JPH04337524A - Optical recording and reproducing method - Google Patents

Abstract

PURPOSE:To prevent light damages and to enhance S/N of reproduction characteristics by executing optical recording while using an inorg. photochromic material added with a rare earth element executing wavelength light emission in a prescribed electron state and executing reading out by the light emission of a prescribed wavelength. CONSTITUTION:A recording layer 2 having the inorg. photochromic material added with the rare earth element is deposited on a base body 1 and a protective film 3 is deposited thereon, by which an optical recording medium 4 is constituted. The light emission of 2nd wavelength light lambda2 is not obtainable with the recording layer 2 by the excitation of 1st wavelength light, lambda1 in the 1st electron state of rare earth ions. The rare earth ions are changed to the 2nd electron state by the photoionization by the irradiation with 3rd wavelength light lambda3. The wavelength light lambda2 is emitted by the excitation of the wavelength light lambda1. The recording of information is executed by the 1st and 2nd electron states with the wavelength light lambda3 as recording light. The reading out of the information is executed by the presence or absence or the magnitude of the emission of the wavelength light lambda2, using the wavelength light lambda1 as the exciting light.

Description

[Detailed description of the invention]

0001

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

0002

BACKGROUND OF THE INVENTION As one of the methods of recording information using light, one that applies the photochromism phenomenon is known. There are several problems with such information recording.

[0003] Photochromism is a phenomenon in which the absorption rate of a substance for a certain light changes due to light irradiation. Therefore, a substance with such properties is used as an information recording medium, and whether the absorption rate value in a certain area, that is, an information recording pit, is above a certain threshold value or below a certain threshold value is corresponded to binary information. and record it. An ordinary information recording method using the photochromism phenomenon takes this form.

However, in this case, in order to cause a change in the absorption rate of the photochromic material, that is, to perform recording or erasing, it is generally necessary to irradiate the photochromic material with a certain amount of strong light.

[0005] For this reason, when repeated recording, reproducing, and erasing operations are performed, there is a high risk that the recording medium itself will be optically damaged, resulting in changes in characteristics and problems with its lifespan.

[0006] Furthermore, when the wavelength of the light irradiated for recording or erasing is close to the wavelength of the light used for reproduction, that is, the wavelength of the light used to detect changes in the light absorption rate in the information recording medium, has problems with reliability and signal-to-noise ratio (C/N), such as recording or erasing portions that do not need to be recorded or erased during reading.

[0007]

Problems to be Solved by the Invention The present invention provides an optical recording and reproducing method that utilizes the above-mentioned photochromism phenomenon. We aim to improve this.

[0008]

[Means for Solving the Problems] In the present invention, as an optical recording medium that causes a photochromism phenomenon, a photochromic material that can emit light at a predetermined wavelength in a predetermined electronic state using an inorganic photochromic material doped with a rare earth element is used. is used as an optical recording medium, and recording can be read out by emitting light of a predetermined wavelength.

That is, in the present invention, an optical recording medium comprising an inorganic photochromic material doped with a rare earth element is used. In this optical recording medium, the first electronic state of the rare earth ion in which light emission at the second wavelength cannot be obtained even by excitation with light at the first wavelength, and the electronic state of the rare earth element by photoionization due to irradiation with light at the third wavelength. and a second electronic state in which light emission at the second wavelength is obtained by excitation with light at the first wavelength.

[0010] Information is then recorded on this optical recording medium using the third wavelength light as recording light according to the first and second electronic states, and the first wavelength light is used as the recording readout excitation light. The above-mentioned recording is read out depending on whether or not the second wavelength light is emitted.

Another aspect of the present invention similarly uses an optical recording medium comprising an inorganic photochromic material doped with a rare earth element. This optical recording medium has a first electronic state of a rare earth ion in which light emission at a fourth wavelength can also be obtained by excitation with light at a first wavelength, and an electronic state of a rare earth element that can be changed by photoionization by irradiation with light at a third wavelength. The above 1st
A second electronic state is adopted in which light emission at the fourth wavelength cannot be obtained by excitation with light at a wavelength of .

[0012] Information is recorded on this optical recording medium using the third wavelength light as recording light according to the first and second electronic states, and the first wavelength light is used as recording readout excitation light. An optical recording and reproducing method characterized in that the recording is read out depending on the presence or absence or magnitude of emission of the fourth wavelength light.

[0013]

[Operation] According to the optical recording and reproducing method according to the present invention described above,
To read out the information, a readout light of a certain wavelength is irradiated, and the emitted light of another wavelength excited by this is extracted as information light. Therefore, as in the conventional photochromism optical recording method mentioned at the beginning, The reproduction output is significantly improved compared to the case where information is read by changing the absorption rate. Therefore, it is possible to improve the S/N (C/N).

