JPH08315420A - Reproducing method for optical recording medium and reproducing device therefor - Google Patents

Abstract

PURPOSE: To sufficiently color a positive photochromic mask layer and to improve an ultra-resolution effect by suppressing the temp. rise by irradiation with a colored light beam in reproduction of an ultra-resolution optical recording medium having this mask layer. CONSTITUTION: The spot shape of a colored light beam spot 2 is formed into a shape larger than a reproducing light beam spot 1 in a track width direction and longer than the track width direction in the longitudinal direction of tracks at the time of coloring the mask layer by irradiating the mask layer while scanning the mask layer with the colored light beam spot 2 prior to the irradiation with a reproducing light beam spot 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing method and a reproducing apparatus for an optical recording medium utilizing the super-resolution effect.

[0002]

2. Description of the Related Art The recording density in optical recording is generally limited by the size of the laser spot irradiated on the optical recording medium, but in recent years, an effective spot smaller than the laser spot determined by the diffraction limit of light is used. Research on high-density recording / reproducing by so-called super-resolution technology has been actively conducted. For example, a super-resolution technique using a mask layer and utilizing a decrease in light absorption of a mask layer portion corresponding to a part of a beam spot has been studied. As such a super-resolution technique, JP-A-5-242524 and JP-A-5-266478 disclose examples in which a reverse photochromic spiropyran is used for a mask layer. Further, JP-A-6-75315 discloses an example in which both a positive photochromic material and an inverse photochromic material are used for a mask layer. Here, the positive photochromic property refers to the reactivity in which the coloring reaction occurs in the photon mode and the thermal decolorization reaction occurs, and the inverse photochromic property refers to the reactivity in which the coloring reaction thermally occurs and the decolorization reaction occurs in the photon mode. Reactivity as it happens.

[0003]

The above super-resolution technique is
Although it is considered to be an effective technique for reproducing information recorded at high density, it has the following problems.

When the reverse photochromic mask layer is used, the mask layer is usually in a colored state, that is, in a state where the transmittance is low, and when the reproducing light is focused and irradiated on the mask layer in this state, it is erased by a photon mode reaction. Cause a reaction,
The transmittance is improved and the information on the recording layer is read by the super-resolution effect. However, due to the reproduction light, the photon mode decoloring reaction and the coloring reaction simultaneously occur due to the temperature rise of the mask layer. Therefore, the transmittance of the mask layer is insufficiently reduced, and the super-resolution effect is reduced.

When a positive photochromic mask layer is used, the mask layer is usually in a decolored state, that is, in a state where the transmittance is high. Irradiate. The irradiation of such reproducing light causes a color erasing reaction in the mask layer, the transmittance of the mask layer is lowered, and information on the recording layer can be reproduced.
Therefore, it is necessary to irradiate the colored light beam to color the mask layer prior to the reproduction light beam.However, when such a colored light is irradiated to the mask layer, the colored light beam is simultaneously irradiated with the coloring reaction in the photon mode. Due to this, the temperature of the mask layer rises and a decoloring reaction of the mask layer occurs, which causes insufficient coloring, and there is also a problem that the super-resolution effect is insufficient.

An object of the present invention is to reproduce an optical recording medium using such a positive photochromic mask layer,
It is an object of the present invention to provide a reproducing method and a reproducing apparatus for an optical recording medium, which can suppress the temperature rise due to irradiation of a colored light beam and can sufficiently color the mask layer to improve the super-resolution effect.

[0007]

The reproducing method of the present invention reproduces a recording layer on which recording marks are formed along a track and an effective spot smaller than a reproducing light beam spot when the recording layer is irradiated with reproducing light. A method of reproducing an optical recording medium comprising a positive photochromic mask layer for increasing the transmittance of reproduction light in a colored region having a low transmittance for a light wavelength, and irradiating a reproduction light beam with a spot. Irradiate the mask layer with a colored light beam having a shape substantially equal to or larger than the reproduction light beam spot in the track width direction and longer than the track width direction in the track length direction while scanning along the track length direction. A step of coloring the mask layer, and a step of irradiating the mask layer and the recording layer with a reproduction light beam after the mask layer is colored to reproduce the recording. It is provided.

