JPH0512750A - Method for detecting information from optical recording medium - Google Patents

Abstract

PURPOSE:To obtain two signals which are a playback signal based upon Kerr ellipticity and a playback signal based upon variation in reflection factor at the same time from the same position on one medium as long as the optical recording medium is a medium which is variable individually in Kerr ellipticity or angle of Kerr rotation and variation in reflection factor, namely, to record and reproduce two bits (quad recording) at the same time at the same position of the medium, and to increase the density of the medium as a result. CONSTITUTION:When the playback signals are is detected from the optical recording medium 1, reflected light reflected by this medium is passed through a 1/4-wavelength plate 13 and a polarization beam splitter 14 having specific azimuths to detect the playback signal based upon the Kerr ellipticity and also detect the playback signal based upon the variation in the reflection factor of the reflected light. Further, while the playback signal based upon the angle of Kerr rotation of the reflected light reflected by the medium is obtained, the playback signal based upon variation in the reflection factor of the reflected light is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention makes a linearly polarized laser spot incident on an optical recording medium and obtains a reproduction signal based on the Kerr ellipticity (η) or Kerr rotation angle (θ _k ) of the reflected light reflected by the medium. On the other hand, the present invention relates to a method of detecting information from an optical recording medium that enables a high density of information by obtaining a reproduction signal based on a change (R) in the reflectance of reflected light.

[0002]

BACKGROUND OF THE INVENTION Magneto-optical recording medium or phase change type light.
The recording medium is a large-capacity memory that allows rewriting of recorded information.
In recent years, research and development have been actively promoted and practically used.
There is. Of these, in the magneto-optical recording medium, the reproduction signal
In general, incident linearly polarized light is a medium as a signal detection means.
When reflected, the polarization of the reflected light depends on the direction of magnetization of the medium.
Face angle θ_kA car that rotates in the opposite direction by (car rotation angle)
Using the effect, this rotation angle (θ _k) To the light intensity with an analyzer
Mainly adopted method of converting and obtaining reproduced signal by this
Has been done. On the other hand, the Kerr rotation angle θ of this Kerr effect_kProfit
Use the Kerr ellipticity η rather than detecting the playback signal using
If it is preferable to obtain the reproduced signal by doing so because the S / N ratio is good.
For example, if the wavelength of light used for detection is small,
The Kerr ellipticity is greater than the Kerr rotation angle.
It is better to obtain a reproduction signal using
Can be obtained and such a detection method is adopted
There is also.

Further, in the case of a phase change type optical recording medium, the fact that the reflectance differs between the crystalline state and the amorphous chamber state is utilized,
The change (R) in the reflectance of the reflected light reflected by the medium is detected, and the reproduction signal is obtained based on this.

By the way, in the optical recording medium as well, there is a demand for higher information density, and various developments are being made. However, conventionally, as described above, in detecting a reproduction signal, in the magneto-optical recording medium, either one of the Kerr rotation angle-based detection method and the Kerr ellipticity-based detection method is adopted. In the phase change type optical recording medium, a detection method based on a change in reflectance is adopted. As described above, only one detection method is adopted, and only the recording / reproducing method of recording only a 1-bit signal at one position on the optical recording medium is adopted. Therefore, there is a problem in that the optical recording medium cannot be densified in spite of the desire to increase the density.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a method for detecting information from an optical recording medium, which can increase the density of the optical recording medium. It is an object.

[0006]

SUMMARY OF THE INVENTION To achieve this object, a method of detecting information from an optical recording medium according to the present invention is a method of detecting a reproduction signal from the optical recording medium, in which linearly polarized light is incident on the optical recording medium. Then, the reflected light reflected by this medium is passed through a quarter-wave plate arranged at an azimuth of approximately 45 ° + 90 ° × n ₁ (n ₁ is an integer), and thereafter, an azimuth of approximately 90 ° × n.
₂ (n ₂ is an integer) is incident on the polarization beam splitter and divided into a P component and an S component, and these P component and S component are detected by a photoelectric detector, respectively, and the P component signal and S component are detected. And a reproduction signal based on the Kerr ellipticity is detected, and a reproduction signal based on a change in the reflectance of the reflected light is detected from the P component signal and the S component signal. Is characterized by.

The reflected light reflected by the medium is directed at an azimuth of 45 ° +
It is passed through a quarter-wave plate of 90 ° x n ₁ (n ₁ is an integer), and then detected with a polarization beam splitter of 90 ° x n ₂ (n ₂ is an integer) divided into P component and S component. Therefore, as will be described later in “Specific Description of the Invention”, a reproduction signal can be obtained by using the Kerr ellipticity η. On the other hand, the reproduction signal based on the change in reflectance is also detected.

