JPS63129537A - Laser driving device - Google Patents

Abstract

PURPOSE:To obtain a prescribed recording output in spite of an ambient temperature, by controlling a reproducing current by applying power control at time of reproducing, keeping a reproducing output at a prescribed level for the change in the ambient temperature, and overlapping a prescribed recording current of the reproducing current just before at time of recording. CONSTITUTION:At the time of reproducing, switches 2 and 8 are turned ON, and switches 5 and 11 are turned OFF, and a semiconductor laser 1 is driven by the reproducing current I1 being controlled at a power servo circuit 7 so as to supply a prescribed reproducing output. In a recording output setting mode, the switches 2, 5, and 11 are turned ON, and the switch 8 is turned OFF, and the laser 1 is driven by the reproducing current I1 just before recorded at a sample/held circuit 9, and the recording current I2 being controlled by a power circuit 10. When the switches 11 is turned OFF after the recording output setting mode, the recording current I2 which supplies a prescribed recording output is stored in a sample/hole circuit 12. At the time of recording, by turning OFF the switches 8 and 11, turning ON the switch 5, and the turning ON/OFF the switch 2 at high speed, an optical output is modulated in pulsewise, then the recording of information is performed.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is used in an apparatus for optically recording and reproducing information,
The present invention relates to a laser driving device that supplies optical pulses for recording information.

Conventional technology FIG. 4 is a configuration diagram of a conventional laser driving device.

In FIG. 4, 21 is a semiconductor laser whose anode is connected to a positive voltage source +V and whose cathode is a switch 2.
2 to a constant current source 23 and a constant current source 24. Constant current source 23 provides reproduction current I, and constant current source 2
4 provides a recording current I2. A switch 26 is connected between the switch 22 and the constant current source 24.
is provided. A part of the light beam from the semiconductor laser 21 is transmitted to the photodetector 2 connected to the power servo circuit 27.
6. The power servo circuit 27 is a switch 28
and a control terminal of the constant current source 23 via the sample and hold circuit 29.

Next, the operation of the above conventional example will be explained. In FIG. 4, during playback, switch 22 and switch 28 are on, and switch 26 is off. That is,
The semiconductor laser 21 is driven by a machine. The current-light output characteristics of the semiconductor laser 21 vary greatly with changes in ambient temperature.

FIG. 2 shows the temperature characteristics of the semiconductor laser 21, and is also used to explain the operation of the conventional example shown in FIG. As shown in FIG. 2, when the temperature of the semiconductor laser increases from T to T', the threshold current
It gets bigger. In the conventional example shown in FIG. 4, the power servo circuit 27 controls the constant current source 23 so that the laser output detected by the photodetector 26 becomes a predetermined reproduction output Pa, so that the processing time is reduced. When it changes to I t ht, the reproduction current also changes to 1', and the predetermined reproduction output PR is maintained regardless of the change in the ambient temperature of the semiconductor laser. Furthermore, as shown in Figure 2, as the temperature of the semiconductor laser rises, the threshold current increases, but the slope of the current-light output characteristic curve hardly changes, only shifting to the right in parallel as the temperature rises. It is. Therefore, by superimposing a predetermined recording current I2 on the reproduction current I2, which is controlled to maintain a predetermined reproduction output PR, a predetermined recording output Pw can be obtained regardless of temperature changes.

In the conventional example shown in FIG. 4, during recording, the constant current source 23
When the switch 28 is turned off, the sample and hold circuit 2
Since it is controlled by the immediately preceding control value held at 9, the immediately preceding regenerative current setting is held. switch 2 at the same time
6 is turned on, and a predetermined recording current is superimposed from the constant current source 24. In other words, a semiconductor laser! , 10I, and a predetermined recording output Pw is obtained. At this time, information is recorded on the information recording medium by rapidly turning on and off the switch 22 to pulse-modulate the light beam from the semiconductor laser 21.

In this way, in the conventional laser drive device described above, during playback, power control with a slow response is applied to control the playback current to keep the playback output constant against changes in ambient temperature, and during recording, the playback current is set in advance to the previous playback current. By superimposing the recorded recording current, it is possible to realize power control that allows a predetermined recording output to be obtained with respect to the high-frequency pulse output, regardless of the ambient temperature, without using power control that responds at high speed.

Problems to be Solved by the Invention However, in the conventional laser driving device described above, as shown in FIG. When the slope of the curve changes from curve (2) to curve (2) due to deterioration over time, etc., the recording current is constant to the reproduction current that provides a predetermined reproduction output PR.

Even if it is superimposed, the recording output will be two units, and the predetermined recording output Pw
The problem was that it was not possible to obtain The present invention solves these conventional problems, and provides an excellent semiconductor laser 1 drive that can obtain a predetermined recording output when outputting high-frequency pulses even if the slope of the current-optical output characteristic of the semiconductor laser changes. The purpose is to provide a device.

