² P ₁ ² b ² ) + t ₁ ³ t ₂ abcos (W ₃ -W ₁ -Px)

96: I _2y = (1/2) (t ₂ ⁴ a ² + t ₂ ² t ₁ ² b ² ) + t ₁ t ₂ ³ abcos (W ₃ -W ₁ -Px)

(97) I _3x = (1/2) (t ₁ ⁴ a ² + t ₂ ² t ₁ ² b ² ) + t ₁ ³ t ₂ ab cos (W ₂ -W ₄ -P + x)

(98) I _3y = (1/2) (t ₂ ⁴ a ² + t ₂ ² t ₁ ² b ² ) + t ₁ t ₂ ³ abcos (W ₂ -W ₄ -P + x)

I _4x = (1/2) (t ₂ ⁴ a ² + t ₂ ² t ₁ ² b ² ) + t ₁ t ₂ ³ abcos (W ₁ -W ₃ -P + x)

I _4y = (1/2) (t ₁ ⁴ a ² + t ₂ ² t ₁ ² b ² ) + t ₁ ³ t ₂ abcos (W ₁ -W ₃ -P + x)

Therefore, the MO signal can be defined by the equation 101.

M = I _1x −I _1y + I _2x −I _2y + I _3x −I _3y + I _4x −I _4y = −2abt ₁ t ₂ (t ₂ ² -t ₁ ² ) sinP [sinx {cos ( W ₄ -W ₂ ) -cos (W _3-
W ₁ )}-cosx {sin (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}]

In Equation 35, 2sinδcosP is t ₁ t ₂ (t ₂ ² -t
_If replaced with ₁ ² ) sinP, it agrees with the equation 101. From the above analysis, it was found that structural dichroism has the same effect as structural birefringence.

The above results are summarized as follows. (1) In case of structural birefringence (i) Tracking signal T

Equation 102] T = -4abcosδsinP [sinx {cos ( W 4 -W 2) + cos
(W ₃ -W ₁ )}-cosx {sin (W ₄ -W ₂ ) + sin (W ₃ -W ₁ )}] (ii) Focusing (noise) signal F

[Equation 103] F = -4ab cos δ sinP [sinx {cos (W ₄ -W ₂ ) -cos
(W ₃ -W ₁ )}-cosx {sin (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}] (iii) Vertical unbalance signal U

[Equation 104] U = 4ab cos δcos P [cosx {cos (W ₄ -W ₂ ) -cos (W
₃ -W ₁ )} + sinx {sin (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}] (iv) MO (noise) signal MO

[Equation 105] M = -4ab sin δcos P [sinx {cos (W ₄ -W ₂ ) -cos
(W ₃ -W ₁ )}-cosx {sin (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}]

(2) Case of structural dichroism (i) Tracking signal T

Equation 106] _{T = -2abt 1 t 2 (t} 1 2 + t 2 2) sinP [sinx {cos (W 4 -
W ₂ ) + cos (W ₃ -W ₁ )}-cosx {sin (W ₄ -W ₂ ) + sin (W ₃ -W ₁ )}] (ii) Focusing (noise) signal F

F = −2abt ₁ t ₂ (t ₁ ² + t ₂ ² ) sinP [sinx {cos (W ₄
-W ₂ ) -cos (W ₃ -W ₁ )} -cosx {sin (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}] (iii) Vertical unbalanced signal (U)

U = 2abt ₁ t ₂ (t ₁ ² + t ₂ ² ) sinP [cosx {cos (W ₄
-W ₂ ) -cos (W ₃ -W ₁ )} + sinx {sin (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}] (iv) MO (noise) signal (MO)

Equation 109] _{M = -2abt 1 t 2 (t} 2 2 -t 1 2) sinP [sinx {cos (W 4 -
W ₂ ) -cos (W ₃ -W ₁ )}-cosx {sin (W ₄ -W ₂ ) -sin (W ₃ -W ₁ )}]

On the basis of the above results, the classifications by aberration type are listed in Table 1.

