Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1999-03-01
2001-04-24
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S053130
Reexamination Certificate
active
06222815
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to methods and devices for recording on an optical disk, such as a CD-R, CD-RW, CD-WO, MD or DVD, by use of light power, and more particularly to a technique for controlling the light power promptly with increased accuracy.
Among various types of known write-once and rewritable optical disks is one having a recording layer of dye or coloring material. Specifically, such dye-layer-type optical disks include a substrate that is coated with a film of dye-based recording material by use of the “spin coat” method. Thus, each of these dye-layer-type optical disks tends to have a nonuniform coating thickness across its radius, due to which its recording sensitivity would substantially differ between the inner and outer circumferential portions. Further, a fingerprint, dust or other foreign matter, adhering to the surface of the optical disk, would sometimes cause undue absorption or scattering of the recording laser light beam, thereby preventing satisfactory recording.
In Japanese Patent Laid-open Publication No. HEI-5-282672, there is proposed an improved optical disk recording method designed to avoid the above-mentioned inconvenience. Specifically, in the proposed optical disk recording method, a reflection of the recording laser light beam from the optical disk is constantly monitored, and the irradiation power of the light beam is controlled in accordance with the monitored reflection levels so that desired pits are formed in the optical disk in a constantly appropriate manner.
However, the proposed optical disk recording method is disadvantageous in that it can not promptly control the power of the laser light beam in an accurate manner, because sampling points of the reflection levels are not specifically set in the proposed method.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical disk recording method and device which can control the light beam power promptly with increased accuracy.
In order to accomplish the above-mentioned object, the present invention provides a method of irradiating a recording light beam onto an optical disk to form therein a series of pits having lengths ranging from 3Ts to 11Ts—where T represents a length of a basic or unit time period in a longitudinal direction of a pit track—which comprises the steps of: sampling and holding a level of a reflection signal, representative of a reflection of the recording light beam from the optical disk, for a predetermined time period between points of 1T and 3Ts after the start of a rising edge of the reflection signal; making a comparison between the level of the reflection signal sampled and held by the step of sampling and holding and a predetermined reference level; and controlling power of the recording light beam on the basis of a result of the comparison.
According to another feature of the present invention, there is provided an optical disk recording device which comprises: an optical pickup section that irradiates a recording light beam onto an optical disk to form therein pits having lengths ranging from 3Ts to 11Ts—where T represents a length of a basic or unit time period in a longitudinal direction of a pit track—and also receives a reflection of the recording light beam from the optical disk to thereby generate a reflection signal; a sample and hold section that samples and holds a level of the reflection signal, generated by the optical pickup section, for a predetermined time period between points of 1T and 3Ts after the start of a rising edge of the reflection signal; a comparator section that makes a comparison between the level of the reflection signal sampled and held by the sample and hold section and a predetermined reference level; and controlling power of the recording light beam on the basis of a result of the comparison by the comparator section.
When a light beam is irradiated onto a dye-layer-type optical disk, the reflection signal presents high levels at the beginning of the light beam irradiation because no pit has not yet been formed in the optical disk. Then, as formation of a pit progresses, the reflectivity of the optical disk gradually decreases, so that the reflection signal becomes correspondingly lower in level and then presents a stable level. Once disturbance occurs in the scattering or absorption of the light beam due to a fingerprint, dust or other foreign matter present on the recording surface of the optical disk, the level of the reflection signal would vary entirely. In order to promptly detect variations in the reflection signal level for efficient control of the irradiated light beam power, it is desirable to properly detect levels at and around the start of an initial rising phase of the reflection signal. However, at the start of the rising phase of the reflection signal, the occurrence of the disturbance would exert very little effect on the resultant reflection signal level; particularly, it is very difficult to identify the disturbance on the basis of detected levels at a right shoulder part of the signal's peak region. Further, since the reflection signal presents rapidly-varying levels at and around the peak region in the rising phase, a complicated circuit is required for sampling and holding the rapidly-varying signal levels, and besides it is sometimes impossible to acquire accurate signal levels due to the fact that the signal levels are saturated through amplification by an HF amplifier before being properly held by the sample and hold circuit. The high-level period of the reflection signal lasts until one unit time period (1T) elapses after the start of the rising phase.
Thus, according to a primary feature of the present invention, the reflection signal is sampled and held for a predetermined time period between points of 1T and 3Ts after the start of the rising edge of the reflection signal. With this feature, levels of the reflection signal can be sampled and held just after arrival of such a time point when detection of any disturbance can be made with ease. Further, with the sampling timing thus set to arrive between the points of 1T and 3Ts after the start of the rising edge of the reflection signal, it is possible to sample only stable levels of the reflection signal even when a shortest pit of a 3T length is to be formed, and thus accurate and prompt feedback control is always achieved with respect to a recording signal having pulse widths or lengths in the range of 3Ts to 11Ts.
An average of the sampled and held levels is used as the predetermined reference level for comparison with each sampled and held level of the reflection signal, and the light beam power is controlled on the basis of the comparison between the sampled and held level and the reference level. Thus, the reference level can be adjusted appropriately in accordance with a waveform of the reflection signal that would vary depending on the reflectivity of the optical disk and selected recording speed as well as the radial (inner or outer) position of the light beam spot on the optical disk. This arrangement allows the recording power to be controlled with even higher accuracy.
Further, the reflection signal may also vary in level depending on a selected recording speed, material, recording sensitivity of the optical disk. Thus, it is also desirable to change the generation timing (time position) and length of sampling pulses in accordance with the type of the optical disk. For this purpose, the optical disk recording device of the invention may further comprise: a storage section that stores therein information indicative of optimum sampling pulses corresponding to a plurality of types of optical disks; a disk identifying section that identifies a particular type of the optical disk; and a sampling pulse generator section that reads out, from the storage section, the information indicative of one of the optimum sampling pulses which corresponds to the type of the optical disk identified by the disk identifying section and generates a sampling pulse based on the read-
Edun Muhammad
Pillsbury & Winthrop LLP
Yamaha Corporation
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