JPH0834006B2 - Optical information recording method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for recording information on an information recording medium using light with high energy density.

[Technical background of the invention] In recent years, information recording media using a high energy density beam such as a laser beam have been developed and put into practical use. This information recording medium is called an optical disc,
It can be used as a disk, an audio disk, and also as a large capacity still image file and a large capacity computer disk memory. Among these information recording media, compact discs (CDs) have been widely put into practical use for reproducing audio such as music.

A conventional audio CD has a pit formed on a substrate in advance (thus, has no recording layer) and is exclusively for reproduction, and has a drawback that information cannot be recorded and edited. Therefore, development of a DRAW (Direct Read After Write, writable) type optical disc is desired.

Also, for files such as documents, data, and still images, CD-ROM (Read Only Memory) or CD-I (Inter
DRAW type optical disc of the same format as active)
Further, a rewritable optical disc is desired in the future.

An ordinary DRAW type information recording medium has, as a basic structure, a disk-shaped transparent substrate made of plastic, glass or the like, and a metal or a semimetal such as Bi, Sn, In, Te or Ge provided thereon. And a recording layer. Writing of information to the recording medium is performed by, for example, irradiating the recording medium with a laser beam, and the irradiated portion of the recording layer absorbs the light and locally rises in temperature, resulting in a physical phenomenon such as pit formation. Information is recorded by causing a chemical change, such as a change or phase change, to change its optical properties. The reading of information from the optical disk is also performed by irradiating the optical disk with a laser beam or the like, and the information is reproduced by detecting the reflected light or the transmitted light according to the change of the optical characteristics of the recording layer.

Although there are still various problems in the method of recording the information, there are the following problems especially when forming pits. For example, in a recording method in which pits are generated by melting a metal film or the like with laser light, in order to accurately and efficiently generate pits, the distance between the lens and the recording layer should be kept constant, that is, the just focus point. Focusing servo is used to always hold. However, even if such control is performed, it is not always possible to obtain a uniform pit shape formed on the recording layer, and it cannot be said that the shape is uniform. The pit having such a shape naturally causes various problems during reproduction. For example, the peak shift or jitter of the recording signal becomes large, or crosstalk easily occurs, which may cause reproduction failure such as signal reading error.

OBJECT OF THE INVENTION The present invention provides a novel method for recording information on an information recording medium using light of high energy density.

Further, the present invention provides a method of recording information that has small jitter, peak shift and crosstalk, and is therefore highly reliable in recording and reproducing data.

SUMMARY OF THE INVENTION The present invention includes the following steps (1) to (7): (1) A recording layer of an information recording medium is irradiated with a signal recording light modulated by an information signal to be recorded. A step of detecting an error from a focused state of the light by detecting reflected light of the light, (2) moving the objective lens upward or downward on the recording layer based on the error, A step of detecting an error from a focused state of the light by detecting reflected light; (3) a step of the objective lens so that the light is brought into a focused state by repeating the step (2). (4) irradiating the recording layer with the signal recording light while forming a pit on the recording layer while controlling the objective lens in a focused state, and irradiating the light. From the generation of the reflected light,
Detecting the time until the start of attenuation of the reflected light that occurs when pits are formed on the recording layer, (5) move the objective lens upward or downward on the recording layer, and The step of detecting the time from the generation of the reflected light to the start of the attenuation in the same manner as the above), (6) By repeating the above step (5), the time from the generation of the reflected light to the start of the attenuation is minimized. And (7) a pit on the recording layer while controlling the objective lens so that the time from the generation of the reflected light to the start of attenuation is minimized. And a step of recording information by forming an optical information recording method.

Preferred embodiments of the optical information recording method of the present invention are as follows.

1) The step of controlling the position of the objective lens so that the time from the generation of the reflected light to the start of attenuation in the above (4) to (6) is minimized is the inner or outer circumference side of the information recording medium. The optical information recording method described above, which is performed in a manufactures area on the side.

2) The optical information recording method, wherein the recording of the information is performed in a user area.

The in-focus state (just-focused state) means that the focus position is within the range of the depth of focus.

[Advantages of the Invention] As described above, the objective lens controlled to be in focus is
By adjusting the position so that the time from the generation of reflected light to the start of attenuation is minimized, the edges of the pits recorded in the recording layer of the information recording medium become clear and their shape becomes uniform. .