Therefore, if the optical recording medium can change the Kerr ellipticity and the change of the reflectance separately, the reproduced signal based on the Kerr ellipticity and the change of the reflectance can be simultaneously obtained from the same position of one medium. It is possible to obtain two signals, a reproduction signal based on That is, 2-bit (4-level recording) information can be recorded / reproduced at the same position on one medium at the same time, and the density of the recording medium can be increased.

Further, in the second aspect of the present invention, while the reproduction signal based on the Kerr rotation angle of the reflected light reflected by the medium is obtained, the reproduction signal based on the change of the reflectance of the reflected light is obtained. Also in this case, two signals, that is, a reproduction signal based on the Kerr rotation angle and a reproduction signal based on a change in reflectance can be obtained from the same position on one medium at the same time. That is, two bits (four-value recording) can be recorded / reproduced at the same position on one medium at the same time, and the density of the recording medium can be increased.

[0010]

DETAILED DESCRIPTION OF THE INVENTION Two embodiments of the present invention will be described below with reference to the drawings. First, the optical recording medium to which the detection method of the first embodiment is applied is a medium that can change the Kerr ellipticity and the change of the reflectance separately. That is, it has a magneto-optical recording film suitable for recording / reproducing based on the Kerr ellipticity and a phase change film suitable for recording / reproducing based on a change in reflectance. Details will be described later.

In the method of detecting information from the optical recording medium according to the first embodiment, as shown in FIG. 1, a linearly polarized laser beam emitted from a laser 11 which is a semiconductor laser, for example, is a non-polarized beam. The light is incident on the splitter 12, and a part of the light is reflected and then passes through the non-polarizing beam splitter 12, and is condensed and reflected on the optical recording medium 1 by a focusing lens (not shown). The reflected light reflected by the medium 1 contains information based on Kerr ellipticity and information based on reflectance.

This reflected light is guided to a quarter-wave plate (λ / 4 plate) 13 via a non-polarizing beam splitter 12. The quarter wave plate 13 has an azimuth θ of 40 ° + 9.
0 ° × n ₁ ≦ θ ≦ 50 ° + 90 ° × n ₁ , almost 4
5 ° + 90 ° × n ₁ azimuth, and the phase delay amount δ is λ / 4−0.05 λ ≦ δ ≦ λ / 4 + 0.05.
It is set to λ. The reflected light is changed from linearly polarized light to circularly polarized light by passing through such a quarter wave plate 13.

The circularly polarized light is then guided to the polarization beam splitter 14. The polarization beam splitter 14 has an azimuth θ of −5 ° + 90 ° × n.
₂ ≦ θ ≦ 5 ° + 90 ° × n ₂ , almost 90 ° × n ₂
It is arranged in the azimuth. The light converted into circularly polarized light by the polarization beam splitter 14 arranged in this way is
It is divided into P component and S component. These P component and S component are detected by the photoelectric detectors 15a and 15b, respectively.

The P component signal and the S component signal are differentially amplified by the differential amplifier 16, and as a result, a reproduction signal based on the Kerr ellipticity (η) is detected. On the other hand, the P component signal and the S component signal are also supplied to the amplifier 17, whereby a reproduction signal based on the change (R) in the reflectance of the reflected light on the medium is detected.

As described above, the optical recording medium is a medium capable of changing the Kerr ellipticity and the change of the reflectance separately, and the reproduction signal based on the Kerr ellipticity and the reflection from the same position of one optical recording medium. Two signals, a reproduction signal based on a change in the rate, can be obtained at the same time. That is, two bits (four-value recording) can be recorded / reproduced at the same position on one medium at the same time, and the density of the recording medium can be increased. Further, since the signal based on the Kerr ellipticity is differentially detected, a reproduced signal can be obtained with a good S / N ratio.

Next, the principle by which the reproduction signal can be obtained by using the Kerr ellipticity η by the configuration of the detection optical system shown in FIG. 1 will be described. Linearly polarized light is made incident on the optical recording medium, and the azimuth of the polarization direction at this time is set to 0 °. The reflected light including the reproduction information reflected by the optical recording medium 1 is approximately

[0017]

[Equation 1]

It is expressed as follows. The quarter-wave plate 13 arranged in an orientation of about 45 ° (η ₁ = 0)

[0019]

[Equation 2]

It is expressed as follows. The polarization beam splitter 12 arranged in the 0 ° (η ₃ = 0) azimuth has P component and S component respectively.

