JP3083894B2 - Optical playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical reproducing apparatus for optically reproducing data from a recording medium on which predetermined data is recorded.

[0002]

2. Description of the Related Art Conventionally, the following recording apparatuses have been developed to record a large amount of data on a recording medium used in such a reproducing apparatus.

For example, a perpendicular magnetization film (not shown) of a magneto-optical recording medium 2 used in a reproducing optical system (see Japanese Patent Application No. 2-322030) as shown in FIG.
A plurality of marks (ie, magnetic domains) 4 whose magnetization directions are reversed.
Are formed in parallel at a predetermined interval in the track width direction, and data encoded corresponding to the interval between the magnetic domains 4 is recorded. In the figure, a pair of magnetic domains 4
Only shown. Further, a mark set 6 including the plurality of magnetic domains (that is, marks) 4 is formed in the perpendicular magnetization film of the magneto-optical recording medium 2 in the track length direction. Other correspondingly encoded data is recorded. That is, the perpendicular magnetization film of the above-described magneto-optical recording medium 2 has a track width direction and a length direction.
Different data are recorded respectively, and as a result, an improvement in recording density has been achieved. Next, a method of reproducing data from such a magneto-optical recording medium 2 will be described with reference to FIG.
Description will be made with reference to (a) and (b).

[0006] As shown in FIG. 6 (a), a laser beam emitted from a laser light source (not shown) is converted into linearly polarized light by transmitting through a polarizer 8. This linearly polarized laser beam is focused on the magneto-optical recording medium 2 via the objective lens 10.

The perpendicular magnetic film of the magneto-optical recording medium 2 has a characteristic of rotating the polarization direction of a laser beam passing through the perpendicular magnetic film in a predetermined direction by a magneto-optical effect (Faraday effect). Rotation angle at this time (θ _F )
Is called Faraday rotation angle.

More specifically, as shown in FIG.
When the incident direction of the laser beam and the direction of magnetization are the same (that is, when the laser beam passes through the portion of the pair of magnetic domains 4), the polarization direction (Y) of the laser beam rotates clockwise by + θ _F , while When the direction of incidence is different from the direction of magnetization (that is, the direction of transmission through a portion other than the magnetic domain 4), the polarization direction (Y) of the laser beam rotates counterclockwise by −θ _F.

[0007] The two laser beams transmitted through the pair of magnetic domains 4 and each having the polarization direction (Y) rotated by + θ _F are applied to the analyzer 14 via the objective lens 12. The analyzer 14 has a function of extracting the polarized components of the two irradiated laser beams in the same plane (that is, in the transmission axis of the analyzer 14) and causing them to interfere with each other. here,
Assuming that the interval between the pair of magnetic domains 4 for rotating the polarization direction (Y) by + θ _F is (d), the interference condition of the laser beam is: d sin θ = ± mλ (1) where θ = x / D m; λ: coherent light wavelength D: distance between perpendicular magnetization film and observation surface x: position on observation surface

As a result, the interference light formed via the analyzer 14 is converted by the photodetector 16 as an observation surface into the following equation (1).
Is observed. And
The interval between the ± 1st order maxima of this optical interference pattern is
The detected data is detected as the interval information between the magnetic domains 4 whose magnetization directions are inverted, and predetermined data is reproduced.

[0009]

By the way, the photodetector 1
6, the position of the ± first-order maximum value detected as information on the distance between the magnetic domains 4 (ie, marks) is: dsin θ = λ λ; coherent light wavelength

Is defined by Therefore, it can be seen that when the distance between the pair of magnetic domains 4 constituting the mark set 6 is reduced, the angle (θ) corresponding to the position of the ± primary maximum value increases. That is, there is a problem that a ± 1st order maximum value is generated at a position beyond the light receiving angle determined by the NA of the objective lens 12 and data cannot be reproduced. For this reason, the distance between magnetic domains that can be formed on the magneto-optical recording medium 2 cannot be reduced to a predetermined value or less, and as a result, a problem that improvement in recording density is not achieved is caused.

