KR100608253B1 - Phase change optical disc having double recording layer, and tenary data processing method for the optical disc, and apparatus therefor - Google Patents

Abstract

A phase change optical disk having two recording layers includes a substrate; A first recording layer overlying at least one surface of the substrate and composed of a phase change material; An interlayer formed over the first recording layer and composed of a dielectric; And a second recording layer overlying the interlayer and composed of a phase change material. A data processing method for recording and / or reproducing data on a phase change optical disk includes: converting input binary data into ternary data using a ternary channel coding method; And optically modulating the converted ternary data on two recording layers of the optical disc. The above data processing method further comprises the steps of: reproducing ternary data recorded from three optical states obtained by irradiating the optical disk with a single wavelength of laser light; And restoring the reproduced ternary data into binary data by using the inverse transformation of the ternary channel coding scheme described above. In addition, the recording apparatus according to the above-described data processing method includes a ternary converter, laser power modulation and recording means, and the reproduction device includes ternary data reproduction means and binary converter. Thus, the present invention provides a high density recording and reproduction of phase change optical discs having two recording layers, and high density data on the phase change optical discs, which significantly improve the recording density and enable accurate reproduction of data recorded by a single wavelength laser light. It is possible to provide a recording and reproducing system according to a ternary data processing method that is optimal for the characteristics of the recording medium.

Description

Phase change optical disc having double recording layer, and tenary data processing method for the optical disc, and apparatus therefor}

1A is a diagram for explaining four magnetization states in a conventional magneto-optical disk system having two recording layers;

FIG. 1B is a diagram for explaining a method of recording and reproducing data on the magneto-optical disc shown in FIG. 1A;

2 is a diagram showing a multilayer structure of a phase change optical disk having two recording layers, according to an embodiment of the present invention;

3A shows a ternary NRZ recording waveform sequence according to the ternary data processing method of the present invention;

FIG. 3B is a view showing three phase change mark states in which the ternary NRZ waveform sequence of FIG. 3A is recorded in the two recording layers shown in FIG.

3C is a waveform diagram of a reproduction signal corresponding to three optical states obtained based on the phase change marks shown in FIG. 3B;

4 is a graph showing a change in reflectance for each phase change mark state obtained by irradiating laser light of 690 nm when the thickness of the incident layer of the phase change optical disc shown in FIG. 2 is varied;

5 is a graph showing the results of measuring the electric field and energy at the interface of each layer when the thickness of the insulating layer of the phase change optical disk shown in FIG.

FIG. 6A illustrates a structure of a ternary data stream according to a ternary channel coding scheme to be recorded in the two recording layers of FIG. 2 according to an exemplary embodiment of the present invention; FIG.

6B is a view for explaining a ternary NRZ recording method corresponding to the ternary data stream shown in FIG. 6A;

7 illustrates modulation code selection groups for 8 to 12 conversion, as an embodiment of the ternary channel coding scheme of FIG. 6A;

Fig. 8 is a block diagram showing an apparatus for recording and reproducing data on a phase change optical disc having two recording layers, according to one preferred embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

80: two recording layer phase change optical disk 81: ternary converter

82: laser power modulation and recording means 83: optical pickup

84: ternary data reproducing section 85: synchronous restoring section

86: binary conversion unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc having a high recording density, and more particularly to a phase change optical disc having two recording layers, and a ternary data processing method and apparatus for recording / reproducing data on the optical disc.

In general, in order to record and reproduce high-capacity data such as high-definition video data, multi-channel high resolution audio data, and multimedia data on a digital recording medium, it is required to increase the density of an optical disc. As a method for densification of the optical disk, Nikon's deep groove method, Matsushida's dual layer recording method, and Hitachi's magneto-optical material have a double recording layer. A magneto-optical disc method has been proposed.

, 최소시간간격은 (d+1), 재생시의 검출창폭은

, 그리고 기록밀도비는

으로부터 계산된다. 따라서, 기록밀도비를 증가시키기 위해서는 코드변환비 및/또는 최소시간간격을 증가시켜야 한다. 하지만, 광강도변조방식에 따른 2진기록방법은 광의 회절한계로 인해 그 기록밀도비가 제한된다. 즉, 광디스크의 기록층에 기록된 마크패턴이 집광된 빔스팟의 직경보다 작을 경우, 그 재생신호는 사인(Sine)파형이 되고 분해능이 작아져 기록되기 이전의 원래의 데이터를 정확하게 복원할 수 없다. 이를 개선하기 위해 최소시간간격(d+1)을 늘이는 방식이 제안되었으나, 최소시간간격이 커질수록 지터(jitter)의 마진(margin)이 줄어드는 문제점이 발생한다. In order to record digital data on an optical disc according to a deep groove method and a double-sided recording method, a binary recording method corresponding to the presence or absence of a mark is mainly used. The binary recording method channel codes (modulates) the binary bit symbols represented by the bit values '0' and '1' as the codewords of the binary bits according to the characteristics of the channel or recording medium, and modulates the light intensity. Recording is performed on an optical disc or a magneto-optical disc by modulation or magnetic field modulation. Here, in the channel coding scheme, when converting an input m-bit symbol into an n-bit codeword, the minimum run length of the continuous bit value '0' is 'd' and the maximum run length. Follows the run length limited (RLL) modulation rule for converting codewords that satisfy the condition of (maximum run length) to 'k'. As the run-length-limited modulation method for binary recording, (d, k, m, n) is (2,10,8,17), and the EFM modulation method applied to a compact disc, (d, k, m, n) is (2,7,1,2) and the RLL (2,7) modulation scheme mainly applied to magneto-optical disks (MOD), and (d, k, m, n) is (1,7,2) RLL (1,7) modulation method applied to quadruple magneto-optical disk (4X-MOD), (d, k, m, n) is (2,10,8,16) EFM Plus (+) modulation is mainly applied to (DVD). The code conversion ratio according to the run length limit modulation is

The minimum time interval is (d + 1), and the detection window width during playback is

And record density ratio

Is calculated from Therefore, in order to increase the recording density ratio, it is necessary to increase the code conversion ratio and / or the minimum time interval. However, in the binary recording method according to the light intensity modulation method, the recording density ratio is limited due to the diffraction limit of light. That is, when the mark pattern recorded on the recording layer of the optical disc is smaller than the diameter of the condensed beam spot, the reproduction signal becomes a sine waveform and the resolution becomes small so that the original data before recording cannot be accurately restored. . In order to improve this, a method of increasing the minimum time interval d + 1 has been proposed. However, as the minimum time interval increases, a margin of jitter decreases.

A magneto-optical disc having two recording layers, which is proposed as a method for solving such a problem, can express four magnetization states, and thus it is possible to record a large amount of data by magnetic field modulation. Referring to Fig. 1A, a magneto-optical disc having two recording layers made of a magneto-optical material has four magnetization states, namely UP / UP state, UP / DOWN state, DOWN / It has UP state and DOWN / DOWN state. Referring to FIG. 1B, in order to record data on the magneto-optical disk described above, the magnetic field modulation recording method is switched by switching an external magnetic field for each of the four signal levels to be recorded corresponding to the four magnetization states described above. Therefore, binary data is recorded in each recording layer. At the time of reproduction, laser beams having different wavelengths are irradiated to each recording layer to individually reproduce the data recorded in each recording layer. As a result, a large amount of data can be recorded and reproduced on the magneto-optical disk having two recording layers using the magnetic field modulation method.

On the other hand, as the multi-value recording method applied to the magneto-optical disc, there are a fine mark method, a tracking line initialization method, and a method employing all of them. The micro-mark method records the ternary data in the recording layer of the magneto-optical disk in three states consisting of a mark state, a space state, and a fine mark string state. The tracking line initialization method records the multi-value signal on the magneto-optical disc by adjusting the width of the mark to be recorded in two ways.

However, the above-described multi-value recording methods for increasing the density of recording media are applied only to a single / multi-layered magneto-optical disk system employing a magnetic field modulation recording method, and due to their physical characteristics, they are applied to a phase change optical disk system. There is a problem that can not be. In particular, the quaternary recording method employed in the above-described magneto-optical disc system having two recording layers is not applicable to the phase change optical disc system using only the light intensity modulation recording method.

In general, the phase change optical disk method records binary data by forming a phase change mark, which is determined as one of crystalline and amorphous states, in a single recording layer, and records data based on a difference in optical characteristics between the crystalline state and the amorphous state. Play it. In particular, the phase change optical disc method can be used to rewrite data simply by shifting the phase change state of the recording layer to another phase change state without a separate erasing process, and thus it is mainly employed in a high-speed optical disc method that can be repeatedly recorded.

By the way, in the case of applying the magneto-optical recording of the magneto-optical disk method having the above two recording layers to such a phase-change optical disk, the phase change mark of four states corresponding to the binary data to be recorded using only the optical intensity modulation recording method is adopted. Is very difficult to form in the recording layer. In addition, even if phase change quaternary recording is possible, the signal level is maximized from the recorded phase change marks, and the optical contrast divided into four is not easily obtained, and thus the recorded binary data cannot be reproduced accurately. Have

In addition, the magneto-optical disk method having two recording layers shown in FIGS. 1A and 1B can greatly improve the recording density compared to the conventional single-recording magneto-optical disk, but the recording medium has a different recording layer. Since two laser beams having a wavelength must be used, the configuration and reproduction method of the optical pickup become very complicated.

Accordingly, an object of the present invention for solving the above-mentioned problems is to provide two recording layers, which allow data to be accurately reproduced using a single wavelength laser beam while recording data with a significantly improved recording density than conventional optical discs. It is to provide a phase change optical disk having.

Another object of the present invention is to provide a ternary data processing method for recording and / or reproducing data on two recording layers of a phase change optical disk described above.

Another object of the present invention is to provide an apparatus according to the above-described ternary data processing method.

A phase change optical disk for achieving the above object includes a substrate; And two recording layers overlying at least one surface of the substrate and composed of a phase change material.

A ternary data processing method for achieving the above another object is a data processing method for recording and / or reproducing data on an optical disc having two recording layers, which comprises (1) inputting using a ternary channel coding method. Converting binary data into ternary data; And (2) optically modulating the converted ternary data on two recording layers of the optical disc. The above ternary data processing method includes the steps of: (3) reproducing ternary data recorded in the two recording layers from three optical states obtained by irradiating a laser beam of a single wavelength onto the optical disc; And (4) restoring the reproduced ternary data to binary data before conversion to ternary data.

An apparatus for achieving the above another object is an apparatus for recording and / or reproducing data on an optical disc, comprising: a first recording overlying a substrate, at least one surface of the substrate, and composed of a phase change material An optical disc comprising a layer, an interlayer formed over a first recording layer and composed of a dielectric, and a second recording layer overlying the interlayer and composed of a phase change material; A ternary converter converting input binary data into ternary data; And laser power modulation and recording means for optically modulating the ternary data from the ternary conversion section with different laser powers and recording them on two recording layers of the optical disc. The above-mentioned apparatus further comprises: ternary data reproducing means for reproducing ternary data recorded in the two recording layers from three optical states obtained by irradiating the optical disk with a single wavelength laser light; And a binary conversion unit for restoring the ternary data from the ternary data reproducing means into binary data before being converted into ternary data.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, the phase change optical disc according to the present invention includes two recording layers made of a phase change material over at least one surface of a substrate, and three phase change mark states based on the presence or absence of phase change marks for each recording layer. Used to record ternary data. Here, the phase change mark is initially determined as one of the crystalline and amorphous states of each phase change recording layer, and is determined based on the optical characteristics of the phase change optical disc and the recording / reproducing method to be employed. The method for recording data in the two recording layers of the phase change optical disk described above, first converts the input binary data into ternary data using the ternary channel coding method, and ternary data composed of the converted ternary data. After converting the stream into a ternary NRZ waveform, the laser power is adjusted to correspond to the three signal states of the waveform to form phase change marks on the two recording layers. At the time of reproduction, a single wavelength laser beam is irradiated to the above-mentioned phase change optical disc to reproduce the ternary data from three optical states obtained based on the presence or absence of recording of phase change marks on the two recording layers and the recording position thereof. The ternary data is restored to the original binary data by using the inverse transformation of the ternary channel coding method described above.

Referring to FIG. 2, a phase change optical disk according to a preferred embodiment of the present invention is a substrate formed of polycarbonate from a side from which laser light is incident, placed on a substrate, an incident layer formed of a dielectric, and placed on an incident layer. A first recording layer composed of a changeable material, a first recording layer overlying the first recording layer, a second recording layer overlying the interlayer, and a second recording layer composed of a phase change material, A heat insulating layer made of a dielectric material, a heat insulating layer made of a dielectric material, a reflective layer made of a metal such as aluminum, and a protective layer placed on the reflective layer are stacked in this order. Here, the phase change material of each recording layer is selected from one of Ge ₂ Sb ₂ Te ₅ , Ge ₂ Sb _2.3 Te ₅ , and GeSb ₄ Te ₇ , and the interlayer is selected from one of Si, SiC, and SiO 2. In addition, the reflective layer of the multilayer structure shown in FIG. 2 is for reflecting laser light transmitted through the two recording layers toward the recording layers, and is selectively provided according to a recording and reproducing method.

In the phase change optical disc having the two recording layers shown in FIG. 2, when the phase change states of the respective recording layers are combined, they correspond to the 'first recording layer / second recording layer' (1) crystalline / crystalline, (2) There are theoretically possible four phase-change states expressed as amorphous / crystalline, (3) crystalline / amorphous, and (4) amorphous / amorphous.

However, in the present invention, ternary data is recorded in two recording layers made of a phase change material using only light intensity modulation. Therefore, three physical states are represented by a state in which both recording layers are crystalline, one of the two recording layers is crystalline and the other recording layer is amorphous, and both recording layers are amorphous. To be used for recording.

More specifically, when both recording layers are initialized to the crystalline state (at this time, the phase change mark is determined to be in the amorphous state), in response to the &quot; first recording layer / second recording layer &quot; Three states are available: crystalline, (2) amorphous / crystalline, and (3) amorphous / amorphous. In contrast, when both recording layers are initialized to an amorphous state (in this case, the phase change mark is determined to be in a crystalline state), in response to the 'first recording layer / second recording layer' (1) amorphous / amorphous, ( Three states are available: 2) crystalline / amorphous, and (3) crystalline / crystalline.

As described above, depending on whether the initialization state of the two recording layers is a crystalline state or an amorphous state, the three phase change mark states in the above two cases, namely, an initialization state in which phase change marks are not recorded in both recording layers, The phase change mark is recorded only in the first recording layer, and the phase change mark is recorded in both recording layers. Each phase change mark state corresponds to each of the ternary data to be recorded.

3A to 3C, FIG. 3A shows a state of a ternary NRZ waveform string generated corresponding to the converted ternary data and recorded in two recording layers of an optical disc. In the NRZ modulated recording method corresponding to binary data, in modulating a binary data stream into a recording signal waveform sequence, the signal level of the waveform sequence is inverted only at the boundary between bit values '0' and '1' in the binary data stream. Be sure to However, in the present invention, the ternary data stream must be recorded in two recording layers of the phase change optical disk. Therefore, a dual amplitude pulse position modulation (DAPPM) method employing both pulse position modulation (PPM) and amplitude modulation (AM) method is used to input a ternary data stream. The corresponding ternary NRZ waveform string is obtained. The ternary NRZ waveform sequence shown in Fig. 3A has three recording signal levels of low level, intermediate level, and high level whose pulse widths are varied corresponding to each of the ternary data (for example, 0, 1, 2). FIG. 3B shows that the phase change mark is not recorded in both recording layers, the phase change mark is recorded only in the first recording layer, and the two recording layers, corresponding to the three signal levels of the ternary NRZ waveform sequence shown in FIG. 3A. The phase change mark is recorded on all of them. FIG. 3C shows a reproduction signal according to three optical states obtained from the three phase change mark states shown in FIG. 3B.

4 is an experimental example showing the change in reflectance for each phase change mark state obtained by irradiating laser light of 690 nm wavelength when the thickness of the incident layer of the optical disc shown in FIG. 2 is varied. The layer structure applied to this experimental example, the refractive index and the thickness of each layer are shown in Table 1 below.

Floor structure Refraction rate      Thickness (Unit: nm) Entrance layer 2.1 150 to 210 First recording layer 4.84 + 3.53 i; 4.39 + 1.53i 10 Interlayer 2.1 10 Second recording layer 4.84 + 3.53 i; 4.39 + 1.53i 10 Insulation layer 2.1 20 Reflective layer 1.8 + 6.1i 50

In the graph of Fig. 4, the horizontal axis represents a varying thickness of the incident layer, and the vertical axis represents a reflectance expressed as a percentage, and the refractive index of each recording layer is represented by a complex number having a real part and an imaginary part. When the phase change mark state corresponding to the first recording layer / second recording layer of the two recording layers of the phase change optical disk shown in FIG. 2 is 'amorphous / amorphous', the reflectance curve represented by 'RF1' is represented. Reflectance curve labeled 'RF2' for 'Amorphous / Crystal', reflectance curve labeled 'RF3' for 'Crystal / Crystal', Reflectance curve labeled 'RF4' for 'Crystal / Amorphous' Indicates. Referring to the reflectance change graph of FIG. 4 measured under the conditions of Table 1, the reflectance of each curve becomes maximum when the thickness of the incident layer is around 150 to 210 nm, and the reflectance curve can be classified into three types. Therefore, in the experimental example of FIG. 4, it is understood that preferably three optical contrasts of RF3 (crystalline / crystalline), RF4 (crystalline / amorphous), and RF1 (amorphous / amorphous) can be used for the ternary recording and reproduction of the present invention. Can be. Here, it will be apparent to those skilled in the art that the thickness of the other layers shown in FIG. 2 can be properly adjusted from the experimental example of FIG. 4.

The graph of FIG. 5 shows an experimental example in which the electric field and energy at the interface of each layer in the thickness direction in the substrate are measured when the thickness of the heat insulation layer of the phase change optical disk shown in FIG. 2 is varied. In the graph of FIG. 5, the horizontal axis represents the thickness of the insulating layer that varies, and the vertical axis represents the relative ratio of energy. The curves A1, A2, A3, A4, and A5 of the area A are each in the order of the incident layer / first recording layer / interlayer / second recording layer / insulation layer / reflection layer, which are the layer structure of the phase change optical disk of FIG. Correspond to the electric field measured at the interface (/) between the layers, respectively. The curves B1, B2, B3, B4 and B5 in the region B are in absolute order the energy [pointing vector [ S = ( E × H) / μ ₀ ] measured at the boundary planes (/) described above in that order. ] Respectively. Looking at the curves of the region B shown in Figure 5, it can be seen that the amount of energy absorbed in each layer is also different because the measured amount of energy is different for each interface boundary. Accordingly, by controlling the thickness of each layer shown in FIG. 2, the energy absorption rate between the layers is changed so that the phase change mark is applied only to the first recording layer or to both recording layers with the laser power divided for each phase change mark state. It can be seen that it can be recorded. Accordingly, it can be seen that ternary data can be recorded and reproduced by enabling a transition between three phase change mark states in an optical disc having two recording layers made of a phase change material.

In conclusion, within the technical scope based on the technical idea of the present invention, those skilled in the art from the experimental examples of FIGS. 4 and 5 record and / or reproduce data in two recording layers of a phase change optical disc in the ternary recording method according to the present invention. It is apparent that the layer structure and thickness of the phase change optical disk, the optical parameters thereof, and the modifications not mentioned in the composition can be implemented.

Next, referring to Figs. 6A to 7, a ternary data processing method for recording and / or reproducing data at high density on a phase change optical disc having two recording layers according to the present invention will be described.

As described above, in the two recording layers of the phase change optical disc according to the present invention, densification of the optical disc is achieved by recording ternary data converted from binary data in the three phase change mark states described above. The ternary data to be recorded is obtained by performing ternary channel coding of binary data which is processed by digital signal input. In this ternary channel coding method, a preferred embodiment in which the recording medium characteristics of a phase change optical disc having two recording layers according to the present invention are optimized and whose recording density can be significantly improved will be described in detail.

Referring to FIG. 6A, which shows the structure of a ternary data stream converted from binary data, a preferred ternary channel coding scheme expresses an input 8-bit symbol in a tenary code (or ternary code). Eight to twelve modulations (or transformations) to convert to a 12-digit code word. In such 8 to 12 modulation, first, the 8 input bits are converted into 10-digit codewords (d9 to d0) using a run length-limited (RLL) ternary channel coding method, and the converted 10-digit codeword By adding a two-digit merging code (m1, m0) for adjusting the DC component of the reproduction signal based on the digital sum value (DSV), the aforementioned 12-digit codewords d9 to d0 are added. , m1, m0). In addition, since the method of generating and adding the two-digit combining code is obvious to those skilled in the art from the above description, a detailed description thereof will be omitted.

Here, a preferred method of ternary channel coding of eight input bits per symbol with ten digit code words will be described with reference to FIGS. 6B and 7. Referring to FIG. 6B for explaining the ternary NRZ recording method corresponding to the ternary data stream of FIG. 6A, each data '0, 1, 2' in a circle is stored in both recording layers. Example of the ternary data corresponding to each of the 1 phase change mark state, the 2nd phase change mark state in which the phase change mark is recorded only in the first recording layer, and the third phase change mark state in which the phase change mark is recorded in both recording layers. to be. The values '0, 1, and Q' indicated by the arrows indicate states at the time of inversion of each signal level of the ternary NRZ waveform sequence described with reference to FIG. 3A. More specifically, the values '0, 1, Q' indicated by the arrow are the first transition state corresponding to the first phase change mark state without state transition (corresponding to the low level state in FIG. 3A), the first phase. A second transition state between the change mark state and the second phase change mark state (corresponding to the signal level inversion state between the low level state and the intermediate level state in FIG. 3A), and a third between the first phase change mark state and the three phase change mark state. Corresponding to each of the transition states (corresponding to the signal level inversion state between the low level state and the high level state shown in FIG. 3A). As described above, in the ternary recording method of the present invention, after converting the input binary data into ternary data, the two recording layers of the phase change optical disk in the state of the ternary NRZ waveform string according to the light intensity modulation To record. In particular, in a preferred embodiment of the present invention, each of the ternary data converted according to the ternary channel coding method is preferably determined as values (0, 1, Q) corresponding to three transition states of the ternary NRZ wavestream.

Next, a method of converting eight input bits per symbol into ten-digit code words represented by the above-described ternary data (0, 1, Q) using the run length-limited ternary channel coding method will be described in detail. . FIG. 7 shows a preferred implementation of modulation code selection groups to be used in the ternary channel coding scheme based on the run length limitation (RLL) rule for generating the ternary data stream of FIG. 6A. In particular, the modulation codes of FIG. 7 use a minimum run length modulation rule in which the minimum run length (corresponding to 'd' in binary RRL channel coding) of consecutive ternary data '0' is '2'. Have

The first group is a group of modulation codes obtained when only one digit of the ten-digit codeword has the above-mentioned ternary data '1' or 'Q' and the remaining nine digits have the ternary data '0'. The number of modulation codes selectable in the first group is 20, in which the number (10) of the case of 'i' representing the ternary data '1' or 'Q' is multiplied by the number of combinations of 'i' (2). Modulation codes. In the second group, when two digits of the 10-digit codeword have the above-mentioned ternary data '1' or 'Q' and the remaining eight digits have the ternary data '0' under the condition that the minimum run length is '2'. Is a group of 112 modulation codes obtained by multiplying the number of (28) by the number of combinations (4) of (i, i) possible for each case. The third group is the number of cases where three digits of the ten-digit codeword have the ternary data '1' or 'Q' and the remaining seven digits have the ternary data '0' under the condition that the minimum run length is '2'. It is a group of 160 modulation codes obtained by multiplying (20) by 8 possible combinations of (i, i, i) for each number of cases. The fourth group is the number of cases where four digits of the ten-digit codeword have the ternary data '1' or 'Q' and the remaining six digits have the ternary data '0' under the condition that the minimum run length is '2'. (1) is a group of 16 modulation codes multiplied by 16 possible combinations of (i, i, i, i) for each number of cases. Incidentally, the case where all 10-digit codewords are the ternary data '0' is excluded because it is not preferable to adjust the DC component of the reproduction signal. Therefore, 308 modulation codes are generated in accordance with the rule shown in FIG.

According to a preferred embodiment of the present invention, the ternary channel coding method assigns each of 256 patterns of input symbols represented by 8 bits to one of 256 modulation codes arbitrarily selected from the 308 modulation codes generated in FIG. This is done by the 'symbol-sign' assignment. In addition, since the modulation code table according to the above-described 'symbol-codeword' assignment relationship can be easily implemented by those skilled in the art from the above description, a detailed description thereof will be omitted.

According to the foregoing 8 to 12 conversion method and the ternary channel coding method having the minimum run length of '2' according to the preferred embodiment of the present invention, the code conversion ratio is 0.67, the minimum time interval is 3T, the detection window width ( T _W ) is 0.67T, and its recording density ratio is two. Therefore, the recording density of the phase change optical disk having two recording layers of the present invention, which records ternary data according to the above-described ternary channel coding method, is 100% compared to MFM (Modified Frequency Modulation) modulation method, and EFM plus modulation. It offers a 33% improvement in recording density compared to the method.

On the other hand, the stream of ternary data converted according to the above-described ternary channel coding scheme is converted to the above-described ternary NRZ recording waveform sequence, and the light intensity is modulated to correspond to each state of the waveform sequence. The two recording layers are recorded as shown in FIG. 3B. Here, in the light intensity modulation, in order for the converted ternary data or the ternary NRZ waveform sequence to be recorded separately in the above three phase change mark states in the two recording layers made of the phase change material, the optical disc shown in FIG. The structure and thickness of the layer, the optical property parameters, and the composition are appropriately selected in advance as in the experimental examples shown in FIGS. 2, 4 and 5. As a result, a margin of each laser power corresponding to each of the converted ternary data is sufficient. Therefore, it is possible to easily adjust the intensity of the laser power which enables the phase change transition of the two recording layers corresponding to each of the ternary data to be recorded.

For example, first, the thickness and composition of each layer structure of the phase change optical disc, optical characteristic parameters, etc. are appropriately determined by the preferred phase change optical disc of FIG. 2, and the experimental examples of FIGS. 4 and 5. When both recording layers of the phase change optical disc are initialized to an amorphous state (the phase change mark is set to the crystalline state), the ternary data '1' converted from binary data by the ternary channel coding method is used. Correspondingly, when the intensity-modulated laser light is irradiated onto the phase change optical disk with the first laser power P1, only the first recording layer of the two recording layers is shifted from the initialization state to the crystalline state to form a phase change mark. When the laser beam modulated with the second laser power P2 is irradiated onto the phase change optical disk in response to the converted ternary data 'Q', both recording layers are shifted from the initial state to the crystalline states to change the phase. Marks are formed. On the contrary, when both recording layers of the phase change optical disk are initialized to the crystalline state (the phase change mark is set to the amorphous state), the ternary data '1' converted from the binary data by the ternary channel coding method is used. Correspondingly, when the intensity-modulated laser light is irradiated onto the phase change optical disk with the third laser power P3, only the first recording layer of the two recording layers is shifted from the initialization state to the amorphous state to form a phase change mark. When the laser beam modulated with the fourth laser power P4 is irradiated onto the phase change optical disk in response to the converted ternary data 'Q', both recording layers are shifted from the initial state to the amorphous state to change the phase. Marks are formed.

In the light intensity modulation recording corresponding to the three phase change mark states in these two cases, each laser power to be modulated in intensity satisfies the condition of &quot; P1 &lt; P2 &lt; P3 &lt; P4. The laser power of P1 or P3 has a laser power range in which only the first recording layer transitions to a crystalline or amorphous state, and the laser power of P4 is in an amorphous state without destroying both recording layers made of a phase change material. It has a laser power range to transition.

In addition, in order to repeatedly record ternary data on a phase change optical disk having two recording layers according to the present invention, erasing laser power ranges P1 enabling reverse transition of state transitions corresponding to P1 and P3, respectively. ', P3') may be set separately.

On the other hand, when ternary data is recorded by forming three phase change marks on two recording layers of the phase change optical disc by the above-described ternary recording method, the reproduction method will be described. First, when a single wavelength laser beam is irradiated onto the phase change optical disk, the optical signal characteristics of each phase change mark are maximized by the optical characteristics of each phase change mark. Is reproduced as shown in Fig. 3C. Subsequently, the obtained reproduction signal is waveform-formed into an amplified and ternary NRZ waveform sequence, and the ternary data before recording is reproduced by detecting the phase change mark position and detecting the signal level based on the ternary recording method. Accordingly, the reproduced ternary data is restored to binary data before conversion to ternary data by using the inverse transformation of the ternary channel coding method shown in FIGS. 6A to 7. In addition, since the inverse transform can be easily implemented by those skilled in the art from the above-described embodiment of the ternary channel coding method, a detailed description thereof will be omitted.

Next, referring to FIG. 8, an apparatus for recording and / or reproducing data at a high density in the phase change optical disc having the two recording layers of FIG. 2 according to the above-described ternary data processing method will be described.

In the ternary converter 81 shown in FIG. 8, a large amount of data such as video data, audio data, and multimedia data is compressed and input from a digital signal processor (not shown) into a bitstream. The ternary conversion unit 81 converts binary data represented by 8 bits per symbol into a 12-digit code word represented by ternary data using the above-described ternary channel coding method. The laser power modulation and recording means 82 applies three phase change marks to the two recording layers by irradiating the phase change optical disks with each laser power whose light intensity is modulated to correspond to each of the ternary data input from the ternary converter 81. Record as state.

On the other hand, when a single wavelength laser light having a reproducing power range is irradiated to the phase change optical disc 80 having two recording layers by the laser power modulating means, the optical pickup 83 has three phase change marks formed on the two recording layers. A reproduction signal of FIG. 3C is obtained based on three optical contrasts classified by states. In particular, the three optical contrasts are based on the optical properties (light transmittance or reflectance) of the phase change optical disk having two recording layers, and as described above, the layer structure, thickness, refractive index, composition, and the optical disk shown in FIG. The parameters (wavelength, laser power range) of the laser light used are preset to an optimum value. The ternary data reproducing section 84 amplifies and equalizes the reproduced signal obtained by the detector of the optical pickup 83, checks the phase change mark position and signal levels, and restores the ternary data before recording. The synchronization restoring unit 85 restores predetermined synchronization signals (clock synchronization or block synchronization of codewords constrained to 12 digits) from the restored ternary data, and then applies them to the binary conversion unit 86. The binary conversion unit 86 transfers the ternary data input from the ternary data reproducing unit 84 based on the synchronization signals from the synchronous restoring unit 85 by using an inverse transformation of the ternary channel coding method. Reconstruct binary data represented by 8 bits per symbol. The restored binary data is applied to a digital signal processor (not shown) and restored to video data, audio data, and multimedia data before being compressed and encoded.

On the other hand, the phase change optical disc according to FIG. 2 shows an embodiment having two recording layers composed of a phase change material on only one surface of the substrate, but the phase change optical disc having the two recording layers described above on both surfaces of the substrate. It will be apparent to those skilled in the art that the present invention can be implemented within the technical scope of the present invention.

In addition, in the ternary channel coding scheme according to the present invention, from 8 to 12 modulation with the minimum run length '2' mentioned in the above-mentioned preferred embodiment, 8 to 15 ternary numbers with the minimum run length '3' It may be modified in a modulation scheme. Detailed description of this modified embodiment, since those skilled in the art can easily implement from the above-described preferred embodiment will not be described in detail. However, in the ternary modulation method according to this modified embodiment, the code conversion ratio is 0.53, the detection window width is 0.53T, the minimum time interval is 4T, and the recording density ratio is 2.13. Compared with those according to the above 8 to 12 modulation, the detection window width is slightly reduced, but the resolution and recording density ratio are advantageously improved. In addition, in order to further improve the code conversion ratio, the minimum run length d may be modified to an 8 to 9 modulation scheme having a '1'. In this modified embodiment, the code conversion ratio has an advantage of improving to 0.89, but the recording density ratio drops to 1.78.

In addition, the phase change optical disk having two recording layers according to the present invention, its ternary data processing method and apparatus can be applied to both an optical disk system that can only reproduce, and an optical disk system that can be repeatedly recorded and reproduced. It will be apparent to those skilled in the art from the foregoing embodiments within the spirit and scope.

 The present invention provides a phase change optical disc having two recording layers, which has a significantly improved recording density than conventional optical discs and can accurately reproduce data recorded using a single wavelength laser light. In addition, the present invention makes it possible to record and reproduce a large amount of data in a high density on a phase change optical disc having two recording layers, and is optimal for recording medium characteristics of the phase change optical disc, and a data processing method for ternary recording and / or reproduction. And its apparatus.

Claims (34)

In the optical disc, Board; Two recording layers overlying at least one surface of the substrate; And An interlayer formed between the two recording layers and composed of a dielectric material, And the two recording layers are made of a phase change material. delete The method of claim 1, An incident layer overlying one surface of said substrate and composed of a dielectric; A first recording layer overlying the incident layer and composed of a phase change material; An interlayer formed over the first recording layer and composed of a dielectric material; A second recording layer overlying said interlayer and composed of a phase change material; An insulating layer overlying said second recording layer and composed of a dielectric; And And a protective layer overlying the thermal insulation layer. The method of claim 3, wherein And a reflective layer interposed between the heat insulating layer and the protective layer and reflecting the laser light transmitted through the two recording layers back toward the recording layers. The optical disc of claim 1, wherein the two recording layers are made of a phase change material selected from one of Ge ₂ Sb ₂ Te ₅ , Ge ₂ Sb _2.3 Te ₅ , and GeSb ₄ Te ₇ . 2. The first recording medium of claim 1, wherein a phase change mark selected as one of a crystalline and an amorphous state is recorded in the two recording layers, and a first state in which the phase change mark is not recorded in both recording layers. And a third state in which the phase change mark is recorded in only the recording layer and a third state in which the phase change mark is recorded in both recording layers. The method of claim 6, wherein the first to third state is An optical disc corresponding to each of the ternary data to be recorded, and correspondingly three optical states obtained during reproduction. The thickness of each layer is 150-210 / 10/10/10/20/50 nm corresponding to the incident layer / first recording layer / interlayer / second recording layer / insulating layer / reflective layer, respectively. Optical disc. The thickness of each of the layers is 120/12/8/12/0 to 30/50 nm corresponding to each of the incident layer / first recording layer / interlayer / second recording layer / insulation layer / reflective layer. Optical disc. A data processing method for recording and / or reproducing data on an optical disc having two recording layers, (1) converting input binary data into ternary data using a ternary channel coding method; And (2) converting the converted ternary data into a ternary Non-Return Zero (NRZ) waveform sequence, and modulating the light intensity with different laser power for each of the three states of the waveform sequence to record on two recording layers of the optical disc. Data processing method comprising. The data processing method according to claim 10, wherein the two recording layers of the optical disc are made of a phase change material. delete The method of claim 10, wherein step (1) Converts an 8-bit symbol into a 10-digit codeword expressed as a ternary number, and adds a 2-digit merging code to the 10-digit codeword to control DSV. A data processing method for converting digit code words. The method of claim 13, wherein the 8 to 12 transform is A data processing method using a run length limit (RLL) ternary channel coding method having a minimum run length of '2'. 15. The method of claim 14 wherein the 8 to 12 transform is A symbol-sign that assigns each of the 256 patterns of input symbols represented by 8 bits to one of 256 modulation codes randomly selected from among 308 modulation codes generated according to the run length limitation rule having a minimum run length of '2'. Method of data processing carried out in accordance with the allocation rules. delete 11. The method of claim 10, wherein the ternary NRZ waveform sequence A data processing method which is a waveform sequence according to a recording modulation method combining a mark position modulation method and an amplitude modulation method. 12. The optical disc of claim 10, wherein the optical disc overlies at least one surface of the substrate and over the first recording layer made of a phase change material, over the first recording layer and made of a dielectric, and the interlayer. And a second recording layer, which is laid and made of a phase change material, wherein the two recording layers are selectively formed with phase change marks defined in one of crystalline and amorphous states, In the step (2), the first data of the ternary data is in a first state in which the phase change mark is not formed in both of the recording layers, and the second data is only displayed in the first recording layer. A second state in which a change mark is formed, and the third data is recorded in a third state in which phase change marks are formed in both of the recording layers. 19. The method according to claim 18, wherein the phase change mark is determined to be in a crystalline state. The first state corresponds to an initialization state in which both recording layers are formed in an amorphous state, and the second state is a crystalline state only from the initialization state to the crystalline state by the irradiation of the first laser power P1. The third state is a data processing method in which both recording layers transition from the initialization state to the crystalline state by irradiation of a second laser power (P2) larger than the first laser power. 19. The method of claim 18, wherein when the phase change mark is determined to be in an amorphous state, The first state corresponds to an initialization state in which both recording layers are formed in a crystalline state, and the second state is an amorphous state only from the initialization state to the first recording layer by irradiation with a third laser power P3. The third state is a data processing method in which both recording layers are transitioned from an initialization state to an amorphous state by irradiation of a fourth laser power (P4) larger than the third laser power. 21. The thickness and composition of each layer of the optical disc according to claim 19 or 20, wherein each laser power modulated by the light intensity has a predetermined laser power margin and satisfies a condition of P1 &lt; P2 &lt; P3 &lt; P4. The data processing method in which this is determined. The method of claim 10, (3) reproducing ternary data recorded in the two recording layers from three optical states obtained by irradiating a laser beam of a single wavelength onto the optical disc; And (4) restoring the reproduced ternary data to binary data before conversion to ternary data. 23. A phase change mark as set forth in claim 22, wherein a phase change mark designated as one of crystalline and amorphous states is selectively recorded in each of said two recording layers made of a phase change material, In the step (3), the ternary data is reproduced from three optical contrasts obtained based on recording of phase change marks on the two recording layers and positions of the phase change marks. 23. The data processing method according to claim 22, wherein said step (4) recovers said binary data by using an inverse transformation of the ternary channel coding method used when writing ternary data. An apparatus for recording and / or playing data on an optical disc, A substrate, a first recording layer overlying at least one surface of the substrate and composed of a phase change material, an interlayer overlying the first recording layer and composed of a dielectric, and a phase change material overlying the interlayer An optical disk including a second recording layer; A ternary converter converting the input binary data into ternary data by using a ternary channel coding method; And And laser power modulation and recording means for optically modulating the ternary data from the ternary conversion section with different laser powers and recording them on two recording layers of the optical disc. The method of claim 25, wherein the ternary conversion unit An apparatus for converting binary data represented by 8 bits per symbol into a 12-digit codeword represented by a ternary number using a ternary channel coding method. 27. The apparatus of claim 25, wherein the laser power modulation and recording means And converts the converted ternary data into a ternary NRZ waveform sequence, and modulates the laser data into three phase change mark states in the two recording layers by modulating with three different laser powers. 28. The system of claim 27, wherein the ternary NRZ waveform string is A device which is a waveform sequence according to a recording modulation method that further employs an amplitude modulation method in addition to a mark position modulation method. A phase change mark defined in one of crystalline and amorphous states is selectively formed in two recording layers of the optical disc, and the laser power modulation and recording means The first data of the ternary data is in a first state in which the phase change mark is not formed in both recording layers, and the second data is in a second state in which a phase change mark is formed only in the first recording layer. And the third data is recorded in a third state in which phase change marks are formed on both recording layers. 30. The range of each laser power according to claim 29, wherein the laser power modulation and recording means enables a transition between the phase change mark states. And the laser power range is determined according to the thickness and composition of each layer of the phase change optical disk. The method of claim 25, Ternary data reproducing means for reproducing ternary data recorded in the two recording layers from three optical states obtained by irradiating the optical disk with a single wavelength laser light; And And a binary conversion section for restoring the ternary data from the ternary data reproducing means to binary data before conversion to ternary data. 32. The phase change mark defined in one of the crystalline and amorphous states is selectively recorded in each of the two recording layers made of the phase change material, and the ternary data reproducing means And an apparatus for reproducing the ternary data from three optical contrasts obtained based on recording of phase change marks on the two recording layers and the position of the phase change marks. 32. The apparatus of claim 31, wherein the binary conversion unit restores the binary data by using an inverse transformation of a ternary channel coding method used when writing ternary data. 32. The apparatus of claim 31, wherein the ternary data reproducing means further recovers a predetermined synchronization signal from the restored ternary data and supplies it to the binary conversion unit. And the binary conversion unit restores the binary data based on the supplied synchronization signal.

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