JP3161650B2 - Optical recording medium - Google Patents

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 such as an optical disk and an optical card, and more particularly to a method for recording and reproducing high-density information by reducing the diameter of a condensing spot of light such as laser light to be used. And an erasable optical recording medium.

[0002]

2. Description of the Related Art Optical recording media such as optical disks include a read-only type, a write-once type, and a rewritable type.
D) and video discs. The track pitch, shortest recording wavelength, shortest pit length and the like of these optical disks depend on the focused spot diameter of the reproducing apparatus. That is, for example, in the case of the CD, the track pitch is limited to a range in which the focused spot diameter does not detect crosstalk from an adjacent track. Also, the shortest pit length is determined so that the focused spot diameter is limited to a range that does not cause intersymbol interference with the preceding and following pits, and the reproduction signal amplitude has an optimum value.

Specifically, the track pitch is 1.6 μm,
The shortest pit length of 0.83 μm is generally used.
Therefore, the recording density of one side of a 12 cm disk is about 780.
It is megabytes and can record digital audio for about 74 minutes. 3 for video discs
An analog video of about 1 hour on one side can be recorded on a 0 cm disk surface.

However, recently, a high-quality digital moving image of about one hour has been recorded on an optical recording medium having substantially the same size as a CD.
There is a demand for a reproducible optical disk, and for that purpose, a high recording density of about 4 to 10 times that of the current CD must be achieved. However, although it is relatively easy to form high-density tracks or pits on an optical recording medium, if a conventional reproducing apparatus attempts to reproduce a disk having such a very narrow track pitch and a very short pit length, ,
Crosstalk and intersymbol interference increased, and a correct signal could not be obtained.

Therefore, in order to increase the recording density of the optical recording medium, the diameter of the laser beam spot for reproduction must be reduced. As a method of reducing this spot diameter,
For example, a method of shortening the wavelength of the oscillation laser beam used for reproduction, a method of increasing the numerical aperture NA of the condenser lens, and the like have been studied.

For the method of shortening the laser wavelength, for example, a laser using a second harmonic generation element (SHG), or an oscillation wavelength of 400 nm by devising contained elements is used.
A semiconductor laser called a blue laser is known. If these lasers are used, the laser wavelength of about 800 nm currently used for reproducing a CD or a video disc can be reduced to about 1/2, and the recording density can be increased to about 4 times. However, such SHG elements and blue lasers have not reached the stage of practical use in terms of stability, performance, cost, and the like.

In the method using a high NA lens, the manufacturing accuracy such as the thickness of the disk is strict, so that the NA cannot be increased so much. Therefore, the currently feasible reproducing apparatus has a laser oscillation wavelength of 670 nm.
m, the NA is 0.6, and the recording density of the CD is increased by about 2.4 times, so that the requirement of 4 times cannot be satisfied.

Further, as another method for increasing the recording density, for example, JP-A-2-96926 and JP-A-5-28535 disclose nonlinear optical materials such as gallium arsenide, indium arsenide, and indium antimony. A technique for reducing the effective spot diameter of laser light by a layer is described. This technique has a property that the transmittance of the nonlinear optical material increases when the light intensity is high, and remains low when the light intensity is low. Therefore, when irradiating light having a Gaussian distribution in which the intensity distribution is strongest near the center of the spot, such as laser light, only the high intensity portion at the center is transmitted through the nonlinear optical material layer. Can be smaller.

In Japanese Patent Application Laid-Open No. 1-143042, three magnetic films which are magnetically coupled to each other but have different Curie temperatures are provided on a substrate, and the difference in the Curie temperatures of these magnetic films is used. A technique for reproducing by reducing or reversing a recording magnetic domain of a magnetic film is described.

[0010]

However, in the above-mentioned Japanese Patent Application Laid-Open No. 2-96926, when the above-mentioned substance is used as a nonlinear optical material, the repetition characteristics of an optical recording medium are poor and nonlinearity is exhibited by irradiation. However, there are problems such as a low speed at which the substance is used and a high toxicity of the substance itself. The technique disclosed in Japanese Patent Application Laid-Open No. 1-143042 is for a magneto-optical disk using a magnetic film, and has a problem that it cannot be used for other optical recording media that does not use magnetism.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems of the prior art, and an object of the present invention is to record, reproduce and reproduce information by substantially reducing the diameter of a focused light spot. An object of the present invention is to provide an optical recording medium capable of improving each erasing ability and, as a result, achieving a high recording density.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to an optical recording medium for recording, reproducing, or erasing information by using a converging spot. A compound having an atomic group (a) that emits electrons by photoexcitation and an atomic group (b) that accepts the emitted electrons. It contains. The atomic group (a) and the atomic group (b) may be directly bonded, or may be bonded via a linking group (c).