The present invention has been made in order to solve such a problem, and an object of the present invention is to reverse the direction of magnetization of a magneto-optical recording medium to a magnetic domain (ie, mark) in which predetermined data is recorded. By simultaneously irradiating laser beams having different phases from each other and detecting the light intensity formed through these marks, even if the interval between the marks is extremely small, the encoding is performed in accordance with the interval between the marks. An object of the present invention is to provide an optical reproducing apparatus capable of reproducing data with high accuracy.

[0012]

SUMMARY OF THE INVENTION In order to solve such a problem, the present invention is directed to a space between a pair of marks arranged in a track width direction on a magneto-optical recording medium and having reversed magnetization directions. An optical reproducing apparatus for irradiating a reproducing laser beam to a magneto-optical recording medium on which encoded data is recorded and optically reproducing data,

A laser beam for reproduction in which a half of the laser beam has a phase difference of π or an odd multiple thereof is applied to the pair of marks of the magneto-optical recording medium while simultaneously irradiating portions having different phase differences with each other. Scanning means for sequentially scanning in the longitudinal direction,

[0014] By scanning the pair of marks, two polarization components having different phase differences of the reproducing laser beam provided with the magneto-optical effect are taken out on the same plane, and a polarization means for interfering with each other is provided. By detecting the interference pattern given by the means,
Reproducing means for reproducing data from the magneto-optical medium.

[0015]

A reproducing laser beam in which half of the laser beam has a phase difference of π or an odd multiple thereof is irradiated by a scanning means onto a pair of marks recorded on the magneto-optical recording medium at portions having different phase differences. Then, scanning is sequentially performed in the length direction of the track, and a magneto-optical effect corresponding to the direction of magnetization is provided. The two polarized components having different phases of the reproducing laser beam having the magneto-optical effect are extracted in the same plane by the polarization means and made to interfere with each other. Then, this interference is detected by the reproducing means, and the data is reproduced from the magneto-optical recording medium.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical reproducing apparatus according to an embodiment of the present invention will be described below with reference to FIGS. The optical reproducing apparatus of this embodiment is provided with a phase plate 20 for simultaneously focusing two reproducing laser beams having different phases on the magneto-optical recording medium 18. Prior to the description of the present embodiment, characteristics of the phase plate 20 will be described with reference to FIGS. FIG. 2 is a principle diagram for explaining the characteristics of the phase plate 20.

As shown in FIG. 2, the first objective lens 22
The incident-side focal position Y ₁ of the phase plate 20 is provided. The phase plate 20 is an odd multiple of π with respect to the working wavelength (λ) so that the phase of the laser beam passing through the other half is changed by π with respect to the phase of the laser beam passing through the other half. A thin film having a thickness giving a phase difference is deposited. The material of the deposition film 24 is, for example, ZnS,
MgF and the like are preferable, but not limited thereto. Note that the direction in which the phase plate 20 is divided by the vapor-deposited film 24 is the direction of the magneto-optical recording medium 18 (FIG.
(See Marks) in the direction of arrangement of the magnetic domains (that is, marks). As a result, the phase of the half laser beam of the laser beam transmitted through the phase plate 20 changes by π with respect to the other half.

A pair of marks having magnetizations reversed with respect to the other magnetization directions, that is, a magnetic domain 26 (the width of the magnetic domain is b, b) is provided at the emission-side focal position Y ₂ of the first objective lens 22.
A magneto-optical recording medium 18 (see FIG. 1) in which the distance between these magnetic domains is defined as d is provided (FIG. 2 shows only a pair of magnetic domains 26). The data is encoded and recorded in accordance with the distance between the magnetic domains 26. Laser beam transmitted through the phase plate 20 and the first objective lens 22, at the exit side focal position Y _2, the complex amplitude A (u) is,

[0019]

(Equation 1) Given by 2a is the width of the phase plate 20. As a result,

[0020]

(Equation 2) Becomes The intensity distribution I (u) is

[0021]

(Equation 3)

