JP2000123399A - Device for recording and reproducing information and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an information recording and reproducing device increased in recording density to an extent expectable from NA(numerical aperture) even when an NA is raised by using a solid immersion lens. SOLUTION: This information recording and reproducing device is provided with a light source 1, an object lens 6 for focusing the luminous flux from the light source 1 on a medium, a solid immersion lens 7 which is arranged between the object lens and the medium and raises a numerical aperture, and a light receiving part for receiving the luminous flux reflected from the medium, and eliminates a polarized light component perpendicular to linear polarized light of the luminous flux made incident on the medium before reproducing a signal. In this case, such a medium is preferable as information is recorded and reproduced according to differences of reflectance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing apparatus and method for recording / reproducing information using condensed light.

[0002]

2. Description of the Related Art In recent years, in a read-only optical disk optical system, a solid immersion lens has been used as a means for increasing the recording density.
(Solid Immersion Lens) is attracting attention. This is a technique for realizing a high numerical aperture (NA) using a hemispherical lens.

[0003]

According to a recent study by the present inventors, when a recording / reproducing optical system using a solid immersion lens reproduces information recorded due to a difference in reflectance on the surface of an optical disk, the reproduced signal contrast becomes NA. Turned out to be lower than expected. Therefore, even if the NA is increased using a solid immersion lens,
The recording density cannot be increased.

In view of the above problems, the present invention provides an information recording / reproducing apparatus and method capable of increasing the recording density to an extent expected from the NA even when the NA is increased using a solid immersion lens. With the goal.

[0005]

According to the present invention, in order to achieve the above object, a light source, an objective lens for condensing a light beam from the light source onto a medium, and an objective lens between the objective lens and the medium are provided. A solid immersion lens arranged to increase the numerical aperture, and a light receiving unit for receiving a light beam reflected from the medium, and reproducing a signal after removing a polarization component orthogonal to linearly polarized light in a light beam incident on the medium. And an information recording / reproducing apparatus for performing the above.

According to the present invention, a light source, an objective lens for condensing a light beam from the light source onto a medium, a quarter-wave plate disposed between the light source and the objective lens, A solid immersion lens arranged between a lens and the medium, which increases the numerical aperture, and a light receiving unit for receiving a light beam reflected from the medium, and a polarization component parallel to linearly polarized light emitted from the light source. The present invention also provides an information recording / reproducing apparatus for reproducing a signal after the reflected light beam is removed in an optical path from the quarter wavelength plate to the light receiving section.

Further, the present invention also provides an information recording / reproducing method for recording / reproducing information using the information recording / reproducing apparatus. According to the present invention, the light receiving unit further includes a prism, and the light receiving units are two light receiving units that respectively receive the light beams separated by the prism. The light receiving intensity of a component perpendicular to the linearly polarized light emitted from the light source is S1, and the linearly polarized light emitted from the light source is S1. It is preferable that the following conditions be satisfied, where S2 is the received light intensity of the component parallel to the above, and S is the reproduced signal intensity.

S = S1−ε × S2 (0 ≦ ε ≦ 3) It is preferable that the medium is a medium for recording and reproducing information based on a difference in reflectance.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, in the case where information recorded by the difference in reflectance on the surface of an optical disk as a medium is reproduced by a recording / reproducing optical system using a solid immersion lens, the reproduction signal contrast is expected from NA. Explain whether it will be lower than the As shown in FIG. 4, the basic configuration of a conventional information recording / reproducing apparatus is such that light emitted from a semiconductor laser as a light source 1 is converted into a parallel light beam by a collimating lens 2, and a recording / reproducing surface of an optical disk 8 is reproduced by an objective lens 6. Focus on A hemispherical solid immersion lens 7 is arranged near the focal point of the objective lens 6, and as a result, the NA can be increased. For details, for example, 1.Kino, Mansfield, "Solid Im
mersion Lens Photon Tunneling Microscope ", SPIE 155
6

FIG. 5 is an enlarged view of the vicinity of the solid immersion lens 7 shown in FIG. By appropriately selecting the refractive index of the solid immersion lens 7 and the NA of the objective lens 6, it is possible to satisfy NA> 1. When NA> 1, the light flux in the portion where NA is 1 or more becomes an evanescent wave.
Distance between the recording / reproducing surface and the bottom surface of the solid immersion lens 7 is λ / 4 to
It is necessary to approach λ / 10.