[0021]

[Equation 3]

It is expressed as Therefore, the reflected light reflected by the optical recording medium 1 passes through the quarter-wave plate 13 and the electric field vectors E ₁ and E ₂ of the P component and the S component, which are separated by the polarization beam splitter 13, are:

[0023]

[Equation 4]

It is expressed as follows. Therefore, the intensity I of the P component
₁ , the intensity I _{2 of the} S component is

[0025]

[Equation 5]

It is expressed as In this embodiment, since differential detection is performed, the differential signal S is expressed as S = I ₂ −I ₁ = 2η. Since this S formula is expressed only by η which is the Kerr ellipticity, it has been proved that the reproduction signal is obtained by using the Kerr ellipticity by the optical detection system configured as shown in FIG.

Next, a detection method according to the second embodiment of the present invention will be described with reference to FIG. The optical recording medium to which the detection method of the second embodiment is applied is a medium that can change the Kerr rotation angle and the change in reflectance separately. That is, it has a magneto-optical recording film suitable for recording / reproducing based on the Kerr rotation angle and a phase change film suitable for recording / reproducing based on a change in reflectance. Details will be described later.

In the signal detecting method for the optical recording medium according to the second embodiment, as shown in FIG. 2, the linearly polarized laser light emitted from the laser 11 which is a semiconductor laser, for example, is a non-polarizing beam splitter 12. After passing, the light is condensed and reflected on the optical recording medium 1 by a focusing lens (not shown).

The reflected light reflected by the medium 1 is guided to the polarization beam splitter 14 via the non-polarization beam splitter 12. This polarization beam splitter 14
The azimuth θ is 40 ° + 90 ° × n ₃ ≦ θ ≦ 50 ° + 90
The angle is 45 ° + 90 ° × n ₃ and is approximately 45 ° + 90 ° × n ₃ . By the polarization beam splitter 14 arranged in this way, the reflected light is divided into a P component and an S component. These P component and S component are photoelectric detector 15 respectively.
a, 15b.

The P component signal and the S component signal are differentially amplified by the differential amplifier 16, and as a result, a reproduction signal based on the Kerr rotation angle (θ _k ) is detected. On the other hand, the P component signal and the S component signal are also supplied to the amplifier 17, whereby a reproduction signal based on the change (R) in the reflectance of the reflected light on the medium is detected.

As described above, in the second embodiment, the optical recording medium is a medium capable of changing the Kerr rotation angle and the change of the reflectance separately, and the Kerr rotation angle is changed from the same position of one optical recording medium. It is possible to simultaneously obtain two signals, a reproduction signal based on the change in reflectance and a reproduction signal based on the change in reflectance. That is, 1
Two bits (four-valued recording) can be recorded / reproduced at the same position on one medium at the same time, and the density of recorded information can be increased.

Next, an optical recording medium applied to the detection method according to the first and second embodiments of the present invention will be described. The optical recording medium 1 includes a magneto-optical recording film (MO film),
It has at least two layers of recording film with a phase change film. That is, the optical recording medium applied to the first embodiment is a magneto-optical recording film suitable for recording / reproducing based on Kerr ellipticity,
It has a phase change film suitable for recording / reproducing based on a change in reflectance. The optical recording medium applied to the second embodiment is
It has a magneto-optical recording film suitable for recording / reproducing based on the Kerr rotation angle and a phase change film suitable for recording / reproducing based on a change in reflectance.

Magneto-Optical Recording Film A magneto-optical recording film of a type based on both Kerr ellipticity and Kerr rotation angle is (i) at least 1 selected from 3d transition genus.
Or (iii) at least one element selected from rare earths, or (i) at least one selected from 3d transition metals, (ii) a corrosion resistant metal, and (ii)
i) It is preferably composed of at least one element selected from rare earths.

(I) 3d transition metals include Fe and C
O, Ti, V, Cr, Mn, Ni, Cu, Zn and the like are used, and among them, Fe or Co or both are preferable.

This 3d transition metal is contained in the magneto-optical recording film in an amount of 2
It is present in an amount of 0 to 90 atom%, preferably 30 to 85 atom%, more preferably 35 to 80 atom%. (Ii) The corrosion resistance metal can be included in the magneto-optical recording film to enhance the oxidation resistance of the magneto-optical recording film. Such corrosion resistant metals include Pt, Pd,
Ti, Zr, Ta, Nb or the like is used, and among these, Pt, Pd, and Ti are preferable, and Pt, Pd, or both are particularly preferable.

This corrosion resistant metal is contained in the magneto-optical recording film in an amount of 3
It is present in an amount of 0 atomic% or less, preferably 5 to 25 atomic%, more preferably 10 to 25 atomic%, and further preferably 10 to 20 atomic%.

Examples of the rare earth element include the following elements. Gd, Tb, Dy, Ho, Er, Tm,
Yb, Lu, La, Ce, Pr, Nd, Pm, Sm, E
u Of these, Gd, Tb, Dy, Ho, Nd, Sm, Pr
Is preferably used.