## EQU1 ## Therefore, the laser beam transmitted through the phase plate 20 and the first objective lens 22, at the exit side focal position Y _2, has an amplitude distribution and intensity distribution as shown in FIG. As is apparent from the figure, the amplitude of the laser beam on the emission side focal position Y ₂ is reversed, the intensity distribution has a bimodal. That is, at the emission side focal position Y ₂ ,
The laser beam has a characteristic that the phase difference becomes two beam spots shifted from each other by π. Hereinafter, the two laser beams whose phases are shifted from each other by π are referred to as phase-shifted light. Next, such phase-shifted light
The case where the magnetic domains 26 are irradiated will be described. Hereinafter, for the sake of simplicity, it is assumed that a plane wave having the above-described characteristics is incident on the pair of magnetic domains 26.

The phase-shifted light provided with the magneto-optical effect by the pair of magnetic domains 26 is converted into a second objective lens 28
It is guided to the observation position Y ₃ via. This observation position Y ₃
, An analyzer (not shown) is arranged, for example. This analyzer has a function of extracting the polarization components of two laser beams transmitted through the pair of magnetic domains 26 and the second objective lens 28 in the same plane (that is, in the transmission axis of the analyzer) and causing them to interfere with each other. ing. As a result, the observation position Y
₃ , an interference pattern having a complex amplitude distribution P (x ₀ ) and an intensity distribution I _c (x ₀ ) corresponding to the interval between the pair of magnetic domains 26 is formed. The complex amplitude distribution P (x ₀ ) at this observation position Y ₃ is

[0024]

(Equation 4) Becomes The intensity distribution I (x ₀ ) is

[0025]

(Equation 5) (See FIG. 4A). On the other hand, for comparison, the intensity distribution I _c of diffracted light when the laser beam is illuminated with a normal plane wave without phase shift (conventional method)
(X ₀ ) is I _c (x ₀ ) = sinc ² (Bp / 2) · cos ² (D
p / 2) (see FIG. 4B). It should be noted that in FIG.
6 and the distance d between the magnetic domains 26 are given by d = mb

The case where m = 1.2, 1.5 and 2.0 is shown respectively. Note that m corresponds to the interval between the magnetic domains. That is, if b = 1 μm, d = 1.2, 1.5, and 2.0 μm from d = mb.

As a result of the above, in the conventional method (see FIG. 4 (b)), the error occurs in a range that cannot be detected due to the limitation of the NA of the second objective lens 28 (in this case, it is assumed that NA = 0.5). The position of the primary maximum value is determined by using the phase shift method to determine the NA of the second objective lens 28.
(See FIG. 4A).

Specifically, when the distance between the magnetic domains 26 is narrowed as described above (for example, 1.2 μm, 1.5 μm,
μm), the maximum value position can be concentrated with high light intensity within the range of the NA of the second objective lens 28. By using the phase shift method as described above, a minute change in the magnetic domain interval, which cannot be detected by the conventional method, can be detected with high accuracy. This means that the recording density of the magneto-optical recording medium 18 (see FIG. 1) is improved.

Hereinafter, the optical reproducing apparatus of this embodiment provided with the phase plate 20 having the above-described characteristics will be described with reference to FIGS. In the description of the present embodiment, the same components as those described above are denoted by the same reference numerals and description thereof will be omitted. FIG. 1 schematically shows the entire configuration of a transmission type optical reproducing apparatus according to the present embodiment.

As shown in FIG. 1, first, the magneto-optical recording medium 18 is set in an optical reproducing apparatus. On a perpendicular magnetization film (not shown) of the magneto-optical recording medium 18, a pair of marks (that is, magnetic domains) 26 whose magnetization directions are reversed are formed in parallel at predetermined intervals in the track width direction. Data encoded corresponding to the interval between the magnetic domains 26 is recorded. Further, a mark set 30 including a pair of magnetic domains (that is, marks) 26 is formed in the perpendicular magnetization film of the magneto-optical recording medium 18 in the track length direction. Other correspondingly encoded data is recorded. That is, different data is recorded on the perpendicular magnetization film of the magneto-optical recording medium 18 in the track width direction and the length direction, respectively.

