JPH04167227A - Erasing method for optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a desired spot by light for erasing by using a lightweight object lens by a method wherein the size of the spot is set in such a way that the light for erasing can erase two or more adjacent recording tracks. CONSTITUTION:As an optical recording medium 1, a recording layer 3 is formed after a glass substrate 2 is coated with a mixture which is composed of a photochromic material, polystyrene and a solvent, and, after that, a reflection layer 4 such as copper is applied and formed by a vacuum deposition method or the like. Light for recording is irradiated through object lenses 9, 10 and records information. Light for erasing is irradiated through an object lens 12 and erases the information. A spot 20 by the light for erasing is scanned by being stretched over at least two or more recording tracks 21 formed by using the light for recording. Thereby, the spot 20 by the light for erasing may be large, and it is possible to easily obtain the spot 20, by the light for erasing, which has a desired size.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an optical recording medium erasing method for erasing information from an optical recording medium.

(b) Prior art In recent years, research into the use of photochromic materials in the recording layer of media has been actively conducted. Such photochromic materials have properties such that when irradiated with light of a predetermined wavelength, the structure of the molecules changes due to a photochemical reaction, and the optical characteristics for light with a specific wavelength change in accordance with the change in the structure of the molecules. have. Furthermore, when irradiated with light of another predetermined wavelength, the changed molecular structure returns to its original structure.

This type of photochromic material is disclosed, for example, in the magazine "Chemistry and Industry J (1988, Vol. 41, No. 1, page 49). Figure 6 shows the reaction formula of the photochromic material. (A) indicates an open ring state, and (B
) indicates a closed ring state (colored state).

The photochromic material is colored purple by being changed into a ring-closed state by light having a wavelength of 405 nm, and is decolorized by being changed to an open ring state by light having a wavelength of 633 nm from a He-Ne laser.

Therefore, the closed ring state can be used as an information recording state, and the open ring state can be used as an erased state.

(c) Problem to be solved by the invention However, the spot diameter of the light focused on the optical recording medium via the objective lens is determined by the D ratio λ/NA with respect to the numerical aperture NA of the objective lens and the wavelength λ of the light There is a relationship between Therefore, when objective lenses with the same number of lenses are used for recording and erasing, and the wavelength of the erasing light is larger than the wavelength of the recording light as in the conventional example, the spot diameter of the erasing light is It becomes larger than the spot diameter of the recording light. Therefore, the track width is determined by the spot diameter of the erasing light, making it impossible to improve the recording density.

In addition, when increasing the numerical aperture NA of the erasing objective lens to make the spot of the erasing light approximately the same size as the recording light spot, it is necessary to increase the size of the erasing objective lens. There was a problem that the weight of the objective lens became large.

(d) Means for Solving the Problems In view of the above problems, the present invention provides an optical recording medium that records information by irradiating recording light, and an optical recording medium that erases information by irradiating erasing light. In the erasing method, the spot of the erasing light scans across at least two or more recording tracks formed by the recording light.

(E) Effect According to the above configuration, the erasing light spot may be large;
An erasing light spot of a desired size can be easily obtained, and
The recording density of information is not determined by the spot of the erasing light.

(f) Examples The present invention will be described in detail below with reference to the drawings.

In this example, an optical recording medium (±) containing indolylfulgide, which is an otochromic material, was used.

FIG. 1 shows the reaction formula of the photochromic material. Figure 2 shows the absorbance characteristics of this photochromic material.
Its optical properties will be explained. The A-state molecule has an absorption spectrum as shown by a broken line. When the molecules in the A state (ground state) are irradiated with light having a wavelength of about 4° Onm, they enter a photosteady state in which molecules in the A state and molecules in the B state coexist, exhibiting an absorption spectrum shown by a solid line.

Conversely, by irradiating the photochromic material in the photosteady state with light having a wavelength of about 450 to about 800 nm,
can be returned to the state.

Therefore, information can be recorded and erased by setting one of the A state and the optical steady state to the recording state and the other to the erasing state. However, in the following description, the A state is assumed to be an erased state, and the optical steady state is assumed to be a recorded state.

FIG. 3 is a diagram showing the structure of an optical recording medium.