At least one selected from the above group
The rare earth element as a seed is present in the magneto-optical recording film in an amount of 5 to 50 atom%, preferably 8 to 45 atom%, and more preferably 10 to 40 atom%.

In the present invention, a small amount of various elements may be added to the magneto-optical recording film to improve the Curie temperature, the compensation temperature, the coercive force Hc, the Kerr rotation angle θk or reduce the cost. These elements can be used, for example, in a ratio of less than 10 atom% with respect to the total number of atoms constituting the recording film.

Examples of other elements that can be used in combination include the following elements. (I) 3d transition element other than Fe and Co Specifically, Sc, Ti, V, Cr, Mn, Ni, C
u and Zn are used.

Of these, Ti, Ni, Cu, Zn and the like are preferably used. (II) 4d transition element other than Pd Specifically, Y, Zr, Nb, Mo, Tc, Ru, R
h, Ag and Cd are used.

Of these, Zr and Nb are preferably used. (III) 5d transition element other than Pt Specifically, Hf, Ta, W, Re, Os, Ir, A
u and Hg are used.

Of these, Ta is preferably used. (IV) Group IIIB element Specifically, B, Al, Ga, In and Tl are used.

Of these, B, Al and Ga are preferably used. (V) Group IVB element Specifically, C, Si, Ge, Sn, and Pb are used.

Of these, Si, Ge, Sn and Pb are preferably used. (VI) Group VB element Specifically, N, P, As, Sb and Bi are used.

Of these, Sb is preferably used. (VII) VIB group element Specifically, S, Se, Te, and Po are used.

Of these, Te is preferably used. The magneto-optical recording film having the above composition has an easy axis of magnetization perpendicular to the film surface, and in many cases, a perpendicular magnetic and magneto-optically recordable amorphous thin film showing a square loop with good Kerr hysteresis. That is confirmed by wide-angle X-ray diffraction.

In the present specification, the expression of a square loop having a good Kerr hysteresis is the Kerr rotation angle (θk ₁ ) which is the Kerr rotation angle in the maximum external magnetic field and the Kerr rotation angle when the external magnetic field is zero. Car rotation angle (θk
₂ ) and the ratio θk ₂ / θk ₁ is 0.8 or more.

The thickness of this magneto-optical recording film is 100 to 600.
Å, preferably 100-400 Å, more preferably 20
It is about 0 to 350Å. Particularly, magneto-optical recording films suitable for the Kerr ellipticity include TbFe, TbCo and Tb.
FeCo, GdFe, GdCo, GdFeCo, GdT
bFe, GdTbCo, GdTbFeCo, NdFe,
NdCo, NdTbFe, NdTbCo, NdTbFe
Co, DyFe, DyCo, DyTbFe, DyTbC
A magneto-optical recording film made of o, DyTbFeCo, CoPt, CoPd is preferable.

Phase-Change Film Any phase-change film may be used as long as its optical constant changes in accordance with the change of state, such as TeO, TeGeO, TeGe.
Su, TeGeOSu, Te-Ge, TeGeSe, T
eGeSb, TeGeSeSb, InSe, InSeT
lCo, SbTe, SnTeSe, GaSeTe, Ga
A recording film of SeTeGe, BiTe, SbSe or the like can be used.

[0051]

As described above, according to the present invention, the reflected light reflected by the medium is reduced to 1 / of the azimuth of 45 ° + 90 ° × n ₁ .
Since it passes through a four-wave plate and is then detected separately by a polarization beam splitter with an azimuth of 90 ° × n ₂ into a P component and an S component, a reproduction signal can be obtained using the Kerr ellipticity η. . On the other hand, the reproduction signal based on the change in reflectance is also detected.

Therefore, if the optical recording medium is a medium capable of changing the Kerr ellipticity and the change of the reflectance separately, the reproduced signal based on the Kerr ellipticity and the change of the reflectance are simultaneously obtained from the same position of one medium. It is possible to obtain two signals, a reproduction signal based on That is, two bits (four-valued recording) can be recorded / reproduced at the same position on one medium at the same time, and the density of recorded information can be increased.

Further, in the second aspect of the present invention, while the reproduction signal based on the Kerr rotation angle of the reflected light reflected by the medium is obtained, the reproduction signal based on the change of the reflectance of the reflected light is obtained. Also in this case, two signals, that is, a reproduction signal based on the Kerr rotation angle and a reproduction signal based on a change in reflectance can be obtained from the same position on one medium at the same time. That is, two bits (four-valued recording) can be recorded / reproduced at the same position on one medium at the same time, and the density of recorded information can be increased.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a detection optical system to which a signal detection method for an optical recording medium according to a first embodiment of the present invention is applied.

FIG. 2 is a schematic diagram of a detection optical system to which a signal detection method for an optical recording medium according to a second embodiment of the present invention is applied.

