Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Patent
1990-08-07
1992-12-29
Richardson, Robert L.
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
372 29, G11B 700
Patent
active
051757222
ABSTRACT:
A power supply circuit for supplying an electric power to a laser diode which is used for reading digital data on an optical memory medium, where the laser diode emits light when a current flowing therethrough exceeds a threshold level. The power supply circuit includes: a current source for outputting a current; an automatic power control circuit for controlling the current which is output from the current source so that an average power of light which is emitted from the laser diode to be equal to a predetermined value; a high frequency signal generating circuit for generating a high frequency signal; and a high frequency current control circuit for controllng a current which is supplied from the current source to the laser diode so that the current flowing through the laser diode is modulated by the high frequency signal. The minimum level of the current which flows through the laser diode, appears in each cycle of the current modulated by the high frequency signal, and is maintained below the threshold level. The high frequency modulation is carried out when reading data only, or is carried out through the writing and reading operation. Further, in the case the high frequency modulation is carried out when reading data only, the high frequency modulation may be stopped before and after the duration of the data write operation with some margins.
REFERENCES:
patent: 4785443 (1988-11-01), Minami et al.
patent: 4811329 (1989-03-01), Shikama et al.
patent: 4819242 (1989-04-01), Kaku et al.
Minami Akira
Yanagi Shigenori
Fujitsu Limited
Richardson Robert L.
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