JPH0778878B2 - Optical record erasing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to wavelength-multiplexed optical recording having a high recording density, and more particularly to an optical recording / erasing method using the hole burning phenomenon.

[Conventional technology]

Problems in the information recording / reproducing method using light are, for example, improvement of recording density, possibility of rewriting, and improvement of input / output speed. In response to the above problems, in recent years, researches on new optical recording media and wavelength multiplexing utilizing a multiple structure have been actively conducted. Among them, a PHB memory (Photo chemical hole burning) that utilizes the hole burning phenomenon is attracting attention as a future information recording method.
memory). The above-mentioned hole-burning phenomenon is academically interesting and is known as one of high-resolution spectroscopy. The above-mentioned recording method was proposed by IBM in 1978 (Japanese Patent Laid-Open No. 53-99735), and is a wavelength-multiplexed optical memory which is expected to have a large recording density improvement of about 1000 times that of the conventional type. The principle will be described below.

When a photochemically active molecule is placed in a solid matrix at low temperature, its absorption spectrum reflects a subtle difference in the environment in which the molecule is placed, resulting in a heterogeneous structure as shown in Fig. 2 (a). The spectrum width is shown. By irradiating a high-intensity laser beam with a narrow line width at a specific wavelength λ ₁ in the spectrum, only the molecules that resonate with λ ₁ absorb the light, and the first substrate state passes through the excited state. Move to a metastable state different from. This metastable state is 1)
The movement of protons in the molecule due to light absorption, 2) orientation change of molecules in the matrix due to light absorption, 3) photodissociation of molecules due to light absorption, and the like are considered. When the metastable state is maintained, as shown in FIG. 2 (b), a decrease in absorption intensity is observed only at the wavelength λ ₁ irradiated with light,
It can be observed as a hole having a sharp spectrum width on the absorption spectrum. Further, as shown in FIG. 2 (c), a wavelength-multiplexed optical memory can be formed by sequentially changing the wavelength of light irradiation to λ ₂ , λ ₃ ... And forming holes.

As described above, since the PHB memory has a basic principle of subtly changing the state caused by light, it is necessary to pay sufficient attention to recording, that is, the stability of holes on the absorption spectrum. It is known that when the temperature rises by 20 to 30 K, the holes recorded by optical recording cannot be held stably and the holes disappear. For this reason, the entire recording medium used for the PHB memory is stored in a cryogenic state of liquid helium temperature of 4.2K, which has less thermal fluctuations of molecules.

[Problems to be solved by the invention]

As described above, in the research of PHB memory, the search for the recording mechanism and the recording medium is conducted under severe conditions. However, regarding the method of erasing the record, although it is possible to erase the entire recording medium at a high temperature in a batch, there is almost no solution up to now to locally erase a part of the recording medium. There is a situation.

An object of the present invention is to obtain a method for locally enabling recording / erasing of PHB memory under cryogenic conditions.

[Means for solving problems]

The above object is achieved by mixing molecules having a light absorption wavelength region different from that of the recording medium used for the PHB memory into the recording medium and irradiating the mixed recording medium with light having a wavelength absorbed by the molecules.

[Action]

Using a mixed recording medium in which molecules having different light absorption wavelength regions are mixed with the recording medium used for the PHB memory, in a non-uniform absorption spectrum of molecules responsible for recording (hereinafter referred to as PHB molecule), Holes are formed by laser light irradiation, that is, PHB recording is performed. The same laser spot recorded on the PHB is strongly irradiated with light having a wavelength absorbed by a molecule responsible for erasing (hereinafter referred to as erasing molecule). By this operation, the erased molecule is photoexcited, and in the relaxation process, the lattice vibration including the photomatrix is excited to be a thermally excited state. The heat raises the temperature of the entire light-irradiated portion, and as a result, the metastable state of the PHB molecule is disturbed, and the holes on the absorption spectrum disappear. That is, the temperature rises locally due to light irradiation, and the PHB record is erased.

