JPH02278535A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To increase information capacity per one bit in a recording medium and to realize high density recording by forming a recording layer which enables unsaturated recording according to energy level of irradiating light and allowing the recording layer to have plural values of reflectance corresponding to decoloration of the org. dye contained in the recording layer. CONSTITUTION:Some org. dyes such as polymethyne cyanine and azulene show an increase in the modulation degree with increase of irradiating light power and finally saturate. The modulation degree indicates variation in reflectance of a recording bit against the power of irradiating light. The same effect can be easily and accurately realized with constant power of irradiating light and increasing pulse duration for recording. On recording, various duration of pulse is used to give various levels of modulation degrees under saturation, so that multiple informations can be recorded in one bit. A two-bit signal is transformed in a one-bit signal by a multilevel circuit 31 and the signal is sent to a multilevel modulation/demodulation circuit 12 to obtain a binary signal. Thus, high density data signals can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical information recording medium that records information in multivalued form. The present invention is suitable for, for example, optical cards and optical discs.

[Prior Art] Conventionally, media have been used to record information using light and to read recorded information in the form of disks, cards, etc.
Various types such as tape-shaped ones are known. These optical information recording media include those capable of recording and reproduction, and those capable of only reproduction.

Information is recorded on a recordable medium by scanning an information track with a light beam that is modulated according to the recorded information and focused into a minute spot, and the information is recorded as an optically detectable information bit string. Ru.

Furthermore, in order to reproduce information from a recording medium, the information bit string of the information track is scanned with a light beam spot having a constant power such that no recording is performed on the medium, and reflected light or transmitted light from the medium is detected. This is done by

A so-called optical head is used to irradiate a light beam spot onto a recording medium and detect reflected light or transmitted light from the medium as described above. The optical head is movable relative to the recording medium in the information track direction and in a direction transverse to the information track direction, and this relative movement allows the light beam spot to be scanned onto a desired information track.

An optical information recording and reproducing apparatus that records and reproduces information using this type of recording medium has control that follows the surface deflection of the recording medium to always form a light beam spot of a predetermined size on the surface of the medium. Autofocusing (AF) for
It is common to have control means. Further, this type of optical information recording/reproducing device has an automatic system for accurately positioning a light beam spot on the information track by following the deflection of the information track due to the deviation of the information track arrangement with respect to the outer shape of the recording medium. It is common to have tracking (AT) control means.

[Problems to be Solved by the Invention] By the way, when recording and reproducing information using such optical discs and optical cards, it is possible to record only up to bits of a size determined by the beam spot, which hinders higher density. was. It is easy to understand that in order to record information with high density, it is better to reduce the bit size.
There is a problem in that it is difficult to achieve high density because the bit size cannot be made very small considering the problem of diffraction and the influence of dust and fingerprints on the surface of the disk or card.

[Means for Solving the Problems] An object of the present invention is to provide an optical information recording medium that can achieve high density information recording.

The purpose of the above is that the recording layer is composed of at least a transparent protective layer, an organic dye-based recording layer, and a high reflection layer from the side to which light is irradiated, and that the recording layer is unsaturated recording by the optical energy level of the irradiated light beam. After recording information, the recording layer is in an unchanged state, the recording layer is thermally changed by the optical power of the light beam and a hole is opened that reaches the high reflective layer, and the optical power of the light beam is in a state where the recording layer is in an unchanged state. This is achieved by an optical information recording medium characterized by having three forms in which the organic dye is decolored.

In order to achieve high density of information in the - layer, it is preferable that the state in which the organic dye is bleached by the optical power of the light beam has a plurality of reflectances depending on the degree of bleaching.

According to an embodiment of the present invention, for one bit, three bits including an unrecorded part are
By performing three-value recording using a recording medium that can perform two recording states, it is possible to substantially increase the density by about 1.5 times.

[Examples] Hereinafter, the optical information recording medium of the present invention will be described in detail based on specific examples.

First, an optical information recording/reproducing apparatus for recording and reproducing information on an optical information recording medium of the present invention will be explained.

FIG. 1 is a block diagram showing the configuration of an embodiment of an information recording and reproducing apparatus for recording information on an optical card 1 and reproducing information recorded on the optical card.

