JPH07130008A - Reflectivity increase type optical recording medium - Google Patents

Abstract

PURPOSE:To provide a reflectivity increase type optical recording medium which is subjected to normal tracking and does not hinder reproduction by subjecting the optical recording medium to an inter-track pretreatment. CONSTITUTION:This optical recording medium of the reflectivity increase type has a recording layer 2 consisting of an optical characteristic to increase the reflectivity by optical recording on a substrate and conducts recording and reproducing of information by focusing a light spot into the prescribed tracks 3 on this recording layer 2. The recording layer 2 is subjected to the inter-track pretreatment by photoirradiation with which the reflectivity of the part corresponding to the part between the tracks 3 of the recording layer attains the value higher than the time average value of the reflectivity in the tracks 3 after optical recording. This inter-track pretreatment is conducted by irradiating only the part corresponding to the part between the tracks 3 of the recording layer with light of a prescribed light quantity. The inter-track pretreatment is preferably conducted so as to satisfy d1>=dP-dM when the width between the tracks is defined as d1, the width in the crossing direction of the tracks of recording marks 2 to be optical-recorded as dM and the track pitch as dP.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium of the type in which the reflectance of a recording layer is increased by optical recording, and
The present invention relates to a CD compatible reflectance-increasing optical recording medium that can be reproduced by a reproduction-only device such as a compact disc (CD).

[0002]

2. Description of the Related Art Since read-only optical discs such as CDs, which are widely used at present, have the same information content to be recorded, they are produced by a mastering process in which mass production is performed by molding from the same master disc ( (Duplicate), that is, information is recorded. However, this manufacturing method has a drawback that it is not suitable for manufacturing a small amount of optical discs having different information contents to be recorded.
Therefore, in order to deal with such a situation, it is possible to record information by directly irradiating the recording layer of the optical disc with a laser beam modulated according to the record information, and to reproduce the record information by a reproduction-only device such as a CD. A so-called CD-compatible optical disc that can be used (hereinafter referred to as an optical recording medium)
Have been developed.

C obtained based on such information recording
The D-compatible optical recording medium is a perforated type which utilizes changes in optical characteristics due to physical deformation of the recording layer (Japanese Patent Laid-Open No. 2-87339), a phase such as a crystal-amorphous phase of the recording material. A phase change type that utilizes changes in optical properties due to changes (JP-A-64-17234), and a phase separation type that uses changes in optical properties due to phase separation of recording materials (JP-A-3- No. 96389) is known.

Of these optical recording media, the perforated optical recording media have poor reproduction signal quality because the recording of information is dependent on the change of the outer shape of the recording layer. Since organic materials are usually used, they have problems of photodegradation and lack of storage stability. On the other hand, phase-change type and phase-separation type optical recording media have good reproduction signal quality because they do not change the outer shape of the recording layer, and have excellent storage stability because they use an inorganic material as the recording material. It has features. Therefore,
When comparing the two from this point of view, the phase change type and the phase separation type optical recording media are superior. The phase-change type and phase-separation type optical recording media are the reflectance increasing type having an optical characteristic that the reflectance of the recording layer increases by optical recording, and conversely the optical characteristic decreasing the reflectance. There are two types of reflectance reduction type with.

[0005]

By the way, the above-mentioned phase change type and phase separation type optical recording media of the reflectivity increasing type are compared with the reflectivity decreasing type before recording the information on the recording layer. Since it has a large light absorption amount, the recording sensitivity is excellent.

However, in the reflectivity increasing type optical recording medium, when the light spot is focused after the information recording, the reflectivity (time average value) in the track of the recording layer in which the information is recorded is Since the reflectance is higher than the track-to-track reflectance of the recording layer that is not involved in recording, there is a problem in that a reproduction-only device such as a CD that generally adopts a 3-beam method as a tracking control method cannot normally perform reproduction. It was That is, in the tracking control by the normal three-beam method, the main beam for control is set so as to follow the dark portion on the optical recording medium. Therefore, in the case of the above optical recording medium, the main beam is relatively dark portion. Tracks of the recording layer that becomes Therefore, the polarity of the obtained tracking error signal is opposite to that of a general CD, that is, a reflectance decreasing type optical recording medium, and as a result, correct tracking is not performed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical recording medium of the reflectance increasing type which is capable of supporting a tracking control method based on a three-beam method while maintaining excellent recording sensitivity.

