JP2658404B2 - Optical information recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording a signal on an optical information recording member centered on an optical disk for recording and reproducing optical information at high speed and high density using a laser beam or the like, and It relates to a recording device.

2. Description of the Related Art Techniques for reproducing or recording high-density information using a laser beam are known, and are mainly used as optical disks. Optical discs are read-only, write-once,
They can be broadly classified into rewritable types. The read-only type is a compact disc (hereinafter referred to as CD) that stores music information, or a laser video
Discs (hereinafter referred to as LVD) and the like. In these, signals are recorded in advance on an optical disk, and the user can reproduce music and video information, but cannot record signals. The write-once and erasure types record a signal by providing a metal thin film, a Te alloy, an organic thin film, a ferromagnetic thin film, etc. as a recording film on a substrate and irradiating a laser beam to the recording film to cause some change. Since these methods use the temperature rise of the recording medium by irradiation with a laser or the like, they are called heat mode recording. One of the problems of the heat mode recording is that the recording mark shape is not symmetrical in the longitudinal direction but is distorted like a teardrop. This is the case when recording with a signal waveform as shown in FIG.
Due to the preheating effect, the temperature reached by the recording film is lower at the leading end as shown in FIG. As a result, (c)
It becomes a teardrop-shaped recording mark like. This distortion of the recording mark leads to distortion of the reproduced waveform, which causes an increase in jitter. As a method for improving this, there is a method in which the power at the leading end of the recording pulse is made stronger than that at the trailing end (JP-A-58-182144, JP-A-61-144735, JP-A-61-280028, JP-A-61-280028, 62-281124) and a method of irradiating one recording pulse by dividing it into a plurality of pulses (Japanese Patent Laid-Open No. 58-182134).
JP-A-63-160017, JP-A-63-214922, JP-A-63-263632, JP-A-63-266633, and JP-A-64-46231) are proposed. Have been.

Problems to be Solved by the Invention The above-described prior arts have the effect of reducing the tearing of the recording mark, but have problems. The method in which the power at the leading end of the recording pulse is made stronger than that at the end changes while precisely controlling the laser power during recording, and this has the problem that a power control mechanism is required at a high altitude. On the other hand, the method of irradiating a single recording pulse by dividing it into a plurality of pulses is excellent in that it is not necessary to change the laser power during recording, but has problems in the conventional examples. Was. JP
Japanese Patent Application Laid-Open No. 58-182134 proposes a method of converting each recording pulse into a pulse train in which short pulses are arranged at equal intervals as shown in FIG. This is not sufficient, although the shape distortion of the recording mark is reduced as shown in FIG. It is considered that the cause is that the ultimate temperature of the recording film is as shown in FIG. 2B, and the temperature rise due to residual heat is still quite large. JP-A-63-160017 discloses that each recording pulse is divided into a plurality of pulses as shown in FIG.
Further, it has been proposed to make the pulse width of the first pulse larger than the subsequent pulse width if necessary. According to this, although there is an advantage that the recording mark length can be made equal to the pulse width of the recording signal as shown in (c), 1) the method of dividing the recording pulse depends on the pulse width of the recording pulse. It is necessary to generate divided pulses suitable for each of the above, and the recording apparatus becomes very complicated. 2) Since the method of dividing the recording pulse differs depending on the pulse width, the distortion of the recording mark becomes complicated, and the reproduction is performed. There is a problem that causes an error at the time. This problem also applies to the method proposed in Japanese Patent Application Laid-Open No. 63-264632, in which, when the recording mark length is long, the laser beam is irradiated as two pulses divided immediately before the end.

Japanese Patent Application Laid-Open No. 63-214922 discloses that when forming a long recording mark as shown in FIG. 12A with a signal waveform as shown in FIG. 12A, a long pulse followed by a short pulse train of laser light is applied. Suggest a way. Although this is effective in not enlarging the end portion of the recording mark, the temperature rise process is significantly different between a portion irradiated with a long pulse and a portion irradiated with a short pulse train, and as shown in FIG. In some cases, a new distortion of the recording mark occurred in the portion. JP 63
No. 266633 proposes to convert a signal waveform as shown in FIG. 13 (a) into three or more pulse trains in which the leading and trailing pulse widths are widened as shown in FIG. 13 (b). I have. However, in this method, 1) since the pulse width is wide at the end, the shape of the recording mark may also be large at the end as in (c). 2) The pulse width at the end for each recording pulse is wide. Generating the divided pulse requires a complicated recording device. JP-A-64-46231 discloses a recording film in which a signal waveform as shown in FIG. 14A is formed into a pulse train in which the pulse interval gradually widens (or the pulse width gradually narrows) as shown in FIG. Is controlled. This method is an excellent method for improving the symmetry before and after the recording mark as shown in FIG. 3C, but it is necessary to make the optimum pulse trains correspond to signal waveforms having different lengths, and the recording apparatus is extremely difficult. It has the problem of becoming complicated.

