JPH07230623A - Optical readout method - Google Patents

Abstract

(57) [Summary] [Structure] With a player compatible with high-density optical recording media,
In a method of reading information from optical recording media having different recording densities, an optical reading method is characterized in that when reading a low density recording medium, the convergent beam diameter is made larger than when reading a high density recording medium. . [Effect] When a low-density recording medium is reproduced by a player compatible with a high-density medium, if it is reproduced as it is, a waveform distortion occurs and an error becomes very large. It can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of reading information from an optical recording medium, and more particularly to a method of reading information from optical recording media having different recording densities in a high density optical recording medium compatible player.

[0002]

2. Description of the Related Art Recently, information is recorded by laser light,
An optical recording medium that can be reproduced and erased has features such as high capacity and excellent portability, and non-contact recording and reproduction.
Various media such as erasable discs and recording and / or playback players are on the market. And these discs are standardized to maintain compatibility.

On the other hand, in combination with the market needs for higher density and the development of shorter wavelength lasers, the beam diameters are made smaller by using the shorter wavelength lasers, so that high density recording media and / or recording and / or recording media can be obtained. A playback player is being developed. However, when trying to reproduce a conventional low-density recording medium compatible with a laser wavelength with a high-density recording and / or reproducing player compatible with a shorter wavelength laser, the width of the recording pit of the conventional low-density medium is larger than that of a player compatible with a high density. The present inventors have found that the beam diameter becomes larger than the beam diameter of, the reproduced waveform is distorted, the error increases, and the reproduction may not be successful in some cases.

This will be described with reference to the accompanying drawings.
FIG. 1A shows a relationship between a pit size and a beam diameter and a reproduction waveform when a low-density medium compatible player reads a low-density medium, and FIG. 1B shows a high-density medium compatible player having a low density medium. The relationship between the pit size and the beam diameter when the medium is read and the reproduced waveform are shown. For example, a compact disc usually has a laser wavelength of 780 nm and NA0.
It is designed to accommodate 45 optical heads. On the other hand, recently, in order to increase the recording density, the wavelength 670
A recording / reproducing system equipped with an optical head having a smaller beam diameter using a laser of ˜690 nm and a lens of NA 0.55 to 0.60 has been developed. This system has a beam diameter of 71-64% compared to the conventional system.
Although it has a feature that it can be made high density because it is small,
When reading out a conventional 780 nm-compatible medium, particularly a medium with pit edge recording, by using the system, as shown in FIG.
Waveform distortion as shown in (b) occurs, errors increase, and reproduction cannot be performed properly.

That is, the reason why the reproduced waveform is as shown in FIG. 1B is that the beam diameter is not sufficiently large with respect to the width of the pit as shown in FIG. 1B. When the beam hits the edge of the pit, light is largely diffracted by the edge, but when the beam does not hit the edge, such diffraction does not occur. Therefore, the present inventors presume that when the beam hits the edge of the pit, the amount of reflected light is significantly reduced and the reproduced waveform is distorted.

[0006]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The present inventors have successfully reproduced a recording / reproducing player designed for a high-density medium by increasing the error due to the above-mentioned waveform distortion when reading a conventional low-density medium. The present invention has been completed as a result of various studies to improve the above-mentioned drawbacks found by the present inventors who cannot do so.

[0007]

That is, according to the present invention, in a method of reading information from optical recording media having different recording densities by a player for high density optical recording media, a high-density optical recording medium is used when reading low-density recording media. An optical reading method characterized in that a convergent beam diameter is made larger than that in the case of reading a recording medium and reading is performed. Further, when reading a low density medium, a component for changing an optical path length is provided between the medium and the optical head. This is a method of reading by making the convergent beam diameter larger than the case of reading a high-density medium by mounting between them, and when reading a high-density medium by giving a focus offset when reading a low-density medium. This is a read method in which the focused beam diameter is made larger than that of the read.

The optical recording medium in the present invention means a read-only medium, a write-once medium, a rewritable medium and the like. As the read-only medium, for example, a compact disc, a CD-
A medium such as a ROM disk, in which information is transferred to the substrate as pits when a polycarbonate, acrylic or polyolefin resin substrate is molded, and a reflective layer and a protective layer are provided, can be mentioned.

The write-once medium is a medium having a grooved substrate provided with a recording layer that absorbs laser light. As the recording layer, an inorganic thin film made of Te or the like or a thin film made of an organic dye is used. At this time, a reflective layer, a light interference layer, a heat insulating layer or the like may be provided on the recording layer. The medium can record and read information, but cannot erase it.

The rewritable medium is a medium in which a known magneto-optical recording layer such as FeCoTb is provided as a recording layer on a substrate having a groove, and information can be recorded, erased and read.