[Table 1] a: 0th-order light amplitude diffraction factor b: ± 1st-order light amplitude diffraction factor P: Phase difference between 0th-order light and ± 1st-order light W: Wavefront aberration δ: Retardance of birefringence (rad) x: Irradiation position (rad ) T ₁ , t ₂ : amplitude transmissivity in the main direction and the sub direction

A specific configuration of the present invention based on the above analysis will be described based on the embodiment shown in FIGS. 1 to 7 with reference to Table 1. In the embodiment shown in FIG. 1, the return light incident on the MO sensors 25 and 27 is birefringent (δ, t ₁ , t ₂ ) by the objective lens 15 and includes wavefront aberration W.
Therefore, the return light is offset by OS = 8absinδcosPsin2Wcosx or OS = 4abt ₁ t ₂ (t ₂ ² -t ₁ ² ) sinPsin2Wcosx. Here, the coefficients a, b, and P are constants determined by the shape of the magneto-optical disk 17 and so cannot be changed. Therefore, this offset signal OS
To be 0 regardless of birefringence (δ, t ₁ , t ₂ ) and wavefront aberration (W), cosx = 0, that is, x = ± π /
It turns out that it should be set to 2.

Therefore, in the present invention, x = ± π / 2 (1/4 of the groove width) from the center of the width of the recording track 18 (the center of the guide groove 17g on the inner and outer circumferences, the center of the signal recording position) to the inner and outer circumferences. Record the signal at the offset position. Therefore, in normal recording, a signal is recorded at either the inner or outer position with respect to the center of one recording track 18. In the double track method of recording two signals per groove, signals are recorded both inside and outside. Further, when a signal is recorded at a position shifted to the inner and outer circumferences by 1/4 of the groove width by the double track method, a laser beam is irradiated at a position of x = 0 and π, and a different offset depending on each irradiation position. The signal OS is subtracted from the MO signal M. That, MO signal M 'after the correction is, M' a _{= S 25 -S 27 -OS = M} -OS.

"45 ° unbalanced signal" split sensor,
For example, let us say that a signal is obtained in exactly the same manner as the case where the above-mentioned focusing signal F is obtained using a divided sensor which is divided into four by an orthogonal axis corresponding to the diameter direction and the track direction orthogonal thereto. The signal is the same as the focusing signal, but since it is not used as a signal for focusing, all the signals will be referred to as unbalanced signals (45 ° unbalanced signal Q). The 45 ° unbalanced signal Q is expressed by the following formula: Q = 8abcosδsinPsin2Wcosx or Q = 4abt ₁ t ₂ (t ₁ ² + t ₂ ² ) sinPsin2Wcosx. Where the 45 ° unbalanced signal Q
Is in phase with the noise signal input to the split sensor.
Therefore, the MO signal M and the 45 ° unbalanced signal Q are combined as M ′ = M−kQ and an appropriate value for the coefficient k (for example, k =
Crosstalk can be canceled by setting tanP / tan δ).

FIG. 4 shows another embodiment of the optical system of the present invention having a split sensor. Members having the same functions as those of the embodiment shown in FIG. 1 are designated by the same reference numerals.
The return light reflected by the magneto-optical disk 17 and reflected by the second beam splitter 19 is transferred to the fourth beam splitter 3
5, the branched light that has passed through the fourth beam splitter 35 is transmitted, and is guided to the track signal / focus signal detection optical system. On the other hand, the branched light reflected by the reflection / transmission surface 35 a of the fourth beam splitter 35 is guided to the third sensor 37. The third sensor 37 has a light receiving area of 4
In the divided sensor, as shown in FIG. 5, the light receiving area is divided into four by a diametrical direction of the magneto-optical disk (horizontal direction in the drawing) and an orthogonal axis in a track direction (vertical direction in the drawing) orthogonal thereto. Individual divided sensors 37 _{1 to} 3
It is divided into 7 ₄ . Signals obtained from the divided sensor 37 _{1-37 4} (output signal) respectively S37 ₁ ~S37 ₄
And The outputs of the first sensor 31 and the second sensor 33 are S31 and S33, respectively.

In this embodiment, the 45 ° unbalanced signal Q can be obtained by the equation: Q = (S37 ₁ + S37 ₄ )-(S37 ₂ + S37 ₃ ).
By multiplying this 45 ° unbalanced Q signal by an appropriate coefficient k and subtracting it from the MO signal M, M without crosstalk can be obtained.
O signal can be obtained. If the corrected MO signal is M ', then M' = S31-S33-kQ. The coefficient k is, for example, tan δ / tan P in this embodiment.
Becomes

The MO signal M'can be obtained, for example, by the signal processing circuit shown in FIG. Output signals S31, S33 of the sensors 31, 33 for obtaining the normal MO signal M, respectively
The subtractor 51 calculates the difference S31-S33 (= M). The difference between the sensor outputs in the diagonal direction of the divided sensor 37 Q = (S37 ₁ +
S37 ₄ ) − (S37 ₂ + S37 ₃ ) is calculated by the adders 53 and 55 and the subtractor 57, and the difference Q is multiplied by k in the multiplier 59. Then, (S31-S33) and k {(S37 ₁ + S
By taking the difference of 37 ₄ ) − (S37 ₂ + S37 ₃ )}, an accurate MO signal M ′ can be obtained. This can be expressed by the equation: M '= (S31-S33) -k {(S37 ₁ + S37 ₄ )-(S
37 ₂ + S37 ₃ )} = S31-S33-kQ.

