JP2990037B2 - Super-resolution optical head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a super-resolution optical head for high-density recording, and more particularly to a super-resolution optical head which removes side lobes from a super-resolution beam to reduce interference between recording marks. .

[0002]

2. Description of the Related Art There is a demand for an external storage device having both the high-speed accessibility of a magnetic disk used for an information processing device such as a computer and the storage capacity characteristic of an optical disk. It is evolving rapidly. As such a next-generation external storage device, optical recording is required from the viewpoint that it satisfies the conditions of high transfer rate, high-speed random access, and large capacity, is excellent in storage of the medium, and is non-contact and has excellent durability of the medium. Optical discs that use .NET are promising.

An optical system is at the core of the technology relating to an optical disk device. There is a demand for a high-precision optical system that can converge a converged light beam to the diffraction limit. As an optical head for this purpose, various super-resolution optical heads using a light-shielding band have been proposed, for example, in Japanese Patent Application Laid-Open No. H6-180853.

FIG. 5 shows an example of the configuration of a conventional optical head proposed in Japanese Patent Application Laid-Open No. 4-358328. The divergent light from the laser 11 as a light beam generation source enters the collimator lens 12 and becomes parallel light.
A light-shielding band 13 is arranged on the exit side of the collimator lens 12. A part of the parallel light that has exited from the collimator lens 12 is blocked by the light-shielding band 13, but the rest reaches the polarizing beam splitter 14 and passes therethrough. And 1 /
The light passes through the four-wavelength plate 15 and is converted from linearly polarized light to circularly polarized light. The circularly polarized light enters the objective lens 16 and is condensed at a predetermined position on an optical disk 17 disposed in front of the objective lens 16. In this manner, light beam irradiation for recording and reproducing information is performed.

When reading out information, the reflected light from the optical disk 17 is used. This reflected light becomes parallel light through the objective lens 16 and reaches the polarization beam splitter 14 via the quarter-wave plate 15. Here, it becomes a light beam whose polarization axis is converted by 90 degrees with respect to the incident polarized light, and the light beam is polarized by 90 degrees. This light beam is converged by the condenser lens 19. The condenser lens 19 has a numerical aperture NA of 0.1 to 0.2. A spatial filter 21 is arranged at the light condensing position of the condenser lens 19. The spatial filter 21 has a role of shielding the side lobe portion of the convergent beam as described below.

FIG. 6 shows the principle of processing of a light beam by a spatial filter. FIG. 7A shows the light amount distribution near the focal point of the light beam on the optical disk 17. As shown in FIG. 5, since the light-shielding band 13 is disposed behind the collimator lens 12, the central ray of the laser beam reaching the optical disk 17 is kicked. As a result, the total amount of light of the condensed beam on the optical disk 17 decreases. However, around this focusing position, the super-resolution beam 31 as shown by the solid line
Thus, there is an advantage that the beam diameter of e ^-12 is reduced.

However, a side lobe 33 is generated in the super-resolution beam 31 in addition to the main lobe 32 which contributes to high-resolution reading. Therefore, if information is reproduced by receiving the light as it is, interference occurs between the recording marks, and there is a problem that the bit error rate is increased in the case of digital recording. Therefore, as shown in FIG. 2B, the light is passed through a spatial filter 21 to remove the side lobes 33 of the super-resolution beam 31 and leave only the main lobe 32 as shown in FIG. 2C. .

Since the position of the spatial filter 21 becomes the focal position of the light beam, divergent light is incident on the optical sensor 34 disposed behind the spatial filter 21 and the information recorded on the optical disk 17 is read. .

[0009]

The diameter required for the proposed spatial filter 21 is calculated. The laser wavelength used as the light beam is 680 nm (0.68 μm), and the numerical aperture NA of the condenser lens 19 is 0.2. Then, the beam diameter of e ^-12 is represented by the following equations (1) and (2). Here, φ in equation (1) represents a normal beam diameter, and φ _{U in} equation (2) represents a beam diameter for a super-resolution beam. φ = 0.82 × λ / NA (1) φ _U = 0.85 × φ (2)

The diameter of the main lobe 32 depends on the size of the light-shielding band 13, but is about 85% of the normal beam converging diameter. Therefore, the diameter of the main lobe 32 is 2.3 μm from Expressions (1) and (2). Therefore, the optical axis direction of the condenser lens 19 in FIG.
The direction perpendicular to the axis direction and perpendicular to the paper surface in the figure is the X-axis direction,
Assuming that the vertical direction is the Y-axis direction, in order to remove the side lobe 33, the adjustment accuracy of the spatial filter 21 in the X and Y directions needs to be about 0.23 μm, which is 1 of the above value.

