JPH0737281A - Optical recording medium and optical recording medium reproducing device - Google Patents

Abstract

PURPOSE:To make it possible to record and reproduce information having the space frequency exceeding the space frequency regulated by the wavelength of a reading out laser beam at the time of reproducing and the numerical aperture of an objective lens by providing the recording medium with a polarization state changing layer which makes Kerr rotation of the polarization state of the incident reading out light in correspondence to a temp. distribution according to irradiation with the reading out light. CONSTITUTION:A magnetic layer as the polarization state changing layer consists of a ferrimagnetic material having a characteristic of a compensation temp. higher than room temp. and lower than Curie temp. The polarization state changing layer changes the polarization state of the reflected light or transmitted light of a first region AR within the reading out light spot LB on an information recording surface to the state different from the polarization state of the reflected light or transmitted light of a second region XAR within the spot LB in correspondence to the intensity distribution of the reading out light from the outside or the irradiation temp. distribution of the reading out light. As a result, only either of the reading out light of the first and second regions is received, by which the recorded information of either one of the phase pits (P2 or P3) recorded on either of the first or second region is reproduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium in which information is recorded by phase pits and a reproducing apparatus therefor, and more particularly, it exceeds a spatial frequency defined by the wavelength of read light during reproduction and the numerical aperture of an objective lens. The present invention relates to an optical recording medium in which information having a spatial frequency is recorded and a reproducing apparatus therefor.

[0002]

2. Description of the Related Art Conventional CD (Compact Disk) and LD (La
For optical discs such as ser disk), a photodetector detects a decrease in the amount of reflected light caused by diffraction or scattering when the beam spot of the read laser light is irradiated on the (phase) pit or a change in the optical constant of the pit portion. By doing so, the information corresponding to the presence or absence of the pit was taken out. More specifically, when the read laser beam spot is irradiated onto the pits (see FIG. 13A), the return light amount (reflected light amount) due to reflection due to scattering or the like is small, and the read laser beam is provided between the pits. When the light spot is irradiated (see FIG. 13B), the information is read out by utilizing the large amount of returning light.

[0003]

However, the reproduction resolution of the above-mentioned conventional optical disk is limited by the wavelength λ of the read laser light and the numerical aperture NA of the objective lens.
There is a problem that information having frequency components exceeding the spatial frequency f _c = 2NA / λ cannot be reproduced.

Therefore, an object of the present invention is to record information having a wavelength λ of a read laser beam during reproduction and a spatial frequency exceeding a spatial frequency f _c = 2NA / λ defined by the numerical aperture NA of the objective lens. An object is to provide an optical recording medium and an optical recording medium reproducing apparatus capable of reproducing the optical recording medium with good separation.

[0005]

In order to solve the above-mentioned problems, the first invention is an optical recording medium in which information is held by phase pits, and the intensity distribution of read light or read light irradiated from the outside. The first polarization state of the reflected light or the transmitted light in the first region in the read light spot on the information recording surface is changed to the other region in the read light spot in accordance with the temperature distribution accompanying the irradiation of A ferrimagnetic layer having a magnetic layer for changing reflected light or transmitted light in a second region to have a second polarization state different from that of the second polarized state, the magnetic layer having a compensation temperature higher than room temperature and lower than Curie temperature. An optical recording medium made of a material.

A second aspect of the present invention is an optical recording medium reproducing apparatus for reproducing recorded information from the optical recording medium of the first aspect of the invention, which is a light irradiating means for irradiating the optical recording medium with reading light. Separation means for separating only one of the read light having the first polarization state and the read light having the second polarization state from the reflected light or the transmitted light of the read light that has been read out of the optical recording medium, and a separating means. The light receiving means separates the read light separated by the above and outputs it as a read signal, and the reproducing means for reproducing the recorded information on the optical recording medium based on the read signal.

[0007]

According to the first aspect of the invention, the polarization state changing layer is provided within the reading light spot on the information recording surface in accordance with the intensity distribution of the reading light irradiated from the outside or the temperature distribution accompanying the irradiation of the reading light. The first polarization state, which is the polarization state of the reflected light or the transmitted light in the first area, is the polarization state of the reflected light or the transmitted light in the second area, which is the other area in the read light spot. The polarization state is changed so that it is different from the polarization state of No. 2.

Further, since the compensation temperature of the magnetic layer is higher than room temperature and lower than the Curie temperature, if the overall magnetization of the magnetic layer is set to be in the same direction, the first polarization state and the second polarization state. The polarization rotation directions of and are opposite.