In the conventional write-once medium and erasable medium, for example, a semiconductor laser beam of 780 nm has an NA of 0.
It is designed so that recording and reproduction can be performed using an optical head that converges using an objective lens of 5 to 0.45. In this case, usually 1.6 μm to prevent crosstalk.
The recording layer is provided on the substrate having the grooves of the pitch. The width of the recording pit when recording varies depending on the type of the recording layer, but is about 1.0 to 0.6 μm (hereinafter this medium is referred to as a low density recording medium). When reading this medium, for example, it can be read by a commercially available CD player or the like (hereinafter referred to as a low density medium compatible player), and the reproduced waveform thereof has a beam diameter sufficiently larger than the width of the pit. The waveform has no waveform distortion as shown in a).

On the other hand, recently, in order to realize higher density recording, a player that converges a semiconductor laser light of 670 to 690 nm with a beam diameter smaller by using an objective lens of NA 0.55 to 0.6 (hereinafter High-density media compatible player) has been developed. The medium for the high density medium compatible player (hereinafter referred to as high density recording medium) is designed to have a groove pitch of about 1.2 to 1.0 μm.

When the above-mentioned low density recording medium is read by a high density compatible player, the reproduced waveform becomes a distorted waveform as shown in FIG. 1B, and in the case of pit edge recording, it is a bit. The present inventors have found that it causes a shift and causes an error. This waveform distortion is because the diameter of the player's read beam is not large enough for the width of the recording pit, and when the read beam hits the edge of the pit, the light is greatly diffracted by the edge, but the beam becomes the edge. If it is not applied, it is because diffraction does not occur. If the diffraction is large, the amount of reflected light is further reduced, and the reproduction waveform as shown in FIG. The degree of this distortion increases as the width of the recording pit increases.
We estimate that the smaller the read player's beam diameter, the larger it causes the problem of larger errors.

In the present invention, the low density recording medium is read by the high density compatible player in order to prevent an increase in errors due to the distortion of the reproduction waveform when the low density recording medium is read by the high density compatible player. At this time, the convergent beam diameter is read so as to be sufficiently larger than the pit width.

Various means can be used to increase the convergent beam diameter. For example, a part for changing the optical path length between the medium and the head, more specifically, plastic, glass or the like having a refractive index different from that of air, It is preferable to provide a film or thin plate made of metal. Another method for increasing the convergent beam diameter is to provide the focus servo of the player with an offset. In addition,
The degree of increasing the convergent beam diameter can be easily calculated based on the beam diameter used. For example, in the case described above, the beam diameter may be increased to about 1.2 to 1.5 times. . Hereinafter, an example of an embodiment of the present invention will be described with reference to examples.

[0016]

【Example】

Example 1 Information was recorded on a commercially available CD-R medium (Mitsui Toatsu Chemicals, Inc., trade name "Airy") using a Philips writer (model number 521, laser wavelength 780 nm, lens NA 0.5). When this recording medium was reproduced with a commercially available CD player (laser wavelength 780 nm, lens NA 0.47), the error was very small. Also, no waveform distortion was observed when the reproduced waveform was monitored. Next, a player for high-density media (laser wavelength 670 nm, lens N
When reproduced using A0.55), the error was extremely high. Further, when the reproduced waveform was observed, a large waveform distortion was observed. Then, when a 0.2 mm-thick polycarbonate plate was placed on the lens of the optical head of the player for high-density media and reproduced, the error became very small. No distortion was observed in the reproduced waveform.

[0017]

As is apparent from the embodiments, according to the present invention, when a low density recording medium is reproduced by a high density medium compatible player, if reproduced as it is, a waveform distortion occurs and an error becomes very large. By making the beam diameter of the focused laser light larger by changing the optical path length or by giving the focus servo an offset, the waveform distortion at the time of reproduction can be eliminated and the error can be reduced.

[Brief description of drawings]

FIG. 1A shows a relationship between a bit size and a beam diameter when a low-density medium is read by a low-density medium-compatible player, and a reproduction waveform, and FIG. 1B is a high-density medium-compatible player. 2 shows the relationship between the bit size and the beam diameter when reading a low density medium, and the reproduced waveform.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Sumio Hirose 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] 1. A method for reading information from optical recording media having different recording densities by a high density optical recording medium compatible player, when reading a low density recording medium,
An optical reading method characterized in that the convergent beam diameter is made larger and reading is performed than when reading a high-density recording medium. 2. When reading a low density medium, a component for changing the optical path length is attached between the medium and the optical head to read with a larger focused beam diameter than when reading a high density medium. The optical reading method described. 3. The optical reading method according to claim 1, wherein when the low-density medium is read, a focused beam offset is provided so that the convergent beam diameter is larger than that in the case of reading the high-density medium.