Here, the multiplier 59 which gives the coefficient k can be constituted by an analog circuit using an operational amplifier 591, for example. FIG. 7 shows an example thereof. In this embodiment, the coefficient k is changed by changing the resistance value of the variable resistor R2.
You can adjust the value of. The multiplier 59 can also be composed of a digital circuit. An example of this is shown in FIG. In this digital circuit, the coefficient k is written in the ROM 595 in advance, and the arithmetic (multiplication) circuit 593 operates to calculate the coefficient k.
Is read from ROM 595 and used.

The optimum coefficient k is uniquely determined if the magneto-optical disk device is determined. That is, since each coefficient k is different for each disk device, it is set for each disk device. The setting is as follows. First, the optical head is made to cross two or more recording tracks 18 on which no MO signal is recorded, and the amplitude of the sinusoidal MO signal generated at that time, that is, the crosstalk signal, is set to 0.
Determine the value of. This setting is performed by adjusting the variable resistance value in the analog circuit, and by changing the value of the coefficient k stored in the digital circuit. By adjusting the value of the coefficient k in this way, crosstalk can be reduced to zero.

FIG. 9 shows an MO sensor with five-division sensors 47,
49 is an example of using 49 to obtain the focus signal and the track signal from the MO sensor. This 5-division sensor 4
As shown in FIG. 10, reference numerals 7 and 49 denote one split sensor 47 ₃ and 49, which extend around the center line corresponding to the center line of the recording track of the magneto-optical disk 17, respectively.
₃ and four divided sensors 47 ₁ and 47 located on both sides thereof and vertically divided in the figure by an orthogonal line passing through the center.
_2, 47 _4, 47 _5, and 49 _1, 49 _2, 49 _4,
It is equipped with a 49 _5. These five-division sensors 47, 49
According to the tracking signal T, the focus signal F, and
The 5 ° unbalanced signal Q and the MO signal M can be obtained at the same time. The tracking signal T is obtained by the push-pull method, and the focus signal F is obtained by the spot size method. Divided sensors 47 ₁ to 47 _5, and 49 ₁ to 49 ₅
Output signals of S47 ₁ , S47 ₂ , S47 ₃ , S47 ₄ , S47 ₅ ,
And S49 ₁ , S49 ₂ , S49 ₃ , S49 ₄ , S49 ₅ .

In the illustrated embodiment, the tracking signal T, the focus signal F, the 45 ° unbalanced signal Q, and the MO signal M are obtained by the following equations. T = (S47 ₁ + S47 ₂ + S49 ₁ + S49 ₂ )-(S47 ₄ + S47 ₅ + S49 ₄ + S49 ₅ ) F = (S47 ₁ + S47 ₂ + S47 ₄ + S47 ₅ -S47 ₃ )-(S49 ₁ + S49 ₂ + S49 ₄ + S49
₅ -S49 ₃ ) Q = (S47 ₁ + S47 ₅ -S47 ₂ -S47 ₄ )-(S49 ₂ + S49 ₄ -S49 ₁ -S49 ₅ ) M = (S47 ₁ + S47 ₂ + S47 ₃ + S47 ₄ -S47 ₅ )-(S49 ₁ + S49 ₂ + S49 ₃ + S49
₄ + S49 ₅ ) M ′ = M−kQ M is the MO signal before correction and M ′ is the MO signal after correction. As described above, crosstalk can be removed by setting an appropriate value for the coefficient k.

The above is an example of the case where the divided sensor is used, but the present invention can similarly remove the crosstalk without using the divided sensor. In the embodiment shown in FIG.
Crosstalk can be removed by blocking the light receiving area of each sensor 25, 27 with a slit to limit the amount of received light. The first MO sensor 25 shields one diagonal corner portion, that is, the corner portion in the + 45 ° direction and the −135 ° direction by the light shielding plates 26a and 26b, and similarly, the second MO sensor 27 is Diagonal portions in the + 135 ° direction and the −45 ° direction are shielded by the light shielding plates 28a and 28b (see FIG. 3). The shielding amount is set similarly to the adjustment of the coefficient K, and is adjusted for each magneto-optical disk device.