Therefore, by receiving only one of the read light having the first polarization state and the read light having the second polarization state, the first region within the read light spot on the information recording surface is received. Alternatively, it is possible to reproduce the information of only the phase pits (recording information) recorded in any one of the second areas.

According to the second aspect of the invention, the light irradiating means irradiates the optical recording medium with the reading light, and the separating means selects one of the reflected light and the transmitted light of the irradiated reading light from the optical recording medium. Therefore, only one of the read light having the first polarization state and the read light having the second polarization state is separated.

As a result, the light receiving means receives the read light separated by the separating means and outputs it as a read signal to the reproducing means, and the reproducing means reproduces the record information of the optical recording medium based on the read signal.

Therefore, either the read light having the first polarization state from the first region or the read light having the second polarization state from the second region, each of which is part of the read light spot. It is possible to accurately reproduce only the recorded information included in the read light spot, and it is possible to reproduce information having a high spatial frequency when there are a plurality of recording pits in the reading light spot.

[0013]

Next, an optical recording medium and an optical recording medium reproducing apparatus according to a preferred embodiment of the present invention will be described with reference to the drawings. (I) First Example First, the structure of the optical disc according to the present invention will be described. FIG. 1 shows a sectional view of the optical disc.

As shown in FIG. 1A, the optical disc 1 corresponds to the substrate 2 on which phase pits are formed and the polarization state of the incident linearly read light according to the temperature distribution accompanying the irradiation of the read light. And a material layer 3 as a polarization state change layer that is rotated and protective layers 4a and 4b that protect the material layer 3 are provided. In the description below, the material layer 3, the protective layer 4a, and the protective layer 4b are collectively referred to as a magneto-optical layer.

As a concrete structure of the optical disc 1, as viewed from the substrate side, the SiN layer 4a (80
nm), a material layer exhibiting a magneto-optical effect, GdFeCo
Layer 3 (90 nm), SiN layer 4b that is a dielectric protection layer
They are formed in the order of (50 nm). The numerical values in the parentheses show an example of the thickness of each layer. In this case, the rotation of the polarization state is mainly due to the Kerr effect which is the rotation of the polarization plane of the magneto-optical effect due to reflection.

Further, an optical disc 1'shown in FIG. 1 (b).
Also has a layer structure similar to that of the disc 1 shown in FIG. 1A, and includes a substrate 2 and a material layer 3 as a polarization state changing layer.
And protective layers 4a and 4b.

The difference between the optical disc 1'and the optical disc 1 is that a TbFeCo layer is used for the material layer 3 instead of GdFeCo. The rotation of the polarization state in this case is due to the same Kerr effect as the optical disc 1.

In the optical discs 1 and 1'shown in FIGS. 1 (a) and 1 (b), the GdFeCo layer 3 and the TbFeCo layer 3 which are the material layers are thick and the reflectance is high, so that it is not necessary to provide another reflection layer. In order to use a thin or low magneto-optical layer as the magneto-optical layer and use it as the reflection type optical disc 1 ″, it is necessary to provide the reflection layer 5 as shown in FIG. 1 (c). As the reflective layer 5, AlT
i, Al, Au, etc. can be used. The rotation of the polarization state in this case is due to the Kerr effect and the Faraday effect for performing magneto-optical rotation with respect to the transmission polarization plane.

Specifically, in the optical disc 1 ″, when viewed from the substrate side, the SiN layer 4 a which is a dielectric protection layer, the GdFeCo layer 3 which is a material layer exhibiting a magneto-optical effect, and the SiN layer 4 b which is a dielectric protection layer. And the AlTi layer 5 as a protective layer and a reflective layer is further provided in this case. In this case, since the layer thickness of GdFeCo used in the disc 1 is thin, the material layer has a low reflectance.

More specifically, as compensation point materials to which the present invention can be applied, there are the materials represented by the following formulas (1) to (3). TbFe, TbFeCo (Tb> 23 [at%]) (1) GdFe, GdFeCo (Gd> 24 [at%]) (2) DyFe, DyFeCo (Dy> 26 [at%]) (3) ) Others include NdTbFeCo, NdDyFe
Co or the like can be considered. In addition, [at%] is an atomic percentage and represents the number of the atom concerned in the whole. For example, in the notation A _n B _m (4), n + m = 100 (5), and the expression (4) means that n% of A atoms and m% of the total number of atoms are It means that this atom is composed of B atoms.

