JPH064868A - Optical information recording medium and method for recording, reproducing and erasing optical information - Google Patents

Abstract

PURPOSE:To enhance reliability by controlling the recording, reproduction and erasure of optical information in accordance with a sudden temp. rise or a high-temp. state in an optical information recording medium and a drive. CONSTITUTION:A temp. monitor made of a nonlinear optical material is fitted to an arbitrary position of an optical information recording medium. The temp. of the medium can be monitored by detecting the intensity of SHG by temp.- phase matching of the nonlinear optical material and a change in the intensity. Such proper treatment as control of conditions in irradiation with laser beams at the time of recording, reproduction or erasure is carried out with the observed results.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In an optical information recording medium, for example, when a low temperature or normal temperature optical information recording medium is loaded into a high temperature drive, birefringence increases or mechanical characteristics change depending on its constituent material. May occur. Also, the oscillation wavelength of the semiconductor laser may change as compared with normal temperature due to the rise in temperature. When reproduced under such a condition, the data cannot be read, or the recording sensitivity changes during recording to form a recording state different from that at room temperature. Conventionally, as a measure against such temperature,
A temperature sensor is installed in the drive to detect the temperature inside the drive, and when the temperature rises above a certain temperature, recording, playback, and
Some lock the erase operation.

However, it is not the temperature in the drive or its change that is important in this temperature problem.
It is the temperature of the optical information recording medium itself, that is, the temperature of the recording film or the like, or the temperature change of the recording film or the like, and this directly causes inconveniences such as a reproduction error and a change in recording characteristics. Therefore,
It is desirable to control the recording, reproduction and erasing of optical information by monitoring the temperature and temperature change of the optical information recording medium itself in order to improve reliability.

The present invention has been made in view of the above-mentioned circumstances of the prior art, and controls recording, reproduction and erasing of optical information appropriately in response to a rapid temperature rise or high temperature of an optical information recording medium, An object of the present invention is to provide an optical information recording medium and an optical information recording / reproducing / erasing method capable of highly reliable recording / reproducing / erasing.

[0005]

In order to achieve the above object, according to the present invention, in an optical information recording medium having at least a recording film provided on a substrate, nonlinearity is provided at an arbitrary position on the optical information recording medium. An optical information recording medium is provided, which is provided with a temperature monitor unit made of an optical material. Further, according to the present invention, there is provided an optical information recording medium, characterized in that the thermal conductivity of the nonlinear optical material is substantially equal to the thermal conductivity of the recording film. Further, according to the present invention, in the above, there is provided an optical information recording medium having a recording film made of a non-linear optical material. Further, according to the present invention, by using the above optical information recording medium and observing SHG (second harmonic generation) due to temperature phase matching of the non-linear optical material of the temperature monitor, the optical information recording is performed. There is provided an optical information recording / reproducing / erasing method, which is characterized by recording / reproducing / erasing optical information by monitoring a temperature of a medium. Further, according to the present invention, in the above method, SHG
The optical information recording / reproducing / erasing method is provided, wherein the observation is detection of SHG intensity and / or variation of SHG intensity. Further, according to the present invention, in the above method, data indicating temperature characteristics of birefringence and mechanical characteristics of the optical information recording medium is recorded in advance in a part of the recording area of the optical information recording medium, and recording and reproducing are performed. The optical information recording / reproducing / erasing is characterized in that the data is read before erasing, and the laser light intensity condition at the time of recording / reproducing / erasing is controlled based on the read data and the observation data of the temperature monitor. A method is provided.

[0006]

According to the present invention, the temperature and temperature change of the medium itself can be directly measured by observing the SHG intensity and the intensity change from the temperature monitor section made of a non-linear optical material installed at an arbitrary position on the optical information recording medium. It becomes possible to monitor. Therefore, this monitor notifies the user of a temperature abnormality when the temperature exceeds a certain level, prohibits the write operation when the temperature change when the medium is inserted into the drive is more than a certain value, and monitors the temperature and the temperature change. It is possible to perform processing such as controlling the laser intensity so that the sensitivity (corresponding to temperature change) of the medium is optimized based on the data of the birefringence value of the medium material and the mechanical property value corresponding to it. Therefore, the above problems can be solved.

