Information Recording Method of Optical Disc, Laser Driving Apparatus and Optical Disc Apparatus

Abstract

Pulses modulated between the erase power and the bottom power are used instead of cooling pulses for an optical disk medium that needs a write strategy with 4-valued power levels. Consequently, pulse instruction lines for the cooling pulses, power level instruction lines, and corresponding current source within the laser driver can be omitted. Decrease in size and lower power consumption can be accomplished.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a writing method according to the present invention.

FIG. 2 is a diagram illustrating write pulses used to write a DVD-RAM by a well-known method.

FIG. 3 is a circuit diagram of a well-known laser driving apparatus.

FIG. 4 is a schematic diagram of signal lines of an optical disk drive.

FIG. 5 is a diagram illustrating write pulses used to write a DVD-RAM disk.

FIG. 6 is a diagram illustrating write pulses with 3-valued power levels.

FIG. 7 is a diagram illustrating write pulses with 3-valued power levels.

FIG. 8 is a graph showing the results of experiments to investigate the relationship between the write power and jitter when writing was done with write pulses with 3-valued power levels.

FIG. 9 is a graph showing the results of a simulation indicating temperature hysteresis at the ends of write marks and the crystallization rate.

FIG. 10 is a diagram showing the results of a simulation in which 3-valued and 4-valued pulses were compared in terms of overwrite performance.

FIG. 11 is a graph showing the results of experiments showing the relationship between write power and jitter.

FIG. 12 is a graph illustrating another writing method according to the present invention.

FIG. 13 is a diagram showing the configuration of a laser driving apparatus according to the present invention.

FIG. 14 is a diagram showing the configuration of an optical disk according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Prior to description of embodiments of the present invention, experiments and analysis made by the present inventors are described. As described previously, there has been the problem that if a 4.7 GB DVD-RAM medium is overwritten with 3-valued pulses, trailing edges suffer from worse jitter. To analyze the factors, thermal simulations and experiments were performed.

FIG. 9 shows the results of a calculation of temperature hysteresis at the trailing edges of 3T marks. Also, experimentally derived relationship between the temperature of the centers of the tracks and the DC erase ratio is shown. The temperature range in which the maximum erasing performance is exhibited (hereinafter may be referred to as the optimum temperature range), i.e., the DC erase ratio is higher than 30 dB, is in the hatched region (about 370 to 490° C.). It can be seen from the results of the thermal simulation that with write strategies (indicated by 3-valued pulse-1 and 3-valued pulse-2, respectively) shown in FIGS. 6 and 7, the erasing performance stays in the optimum temperature range in a shorter time during the cooling process than where the write strategy (indicated by standard pulses) illustrated in FIG. 5 is used. It can be considered that this leaves the trailing edges unerased during overwriting, deteriorating the jitter.

Accordingly, we have devised a write strategy as shown in FIG. 1. A pulse train (hereinafter referred to as the cooling assisting pulse train) modulated between bias power 1 and bias power 3 at intervals of 1 Tw is applied during the period of the cooling pulses. Consequently, the average thermal energy of light pulses applied to the medium during the period of the cooling pulses can be made equivalent to that of the standard pulses. In this case, the average thermal energy can be adjusted by adjusting the duty cycle of the cooling assisting pulse train.

More specifically, in the same way as when the power value of the cooling pulses is determined, conditions under which the overwrite jitter is minimized are found, using the duty cycle of the cooling assisting pulse train as a parameter. As shown in FIG. 9, use of the write strategy according to the present invention makes it possible to give a temperature hysteresis equivalent to that of standard pulses to the medium. Furthermore, the temperature rises and falls repeatedly during the cooling period. Therefore, it can be expected that crystal nuclei of the recording film will be created frequently during temperature decrease and that the crystal nuclei will be grown efficiently during temperature rise. The differences of crystallization mode of phase-change recording materials caused by variations in the temperature in this way are well known characteristics. Since detailed description of the characteristics is beyond the scope of the present invention, the description is omitted herein.

FIG. 10 shows the results of calculations of differences of the shape of marks and readout signals for first cases in which 3 Tw marks were recorded on unrecorded portions and for second cases in which 3 Tw marks were made to overwrite 11 Tw marks. The first cases include a case in which there were cooling pulses and a case in which there were no cooling pulses. Also, the second cases include a case in which there were cooling pulses and a case in which there were no cooling pulses. The upper part of FIG. 10 shows the results of the write strategy of FIG. 6. As can be seen from the figure, where 3 Tw marks were made to overwrite 11 Tw marks, the trailing edge of the mark extended rearwardly unlike the case in which 3 Tw marks were recorded on unrecorded portions of the crystal. With respect to the leading edges, the difference between both strategies was smaller. On an actual disk, a new data signal is overwritten with no correlation with the underlying base signal. Therefore, shifts of the trailing edges appearing here are produced at random, increasing jitters at the trailing edges.

The lower part of FIG. 10 shows the results of writing by the write strategy of FIG. 5. Because of addition of cooling pulses, the differences between the positions of the trailing edges of 3 Tw marks were reduced. It can be expected that the overwrite jitter will be improved.

