JPH0518185B2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to a semiconductor used in an optical recording/reproducing device that records, reproduces, erases, etc. information by irradiating an optical recording medium with light emitted from a semiconductor laser. The present invention relates to a laser light amount control device.

<Prior Art> A light amount control device for a semiconductor laser used in a conventional optical recording/reproducing device will be described using a magneto-optical disk system as an example of the optical recording/reproducing device.

The already known structure of a magneto-optical disk is to deposit an amorphous thin film of a rare earth-iron alloy by sputtering on a substrate such as a glass substrate, and cover it with a magnetic film having an axis of easy magnetization perpendicular to the film surface. A magneto-optical disk system for recording, reproducing, and erasing information is constructed by arranging an optical head that irradiates a semiconductor laser beam facing the magneto-optical disk.

In this magneto-optical disk system, information is recorded by irradiating the surface of the magnetic film with a laser beam focused to a diameter of approximately 1 μm to locally increase the temperature of the magnetic film, thereby increasing the coercive force of the temperature-increased portion. At the same time, by applying an auxiliary magnetic field from the outside, the direction of magnetization is reversed (erasing can also be done by the same method). In addition, to reproduce recorded information, the surface of the recorded magnetic film is irradiated with linearly polarized light from a semiconductor laser with a weaker light intensity than during recording, and the reflected light is reproduced by utilizing the tilt of the polarization plane due to the influence of the magnetic field. This is done by changing the strength of the light and detecting it with a photodetector.

From the above structure, the semiconductor laser needs to be configured to emit high-power laser light during recording and low-power laser light during playback, and it is important to quickly switch between these two levels of output by some means. required for the drive unit.

Furthermore, the optical output of a semiconductor laser has temperature characteristics.
Since the threshold current value and the slope in the linear portion above the threshold value vary depending on the ambient temperature, the output intensity of laser oscillation with respect to the drive current value changes depending on the temperature. As a result, the output light intensity fluctuates during high-output oscillation of the laser during recording, causing insufficient or excessive writing of information to the recording medium, and the error rate of information processing of the entire system deteriorates. This is also true when the laser oscillates at low output during reproduction (when reproducing information), and if the output light intensity fluctuates, this will appear as a deterioration in the S/N ratio of the reproduced signal.

For the above reasons, it is clear that it is essential to stably oscillate laser light at both high and low output levels.

In view of the above points, a structure as shown in FIG. 4 has already been proposed as a light amount control device for a semiconductor laser. The device shown in the figure is provided with two current sources that supply driving current to the semiconductor laser, and when reproducing information from a recording medium, the semiconductor laser 4 is driven only by the driving current _I1 from the low-output current source 1. It is. Furthermore, when recording information on a recording medium, a high-output laser beam is obtained by adding the drive current _I2 from another current source, high-output current source 2, to the drive current _I1 . be.

Here, for the low output current source 1, the intensity of the output light of the semiconductor laser 4 is detected by the photodetector 5,
The signal is introduced into a sample hold circuit 7 through a preamplifier 6. The sample and hold circuit 7 holds data when the hold timing signal _S4 is at a high level, and passes the data as is when it is at a low level. This data is compared with a reference voltage source 9 in a comparator 8, and the low frequency component after passing through a low-pass filter 10 is input to a power amplifier 11 to control the output current _I1 of the low output current source 1. If the hold timing signal _S4 is always at a low level, this control will always keep the low output light intensity constant regardless of the temperature characteristics of the semiconductor laser.
Note that automatic light output control for obtaining such output light with a constant intensity is called APC.

Next, during high output oscillation (when recording information), the hold timing signal _S4 is first set to high level to hold data. That is, APC is frozen. The AND gate 20 uses the hold timing signal _S4 to send the recording data signal _SD to the switching circuit 19 only during recording. According to the recording data signal S _D , the high output current (recording current) I ₂ changes to the low output current
It is added to _I1 and recorded on the medium. APC
The purpose of freezing is to avoid lowering the output intensity in response to high-output oscillation. By making the freezing time sufficiently short compared to the time for changes in the temperature characteristics of the semiconductor laser, APC can operate without any problems in practice.

