JP2867993B2 - Optical media recording method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical medium recording method for writing information on a medium by light. 2. Description of the Related Art A medium such as an optical disk, a magneto-optical disk, an optical card, a magneto-optical card, etc., that is, a medium for writing digital data by moving an optical beam relative to the medium (hereinafter simply referred to as an optical medium) Conventionally, a laser (semiconductor laser) is driven in binary (light / dark) by a digital data signal to be recorded, and the laser spot is irradiated on the medium while the laser spot and the medium are relatively moved. I am moving it and writing digital data. More specifically, a laser diode is driven by applying a rectangular pulse current having a pulse width corresponding to data to be recorded. The laser power is controlled not to make the low level completely zero. However, in an apparatus using this kind of optical medium, it always exceeds a certain level to obtain servo signals such as tracking and focusing. Is required. Also here
The output (laser power) of the laser diode is proportional to the difference between the drive current and the threshold current. The power (peak value) of a laser spot applied to an optical medium that moves relatively (an optical medium moves or a laser beam moves) has a length (recording pit) of a recording unit (recording pit). It is known that the length in the moving direction), that is, if the medium is a disk (disk) that rotates, this affects the circumferential dimension of the disk. Laser drive current or pulse for irradiating the medium with the optimum laser power according to various conditions such as the type of medium, the moving speed of the medium, and the ambient temperature used so that the recording pit can be accurately formed. The wave intensity (current value) was preset and applied to the laser diode. [0005] In the prior art,
Even if the laser power applied to the medium changes sharply as shown in FIG. 3A, the maximum temperature at each point of the recording layer of the medium that moves relatively to the applied laser spot is the heat capacity of the medium. Fig. 3
As shown in (2), the rise and fall are delayed. Here, the principle of magneto-optical recording will be described as an example of optical medium recording (thermal recording) in which information is written by heating the medium with light. First, a pulsed laser beam as shown in FIG. 3A is applied to an optical medium. The maximum temperature at each point of the recording layer of the medium that moves relatively to the irradiated laser spot rises as shown in FIG. In the portion where the recording temperature of the medium exceeds the recordable temperature T0, the magnetization direction of the perpendicular magnetization film as the recording layer is in a state where it can be easily changed. As it descends, the magnetization direction is fixed and
Binary recording is performed as shown in (3). In FIG. 3, the hatched portion has a different perpendicular magnetization direction from the other portions, and this is hereinafter temporarily referred to as [1]. When the ambient temperature fluctuates, the maximum temperature at each point of the recording layer of the medium which moves relatively to the irradiated laser spot shifts vertically as shown in FIG. The length of the binary signal [1] obtained from the intersection of the maximum temperature profile and the recordable temperature T0 varies as shown in FIG. 4 (2). In other words, when recording is performed with the same laser power, recording is performed when the ambient temperature increases [1].
Increases in length and contracts when the ambient temperature drops. That is, the ambient temperature dependence of the optimum recording power. In other words, in order to perform recording with the same recording length at any ambient temperature, it is necessary to adjust the laser power, that is, the laser drive current applied to the recording medium according to the fluctuation of the ambient temperature. Further, when the frequency of the recording signal (laser driving current) is high and the laser power changes as shown in FIG. 5 (1), the duration of one pulse is reduced to about the thermal time constant of the recording layer. Since the temperature change of the recording layer of the medium cannot follow the change of the pulse, the recording of the medium (moving by rotation of the medium, that is, the disk, in the case of a magneto-optical disk) that moves relatively to the irradiated laser spot is performed. The highest temperature at each point in the formation is the high temperature (mountain). The low-temperature portion (trough) does not reach the steady temperature, and the difference (amplitude) between the crest and the trough is reduced as shown in FIG. Therefore, when the recording signal has a high frequency, there is a problem that an accurate pit length cannot be obtained with the optimum recording power at a low frequency. That is, the recording frequency dependency of the optimum irradiation laser power. Accordingly, an object of the present invention is to improve the above-mentioned problem, that is, the dependence of the optimum recording power on the ambient temperature and the recording frequency. [0010] In order to improve the above-mentioned problem, that is, the dependence of the optimum recording power on the ambient temperature and the recording frequency, the first invention controls the laser power in accordance with a digital input signal. In the optical medium recording method for recording the digital input signal by irradiating the medium with a light beam and increasing the medium temperature of the irradiating section, when recording the digital input signal having a length of 2 bits or more, the power is reduced. The power is set to a constant value for a period corresponding to the length of one bit of the digital input signal from the rise of the digital input signal, and thereafter, the power is changed to a power lower than the constant value. According to a second aspect of the present invention, there is provided an optical medium recording apparatus for irradiating a medium with a light beam by controlling the power of a laser in accordance with a digital input signal and recording the digital input signal by increasing the medium temperature of the irradiating section. Superposing a correction power on the power for steeping a temperature change of the medium for a period corresponding to one bit length of the digital input signal from a rise and a fall of the digital input signal. I do. In these methods, for example, a correction current is added to a laser drive current at the time of recording, and the rising and / or falling of the laser power applied to the medium is emphasized to minimize the delay in following the temperature change of the recording layer. This can be achieved by performing In the present invention, since the rise and / or fall of the laser power is emphasized, for example, FIG.
