JPH0340222A - Optical recording and reproducing method - Google Patents

Abstract

PURPOSE:To acquire a high modulation factor with a high reflection factor by irradiating the recording layer of an optical recording medium with light, recording information while changing the diffraction factor of the recording layer and reproducing the information by detecting the intensity of the light based on interference using phase difference to be generated by the change in the diffraction factor of the recording layer. CONSTITUTION:A disk D is composed of a transparent substrate 1, recording layer 2, reflecting film 3 and protecting film 4. The information are recorded by irradiating the recording layer 2 of the optical recording medium with the light and changing the diffraction factor of the recording layer 2. At the time of reproducing, the information are reproduced by detecting the intensity of the light based on the interference using the phase difference to be generated by the change in the diffraction factor of the recording layer 2 to be generated between light to pass the recording layer 2 and light not to pass the recording layer when the optical recording medium is irradiated with the light. Thus, the medium with low absorption factor, namely, with the high reflection factor can be utilized and further, since the phase difference is utilized, the high modulation factor can be acquired.

Description

[Detailed description of the invention] (b) Industrial application fields The present invention relates to an optical information recording and reproducing method.

(Ex) Conventional technology Various optical information recording and reproducing methods have been proposed in the past, but the ones that can record include magneto-optical disks, write-once disks that form holes (bits) or bubbles, and phase change disks. type discs are known.

Since magneto-optical disks require a magnetic field for recording and erasing, the configuration of the optical head system is complicated, and reproduction is performed by detecting the rotation angle of the polarization plane of reflected light, but the rotation angle of this polarization plane is Since it is minute, it is difficult to obtain a high degree of modulation.

Write-once pit-forming discs record information by forming holes (pits) in the recording layer by heating and vaporizing the recording layer with laser light, and bubble-forming discs record information by heating and vaporizing the recording layer with laser light. By heating and vaporizing the recording layer, the recording layer is deformed and bubbles are formed to record information. Both discs utilize the fact that the bit part or bubble part has lower reflectance than other parts. , to reproduce information. These methods heat the recording layer to a high temperature, so it is necessary to increase the absorption efficiency of the laser beam in the recording layer, and as a result, the reflectance of the areas where bits or bubbles are not formed is also low. It was difficult to obtain a high modulation degree and a high CN (quinaria/noise) ratio.

Phase change discs perform playback based on the difference in reflectance between the crystalline and amorphous states of the recording layer.
About 20% when the reflectance is high and 10-15 when it is low.
%, and therefore it was difficult to obtain a high modulation degree and a high CN ratio.

(c) Problems to be Solved by the Invention The present invention aims to enable an optical recording and reproducing method that provides a high reflectance and a high degree of modulation.

(d) Means for Solving the Problems In the present invention, information is recorded by irradiating the recording layer of an optical recording medium with light to change the refractive index of the recording layer. During playback, the optical recording medium is irradiated with light, and the intensity of the light is based on interference using the phase difference that occurs due to the change in the refractive index of the recording layer between the light that passes through the recording layer and the light that does not pass through the recording layer. is detected and played.

To separate light into light that passes through the recording layer and light that does not pass through the recording layer during playback, a partially transparent reflective film may be formed on the top surface of the recording layer, or the light beam irradiated onto the recording medium during playback may be separated from the recording layer. The structure is such that both the recording layer portion and the non-recording layer portion are irradiated.

(e) If a large phase difference can be provided between the light that passes through the operational recording layer and the light that does not pass through, recording and reproduction with a high degree of modulation will be possible. In the present invention, such a phase difference is provided by changing the refractive index of the recording layer.

For the recording layer, materials whose refractive index changes can be used regardless of whether it is in photon mode or heat mode, but especially in the case of a heat mode type recording layer, the recording layer is heated strongly as in the conventional bit or bubble forming type. Since it is not necessary, the absorption rate can be lowered, and as a result, the reflectance can be increased, and a high modulation degree can be obtained.

(f) Example The example shown in FIG. 1 is an example in which recording is performed in the groove (group) portion, and the disk (D) includes a transparent substrate (1), a recording layer (2), and a reflective IN! i(3), the bottom of the groove is lower than that of the protective film (4). A groove (1a) is formed in the transparent substrate (1), and recording is performed on the recording layer (2) in this groove (la). The readout beam (Bo) converged by a suitable optical system is irradiated across the recording layer (2) portion and the non-recording layer portion.