According to this expression, the material of the polarization state changing layer 3 in the disc 1 of the present invention is represented by Gd ₂₅ (Fe ₇₀ Co ₃₀ ) ₇₅ [at%] (6), etc., and the optical disc 1 ' The polarization state change layer 3 ′ in is represented by Tb ₂₅ (Fe ₈₀ Co ₂₀ ) ₇₅ [at%] (7) or the like.

Next, the characteristics of the magneto-optical material used in the magneto-optical disk of this embodiment will be described with reference to FIGS. Recently, as many magneto-optical recording materials, rare earth metal RE (Rare Earth) -transition metal TM (Transiti
on Metal) Amorphous alloy is used. As its magnetic property, it exhibits ferrimagnetism in which the partial magnetizations of a transition metal and a heavy rare earth metal are antiparallel.

As shown in FIG. 5, depending on the magnitude relation of these partial magnetizations, the direction of the whole magnetization becomes the partial magnetization direction of the transition metal as shown in FIG. 5A (TM-rich).
As shown in FIG. 5B, the direction of partial magnetization of the rare earth metal is changed (RE-rich). In FIG. 5, the solid line is the partial magnetization of the transition metal, and the broken line is the partial magnetization of the rare earth metal. The direction of the arrow indicates the direction of magnetization, and the length of the arrow indicates the strength of magnetization.

Further, among the above ferrimagnetic materials,
The partial magnetization of rare earth metals is at a higher temperature than the partial magnetization of transition metals.
Depending on the composition of the alloy,
Compensation Temperature (Tcomp)
It may have a temperature at which the magnetization direction reverses. like this
A medium with characteristics is called a compensation point material, which is shown in Fig. 6.
You Before the total magnetization Ms approaches the Curie temperature Tc,
Drastically reduced, compensation temperature T _compIs apparently
And the holding force Hc becomes very large.

The atomic magnetic moment of the rare earth RE is μ _R ,
Letting the atomic magnetic moment of the transition metal TM be μ _T , the average atomic magnetic moment μ _RT in the rare earth metal RE-transition metal TM alloy, RE ₁ -X TM _x is given by equation (8).

Μ _RT = | (1-X) μ _R ± X μ _T | (8) where + is applied to the light rare earth and − is applied to the heavy rare earth. Therefore, in the magneto-optical medium adapted to the present invention, the direction of the total magnetization, which is the coupling of the magnetization moments of both RE and TM, does not change even if it is below the compensation temperature Tcomp or above it. Only the directions of partial magnetization are mutually inverted. The medium exhibiting these properties includes C as a transition metal such as GdCo and TbCo.
Those using o are known (December 1986: Seminar of Applied Magnetics Society of Japan, Shin Ouchiyama, Nagoya University). As a result, the magnetization Ms of the entire alloy is observed as the difference between the partial magnetization of the transition metal and the partial magnetization of the rare earth metal.

The arrow at the bottom of FIG. 6 shows the state of partial magnetization at this time based on the expression of FIG. In the magneto-optical medium according to the present invention, in such a compensation point material, the room temperature T _R and the low temperature region temperature T _low at the time of irradiation of the reading light are set.
Is equal to or lower than the compensation temperature T _{comp, and the high} temperature region temperature T _high at the time of irradiation of the reading light is equal to or higher than the compensation temperature T _comp . In FIG. 6, this state is shown by the relationship between the room temperature point T _R (*) and the high temperature region temperature T _high and the low temperature region temperature T _low when the reading light is irradiated. On the other hand, it is known that the ferrimagnetic material in the magneto-optical medium having the above characteristics has the wavelength dependence of the Kerr rotation angle shown in FIG. 7 (Doctoral thesis: KD
Fujio Tanaka (Waseda Univ.)). In the figure, the Kerr rotation angle has almost the same value irrespective of the rare earth element, and in each case, it slightly increases with respect to the wavelength. In particular, such RE
The Kerr rotation angle in the TM-based magneto-optical medium depends on the magnetization of the transition metal TM at a long wavelength (wavelength 600 [nm: nanometer]) or more. As a result, in the magneto-optical medium using the compensation point material, when a laser having a long wavelength is used as the reading light, the Kerr rotation angle due to the reflected light changes substantially in proportion to the direction of partial magnetization of the transition metal TM. I understand.