Furthermore, since the readout light, that is, the excitation light, and the information light emitted by the light emitted from the readout light have different wavelengths, it is easy to separate the two, and the optical pickup mechanism is mounted on the same side of the optical recording medium. It is possible to adopt a simple configuration in which excitation light is irradiated and information light is extracted from. In other words, in order to detect a change in absorption rate using transmitted light, for example, when reading out a change in absorption rate, there is no need to adopt an optical pickup configuration in which a light source section and an information light reading section are arranged with an optical recording medium in between. The structure is extremely simplified.

[0015] Furthermore, the light intensity for recording and erasing, which will be described later, does not need to be increased significantly by using this type of inorganic chromic material containing rare earth elements, so Even if repeated recording and erasing is performed, the optical damage caused by the recording and erasing can be sufficiently reduced, and reliability can be improved and the service life can be extended.

[0016]

[Example] An optical recording medium 4 used in the optical recording and reproducing method according to the present invention has an inorganic photochromic material doped with a rare earth element on a substrate 1, as shown in a schematic cross-sectional view in FIG. A recording layer 2 consisting of the following materials is deposited, and a light reflecting film or a protective film 3 made of SiN, SiO2 or the like is deposited thereon as required.

The substrate 1 is made of, for example, glass or, for example, P.
It can be constructed from a light-transparent substrate made of a light-transparent resin such as C (polycarbonate).

The recording layer 2 is a photochromic inorganic compound in which a rare earth element is added to an inorganic crystal such as a metal oxide, sulfide, halide, etc. in an amount of about 1 mol % or less. The material is deposited by coating, vapor deposition, sputtering, or the like.

Examples of this photochromic material include SrF2:Sm, Eu, or BaF2:Sm,
Eu, or SrS:Ce, Sm, or SrS:Eu
, Sm, etc. can be used.

Embodiment 1 In this embodiment, SrF2:Sm,Eu is used as the photochromic material in the optical recording medium 4 shown in FIG. 1, and reading is performed using a light reflection type method.

The recording layer 2 of the optical recording medium 4 is composed of a photochromic material SrF2:Sm, Eu to which 1 mol % of Sm and Eu are added to the SrF2 matrix.

In this case, as shown schematically in FIG. 3, the energy level of the rare earth ion is as shown in FIG. 3A in the initial state. The electronic state of the rare earth ion exhibits an energy level at which no light emission at the wavelength λ2 = 690 nm occurs, that is, the first electronic state is the trivalent Sm state and the divalent Eu state.

In this state, as shown in FIG. 3B, when light of the third wavelength λ3, that is, ultraviolet rays, is irradiated, one electron is desorbed from Eu and transferred to Sm due to photoionization, so that each Eu becomes 3 The valence, Sm, becomes divalent. That is, the energy level of the rare earth ion changes. In this state, as shown in FIG. 3C, when excitation is performed with light having a first wavelength λ1 = 488 nm, a second electronic state is created in which divalent Sm emission of λ2 = 690 nm occurs.

In this second electronic state, if Sm is returned to trivalent state and Eu is returned to divalent state by irradiation with light of the fifth wavelength λ5, the first electronic state shown in FIG. 3A is achieved. can be migrated. In other words, initialization (erasing) can be performed.

Therefore, in Example 1, the third wavelength λ3 light, that is, ultraviolet rays, is used as recording light, and the first electronic state shown in FIG. 3A and the second electronic state shown in FIG. 3C are created by turning off and on the irradiation. For example, “0”, “1” depending on the electronic state of
” is recorded.

Then, light with a first wavelength λ1 = 488 nm is irradiated as readout light, and due to excitation by this, the state is changed to either the first electronic state or the second electronic state depending on whether or not light is emitted with a second wavelength λ2 = 690 nm. , that is, “0” “1”
” records can be read.

FIGS. 4 and 5 show SrF2:Sm,Eu in the first and second electronic states at a wavelength of 488 nm (λ1
) shows an emission spectrum diagram when photoexcited. In this case, orange light emission of about 607 nm is obtained in the first electronic state, and red light emission of about 690 nm is obtained in the second electronic state.

Recording, reproduction (reading), and erasing in this embodiment 1 are performed using at least a light source section 21 disposed on the side of the optical recording medium 4 facing, for example, the light-transmitting substrate 1, as shown in FIG. This is performed by an optical recording/reproducing means having a photodetector section 22. In this case, the light source section 21 includes a light source with a first wavelength λ1 = 488 nm, an ultraviolet light source with a third wavelength, and a light source with erasing light with a fifth wavelength.

First, for recording, the third wavelength λ3 light, in this example, ultraviolet light, is modulated on and off in accordance with the recording information to change from the first electronic state to the second electronic state. or “0” without changing it.
1” is recorded.

