JPH04290794A - Optical recording medium and optical recording method - Google Patents

Abstract

PURPOSE:To obtain an optical recording medium capable of using a semi-conductor laser as a light source for recording and deletion by providing a thin film layer containing a blend of a rewritable optical recording material of a photochromic chemical compound and the fine crystal of the secondary or tertiary non-linear optical material on a support. CONSTITUTION:A thin film layer provided on a support 3 consists of a blend of rewritable optical recording material 1 of a photochromic chemical compound and the fine crystal of the secondary or tertiary non-linear optical material. When recording or deleting data in this optical recording medium, it is irradiated using a recording light or a deleting light emitted from two different types of semi-conductor laser with different wavelengths from each other. Then the wavelength of the recording light or the deleting light is converted on the optical recording medium for recording or deleting process. Subsequently, recording, regeneration and deletion can be performed on a recording medium using the photochromic material using a currently commercialized two different types of semi-conductor laser.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording method and an optical recording medium.

0002

2. Description of the Related Art In recent years, with the increase in recording capacity, the recording method is changing from a magnetic recording method to an optical recording method. This is because not only does the optical recording system have a larger recording capacity than the magnetic recording system, but it is also almost unaffected by dust on the medium, which is a problem with the magnetic recording system. Conventional optical recording media capable of recording and reproducing are known as write-once optical discs, in which recorded information cannot be erased after information has been recorded, and rewritable optical discs, in which recorded information can be erased after information has been recorded, and information can be recorded again. ing. A write-once optical disc has a low-melting metal film or a sublimable pigment film formed on a glass or plastic substrate. Information is recorded by irradiating laser light and using the heat to create holes in the metal film or pigment film. This is done by opening the holes, and the recorded information is read out by irradiating a weak laser beam and detecting the presence or absence of holes from changes in the intensity of the reflected light. These recording methods perform recording by converting light into thermal energy, and are therefore called heat mode recording. On the other hand, rewritable optical disks use a method that utilizes magneto-optical effects such as the Kerr effect, a method that utilizes phase change between crystals and amorphous, and thermal expansion and relaxation of an organic dye film dissolved or dispersed in a thermoplastic resin. In addition to heat mode recording such as a method using , a method using a reversible photoisomerization reaction of a photochromic compound has also been proposed. This recording method is called photon mode recording because it directly uses the energy of photons. The principles of recording and reproducing information on these rewritable optical discs are different, but for example, in the photon mode recording method using photochromic compounds, information is recorded by coloring or discoloring the irradiated area with laser light irradiation, and erasing is performed by irradiating the irradiated area with laser light. This is performed by irradiating a laser beam of a different wavelength to return the colored or discolored portion to its original state, and reading is performed using a weak laser beam of one of the above wavelengths or a third wavelength.

0003

[Problems to be Solved by the Invention] The recording and erasing light source used in optical recording is based on the use of a semiconductor laser, but when using a photochromic compound as a rewritable optical recording material, two Since the wavelength region of the absorption spectrum of an isomer does not match the semiconductor laser oscillation wavelength in many cases, practical recording devices and recording media have not yet been developed.

0004

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical recording medium and an optical recording method that can use a semiconductor laser as a light source for recording and erasing.

The invention of this application is as follows: (1) An optical recording device in which a thin film layer containing a mixture of a rewritable optical recording material made of a photochromic compound and a secondary or tertiary nonlinear optical material is provided on a substrate. It is a medium. (2) An optical recording medium in which a thin film layer containing a solid solution of a rewritable optical recording material made of a photochromic compound and a microcrystal of a second-order or third-order nonlinear optical material is provided on a substrate. (3) An optical recording medium in which a thin film layer containing a rewritable optical recording material made of a photochromic compound and a thin film layer containing a secondary or tertiary nonlinear optical material are laminated on a substrate. (4) An optical recording medium in which a thin film layer containing a rewritable optical recording material made of a photochromic compound is provided on a substrate containing a second-order or third-order nonlinear optical material.