Means for Solving the Problems In order to achieve the above object, the present invention provides a photodetector for detecting semiconductor laser output, a comparator for comparing the detected semiconductor laser output with a predetermined recording output, and an output current. A constant current source for recording current whose value is variable, a holding circuit that can hold an arbitrary recording current value, and a constant current source for reproduction current that provides a reproduction current that maintains a predetermined reproduction output are provided, and a constant current source for reproduction current that provides a reproduction current that maintains a predetermined reproduction output is provided. The recording current value can be set at any time to obtain a predetermined recording output by superimposing it on the reproduction current that gives the output.

Effect: With the above-described configuration, the present invention superimposes the recording current from the recording current source on the reproduction current that gives a predetermined reproduction output from the reproduction current source, and generates a laser beam detected by a photodetector. In order to change the recording current while comparing the output with a predetermined recording output using a power servo circuit, the recording current value that gives the predetermined recording output is detected, and that value is held in a holding circuit, and the predetermined recording is performed. It can be used as a recording current value that provides an output. This operation can be performed at any time when the semiconductor laser driver is powered on or during standby, so even if the current-optical output characteristics of the semiconductor laser change due to deterioration over time, the power output can respond quickly. A predetermined recording output can be obtained when high-frequency pulses are output without using control.

Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a semiconductor laser, the anode of which is connected to a positive voltage source +V, and the cathode connected to a constant current source 3 and a constant current source 4 via a switch 2. A constant current source 3 provides a reproduction current 11, and a constant current source 4 provides a recording current I.
, J-give. A switch 6 is provided between the switch 2 and the constant current source 4. A part of the light beam from the semiconductor laser 1 is incident on a photodetector 6 connected to a power servo circuit 7 for reproduction output and a power servo circuit 10 for recording output. The reproduction output power servo circuit 7 is connected to a control terminal of the constant current source 3 via a switch 8 and a sample hold circuit 9. Recording output power servo circuit 10
is connected to the constant current source 4 via a switch 11 and a sample and hold circuit 12.

Next, the operation of the above embodiment will be explained. In FIG. 1, during playback, switches 2 and 8 are on, and switches 5 and 11 are off. That is, the semiconductor laser 1 is driven by a reproduction current controlled by a power servo circuit 7 so as to provide a predetermined reproduction output.

In the recording output setting mode, switches 2, 6, and 11 are on, and switch 8 is off. That is, the semiconductor laser 1 is driven by the previous reproduction current 11 recorded in the sample hold circuit 9 and the recording current I2 controlled by the power servo circuit 1o so as to provide a predetermined recording output. If the switch 11 is turned off after the recording output setting mode continues for a time sufficiently longer than the response time of the power servo circuit 10, the recording current I2 that provides a predetermined recording output is stored in the sample and hold circuit 12.

During recording, switches 8 and 11 are off, and switch 6 is on. At this time, if switch 2 is turned on, the semiconductor laser is driven at 11+12, and a predetermined recording output is obtained. When the switch 2 is turned off, the drive current for the semiconductor laser disappears, so the optical output becomes zero. Therefore, by rapidly turning on and off the switch 2, the optical output is pulse-modulated and information is recorded on the information recording medium.

Effects of the Invention As is clear from the above embodiments, the present invention has the following effects.

(1) During playback, power control is applied to control the playback current to keep the playback output constant despite changes in ambient temperature, and during recording, a predetermined recording current is superimposed on the previous playback current, so It is possible to realize power control that allows a predetermined recording output to be obtained regardless of the temperature.

(2) The response of the power servo circuit during playback does not need to be high-speed, and the power servo circuit is not working during recording to give a high-frequency pulse output. Power control can be realized for pulse output.

(3) Since the recording current value to be superimposed on the reproduction current can be set at any time during recording, a predetermined recording output can be obtained even if the current-optical output characteristics of the semiconductor laser change due to aging etc. .

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a laser driving device according to an embodiment of the present invention, FIG. 2 is a characteristic diagram illustrating temperature changes in the current-light output characteristics of a semiconductor laser, and FIG. 3 is a diagram showing current-light output characteristics of a semiconductor laser. Characteristic diagram explaining changes in output characteristics over time, No. 4
The figure is a schematic block diagram showing a conventional laser driving device. 1... Semiconductor laser, 2, 5, 8, 11.22
......switch, 3,4...constant current source,
6...Photodetector, 7,10...Power servo circuit, 9,12...Sample hold circuit. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] Information is generated by irradiating an information recording medium on which information can be recorded with a light beam modulated in a pulse between an intensity above the predetermined value and an intensity below the predetermined value by irradiating a light beam with an intensity above a predetermined value from a laser light source. In an optical recording and reproducing apparatus that records information and reproduces the recorded information by irradiating a beam with a constant intensity equal to or less than the predetermined value, the optical recording and reproducing apparatus includes: a photodetector that receives light emitted from a laser light source; a current source for the laser light source whose output is controlled so that the detected optical output approaches a preset optical output setting value;
It includes a sample hold circuit that stores a laser drive current value that provides an optical output equivalent to the optical output setting value, and also applies power control only to the constant intensity optical output during reproduction, and applies power control to the pulsed optical output during recording. is applied at any time to the laser drive current during reproduction stored in the sample hold circuit.
A laser driving device having means for providing a luminous flux with the intensity necessary for information recording by superimposing a resettable constant current value.