The optical recording medium (1) has a track pitch of 0.8 μm, a diameter of 5.25 inch glass substrate (2) having groups with a radius of 0.5 μm, and 0.5 g of the above 7 otochromic materials and polystyrene. A solution prepared by mixing 5 g of toluene and 100 g of toluene as a solvent was coated using a spin code method to form a recording layer (3) with a thickness of 0.7 μm, and then a reflective layer (4) of copper or the like was applied using a vacuum evaporation method. Film thickness is approximately 1000
It was produced by forming a thick layer.

FIG. 4 shows a schematic diagram of an optical system for recording and erasing information on this optical recording medium.

(5) and (6) are semiconductor laser sources for recording information on the optical recording medium (±). This semiconductor laser source (5)
(6) are arranged at predetermined intervals on the optical recording medium (1) so that adjacent recording tracks are formed. Two of these semiconductor laser sources (5) and (6) are used for frame recording, for example.

The semiconductor laser sources (5) and (6) each output laser light with a wavelength of 800 nm. The above laser beam is transmitted to the SHG element (7) (
8), the light is converted into recording light with a wavelength of 400 nm. These recording lights pass through objective lenses (9) and (10) and are focused onto an optical recording medium (±) with a spot diameter of about 0.5 μm.
A recording track is formed by recording information on the track.

(11) is a He-Ne laser source for erasing information. This He-Ne laser source (11) has a wavelength of 633
Outputs nm erasing light. This erasing light passes through the objective lens (12) and is focused onto the optical recording medium (1). This focused spot has a diameter of about 1.5 μm so that the two recording tracks of the recording light can be scanned. Therefore, the objective lens (12) may have a small numerical aperture and be lightweight. Note that the spot does not have to be circular. For example, if the spot shape is an ellipse, the spot diameter may be the long axis diameter of the ellipse.

As shown in FIG. 5, this erasing light spot (20)
can erase information by scanning two adjacent recording tracks (21).

If the above-mentioned erasing method is used, the erasing light will be applied to two adjacent
Since the size of the spot is set to erase one recording track, the desired spot of the erasing light can be obtained using a lightweight objective lens, and the recording density is determined by the spot diameter of the erasing light. There is no fear that it will happen. Furthermore, since information on two recording tracks is erased, erasure can be performed at high speed.

In this embodiment, a fulgide-based photochromic material was used as the optical recording medium, but other photochromic materials can also be used. Furthermore, the wavelengths of the recording light do not have to be the same, and furthermore, the relationship in magnitude between the wavelengths of the recording light and the erasing light may be opposite to that described above. Further, the above-mentioned optical recording medium may be any medium such as an optical disk or an optical tape on which information can be recorded and erased by irradiation with light. Further, in the above embodiments, a reflective optical recording medium has been described, but it is obvious that a transmissive optical recording medium may also be used.

In some cases, the same SHG element and objective lens can be used for multiple recording lights. In some cases, the same objective lens can be used for recording light and erasing light. Further, the optical recording medium does not need to have groups. Furthermore, depending on the wavelength of the recording light, it is not necessary to use an SHG element.

Furthermore, the spot of the erasing light may scan and erase three or more recording tracks.

(G) Effects of the Invention In the present invention, the size of the spot of the erasing light is set so that it erases two or more adjacent recording tracks, so a desired spot of the erasing light can be set using a lightweight objective lens. Furthermore, there is no possibility that the recording density will be determined by the spot of the erasing light.

[Brief explanation of the drawing]

Figures 1 to 5 relate to an embodiment of the present invention; Figure 1 is a diagram showing the reaction formula of 7 otochromic materials, Figure 2 is a diagram showing the absorption luminous intensity characteristics, and Figure 3 is a diagram showing the absorption luminous intensity characteristics of the optical recording medium. FIG. 4 is a conceptual diagram showing an optical system for recording and erasing information, and FIG. 5 is a conceptual diagram showing a state in which a spot of erasing light scans a recording track. FIG. 6 is a diagram showing a reaction formula of a material that is an example of a photochromic material. (1)...Optical recording medium, (20)...Erasing light spot, (21)...Recording track.

Claims (1)

[Claims] (1) In an optical recording medium erasing method in which information is erased by irradiating erasing light onto an optical recording medium on which information is recorded by irradiating recording light, the spot of the erasing light is 1. A method for erasing an optical recording medium, comprising scanning over at least two recording tracks formed by the method.