A reproducing laser beam emitted from a semiconductor laser (not shown) is applied to a phase plate 20, and the phase plate 20 causes the phase of the reproducing laser beam in half to be π with respect to the other half. Be changed. The reproducing laser beam (that is, reproducing phase-shifted light) to which optical characteristics are given by the phase plate 20 is applied to the magneto-optical recording medium 18 via the first objective lens 22 and has a phase difference of π with each other. The two beam spots are shifted and simultaneously focused. Then, when these two beam spots are applied to the pair of magnetic domains 26 described above, the magnetic domains 26 provide the magneto-optical effect described above.
The phase shift light for reproduction having magneto-optical characteristics is applied to the analyzer 32 via the second objective lens 28.

The transmission axis of the analyzer 32 is a pair of magnetic domains 2
It is arranged so as to be perpendicular to the polarization direction of the phase-shifted light for reproduction, which transmits a magnetic domain other than 6 and has a predetermined magneto-optical effect. Therefore, the analyzer 32 can only output the respective polarization components of the phase shift light for reproduction given the magneto-optical effect via the pair of magnetic domains 26 in the same plane (that is, in the same plane).
It has a function of taking out light to the inside of the transmission axis of the analyzer 32 and causing it to interfere with each other.

As a result, interference light having an intensity distribution as shown in FIG. 4A is generated. The interference light is received by the photodetector 34 and, for example, by detecting the ± first-order maximum value thereof, the data in the track width direction encoded corresponding to the interval between the pair of magnetic domains 26 is reproduced. be able to.

When data recorded in the track length direction is reproduced, the phase shift light for reproduction is sequentially applied to the mark set 3.
It is performed by irradiating 0 and detecting a change in the maximum value or the minimum value of the interference light that changes according to the interval between the mark sets 30.

As described above, in the optical reproducing apparatus of the present embodiment, as shown in FIG. 4A, even if the magnetic domain interval (d) is narrowed, the maximum value position of the interference light is set to the second position. Objective lens 2
In the range of 8 NAs, it is possible to concentrate with high light intensity. As a result, a minute change in the magnetic domain interval, which cannot be detected by the conventional device, can be detected with high accuracy. Therefore, the recording density of the magneto-optical recording medium 18 can be improved.

While such reproduction is being performed,
It goes without saying that the focus / tracking servo works so as to converge the optimal phase shift light on the track of the magneto-optical recording medium 18. Also, the present invention
The present invention is not limited to the configuration of the embodiment described above, and can be applied to, for example, a reflection type optical reproducing apparatus as shown in FIG.

Hereinafter, a reflection type optical reproducing apparatus according to a modification will be described with reference to FIG. In the description of the present modification, the same components as those in the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The reproducing laser beam emitted from the semiconductor laser 36 is incident on the above-mentioned phase plate 20 via the collimator lens 38. The phase-shifted light for reproduction transmitted through the phase plate 34 then enters the polarization beam splitter 40. The polarization beam splitter 40 has a characteristic of transmitting a component (P component) oscillating in a direction parallel to the incident surface and reflecting a component (S component) oscillating in a direction perpendicular to the incident surface. The phase shift light for reproduction formed by the phase plate 20 used in the present embodiment has only a relatively phase difference π, and its polarization direction does not change at all. Therefore, the phase shift light for reproduction that has entered the polarization beam splitter 40 transmits only its P component, and
The light enters the wave plate 42. The phase shift light for reproduction that has entered the quarter-wave plate 42 is converted from linearly polarized light into circularly polarized light,
The light is focused on the pair of magnetic domains 26 of the magneto-optical recording medium 18 via the objective lens 44. The phase shift light for reproduction when condensed on the magneto-optical recording medium 18 has an amplitude distribution and an intensity distribution as shown in FIG.