[0013]

In the optical recording medium of the present invention, a transmittance changing layer containing a compound containing at least an atomic group that emits electrons by photoexcitation and an atomic group that receives the emitted electrons is provided with a laser light or the like. It is provided within the focal depth of the focused spot. Therefore, as the compound, usually, the transmittance of the wavelength region of the condensed spot is low, but when irradiated with light of a certain intensity or more, the movement of electrons by photoexcitation occurs,
By using a compound whose transmittance increases due to a change in the absorption spectrum of the compound itself, the substantial focused spot diameter is reduced and information with a high recording density can be reproduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an example of a read-only optical disk according to the present invention. In this optical disc 1, a large number of pits 3 for recording information are provided on a transparent disc substrate 2 made of polycarbonate or the like, and a transmittance changing layer 4 according to the present invention is further formed thereon. It is covered with a layer 5 and a protective layer 6. Such an optical disc 1 can be manufactured by a known method. Although the transmittance changing layer 4 is provided adjacent to the pits 3, it does not have to be adjacent to the pits 3 as long as it is within the range of the focal depth of the reproducing laser light of the reproducing apparatus of the optical disk 1.

The compound contained in the transmittance changing layer 4 exhibits a phenomenon called saturated absorption. This phenomenon of saturation absorption means that the number of molecules whose electrons remain excited due to excessive absorption of light increases (that is, the number of molecules whose electrons are in the ground state decreases). It means that the transmittance increases. The compound according to the present invention expresses nonlinearity by utilizing the property of the saturated absorption.

In order to express the above-mentioned saturated absorption, it is necessary to maintain the excited state to some extent. The compounds, including a triplet state by electron light absorption in the atomic group (a)
The excited electrons are excited to a higher order state , and the excited electrons move to the atomic group (b) in the molecule to form an ion pair, so that a certain time until the electrons return to the ground state can be secured.

In a higher-order excited state such as the triplet state, the wave region of electrons excited by the atomic group (a) is
It is considered that even if the linking group (c) exists and the distance to the atom group (b) via the linking group (c) is considerably long, it is exuded to the atom group (b) side. Therefore, the probability that the excited electrons move from the atomic group (a) to the atomic group (b) increases. In addition, by selecting the linking group (c) and adjusting the distance between the atomic group (a) and the atomic group (b), the probability of the excited electrons seeping into the atomic group (b) and the atomic The probability of returning to group (a), that is, the time, can be controlled.

As described above, when electrons excited by high-intensity light move from the atomic group (a) to the atomic group (b), the potential of each atomic group in the molecule becomes (a) ^* -(c)-( b)-("
^* "Represents an excited state. ) Or (a) ⁺ -
As shown in (c)-(b) ^- , the light absorption spectrum greatly changes. Therefore, considering light of a specific wavelength, the transmittance changes before and after the movement of the electrons, or the non-transmitted light can be transmitted.

When light is no longer irradiated,
Since the atomic group (a) and the atomic group (b) are directly connected or have a specific positional relationship through the linking group (c), the electrons return to the original atomic group (a). Can be. Therefore, the above-mentioned light absorption spectrum is also the same. Therefore, a stable result can be obtained even if light irradiation is intermittently repeated. This mechanism is clearly advantageous in a system in which a donor and an acceptor are simply mixed, in that the probability that electrons excited to move to the acceptor return to the original donor when returning to the ground state is extremely low.

That is, the compound has a low light transmittance in a specific wavelength region, but when irradiated with light of a certain intensity or more, the electrons move and the transmittance in the specific wavelength region is good. If a compound is used, the focused spot of a laser beam or the like has a Gaussian distribution, so that only high-intensity light at the center of the spot is transmitted, and the substantial focused spot diameter is reduced to the diffraction limit or less. High-density information can be reproduced. The transfer and return of the excited electrons due to the light absorption is very fast, and
As described above, since the transfer of electrons is reversible, it can withstand repeated use in an optical recording medium and has little deterioration.