For reading, the first wavelength λ
By irradiating light of 1 = 488 nm, second wavelength light λ2 = 690 nm is emitted from the recording layer 2 of the optical recording medium 4, and this red emission is filtered or a mirror that reflects the light of this wavelength. 23 and introduced into the photodetecting section 22, and the information of "0" and "1" is read out depending on the presence or absence of light emission of this second wavelength λ2.

In this case, the excitation light of the first wavelength λ1 = 4
Since there is a large difference in wavelength between light with a wavelength of 88 nm and light with a second wavelength λ2 = 690 nm, that is, information light, the light can be reliably separated from the excitation light and detected, so the S/N ( C/N) can be read.

The photodetector 22 is constituted by, for example, a photodiode, and its output is amplified by an amplifier. Alternatively, a photomultiplier can also be used as the photodetector 22.

In the above example, light irradiation and reading are performed from the substrate 1 side of the optical recording medium 4, but the protective film 3 side is made transparent and the substrate 1 is coated with a reflective surface such as Al. It is also possible to form it on the adhering surface side of the recording layer 2 and perform light irradiation and reading from the protective film 3 side.

In the example shown in FIG. 2, the optical recording medium 4 is irradiated with excitation light, that is, the first wavelength light, and detected with the information light, that is, the second wavelength light. However, it is also possible to sandwich them with an optical recording medium in between, irradiate readout light from one side, and detect information light from the other side.

Example 2 In Example 1 described above, the presence or absence of the second electronic state, that is, the case where the second wavelength λ2 light is used as information light, is the case, but in this example, the presence or absence of the first electronic state,
That is, the same recording and reproducing method as in the first embodiment is used except that the light having the fourth wavelength λ4 in FIG. 4 is used as the information light.

In the above-described configuration, the photochromic material of the optical recording medium generally exhibits high luminous efficiency when the excitation light wavelength λ3 is smaller than the emission wavelengths λ2 and λ4. When extracting the signals, λ3 < λ2, λ4 is set as much as possible. Further, by setting λ3 <λ1, λ4, the inconvenience of recording during reproduction (reading) can be avoided, and so-called non-destructive reading can be performed. Also, λ5 <λ
1, erasure during playback can be avoided.

It has been confirmed that the optical recording media made of each of the above-mentioned photochromic materials have stable characteristics and do not show any change over time, and do not cause optical damage to the materials themselves.

As described above, according to the present invention, the optical recording, that is, the excitation light for reading information, that is, the first wavelength λ1 light, can record information of, for example, "0" and "1". Since the excitation is performed using light of a first wavelength different from the writing wavelength, that is, the light of the third wavelength λ3, erroneous recording can be avoided during this reading.

Further, the information light has a second wavelength λ2 different from the first wavelength light λ1 of the excitation light for reading out the information light.
or the fourth wavelength λ4 light, the information light can be easily separated. Therefore, the optical recording medium 4 can be irradiated with light such as read light and the information light on the same side, and the structure of the optical pickup means can be simplified.

Furthermore, since the information lights of λ2 and λ4 are emitted, the reproduction output is improved and the S/N (C/N) is improved.
N) can be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic enlarged cross-sectional view of an example of an optical recording medium used in the optical recording and reproducing method according to the present invention.

FIG. 2 is a schematic diagram of an example of the optical recording and reproducing method according to the present invention.

FIG. 3 is an energy level diagram of rare earth ions for explaining the operation of the optical recording and reproducing method of the present invention.

FIG. 4 is an emission spectrum diagram of SrF2:Sm, Eu in a first electronic state.

FIG. 5 is an emission spectrum diagram of SrF2:Sm, Eu in a second electronic state.

[Explanation of symbols]

1 Base 2 Recording layer 3 Protective film 4 Optical recording medium 21 Light source section 22 Photo detection section

Claims (2)

[Claims] 1. An inorganic photochromic material doped with a rare earth element, comprising a first electronic state of a rare earth ion in which light emission at a second wavelength cannot be obtained even by excitation with light at a first wavelength; Using an optical recording medium that adopts a second electronic state in which the electronic state of the rare earth ion is changed by photoionization by wavelength light irradiation and the second wavelength light emission is obtained by the first wavelength light excitation, The third wavelength light is used as recording light to record information according to the first and second electronic states, and the first wavelength light is used as recording readout excitation light to determine whether or not the second wavelength light is emitted. An optical recording and reproducing method characterized in that the above-mentioned recording is read out depending on the size. Claim 2: Comprised of an inorganic photochromic material doped with a rare earth element, the fourth photochromic material is
The electronic state of the rare earth ion is changed by photoionization by irradiation with a third wavelength light, and the fourth wavelength light is emitted by excitation with the first wavelength light. using an optical recording medium that adopts a second electronic state in which no light emission is obtained;
Information is recorded by using the wavelength light as recording light according to the first and second electronic states, and the first wavelength light is used as recording readout excitation light depending on the presence or absence or size of emission of the fourth wavelength light. An optical recording and reproducing method characterized by reading out recorded information.