Therefore, if the direction of the overall magnetization is always aligned in one direction by the reproducing magnetic field, the room temperature point T in FIG.
The direction of the partial magnetization of the transition metal TM at _R (* point) and the low temperature region temperature T _low of the irradiation light and the direction of the partial magnetization of the transition metal TM on the medium at the _high temperature region temperature T _high of the read light are They are opposite to each other, and therefore the direction of car rotation is also reversed.

Next, the reproducing principle of the magneto-optical medium according to the present invention will be described. In the initial state shown in FIG. 2 (a), the magnetization means MG1 such as a permanent magnet causes the perpendicular magnetization directions of all regions of the magneto-optical layer of the magneto-optical disk to be the same (downward in the drawing). To At this time,
The magnetization in the high temperature region is carried by the transition metal TM, and the overall magnetization at the place where the light spot has passed and returned to room temperature is carried by the rare earth metal RE.

At the time of reproduction, as shown in FIG. 2B, when a light spot whose output of read light is adjusted is irradiated, at least the temperature of the high temperature area of the area irradiated with the light spot is compensated. When the temperature exceeds T _comp , the partial magnetization structure in this high temperature region changes, and the total magnetization changes to the transition metal TM.
Will be carried by.

As a result, the overall Kerr effect or Fara
The rotation angle due to the magneto-optical effect of the Day effect is
Since it is determined by the spin, −θ in the high temperature region_kaof
The polarization state is given, and in other room temperature and low temperature regions
Predetermined angle depending on material + θ _kbGiven the polarization state of
It

Therefore, the incident read-out light is received by the detector in the polarization state of −θ _ka with the read-out light in the high temperature region, and the read-out light is + θ _{kb in the} low temperature region excluding the high temperature region in the light spot. Reconstructed light having a rotated polarization state is received by the detector.

Therefore, if the two kinds of reproduction light beams having different polarization states are separated by using a separating means such as a polarization filter or a differential optical system, information of pits existing in a part of the reading light spot can be selectively selected. Can be detected.

This means that a pinhole having an opening smaller than the diameter r of the reading light spot, which is optically defined by the wavelength λ of the reading light and the numerical aperture NA of the objective lens, is provided on the information recording surface of the optical disk. This is equivalent to the above, and it becomes possible to reproduce the information of the phase pits of a minute size such that a plurality of phase pits exist in the reading light spot, that is, the phase pits having a high spatial frequency f (f> f _C ).

It is not always necessary to have the perpendicular magnetic anisotropy, and when the perpendicular magnetization is not formed, the reproducing magnetic field Hr
By applying an external magnetic field, the magnetization of the curtain can be aligned vertically.

FIG. 3 shows the structure of the main part of the optical disk reproducing apparatus. The optical disk reproducing apparatus 10 includes a laser diode 11 that emits a laser beam that is a reading beam, and a beam splitter 12 that transmits a laser beam that is incident from the laser diode 11 and that reflects a laser beam that is incident from a mirror described later.
A mirror 13 for guiding the laser beam, and an objective lens 14 for focusing the laser beam on the information recording surface of the optical disc DK.
And a half-wave plate for adjusting the ratio of the reflected light amount and the transmitted light amount of the laser light from the non-reading region (low temperature region) of the laser light (reproduced light) reflected by the beam splitter 12, which will be described later. (Halfwave pla
te) 15, a polarized beam splitter 16 that transmits only polarized light having a predetermined polarization state and reflects other light, and the polarized light reflected by the polarized beam splitter are received, and the first read signal R ₁ (RF signal ) And a second light receiving element 17b for receiving the polarized light transmitted through the polarization beam splitter 16 and outputting it as a second read signal R ₂ (RF signal), a decoder, an amplifier and the like for reading. A reproduction circuit 18 for converting the signal R into a reproduction signal S and outputting it.
And a magnet MG ₁ for aligning the perpendicular magnetization direction of the optical disk DK in a fixed direction.

Next, the operation of this embodiment will be described with reference to FIG. First, the magnet MG _{1 is formed on the} magneto-optical layer of the optical disc DK.
Is used to apply an external magnetic field H _i to initialize the perpendicular magnetization direction before reading recorded information to a fixed direction (initialization: downward direction in the drawing). The initialization may be performed when the coercive force of the medium is lowered by irradiating the beam spot, or by a strong external magnetic field exceeding the coercive force.