In FIG. 1, numeral 19 indicates a recording/reproducing device, and the device 1
9 is connected to a CPU 50 which is a higher-level control device. In the recording and reproducing apparatus 19, 14 introduces the optical card 1 into the recording and reproducing apparatus via a transport mechanism (not shown), moves it back and forth in the R direction at a predetermined recording and reproducing position, and then ejects it from the apparatus. It is a drive motor for.

Reference numeral 17 denotes a light beam irradiation optical system including a light source, which forms a light beam spot on the optical card 1 during information recording and information reproduction. In this embodiment, three light beam spots are formed on the optical card during recording and reproduction.

22 to 24 are photodetectors, each of which can receive the reflected light of the three light beam spots on the optical card 1. Reference numeral 15 is for performing autofocusing (AF) by driving a part of the light beam irradiation optical system 17 to move the focus position of the light beam spot on the optical card surface in the Z direction, that is, in a direction perpendicular to the optical card surface. AF actuator. 16 drives a part of the light beam irradiation optical system 17 to direct the light beam spot on the optical card surface in the Y direction (i.e., R
direction (direction perpendicular to both the direction and the Z direction)
This is an AT actuator for performing T.

The light beam irradiation optical system 17, detectors 22 to 24, AF
An optical head 18 includes an actuator 15 and an AT actuator 16.

Reference numeral 13 denotes a drive motor for moving the optical head in the Y direction to access the optical beam spot to a desired track on the optical card.

The drive motor 13 and the drive motor 14 are MPU10.
controlled by Further, the outputs of the photodetectors 22 to 24 are input to the AT/AF control circuit 11, and based on this, the control circuit 11 controls the AF actuator 15 and the AT/AF control circuit 11.
The actuator 16 is controlled to perform AF and AT.

The outputs of the photodetectors 22 to 24 are also transmitted to a multi-value circuit 31.
The read information is converted into a binary information signal and input to the multi-value modulation/demodulation circuit 12, where the read information is demodulated, and the demodulated signal is sent to the MPU10. Further, the multi-value modulation/demodulation circuit 12 converts the information signal sent from the MPU10 into multi-value information using the multi-value converting circuit 31, modulates it by a predetermined modulation method, changes the light intensity according to the modulation signal, and The beam irradiation optical system 17 is driven to record information.

The MPU10 is controlled by the CPU 50 and exchanges data with the CPU 50.

FIG. 2 is a perspective view showing details of the optical head portion of FIG. 1.

In FIG. 2, 27 is a semiconductor laser as a light source, 28 is a collimator lens for collimating the light beam, 29 is a light beam shaping prism, 30 is a diffraction grating for splitting the light beam, 20 is a beam splitter, 25 is a reflecting prism, 26 21 is an astigmatism condensing lens system; 22 is an objective lens that condenses light;
-24 are the above-mentioned photodetectors.

The light beam emitted from the semiconductor laser 27 becomes a diverging light beam and enters the collimator lens 28, and is converted into a parallel light beam by the lens. The parallel light beam is shaped into a predetermined light intensity distribution by the light beam shaping prism 29, and then enters the diffraction grating 30, which divides the collimated light beam into three effective light beams (O-order diffracted light and ±1st-order diffracted light). ). These three light beams then enter the beam splitter 20, pass through the beam splitter 20, and then pass through the reflective prism 25.
It is reflected by the lens, enters the objective lens 26, and is focused by passing through this, resulting in three minute light beam spots St (corresponding to the +1st-order diffracted light) and 52 (corresponding to the O-th order diffracted light) on the optical card 1. 53 (corresponding to -1st order diffracted light).

The light beam spots Sl and S3 are located on adjacent tracking tracks 5, and the light beam spot S2 is located on the information track 4 between the tracking tracks.

In this way, the reflected light from the light beam spot formed on the optical card 1 passes through the objective lens 26, is made almost parallel, is reflected by the reflection prism 25, is further reflected by the beam splitter 20, and is reflected by the focusing lens system 21. The light is focused by the light beam and incident on the photodetectors 22, 23, and 24.

FIG. 3 is a diagram showing the configuration of the photodetectors 22-24. The photodetector 23 is a 4-split photodetector, and the AF operation is performed by this photodetector 23. In addition, the photodetector 22.
AT operation is performed by 24.