According to the reproducing apparatus of the present invention, the recording layer having recording marks formed along the track and the effective spot smaller than the reproducing light beam spot when the recording layer is irradiated with the reproducing light have a transmittance for the reproducing light wavelength. A device for reproducing an optical recording medium having a positive photochromic mask layer for increasing the transmittance of reproduction light in a low colored region, a reproduction light source emitting a reproduction light beam, and a mask layer. A colored light source that emits a colored light beam for coloring the light, an optical system for condensing the reproduction light beam and the colored light beam on the optical recording medium, and a reproduction after the recording layer of the optical recording medium is irradiated. A means for detecting light and photoelectrically converting it, and a spot shape of the colored light beam is approximately equal to or larger than the reproduction light beam spot in the track width direction, and is tracked in the track length direction. And a spot shape control means for a long shape than the width direction.

The positive photochromic mask layer in the present invention can be formed of, for example, a positive photochromic dye pigment. Such a positive photochromic coloring matter pigment may be contained in a polymer to form a polymer film, or the coloring matter pigment may be directly vapor-deposited to form a film.

[0010]

1 is a plan view for explaining the reproducing method of the present invention. Referring to FIG. 1, a reproduction light beam spot 1
Prior to, the colored light beam spot 2 is scanned in the A direction. The colored light beam spot 2 has a diameter larger than that of the reproduction light beam 1 in the track width direction, that is, in the direction perpendicular to the A direction which is the scanning direction. Further, the colored light beam 2 has an elliptical shape having a diameter longer in the track length direction, that is, in the A direction than in the track width direction.

When the colored light beam 2 is scanned in the direction A, the mask layer is colored by the photon mode reaction, and the transmittance of the reproduction light is lowered. Therefore, by scanning the colored light beam 2, the mask layer colored portion 3 as shown in FIG. 1 is formed. The mask layer colored portion 3 masks the recording mark of the track to be read by the reproduction light.

The reproduction light beam 1 is scanned after the colored light beam 2, and the reproduction light beam 1 irradiates the mask layer colored portion 3. Since the decoloring reaction of the mask layer occurs due to the temperature rise due to the irradiation of the reproduction light, the transmittance of the mask layer increases in the latter half of the reproduction light beam 1 and the mask layer is in the decolored state. Therefore, an effective spot 6 as shown in FIG. 1 is formed in the latter half of the reproduction light beam 1. The reproducing light reaches the recording layer with the size of the effective spot 6, and the recording mark 5 is read. Therefore, reproduction is performed with an effective spot 6 smaller than the reproduction light beam 1, and a super-resolution effect can be obtained. Therefore, the reproduction can be performed without being affected by the crosstalk of the recording marks 7 of the adjacent tracks. After the reproduction light beam 1 is scanned, the mask layer erasing portion 4 is formed as the locus of the effective spot 6.

FIG. 2 shows a reproducing state in the conventional reproducing method, and parts corresponding to those in FIG. 1 are designated by the same reference numerals. Compared with the colored light beam 2 shown in FIG.
The colored light beam 2 of the present invention shown in 1 has a shape larger than the reproduction light beam 1 in the track width direction and longer than the track width direction in the track length direction.
Therefore, when the colored light beam 2 of the present invention as shown in FIG. 1 is irradiated, the energy density of the colored light beam 2 can be reduced. In that case, the same portion of the mask layer is irradiated for a longer time, and as a result, the integrated light amount can be set to a sufficient light amount for coloring the mask layer. Moreover, since the energy density of the colored light beam is low, it is possible to prevent the temperature rise of the mask layer from occurring easily.
The decoloring reaction of the mask layer due to the thermal reaction can be suppressed.

Therefore, according to the reproducing method of the present invention, the temperature rise due to the irradiation of the colored light beam can be suppressed, and the super-resolution effect can be further improved. In the present invention, the crosstalk between adjacent tracks can be reduced by setting the diameter of the colored light beam in the track width direction to be larger than the track width.

[0015]

EXAMPLE FIG. 3 is a diagram showing a sectional structure of an optical recording medium used in an example according to the present invention. Referring to FIG. 3, on a glass disk substrate 10 having a thickness of 1.2 mm,
A positive photochromic mask layer 11 having a film thickness of 0.05 μm was formed by a vacuum evaporation method. The mask layer 11 was formed from a positive photochromic spiropyran having a structure shown in (Chemical Formula 1) below.