In the following description, the optical disc is
The perpendicular magnetization direction of all areas of the disk DK is changed to the magnet MG.₁By
The case of initialization is described below. Laser diode
Read light (laser light) which is linearly polarized light emitted from 11
The spot LB of the mirror 13 and the beam splitter 1
2. Information recording on the optical disc DK via the objective lens 14.
The light is focused on the surface and, as shown in FIG.
₁A read-out spot LB is formed on the read-out spot L
B is a track T due to the rotation of the disk DK.₁Move up
It

By the way, the track T₁Above the reading light
The sky defined by the wavelength λ and the numerical aperture NA of the objective lens 14.
Inter-frequency f_c= Spatial frequency f (f >> 2NA / λ)
f_C) Are formed. Specifically
Is a plurality of phase pits P in the reading light spot LB.₂,
P₃Exist, and the phase pits P are left as they are.₂,
P₃Information cannot be separated and correct playback is not performed.
I can't. Similarly, as shown in FIG.
A plurality of tracks T in the reading light spot LB. ₀’、 T
₁’、 T₂′ Is included, correct playback is performed.
I can't follow.

Therefore, when the output of the reading light is adjusted, the result shown in FIG.
As shown in (c), the temperature of the material layer rises above the Curie temperature Tc and above the compensation temperature T _comp (the position of T _high in FIG. 6) in the region AR at the rear part of the read light spot LB, For example, in the case shown in FIG. 4A, the transition metal TM in the area AR where the phase pit P ₂ exists.
The direction of partial magnetization of is reversed.

As a result, in the region AR in which the partial magnetization of the transition metal TM is reversed, the polarization state of the reproduction light, which is the reflection light of the read light by the information recording surface, changes from the polarization state of the read light to the material by the magneto-optical effect. The polarized state rotated by the dependent angle (−θ _ka ) returns to the light receiving element side. On the other hand, in the region XAR where the phase pits P ₃ are present in the read light LB excluding the region AR, the polarization state of the reproduction light is higher than that of the read light by a certain angle depending on the material layer due to the magneto-optical effect. It will return to the light-receiving element side after being rotated by (+ θ _kb ).

Although the reproduction light from the area AR and the area XAR reaches the light receiving elements 17a and 17b in a mixed state, the amount of the reproduction light from the area XAR is adjusted to the first light receiving element 17a by adjusting the half-wave plate 15 and the like. And the second light receiving element 17b are set so as to be incident in equal amounts, the first read signal R ₁
And the second read signal R ₂ (differential output), the area X
The signal component due to the reproduction light from the AR is canceled out, and the area XA
R is apparently shielded. Therefore, in the reproducing circuit 18, only the information of the area AR, that is, the phase pit P ₂ can be read, and the reproducing signal S includes only the information of the phase pit P ₂ .

As described above, according to the first embodiment, the spatial frequency exceeding the spatial frequency f _C (= 2NA / λ) defined by the wavelength λ of the reading light and the numerical aperture NA of the objective lens 14. It becomes possible to reproduce the information having f. In addition, since there is a difference in polarization state of θ _ka + θ _kb between the reproduction light of the area AR and the reproduction light of the area XAR,
The C / N (Carrier to Noise ratio) characteristic is better than a system having a polarization angle difference of only θ _ka .

Further, since the optical system in the above embodiment is equivalent to the rewritable magneto-optical disk recording / reproducing device which is widely used at present, the device can be shared.

Further, since the apparently shielded area can be set by adjusting the half-wave plate 15 or the like, as shown in FIG. 4B, not only the pit row direction but also the track pitch direction. Even with a high-density optical disk, the occurrence of crosstalk between tracks and crosstalk between pits can be reduced or neglected, so that information of only desired phase pits can be accurately reproduced. . (Ii) Second Embodiment In the optical disk reproducing apparatus of the first embodiment, the recorded information is reproduced by using the differential optical system having two light receiving elements. This is an example of a case where an optical system is configured by using one light receiving element.

FIG. 8 shows the structure of the main part of the optical disk reproducing apparatus. The same parts as those in the first embodiment of FIG. 6 are designated by the same reference numerals, and detailed description thereof will be omitted. The optical disk reproducing device 10A includes a laser diode 11 that emits a laser beam that is a reading beam, a beam splitter 12 that transmits a laser beam that is incident from the laser diode 11 and that reflects a laser beam that is incident from a mirror described later, and a laser beam. Mirror 13 for guiding light, objective lens 14 for condensing laser light on the information recording surface of optical disc DK, and beam splitter 1
Of the laser light (reproduced light) reflected by 2, the polarizing plate that transmits only the laser light from the reading area, and the light receiving element that receives the polarized light that has passed through the polarizing plate and outputs it as a reading signal R ′ (RF signal) 17 ', and a reproduction circuit 1 including a decoder, an amplifier, etc., for converting the read signal R into a reproduced signal S and outputting the reproduced signal S.
8 is provided.