[Explanation of symbols]

1 Optical recording film 13 1/4 wave plate (1/4 λ plate) 14 Polarizing beam splitter 15a, 15b Photoelectric detector

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[Procedure amendment]

[Submission date] October 1, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Method for detecting information from optical recording medium

[Claims]

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention makes a linearly polarized laser spot incident on an optical recording medium and obtains a reproduction signal based on the Kerr ellipticity (η) or Kerr rotation angle (θ _k ) of the reflected light reflected by the medium. On the other hand, the present invention relates to a method of detecting information from an optical recording medium that enables a high density of information by obtaining a reproduction signal based on a change (R) in the reflectance of reflected light.

[0002]

BACKGROUND OF THE INVENTION A magneto-optical recording medium or a phase-change type optical recording medium has been actively researched and developed in recent years as a large capacity memory capable of rewriting recorded information, and has been practically used. Among them, in a magneto-optical recording medium, as a reproduction signal detecting means thereof, generally, when incident linearly polarized light is reflected by the medium, the plane of polarization of the reflected light is an angle θ _k (Kerr rotation) depending on the direction of magnetization of the medium. Angle) is used to convert this rotation angle (θ _k ) into light intensity with an analyzer,
A method of obtaining a reproduced signal by this is mainly adopted. On the other hand, when it is preferable to obtain the reproduction signal by using the Kerr ellipticity η rather than the reproduction signal is detected by using the Kerr rotation angle θ _k of the Kerr effect, for example, the detection is performed. When the wavelength of the light used for is small, the Kerr ellipticity is larger than the Kerr rotation angle, and when the Kerr ellipticity is used to obtain the reproduced signal, the reproduced signal having a good S / N ratio can be obtained. Such a detection method may be adopted.

Further, in the case of a phase change type optical recording medium, the fact that the reflectance differs between the crystalline state and the amorphous chamber state is utilized,
The change (R) in the reflectance of the reflected light reflected by the medium is detected, and the reproduction signal is obtained based on this.

By the way, in the optical recording medium as well, there is a demand for higher information density, and various developments are being made. However, conventionally, as described above, in detecting a reproduction signal, in the magneto-optical recording medium, either one of the Kerr rotation angle-based detection method and the Kerr ellipticity-based detection method is adopted. In the phase change type optical recording medium, a detection method based on a change in reflectance is adopted. As described above, only one detection method is adopted, and only the recording / reproducing method of recording only a 1-bit signal at one position on the optical recording medium is adopted. Therefore, there is a problem in that the optical recording medium cannot be densified in spite of the desire to increase the density.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a method for detecting information from an optical recording medium, which can increase the density of the optical recording medium. It is an object.

[0006]

SUMMARY OF THE INVENTION To achieve this object, a method of detecting information from an optical recording medium according to the present invention is a method of detecting a reproduction signal from the optical recording medium, in which linearly polarized light is incident on the optical recording medium. Then, the reflected light reflected by this medium is passed through a quarter-wave plate arranged at an azimuth of approximately 45 ° + 90 ° × n ₁ (n ₁ is an integer), and thereafter, an azimuth of approximately 90 ° × n.
₂ (n ₂ is an integer) is incident on the polarization beam splitter and divided into a P component and an S component, and these P component and S component are detected by a photoelectric detector, respectively, and the P component signal and S component are detected. And a reproduction signal based on the Kerr ellipticity is detected, and a reproduction signal based on a change in the reflectance of the reflected light is detected from the P component signal and the S component signal. Is characterized by.

The reflected light reflected by the medium is directed at an azimuth of 45 ° +
It is passed through a quarter-wave plate of 90 ° x n ₁ (n ₁ is an integer), and then detected with a polarization beam splitter of 90 ° x n ₂ (n ₂ is an integer) divided into P component and S component. Therefore, as will be described later in “Specific Description of the Invention”, a reproduction signal can be obtained by using the Kerr ellipticity η. On the other hand, the reproduction signal based on the change in reflectance is also detected.

Therefore, if the optical recording medium can change the Kerr ellipticity and the change of the reflectance separately, the reproduced signal based on the Kerr ellipticity and the change of the reflectance can be simultaneously obtained from the same position of one medium. It is possible to obtain two signals, a reproduction signal based on That is, 2-bit (4-level recording) information can be recorded / reproduced at the same position on one medium at the same time, and the density of the recording medium can be increased.

Further, in the second aspect of the present invention, while the reproduction signal based on the Kerr rotation angle of the reflected light reflected by the medium is obtained, the reproduction signal based on the change of the reflectance of the reflected light is obtained. Also in this case, two signals, that is, a reproduction signal based on the Kerr rotation angle and a reproduction signal based on a change in reflectance can be obtained from the same position on one medium at the same time. That is, two bits (four-value recording) can be recorded / reproduced at the same position on one medium at the same time, and the density of the recording medium can be increased.