[0008]

In order to achieve the above object, the reflectance-increasing optical recording medium of the present invention has at least a recording layer having an optical characteristic that the reflectance is increased by optical recording on a substrate. Then, in an optical recording medium of the reflectance increasing type in which information is recorded and reproduced by focusing a light spot in a predetermined track on the recording layer, the reflectance of a portion corresponding to the tracks of the recording layer is Is characterized in that the inter-track pretreatment is performed by light irradiation so that the value becomes larger than the time average value of the reflectance in the track after the optical recording.

Here, the inter-track pretreatment can be performed by irradiating a portion of the recording layer corresponding to the space between the tracks with a predetermined amount of light, and the light irradiation is performed by a light irradiating device dedicated to the pretreatment. Alternatively, the optical recording head of the optical recording device may also be used. The processing time is not particularly limited as long as it is before the recording of information.
Further, the processing time can be shortened by performing the pretreatment while rotating the optical recording medium (disc) at a speed higher than the rotation speed (linear velocity) at the time of reproduction.

In the inter-track pre-processing, if the width of the processing portion (between tracks) is d _I , the width of the recording mark to be optically recorded in the cross-track direction is d _M , and the track pitch is d _P , It is desirable to perform it so as to satisfy the relationship of d _I ≧ d _P −d _M. In this case, the width of the recording mark formed by the optical recording is limited by the pre-processing unit between adjacent tracks, and the mark width can be made constant regardless of the length of the mark. As a result, it is possible to perform optical recording and reproduction in which a high quality reproduction signal with little jitter can be obtained.

The above reflectances are the ratios of the amount of reflected light returning from the medium to the photodetector to the amount of incident light when the light spot is focused on the surface of the optical recording medium. Also,
The time average value of the reflectance in the track after optical recording is
Although it can be measured by a normal tracking error signal circuit, it can be calculated by, for example, a circuit including a low pass filter for averaging the signal components after the photodetector. Therefore, it is desirable that the reflectance of the inter-track processing section is larger than the time average value of the reflectance in the track, but it is usually 1.1 times or more, preferably 1.2 times or more.

The recording layer is composed of a phase-separation type or phase-change type recording material of which the reflectance increases by optical recording.

In addition to the recording layer, an underlayer, an interference layer, a protective layer, a reflective layer and the like may be appropriately laminated on the substrate. A substrate provided with a pre-groove is usually used as this substrate, but a substrate not provided with a pre-groove can also be used.

[0014]

According to the technical means as described above, since the inter-track pretreatment is performed, after the information is recorded by the optical recording, the reflectance (time average value) of the in-track of the recording layer is Has a smaller reflectance between the tracks, and as a result, the inside of the track is relatively darker than the area between the tracks. As a result, even an optical recording medium of the reflectance increasing type can be adapted (adapted) to the tracking control by the normal three-beam method.

[0015]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples.

Example 1 First, an optical recording medium of reflectance increasing type provided with a phase separation type recording layer made of SbO _x is prepared. On a 1.2 mm-thick polycarbonate substrate with a groove formed, a SiO ₂ base layer having a thickness of 80 nm and a SbO layer having a thickness of 40 nm are formed.
_A recording layer made of _x (for example, x is about 2.0), a SiO ₂ interference layer having a thickness of 60 nm, an Al reflection layer having a thickness of 60 nm, and a UV-curable resin protective layer having a thickness of 10 μm are laminated in this order. An optical recording medium was obtained by forming. The respective layers were laminated by the ion plating method for the recording layer, the RF magretron sputtering method for the underlayer, the interference layer and the reflection layer, and the spin coating method for the protective layer.

This optical recording medium has an initial reflectance of about 25% in its recording layer, and the irradiation of the semiconductor laser light causes phase separation in the recording material to increase the reflectance.

Then, this optical recording medium was subjected to the following track pretreatment using an optical recording device equipped with a semiconductor laser as a light source of an optical head to obtain an optical recording medium of the present invention. That is, the optical recording apparatus uniformly irradiates a laser beam to a portion corresponding to a track between recording layers of an optical recording medium by a push-pull method to selectively irradiate only the recording material in that portion. Phase separated to 65% reflectance
Raised to the extent.

Next, optical recording was performed on the optical recording medium which had been subjected to inter-track pretreatment by the above optical recording device. The optical recording is performed at a predetermined EF while tracking is performed on a portion where the inter-track pretreatment is not performed, that is, the inside of the track.
A recording mark was formed in the track by irradiating a recording light spot corresponding to the M signal.