As described above, in the conventional optical system shown in FIG. 5, the spatial filter 21 is used to remove the side lobe 33 existing in the return light from the optical disk 17, but the mechanical adjustment thereof is not performed. There was a problem that it was extremely difficult. In addition, it is necessary to accurately set the size of the spatial filter 21 so as to remove only the side lobe 33 while leaving the main lobe 32 from the super-resolution beam 31,
Conventionally, this was realized by processing a nickel film by a method such as etching, but there was a problem that processing accuracy was not sufficient.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a super-resolution optical head capable of obtaining a recording / reproducing characteristic having a high optical modulation degree without performing position adjustment or processing of a spatial filter for removing a side lobe.

[0013]

According to the first aspect of the present invention, there are provided (a) a light beam generating source, and (b) a collimator lens which receives the light beam generated by the light beam generating source and converts the light beam into parallel light. (C) light-blocking means disposed behind the collimator lens to block only the center of the incident light beam; and (d) light beam lacking the center by the light-blocking means.
A first focusing means for focusing the beam to a predetermined position of the recording medium, and second focusing means for focusing the light beam reflected from the predetermined position described above (e), (to) this Second concentrator
The above-mentioned is applied to the filter material disposed
Irradiate the light beam reflected from the recording medium and calculate the ratio
Transmits light only in areas where relatively high power is irradiated
Form a spatial filter by changing to locations
Spatial filter forming means, and (g) forming the spatial filter.
The spatial filter formed by the
The super-resolution optical head is provided with an optical sensor for detecting the light beam condensed by the second light condensing means and passing through the spatial filter in the state of being arranged as it is.

That is, according to the first aspect of the present invention, when a side lobe of a light beam reflected from a recording medium such as an optical disk is removed by a spatial filter at a position where the side lobe is focused by the second focusing means, this light beam is collected. The position was irradiated with a predetermined light beam, and the irradiated area was changed to a light transmitting area to form a spatial filter. Therefore, the spatial filter can be formed by using part or all of the optical system of the super-resolution optical head, and there is no need to adjust the position of the spatial filter or perform mechanical processing.

Further, in the invention according to claim 1, the spatial filter has a functional thin film whose function is changed so that a portion irradiated with a light beam having a power equal to or higher than a predetermined value transmits the light beam. Features.

Here, the functional thin film is irradiated with a light beam having a power equal to or more than a certain value for a certain irradiation time for a certain irradiation time as described in claim 2 so as to be in a crystalline or non-crystalline state having different light beam transmittances. It may be a phase-change medium that changes, or a functional thin film that shields side lobes by other principles.

According to the third aspect of the present invention, the predetermined light beam is obtained from a light beam source when a mirror having a high reflectivity is arranged at that position instead of the recording medium, and is reflected by the reflecting mirror. Then, the light is collected by the second light collecting means.

That is, when it is required that the power of the light beam is somewhat strong in order to form a spatial filter, instead of using an actual recording medium having a low reflectivity, the reflectivity is set at that position. In this case, a mirror having a high power is arranged to obtain reflected light having higher power. As a result, the light beam can be efficiently used, and a spatial filter can be created using a light beam source such as a laser diode that is actually used.

According to a fourth aspect of the present invention, the mirror having a high reflectivity according to the fourth aspect of the present invention is a multi-phase film reflector, and the converging lens having a small numerical aperture has an aperture pupil having a stop of 95% of the incident beam. The above structure reflects the light beam condensed. As a result, the light beam can be efficiently used as in the case of the fourth aspect.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows the configuration of a super-resolution optical head according to an embodiment of the present invention. The divergent light from the laser 41 composed of a laser diode or the like enters the collimator lens 42 and becomes parallel light. Also in this embodiment, a light-shielding band 43 is arranged on the emission side of the collimator lens 42. A part of the parallel light that has exited the collimator lens 42 is blocked by the light-shielding band 43, but the rest of the light reaches the polarizing beam splitter 44, passes through it, passes through the quarter-wave plate 45, and then is linearly polarized Is converted into circularly polarized light. The circularly polarized light enters the objective lens 46 and is condensed at a predetermined position on an optical disc 47 disposed in front of the objective lens 46. In this manner, light beam irradiation for recording and reproducing information is performed.

When reading out information, the reflected light from the optical disk 47 is used. This reflected light becomes parallel light through the objective lens 46, and reaches the polarization beam splitter 44 via the 板 wavelength plate 45. Here, it becomes a light beam whose polarization axis is converted by 90 degrees with respect to the incident polarized light, and the light beam is polarized by 90 degrees. This light beam is converged by the condenser lens 49. As the condenser lens 49, one having a small numerical aperture NA of 0.1 to 0.2 and an aperture pupil having a stop of 95% or more of the incident beam is used. A spatial filter 51 is arranged at the light collecting position of the light collecting lens 49. The spatial filter 51 has a role of shielding the side lobe portion of the convergent beam. The light beam diverged through the spatial filter 51 enters the converging lens 52 and becomes convergent light,
The information converged on the optical sensor 53 and the information recorded on the optical disk 47 is read.