[0010]

DETAILED DESCRIPTION OF THE INVENTION Two embodiments of the present invention will be described below with reference to the drawings. First, the optical recording medium to which the detection method of the first embodiment is applied is a medium that can change the Kerr ellipticity and the change of the reflectance separately. That is, it has a magneto-optical recording film suitable for recording / reproducing based on the Kerr ellipticity and a phase change film suitable for recording / reproducing based on a change in reflectance. Details will be described later.

In the method of detecting information from the optical recording medium according to the first embodiment, as shown in FIG. 1, for example, linearly polarized laser light emitted from a laser 11 which is a semiconductor laser is converted into a beam splitter 12. Is incident on the optical recording medium 1 after passing through the beam splitter 12 after being partially reflected. The reflected light reflected by the medium 1 contains information based on Kerr ellipticity and information based on reflectance.

The reflected light is guided to the quarter-wave plate (λ / 4 plate) 13 via the beam splitter 12. The quarter wave plate 13 has an azimuth θ of 40 ° + 90 ° × n.
₁ ≤ θ ≤ 50 ° + 90 ° x n ₁ , almost 45 ° + 9
It is arranged in the direction of 0 ° × n ₁ and its phase delay amount δ
Is set to λ / 4−0.05λ ≦ δ ≦ λ / 4 + 0.05λ. The reflected light is generated by such a quarter wave plate 13
Is changed from linearly polarized light to circularly polarized light.

The circularly polarized light is then guided to the polarization beam splitter 14. The polarization beam splitter 14 has an azimuth θ of −5 ° + 90 ° × n.
₂ ≦ θ ≦ 5 ° + 90 ° × n ₂ , almost 90 ° × n ₂
It is arranged in the azimuth. The light converted into circularly polarized light by the polarization beam splitter 14 arranged in this way is
It is divided into P component and S component. These P component and S component are detected by the photoelectric detectors 15a and 15b, respectively.

The P component signal and the S component signal are differentially amplified by the differential amplifier 16, and as a result, a reproduction signal based on the Kerr ellipticity (η) is detected. On the other hand, the P component signal and the S component signal are also supplied to the amplifier 17, whereby a reproduction signal based on the change (R) in the reflectance of the reflected light on the medium is detected.

As described above, the optical recording medium is a medium capable of changing the Kerr ellipticity and the change of the reflectance separately, and the reproduction signal based on the Kerr ellipticity and the reflection from the same position of one optical recording medium. Two signals, a reproduction signal based on a change in the rate, can be obtained at the same time. That is, two bits (four-value recording) can be recorded / reproduced at the same position on one medium at the same time, and the density of the recording medium can be increased. Further, since the signal based on the Kerr ellipticity is differentially detected, a reproduced signal can be obtained with a good S / N ratio.
Further, the λ / 4 plate 13 and the polarization beam splitter 14
By inserting a λ / 2 plate in between, to determine the azimuth angle appropriately
The P and S components generated in optical elements and optical recording media
The phase difference between and can be canceled, and the S / N ratio of the reproduced signal can be further improved.
It is also possible to improve.

Next, the principle by which the reproduction signal can be obtained by using the Kerr ellipticity η by the configuration of the detection optical system shown in FIG. 1 will be described. Polarization of linearly polarized light incident on the optical recording medium
The light direction is defined as an azimuth of 0 °.

Jones vector of electric field vector of incident light
Le

[0018]

[Equation 1]

Then, the reproduction information reflected by the optical recording medium is
The reflected light Jones vector including the information is approximately

[0020]

[Equation 2 ]

Is represented as Jones matrix of quarter-wave plate 13 arranged at an angle of approximately 45 ° (η ₁ = 0)
Su

[0022]

[Equation 3 ]

It is expressed as follows. Jones matrix of the polarization beam splitter 12 arranged in the 0 ° (η ₃ = 0) direction
Box is, P component, for each S component,

[0024]

[Equation 4]

It is expressed as Therefore, the reflected light reflected by the optical recording medium 1 passes through the quarter-wave plate 13 and the electric field vectors E ₁ and E ₂ of the P component and the S component, which are separated by the polarization beam splitter 13, are:

[0026]

[Equation 5]

It is expressed as follows. Therefore, the intensity I of the P component
₁ , the intensity I _{2 of the} S component is

[0028]

[Equation 6]

It is expressed as follows. In this embodiment, since differential detection is performed, the differential signal S is expressed as S = I ₂ −I ₁ = 2η _k . This differential signal S has a Kerr ellipticity η _k
Since it is represented only by, it has been proved that the optical detection system configured as shown in FIG. 1 obtains a reproduction signal by using Kerr ellipticity.