Means for Solving the Problems In order to solve the above problems, in order to form one recording mark when digital information is recorded on an optical disk by changing the recording mark length and the recording mark interval by the edge position of the recording mark. Is composed of a recording pulse train composed of a plurality of pulses, and the pulse width of at least one of the first two pulses of the recording pulse train is larger than the pulse width of each pulse in the succeeding subsequent pulse train and is stored. Irrespective of the mark length, the pulse width and the pulse period of each pulse in the subsequent pulse train are the same, and the number of pulses in the subsequent pulse when forming the n-th recording mark is na + b (A and b are constants, a is a positive integer, and b is an integer) to realize a recording method in which one recording mark is formed. As a means for generating a recording pulse train composed of a plurality of pulses, a pattern setter for previously setting the pattern of the recording pulse train corresponding to the longest pulse width of the input signal, and a pulse width smaller than that The pattern of the recording pulse train is a modulator that cuts out a necessary length from the beginning of the setting pattern of the pattern setting device to turn the input signal pulse into a pulse train, and emits a laser by the pulse train signal from the modulator to generate a signal. Recording means for recording optical information.

Operation As described above, since the pulse width near the head is wide, the ultimate temperature of the recording film is sufficiently high even at the front end, so that teardrop-like distortion of the recording mark can be reduced. The optical information recording apparatus according to the present invention realizes the above recording method with a very simple configuration in order to generate all necessary signal patterns from one preset signal pattern.