Next, the operation will be described. Laser diode 1
The laser light emitted from No. 1 passes through the beam splitter 12, is reflected by the mirror 13, and is further reflected by the objective lens 14
Thus, the laser light is focused on the information recording surface of the optical disc DK.

At this time, the optical disc D in the beam spot
In the state of K, as shown in FIG. 9, the region in the forward direction of the beam is the low temperature region A _{L and the} Kerr rotation angle (+ θ _kb ) (almost constant value), and the region in the backward direction of the beam is the high temperature region A _H.
And becomes the Kerr rotation angle (-θ _ka ) (almost constant value).

Therefore, if the polarizing plate 15 is set so as to pass the light having the polarization plane at an angle (-θ _ka ) with the incident light from the laser diode side, the reflected light from the low temperature region A _L will pass through the polarizing plate 15. Since it becomes difficult to transmit, only the reflected light (Kerr rotation angle (−θ _ka )) from the high temperature region A _H is transmitted through the polarizing plate 15 and is received by the light receiving element R ′, and is reproduced by the reproducing circuit 18 as the reproduced signal S. It will be output.

That is, the low temperature area A _L serves as a mask area and the high temperature area A _H serves as a read area. Therefore, the recording density can be improved also in the track pitch direction,
It becomes possible to reproduce recorded information having a higher spatial frequency. (Iii) Third Embodiment In an optical disc having a high density also in the track pitch direction, in order to reduce crosstalk and obtain a good reproduction signal, the mask area is read in a rewritable magneto-optical disk reproducing apparatus. Since it needs to be inverted with respect to the area, it is necessary to adjust the half-wave plate, and it has been difficult to share it with the optical system of the conventional rewritable magneto-optical disk reproducing apparatus.

Therefore, in this embodiment, the optical system is common to the optical system of the rewritable magneto-optical disk reproducing apparatus, and the optical disk densified in the track pitch direction by signal processing can be read. .

FIG. 10 shows the structure of the main part of the optical disk reproducing apparatus. The optical disk reproducing device 10B includes a laser diode 11 that emits laser light that is read light, a beam splitter 12 that transmits the laser light that is incident from the laser diode 11 and that reflects the laser light that is incident from a mirror described later, and a laser light. Of the laser light from the non-reading area of the laser light (reproduction light) reflected by the beam splitter 12 and the mirror 13 for guiding the laser light, the objective lens 14 for condensing the laser light on the information recording surface of the optical disc DK. Half-wave plate 15 for adjusting the ratio of the amount of reflected light and the amount of transmitted light in the polarization beam splitter described later.
And a polarized beam splitter 16 that transmits only polarized light having a predetermined polarization state and reflects other light, and the polarized light reflected by the polarized beam splitter is received and output as a first read signal R ₁ (RF signal). First light receiving element 17a
And a polarized light transmitted through the polarization beam splitter 16 is received and is output as a second read signal R ₂ (RF signal).
A light receiving element 17b, a reproducing circuit 18a including a decoder, an amplifier, etc., for converting the read signal R into a reproduced signal S and outputting the reproduced signal S,
And a magnet MG ₁ for aligning the perpendicular magnetization direction of the optical disk DK in a fixed direction.

FIG. 11 shows the structure of the main part of the reproducing circuit 18a. The reproduction circuit 18a receives the first read signal R ₁ and the second read signal R ₂ and adds them to add the sum signal SUM.
The adder 30 that outputs (= R ₁ + R ₂ ) and the first read signal R ₁ and the second read signal R ₂ are input, and the subtraction signal DIFF is performed by subtracting the second read signal from the first read signal R ₁ . (=
A first subtractor 31 for outputting R ₁ -R ₂ ) and a subtraction signal D
A multiplier 32 that multiplies IFF by a coefficient K (= 1 / tan (θ _ka + θ _kb )) and outputs a multiplication signal MUL (= K × DIFF), and a reproduction signal S by subtracting the multiplication signal MUL from the addition signal SUM. And a second subtractor 33 that outputs

Next, the operation will be described. As shown in FIG. 12, the vector indicating the component of the read signal (Kerr rotation angle = −θ _ka ) is a ₁ , the component incident on the first light receiving element 17a is a ₁ , and the component incident on the second light receiving element 17b. The component is a ₂ , the vector indicating the component of the signal to be masked (Kerr rotation angle = θ _kb ) is b, the component incident on the first light receiving element 17a is b ₁ , and the component incident on the second light receiving element 17b. B
_{If 2} , then R ₁ = a ₁ + b ₁ R ₂ = a ₂ + b ₂ holds.