Next, a detection method according to the second embodiment of the present invention will be described with reference to FIG. The optical recording medium to which the detection method of the second embodiment is applied is a medium that can change the Kerr rotation angle and the change in reflectance separately. That is, it has a magneto-optical recording film suitable for recording / reproducing based on the Kerr rotation angle and a phase change film suitable for recording / reproducing based on a change in reflectance. Details will be described later.

In the signal detection method for the optical recording medium according to the second embodiment, as shown in FIG. 2, the linearly polarized laser light emitted from the laser 11, which is a semiconductor laser, for example, passes through the beam splitter 12. Then, it is condensed on the optical recording medium 1 and reflected by an unillustrated stop lens.

The reflected light reflected by the medium 1 is guided to the polarization beam splitter 14 via the beam splitter 12. This polarization beam splitter 14 has an azimuth θ of 40 ° + 90 ° × n ₃ ≦ θ ≦ 50 ° + 90 ° × n
_3, which is approximately 45 ° + 90 ° × n ₃ azimuths. Polarizing beam splitter 1 arranged in this way
According to 4, the reflected light is divided into a P component and an S component.
These P component and S component are photoelectric detectors 15a and 1a, respectively.
Detected by 5b.

The P component signal and the S component signal are differentially amplified by the differential amplifier 16, and as a result, a reproduction signal based on the Kerr rotation angle (θ _k ) is detected. On the other hand, the P component signal and the S component signal are also supplied to the amplifier 17, whereby a reproduction signal based on the change (R) in the reflectance of the reflected light on the medium is detected.

As described above, in the second embodiment, the optical recording medium is a medium capable of changing the Kerr rotation angle and the change of the reflectance separately, and the Kerr rotation angle is changed from the same position of one optical recording medium. It is possible to simultaneously obtain two signals, a reproduction signal based on the change in reflectance and a reproduction signal based on the change in reflectance. That is, 1
Two bits (four-valued recording) can be recorded / reproduced at the same position on one medium at the same time, and the density of recorded information can be increased.

Next, an optical recording medium applied to the detection method according to the first and second embodiments of the present invention will be described. The optical recording medium 1 includes a magneto-optical recording film (MO film),
It has at least two layers of recording film with a phase change film. That is, the optical recording medium applied to the first embodiment is a magneto-optical recording film suitable for recording / reproducing based on Kerr ellipticity,
It has a phase change film suitable for recording / reproducing based on a change in reflectance. The optical recording medium applied to the second embodiment is
It has a magneto-optical recording film suitable for recording / reproducing based on the Kerr rotation angle and a phase change film suitable for recording / reproducing based on a change in reflectance.

Magneto-Optical Recording Film The magneto-optical recording film used in the present invention is particularly
Although not limited, for example, at least one selected from (A) (i) 3d transition metals
Element and at least one selected from (iii) rare earths
An alloy consisting of the element (B), (i) at least one selected from 3d transition metals
Elements, (ii) corrosion-resistant metals, and (iii) rare earths
Alloy consisting of at least one element selected from (C) (i) at least one selected from 3d transition metals
Examples of the alloy include the alloy of (1 ) and (ii) a corrosion resistant metal, (D) Pt / Co composition modulation film, or (E) Pd / Co composition modulation film.

Examples of the 3d transition metal include Fe and C
o, Ti, V, Cr, Mn, Ni, Zn, etc. are used.
It In the alloy films of (A) and (B) above, 3d
The content of transition metal is 20 to 90 atomic%, preferably 3
0 to 85 atomic% is desirable, and (C)
In the gold film, the content of 3d transition metal is 10 to 60 original
Child% is desirable.

As the rare earth element, for example, Gd,
Tb, Dy, Ho, Er, Tm, Nd, Sm, Pr, etc.
Used. Odor in the alloy films of (A) and (B) above
The content of the rare earth element is 5 to 50 atomic%, preferably
Is preferably 8 to 45 atomic%.

Examples of the corrosion resistant metal include Pt and P
d, Ti, Zr, Ta, Nd or the like is used. the above
In the alloy film of (B), the content of corrosion resistant metal is 3
0 atomic% or less, preferably 5 to 25 atomic%
desirable. Also, in the alloy film of (C) above, corrosion resistance
The content of the functional metal is preferably 90 to 40 atomic%.
Yes.

Especially, a magneto-optical recording suitable for the case of Kerr ellipticity
As the recording film, TbFe, TbFeCo, GdFe, G
dFeCo, GdTbFe, GdTbFeCo, NdT
bFe, NbTbFeCo, CoPt, CoPt, Co
Pd, DyTbFe, DyTbFeCo, TbCo, G
It consists of dCo, GdTbCo, DyTbCo, NdFe
A magneto-optical recording film is preferable.

