JPS63220434A - Optical disk and its recording and reproducing method - Google Patents

Abstract

PURPOSE:To record and reproduce information on both planes of a recording layer at a side opposite to incidence, by making incident light of wavelength lambda1 from second recording layer side, and making incident light of wavelength lambda2 from first recording layer side. CONSTITUTION:The recording layers 1 and 2 consisting of different organic pigments are applied on both planes of an optical disk substrate 3. The light 10 of wavelength lambda1 is focused by a lens system 5, and the light of wavelength lambda1 is made incident from a transparent recording layer 2 side, and furthermore, it passes the transparent disk substrate 3, and is focused on the recording layer 1 which absorbs the light of wavelength lambda1, and the information is recorded on the recording layer 1. Meanwhile, when the information is recorded by projecting the light of wavelength lambda2, the light 20 of wavelength lambda2 is focused by a lens system 5', and the information is recorded on the recording layer 2 which absorbs the light of wavelength lambda2. In such a way, it is possible to obtain an optical disk that is a single plate and capable of recording and reproducing the information on both planes.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a writable optical recording medium, particularly a high-density optical disk and a recording and reproducing method thereof.

2. Description of the Related Art Optical recording media, especially optical disks, have been making remarkable progress in recent years, and as the market expands, it is expected that they will be used for a wide variety of purposes and applications. Generally, optical discs are broadly classified into two types: read-only discs and writable discs. The representative of the former is the compact disc (hereinafter referred to as CD) for music.On the other hand, various types of writable optical discs have been developed, such as the perforated type, phase change type, and magneto-optical type. has been done.

Incidentally, various methods have been proposed to further increase the recording density of these disks. For example, shortening the wavelength of the light used during recording, narrowing the track pitch,
One method is to increase the recording frequency, but another method is to simply double the recording density by using both the front and back sides.

FIG. 2 schematically shows a double-sided recordable and reproducible type optical disc in which information is recorded and reproduced through a single optical disc substrate. Recording layers 31 and 31' made of the same recording medium are provided on both sides of the substrate 32. The laser beam focused by the lens 34 passes through the recording layer 31' and the substrate 32, and is focused on the recording layer 31'.

Problems to be Solved by the Invention In this type of optical disc, the recording medium needs to absorb a certain amount of laser light during recording. Furthermore, in order to increase the contrast and especially for tracking performance and focusing during recording, it is better that the reflectance is high to some extent.

When recording media having such spectral characteristics are provided on both sides of the optical disc substrate, the recording film 3 on the laser beam incident side
1° undergoes some change by the laser. moreover,
The laser beam is reflected by the recording film 31 on the incident side,
Since the light is absorbed, the amount of transmitted light that enters the substrate 32 is reduced, making it difficult to record at the focal point 33, which is a problem.

Means for solving the problem: An optical disk substrate is used that is transparent to the wavelength of the light used, and one side of this substrate absorbs light with a wavelength of λ1, and
A first recording layer having spectral characteristics that is transparent to light with a wavelength λ2 different from the wavelength of 1 is provided on the other side of the substrate. The above problems can be solved by providing a second recording layer with transparent spectral characteristics. Organic dyes are desirable for the recording layer because they can be easily obtained from a variety of dyes.

When recording action information, light with a wavelength λ1 is made incident from the second recording layer side, and light with a wavelength λ2 is made incident from the first recording layer side, so that the recording layer on the incident side of each light The recording layer transmits the incident light, and each incident light is absorbed by the recording layer on the opposite side to the incident light, and information can be recorded by the recording layer undergoing melting, decomposition, evaporation, phase change, etc. Regeneration is possible by keeping the light output low.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view schematically showing an optical disc according to the present invention. Both sides of the optical disc substrate 3 are coated with recording layers 1.2 made of different organic dyes.

Although the optical disc of the present invention is capable of double-sided recording and reproduction, the wavelengths of the laser beams used are different. Further, in FIG. 1, since the lens system of 5.5° is attached to both sides of the disk so as to sandwich the disk, recording or reproduction can be performed on both sides of the disk. Of course, it is also possible to arrange the lens systems 5 and 5 degrees on the same side and use the optical disk while inverting it.

Now, when recording information by irradiating light with wavelength λ1,
The light 10 with a wavelength λ is focused by the lens system 5, and the light with a wavelength λ1 is incident from the side of the transparent recording layer '2,
Furthermore, the energy of the light with the wavelength λ1 is effectively used in the recording layer 1, which passes through the transparent disk substrate 3 and focuses on the recording layer 1 which absorbs the light with the wavelength λ1, and information is recorded on the recording layer l. .

On the other hand, when recording information by irradiating light with wavelength λ2, the light 20 with wavelength λ2 is focused by the lens system 5', and the light with wavelength λ2 enters from the transparent recording layer 1 side. The light of wavelength λ2 is focused on the recording layer 2 that passes through the transparent disk substrate 3, and information is recorded on this layer.

Wavelength λ1. Various kinds of λ2 light can be used, but light in the visible region such as semiconductor laser region or He-No laser is desirable for miniaturization, weight reduction, and high-density recording. As the transparent optical disk substrate, glass or transparent resin such as acrylic or polycarbonate can be used.

As a specific example, on an acrylic substrate with 1.6 μm pinch pre-groups on both sides, a polymethine dye having the spectral characteristics shown in Figure 3 is coated on one side, and a polymethine dye is coated on the other side. Victoria Blue having the spectral characteristics shown in Figure 4 was coated to obtain an optical disc. 830 on this optical disc
Recording was performed on the polymethine dye layer by irradiating the Victoria Blue recording layer side with semiconductor laser light of 50 nm wavelength. The written signal is a pulse of 500KIIz and a duty ratio of 50:50. When this recording section was reproduced using the same low power laser, the C/N ratio was 52 dB.

On the other hand, this optical disc was irradiated with a 633 nm He-Ne laser beam from the polymethine dye side to record in a victorious single layer. This is also reproduced with the same low power laser and C
When the /N ratio was measured, it was 50 dB.

Effects of the Invention According to the present invention, it is possible to obtain a single-disc optical disc capable of recording and reproducing on both sides. Furthermore, since the laser beam is focused through the substrate, the influence of dust and the like adhering to the surface on the incident side can be reduced, and the occurrence of errors can therefore be reduced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an outline of an optical disc according to the present invention;
FIG. 2 is a cross-sectional view of an optical disk having the same recording layer on both sides, FIG. 3 is a graph showing the spectral transmittance of polymethine dye, and FIG. 4 is a graph showing the spectral transmittance of Victoria Blue. 1...Recording layer, 2...Recording layer having spectral characteristics different from 1, 3...Optical disc substrate, 5,5゛...Lens system ,31,31"...
. . . Same recording layer, 32 . . . Optical disc substrate.

Claims (2)

[Claims] (1) An optical disk substrate that is transparent to the wavelength of the light used, and one side of the substrate that absorbs light of wavelength λ_1,
and a recording layer having spectral characteristics that is transparent to light with a wavelength λ_2 different from the wavelength λ_1; and a recording layer having spectral characteristics that are transparent. (2) an optical disc substrate that is transparent to the wavelength of the light used; one side of the substrate absorbs light of wavelength λ_1;
and a recording layer having spectral characteristics that is transparent to light with a wavelength λ_2 different from the wavelength λ_1; When recording and reproducing on an optical disk consisting of a recording layer with transparent spectral characteristics,
A method for recording and reproducing an optical disc, characterized in that light used for recording and reproducing is focused onto a recording layer through a transparent optical disc substrate.