[0007]

EXAMPLES The present invention will be described in detail below based on examples. The optical information recording medium of the present invention is constructed by providing a temperature monitor section made of a non-linear optical material at an arbitrary place on the medium. There is a correlation described below between SHG and temperature of the nonlinear optical material, and the temperature of the medium itself can be known by monitoring the SHG, and highly accurate temperature evaluation can be performed. The temperature monitor may be provided at any position on the medium, but for example, in the case of an optical disk that rotates on a turntable, the temperature near the inner circumference is considered to have the highest temperature and the highest temperature gradient. It is desirable to install it near In this case, it is preferable that a bulk or thin film non-linear optical material is locally provided at one or a plurality of locations, or continuously provided in a ring shape, for example, as a configuration of the monitor section. Further, as the installation method, a bulk or thin film nonlinear optical material is attached to a desired place with an adhesive or the like, and in the case of a thin film, sputtering,
Means such as vapor deposition and spin coating can be used. If you want to know the temperature of the medium more accurately,
As the non-linear optical material, a material that allows good heat transfer or a non-linear optical material having a thermal conductivity similar to that of the recording film is used. The recording layer itself may be made of a non-linear optical material, and a part of it may be used as a monitor. The material used for the monitor may be a substance whose refractive index with respect to extraordinary rays changes with temperature. That is, any substance whose SHG efficiency changes depending on temperature even if phase mismatching is used. Preferably, a substance that achieves a temperature phase matching state in a realistic temperature range is preferable. Specific materials include LiNbO ₃ and BaNaNb ₅
A substance such as O ₁₅ (BNNO) that easily achieves temperature phase matching, or KDP or LiI as a general substance
Inorganic crystals such as O ₃ and ADP, organic crystals such as urea, α-resorcinol, m-nitroaniline, MNA and POM, polymer substances such as polyvinylidene fluoride, polymer liquid crystals, polymer compositions, polymer liquid crystals A composition etc. are mentioned.
The light source used for this monitor may be a laser beam for recording, reproduction, erasing or another laser beam, and SHG detection uses only the second harmonic of the original laser beam. It is carried out by a photodiode or a photomultiplier through a means such as a filter for transmitting light. It is preferable to manage the intensity of the detected SHG data and its temporal variation. These data show beforehand the temperature dependence of the second harmonic intensity with respect to the laser light wavelength used of the nonlinear optical material used (for example, the ROM of the drive).
The temperature of the optical information recording medium can be known by monitoring the intensity of the SHG by comparing it with the data recorded inside or in a part of the recording area of the medium, so the following measures are taken, for example. . When the medium temperature exceeds a predetermined temperature, the user is notified of it by means such as a temperature abnormality lamp and a warning sound provided in the drive. When the temperature change of the medium when the medium is loaded in the drive is more than a predetermined value, the writing operation is prohibited. The recording / reproducing / erasing position of the medium, the temperature at the position and the birefringence value corresponding to the temperature change, the intensity of the SH wave monitored, and the actual temperature and temperature change value of the medium calculated from the intensity change are also included. Then, the laser intensity is controlled to be optimum for the sensitivity of the medium (corresponding to the temperature change). In the case of performing the above control, data indicating the temperature characteristics of the birefringence and mechanical properties of the optical information recording medium is recorded in advance in a part of the recording area of the optical information recording medium before recording, reproducing, or erasing. It is preferable that the data is read and the laser light intensity at the time of recording, reproducing, and erasing is controlled on the drive side based on the read data and the observation data of the temperature monitor.