In FIG. 1, the rise and fall of the laser power are emphasized, so that the maximum temperature at each point of the recording layer is as shown in FIG.
As described above, the rise and fall delays are improved. That is, referring to FIG. 1A, at time I, the laser is turned on at the writing level, and the power at this time is stronger than usual. For this reason, the rise of the medium temperature rises more steeply than usual. At time II, since the medium temperature has risen sufficiently and exceeded the temperature T0 required for recording, the medium is turned on with normal recording power. The writing is completed at time III, but the power is lowered from the normal power in order to speed up the drop of the medium temperature.
This section can be solved by setting the time such that even if the power becomes almost zero, the servo control of the recording apparatus is not affected at all even if the power becomes almost zero. According to the above-described process, the recording layer of a medium (in the case of an optical disk, a magneto-optical disk, an optical card, or a magneto-optical card, which is caused by the rotation of the medium or the movement of the card) relative to the irradiation laser spot. The maximum temperature at each point (that is, each point on the track) has a large rising and falling slope as shown in FIG. 1 (2), so that the ambient temperature dependency and the recording frequency dependency of the optimum power are improved. . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The duration of the correction current can be set to an appropriate time by rising and / or falling. However, in the following embodiments, the rising and the rising will be described in order to facilitate the description. It corrects the falling, and the correction time for both the rising and the falling is exactly one time of the recording signal.
A case where the length is a bit length will be described. Of course, the circuit configuration is the same when the correction time is not one bit of the signal. FIG. 6 is a block diagram of one embodiment of the semiconductor laser drive current generating circuit of the optical medium recording apparatus of the present invention. The recording pulse current generating circuit 1 generates a normal recording pulse current as shown in FIG. 6B from a digital recording signal having a signal waveform as shown in FIG. The pulse edge detection circuits 2 and 4 detect the rise and fall of the recording signal, respectively, as shown in FIG.
A trigger signal as shown in (c) and (e) is generated. The correction pulse current generation circuits 3 and 5 capture the trigger signal and generate the plus and minus correction pulse currents as shown in FIGS. 6 (d) and (f) by the length of one bit. The recording pulse current (FIG. 6B) and the correction pulse current (FIGS. 6D and 6F) are added to form a current waveform shown in FIG. 6G and drive the laser diode. Although the waveform of the correction current is rectangular in FIG. 6, any waveform may be used as long as the waveform of the correction current emphasizes the rise and fall, for example, a sawtooth wave. FIG. 7 shows a second embodiment in which the correction current is a sawtooth wave. The recording pulse current generating circuit 1 generates a normal recording pulse current similarly to the circuit 1 of FIG. In the differentiating circuit 6, the recording signal is differentiated, and FIG.