Examples of the compounds according to the present invention described above are shown below. Examples of the molecules forming the atomic group (a) include porphyrin-based, phthalocyanine-based, and dyes such as metal complex salts of zinc, copper, cobalt, nickel, iron, manganese, vanadium, and silicon. Such a dye is sensitive to the light source of the recording / reproducing device of the optical disc 1, and therefore, electrons are excited by light absorption to exhibit saturation absorption.

The compounds forming the atomic group (b) include quinones such as benzoquinone, naphthoquinone, anthraquinone, monochlorobenzoquinone, trichlorobenzoquinone, methylbenzoquinone and 1,4-dimethoxybenzene, methyl viologen, ethyl viologen, and benzyl viologen. And N-hexylpyrromelic acid diimide, and the like. Further, examples of the linking group (c) which may be present in the compound include a phenylene group, a (poly) methylene group, a group having a skeleton of bicyclooctane, bibicyclooctane, or the like.

In order to synthesize a compound having the above-mentioned atomic group (a) and atomic group (b) (and a linking group (c)), for example, a method described in “J. Am. Chem. Soc.” A known method described in, for example, Vol. 106, page 6090 (issued in 1984) can be used. The compounds synthesized using these methods may be used alone or as a mixture of two or more. The method of applying these compounds to the transmittance changing layer 4 is not limited, but a method of dispersing the compound in a transparent resin or the like is preferable.

The irradiation light source laser used for reproducing the optical disk 1 according to the present invention can be appropriately selected in consideration of the light absorption region of the compound. For example, an Ar laser (wavelength λ = 488 nm), a He—Ne laser (Λ = 633n
m), semiconductor lasers (λ = 670, 690 nm) and the like can be used.

Hereinafter, embodiments of the present invention will be described in more detail. Based on the above synthesis method, a zinc complex of tetraphenylporphyrin (donor: atomic group (a)), 1,4-benzoquinone (acceptor: atomic group (b)) and bicyclooctane (non-conjugated linking group (c)) A compound represented by the following formula 1 having a structure consisting of

[0026]

Embedded image

The compound of formula 1 was purified, and the absorption spectrum was measured in tetrahydrofuran (THF). The results are shown in FIG. 2, and it was confirmed that there was a strong absorption band near 535 nm. Next, the absorption spectrum was measured again while irradiating the compound with light of sufficiently high intensity. As a result, the absorption band at 535 nm was shifted to around 460 nm, and thus the transmittance near 535 nm was high.

The compound of the above formula (1) is dissolved in THF, this is dispersed in a polyurethane-based transparent polymer, and a film is formed on a transparent disk substrate 2 so as to have a thickness of 0.1 to 1.0 μm, and is transmitted. The rate change layer 4 was obtained. The optical disc 1 was manufactured by covering the upper surface of the transmittance changing layer 4 with a reflective layer 5 made of aluminum or the like and a protective layer 6 made of an ultraviolet curing agent or the like in this order as in the conventional product.

Using the optical disc 1, λ = 532n
m was used as a light source, and light having a spot diameter of 1.0 μm focused by a lens having an NA of 0.5 was applied. As a result, the diameter of the focused spot transmitted through the transmittance changing layer 4 is 0.6.
It was observed that it was reduced to μm. The focused spot diameter was measured with a laser spot shape measuring device.
Further, the laser light irradiation was intermittently repeated 500 times, and the focused spot diameter was stable at 0.6 μm.

[0030]

As described above, the optical recording medium of the present invention has the transmittance changing layer within the focal depth of the converging spot,
The transmittance change layer contains a compound having an atomic group that emits electrons by photoexcitation and an atomic group that receives the emitted electrons. Therefore, since the diameter of the condensed spot that passes through the transmittance changing layer can be reduced, the capability of recording, reproducing, or erasing information can be improved, and as a result, a high recording density can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a read-only optical disc according to the present invention.

FIG. 2 is an absorption spectrum of the compound of formula 1 according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical recording medium (optical disk), 2 ... Substrate, 3 ... Pit, 4 ... Transmissivity change layer, 5 ... Reflective film, 6 ... Protective film.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-28498 (JP, A) JP-A-5-40963 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/24

Claims (1)

(57) [Claims] 1. An optical recording medium in which information can be recorded, reproduced or erased by a converging spot, wherein the optical recording medium has a transmittance changing layer within a focal depth of the converging spot. An optical recording medium characterized in that the variable layer contains a compound having an atomic group that emits electrons by photoexcitation and an atomic group that receives the emitted electrons.