As a result, jitter, peak shift and crosstalk can be reduced, and among others, jitter can be minimized, and therefore reliability in recording and reproducing information can be significantly improved.

[Detailed Description of the Invention] The optical information recording method of the present invention is performed as follows, for example.

As a basic structure, a laser beam is applied to an information recording medium having a recording layer made of a metal such as Bi, Sn, In, Te, or Ge or a semimetal provided on a disk-shaped transparent substrate made of plastic or glass. Information is recorded by irradiation. The irradiated portion of the irradiated recording layer absorbs the light and locally rises in temperature, resulting in a physical change such as pit formation or a chemical change such as a phase change to change its chemical characteristics. Records information. Particularly, in the present invention, information is recorded by forming pits by irradiation with laser light. With respect to the formation of pits, usually, the waveform of the input signal is modulated into pulses, and the pits are formed by irradiating the information recording medium with the pulse-modulated laser light. that time,
Focusing servo is used to maintain a constant distance between the objective lens and the recording layer in order to accurately and efficiently form pits, that is, to always maintain a focused state (just focus state). . However, even if such control is performed, it is not always possible to obtain a uniform pit shape formed on the recording layer, and it cannot be said that the pit shape is uniform. The pit forming method of the present invention can solve such a problem.

According to the present invention, when a recording layer of an information recording medium is irradiated with light for recording information, an objective lens that is controlled to be in a focused state is provided with pits on the recording layer due to generation of reflected light by light irradiation. Information is recorded by forming pits while controlling the time until the start of attenuation of reflected light that occurs as it is formed.

That is, the present invention first functions to maintain the focused state of the signal recording light modulated by the information signal to be recorded on the recording layer of the rotating information recording medium by using the reflected light. Irradiate under the control of the focusing servo to form pits. The control is performed by moving the objective lens up and down. That is, the recording layer, by irradiating the light for recording, detects the error from the focused state of the light by detecting the reflected light of the light, based on the error,
By moving the objective lens up or down on the recording layer to detect the reflected light, the error from the focused state of the light is detected again, and by repeating the error detection,
The position of the objective lens is controlled so that the light is in focus. When the recording layer is irradiated with light for signal recording under the control of the focusing servo to form pits on the recording layer, the pits are formed on the recording layer and the reflected light is attenuated. The time from the generation of the reflected light due to the irradiation of to the start of the attenuation is detected, then the objective lens is moved upward or downward on the recording layer, and again from the generation of the reflected light to the start of the attenuation as described above. Is detected and the detection of this time is repeated to control the position of the objective lens so that the time from the detection of the reflected light to the start of the attenuation is minimized. That is, this control is performed by detecting the moving distance (that is, the offset amount) of the objective lens controlled to the in-focus state to the position where the time until the start of attenuation is minimized. Then, information is recorded by forming pits on the recording layer while controlling the objective lens so as to minimize the time from the detection of the reflected light to the start of attenuation.

In this way, by controlling the objective lens controlled to the in-focus state so that the time from the generation of the reflected light due to the irradiation of the recording light to the start of the attenuation of the reflected light is minimized, the pit ends are It will be clear and its shape will be neat. This makes it possible to reduce jitter, peak shift, and crosstalk, among other things, minimize jitter, and therefore, it is possible to record information extremely accurately, and to improve the reliability in reproduction thereof. .

The method of recording the above information will be described in detail with reference to FIGS. 1 and 2.

FIG. 1 is an example of a block diagram showing an outline of an optical information recording method of the present invention. The laser light emitted from the semiconductor laser 1 passes through the collimator lens 2 and the objective lens 3 and is condensed to form the substrate 5 of the information recording medium 4.
And is focused on the recording layer 6. Recording layer 6
The laser light reflected by the laser beam passes through the objective lens 3 again and is polarized by the polarization beam splitter 7, so that the laser light is bent at a right angle. Then, the bent laser light is divided into two by the semitransparent mirror 8, the laser light bent at a right angle is processed by the processing system for focusing servo, and the straight laser light is detected as attenuation of reflected light caused by pit formation. Used for each.

The laser light bent at a right angle by the semi-transparent mirror 8 passes through the cylindrical lens 13 so that it is slightly condensed in the lateral direction, and then passes through the converging lens 14 to
The voice coil magnet is focused on the split detector 15 to detect the error from the focused state (deviation from just focusing) and adjust the error from the focused state.
A voltage is applied to 16 to correct the position of the objective lens.
The focusing servo works in this way.