Next, the relationship between SHG and temperature and temperature phase matching will be described with reference to specific examples. Here, an optical disk in which a LiNbO ₃ crystal is installed in a bulk form in the non-recording area of the inner peripheral portion will be described as an example. When the angular frequency of the fundamental wave is ω ₁ and the angular frequency of the second harmonic wave is ω ₂ , ω ₁ and ω ₂ are n ₁ and n ₂ , the fundamental wave and the second harmonic wave are both plane waves. Assuming that they propagate in the same direction, the phase matching condition is expressed by the following equation (1). ω ₂ n ₂ = 2ω ₁ n ₁ (1) Generally, in a crystal without absorption, the change in refractive index shows ordinary dispersibility, and the following relational expression holds. n ₂ ′ −n ₁ ′> 0 n ₂ ″ −n ₁ ″> 0 (2) where n ₁ ′ and n ₂ ′ are ordinary refractive indices for ω ₁ and ω ₂ ,
n ₁ ″ and n ₂ ″ are the extraordinary ray refractive indices for ω ₁ and ω ₂ . Due to the above relationship, if an ordinary ray or an extraordinary ray is used for the incident wave (fundamental wave) and the second harmonic, ω ₂ = 2ω
Equations ₁ and (1) are incompatible. However, if one is an ordinary ray and the other is an extraordinary ray, both equations can be satisfied at the same time. That is, as shown in FIG. 1, at the angle of θi, ω ₂
The phase matching is achieved by matching the extraordinary ray refractive index n ₂ ″ (θi) of ω _{1 with} the ordinary ray refractive index of ω _{1. In} the case of a negative uniaxial crystal, the following equation (3) is related to the phase matching angle θi. Sin ² θi = {(1 / n ₁ ') ^2- (1 / n ₂ ') ² } ÷ {(1 / n ₂ ") ^2- (1 / n ₂ ') ² } ... (3 ) In the case of LiNbO ₃ crystal, ω ₁ = 1.064 (μm),
If ω ₂ = 0.532 (μm), then n ₁ '= 2.15
Since 2, n ₂ '= 2.2304 and n ₂ "= 2.3224, θi ≈ 77 ° from the above equation (3). However, under this phase matching condition, as can be seen from FIG. ω
_When the fundamental wave of ₁ is incident in the direction of θ i, the ray direction of the second harmonic, which is an extraordinary light, has an angle of ψ with respect to the incident fundamental wave, and the coupling relation of the light waves becomes complicated, and SH
G becomes imperfect. Therefore, in SHG, a phase matching angle of θi = 90 ° is desirable. In this condition, the equation (3) becomes the following equation. _{n 1 '-n 2 "= (} n 2' -n 2") - a _{(n 2 '-n 1')} = 0 ··· (4). The phase matching of the equation (4) can be satisfied by utilizing the temperature change of the refractive index. For example LiNbO ₃
In the case of, when the angular frequency of the incident fundamental wave is 1.064 μm, the following relational expression is satisfied. d (n ₂ '−n ₂ ″) /dT=−4.5×10 ⁻⁵ d (n ₂ ′ −n ₁ ′) /dT=1.21×10 ⁻⁵ (5) Therefore, LiNbO _When the temperature T of ₃ reaches about 80 ° C, θi
= 90 ° C phase matching is obtained. At this time, the SHG conversion efficiency becomes maximum. Conversely, in the case of the present example, if the phase matching state approaches (that is, if the medium temperature approaches 80 ° C.), S
The intensity of HG increases, and conversely, if it goes away from the phase matching state (that is, if the medium temperature deviates from 80 ° C.), the intensity of SHG decreases, and the crystal temperature can be known by observing the intensity of SHG. You can

[0009]

As described above in detail, according to the present invention, since the temperature monitor section made of the non-linear optical material is provided at any place of the optical information recording medium, the high temperature state of the medium and the rapid temperature change. It is possible to appropriately process a reproduction error and a change in recording characteristics in the generated state, and it is possible to realize highly reliable recording, reproduction, and erasing of optical information.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of SHG phase matching conditions when a negative crystal is used.

Claims (6)

[Claims] 1. An optical information recording medium having at least a recording film provided on a substrate, wherein an optical information recording medium is provided with a temperature monitor section made of a non-linear optical substance at an arbitrary position of the optical information recording medium. Medium. 2. The optical information recording medium according to claim 1, wherein the thermal conductivity of the non-linear optical material is substantially equal to the thermal conductivity of the recording film. 3. The optical information recording medium according to claim 1, wherein the recording film is made of a non-linear optical material. 4. Using the optical information recording medium according to claim 1, by observing SHG due to temperature phase matching of the non-linear optical material of the temperature monitor, the temperature of the optical information recording medium and / or Alternatively, an optical information recording / reproducing / erasing method is characterized in that the optical information is recorded / reproduced / erased by monitoring a temperature rise. 5. The SHG observation is based on SHG intensity and //
Alternatively, the optical information recording / reproducing / erasing method according to claim 4, wherein detection of variation in SHG intensity is performed. 6. Data indicating the temperature characteristics of birefringence and mechanical properties of the optical information recording medium is previously recorded in a part of the recording area of the optical information recording medium, and the data is recorded before recording, reproducing and erasing. 6. The optical information recording / reproducing / erasing according to claim 4 or 5, wherein the data is read and the laser light intensity at the time of recording / reproducing / erasing is controlled based on the read data and the observation data of the temperature monitor. Method.