[0006] Furthermore, as a method for recording or erasing on these optical recording media, recording or erasing is performed by irradiating the optical recording medium with recording light or erasing light emitted from two types of semiconductor lasers having different wavelengths. This optical recording method is characterized in that recording or erasing is performed by converting the wavelength of either recording light or erasing light on the optical recording medium.

[0007]

[Action] Among the photochromic compounds that are being considered for application to recording materials, for example, spirothiopyran (hereinafter S
(abbreviated as P), the maximum absorption wavelength of the closed ring is 400n
m, and that of the open ring form is around 700 nm. on the other hand,
The oscillation wavelengths of semiconductor lasers used as recording light and erasing light in optical recording are 830, 780, and 670 nm. Therefore, if the wavelength of 830 nm light is converted to 415 nm and used as recording light, and the 670 nm light is used as is without wavelength conversion, the wavelength of these lights will be in the wavelength range of the absorption spectra of the two isomers of SP mentioned above. Can be matched.

An example of a nonlinear optical material that can convert light with a wavelength of 830 nm to 415 nm with high efficiency and at the same time has a wavelength conversion efficiency of 0 or negligible for light with a wavelength of 670 nm is, for example, N-(4-nitrophenyl)-(L)-. Prolinol (hereinafter abbreviated as NPP) is mentioned.

The nonlinear optical material is disposed uniformly over the entire recording surface of the recording medium by dissolving or dispersing it in the recording film or substrate, or by laminating it as a thin film on the recording film. It is particularly desirable to use an alignment film in which the wafers are aligned in a certain direction. This is because, in general, second-order or third-order nonlinear optical effects have angular dependence on the incidence and exit of light from material molecules. Therefore, when a nonlinear optical material is laminated as an alignment film on a recording film and laser light is incident from an appropriate angle, the maximum output light intensity can be obtained in a specific direction.

[0010] In cases where the nonlinear optical material is formed and laminated without orientation, when microcrystals are dispersed in the recording film or substrate, or when the film is formed by forming a solid solution with the recording material, etc. , wavelength conversion efficiency decreases, and a relatively high-power light source must be used.

[0011]

EXAMPLES The present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples. In addition, in the examples, parts represent parts by weight.

FIGS. 1(A), (B), (C), and (D) are rewritable optical recording media according to embodiments of claims (1), (2), (3), and (4), respectively. FIG. Figure 1 (A
) The recording medium shown in ) was prepared by dissolving 2.0 parts of SP in 96.0 parts of cyclohexanone and adding 2.0 parts of NPP microcrystals (NPP is insoluble in cyclohexanone). A suspension solution was placed on a grooved glass substrate. It was dropped, rotated at a rotation speed of 600 rpm for 20 seconds, and then dried at 80° C. for 20 minutes. The thickness of the thin film layer on the resulting medium is 100
It was 0A. While rotating this optical recording medium so that the linear velocity of the recording track is 11.3 m/s,
Pulse signal of 30 nm semiconductor laser light at 50 mW, 1
Recording was performed by irradiating from the substrate side at a frequency of MHz. Next, when this track was irradiated with a semiconductor laser beam of wavelength 830 nm and 5 mW to reproduce the recording, the CN
R was 43 dB. Furthermore, this recording medium has 670
The recording was erased by irradiation with semiconductor laser light of 7.0 mW. Furthermore, new recording, playback, and erasing could be repeated.