Here, the addition signal SUM and the subtraction signal DI
When FF is represented by the above components, SUM = R ₁ + R ₂ = (a ₁ + b ₁ ) + (a ₂ + b ₂ ) DIFF = R ₁ −R ₂ = (a ₁ + b ₁ ) − (a ₂ + b ₂ ). = B ₁ −b ₂ Here, if the reproduced signal S is defined as S = SUM−K × DIFF, then S = 2 (a ₁ + a ₂ ) + b ₁ + b ₂ −K (b ₁ −b ₂ ) Since the signal component is 2 (a ₁ + a ₂ ), the constant K should be determined so as to satisfy b ₁ + b ₂ −K (b ₁ −b ₂ ) = 0. That is, K = (b ₁ + b ₂ ) / (b ₁ −b ₂ ) ... (A).

As can be seen from FIG. 12, tan (θ _ka + θ _kb + (π / 4)) = b ₁ / b ₂ , so that b1 / b ₂ = (1 + tan (θ _ka + θ _kb )) / ( 1-tan (θ _ka + θ _kb )) (B).

Therefore, from the equations (A) and (B), K = 1 / tan (θ _ka + θ _kb ) (C)

As a result, if reproduction is performed using the reproducing circuit of FIG. 11 using the coefficient K shown in the equation (C), crosstalk will occur using the optical system of the conventional rewritable magneto-optical disk reproducing apparatus. It is possible to reliably reproduce the recorded information without any occurrence.

In this case, the method for optimizing the coefficient K is as follows: 1) Assuming that the fluctuation in the optical disk can be ignored, the Kerr rotation angles θ _ka and θ _kb are measured in advance and the coefficient K is set.

2) The signalless portions are provided at regular intervals in the optical disk, and the Kerr rotation angles θ _ka and θ _kb are measured in synchronization with this to set the coefficient K. 3) An auxiliary beam for measuring the Kerr rotation angle θ _K is provided separately from the reading beam, the Kerr rotation angles θ _ka and θ _kb are measured, and the coefficient K is set. Etc. are possible.

When θ _K is emphasized by the optical system, it is necessary to add this emphasis to the coefficient K. Other Modifications In each of the above embodiments, the magneto-optical recording material has been described, but the polarization state is not limited to the magneto-optical recording material, and the polarization state of the initial polarization state depends on the intensity of light to be irradiated or the temperature of the material layer. The present invention can be applied to any material that changes with respect to (for example, a photochromic material or the like).

Further, in each of the above embodiments, the laser light emitted from the laser diode 11 is emitted from the beam splitter 1.
Although the information recording surface of the optical disk DK was directly irradiated via the mirror 2, the objective lens 14 and the mirror 2, a polarizing plate is provided in the optical path between the laser diode 11 and the beam splitter 12 in order to improve linear polarization. The optical disc DK may be provided and irradiated onto the optical disc DK via a polarizing plate.

Furthermore, in each of the above embodiments,
Although the case where the readout light is linearly polarized light has been described, it may be configured to use elliptically polarized light. Also,
Since the polarization states are not limited to two types, the reproduction light having one polarization state may be separated from the reproduction light having a plurality of polarization states.

[0064]

According to the first aspect of the present invention, the polarization state change layer has an information recording surface corresponding to the intensity distribution of the read light which is linearly polarized light externally irradiated or the temperature distribution accompanying the irradiation of the read light. The first polarization state, which is the polarization state of the reflected light or the transmitted light in the first area in the upper read light spot, is changed to the reflected light or the transmitted light in the second area, which is the other area in the read light spot. Since it is changed so as to be different from the second polarization state, which is the second polarization state, it is necessary to receive only one of the read light having the polarization state of the first polarization state and the read light having the second polarization state. As a result, it becomes possible to reproduce only the information of the phase pits (recording information) recorded in either the first area or the second area in the reading light spot on the information recording surface.