The film thickness of this magneto-optical recording film is preferably 50.
~ 600 angstrom, more preferably 50-40
0 angstrom, more preferably 50-350 on
It is about Gstrom.

Phase Change Film Any phase change film may be used as long as its optical constant changes in accordance with a change in state, such as TeO, TeGeO, TeGe.
S n, TeGeOS n, TeGe, TeGeSe, Te
GeSb, TeGeSeSb, InSe, InSeTl
Co, SbTe, SnTeSe, GaSeTe, GaS
A recording film of eTeGe, BiTe, SbSe, or the like can be used.

[0043]

As described above, according to the present invention, the reflected light reflected by the medium is reduced to 1 / of the azimuth of 45 ° + 90 ° × n ₁ .
Since it passes through a four-wave plate and is then detected separately by a polarization beam splitter with an azimuth of 90 ° × n ₂ into a P component and an S component, a reproduction signal can be obtained using the Kerr ellipticity η. . On the other hand, the reproduction signal based on the change in reflectance is also detected.

Therefore, if the optical recording medium is a medium which can change the Kerr ellipticity and the change of the reflectance separately, the reproduced signal based on the Kerr ellipticity and the change of the reflectance can be simultaneously obtained from the same position of one medium. It is possible to obtain two signals, a reproduction signal based on That is, two bits (four-valued recording) can be recorded / reproduced at the same position on one medium at the same time, and the density of recorded information can be increased.

Further, in the second aspect of the present invention, while the reproduction signal based on the Kerr rotation angle of the reflected light reflected by the medium is obtained, the reproduction signal based on the change of the reflectance of the reflected light is obtained. Also in this case, two signals, that is, a reproduction signal based on the Kerr rotation angle and a reproduction signal based on a change in reflectance can be obtained from the same position on one medium at the same time. That is, two bits (four-valued recording) can be recorded / reproduced at the same position on one medium at the same time, and the density of recorded information can be increased.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a detection optical system to which a signal detection method for an optical recording medium according to a first embodiment of the present invention is applied.

FIG. 2 is a schematic diagram of a detection optical system to which a signal detection method for an optical recording medium according to a second embodiment of the present invention is applied.

[Explanation of Codes] 1 Optical recording film 13 1/4 wavelength plate (1/4 λ plate) 14 Polarization beam splitters 15a, 15b Photoelectric detector ─────────────────── ───────────────────────────────────

[Procedure amendment]

[Submission date] October 5, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0042

[Correction method] Change

[Correction content]

Phase Change Film Any phase change film may be used as long as its optical constant changes in accordance with a change in state, such as TeO, TeGeO, TeGe.
Sn, TeGeOSn, TeGe, TeGeSe, Te
GeSb, TeGeSeSb, InSe, InSeTl
Co, SbTe, SnTeSe, GaSeTe, GaS
A recording film of eTeGe, BiTe, SbSe, or the like can be used. The thickness of this phase change film is preferably 50-
2000 angstrom, more preferably 50 to 10
It is 00 angstrom.

Claims (2)

[Claims] 1. A method for detecting information recorded on an optical recording medium from the optical recording medium, wherein linearly polarized light is incident on the optical recording medium, and reflected light reflected by the medium has an azimuth of about 45 °. Pass through a quarter-wave plate arranged at + 90 ° × n ₁ (n ₁ is an integer), and then
It is incident on a polarization beam splitter arranged at an azimuth of approximately 90 ° × n ₂ (n ₂ is an integer), and is divided into a P component and an S component, and these P component and S component are detected by a photoelectric detector, respectively, and P The information recorded on the optical recording medium is obtained by differentially amplifying the signal of the component and the signal of the S component and detecting the reproduction signal based on the Kerr ellipticity, while the signal of the P component and the signal of the S component are obtained. From the above, the information recorded on the optical recording medium is obtained by detecting the reproduction signal based on the change of the reflectance of the reflected light. 2. A method of detecting a reproduction signal from an optical recording medium, wherein linearly polarized light is incident on the optical recording medium, and reflected light reflected by this medium has an azimuth of approximately 45 ° + 90 ° × n ₃ ( n ₃ is an integer) and is incident on a polarization beam splitter, and is divided into a P component and an S component. These P component and S component are respectively detected by a photoelectric detector, and a P component signal and an S component signal are detected. Is differentially amplified to obtain the information recorded on the optical recording medium by detecting the reproduction signal based on the Kerr rotation angle, while the reflectance of the reflected light is calculated from the P component signal and the S component signal. A signal detection method for an optical recording medium, characterized in that the information recorded on the optical recording medium is obtained by detecting a reproduction signal based on the change of