The phenomenon described above is a local phenomenon that occurs only in the light irradiation spot, and does not have any effect on the peripheral recording portion other than the local area. Further, it is also possible to re-record in the portion which has disappeared by the above method. Therefore,
It is possible to erase and rewrite a part of the recording on the recording medium.

The desirable characteristics of the erasing molecule are, firstly, that it is a molecule having a large absorption coefficient, and it is considered that, for example, a dye molecule is suitable. Second, molecules that have a large interaction with the host matrix are desirable. This is because the large interaction with the matrix can improve the heat conduction efficiency from the erasing molecule and easily eliminate the metastable state of the PHB molecule.

Further, as factors that affect the erasing efficiency, there are the intensity and time of light irradiation, and the density of erasing molecules in the recording medium. Above all, the density of the erasing molecule is an important factor, and in order to enhance the erasing efficiency, it is desirable that the density is higher than that of the PHB molecule.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of an optical recording / erasing method according to the present invention, wherein (a) is a chemical formula of dye molecules mixed for erasing,
(B) is an absorption spectrum diagram of the recording medium, (c) is an absorption spectrum diagram showing the PHB memory before the erasing operation, and (d) is an absorption spectrum diagram after the erasing operation. Metal-free phthalocyanine (hereinafter referred to as H ₂ Pc) and the dye molecule shown in FIG. 1 (a) (hereinafter referred to as dye) at a concentration of 1 × 10 ⁻⁵ M and 1 × 10 ⁻⁴ M, respectively, A recording medium dispersed in polymethylmethacrylate was prepared and stored at 4.2K.
The absorption spectrum of the mixed recording medium is shown in Fig. 1 (b).
As shown in. First, using a wavelength tunable dye laser, optical recording of PHB memory based on proton transfer was performed in the absorption band of H ₂ Pc in the nonuniform width of 600 to 700 nm.
The above record is a binary code consisting of holes as shown in FIG. 1 (c).

Next, the recording portion within 1 μm of the laser spot was irradiated with a GaAlAs semiconductor laser that matched the absorption (800 to 900 nm) of the dye responsible for erasing. The irradiation time and intensity were 10 times as high as the recording time. As a result, the holes of PHB memory formed in the absorption band of H ₂ Pc disappeared completely as shown in Fig. 1 (d).
B Memory erase has been achieved. Furthermore, it was confirmed that a hole in the PHB memory could be newly formed (re-recorded) in the erased part. In addition, in the above erasure, the record of the adjacent spot was still stored.

〔The invention's effect〕

As described above, the optical recording / erasing method according to the present invention uses an optical recording medium obtained by mixing a substance capable of hole burning by light irradiation with a molecule having a light absorption wavelength different from that of the substance, and burning the optical recording medium. By irradiating the recorded light with light absorbed by the molecule and erasing the recording, it is not necessary to adjust the temperature of the entire recording medium, and the simple operation of irradiating light from the outside enables the PHB memory It is possible to locally erase and rewrite the record.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an optical recording and erasing method according to the present invention. (A) is a chemical formula of dye molecules mixed for erasing, (b) is an absorption spectrum diagram of a recording medium, (c). Is an absorption spectrum diagram showing the PHB memory before the erase operation,
(D) is an absorption spectrum diagram after the erasing operation, FIG. 2 is a diagram for explaining the basic principle of a conventional PHB memory, (a) is an absorption spectrum diagram of a photochemically active molecule, and (b) is a laser beam. FIG. 3C is an absorption spectrum diagram showing hole burning by irradiation, and FIG. 6C is a diagram showing absorption spectra when the wavelength of the light irradiation is sequentially changed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masahiro Ojima Inventor Masahiro Ojima 1-280 Higashi Koigakubo, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72) Inventor Akio Taniguchi 1-280 Higashi Koigakubo, Kokubunji, Tokyo Hitachi Ltd. Factory Basic Research Center

Claims (1)

[Claims] 1. An optical recording medium comprising a substance capable of hole burning by light irradiation and a molecule having a light absorption wavelength different from that of the substance is used, and the molecule is absorbed in a burned record on the optical recording medium. An optical recording erasing method for erasing the above-mentioned record by irradiating the recording light.