The reflected phase-shifted light for reproduction to which the magneto-optical effect (Kerr effect) is given by the pair of magnetic domains 26 of the magneto-optical recording medium 18 is again regulated by the objective lens 44 into a parallel light beam, and the quarter-wave plate 42. When transmitted through the quarter-wave plate 42, the polarization plane of the reflected phase-shifted light for reproduction is converted into linearly polarized light rotated by 90 ° from the first linearly polarized light. Therefore, the reflected phase-shifted light for reproduction is reflected by the polarization beam splitter 40 and enters the analyzer 32. The analyzer 32 has a function of extracting the respective polarization components of the reflected phase-shifted light for reproduction into the same plane (that is, within the transmission axis of the analyzer 32) and causing them to interfere with each other. Therefore, interference light having an intensity distribution as shown in FIG. 4A is generated. This interference light is received by the photodetector 34 and its ± first-order maximum value is detected, whereby data in the track width direction encoded corresponding to the interval between the pair of magnetic domains 26 can be reproduced. it can. Note that the reproduction of data in the track length direction is the same as that of the above-described transmission type reproducing apparatus, and thus the description is omitted.

As described above, also in the reflection type optical reproducing apparatus of this modification, even if the magnetic domain interval (d) is narrowed, the position of the maximum value of the interference light is kept within the range of the NA of the objective lens 44. It can be concentrated by light intensity. As a result, a minute change in the magnetic domain interval, which cannot be detected by the conventional device, can be detected with high accuracy. Therefore, the recording density of the magneto-optical recording medium 18 can be improved. As means for forming the transfer shift light, a TEM of a laser beam is used.
Various means such as selectively taking out and using the ₀₁ mode are possible.

[0041]

According to the optical reproducing apparatus of the present invention, two beam spots having different phases are simultaneously focused on a magneto-optical recording medium, and the intensity distribution of interference light from a plurality of magnetic domains (marks) is detected. As a result, it is possible to reproduce data encoded corresponding to the distance between magnetic domains with high accuracy. As a result, the magnetic domain interval formed on the magneto-optical recording medium can be made narrower than before, so that the recording density can be improved.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an entire transmission type optical reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a principle diagram for explaining characteristics of a phase plate used in the optical reproducing apparatus of FIG. 1;

FIG. 3 is a diagram showing an amplitude distribution and an intensity distribution of a laser beam when the laser beam is condensed at an emission-side focal position shown in FIG. 2;

FIG. 4A is a diagram illustrating a light intensity distribution when a phase shift method is used, and FIG. 4B is a diagram illustrating a light intensity distribution when a phase shift method is not used.

FIG. 5 is a view schematically showing an entire reflection type optical reproducing apparatus according to a modification of the present invention.

FIG. 6A is a diagram schematically showing the entirety of a conventional optical reproducing apparatus, and FIG. 6B is a diagram showing the polarization of the laser beam corresponding to the relationship between the incident direction of the laser beam and the direction of magnetization. The figure which shows the state in which the rotation direction of a direction changes.

[Explanation of symbols]

Reference numeral 18: magneto-optical recording medium, 20: phase plate, 22: first objective lens, 32: analyzer, 34: photodetector.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 11/105

Claims (1)

(57) [Claims] 1. A reproducing laser on a magneto-optical recording medium on which data encoded in accordance with the interval between a pair of marks whose magnetization directions are reversed in the track width direction on the magneto-optical recording medium is recorded. An optical reproducing apparatus for reproducing data optically by irradiating a beam with a reproducing laser beam in which half of the laser beam has a phase difference of π or an odd multiple thereof, Scanning means for sequentially scanning the pair of marks in the longitudinal direction of the track while simultaneously irradiating portions having different phase differences from each other; and the reproducing laser provided with a magneto-optical effect by scanning the pair of marks. Polarizing means for extracting two polarized components having different beam phase differences in the same plane and interfering with each other, and detecting an interference pattern given by the polarizing means And by an optical reproducing apparatus comprising: a reproduction means for reproducing data from the magneto-optical medium.