[0016]

Embedded image

This photochromic dye material reacts in the photon mode when irradiated with ultraviolet rays, and has a wavelength of 600 to 7
Absorption around 00 nm increases and becomes a colored state, and heating or light irradiation at the same wavelength causes a decrease in absorption in the same wavelength region in a heat mode or a photon mode, resulting in a decolored state.

On the positive photochromic mask layer 11, a TbFeCo type magneto-optical recording layer 12 as a known optical recording material was formed with a thickness of 0.05 μm. Further, a dielectric layer 13 made of SiN and having a film thickness of 0.04 μm was formed on the magneto-optical recording layer 12. On top of this dielectric layer 13,
The reflective layer 14 made of Al and having a film thickness of 0.15 μm was formed.

An optical disc as shown in FIG. 3 was reproduced using the recording / reproducing apparatus shown in FIG. A magnetic field modulation coil 21 that changes an applied magnetic field according to a recording signal is provided on the side of the optical disc 20 opposite to the light irradiation side. Due to the action of the magnetic field modulation coil 21, magnetic field modulation recording is performed. On the light irradiation side of the optical disc 20, an objective lens 2 for condensing the recording light and the reproducing light onto the optical disc 20 is provided.
3 is provided. A semiconductor laser 26 having a wavelength of 670 nm is provided as a light source that emits recording light and reproducing light. The light beam from the semiconductor laser 26 passes through the collimate lens 25 and the half mirror 24, enters the dichroic mirror 29, passes through the objective lens 23,
It is focused on the optical disc 20.

A HeCd laser 34 having a wavelength of 365 nm is provided as a colored light source that emits a colored light beam. The colored light from the laser 34 passes through the light intensity adjusting filter 33, the colored light beam control element 32, the collimator lens 31, and the colored light spot shape control optical element 30 and is applied to the dichroic mirror 29. The colored light with which the dichroic mirror 29 is irradiated is reflected, passes through the objective lens 23, and is condensed on the optical disc 20. The spot shape of the colored light spot is controlled by the control optical element 30 to be an elliptical shape that is larger than the reproduction light beam spot in the track width direction and longer than the track width direction in the track length direction. In this embodiment, a cylindrical lens is used as the optical element 30 for controlling the colored light spot shape.

After the mask layer is colored with the colored light beam, the reproducing light beam is irradiated and reproduced by an effective spot smaller than the reproducing light beam spot due to the super-resolution effect as shown in FIG. The reproduction light that is irradiated onto and reflected from the recording layer of the optical disc 20 passes through the objective lens 23 and the dichroic mirror 29 again, is reflected by the half mirror 24, enters the servo / signal detection optical system 28, and is detected. . Here, it is taken out as a reproduction signal by the photoelectric conversion means. A servo control signal is sent to the control circuit 27, and a signal for track servo is sent from the control circuit 27 to the control system of the objective lens 23.

As a method of causing the colored light spot to precede the reproduction light spot, a method of slightly inclining the incident angle of the beam with respect to the objective lens can be adopted.

In the present embodiment, the reproducing light beam spot has a substantially circular shape and a spot diameter of 1.3 μm.
The colored light beam spot had an elliptical shape as shown in FIG. 1 and had a spot shape with a diameter in the track length direction of 4 μm and a diameter in the track width direction of 2.5 μm.

With respect to the above optical disk, a device as shown in FIG. 4 is used, and when the mask layer is in a decolored state, that is, a state where the transmittance is high, a semiconductor laser having a wavelength of 670 nm is used and a frequency of 300 k. Magnetic field modulation recording of a signal of up to 1.5 MHz was performed at a recording power of 4 mW and a relative speed of 1.4 m / s. The optical disk on which magnetic field modulation recording was performed was reproduced with a reproduction light beam power of 3 mW and a coloring light beam power of 6 mW, and the relationship between frequency and reproduction output was measured. The result is shown in FIG.

For comparison, the relationship between the frequency and the reproduction output when the reproduction was performed using the spot shape of the colored light beam spot having the same size and shape as the reproduction light beam spot was measured. Results are shown in FIG.