Note that the light beam spot S2 is used for recording and reproduction, and the light beam spots SL and S3 are used for l.racking. Therefore, the intensity of the ±1st-order diffracted light (Sl, S3) created by the diffraction grating 30 is such that even when spot S2 is recorded, it is not recorded, and spot S2 is not recorded.
2 needs to be set so that tracking servo can be used even during playback. Specifically, it is important to set the intensity ratio between the light transmitted through the diffraction grating 30 (O-order diffracted light) and the ±1st-order diffracted light. If it is difficult to set such an intensity with the diffraction grating 30, the hologram element proposed by the present applicant in Japanese Patent Application No. 167889/1989 may be used as the beam splitting means, so that the intensities of the light beam spots SL and S3 can be adjusted to a predetermined level. It is best to create the hologram while adjusting it so that the intensity is as follows.

Furthermore, if necessary, it is also possible to configure an embodiment in which the lasers that generate the light beam spots Sl and S3 and the laser that generates the light beam spot S2 are different lasers, and in that case, the above settings can be made. Although this method has the advantage that it is not necessary to perform this process, it has the disadvantage that at least a plurality of laser light sources are required, which increases the cost.

Next, an example will be described in which the multi-value level of the recording medium is selected as three values.

FIG. 4(I) is a diagram showing an enlarged sectional view of such an information recording medium according to the present invention.

FIG. 4 (II) is a diagram showing the optical power during recording, and FIG. 4 (III) is a diagram showing the reflectance.

In FIGS. 4(I) to (III), ternary recording medium 1
, transparent protective layer 101, recording layer 102, high reflectance 104
, a back side protective layer 105, and at position a,
Recording is performed at a first recording power of 40, and the recording layer 102 is decolored by thermal changes, thereby forming pits 103a. Further, at the position b, recording is performed with a second recording power 42 that is higher than the first recording power, a hole is formed in the recording layer 102 due to thermal deformation, and the bit 103 with the high reflective layer 104 exposed
I can do b. Pit 103a created in this way
It can be easily predicted that the waveform reproduced from 103b will be as shown in FIG. 4 (III).

The reproduction signal obtained from the ternary recording medium 1 as described above is input to the ternarization circuit 31. This ternarization circuit 3
1 converts the information signal from the optical head into three values, one level is based on the level of the unrecorded part, another level is a predetermined value lower than this reference level, and yet another level is This is performed at a level higher than this reference level by a predetermined value.

FIG. 5(I) is a diagram showing a specific configuration example of the ternarization circuit 31, and FIGS. 5(II) and (III) are diagrams showing signals obtained from the ternarization circuit 31, respectively. .

In FIG. 5(I), the reproduced signal 31a is transmitted to the subtracter 31b.
As a result, the difference between the original signal and the DC component (reference level) of the unrecorded portion that has passed through the LPF is taken, resulting in a signal 31v.

This signal 31v becomes a signal that changes from positive to negative as shown in FIG. 5 (II). Therefore, the comparators 31c and 31d are used to generate binary level signals 31f'' and 31f-, and the adder 31e generates +1 as shown in FIG. 5(III).
, 0° and 1, resulting in a signal 31h, and the ternarization is completed.

Next, the point that ternary recording achieves high density recording approximately 1.5 times as high as binary recording will be explained using FIG. 6.

In Fig. 6, the left column shows all data equivalent to 3 bits of binary recorded data, and each data can be completely expressed by data equivalent to 2 bits of ternary recorded data as shown in the right column. It shows.

Next, a recording medium of the present invention that realizes multi-value recording of four or more values will be described.

First, the characteristics of the recording medium required for such multi-value recording (including the above-mentioned three-value recording) will be described.

FIG. 7(I) shows the degree of modulation (changed amount of reflected light/original amount of reflected light) that determines the change in reflectance of a recorded bit with respect to the irradiation light power of 1 for an information recording medium. As the irradiation power increases, the modulation degree gradually increases and eventually reaches saturation. Such optical recording materials include dye-based materials (organic dye-based materials, such as polymethine-based cyanines and azecines). On the other hand, even when the irradiation power is kept constant and the irradiation time, that is, the recording pulse width is gradually increased, the amount of irradiation light is changed.
A similar characteristic curve is obtained as shown in Figure (II). In FIG. 7 (II), a, b.

C is the recording pulse width at which the degree of modulation is equal to or less than the saturation value.