By doing so, the evanescent light seeping out from the bottom surface of the solid immersion lens 7 can be used for recording and reproducing information. As shown in FIG. 6, a guide groove for tracking servo is formed on the recording / reproducing surface of the optical disk 8, and a recording pit 16 having a difference in reflectance according to information is recorded thereon. When the converging spot 2 scans over this, a signal intensity as shown in FIG. 7 is obtained from the difference in reflectance between the portion A with the recording pit 16 and the portion B without the recording pit 16. This is the signal reproduction of the intensity modulation disk using the solid immersion lens 7.

When the solid immersion lens 7 is used, since the NA exceeds 1, the incident angle of the light beam impinging on the recording surface becomes very large. For example, if NA = 1.5 and the refractive index of a hemispherical solid immersion lens = 1.8, the maximum incident angle is 56.
It is as large as 4 °. In such a case, when linearly polarized light is incident, the reflectance of the p component and the s component of the reflectance of the light that strikes the recording surface is different, so that the polarization state of the reflected light is not preserved and the reflected light rotates. FIG. 8 is a diagram showing how this rotation of the polarization state is performed on the objective lens pupil 20. As can be seen from FIG. 8, even if the vibration surface 21 of the electric field of the incident wave is constant, the vibration surface 22 of the electric field of the diffracted wave rotates depending on the position on the objective lens pupil 20.

That is, even if the incident light is polarized in the X direction, the reflected light also has a polarized component of the Y component, so that the polarized light is distributed as shown in FIG. In addition, since the reflection phase difference is not constant on the pupil, strictly speaking, the light is not linearly polarized light but rather elliptically polarized light. That is, the rotation of the slightly elliptical polarized light is distributed on the objective lens pupil 20.
This tendency is emphasized as the NA increases.

This phenomenon that the polarization is disturbed is observed not only in the reflected light (zero-order diffracted light) but also in the diffracted light (including high-order diffracted light). A similar phenomenon occurs when the incident polarized light is circularly polarized light. That is, the reflected light and the reflected diffracted light from the surface of the optical disk 8 become elliptically polarized light due to the difference in the reflection phase and the reflectance between the p component and the s component. Therefore, when this light beam is viewed through a quarter-wave plate (λ / 4 plate) 4, the light beam is not completely linearly polarized, but the polarization is disturbed and distributed on the objective lens pupil as shown in FIG.

If the NA is, for example, about 0.5, λ / 4
After transmission through plate 4, it should be almost completely converted to linearly polarized light. However, when the solid immersion lens 7 is used, since the NA is very large, it is not converted into linearly polarized light for the above-described reason. As described above, the reproduced signal is reduced due to the polarization disorder. In the present invention, as shown in the following embodiments, a reproduced signal is improved by removing a signal component caused by polarization disorder or by taking a difference from a signal component of a polarization parallel to the incident polarized light. Let me.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Assuming that there is no polarization disturbance, let S1 be a signal component to which a light beam contributes, and let S2 be a signal component generated by the polarization disturbance. When the NA is small, no polarization disturbance occurs, so that only S1 is provided. In order to separate a signal component caused by polarization disorder, the following is performed. (Method 1: Linearly Polarized Light is Used for Incident Light) Hereinafter, description will be made with reference to FIG. The recording / playback surface of the optical disc 8
Illuminated with TE polarized light 18 or TM polarized light 19. Here, as shown in FIG. 6, the TE polarized light 18 is a polarized light in which the side wall of the recording pit 16 and the vibration plane of the incident electric field are parallel.
The TM polarized light 19 is, as shown in FIG.
The side wall 6 and the vibration plane of the incident electric field are polarized light perpendicular to each other.

The light beam reflected by the recording / reproducing surface is reflected by the beam splitter 3 or a half mirror. The reflected light includes a polarization component (main signal component) of the incident light and a component perpendicular to the polarization component (orthogonal component). This is separated by the polarizing beam splitter 9. There are two light receiving units, and the first light receiving unit 11 has a signal component of polarization parallel to the incident light, the second light receiving unit 1
2, a vertically polarized signal component is guided to it. The light intensity at the first light receiving unit 11 and the light intensity at the second light receiving unit 12 are S1 and S2, respectively.