The laser light traveling straight through the semitransparent mirror 8 is condensed by the converging lens 9, and the condensed laser light is detected by the detector 10.
The amount of light is detected by, and after being amplified by the amplifier 11, the time until the start of attenuation of the reflected light is measured and detected by the delta / tau detector 12. In order to minimize the time until the attenuation starts, the distance between the lens and the recording layer of the information recording medium can be electrically changed by applying a voltage to the voice coil magnet 16.

The method of controlling the objective lens controlled to the in-focus state according to the present invention so as to minimize the time from the generation of the reflected light due to the light irradiation to the start of the attenuation of the reflected light is performed as follows. Under the control of the focusing servo that functions by detecting the reflected light with the four-division detector 15,
The detector 10 detects the start of attenuation of the reflected light caused by the irradiation of light and the formation of pits, and the time until the attenuation starts is measured by the delta tau detector 12. Then, in order to minimize the time until the start of the attenuation, the voice coil magnet 16 is provided with a voltage amount obtained by adding a positive or negative voltage to the voltage for controlling the focusing servo focus state. Is operated to electrically move the objective lens up and down to change the distance between the objective lens and the recording layer of the information recording medium. Then, the moving distance (offset amount) of the lens that minimizes the time until the start of the attenuation, that is, the offset voltage (the above-mentioned applied voltage) necessary for moving the distance is measured.

In order to explain the time until the start of the attenuation of the reflected light,
FIG. 2 shows a change in energy of reflected light. Second
The position where the energy of the reflected light rises in the figure indicates the moment when the laser light is irradiated, and after the time τ has elapsed, the energy of the reflected light is rapidly attenuated because the formation of pits has started on the information recording medium. A certain amount of reflected light energy after that indicates pit formation, and the reflected light energy disappears,
The state where the irradiation of the laser light is stopped is shown. The pits 21 formed after the time τ has elapsed and before the irradiation of the laser light is stopped are shown below the graph of the energy change of the reflected light. In the present invention, the control is performed as described above so as to minimize the time τ.

The step of controlling the position of the objective lens so that the time until the start of such attenuation is minimized is performed in the manufacturer's area on the inner peripheral side or the outer peripheral side of the information recording medium, and specifically, For a 5.25-inch optical disc, within the range of 29.7 to 30.0 mm from the center of the information recording medium or 60.0
It is preferable to carry out in the range of 60.5 mm.

After that, information is recorded by focusing the offset voltage (corresponding to the moving distance) so that the objective lens controlled to be in the focused state is at a position where the time until the start of attenuation of reflected light is minimized. This is performed by operating a voice coil magnet to form a pit in superposition with a servo drive amplifier or the like. Since it is not necessary to detect the moving distance in the recording of the information, the semitransparent mirror 8
The block that uses the laser light that went straight on is not used.

That is, the above-mentioned information recording is an optical information recording in which the objective lens controlled to the in-focus state is adjusted to a position where the time from the generation of reflected light due to light irradiation to the start of attenuation of reflected light is minimized. If it is an apparatus, it is possible to record information by a known optical information recording apparatus by the recording method of the present invention. Therefore, information is recorded in the user area, specifically, in the case of a 5.25-inch optical disc, it is preferable that the information is recorded within a range of more than 30.0 mm and less than 60.0 mm from the center of the information recording medium.

According to the recording method of the present invention, even if the shape of the groove or the shape of the pit for tracking the information recording medium, the type of recording layer, the layer thickness, or the like is different, the above adjustment is performed for each information recording medium. Since it can be performed, it can be said that it is a method that can record and reproduce information extremely accurately.

In addition, the recording method of the present invention includes an optical information recording apparatus, an objective lens controlled to be in a focused state, and a position where the time from generation of reflected light due to light irradiation to start of attenuation of reflected light is minimized. It is also possible to use the method of adjusting the optical information recording device according to an arbitrary information recording medium.

The recording method of the present invention is effective for both pit-to-pit recording and pit-length recording, but especially for a method of optically recording a CD format signal on a DRAW type information recording medium, the constant linear velocity during recording is 1.2. The recording method of the present invention is extremely effective because it is as slow as ~ 1.4 m / sec and is advantageous in utilizing heat energy.