Now, when performing reproduction, it is assumed that reproduction is performed so that the readout beam reflected light from the non-recorded portion becomes strong and the readout beam reflected light from the recorded portion becomes weak. The depth of the groove is β, the refractive index of the recording layer in the unrecorded state is n, and the refractive index in the recorded state is 0゛.
If the refractive index of the substrate is no and the wavelength of the laser beam in vacuum is λ, it is unrecorded! ! I (Fig. 1a), the position of the reflected light (B,) passing through the grooves, that is, the recording layer (2), and the reflected light (B1) passing between the grooves, that is, the non-recording layer part. When the phase difference is an even number multiple of a half wavelength, the reflected light becomes strong. That is, (βno-βn)×2-λ/2・2m... ■(ms
On the other hand, in the recording state (Fig. 1b), the reflected light (B, ) passing through the recorded portion (2a) of the recording layer (2) and the reflected light (B, ) passing through the non-recording layer section. ), the reflected light becomes weaker when the phase difference with the wavelength is an odd multiple of a half wavelength. That is, (βno−βn')
X 2 = λ/2・(2m'+ 1)... ■(m
(゛; integer) The change in refractive index △n is ■, from the formula △n=n'-n=λ/4β・12(m-m')-11・
... ■As the simplest example, if m = 1 and m' = 0, △n = λ/4β ... ■ Therefore, for example, if the wavelength is determined, n that satisfies the formula ■ in the unrecorded state , no is selected, and β is determined according to the refractive index change Δn using the equation (2), recording and reproducing becomes possible.

FIG. 2 shows a second embodiment, in which recording is performed on a recording layer (2) between grooves (1a).

In this case, the recording layer (2) is used to split the read beam light.
A semi-transparent thin film reflective layer (5) is formed on the surface. A part of the beam light (B,) is directly reflected by this reflective film (5) without passing through the recording layer (2), and the remaining beam light (B1) is reflected after passing through the recording layer (2). layer(
3) is reflected. Therefore, the beam light (Bl) (Bl
) can be used. As in the previous embodiment, in the unrecorded state (FIG. 2a), the phase difference is set to an even multiple of a half wavelength to intensify the reflected light. That is, 2βn=λ7/2・2m (m: integer)... ■Here, β is the thickness of the recording layer (2>), and since the thickness of the reflective layer (5) is thin, it is ignored. , in the recording state (Fig. 2b), the reflected light is weakened by setting the phase difference to an odd multiple of a half wavelength. That is, 2βn'=λ/2 ・(2m'+ 1)(r+':
Integer)... ■As a simple example, if m = m' = 1,
Δn=n'-n=λ/4β...■ Therefore, if β is determined according to the refractive index change Δn using the equation (2) in the same way as in the previous embodiment, recording and reproduction becomes possible.

If the refractive index change △n can be controlled, first determine β, and then change △ so that the formula ■ or formula ■ holds true.
n may be determined. Furthermore, if λ can be freely selected, λ may be determined according to Δn and β.

For example, a photochromic material can be used as the material for the recording layer (2) of the present invention (Reference: Optical Memory Symposium 86 Proceedings, pages 75-80).

(g) Effects of the Invention According to the present invention described above, since bits or bubbles are not formed in the recording layer, there is no need to heat it to high temperatures, and therefore a material with low absorption rate, that is, high reflectance can be used. Furthermore, since a phase difference is utilized, it is possible to obtain a high degree of modulation.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams for explaining the optical recording and reproducing method according to the present invention. (1)...Transparent substrate, (2)...Recording layer, (3)(
5)... Reflective film, (4)... Protective film.

Claims (3)

[Claims] (1) During recording, information is recorded by irradiating the recording layer of the optical recording medium with light to change the refractive index of the recording layer,
Light based on interference using a phase difference generated due to a change in the refractive index of the recording layer, which occurs between the light that passes through the recording layer and the light that does not pass through the optical recording medium during reproduction. An optical recording and reproducing method characterized in that playback is performed by detecting the strength and weakness of the signal. (2) During recording, information is recorded by irradiating the recording layer of the optical recording medium with light through a semi-transparent reflective film to change the refractive index of the recording layer, and during reproduction, the information is recorded on the optical recording medium. The amount of light that is generated due to a change in the refractive index of the recording layer, which occurs between the light that is irradiated with light and passes through the recording layer, and the light that is reflected by the reflective film and does not pass through the recording layer. An optical recording and reproducing method characterized by detecting and reproducing the strength of light based on interference using phase difference. (3) During recording, information is recorded by irradiating the recording layer of the optical recording medium with light to change the refractive index of the recording layer,
At the time of reproduction, light is irradiated across the recording layer portion and the non-recording layer portion of the optical recording medium, resulting in a change in the refractive index of the recording layer that occurs between the light that passes through the recording layer and the light that does not pass through the recording layer. An optical recording and reproducing method characterized by detecting and reproducing the strength of light based on interference using a phase difference generated by the optical system.