As shown in FIG. 5, the frequency is 300 kHz.
When the output of z is set to 0 dB as a reference and the output when the output is reduced by 6 dB is compared, it is about 1 MHz in the comparative example, whereas it is 1.4 MHz in the example according to the present invention, and the line recording is significantly It can be seen that the density is improved. According to the present invention, a colored light beam whose spot shape is longer in the track length direction than in the track width direction is used, and the temperature rise due to the colored light beam is suppressed, and the mask layer is sufficiently colored for reproduction. It is considered that this is because the super-resolution effect is further improved.

The mask layer used in the present invention is not limited to the mask layer of the above embodiment, and the present invention can be applied as long as it is a mask layer having a positive photochromic property. Further, the reproducing apparatus is not limited to the one having the structure of the above embodiment, and various modifications can be made.
For example, as a colored light beam light source, an SHG laser,
A blue semiconductor laser or the like which is expected to be put to practical use in the future can also be used. Although the colored light beam and the reproduction light beam are condensed on the optical recording medium by using the same objective lens in the above-mentioned embodiment, they may be condensed by different optical systems.

The optical recording medium to which the reproducing method and the reproducing apparatus of the present invention are applied is not limited to the optical recording medium by the magneto-optical recording as in the above embodiment, but a phase change type optical recording medium, or It is also applied to read-only type and write-once type optical recording media. Further, the present invention is also applied to an optical recording medium such as a compact disc which is recorded with concave and convex recording pits.

Further, in the above embodiment, the optical recording medium in which the mask layer is provided on the light incident side with respect to the recording layer is used, but the light provided with the mask layer on the opposite side to the light incident side with respect to the recording layer is used. The present invention can be applied to a recording medium.

[0030]

According to the present invention, the temperature rise due to the irradiation of the colored light beam can be suppressed, and the mask layer can be sufficiently colored to improve the super-resolution effect. Therefore,
According to the present invention, it is possible to achieve a higher recording density by using a super-resolution optical recording medium having a positive photochromic mask layer.

[Brief description of drawings]

FIG. 1 is a plan view for explaining a reproducing method according to the present invention.

FIG. 2 is a plan view for explaining a conventional reproducing method.

FIG. 3 is a sectional view showing the structure of an optical recording medium used in an example according to the present invention.

FIG. 4 is a schematic configuration diagram showing a recording / reproducing apparatus used in an embodiment of the present invention.

FIG. 5 is a diagram showing frequency characteristics of reproduction output in the embodiment according to the present invention.

[Explanation of symbols]

 1 ... Reproducing light beam spot 2 ... Colored light beam spot 3 ... Mask layer colored portion 4 ... Mask layer decolored portion 5 ... Recording mark 6 ... Effective spot 7 ... Adjacent track recording mark 10 ... Glass substrate 11 ... Positive photochromic mask Layer 12 ... Magneto-optical recording layer 13 ... Dielectric layer 14 ... Reflective layer 15 ... Playback light beer or colored light beam

Claims (2)

[Claims] 1. A recording layer in which recording marks are formed along a track, and an effective spot smaller than a reproduction light beam spot when irradiating the recording layer with reproduction light is provided in a colored region having a low transmittance for the reproduction light wavelength. A method for reproducing an optical recording medium having a positive photochromic mask layer for increasing the transmittance of reproduction light in a recording medium, wherein the spot shape is the reproduction light in the track width direction prior to irradiation of the reproduction light beam. The mask layer is colored by irradiating the mask layer with a colored light beam having a shape substantially equal to or larger than the beam spot and longer in the track length direction than in the track width direction while scanning along the track length direction. A step of irradiating the mask layer and the recording layer with a reproduction light beam after the mask layer is colored to reproduce the recording. The method of playback recording media. 2. A recording layer having recording marks formed along a track, and an effective spot smaller than a reproduction light beam spot when the recording layer is irradiated with reproduction light in a colored region having a low transmittance for the reproduction light wavelength. A device for reproducing an optical recording medium, which comprises a positive photochromic mask layer for increasing the transmittance of reproduction light to form a reproduction light source for emitting a reproduction light beam, and coloring the mask layer. A colored light source for emitting a colored light beam for reproducing, an optical system for condensing the reproduction light beam and the colored light beam on an optical recording medium, and reproduction after irradiation on a recording layer of the optical recording medium. Means for detecting light and photoelectrically converting the spot shape of the colored light beam in the track width direction to be substantially equal to or larger than the reproduction light beam spot in the track length direction. Reproducing apparatus for an optical recording medium and a spot shape control means for a long shape than the track width direction have.