Now, the characteristics of the oscillation operation control during information recording in the light amount control device described above are that only the oscillation threshold changes due to the temperature characteristics of the semiconductor laser, and the linear portion above the threshold in the drive current vs. optical output curve of the semiconductor laser The point is that control is performed under the assumption that the slope of does not change.

This will be explained below using FIG. In the figure, it is assumed that two optical output curves, states A and B, exist due to differences in ambient temperature. First, in state A, a drive current I ₁ A is output from a low output current source for a low output light intensity P ₁ . Assume that only the threshold value changes due to a change in the ambient temperature, and the state moves from state A to state B. Then, the low output light intensity P ₁ due to APC
Control works to keep constant, and the drive current from the low output current source changes from I ₁ A to I ₁ B. Therefore, if a constant current source I ₂ is added to the high output current source during recording, the slope of the linear portion above the threshold value is constant, so the high output light intensity P ₁ +P is constant in both state A and state B. ₂ is obtained. That is, if APC for low output light intensity is performed, APC for high output light intensity should be simultaneously realized in a pseudo manner.

However, the conventional light amount control device described above cannot maintain a constant high output intensity. This is because the slope of the linear portion of the drive current vs. optical output of the semiconductor laser above the threshold value changes depending on the aging of the laser and the ambient temperature.
In other words, constant current I ₂ from the second current source 2 for high output
Only the addition of high output light intensity due to the above reasons
_P2 changes, and as a result, good recording (erasing) characteristics cannot be obtained.

Therefore, in order to obtain a predetermined high output light intensity, it is necessary to control the output current value I ₂ of the high output current source 2 separately from that of the low output current source. In addition, this control method is similar to APC with low output light intensity, and if it is constantly controlled at a time interval sufficiently smaller than the change in temperature characteristics of the semiconductor laser, the time interval from one high output oscillation to the next high output oscillation will change due to the change in temperature characteristics. Even if the length is so long as to cause , stable high-output oscillation can be obtained instantaneously, which is preferable.

<Object of the Invention> In view of the problems in the prior art described above, the object of the present invention is to provide a light amount control device for a semiconductor laser that can instantaneously obtain both stable low-output light and high-output light as needed. It is about providing.

<Example> Hereinafter, a case in which the light amount control device for a semiconductor laser according to the present invention is applied to a magneto-optical disk device will be described in detail as an example.

FIG. 1 is a block diagram showing a light amount control device according to an embodiment of the present invention. FIG. 2 is a drive current-optical output curve and waveform diagram for the operation of the device of FIG. 1. FIG. 3 shows the timing waveforms required for the apparatus of FIG.

In FIG. 1, the semiconductor laser 4 records (erases);
The reproduction operation is driven by a low output current source 1 and a high output current source 2, but in order to control the high output light intensity, a test shot current source 3 for test firing is newly provided. In other words, when reproducing information from a recording medium, only the output current _I1 of the low-output current source 1 is applied, when recording information, the output current I2 of the high-output current source 2 is applied, and when performing a test firing, the output current _I2 of the high output current source 2 is applied. Branch current source 3
The output current I ₃ is added to the low output current I ₁ to drive the semiconductor laser. Note that, compared to the conventional light amount control device shown in FIG. 4, a new loop for controlling the output current I ₂ of the high output current source 2 is added.

In the light amount control device shown in FIG. 1, APC for the low output current source 1 during low output oscillation is realized as follows. First, the intensity of the output light of the semiconductor laser 4 is detected by a photodetector 5, and this detection output is passed through a preamplifier 6 to a sample hold circuit 7.
will be introduced in Here, the sample and hold circuits 7 and 13 hold data when the hold timing signals S ₁ , S ₄ and S ₃ are at high level, and pass the data as is when they are at low level. Next, the output of the sample and hold circuit 7 is the reference voltage of the reference voltage source 9.
It is compared with V ₁ in a comparator 8, passes through a low-pass filter 10 and is directly introduced into a power amplifier 11, and the output current I ₁ of the low output current source 1 is controlled by this output. This control keeps the low output light intensity constant regardless of the temperature characteristics of the semiconductor laser.