The recording medium shown in FIG. 1(B) is SP2.
0 parts and 2.0 parts of NPP were dissolved in 96.0 parts of chloroform (SP and NPP are easily soluble in chloroform), and the solution was dropped onto a grooved glass substrate and rotated at a rotation speed of 600 rpm for 20 seconds. It was manufactured by drying at ℃ for 20 minutes. The thickness of the thin film layer of the obtained medium was 810A. While rotating this optical recording medium so that the linear velocity of the recording track was 11.3 m/s,
m semiconductor laser light pulse signal of 50 mW, 1 MHz
Recording was performed by irradiating from the substrate side at a frequency of . Next, when this track was irradiated with a semiconductor laser beam of 830 mn wavelength and 5 mW to reproduce the recording, the CNR was 4.
It was 0dB. Furthermore, this recording medium has a wavelength of 670 nm,
The recording was erased by irradiation with 7.0 mW semiconductor laser light. Furthermore, new recording, playback, and erasing could be repeated.

The recording medium shown in FIG. 1(C) is produced by forming a film of oriented NPP on a grooved glass substrate by a vacuum evaporation method, and then evaporating SP on top of this to form a film with a film thickness of 800A.
It was manufactured by forming a film. While rotating this optical recording medium so that the linear velocity of the recording track is 11.3 m/s, a pulse signal of an 830 nm semiconductor laser beam is transmitted over a 50 m/s.
Recording was performed by irradiating from the substrate side at a frequency of W, 1 MHz. Next, when this track was irradiated with a semiconductor laser beam having a wavelength of 830 nm and a power of 5 mW to reproduce the recording, the CNR was 48 dB. Furthermore, the recording was erased by irradiating this recording medium with a semiconductor laser beam of 670 nm and 7.0 mW. Furthermore, new recording, playback, and erasing could be repeated.

The recording medium shown in FIG. 1(D) is an NPP5
．． A solution consisting of 2.0 parts of SP and 98.0 parts of ethanol was dropped onto a grooved substrate formed by molding a mixture of 0 parts of SP and 95.0 parts of polycarbonate, and the mixture was heated at 600 rpm.
After rotating at a rotation speed of 20 seconds, the product was manufactured by drying at 80° C. for 20 minutes. The thickness of the thin film layer of the obtained medium was 77
It was 0A. While rotating this optical recording medium so that the linear velocity of the recording track is 11.3 m/s,
Pulse signal of 30 nm semiconductor laser light at 50 mW, 1
Recording was performed by irradiating from the substrate side at a frequency of MHz. Next, when this track was irradiated with a semiconductor laser beam of wavelength 830 nm and 5 mW to reproduce the recording, the C
NR was 44 dB. Furthermore, this recording medium has 67
The recording was erased by irradiation with 0 nm, 7.0 mW semiconductor laser light. Furthermore, new recording, playback, and erasing could be repeated.

[0016]

[Effects of the Invention] As described above, according to the present invention, data can be recorded, reproduced, and erased using two types of semiconductor lasers currently in practical use on recording media using known photochromic storage materials. It has the effect of being able to.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an optical recording medium according to an embodiment of the invention.

[Explanation of symbols]

1. Rewritable optical storage material 2. 2nd or 3rd order nonlinear optical material 3. Substrate

Claims (5)

[Claims] 1. An optical recording medium comprising, on a substrate, a thin film layer containing a mixture of a rewritable optical recording material made of a photochromic compound and microcrystals of a second-order or third-order nonlinear optical material. 2. An optical recording medium comprising, on a substrate, a thin film layer containing a solid solution of a rewritable optical recording material made of a photochromic compound and a second-order or third-order nonlinear optical material. 3. An optical recording medium in which a thin film layer containing a rewritable optical recording material made of a photochromic compound and a thin film layer containing a second-order or third-order nonlinear optical material are laminated on a substrate. 4. An optical recording medium comprising a thin film layer containing a rewritable optical recording material made of a photochromic compound on a substrate containing a second-order or third-order nonlinear optical material. 5. An optical recording method in which recording or erasing is performed by irradiating the optical recording medium according to claims 1 to 4 with recording light or erasing light emitted from two types of semiconductor lasers having different wavelengths, An optical recording method characterized in that recording or erasing is performed by converting the wavelength of either recording light or erasing light on the optical recording medium.