The optical information recording method of the present invention has been mainly described so far as the writable type (DRAW type) pit formation type. However, it can be used for a rewritable type that utilizes the phase change of the recording layer and a magneto-optical disk. It is possible to use it. All of these can minimize the jitter by detecting the generation of reflected light at the time of light irradiation and the start of the attenuation of the reflected light that occurs with the formation of pits, and minimizing the time until the attenuation. The method of the invention can be applied.

The information recording medium that can be used in the optical information recording method of the present invention can be manufactured, for example, by the following method.

The substrate used in the present invention can be arbitrarily selected from various materials used as substrates for conventional information recording media. From the viewpoint of optical characteristics, flatness, processability, handleability, temporal stability and manufacturing cost of the substrate, examples of the substrate material include glass such as soda lime glass; cell cast polymethyl methacrylate, injection molded polymethyl methacrylate. Acrylic resins such as; polyvinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymers; epoxy resins; and polycarbonates; amorphous polyolefins. Of these, preferred are polymethylmethacrylate, polycarbonate, epoxy resin, amorphous polyolefin and glass.

On the surface of the substrate on which the recording layer is provided, for the purpose of improving flatness, improving adhesive strength and preventing alteration of the recording layer,
An undercoat layer may be provided. Examples of the material for the undercoat layer include polymer substances such as polymethylmethacrylate, acrylic acid / methacrylic acid copolymer, nitrocellulose, polyethylene, polypropylene and polycarbonate; organic substances such as silane coupling agents: and inorganic oxides. Inorganic substances such as (SiO ₂ , Al ₂ O ₃ etc.) and inorganic fluorides (MgF ₂ ) can be mentioned.

In the case of a glass substrate, a hydrophilic group such as a styrene / maleic anhydride copolymer and / or maleic anhydride is used in order to prevent the recording layer from being adversely affected by alkali metal ions and alkaline earth metal ions released from the substrate. It is desirable that an undercoat layer made of a polymer having a group be provided.

The undercoat layer can be formed, for example, by dissolving or dispersing the above substance in a suitable solvent and then applying the coating solution to the surface of the substrate by a coating method such as spin coating, dip coating or extrusion coating.

Further, a pre-groove layer may be provided on the substrate for the purpose of forming a groove for tracking or an unevenness representing information such as an address signal. As a material for the pre-groove layer, a mixture of at least one monomer (or oligomer) of acrylic acid monoester, diester, triester and tetraester and a photopolymerization initiator can be used. The layer thickness of the pre-groove layer is generally in the range of 0.05 to 100 μm, preferably 0.1 to 50 μm.
Is in the range. In the case of a plastic substrate, the pregroove may be formed directly on the substrate surface.

An intermediate layer such as a chlorinated polyolefin layer and an organic material layer is provided on the substrate of the information recording medium of the present invention (via a pregroove layer or an undercoat layer if desired). This allows
It is possible to reduce the loss of heat energy due to laser beam irradiation from the recording layer to the substrate due to heat conduction, and to facilitate the formation of bubbles, thus increasing the recording sensitivity and reducing the read error (bit error rate). be able to.

As a coating method, a spray method, a spin coating method, a dipping method, a roll coating method, a blade coating method, a doctor roll method, a screen printing method or the like can be used. The thickness of the intermediate layer is generally in the range of 10 to 1000Å,
It is preferably in the range of 100 to 500Å.

As a material of the recording layer, a composition of low melting point indium and at least one metal compound selected from the group consisting of metal sulfides, metal fluorides and metal oxides is used.

Examples of the metal compound include CrS, Cr ₂ S, Cr ₂ S ₃ and Mo.
_{S 2, MnS, FeS, FeS} 2, CoS, Co 2 S 3, NiS, Ni 2 S, PbS, Cu
₂ S, Ag ₂ S, ZnS, In ₂ S ₃ , In ₂ S ₂ , GeSx (0.5 <X ≦ 2.
0), SnS, SnS ₂ , As ₂ S ₃ , Sb ₂ S ₃ and Bi ₂ S ₃ metal sulfides; MgF ₂ , CaF ₂ and RhF ₃ metal fluorides; and MoO, In ₂ O, In Mention may be made of metal oxides such as ₂ O ₃ , GeO and PbO.