FIG. 1 schematically shows the film surface of the recording layer in the optical recording medium at this time. In the figure, a shaded portion 1 indicates a pretreatment portion between tracks, and 2 indicates a recording mark. As shown in this figure, the recording mark 2 corresponding to the EFM signal is
Between the processing units 1 that have performed the inter-track processing, that is, the track 3
Formed side by side.

At this time, the reflectance of the lowest reflection portion of the recording mark 2 is 25%, the reflectance of the highest reflection portion is 65%, and C
It satisfied the standard for D. Further, the time average value of the reflectance in the track after this recording is 45
It was about%. Therefore, in the optical recording medium after the optical recording, the reflectance between the tracks 1 is larger than (the time average value of) the reflectance inside the tracks 3.

Then, when this optical recording medium on which the optical recording was carried out was put into a commercially available CD player adopting a tracking control method by a three-beam system and an attempt was made to reproduce the same, a tracking error signal of the same polarity as a general CD etc. was obtained. In addition to being obtained, a reproduced signal corresponding to the recorded EFM signal was also accurately obtained, and normal reproduction could be performed.

Next, the formation of recording marks and the reproduction characteristics when the laser power during the inter-track pretreatment was changed were examined, and the width d _{I of the} inter-track pretreatment portion was increased by increasing the laser power.
Becomes larger, but its width d _I is d _I ≧ d _P −d _M (d
_M : width of the recording mark to be recorded in the cross-track direction,
d _P : track pitch) (Fig. 1)
Since the width d _M of the recording mark 2 is limited by the inter-track pre-processing section 1 adjacent to each other, even when a long recording mark is formed along the track direction, the mark tears due to a heat storage effect or the like. It was confirmed that the mark shape deformed into a mold is unlikely to occur, and as a result, the jitter of the reproduced signal at that time becomes smaller than that in the case where the above relational expression is not satisfied, and a good signal can be stably obtained.

In the above embodiment, the optical recording medium having the phase-separated recording layer is described as an example, but the recording layer utilizes a phase change between crystal-amorphous and crystal-crystal. Similar effects can be obtained even in the case of an optical recording medium provided with a phase change recording layer.

Comparative Example 1 An optical recording medium having the same structure as in Example 1 was prepared except that the pretreatment between tracks was omitted. Then, optical recording based on the EFM signal was performed in the track of the optical recording medium in the same manner as in Example 1. At this time, the reflectance of the lowest reflection portion of the recording mark 2 is 25%, and the reflectance of the highest reflection portion is 65%.
Thus, the standard for CD was satisfied.

When the optical recording medium after recording was put on the same commercially available CD player as in Example 1, the polarity of the tracking error signal was reversed from that set by the player, and normal reproduction could not be performed. It was

[0027]

As described above, the reflectance-increasing optical recording medium of the present invention is subjected to inter-track pretreatment, so that after optical recording, the reflectance of the recording layer in the track is increased. Since the (time average value of) is smaller than the reflectance between tracks, it is an optical recording medium of the reflectance increasing type, but it is a read-only device such as a CD adopting the usual three-beam type tracking control method. Also, normal tracking is performed and playback can be performed without any trouble.

Further, since this optical recording medium is only subjected to inter-track pretreatment by light irradiation, the recording sensitivity inherent to the reflectance increasing type optical recording medium is maintained without being impaired. Moreover, if the pre-processing is performed so that the width of the processing portion by the inter-track pre-processing becomes appropriate, the width of the recording mark in the cross-track direction is limited by the adjacent inter-track pre-processing portion, and the length of the mark is reduced. It is possible to make the mark width constant irrespective of the above, and thus it is possible to provide an optical recording medium from which a good quality reproduction signal can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram schematically showing a state of a recording surface of an optical recording medium according to an example of the present invention.

[Explanation of symbols]

1 ... Track processing unit, 2 ... recording mark, 3 ... track.

Claims (1)

[Claims] 1. Recording and reproduction of information by concentrating a light spot in a predetermined track on the recording layer having at least a recording layer having an optical characteristic of which reflectance increases by optical recording on the substrate. In the reflectance-increasing type optical recording medium, the track by light irradiation is such that the reflectance of the portion corresponding to the track of the recording layer is larger than the time average value of the reflectance in the track after optical recording. A reflectance-increasing optical recording medium characterized by being subjected to pretreatment.