A trigger signal as shown in FIG. The correction pulse current generation circuit 7 generates a sawtooth correction pulse current of 1 bit length as shown in FIG. 7D based on the trigger signal. The recording pulse current (FIG. 7B) and the correction pulse current (FIG. 7D) are added to form a current waveform shown in FIG. 7E and drive the laser diode. FIG. 8 shows a third embodiment of the present invention. In this embodiment, each of the correction pulse current generating circuits 8 and 9 can be adjusted by adjusting the duration of the correction current within 1 bit, and is the same as the circuit shown in FIG. 6 except for this point. FIG.
8A to 8G show current waveforms at various points in the circuit of FIG. FIG. 9 shows a fourth embodiment of the present invention. In this embodiment, the duration of the correction current (FIG. 9 (d)) by the sawtooth wave correction pulse current generation circuit 10 can be adjusted within a time shorter than 1 bit. This is the same as the circuit of FIG. The four embodiments have been described above. The features of each embodiment will be described below. In the third embodiment shown in FIG. 8, the correction time can be finely adjusted as compared with the first embodiment shown in FIG. 6, so that the correction time can be optimized. The second embodiment shown in FIG. 7 has a greater effect of edge enhancement than the first embodiment shown in FIG. The fourth embodiment shown in FIG. 9 can optimize the correction time as compared with the second embodiment in FIG. In the embodiment, the correction by the pulse (first,
In the third embodiment), the edge detection circuits 2 and 4 are used, but the differentiation circuit 6 can of course be used. The correction by the sawtooth wave (the second and fourth embodiments) is performed by the differentiating circuit 6, but the edge detecting circuits 2 and 4 can of course be used. Further, other edge portion detecting means can be used. Although the embodiment corrects both the rise and the fall, it is needless to say that either of them may be corrected. Further, the correction period is not limited to one bit or less. However, the circuit configuration is 1 as in the embodiment.
Making it a bit makes things easier. As described above, according to the present invention, in the profile of the maximum temperature of the recording layer, the temperature rise or fall at the portion corresponding to the rise and / or fall becomes sharper, and therefore the optimum recording power is obtained. , The ambient temperature dependency and the recording frequency dependency can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a pulse waveform of laser power and a maximum temperature at each point of a recording layer according to an embodiment of the present invention. FIG. 2 is a waveform diagram of a conventional laser drive current. FIG. 3 is a diagram showing a relationship between a laser output waveform, a maximum temperature and a recording pit at each point of a recording layer. FIG. 4 is a diagram showing that when the ambient temperature changes, the maximum temperature moves in parallel, and the recording pit length changes. FIG. 5 is a diagram illustrating a relationship between a laser output waveform and a maximum temperature of a recording layer when a recording frequency is high. FIG. 6 is a block diagram and a waveform diagram of a semiconductor laser drive current generation circuit used in an embodiment of the present invention. FIG. 7 is a block diagram and a waveform diagram of a semiconductor laser drive current generation circuit used in a second embodiment of the present invention. FIG. 8 is a block diagram and a waveform diagram of a semiconductor laser drive current generation circuit used in a third embodiment of the present invention. FIG. 9 is a block diagram and a waveform diagram of a semiconductor laser drive current generation circuit used in a fourth embodiment of the present invention. [Description of Signs] 1... Recording pulse current generation circuit, 2, 4,... Pulse edge detection circuit, 3, 5, 8, 9,... Correction pulse current generation circuit, 6,. Sawtooth wave correction pulse current generation circuit.

Claims (1)

(57) [Claims] An optical medium recording method for controlling the power of a laser in accordance with a digital input signal to irradiate a medium with a light beam and recording the digital input signal by increasing the medium temperature of the irradiating section. When recording the input signal, the power is set to a constant value for a period corresponding to the length of one bit of the digital input signal from the rise of the digital input signal, and then changed to a power lower than the constant value. Optical medium recording method. 2. An optical medium recording method for recording a digital input signal by controlling the power of a laser according to a digital input signal to irradiate a light beam to a medium and increasing the medium temperature of the irradiating section, wherein the rise and rise of the digital input signal A period corresponding to the length of one bit of the digital input signal from the downstream;
An optical medium recording method, wherein a correction power for making a temperature change of the medium sharp is superimposed on the power.