FIG. 11 shows the results of an experiment indicating the relationship between peak power and jigger in a case where a 8-16 modulated random data signal is overwritten. The width and power of the write strategy of FIG. 5 denoted by the standard pulses were set to 2.0 Tw and 4.6 Tw, respectively. In the case of the write strategy of the present invention shown in FIG. 1, the duty cycle of the cooling assisting pulse train was set to 23/32 Tw. The other power conditions are the same as the conditions described previously. Comparison with the write strategy of FIG. 6 denoted by “3-valued Pulse-1” has confirmed that the write strategy of the present invention produces a jitter value equivalent to the jitter value obtained when the standard pulses are used.

In this way, good writing characteristics could be obtained by the write strategy not using a power control system dedicated to cooling pulses. Consequently, the scale of the circuit of the laser driver IC and the number of signal lines on the FPC could be reduced.

Good writing characteristics can be obtained by a write strategy not using a power control system dedicated to cooling pulses by the use of recording method, laser driving apparatus, and optical disk drive using them. A small-sized, low-cost, low-power consumption optical disk drive can be offered.

The present invention is hereinafter described in detail using its embodiments.

Embodiment 1

Recording Method

FIG. 12 shows an embodiment in which another form of write strategy of the present invention is shown. The difference between the write strategies of FIGS. 12 and 1 is that a cooling assisting pulse train starts immediately after the end of the last pulse. Where the thermal diffusion from the medium is large compared with the rise/fall time of the waveform of emitted laser light (e.g., where the write speed is low or where the thermal conductivity of the recording medium is large), the cooling rate can be reduced by this method. The temperature of the recording film can be prevented from decreasing to below the optimum temperature range shown in FIG. 9.

Embodiment 2

Laser Driving Apparatus

FIG. 13 is a schematic diagram showing the structure of a laser driving apparatus of the present invention. In the figure, a laser power/pulse controller 120 is mounted on a main board 170. A laser driver 116 and a semiconductor laser (laser diode) 112 are mounted on an optical head 110. The laser driver 116 is designed to incorporate the plural current switches shown in FIG. 3. (a) ON/OFF instructions for the current switches (pulse conditions) are sent from the laser power/pulse controller 120 to the laser driver 116 via an FPC 180 by an LDVS method. (b) The amount of currents to be fed to the current switches (power conditions) are sent as an analog voltage level from the laser power/pulse controller 120 to the laser driver 116 via the FPC 180. The laser power/pulse controller 120 has functions of precisely controlling the various signals and achieving the write strategy of the present invention shown in FIGS. 1 and 12.

Embodiment 3

Optical Disk drive

FIG. 14 is an embodiment showing the structure of an optical disk drive of the present invention. An optical disk medium 100 is rotated by a motor 160. During playback, a controller 120 for laser power level and pulse width controls the electrical current supplied to a semiconductor laser 112 via a laser driver 116 incorporated within an optical head 110 such that a light power instructed by a CPU 140 is achieved, and produces laser light 114. The laser light 114 is focused by an objective lens 111 and forms a light spot 101 onto the optical disk medium 100. Reflected light 115 from the light spot 101 is detected by a photodetector IC 113 via the objective lens 111. The photodetector IC is made up of plural split photodetectors. A readout signal processing circuit or signal processor 130 reproduces information recorded on the optical disk medium 100 using the signal detected by the optical head 110. During recording, the laser power/pulse controller 120 converts given recorded data into a given recorded pulse current and sends an instruction signal to the laser driver 116. The laser power/pulse controller 120 controls the semiconductor laser 112 to emit pulsed light from it. Because of the structure described so far, an optical disk apparatus of the present invention can be offered.

The present invention can be used for recording method, laser driving apparatus, and optical disk drive for recording data onto a recordable optical disk medium.

It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.

Claims

1. A method of recording information on an optical disk medium prerecorded with leading edge positions and trailing edge positions of plural pulses and values of power levels of the pulses as recommended recording conditions, wherein said plural pulses include a first pulse, multiple intermediate pulses, a last pulse, and cooling pulses,wherein the power levels of the plural pulses are respectively a peak power for recording, a power level being a first bias power and used for erasure, a power level of the cooling pulses being a second bias power, and a bottom power level of said multiple intermediate pulses being a third bias power, andwherein a pulse train modulated between the first bias power level and the third bias power level is applied as said cooling pulses.

2. A laser driving apparatus for controlling light emission from a laser light source to record information on an optical disk medium prerecorded with leading edge positions and trailing edge positions of plural pulses and values of power levels of the pulses as recommended recording conditions, wherein said plural pulses include a first pulse, multiple intermediate pulses, a last pulse, and cooling pulses,wherein the power levels of the plural pulses are respectively a peak power for recording, a power level being a first bias power and used for erasure, a power level of the cooling pulses being a second bias power, and a bottom power level of said multiple intermediate pulses being a third bias power, andwherein a pulse train modulated between the first bias power level and the third bias power level is applied as said cooling pulses.

3. An optical disk drive capable of recording information on an optical disk medium prerecorded with leading edge positions and trailing edge positions of plural pulses and values of power levels of the pulses as recommended recording conditions, wherein said plural pulses include a first pulse, multiple intermediate pulses, a last pulse, and cooling pulses,wherein the power levels of the plural pulses are respectively a peak power for recording, a power level being a first bias power and used for erasure, a power level of the cooling pulses being a second bias power, and a bottom power level of said multiple intermediate pulses being a third bias power, andwherein said optical disk drive is equipped with a laser driving apparatus having a function of applying a pulse train modulated between the first bias power level and the third bias power level as said cooling pulses.