Alternatively, the apparatus shown in FIG. 2 is used. Here, the recording / reproducing surface is illuminated with the TE polarized light 18 or the TM polarized light 19. A part of the light beam reflected by the recording / reproducing surface is reflected by the polarization beam splitter 9. This is the signal component of the polarization perpendicular to the incident light, which is S2. The light transmitted through the polarization beam splitter 9 is all signal components parallel to the incident polarized light. This is guided to the first light receiving unit 11 by the beam splitter 3 or the half mirror. This is S1. (Method 2: Using Circularly Polarized Light for Incident Light) The apparatus shown in FIG. 3 is used. The linearly polarized light emitted from the semiconductor laser which is the light source 1 is converted into circularly polarized light by the λ / 4 plate 4 and condensed on the recording / reproducing surface.

The reflected light is again converted into linearly polarized light orthogonal to the incident light by the λ / 4 plate 4. However, due to the above-mentioned disturbance of the polarization plane, the light is not completely linearly polarized light but becomes elliptically polarized light. The s component of the elliptically polarized light is divided by the polarizing beam splitter 4 and received by the first light receiving unit 11. This is S1
Becomes The p component is output from the beam splitter 3 to the second light receiving unit 1.
It is led to 2. This is S2 caused by signal disturbance.

In any case of the polarized light, the polarized light component which would not be generated if the NA is small is separated. A comparison will be made between the reproduction signal contrast when the component S2 due to the polarization disturbance separated as described above is removed from the total light amount, when the difference between S1 and S2 is obtained, and when the total light amount S1 + S2 is received. [First Embodiment] Consider a reproduced signal when a focused spot crosses a one-dimensional pit. The calculation model is shown in FIG. 9 and Table 1.
Shown in Since the guide groove does not contribute much to the signal characteristics, it is not considered here.

[0021]

Refractive index = 2.0 Air layer Refractive index = 1 Thickness = 50 nm ZnS-SiO2 Refractive index = 2.1 Thickness = 80 nm Ge2Sb2Te2 in crystalline state Refractive index = 4.2 + 3.5i Thickness = 20 nm Ge2Sb2Te2 in non-crystalline state Refractive index = 4 + 1.8i Thickness = 20 nm ZnS-SiO2 Refractive index = 2.1 Thickness = 20 nm Aluminum substrate Refractive index = 1 + 5i CT (1 + 2) described below indicates the reflected light. This is the reproduction signal contrast when all are integrated on the pupil. In a conventional detection system, this is used for a reproduced signal.

CT (1) is the reproduction signal contrast of S1, and CT (1-2) is the difference between S1 and S2. The calculation is based on K. Otaki et.al. "Reading Optical
ROM with Near Field of SIL ", Technical Digest of OD
S '98, 134-135 (1998). The definition of contrast is as follows. Reproduction signal contrast = (Imax + Imin) / (Imax-Imin) Imax = Absolute value of maximum amplitude of the reproduction signal Imin = Absolute value of minimum amplitude of the reproduction signal Here, when the conditions shown in Table 2 are set, the result is as follows. Table 3 below.

[0023]

[Table 2] Wavelength 600 nm NA 1.5 Groove cycle 360 nm Groove width 180 Air layer thickness 50 nm

[0024]

[Table 3] Incident polarized light CT (1 + 2) (%) CT (1) (%) CT (1-2) (%) TE polarized light 10.2 14.5 100 TM polarized light 18.4 26.1 100 yen Polarization 12.5 28.9 100 From these results, for any polarization, the signal contrast is improved in CT (1) or the differential signal CT (1-2) from which the polarization disorder has been removed. CT (1-2) is 100%
Is because the differential signal S1-S2 crosses zero. (See FIG. 10) The reason why the above result was obtained is considered as follows.

Consider circularly polarized light incidence in each of the above conditions.
The tendency is the same for linearly polarized light. In this case, the light reflected on the recording / reproducing surface becomes substantially linearly polarized light after passing through the λ / 4 plate 4. The signal amplitude of the polarization component in this direction is S1, and the polarization component orthogonal to this is S2. In the conventional optical system having a small NA, the signal amplitude is only S1, and the signal amplitude is S1.
2 is almost 0.

On the other hand, when NA = 1.5, the S2 component caused by the polarization disorder cannot be ignored and contributes to the signal. This is shown in FIG. FIG. 10 shows the reproduction signal contrast when the converging spot 17 crosses the one-dimensional recording pit 16. As shown in this figure, S2 is almost constant. Therefore, when the total light amount = S1 + S2, the contrast is lower than that in the case of S1 alone.

In this way, by removing the DC component,
The signal contrast is improved by the CT of the first embodiment.
(1). The reason why S2 is almost constant is that the polarization disorder component (the Y component in FIG. 8) in the reflectance of the crystal region.
And the component of the polarization disorder of the reflectance of the amorphous region (see FIG. 8)
This is because the difference with the Y component in the middle is small. [Second embodiment] If the configuration shown in FIG. 9 and Table 1 is adopted, and the air layer thickness is set to 25 nm among the conditions in Table 2, and the other conditions are the same as those in the first embodiment, the results are as shown in Table 4 below. It is as shown in.

[0028]

[Table 4] Incident polarization CT (1 + 2) (%) CT (1) (%) CT (1-2) (%) Circular polarization 28.1 42.3 79.2 CT (1) when the originating S2 component is removed, or CT (1-2) when the differential is taken
The signal contrast is improved. FIG. 11 is a diagram showing the signal intensity when the converging spot 17 crosses the recording pit 16 at this time. Again, since the component S2 due to the polarization disorder has a constant intensity, the signal contrast is reduced.

As described above, the degree of signal reduction due to polarization disorder is emphasized as NA increases. Further, the larger the air layer 15 is, the more emphasized it is. Therefore, NA and air layer 1
It is only necessary to determine whether to remove or take a differential according to the size of 5. For example, in the first embodiment, it is better to remove the S2 component. In this case, only one light receiving unit is required. In the second embodiment, it is better to take the difference between the S2 component and the S1 component. In this case, assuming that the signal reproducing system has two light receiving sections, a signal of S = S1−ε × S2 (0 ≦ ε ≦ 3) may be used as a reproduction signal. Where ε
Is the gain of the light receiving unit of S2 (channel 2) with respect to the light receiving unit of S1 (channel 1). Of course, when ε = 0, it corresponds to the case of removing a component caused by polarization disorder.

Instead of receiving S2 and subtracting it from S1, the DC component may be electrically removed from S1 + S2 or S1. In this case, only one light receiving unit is required. The DC component to be removed can be calculated in advance. The signal S desirably has a symmetric polarity, that is, DC component = 0. In such a case, the position of the recording mark can be easily determined. To obtain such a signal, ε = 0.9 in the example shown in FIG.
In the example shown in FIG. 11, ε = 2 may be set. However, even when S2 is smaller than S1, the DC component can be set to 0 by increasing the coefficient ε, but the noise also increases at the same time. Therefore, it is meaningless to make ε too large, and the upper limit of ε is preferably about 3.

In the present invention, the reproduction signal contrast is reduced by the polarization disturbance peculiar to the high NA optical system.
It has been shown that the reproduction signal contrast is improved by removing the signal component caused by the polarization disorder or by taking the differential signal. As an example of the means, in the present invention, when the incident light is linearly polarized light, a polarization beam splitter is used. When the incident light is circularly polarized light, the signal light is orthogonalized by using a combination of a λ / 4 plate and a polarization beam splitter. Separated into polarized light components.

Of course, other means such as using a polarizing plate instead of the polarizing beam splitter may be used. The important thing is
This is to separate the polarization disturbance generated when the NA becomes large. In addition, a supplementary explanation will be given to the expression “polarization disorder” used in this specification. On the recording / reproducing surface of the optical disk 8, polarized light parallel to the side wall of the recording pit 16 (TE polarized light 1)
8), when the light flux reflected by the recording / reproducing surface is polarized perpendicular to the recording pit 16 side wall (TM polarized light 1).
9) causes polarization disorder.

In the case of circularly polarized light, it is somewhat confusing, but it is as follows. When circularly polarized light is incident on the optical disk 8,
For example, as shown in FIG. 3, the light enters the polarization beam splitter 9 with p-polarized light, is converted into circularly polarized light by the λ / 4 plate 4, and returns to s-polarized light by the λ / 4 plate 4 on the return path. Is a p-polarized light orthogonal to the s-polarized light.

Conversely, when the s-polarized light enters the polarization beam splitter 9 on the outward path, the s-polarized light is disturbed after transmission through the polarization beam splitter 9 on the return path.

[0035]

As described above, according to the present invention, it is possible to provide an information recording / reproducing apparatus and method capable of increasing the recording density to an extent expected from NA even when the NA is increased using a solid immersion lens. It is now possible.

