JPS6266432A - Optical disc device - Google Patents

Abstract

PURPOSE:To attain stable recording by providing the 1st current drive circuit driving a laser diode in terms of DC, the 2nd current drive circuit changing a current corresponding to a write operation signal and driving the laser diode pulsatingly. CONSTITUTION:The 1st current source 2 flows a current required to stimulate a power for required read in an optical disc device to the laser diode 1. The 2nd current source 3 flows a current required to stimulate the power required for the write to the laser diode 1 as a pulse current corresponding to a write data P to detect the start of a write operation signal G thereby flowing a current C at the write start larger than the current at the steady-state. A larger a writing current at the start flows than that at the steady-state, then the beam diameter in the state of out of focus exceeding the writable power T is equal to the beam diameter exceeding the writable power T of the power distribution A when a focus F1 exists on a medium face 4 so as to apply sufficient recording. Then stable recording is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disk device, and more particularly to a drive circuit for a laser diode serving as a light source.

[Conventional technology]

Conventionally, an optical disk device using a laser diode as a light source includes a drive circuit for obtaining power during reading and a drive circuit for obtaining power during writing. The power during reading and the power during writing were controlled by each drive circuit so that these were constant values.

[Problem that the invention seeks to solve]

A laser diode, which is a light source for an optical disk device, has a drawback in that the light emitting point moves within the laser diode chip depending on the light emitting power. As shown in FIG. 4, the light emitted by the laser diode 1 at the light emitting point 1 is passed through the collimating lens 7 and the objective lens 6 to the imaging point F.
When the light emitting point moves to ■2 in an optical system adjusted to focus on □, the imaging point moves to F2. 5 is an objective lens drive coil. If focus servo is applied to focus on the surface of the medium 4 during the read operation, when the power of the laser diode 1 increases in the write operation, the focus position of the write beam will change due to the movement of the light emitting point. It comes off above the surface of the media. In other words, the beam diameter is expanded on the medium surface, and the power density of the writing beam is reduced, making it impossible to perform sufficient recording on the medium.

The present invention solves the above problems and provides an optical disc device that performs stable recording.

[Means for solving problems]

The optical disk device of the present invention includes a first current drive circuit that drives the laser diode in a direct current manner, and a second current drive circuit that changes the current in response to a write operation signal and drives the laser diode in a pulsed manner. [Embodiment] Next, an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, the present invention includes a first current source 2 that drives the laser diode l in a direct current manner, and a second current source that changes the current in response to a write operation signal and drives the laser diode l in a pulsed manner. source 3. Second current source 3
As shown in FIG. 3, it consists of switches 8 and 9, a bias power supply 10, a transistor 11, resistors 12 and 13, and a capacitor 14.

The first current source 2 supplies the laser diode 1 with a current necessary to emit the power necessary for performing a read operation in the optical disc device. The second current source 3 is shown in FIG.
As shown in α), (b), and (c), a current necessary to emit the power necessary for performing a write operation is passed through the laser diode 1 as a pulse current corresponding to the write data P. Further, the second current source 3 detects the start of the write operation signal G, and can flow a current C larger than that during normal operation at the start of writing. In order to read and write data on an optical disk medium, an optical disk device has an optical system and a servo system that always focus the emitted light from a laser diode on the medium. The band of the servo system is finite and approximately IKI (z is a common value. The laser diode l used as the light source
moves within the chip due to its luminous power. Fourth
Referring to the figure, the light emitting point e when the laser diode 1 emits the power necessary to perform a read operation
When L, the servo system moves the objective lens 6 so that the focal point F1 is focused on the medium surface 4.

When switching to the recording mode, the laser diode 1 is driven to emit light with the power necessary to perform a write operation. At this time, when the light emitting point moves from 11 to I2, the focus created by the objective lens 6 moves to F2. Therefore, the diameter of the light on the medium surface 4 spreads, and the power density decreases in inverse proportion to the square of the diameter, making it difficult to perform recording. Writing on a medium is caused by the rise in temperature caused by the accumulation of heat in the area irradiated with laser light, which changes the surface of the medium, so if the time of the write light pulse is fixed, it is determined by the power level of the irradiated light. be done. As shown in Figure 5, power is plotted on the vertical axis.
Looking at the graph with beam diameter on the horizontal axis, objective lens 6
When the power passing through is constant, the focus F on the medium plane 4
It is clearly seen that the power distribution B of the spread light on the medium surface when the focus shifts to F2 is smaller than the power distribution A when F1 is present, and the diameter where the power T that is available for writing is greater than that is smaller.

The servo system corrects the position of the objective lens so that even if the focal point moves from Fl to F2, the focus will eventually be on the medium surface 4, so eventually the focal point F2 will be on the medium surface 4. , during which insufficient recording is performed.

The optical disk device according to the present invention detects the start of the write operation signal G and makes the write current larger than the normal state at the start. By doing this, even if the focus is shifted as shown in FIG. It becomes equal to the beam diameter exceeding , and sufficient recording can be performed. The amount of current increased at the start of writing is adjusted so as to satisfy this condition. It will be more effective if the time and inclination for returning to the deviated steady state value are matched to the time and inclination for correcting the servo system so that the deviated focal point F2 is brought to the medium surface.

〔Effect of the invention〕

As explained above, according to the present invention, the light emitting point of the laser diode moves when the reading operation shifts to the writing operation, so the focal position moves and the diameter of the writing beam on the medium surface expands, causing the writing This has the effect of making it possible to perform stable recording by compensating for the inability to perform sufficient recording due to a decrease in the power density of the beam.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 (
α), (b), and (c) are timing charts showing an example of changes in the write current signal in the present invention;
The figure is a circuit diagram showing an embodiment of the second current source in the present invention, FIG. 4 is a diagram showing the state of defocus in the present invention,
FIG. 5 is a diagram showing the power distribution of the writing beam in the present invention. l...Laser diode 2...First current source 3...Second current source 4...Medium 5...Objective lens drive coil 6...Objective lens 7...Collimating lens 8 , 9...Switch 10...Bias power supply 11...Transistor 12.13...Resistor 14...Capacitor Patent applicant NEC Corporation Figure 1 Figure 2 Figure 5

Claims (1)

[Claims] (1) It has a first current drive circuit that drives the laser diode in a direct current manner, and a second current drive circuit that changes the current in response to a write operation signal and drives the laser diode in a pulse manner. Characteristic optical disc device.