FIG. 2 shows the configuration of a spatial filter in the super-resolution optical head of this embodiment. The spatial filter 51 of the present invention is formed by forming a film such as a phase change medium whose light transmittance changes depending on, for example, a crystalline state and an amorphous state (amorphous). In this embodiment, a protective film 62 made of a composite film of silicon glass and zinc sulfide (SiO ₂ -ZnS) is formed on one surface of a glass substrate 61, and further, for example, germanium, antimony, tellurium (Ge)
A functional film 63 as a phase change medium made of an SbTe) film is formed. Finally, a protective film 64 made of a composite film of silicon glass and zinc sulfide is formed. In the drawing, the dashed line 66 indicates the direction in which the light beam travels.

FIG. 3 is for explaining the change of the functional film as a phase change medium in this spatial filter. In this figure, the horizontal axis represents the irradiation time (nS) of the laser beam, and the vertical axis represents the power (mW) of the laser beam. In this figure, the symbol A indicates a region where the functional film 63 is in an amorphous state, and the symbol B indicates an invariable region where no change occurs. Reference numeral C indicates a region where the functional film 63 is in a crystalline state, and reference numeral D indicates a state where a hole is opened due to melting or sublimation of the functional film 63, not a change of the functional film 63 itself.

From this figure, when the power of the laser beam as a light beam is increased to some extent and the spatial filter 51 of the present embodiment is irradiated with the power, the functional film 63 in the irradiated portion is irradiated.
Changes from the invariable region B to the amorphous region A. Therefore, if the material that blocks the light beam in the invariable region B and transmits the light beam in the amorphous region A is set as the functional film 63, only the portion where the power of the laser beam is relatively strong is transmitted. The spatial filter 51 can be obtained. That is, FIG.
As shown in (a), the power of the light beam of the main lobe 32 of the super-resolution beam 31 is larger than that of the side lobe 33. Therefore, if the level of the super-resolution beam 31 is appropriately adjusted, The spatial filter 51 that transmits only the central portion of the light beam corresponding to the lobe 32 can be created.

FIG. 4 shows how the spatial filter of this embodiment is created. A jig 72 is mounted on a main part 71 of the head in a state where an optical system part above the polarization beam splitter 44 of the super-resolution optical head shown in FIG. It is supposed to do. The reason why the spatial filter 51 is formed using the jig 72 in this manner is that the power of the return light from the optical disk 47 is relatively small.

That is, the reflectivity of a normal magneto-optical recording medium is 25% or less, and in the case of a disk using a phase-change medium, the reflectivity differs between the initialization stage and the recorded state. % And 7%. The amount of light reflected from the medium having such a low reflectance does not have sufficient power to form the spatial filter 51, and the light can escape from the invariable region B in FIG. Can not.

Therefore, in this embodiment, a jig 72 on which a reflection mirror 74 having a multilayer structure is arranged is used instead of the optical disk 47 shown in FIG. Then, the light beam passing through the polarizing beam splitter 44 and entering the jig 72 is focused on the reflection mirror 74 by using a collimator lens 75 having a numerical aperture NA of about 0.2. I have. Since the collimator lens 75 having a small numerical aperture NA is used as described above, the “kick” of the light beam is small, and the beam use efficiency can be improved.

The reflection mirror 74 of the jig 72 has a multilayer structure and has a reflectivity of almost 100%, so that the power of the light beam reaching the spatial filter 51 via the condenser lens 49 can be recorded or erased in a normal manner. The power can be increased to 4 to 14 times the power used in the above. When the power of the light beam is increased four times or more during the formation of the spatial filter 51 in this manner, a change from the invariable region B to the amorphous region A in FIG. 3 becomes possible.

When the functional film 63 of the spatial filter 51 is formed using the light source of the super-resolution optical head itself as described above, the jig 72 is removed, and information is read from and written to the optical disk 47 using the objective lens 46. Or erasure is performed. When information is reproduced, the transmitting portion (amorphous region A) of the light beam of the spatial filter 51 is formed by the main lobe 32, so that its position and size are accurate, and the super solution Image beam 31
Therefore, only the side lobe 33 can be reliably removed. Therefore, interference between recording marks in information read from the optical disk 47 is reduced, and information can be reproduced with the bit error rate sufficiently reduced.

Further, in the super-resolution optical head of this embodiment, the spatial filter 51 is formed in a state where the power of the light beam is made stronger than usual by using the jig 72. Characteristics do not change.

In the embodiment, the case where the present invention is applied to the optical disk 47 has been described. However, the super-resolution optical head of the present invention can be applied to any recording medium from which information can be obtained as reflected light. Is natural.