Embodiments The present invention will be described below in detail with reference to the drawings. The greatest feature of the optical information recording method according to the present invention is that a digital signal whose length discretely changes from 3T to 11T, for example, as shown in FIG. 1A, is shaped as shown in FIG. And recording a signal on an optical disc.
First, the reason for modulating the laser light as shown in FIG. 1B will be described. When recording a signal as shown in FIG. 9 (a) in the heat mode recording, if the laser beam is directly modulated by the signal waveform, a recording mark distortion as shown in (c) will occur. Has been proposed. These methods propose a means for controlling the heat of the laser beam irradiation part to keep the ultimate temperature of the entire recording mark constant, and prevent the recording mark from becoming thicker toward the end and becoming tear-drop-like. I'm going. However, in practice, 1) the effect of preventing the recording mark from becoming teardrop-shaped is small, 2) the recording device becomes complicated, 3) the recording mark can be prevented from becoming teardrop-shaped, but new distortion occurs. And so on.
Therefore, the inventors have studied in detail a method for reducing the distortion of the recording mark and not complicating the device configuration. As a result, in order to prevent tear marks in the recording mark, 1)
It is effective to modulate a signal pulse for forming one recording mark into a pulse train composed of a plurality of pulses, and 2) to make the width of the first or second pulse of the pulse train wider than that of the succeeding pulses and to optimize the pulse width. It turned out to be a target. Next, in order to realize a simple apparatus configuration, 3) the recording power is kept constant and the attained temperature is controlled by changing the pulse width. 4) When the signal pulse is formed into a pulse train,
The pulse width of the signal pulse and the number of pulses included in the pulse train maintain a constant relationship. For example, if the pulse width of the signal pulse is increased by one, the number of short pulses included in the pulse train is increased by one. 5) The pulse width of the added short pulse needs to be always constant. As a recording method satisfying the above 1) to 5), for example, a modulation method as shown in FIG. 1B is proposed. In other words, only the leading pulse is a pulse train with a pulse width narrower than the following pulse, and all the subsequent pulses have the same pulse width. One pulse is added as the pulse width of the input signal becomes longer by T, and the subsequent pulse is added. Is T. Such a modulation method can be easily realized by the optical information recording apparatus of the present invention, which will be described later in detail, and furthermore, teardrop-like distortion of a recording mark can be greatly reduced. Next, an optical information recording apparatus according to the present invention will be described. FIG. 2 shows a block diagram thereof. The biggest feature of this device is that the modulation pattern corresponding to the longest signal pulse is set in advance, and for shorter signal pulses, the required length from the beginning of the modulation pattern for that modulation pulse The pulse train is cut out. The signal s1 to be recorded is first input from the signal generator 1 to the modulator 2. This signal is a digital signal that has been subjected to pulse width modulation (PWM). Conventionally, this signal itself generally drives and records a laser. However, the modulator according to the present invention further modulates the input signal into a pulse train corresponding to the pulse width. In the modulation method, a conversion pattern including a pulse train corresponding to the pulse having the longest pulse width included in the input signal s1 is set in the pattern setting device 3 in advance. Then, the pulse width of the input signal s1 is detected, the necessary length is cut out from the beginning of the setting pattern of the pattern setting device according to the length, a pulse train is generated, and the pulse train is output from the modulator. The semiconductor laser incorporated in the head 5 emits light and collects light on the optical disk 7 to record a signal. Therefore, for a pulse having a different pulse width included in the input signal, all patterns can be converted into a pulse train only by setting one pattern. Further, the shape of the pattern to be set can be easily optimized so that the reproduced waveform distortion is minimized. Note that the input signal generator, modulator, and pattern setter must be connected to the same clock C1 (an integer multiple of the input signal clock) so that the edge position of the input signal from the signal generator does not fluctuate due to the pulse train modulation. It is preferable to suppress the jitter of the recording signal by synchronizing with a clock having a good frequency. FIG. 3 shows a specific configuration of the modulator. The rising detector 8 detects the rising edge position of the pulse of the input signal s1 and sends a start signal to the pattern generator 10. After calling the pulse train pattern set in the pattern setting unit 3 by the start signal, the pattern generator starts sending as a modulation signal one step at a time from the beginning. Thereafter, the falling edge of the pulse of the input signal is detected by the falling detector 9 and a stop signal is sent to the pattern generator. In response to the stop signal, the pattern generator stops sending the set pattern, that is, the modulated signal, and waits for the next input signal pulse. Therefore, a pulse-like modulation signal s4 having a length corresponding to the input pulse width is always transmitted from the pattern generator. In this case, the rising detector, falling detector, and pattern generator all operate in synchronization with the clock C1, so that the jitter of the modulated signal to be recorded can be suppressed. The present invention can be applied to all optical disks of so-called heat mode recording, in which a signal is recorded by causing some kind of optically detectable change in the recording film by increasing the temperature by irradiation with laser light or the like. Optical disc substrates include polymethyl methacrylate (PMMA),
Polycarbonate (PC) or glass can be used. The recording film may be either a write-once type or a rewritable type. As a write-once type, for example, a metal thin film, a Te alloy, an organic thin film, etc. are provided as a recording film, and a punching type for recording a signal by piercing with a laser beam or an amorphous thin film such as a Te alloy is provided. There is a phase change type that is crystallized and recorded. In addition, as a rewritable type, a Te alloy or the like is provided as a recording film, and a phase change type utilizing the reversible state change of the amorphous and the crystal, or a signal is recorded by controlling a magnetization direction using a ferromagnetic thin film. There is a magneto-optical type. Next, specific examples of the present invention will be described.