As described above, the present invention is based on the analysis result that the phase of the unbalanced signal in the diagonal direction of the sensor has the same phase as the noise signal mixed in the detection signal. So, based on this analysis, M
The structure of the O sensor is not limited to the illustrated embodiment, and in other configurations, crosstalk can be canceled by multiplying the 45 ° unbalanced signal Q by a predetermined coefficient k and combining with the MO signal M.

[0068]

As described above, according to the present invention, the reflected light reflected by the recording track of the magneto-optical disk is branched into a plurality of beams, one of the branched beams is received by the split sensor, and the predetermined difference signal of the predetermined split sensor is given. Since the recording signal is detected from the signal multiplied by the coefficient and the detection signal of each sensor that receives the other branched light, it is possible to obtain the recording signal without crosstalk.

[Brief description of drawings]

FIG. 1 is an optical path diagram showing an embodiment of an optical system of a magneto-optical disk device to which the present invention is applied.

FIG. 2 is a diagram showing a relationship between a magneto-optical disk and a beam irradiation position in the example.

FIG. 3 is a diagram showing an example of a light blocking state of a sensor in the same embodiment.

FIG. 4 is an optical path diagram showing another embodiment of the present invention.

5 is a diagram showing a configuration of a sensor of the embodiment shown in FIG.

FIG. 6 is a block circuit diagram showing an embodiment of a signal processing circuit for obtaining an MO signal M ′.

FIG. 7 is a circuit diagram showing an embodiment of an analog coefficient k multiplication circuit in the signal processing circuit.

FIG. 8 is a circuit diagram showing an embodiment of a digital coefficient k multiplication circuit in the signal processing circuit.

FIG. 9 is an optical path diagram showing still another embodiment of the present invention.

FIG. 10 is a diagram showing a configuration of a sensor of the embodiment shown in FIG.

FIG. 11 is a diagram illustrating a relationship between polarized light and reflection / transmission.

FIG. 12 is an optical path diagram for explaining the relationship between the objective lens of the magneto-optical disk device and the magneto-optical disk.

[Explanation of symbols]

 11 Laser Light Source 13 First Beam Splitter 15 Objective Lens 17 Magneto-Optical Disk 18 Recording Track 19 Second Beam Splitter 21 λ / 2 Wave Plate 23 Polarizing Beam Splitter 25 First Sensor 27 Second Sensor 31 First Sensor 33 2nd sensor 37 3rd sensor (4 division sensor) 47 1st sensor (5 division sensor) 49 2nd sensor (5 division sensor)

Claims (4)

[Claims] 1. A reflected beam reflected by a recording track of a magneto-optical disk is branched into at least two by a beam splitter, each branched light is received by a sensor, and recording is performed based on a detection signal of at least two sensors. A magneto-optical disk device for detecting a signal, further comprising: a branching unit that further branches the reflected light; and a split sensor that receives the split light, and a predetermined coefficient is added to a predetermined difference signal of a plurality of output signals of the split sensor. And the one
A magneto-optical disk device comprising: a detection unit that detects a recording signal from the detection signals of the sensors. 2. The divided sensor according to claim 1,
Having a plurality of received light amounts divided by the orthogonal axis corresponding to the diametrical direction of the magneto-optical disk and the track direction orthogonal to this, the difference signal is a sum signal of the output signals of the divided sensor in one diagonal direction, A magneto-optical disk device, which is the difference between the output signal of the other divided sensor in the diagonal direction and the sum signal. 3. A reflected beam reflected by a recording track of a magneto-optical disk is branched into at least two by a beam splitter, each branched light is received by a sensor, and recording is performed based on a detection signal of at least two sensors. A magneto-optical disk device for detecting a signal, wherein each of the sensors is one divided sensor extending in a direction corresponding to the track direction of the magneto-optical disk, and located on both sides of the divided sensor. It is composed of four divided sensors divided by an orthogonal axis corresponding to a track direction orthogonal to this, and a signal obtained by multiplying a predetermined difference signal of the output signal of the divided sensor by a predetermined coefficient, and a detection signal of each sensor. A magneto-optical disk device, comprising: a detection unit that detects a recording signal from the optical disk. 4. A reflected light reflected by a recording track of a magneto-optical disk is branched into at least two, each branched light is received by a respective sensor, and a recording signal is detected based on a detection signal of at least two sensors. A magneto-optical disk device according to claim 1, wherein predetermined light-receiving portions of the sensor are shielded from light by predetermined distances.