In the embodiment, the condensing lens 49 is
Although the numerical aperture NA is as small as 0.1 to 0.2 and the aperture pupil aperture is 95% or more of the incident beam, a functional thin film having no particular problem in light beam use efficiency and irradiation time is used. In this case, it is possible to use a device having characteristics that are inferior to the above, thereby achieving a reduction in cost and size of the device.

Further, in the embodiment, a special jig 72 is prepared for forming the spatial filter 51. However, depending on the functional thin film, the reflection of the actual recording medium can be utilized without using such a jig. Needless to say, it is also possible to create a spatial filter by using a member such as a special disk having a high reflectance instead.

Further, in the embodiment, the light beam passing through the spatial filter 51 is converged on the optical sensor 53 by the converging lens 52, but it is also possible to radiate the divergent light onto the optical sensor 53 as in the conventional case. is there.

[0036]

As described above, claims 1 to 4 are described.
According to the described invention, when removing the side lobe of the light beam reflected from the recording medium such as the optical disk by the spatial filter at the position where the side lobe is collected by the second focusing unit,
A predetermined light beam was applied to the light condensing position, and the irradiated area was changed to a light transmitting area to form a spatial filter. Therefore, the spatial filter can be formed by using a part or the whole of the optical system of the super-resolution optical head, and there is no need to adjust the position of the spatial filter or perform high-precision mechanical processing. The cost can be reduced by reducing the cost and improving the yield.

According to the third and fourth aspects of the present invention, instead of using an actual recording medium having a low reflectivity, a mirror having a high reflectivity is arranged at the position of the actual recording medium, and a reflection having a higher power is provided. I decided to create a spatial filter by obtaining light. This makes it possible to use the light beam efficiently, using a light beam source such as a laser diode that is actually used, in a shorter time, and without putting an excessive burden on the light beam source. It is possible to create a spatial filter.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a configuration of a super-resolution optical head according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of a spatial filter in the super-resolution optical head of the present embodiment.

FIG. 3 is a characteristic diagram showing a change in a functional film of a spatial filter used in the present embodiment.

FIG. 4 is a schematic configuration diagram showing how a spatial filter of the present embodiment is created using a jig.

FIG. 5 is a schematic configuration diagram showing a configuration of a conventionally proposed super-resolution optical head.

FIG. 6 is an explanatory diagram showing a principle of removing a side lobe of a spatial filter according to this proposal.

[Explanation of symbols]

 REFERENCE SIGNS LIST 31 super-resolution beam 32 main lobe 33 side lobe 41 laser 42 collimator lens (of super-resolution optical head) 43 light-shielding band 44 polarization beam splitter 45 quarter-wave plate 46 objective lens 47 optical disk 49 condenser lens 51 spatial filter 52 convergent lens 53 Optical Sensor 63 Functional Film 71 Head Constituent Body 72 Jig 74 Reflecting Mirror 75 Collimator Lens (of Jig)

Claims (4)

(57) [Claims] 1. A light beam source, a collimator lens for entering a light beam generated by the light beam source to collimate the light beam, and a central part of the incident light beam disposed behind the collimator lens. Light-shielding means for shielding light, first light-collecting means for condensing a light beam lacking a central portion by the light-shielding means at a predetermined position on a recording medium, and condensing the light beam reflected from the predetermined position Second
Irradiating the light beam reflected from the recording medium to the filter material disposed at the light condensing position of the second light condensing means, and irradiating a relatively strong portion of the light beam. And a spatial filter forming means for forming a spatial filter by changing only the spot to a light transmitting spot, and the spatial filter formed by the spatial filter forming means is arranged at the condensing position as it is, and of the focusing means comprises an optical sensor for detecting the light beam having passed through the spatial filter is condensed, wherein the spatial filter is a light beam of a predetermined value or more power
Function change so that the irradiated part transmits the light beam
1. A super-resolution optical head having a functional thin film that performs the following steps . 2. The functional thin film is a phase-change medium that changes to a crystalline or non-crystalline state having a different light beam transmittance by being irradiated with a light beam having a power of a certain value or more for a certain irradiation time or more. 2. The super-resolution optical head according to claim 1, wherein: 3. The predetermined light beam is obtained from the light beam source when a mirror having a high reflectivity is arranged at that position instead of the recording medium, and is reflected by the reflection mirror to form the second light beam. 2. The super-resolution optical head according to claim 1, wherein the super-resolution optical head is collected by an optical unit. 4. The mirror having a high reflectivity is a multi-phase film reflector. The converging lens having a small numerical aperture reflects an optical beam condensed by an aperture pupil having an aperture of 95% or more of an incident beam. 4. The super-resolution optical head according to claim 3, wherein: