JP2650357B2 - Recording method for optical information recording member - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording method of an optical information recording member for recording and erasing information on a rotating optical disk using a laser beam or the like.

2. Description of the Related Art Techniques for recording / reproducing information using a laser beam are already known, and their application to document files and data files is currently being actively carried out. In addition, research and development cases of rewritable recording systems having an erasing function are being reported.

One of these methods is a so-called phase-change type optical disk utilizing a reversible state change between amorphous and crystal or between crystal and crystal. The recording thin film used in this method has a feature that it takes an amorphous state or a crystalline state and reversibly changes between the two states depending on heating and cooling conditions by laser light. A complex refractive index consisting of a refractive index n and an extinction coefficient k is different between the amorphous state and the crystalline state, and signal recording is performed using the resulting difference in transmittance or reflectance.

To realize these, the recording power Pw and the erasing power Pe
There is a method of irradiating a recording medium with a laser beam modulated between two power levels (Pw> Pe) (JP-A-56-1455).
No. 30). That is, when the recording material is irradiated with a laser beam whose intensity is modulated in accordance with the signal, the irradiated portion of the recording power Pw becomes amorphous even if the previous state is either amorphous or crystalline. The portion irradiated with the erasing power Pe is in a crystalline state. As a result, overwriting can be performed at one spot. Here, the state change between the amorphous state and the crystal state has been described. However, even in the state change between the crystal state and the crystal state, equivalent characteristics can be obtained by changing the above-mentioned amorphous state into a metastable crystal state.

As another method, there is a method called magneto-optical recording. The principle is that when a magnetic thin film having anisotropy in the thickness direction is irradiated with laser light, the amount of deflection of the reflected light varies depending on the magnetization direction (Kerr effect). In this method, a signal is reproduced by detecting the difference in the amount of deflection.

In order to realize these, the magnetic thin film is magnetized in a predetermined direction in advance, and then a magnetic field in a direction opposite to the magnetization direction is applied from the outside, and the recording power Pw and zero at the same time according to the signal to be recorded. Irradiate a laser beam whose power has been modulated. The temperature of the magnetic thin film at the portion irradiated with the light of the recording power Pw exceeds the Curie temperature, and the magnetization direction is reversed. As a result, a magnetization reversal pattern corresponding to the signal is recorded on the magnetic thin film. When erasing, a laser beam equivalent to the recording power Pw is continuously irradiated while a magnetic field is applied from the outside.

Problems to be Solved by the Invention Recording is performed on an optical disk by irradiating a laser beam modulated between two power levels. However, when the recording and erasing of the signal are repeated many times, the recording medium gradually deteriorates due to the thermal history, and as a result, the amplitude of the reproduced signal tends to decrease. In particular, after repeatedly recording a certain pattern of signals in the same location on the recording medium,
When signals of different patterns are recorded, the amplitude of the signal is distorted, and there is a problem that a data reading error (bit error) occurs in the process of demodulating the signal. The number of repetitions at which this bit error occurs is significantly smaller than that when different signals are repeated and recorded.

In this phenomenon, when comparing the points on the recording medium when the same pattern signal is repeatedly recorded, a portion where a strong laser beam is concentrated and a portion where only a weak laser beam is irradiated occur. For this reason, a state where portions having different numbers of repetitions are mixed in the track direction of the optical disc is mixed, and when a signal of a different pattern is recorded thereon, depending on what kind of laser light irradiation the recording unit has previously received. This is considered to be due to a difference in the reproduction amplitude of the recorded signal. That is, the reproduction amplitude of the portion where the strong laser irradiation is concentrated is small, and the reproduction amplitude of the portion where only the weak laser light is irradiated is equal to the initial value. It is considered that such a difference between the amplitudes causes a peak shift or loss of a signal when demodulating the data signal, resulting in a bit error. In actual recording, it is unlikely to record exactly the same signal repeatedly. However, in the case of a data signal, even if the data value itself changes, there may be a case where the signal between data and the clock signal portion and the like have the same pattern. In view of the above, an object of the present invention is to provide a method for improving the number of recording / erasing repetitions by improving the irradiation conditions of laser light.

A method of recording a signal on an optical information recording member having two or more optically identifiable states, or recording a new signal while erasing an old signal, comprising: Recording gate generating means for generating a reference gate signal based on a format signal on a member; delay means for delaying the reference gate signal with a plurality of types of delay time widths; and randomly selecting the type of delay time width of the delay means. Using a selecting means for selecting, changing a recording start position in the information layer for each repetitive recording, and when recording the information signal on the recording medium, the delay time width is synchronized with a clock of the information signal. The step is based on the clock cycle.

The starting point of the drive signal of the laser according to the present invention and the relative positional relationship of the optical information recording member are changed for each repetitive recording, so that even when the recording and erasure of the signal of the same pattern are repeatedly performed, the recording medium Above, recording marks are formed at different positions. For this reason, each point on the recording medium becomes an average thermal history, and local distortion of amplitude can be eliminated. Therefore, the repetition life of the recording medium is improved.

Embodiment A recording method for an optical information recording member according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1a shows a format signal generated from an optical disk, and b to k show timing charts of a recording signal used to demonstrate the present invention. b denotes a reference gate of a signal to be recorded, and a data signal to be recorded is
It is obtained by synchronizing with the format signal a of the optical disk. C is a clock signal formed from the data signal to be recorded. By forming the clock signal based on the data signal to be recorded, the circuit configuration can be simplified. d to k are recording gate signals having a certain time delay from the reference gate b, and d is IT,
e indicates the case of 2T, f indicates the case of 3T, and k indicates the case of 8T. Thus, a total of eight types of gates are provided at intervals of 1T. Conventionally, recording has been performed using only this b gate. In the method according to the present invention, when recording not only one pattern but also a signal, the recording gate is selected by selecting one of a plurality of gates having different delay times with respect to the reference gate b. In other words, changing the delay time of such a gate is equivalent to changing the relative position of the optical disk and the drive signal of the laser used for recording. According to this method, even if a signal of the same pattern is repeatedly recorded on the same track each time, marks are formed at slightly different positions on an actual optical disk every time. As a result, each point on the repeatedly recorded track is
Irradiation of substantially equal laser light results in a uniform thermal history. For this reason, even when the amplitude is reduced due to repetition, the amplitude of the signal reproduced from the adjacent mark is equal, so that the peak shift of the reproduced waveform and the loss of the signal are less likely to occur, and no bit error occurs.

FIG. 2 is a configuration diagram showing an example of an optical disk recording apparatus using this method. This apparatus comprises a rotating optical disc A,
An optical system B for condensing the laser light on the optical disk A, an information recording unit C for modulating the laser light, and a reproduction control unit E for reproducing information from the optical disk A and controlling a light spot. Be composed.

The optical disc A includes a substrate 1 and a recording thin film 2 on the substrate 1. As the substrate 1, a resin such as polymethyl methacrylate (PMMA) or polycarbonate (PC) or glass can be used.

The recording material 3 for recording a signal using a phase change by light irradiation includes GeTe, Ge in an amorphous-crystal phase change.
Sb ₂ Te ₄ , Ge ₂ Sb ₂ T ₅ , InSe, InSeTlCo, GeSnTeAu,
GeSbTeSe, SeSnTeO, SeTeS, and the like can be used. In addition, as a crystal-to-crystal phase change material, InSb-based, Ag
Zn-based or the like can be used. Recording materials for magneto-optical recording include TbFeCO and GdTbFe.

A data signal to be recorded on the optical disc is guided to the information recording section C, and is first temporarily stored in the buffer memory 3. The data in the buffer memory 3 is stored in a recording gate generator 4.
Are read out in synchronization with the output gate signal, and are subjected to, for example, 2-7 modulation by the modulation circuit 5. The modulation circuit 3 not only performs 2-7 modulation of the recording data, but also generates a sector signal, a synchronization signal, a cue signal and the like in accordance with a predetermined format and inserts them into the modulation data. The drive circuit 6 generates a pulse having a waveform corresponding to the 2-7 modulated data in synchronization with the write gate from the recording gate generator 4. The gate signal from the recording gate generator 4 has a random time delay caused by the gate delay circuit 7.

The optical system B used a semiconductor laser 8 having a wavelength of 780 nm as a light source. The light of the semiconductor laser 8 is turned into parallel light by the collimator lens 9 and is deflected by the deflecting beam splitters 10 and 1 /.
The light passes through the four-wavelength plate 11 and is condensed by the objective lens 12 onto the recording thin film 2 of the optical disc A to a spot diameter of 1 μm, which is the wavelength limit. The reflected light from the recording thin film 2 passes through the objective lens 12 and the quarter-wave plate 11 again, is reflected by the deflection beam splitter 10, and is received by the photodetector 13. The signal photoelectrically converted by the photodetector 13 is amplified by the preamplifier 14 of the reproduction controller E.

The playback / control unit E is a focus / tracking control unit.
15 converts the signal from the preamplifier 14 into a control signal using a low frequency component, drives a voice coil 16 that supports the objective lens 12, and performs focusing and tracking of a spot on an optical disk. On the other hand, the demodulation circuit 16 demodulates the data signal from the mark formed on the optical disc A using the high frequency component of the signal from the preamplifier 14. The demodulated reproduced data is stored in the buffer memory.
Stored temporarily in 17. By reading the data stored in the buffer memory 17, the reproduction of the optical disk is performed.

FIG. 3 is a configuration diagram showing an example of the gate delay circuit 7 of FIG. The reference gate signal (b) and the clock signal (c) generated by the recording gate generator 4 based on the data signal and the format signal on the optical disk are shifted by a shift register.
Join 18 In the shift register, eight types of signals (d) to (k) are generated with a time delay of 1T. Each signal waveform is shown in FIG. The gate signal is applied to the counter 19, and the binary count signal (l) to
(N) is output. In the selector 20, the counter 19
Select the gate signal of the address specified by the signal from the shift register 18, that is, output one of the signals (d) to (k) from the shift register 18 as the recording gate signal (o). As a result, a recording gate having eight types of time delays with respect to the initial recording gate (b) is obtained. Although an 8-bit system has been described here, the number of bits, that is, the number of delay gate patterns can be increased or decreased as necessary.

Here, in order to clarify the effect of actually delaying the recording gate, the correlation between the delay time width of the recording gate and the maximum number of repetitions in which no bit error occurs when the recording is repeatedly performed on the optical disk is shown in FIG. FIG.

The optical disc A has a substrate 1 made of a polycarbonate resin having guide tracks for address signals and tracking on its surface, GeSb ₂ Te _{4 on} a recording thin film, and Zn on both sides of the recording thin film.
The configuration was such that a protective layer made of S was provided. Optical discs are
The recording unit was rotated at a speed such that the linear velocity became 10 m / s. 2-7R for the modulation method of the data signal used for recording
The LL code pit position modulation recording was used, and the transfer rate was 5 Mbps. In addition, a Reed-Solomon code was used as a signal error correction method. Recording (overwriting) on the optical disk is performed by modulating the power of the semiconductor laser 8 between the recording power and the erasing power according to the data signal. The power on the optical disk was 16 mW for recording power, 8 mW for erasing power, and 1 mW for reproducing power.

Recording was repeatedly performed under the above recording conditions. Two types of data signal patterns to be recorded are set, the first pattern signal is repeatedly recorded 1000 times, then the second pattern signal is recorded, and then a reproduction signal by a recording mark on the optical disk and the second pattern signal are recorded. A bit error is detected by comparing. These 1000 recording and bit error measurement cycles are repeated until a bit error is detected in the reproduced signal. At that time, the recording gate changes according to the pattern generated by the gate delay circuit for each repetition count. The interval of the delay time D of each gate pattern is
The clock cycle of the data signal to be recorded was 1T. The types of the gate patterns are four types of maximum gate delay time of 1T to 4T for 4T, and 20 types of 1T to 20T for 20T.
The result of the measurement under the above conditions is shown in FIG.
It is a diagram showing a constant value when the number of repetitions increases as the gate delay time width increases and the delay time width becomes 16T or more. As described above, by randomly changing the timing of recording the data signal, the thermal history at each position on the recording thin film can be averaged. And the tendency of the averaging becomes remarkable with the delay time width. On the other hand, as the delay time increases, the recording gate width for recording data between the format signals of the optical disk decreases, and the total capacity of the optical disk decreases. Therefore, in practice, it is obvious to use the minimum delay time width at which the effect of improving the number of repetitions is maximized, that is, 16T. Further, the delay time can be selected according to the required data capacity and the number of repetitions according to the use of the optical disk. As shown in FIG. 4, the effect of adding a delay to the recording signal is that the maximum number of repetitions can be improved 10 times even when the maximum delay time is in the range of 4T to 8T. If so, these ranges can be set as the maximum delay time.

Since the delay time 16T at which the number of repetitions saturates corresponds to four times the maximum level inversion one interval 4T of the 2-7 RLL code, it is considered that the irradiation history of the laser beam at each point on the recording track is averaged. The measurement system and the rotation of the disk always include jitter. In a system with a large jitter, the same effect can be obtained even when the delay time is 16T or less. Conversely, in a system with a small jitter, it is necessary to further increase the delay amount. In this measurement system, the pitch of the gate delay time was 1T, but the shortest mark interval of the 2-7RLL code was 1.5T, and the jitter of the measurement system was 0.
If it becomes 5T or less, a small area with a small light irradiation history is formed around one recording mark. To address this, a shorter gate delay time pitch, for example, 0.5T,
0.25T is better. Each of the gate delay time pitches 1T, 0.5T, and 0.25T described above is a cycle of an integer fraction of the clock frequency, and these cycles are the clock itself used in the process of generating the data signal or the process of generating the clock. It is possible to easily extract from the higher-order frequency components used in the above, and to obtain a predetermined delay time with a simple circuit.

In the present embodiment, the result is obtained in the case of the modulation method of the 2-7 RLL code, but the present method can be similarly applied to other modulation methods. For example, also in this case, when the maximum gate delay time is D and the maximum signal inversion interval of the modulation method is Tmax, the gate delay time may be set so that the relationship of Dmax ≧ 4Tmax holds. The present method can be similarly applied to other phase change type recording media and magneto-optical recording media.

As described above, it is possible to improve the number of times of repetitive recording of the optical disk with a simple circuit configuration by randomly changing the recording timing of the recording signal pulse split of the optical disk every time the recording timing is recorded based on the information signal as described above. it can.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a recording system in one embodiment of the present invention, FIG. 2 is a configuration diagram of a recording / reproducing apparatus using this system, FIG. 3 is a configuration diagram showing an example of a gate delay circuit, FIG. The figure is a characteristic diagram showing the relationship between the delay time width of the recording gate and the number of repetitions. a: optical disk format signal, b: reference gate signal, c: clock signal, d, e, f, k: gate delay signal.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-62-159376 (JP, A) JP-A-60-219675 (JP, A) JP-A-63-229625 (JP, A) JP-A 61-159 194640 (JP, A) JP-A-59-116906 (JP, A) JP-A-62-54830 (JP, A) JP-A-56-148740 (JP, A)

Claims (4)

(57) [Claims] 1. A method for repeatedly recording an information signal on an optical information recording member having an information layer reversibly changing between optically identifiable states, comprising: Recording gate generating means for generating a reference gate signal based on the delay signal; delay means for delaying the reference gate signal with a plurality of types of delay time widths; and selection means for randomly selecting the type of delay time width of the delay means. Used, the recording start position in the information layer is changed for each repetitive recording, and when recording the information signal on the recording medium, the delay time width is synchronized with the clock of the information signal, and the cycle of the clock is used. A recording method for an optical information recording member, wherein the recording is performed based on the information. 2. When the maximum value of the delay time width is Dmax and the maximum level inversion interval of the modulation scheme of the information signal is Tmax, Dmax
2. The recording method for an optical information recording member according to claim 1, wherein the relationship is ≧ 4Tmax. 3. An interval Dstep for setting a plurality of types of delay time widths.
The optical information recording member recording method according to claim 2, wherein, when the period of the clock signal is T, Dstep ≧ T. 4. The recording method for an optical information recording member according to claim 1, wherein a shift register is used as delay means, and a time delay of information is given by a clock cycle of the information signal.