Embodiment 1 FIG. 4 shows a block diagram of a circuit used in this embodiment.
EFM used for music playback CD as input signal
(8-14 modulation) signal was used. EFM is a PWM composed of 9 types of pulses with different pulse widths from 3T to 11T
Signal. Here, T is a clock cycle, and T = 23.
0 nsec. The modulated pulse train signal is input to the laser drive circuit as in FIG. 2, and the signal is written to the optical disk via the optical head. The optical disk used was a rewritable phase change type. The optical disk substrate used was a 5 ″ PC substrate on which signal recording tracks had been formed in advance. The recording film was made of a TeSeGeSb-based material and had a film thickness of 1000 °.
Further, a Zns layer is provided above and below the recording film to protect the substrate. The signal recording and erasing correspond to the amorphous state and the crystalline state of the recording film, respectively. The signal recording track was crystallized (erased) in advance, and the signal was recorded after being made amorphous by laser light irradiation. . The relative speed of the recording spot of the laser beam converged with the optical disk was 1.25 m / sec. The recorded signal was evaluated by measuring the jitter of the reproduced signal. The jitter was defined as the standard deviation by repeatedly measuring the time from one zero cross to the next zero cross for each of nine types of pulses having different pulse widths, using the zero cross of the reproduced waveform as a judgment level. Here, the operation principle of the circuit of FIG. 4 will be described with reference to the timing chart of FIG. This circuit has the longest pulse width of 11T
In advance, a pulse train consisting of 44 areas is set in the pattern setting device in advance, and a pulse train of the required length from the beginning of the set pattern is set according to the pulse width of the input 3T to 11T pulse. It is to be sent to the laser drive circuit. That is, T / 4 obtained by dividing the clock cycle T of the EFM signal s5 into four is the clock c2 of this circuit system. The timing chart in FIG. 5 shows a case where a 4T pulse is converted into a pulse train. First, when the EFM signal s5 is input, the data flip-flops DFF11 and DFF12 and
The start signal s9 is generated by the NAND 15, and the parallel-in / serial out-shift register: PS / SR17 is started. PS / SR1
7 calls a set pattern from the pattern setter 18 and sends out the set pattern one step at a time in synchronization with the clock c2. As a method of setting the pattern, a method corresponding to the longest pulse width of 11T is used.
This is performed by providing switches SW1 to SW44 for each of the steps, so that an arbitrary pattern can be set by turning on / off each switch. Next, DFF11, DF
The stop signal s10 is generated by F12 and NAND16. In the case of a 4T pulse, the stop signal s10 is output in synchronization with the 16th clock. By this stop signal, the output from the PS / SR 17 after step 17 is stopped, and s12 becomes a pulse train as shown in FIG. The DFF 13 synchronizes the pulse train with the clock again to reduce jitter, and then inputs the pulse train to the laser drive circuit. In this manner, all the pulses of 3T to 11T can be formed into a pulse train in the shape of the set pattern. This apparatus uses the modulation waveform (b) in the case of 11T in FIG. 1 as a setting pattern, converts the EFM signal into a pulse train according to this pattern, modulates the laser, records the signal, reproduces the signal, and reproduces the jitter of the reproduced signal. Was measured. Fig. 6 shows the recording power (value on the optical disc surface)
And the relationship between jitter and jitter. FIG. 6 shows, for comparison, the results of measuring jitter when recording was performed by a conventional method of recording a signal by directly modulating a laser with an EFM signal. As is apparent from FIG. 6, according to the recording method and the recording apparatus of the present invention, the waveform distortion of the recording mark is reduced, so that the jitter of the reproduced waveform is also reduced. Therefore, the error rate of the reproduced signal can be reduced and the recording density can be reduced. Can be improved. In FIG. 4, the pattern setting is performed by turning on / off the switches SW1 to SW44. However, the pattern setting device may be a ROM (reproduction only memory) in which a setting pattern is recorded in advance. If a ROM is used, this circuit does not include a delay element or the like, so that the circuit can be integrated and the device can be miniaturized.

(Example 2) Next, using the apparatus shown in Example 1, various waveforms set in the pattern setting device were variously changed, and an optimum pattern was obtained. The method for measuring the input signal, the optical disk, the relative speed between the optical disk and the recording spot, and the jitter are the same as those in the first embodiment. FIG. 7 shows the set pattern shapes, and Table 1 shows jitter values measured for signals reproduced after recording with respective waveforms. The jitter is the minimum value when the recording power is changed, and the recording power at that time is also shown in Table 1.

As can be seen from Table 1, patterns (h), (k),
Except for (l), the jitter is as small as 100 nsec or less. Patterns (h), (k) and (l) are comparative examples for the present invention. Pattern (l) is equivalent to the method of driving the laser with the EFM signal itself and shows a large jitter. The pattern (k) is recorded by a pulse train in which short pulses having the same pulse width are arranged at equal intervals, and has a large jitter although it is improved as compared with the pattern (l). Also in the pattern (h), the jitter is large. This is considered to be because the temperature does not rise sharply at the leading portion because three leading pulses having a large pulse width are used. In any case, it can be seen that jitter can be suppressed to a small value if the conditions described in claim 1 are satisfied. From FIG. 7 and Table 1, the patterns in which the jitter is extremely small are (a), (f), (g),
(J). These features are such that the first or second pulse width is increased, and subsequent pulses have the same pulse width and pulse interval, and one pulse is added when the recording mark length increases by one. The period of the subsequent pulse is T. In particular, the smallest jitter was obtained in (f) and (g) where the second pulse width from the top was increased. (A),
The patterns (f), (g), and (j) correspond to (a), (j): a = 1, b = 0, (f), (g): a = 1, b =
This is the case of -1. Also, patterns (a), (b),
As can be seen from the comparison of the recording powers in the case (c), a large recording power is required when the pulse width of the subsequent pulse (that is, the irradiation time of the laser beam) becomes short. Considering that the power of a semiconductor laser which is inexpensive and easily available at present is about 10 mW or less on the surface of an optical disc, the pulse width is preferably T / 2 or more.