FIG. 7(IV) shows the modulation degree of each recording pit when recording is performed at different positions with recording pulse widths a, b, and c as shown in FIG. 7(III).

By setting the recording pulse widths to a, b, and c in the manner described above, information can be recorded in one pit in four states, including the unrecorded portion. This method of making unsaturated recording possible by changing the recording pulse width has the advantage of being easier and more accurate than the method of changing the irradiation power itself. , Unsaturated recording refers to recording at a level where the modulation degree is less than the saturation value, and in order to realize multi-value recording with good S/N, the modulation degree must be adjusted to the recording energy change that is the interval between the multi-value values. It is preferable that the temperature changes largely and evenly, and a recording medium that changes like a threshold is not preferable.

Reproduction signal S of information recorded using such a recording medium
, is manually operated by a multilevel converting circuit 31 as shown in FIG.

FIG. 8(I) is a block diagram of the multi-level conversion circuit 31, and FIG.
I) to (IV) are the respective signal diagrams.

The manually generated reproduction signal S, (see FIG. 9(I)) is input to the clock generation circuit 60, and the reproduction clock signal S, (see FIG. 9(I)) is input to the clock generation circuit 60.
(See FIG. 9 (II)) is created. At the same time, the playback signal S
, are manually input to the sample and hold circuit 61, and are sampled and held in accordance with the reproduced clock signal Sc to become a multilevel signal Sm (see FIG. 9 (III)). By A-D converting this multilevel signal S0, binary signals S, (
(see FIG. 9(rv)). S□ and 86
A correspondence table is shown in Figure 10. In this way, the 1-bit information signal S□ can completely represent the 2-bit signal Sd. That is, the multilevel signal S□ is input to the multilevel modulation/demodulation circuit 12 including an A/D conversion circuit, becomes a binary signal, and can be demodulated into a data signal.

In the above embodiment, the case where recording is performed using three types of recording pulses to create four types of recording states including a non-recorded state has been described, but the present invention is not limited to this. It is clear from the content of the present invention that it is possible to create more recording states and increase the density of information.

[Effects of the Invention] As explained above, according to the optical recording medium of the present invention, at the time of recording, at least two types of light, which produce unsaturated recording with a predetermined optical power and which produce unsaturated recording, are produced with a predetermined optical power. By recording with pulses, the amount of information per bit can be increased and density can be increased.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical information recording/reproducing apparatus implementing the present invention. FIG. 2 is a detailed view of the optical head. FIG. 3 is a diagram of the light receiving element of the optical head. FIG. 4 is a diagram for explaining a ternary recording medium according to the present invention. FIG. 5 is a block diagram of the ternarization circuit and a diagram explaining its operation. FIG. 6 is a diagram explaining the correspondence between ternary data and binary data. FIG. 7 is a diagram for explaining a multilevel recording medium according to the present invention. FIGS. 8 and 9 are block diagrams of the multi-level quantization circuit and diagrams for explaining its operation. FIG. 10 is a diagram illustrating the correspondence between quaternary data and binary data. 1: Optical card, 12: Multi-level modulation/demodulation circuit, 18: Optical head, 31: Multi-level conversion circuit. Agent Patent Attorney Minoru Yamashita Figure (n) Figure (I [) (III) Figure (I) (I [) Figure A (m) (IV) May 31, 1999 Director General of the Japan Patent Office Yoshi 1) Indication of the case of Takeshi Moon Patent Application No. 1-97262 Name of the invention Optical information recording medium Person who makes the amendment Relationship to the incident Patent applicant address 3-30-2 Shimomaruko, Ota-ku, Tokyo Name (10
0) Canon Co., Ltd.

Claims (2)

[Claims] (1) A characteristic that the recording layer is composed of at least a transparent protective layer, an organic dye-based recording layer, and a high reflection layer from the side to which light is irradiated, and that unsaturated recording is possible depending on the optical energy level of the light beam that is irradiated to the recording layer. After recording information, the recording layer is in an unchanged state, the recording layer is thermally changed by the optical power of the light beam and a hole is opened that reaches the high reflection layer, and the organic dye is decolorized by the optical power of the light beam. An optical information recording medium characterized by having three types of states. (2) The optical information recording medium according to claim 1, wherein the state in which the organic dye is bleached by the optical power of the light beam has a plurality of reflectances depending on the degree of bleaching.