Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Patent
1990-03-05
1998-11-10
Edun, Muhammad N.
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
369 54, G11B 700
Patent
active
058354760
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a laser diode driving apparatus for driving a laser diode that irradiates an optical disk with a laser beam. More particularly, it relates to a laser diode driving apparatus used for irradiating a write-once or overwrite optical disk with a laser beam.
BACKGROUND ART
In the case of an optical disk, which is dedicated to reproduction and on which audio data or video signal are recorded in advance, the laser power irradiated on the disk for reading out recorded data on the disk is rather low and reproduction characteristics are not deteriorated to any marked extent as long as the laser power output is within the range of a certain reference level.
However, in the case of a recordable optical disk, such as the write-once or overwrite optical disk, which is being put to application at a rapid rate, the laser power consumed during recording is increased by a factor of seven to ten as compared with the power consumed during reproduction, while the optimum value of the laser power irradiated during recording on the optical disk is restricted to a narrow range.
Thus, when the laser power is increased excessively, the size and the shape of the recording pattern formed on the recording surface of the disk differs markedly from the predetermined size and shape, thus increasing the error rate or giving rise to crosstalk.
Also, when the laser power is lowered, the temperature on the recording surface falls short of the predetermined recording temperature to detract from the quality of the recorded data.
FIG. 1 shows diagrammatically a conventional APC (Auto Power Control) circuit for controlling the laser power, wherein 1 denotes a write-once type optical disk, and a portion encircled by a chain-dotted line 2 denotes an optical head for irradiating the optical disk 1 with a laser beam.
The optical head 2 is provided with a semiconductor laser diode 3. The light emitting from the semiconductor laser diode 3 is directed by way of a beam splitter BS and an objective lens L to the recording surface of the optical disk 1. The beam reflected from the semiconductor laser diode 3 is detected by a monitoring detector 4.
The numeral 5 denotes an amplifier for amplifying an electrical signal of the laser power detected by the detector 4, the numeral 6 comparator means to which a reference signal E.sub.1 for the recording mode, a reference signal E.sub.2 for the reproduction mode and a reference signal E.sub.3 for the erasure mode are selectively applied, the numeral 7 a low-pass filter, the numeral 8 a summation circuit for summing a record data signal E.sub.D to the output of the comparator means 6, the numeral 9 a driver circuit for driving the semiconductor laser diode 3 and the numeral 10 a mode switch for selecting the reference signals E.sub.1, E.sub.2 and E.sub.3 for the respective modes.
The summation circuit 8 is fed with the recording data signal E.sub.D at a constant amplitude during recording, and operates to sum the d.c. current supplied to the semiconductor laser diode 3 (the output of the low-pass filter 7) and the recording data signal E.sub.D -together and to supply the summation output to the driver circuit 9.
The optical disk 1 has its recording surface formed of a material on which recording may be made magneto-optically.
As the optical disk 1 is rotated, the laser beam emitting from the semiconductor laser diode 3 is on-off controlled on the basis of the recording data signal E.sub.D. The temperature of the portion of the optical disk 1 irradiated by the laser beam is raised suddenly to higher than the Curie temperature so that the direction of magnetization of the recording surface of the disk is changed and the recording data signal E.sub.D is recorded as the record pattern by a change in the magnetization direction.
The laser power of the laser beam emitted from the semiconductor laser diode 3 is detected by the detector 4, and the detection signal is compared at the comparator means 6 with the reference signal E.sub.1 of the record mode. When the laser power i
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Iimura Toshiaki
Terayama Yasunori
Yamasaki Yoshimari
Edun Muhammad N.
Frommer William S.
Sony Corporation
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