Laser device driven by a periodic waveform optimized for reducing laser noise
AssigneeHitachi, Ltd.
InventorsHirofumi Sukeda, Shigeru Nakamura
Life of this patent
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Abstract
The optical information recording and reproducing method and apparatus include a method for controlling a high frequency pulse current for driving a semiconductor laser device by which noise due to returning laser light is hardly produced, and an apparatus for increasing access speed owing to decrease in the weight of an optical pick-up movable part. Loser noise is suppressed satisfactorily by detecting the position of the optical pick-up movable part in a split optical system by means of a scale, and generating a pulse current for modulating the laser having a frequency optimum for reducing the laser noise to drive the semiconductor laser device.
Claims17
An optical information recording and reproducing method by which a recording medium is irradiated with laser light pulses emitted by a laser device so that information is recorded and reproduced by locally changing characteristics of said recording medium by thermal energy of said laser light pulses, wherein said laser device is oscillated so as to emit laser light pulses and the frequency of an on-off-modulated high-frequency current driving said laser device is controlled depending on an optical length between a light emitting point on said laser device and said recording medium so that returning light reflected by said recording medium arrives at the light emitting point when the laser device is off.
An optical information recording and reproducing apparatus in which a recording medium is irradiated with laser light pulses emitted by a laser device so that information is recorded and reproduced by locally changing characteristics of said recording medium by thermal energy of said laser light pulses, comprising:
- means for on-off modulating light emitted by said laser device at a modulating frequency capable of reducing laser noise;
- means for varying an optical length from a light emitting point of said laser device to said recording medium, wherein said modulating frequency is a function of said optical length;
- means for discriminating said optical length;
- and
- means for supplying a control signal for controlling the modulating frequency of the light emitted by said laser device to said means for modulating the light emitted by said laser device.
An optical information recording and reproducing apparatus in which a recording medium is irradiated with laser light pulses emitted by a laser device so that information is recorded and reproduced by locally changing characteristics of said recording medium by thermal energy of said laser light pulses, comprising:
- means for on-off modulating light emitted by said laser device at a modulating frequency capable of reducing laser noise;
- means for varying an optical length from a light emitting point of said laser device to said recording medium, wherein said modulating frequency is a function of said optical length;
- and
- means for setting the light modulating means and the optical length varying means according to the following relation:
- T (on)/T (off).ltoreq.L (min)/L (max)
- where L (min) represents a minimum value of the optical length;
- L (max) a maximum value of the optical length;
- T (on) an on-time width of the light emitted by said laser device;
- and T (off) an off-time width of the light emitted by said laser device.
An optical information recording and reproducing apparatus, comprising:
- measuring means for measuring an optical length between a light source and a recording medium;
- driving frequency control means for controlling a driving frequency for driving said light source based on said optical length;
- and
- optical means for conducting a light beam, having the driving frequency, from said light source to said recording medium.
An optical information recording and reproducing method by which a recording medium is irradiated with laser light pulses emitted by a laser device so that information is recorded and reproduced by locally changing characteristics of said recording medium by thermal energy of said laser light pulses, wherein said laser device is oscillated so as to emit laser light pulses and the on-off time of an on-off-modulated high-frequency current driving said laser device is controlled depending on an optical length between a light emitting point on said laser device and said recording medium so that returning light reflected by said recording medium arrives at the light emitting point when the laser device is off.
An optical recording and reproducing apparatus, comprising:
- split optics including a fixed part and a movable part;
- said first part including a light source and a first optical system for converting at least a light beam emitted from said light source into a parallel light beam;
- said movable part including a second optical system for focusing said parallel light beam on a recording medium, wherein said optical system moves in a predetermined region along a radial direction of said recording medium;
- and
- laser driving means for determining and supplying a driving current waveform to said light source depending on said predetermined region.
An optical information recording and reproducing method, comprising the steps of:
- (a) driving periodically a semiconductor laser device to irradiate a light beam emitted by said semiconductor laser device to a recording medium;
- (b) re-entering a part of light reflected from said recording medium into said semiconductor laser device while said semiconductor laser device is not being driven;
- and
- (c) reproducing information recorded on said recording medium in response to said reflected light part, and recording new information on said recording medium by using said light beam;
- wherein step (a) is effected by means for driving said semiconductor laser device, a fixed optical system including said semiconductor laser device, and a movable optical system moving in a radial direction of said recording medium for scanning said light beam on said recording medium;
- and
- wherein a driving frequency of said semiconductor laser device is determined in accordance with a position of said movable optical system.
Dependencies are inferred from the claim text.