According to the second invention, the read light having the first polarization state from the first region or the second polarization state from the second region, each of which is a part of the read light spot. It is possible to reproduce only the recorded information included in only one of the read light beams having the read light, and it is possible to reproduce the information having the high spatial frequency when there are a plurality of read light spots.

As described above, according to the present invention, a signal having a high spatial frequency can be read out with high resolution due to a large difference in the polarization rotation angle. Further, since the read light mask can be realized by only one layer, it is possible to realize a structure in which the magneto-optical layer is thin and a reflection film is provided. In this way, the Kerr ellipticity can be used more easily, and therefore, the circular deflection can be used as the incident light and the mask can be used as the reflectance changer. Therefore, the super-resolution optical disk of the present invention can also be reproduced by using a normal LD or CD pickup.

Further, the magneto-optical film can be made thin and a reflective film having a large thermal conductivity can be placed close to the medium to better mold the thermal mask.

[Brief description of drawings]

FIG. 1 is a sectional view showing a detailed structure of an optical disc in a first embodiment.

FIG. 2 is a diagram illustrating a principle of reproducing an optical disc according to an embodiment of the present invention.

FIG. 3 is a configuration diagram of a main part of the optical disc reproducing apparatus in the first embodiment.

FIG. 4 is an explanatory diagram of a reproducing operation according to the first embodiment.

FIG. 5 is an explanatory diagram of directions of partial magnetization and total magnetization in a ferrimagnetic material.

FIG. 6 is a diagram illustrating a change of a magnetization curve in a compensation point material.

FIG. 7 is a diagram for explaining the wavelength dependence of the Kerr rotation angle in the ferrimagnetic material.

FIG. 8 is a configuration diagram of a main part of an optical disc reproducing apparatus in a second embodiment.

FIG. 9 is a diagram for explaining the operation in the second embodiment.

FIG. 10 is a configuration diagram of a main part of an optical disk reproducing device according to a third embodiment.

FIG. 11 is a detailed configuration diagram of a reproducing circuit in the third embodiment.

FIG. 12 is a diagram illustrating an operation in the third embodiment.

FIG. 13 is an explanatory diagram of a conventional information reading principle.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical disc 2 ... Substrate (with phase pit) 3 ... Magneto-optical layer (GdFeCo layer) 3 '... Magneto-optical layer (TbFeCo layer) 4a ... Dielectric layer (SiN layer) 4b ... Dielectric layer (SiN layer) 5 ... Reflective layer (AlTi layer) 10 ... Optical disc reproducing device 11 ... Laser diode 12 ... Beam splitter 13 ... Mirror 14 ... Objective lens 15 ... Half wave plate 16 ... Beam splitter 17a ... First light receiving element 17b ... Second light receiving element 17 '... Light receiving element 18, 18a ... Regeneration circuit 30 ... Adder 31 ... First subtractor 32 ... Multiplier 33 ... Second subtractor A _H ... High temperature region A _M ... Medium temperature region A _L ... Low temperature region R ₁ ... First read signal R ₂ ... second read signal R '... read signal DIFF ... subtraction signal SUM ... addition signal MUL ... multiplied signal MG ₁ ... magnet LB ... reading light spot P ₁ to P ₄ ... phase pit T _C ... Curie temperature T _comp ... compensation temperature T _low ... low-temperature region the temperature T _high ... hot zone temperature T _R ... rt

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G11B 7/135 Z 7247-5D 7/24 511 7215-5D

Claims (2)

[Claims] 1. An optical recording medium in which information is held by phase pits, on the information recording surface corresponding to an intensity distribution of read light emitted from the outside or a temperature distribution accompanying the irradiation of the read light. Of the first polarization state of the reflected light or the transmitted light in the first area in the read light spot of the second polarized light or the transmitted light in the second area which is the other area in the read light spot. An optical recording medium comprising a ferrimagnetic material having a characteristic that the compensation temperature is higher than room temperature and lower than the Curie temperature. 2. An optical recording medium reproducing apparatus for reproducing recorded information from the optical recording medium according to claim 1, wherein the optical recording medium is irradiated with read light, and a light irradiation unit for irradiating the irradiated read light is used. Separation means for separating only one of the read light having the first polarization state and the read light having the second polarization state from the reflected light or the transmitted light of the optical recording medium, and the separation means. An optical recording device comprising: a light receiving unit that receives the reading light separated by the above and outputs it as a reading signal; and a reproducing unit that performs a reproducing operation of the recorded information of the optical recording medium based on the reading signal. Media playback device.