(Example 3) Further, using the same apparatus as in Examples 1 and 2, the patterns (g) and (d) of Example 2 are set in the pattern setting unit,
The value of jitter was determined while changing the relative speed between the optical disk and the recording spot. The measuring method of the input signal, the optical disk, and the jitter is the same as in the first embodiment. FIG. 8 shows the relationship between the jitter value measured in the reproduced signal and the relative speed. For the jitter, the minimum value was obtained by changing the recording power, and the value was recorded. In both patterns (g) and (d), the jitter increased when the relative speed was high. The increase in jitter is at a point where the relative speed is lower in (g) than in pattern (d), and the point is the repetition period τ of the subsequent pulse [T = 230 nsec in pattern (g), T / 2 in (d). = 115nsec]
Is λ / L (λ is the wavelength of the laser in this embodiment 0.83 μm,
L coincides with the increase of the relative speed). This is because the distortion that occurs in the recording mark due to the intermittent irradiation of the laser light is of the order of the wavelength of the laser light and is optically reproduced, resulting in distortion of the reproduced waveform and increased jitter. Conceivable. Therefore, it is better to set the repetition period of the subsequent pulse so as to satisfy τ ≦ λ / L τ: repetition period of the erroneous pulse λ: laser wavelength L: relative speed between the optical disk and the recording spot

According to the optical information recording apparatus of the present invention, it is possible to form a recording mark with a small shape distortion and a small jitter with a very simple apparatus configuration. This leads to a reduction in the error rate of the optical disk, and thus the recording capacity of the optical disk can be increased.

[Brief description of the drawings]

FIG. 1 is a waveform diagram showing an example of the optical information recording method according to the present invention, FIG. 2 is a block diagram schematically showing an optical information recording device according to the present invention, and FIG. FIG. 4 is a block diagram showing a specific example, FIG. 4 is a circuit diagram showing a specific example of an optical information recording apparatus according to the present invention, FIG. 5 is a timing chart showing a signal flow in FIG. 4, and FIG. FIG. 7 is a waveform diagram showing a setting pattern, FIG. 8 is a diagram showing the relationship between jitter and relative speed, and FIGS. 9 to 14 explain a conventional recording method. FIG. 4 is a recording waveform diagram and a shape diagram of a recording mark. DESCRIPTION OF SYMBOLS 1 ... Signal generator, 2 ... Modulator, 3 ... Pattern setting device, 4 ... Laser drive circuit, 5 ... Optical head, 6 ...
... Spindle motor, 7 ... Optical disk, 11, 12, 13 ...
... data flip-flops, 14 ... inverters, 15,
16… NAND circuit, 17… Parallel serial shift register, 18… Pattern setting device.

Claims (3)

(57) [Claims] When recording information by forming a recording mark on an optical information recording medium by irradiating a laser beam or the like, digital information is recorded based on the edge position of the recording mark by changing the recording mark length and the recording mark interval. In the optical information recording apparatus, the formation of one recording mark is performed by irradiating a laser beam or the like onto an optical information recording medium after converting an input pulse into a recording pulse train composed of a plurality of pulses. As a means for generating, a pattern setting device for setting a pattern of the recording pulse train corresponding to the longest pulse width of the input signal in advance, and a pattern of the recording pulse train corresponding to a pulse width less than the setting value of the pattern setting device. A modulator that cuts out the required length from the beginning of the pattern and turns the input signal pulse into a pulse train Recording apparatus of the optical information; and a means for recording a signal by emitting the laser by the pulse Stringified signal from the modulator. 2. A method according to claim 1, wherein a rising edge of the input signal is detected to start generation of the set pattern, and a falling edge is detected to end the generation of the set pattern, thereby obtaining a length corresponding to each pulse width of the input signal. 2. The optical information recording apparatus according to claim 1, wherein a pulse train is generated to convert the input signal pulse into a pulse train. 3. The optical information recording apparatus according to claim 1, wherein the operation of the input signal generator, the modulator, and the pattern generator is controlled by the same clock signal.