The recording layer further includes a low melting point metal such as Te, Sn, Pb and Bi,
And Ag, Al, Cu, Ga, Au, Co, Mo, Ni, Si, Be, Cr,
A metal having a high surface tension such as V, Fe, Mn, Nb, Pd, Ti, and Zn may be contained.

The recording layer is formed on the chlorinated polyolefin layer by a known method such as vapor deposition, sputtering or ion plating using the above recording layer material.

The recording layer may be a single layer or multiple layers, but the total layer thickness must be 300 Å or more in view of the optical density required for optical information recording. From a practical point of view, the layer thickness is 2000
It is preferably Å or less. Particularly preferred layer thickness is 700
It is in the range of ~ 1500Å.

Preferably, a protective layer is provided on the recording layer.
The protective layer is preferably a laminate of a soft protective film made of a soft resin material and a hard protective layer made of a hard resin material.
This laminated body is laminated on the recording layer with the soft protective layer side being the recording layer side. Examples of the soft resin material include polyurethane, polyvinylidene chloride, ethylene / vinyl acetate copolymer, silicone rubber, styrene / butadiene rubber, polyvinylidene chloride, and polyacrylic acid ester. Usually, these are applied on the recording layer by a method such as solution coating, latex coating, and melt coating, and if necessary, they are dried, heated and the like to be a soft protective layer. The layer thickness of the soft protective layer is usually in the range of 100Å to 5 μm, preferably in the range of 0.3 to 3 μm. Examples of hard resin materials include ultraviolet curable resins and thermosetting resins. Usually, these are applied on the soft protective layer by a method such as solution coating and, if necessary, subjected to treatments such as ultraviolet irradiation and heating to form a hard protective layer. The layer thickness of the hard protective layer is usually in the range of 0.1 to 10 μm, preferably 1 to 3 μm.

On the surface of the substrate opposite to the side where the recording layer is provided,
In order to improve scratch resistance and moisture resistance, for example, a thin film made of an inorganic substance such as silicon dioxide, tin oxide, or magnesium fluoride, or a polymer substance such as a thermoplastic resin or a photocurable resin is vacuum-deposited, sputtered or It may be provided by a method such as coating.

The bonded type information recording medium can be manufactured by joining the two substrates having the above-described configuration using an adhesive or the like. In an air-sandwich type recording medium, at least one of the two disc-shaped substrates has a substrate having the above-described configuration, and is disposed on a ring-shaped outer spacer and an inner spacer, or on one or both substrates. It can be manufactured by joining via provided projections.

[Brief description of drawings]

FIG. 1 is an example of a block diagram showing recording of information by light according to the present invention. FIG. 2 is a diagram showing a change in energy of reflected light of the light applied to the information recording medium. 1: Semiconductor laser 2: Collimating lens 3: Objective lens 4: Information recording medium 5: Substrate 6: Recording layer 7: Polarizing beam splitter 8: Semi-transparent mirror 9, 14: Converging lens 10: Detector 11: Amplifier 12: Delta Tau detector 13: Cylindrical lens 15: 4-division detector 16: Voice coil magnet 21: Pit τ: Time until attenuation of reflected light energy

Claims (1)

[Claims] 1. The following steps (1) to (7): (1) A recording layer of an information recording medium is irradiated with signal recording light modulated by an information signal to be recorded, A step of detecting an error from a focused state of the light by detecting the reflected light, (2) based on the error, moving the objective lens upward or downward on the recording layer to detect the reflected light Detecting the error from the focused state of the light by (3) repeating the step (2) to control the position of the objective lens so that the light is brought into the focused state (4) The recording layer is irradiated with the signal recording light while controlling the objective lens in a focused state to form pits on the recording layer, and the reflected light of the reflected light is irradiated by the irradiation of the light. From the outbreak,
Detecting the time until the start of attenuation of the reflected light that occurs when pits are formed on the recording layer, (5) move the objective lens upward or downward on the recording layer, and The step of detecting the time from the generation of the reflected light to the start of the attenuation in the same manner as the above), (6) By repeating the above step (5), the time from the generation of the reflected light to the start of the attenuation is minimized. And (7) a pit on the recording layer while controlling the objective lens so that the time from the generation of the reflected light to the start of attenuation is minimized. A step of recording information by forming the optical information recording method;