On the other hand, for high output current source 2 during high output oscillation,
APC is realized as follows. First, the hold timing signal _S1 is set to a high level to freeze the APC (sample and hold circuit 7) during low output oscillation. Next, the output current _I3 of the test shot current source 3 is added to the low output current _I1 at the timing of the test shot signal S2 applied to the switching circuit ₁₂ , and is driven by this added current to drive the semiconductor laser 4. A test shot will be conducted. The light intensity of this test output is detected by a photodetector 5 and inputted to a sample and hold circuit 13 through a preamplifier 6. Here, the data is held by the hold timing signal _S3 , and this output
A divider 14 outputs V ₃ /I ₃ which is equivalent to the slope of the drive current-optical output curve from the threshold value of the semiconductor laser from V ₃ and the test emission current I ₃ . Next, in the divider 15, this value is combined with the output of the reference voltage source 16.
Using V ₂ , V ₂ /(V ₃ /I ₃ ), which is equivalent to the drive current, is calculated and input to the power amplifier 18 through the low-pass filter 17. Controls the output current value _I2 .

After the APC for high-output oscillation is realized as described above, in the AND game 20, the hold timing signal _S4 is also used as a recordable signal, and the switching circuit 19 is activated using the recording data signal _SD .
The high output current _I2 is added to the low output current _I1 .

Control of the drive current of the light amount control device described above will now be explained using FIG. 2.

As shown by curves A and B in Figure 2, the threshold value of the semiconductor laser and the driving current from the threshold value -
The slope of the optical output curve changes depending on the temperature characteristics of the semiconductor laser and changes over time. During low output oscillation
Since the output light intensity P ₁ is always maintained by the action of APC, the drive current in state A is I ₁ A, and in state B it is I ₁ B. Furthermore, during high-output oscillation, the high-output light intensity P ₂ added to the low-output light intensity P ₁ may be kept constant. That is, in order to realize high output light intensity P ₂ , the output current value of the high output current source 2 is I ₂ A in state A, but becomes I ₂ B in state B.

In this way, in order to keep the light intensity constant during low-output oscillation and high-output oscillation, the output currents I ₁ A, I ₁ B of the low-output current sources and the output currents I 2 A, I ₂ A,
It is necessary to control each of I ₂ B.

Next, regarding the control of the output current of the high-output current source 2, only state A will be described below. The same applies to state B. First, the output current I ₃ A of the test firing current source 3
By adding P 3 A to the low output current I ₁ A, the output light intensity P ₃ A of the trial shot is detected by the photodetector 5.
This determines the slope P ₃ A/I ₃ A of the drive current vs. optical output curve from the threshold value. High output light intensity _P2
In order to obtain a high output current that satisfies the following conditions:
Just add I ₂ A to the low output current I ₁ A.

P ₂ = P ₃ A / I ₃ AI ₂ A ... (1) If the outputs of the photodetector 5 for the high output spectral intensity P ₂ and the test output spectral intensity P ₃ A are respectively V ₂ and V ₃ A, ( 1) Equation can be rewritten as follows.

V ₂ = V ₃ A/I ₃ AI ₂ A ……(2) Therefore, the output current value I ₂ A of high output current source 2 is (2)
From the formula, I ₂ A=V ₂ /V ₃ A/I ₃ A ……(3) Similarly, in state B, I ₂ B=V ₂ /V ₃ A/I ₃ A ……(4) Formula (3) , as shown in equation (4), the reference voltage V ₂ and the slope of the drive current vs. optical output curve V ₃ A/I ₃ A,
The drive current I ₂ A (I ₂ B) during high output oscillation can be controlled only by (V ₃ B/I ₃ B).