[Brief description of the drawings]

FIG. 1 shows the device according to the invention when reproducing with linearly polarized light.

FIG. 2 shows the device according to the invention when reproducing with linearly polarized light.

FIG. 3 shows the device according to the invention when reproducing with circularly polarized light.

FIG. 4 is a diagram showing a conventional optical disk recording / reproducing optical system.

FIG. 5 is an enlarged view near a solid immersion lens.

FIG. 6 is a diagram in which a focused spot scans over a recording pit.

FIG. 7 is a diagram showing a reproduction signal.

FIG. 8 is a diagram showing a distribution of polarization of reflected light as viewed on an objective lens pupil.

FIG. 9 is a diagram illustrating a model according to an embodiment;

FIG. 10 is a diagram illustrating a reproduction signal intensity when reproduction is performed using circularly polarized light in the first embodiment.

FIG. 11 is a diagram illustrating a reproduction signal intensity when reproduction is performed using circularly polarized light in the second embodiment.

[Description of sign]

 1: light source 2: collimating lens 3: beam splitter 4: 1/4 λ plate 5: galvanometer mirror 6: objective lens 7: solid immersion lens 8: optical disk 9: polarization beam splitter 10: light receiving unit 11: first light receiving unit 12: Second light receiving unit 13: Vibration surface of electric field perpendicular to the paper surface 14: Vibration surface of the electric field parallel to the paper surface 15: Air layer 16: Recording pit 17: Focusing spot 18: Vibration surface of incident electric field (TE polarization) 19: Vibration plane of incident electric field (TM polarization) 20: Objective lens pupil 21: Vibration plane of electric field of incident wave 22: Vibration plane of electric field of diffracted wave 23: ZnS-SiO2 24: Ge2Sb2Te2 in crystalline state 25: Ge2Sb2Te2 in non-crystalline state 26: Aluminum substrate 27: Vibration state of electric field of circularly polarized light

Claims (6)

[Claims] 1. A light source, an objective lens for condensing a light beam from the light source onto a medium, a solid immersion lens arranged between the objective lens and the medium to increase the numerical aperture, and reflecting from the medium An information recording / reproducing apparatus, comprising: a light-receiving unit for receiving the light beam; and reproducing a signal after removing a polarization component orthogonal to linearly polarized light from the light beam incident on the medium. 2. A light source, an objective lens for condensing a light beam from the light source onto a medium, a solid immersion lens disposed between the objective lens and the medium to increase the numerical aperture, and reflecting from the medium. A prism that separates the separated luminous flux into a component parallel to the linearly polarized light incident on the medium and a vertical component, and two light receiving units that respectively receive the luminous fluxes separated by the prism. An information recording / reproducing apparatus that satisfies the following conditions, where S1 is the received light intensity of the component parallel to the incident linearly polarized light, S2 is the received light intensity of the component perpendicular to the linearly polarized light entering the medium, and S is the reproduced signal intensity. . S = S1−ε × S2 (0 ≦ ε ≦ 3) 3. A light source, an objective lens for condensing a light beam from the light source onto a medium, a quarter-wave plate disposed between the light source and the objective lens, the objective lens and the medium And a solid immersion lens that increases the numerical aperture, and a light receiving unit that receives a light beam reflected from the medium, and a polarization component parallel to linearly polarized light emitted from the light source,
An information recording / reproducing apparatus that reproduces a signal after the reflected light flux is removed in an optical path from the quarter-wave plate to the light receiving unit. 4. A light source, an objective lens for condensing a light beam from the light source onto a medium, a quarter-wave plate disposed between the light source and the objective lens, the objective lens and the medium A immersion lens that increases the numerical aperture, a prism that separates a light beam reflected from the medium into a component that is perpendicular to linearly polarized light emitted from the light source and a component that is parallel to the polarized light, and And two light receiving portions for receiving the separated light beams, respectively, wherein S1 is a light receiving intensity of a component perpendicular to the linearly polarized light emitted from the light source, S2 is a light receiving intensity of a component parallel to the linearly polarized light emitted from the light source. An information recording / reproducing apparatus that satisfies the following conditions when the signal strength is S. S = S1−ε × S2 (0 ≦ ε ≦ 3) 5. The medium according to claim 1, wherein said medium is a medium for recording and reproducing information by a difference in reflectance.
An information recording / reproducing device according to the above. 6. An information recording / reproducing method for recording / reproducing information using the information recording / reproducing apparatus according to claim 1.