The operation timing of the semiconductor laser light amount control device according to the present invention configured as described above will be explained below. In FIG. 3a, there are a plurality of header sections 2 per track on the magneto-optical disk disk 22.
3 exists. No information is recorded in the header section 23. Test firing is data part 24 and data part 2
This is carried out for each header section 23 sandwiched between the sections 4 and 4. First, we tested the APC of the low output current source by test firing.
In order to prevent the APC from responding, the header section 23 freezes the APC of the low output current source ₁ by generating a hold signal S1 as shown in FIG. 3B. During this freezing period, a test shot is performed using a test shot signal _S2 , and data on the output light intensity at this time is held using a hold timing signal _S3 . The output current of the high output current source 2 can be controlled at all times using the above timing.
When recording information, high output oscillation is caused by low output current source.
A record enable signal S ₄ is applied to the sample and hold circuit 7 together with a hold timing signal S ₁ so as not to respond to APC. Information is then written using the recording data signal _SD .

In the semiconductor laser light quantity control device with the above configuration, APC of the high-output current source by test firing is performed for each header section 23, so the control of the optical output light intensity is instantaneous and stable during high-output oscillation (information recording). will be carried out.

In the above configuration, the test shot current source 3 is provided as the third current source for the semiconductor laser 4, but the test shot current source 3 is not provided separately, and the high output current source 2 is temporarily used as the test shot current source 3. It is also possible to reduce the number of parts by using it as a

<Effects of the Invention> In the present invention as described above, it is possible to constantly achieve high-output oscillation APC by test firing, and in addition, by freezing the low-output oscillation APC during high-output oscillation, high-output laser light is generated. Strength can be stabilized. Therefore, it is possible to obtain a semiconductor laser light amount control device with good characteristics for an information recording/reproducing apparatus using a magneto-optical disk or the like as a recording medium.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a light amount control device according to an embodiment of the present invention, FIG. 2 is a drive current-light output curve and waveform diagram for explaining the operation of the device in FIG. 1, and FIG. 3b is a diagram of the timing waveform necessary for the operation of the device shown in FIG. 1, FIG. 4 is a block diagram of a conventional semiconductor laser light amount control device, and FIG. 5 is the operation of the device shown in FIG. 4. FIG. 2 is a drive current-light output curve and waveform diagram for explaining. In the figure, 1...low output current source, 2...high output current source, 3...test shot current source, 4...semiconductor laser, 5...photodetector, 6...preamplifier, 7...
Sample and hold circuit, 8... Comparator, 9... Reference voltage source, 10... Low pass filter, 11...
Power amplifier, 12...Switching circuit, 13
... Sample hold circuit, 14, 15 ... Divider, 16 ... Reference voltage source, 17 ... Low pass filter, 18 ... Power amplifier, 19 ... Switching circuit, 20 ... AND gate, 21 ... OR gate , 22... disk, 23... header section, 24... data section, 31... first control circuit, 32... second control circuit.

Claims (1)

[Scope of Claims] 1. A light amount control device for a semiconductor laser 4 incorporated in an optical recording/reproducing device, which comprises a first light amount control device for oscillating the semiconductor laser 4 to a level necessary for reproducing information from a recording medium. a current source 1; a second current source 2 for oscillating the semiconductor laser 4 to a level necessary for recording or erasing information on a recording medium by applying current to the first current source 1; By adding current to current source 1 of
a third current source 3 that causes the semiconductor laser 4 to oscillate to a level necessary for test firing to control the current source 2 of the semiconductor laser 4; a detector 5 that detects the output light intensity of the semiconductor laser 4; and a detector 5 during reproduction. A first control circuit 3 that controls the output current value of the first current source 1 according to the detection result of
1, and a first detector 5 that retains the detection result of the detector 5 which detects the output light intensity of the semiconductor laser 4 driven by the first current source 1 when recording or erasing information on the recording medium and during sight shooting. a second holding circuit 13 that holds the detection result of the detector 5 that detects the output light intensity of the semiconductor laser 4 during test firing driven by the third current source 3; a division circuit 14 that calculates the ratio of the output light intensity of the semiconductor laser 4 to the additional current from the data held in the holding circuit 13; and a division circuit 14 that records or erases information according to the value of the ratio calculated by the division circuit 14. Second current source 2 at time
A light amount control device comprising: a second control circuit 32 for controlling an output current of the light amount controller. 2. A light amount control device according to claim 1, characterized in that the second current source also serves as the third current source.