JPS58151082A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To secure and stabilize the operation and make the power constant by a method wherein an external input signal is clamped based on the difference between the peak value of the laser output at the time of recording and reproduction, and the constant reference voltage. CONSTITUTION:The output of the laser 1 is photoelectrically converted 3, thus the level of the minimum power Pb is detected 12, and the difference between it and the constant reference voltage Vr is obtained, regardless of the time either reproduction or recording, into a clamp level. The input signal is clamped 13 by this level, and accordingly the laser 1 is driven 7. By a clamp circuit 13, regardless of duty cycles, the Pb becomes constant even in the presence of non-modulated regions, and then the detected output 12 operates so as to be coincident to Vr. Since the slope of the I-P characteristic is constant without depending on temperatures at the oscillation region for the laser 1, the maximum power Pp also becomes constant when the input signal is constant in amplitude. By this constitution, the recording quality is improved without the necessity of switching the reference voltage at the time of recording and reproduction (modulation and non-modulation).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser device, and particularly to an information recording/reproducing device that uses a semiconductor laser to record or reproduce information. The present invention relates to a semiconductor laser device including an ALPC (hereinafter abbreviated as ALPC) circuit.

FIG. 1 is a characteristic (hereinafter referred to as IP characteristic) diagram showing the relationship between the drive side 1 and output power P of a semiconductor laser. As is well known, the threshold point of a semiconductor laser changes greatly depending on the temperature, as shown in the figure. Therefore, when driving with a constant current of 10, the concentration increases due to ohmic loss and the output power changes from Pl to P2, roughly P
2 to P3, and oscillation stops. In order to prevent this, ALPC circuits have been proposed to keep the output power constant.

FIG. 2 is a block diagram of a semiconductor laser @ stomach including a conventional ALPC circuit. In the configuration, the semiconductor laser 1 has the following configuration:
Laser light (emitted light) 2 is generated by this drive. A portion of the laser beam 2 is detected by a photoelectric conversion circuit 3. The charging conversion circuit 3 converts the power of the laser beam 2 into an electric signal and supplies it to the smoothing low-pass filter 4. Low pass filter 4
The output μ is given as the comparison input (-) of the differential amplifier 6. A reference voltage output from the reference voltage generation circuit 5 is input to a reference input terminal (+) of the differential amplifier 6 .

The output of the differential amplifier 6 is input to a drive circuit 7.

A signal input to an input terminal 8 is input to the driver circuit 7 via a capacitor 9. An external input signal for modulating the semiconductor laser 1 is applied to the input terminal 8 .

FIG. 3 is a diagram showing the modulation characteristics of a semiconductor laser. w4
FIG. 4 is a diagram showing the relationship between the output power and duty cycle of the semiconductor laser to explain the operation of FIG. 2.

Next, the second factor operation in the case where the semiconductor laser 1 is modulated with a rectangular wave signal will be explained with reference to FIGS.'I/s1 to FIG. For example, as shown in FIG.
Assume that at iP1, the drive circuit 7 drives the semiconductor laser 1 with a current waveform 10 with an average drive of 11*Ia1. At this time, laser light 2 generated from semiconductor laser 1 is detected by photoelectric conversion circuit 3. Its output change mt
@ is shown by the 11 waveforms in the 1N3 diagram. By smoothing this output modulation signal 11, the low-pass filter 4
The average voltage ■a is determined and applied to the differential amplifier 6.

On the other hand, the reference voltage generation circuit 5 provides the reference voltage ``'' to the differential amplifier 6. Therefore, the differential amplifier 6 calculates the difference voltage (Vr - Va) between both inputs and amplifies it. It is applied to the drive circuit 7. In this way, the ALPC circuit is configured by a closed loop that negatively feeds back the output of the semiconductor laser 1.

The aforementioned ALPC circuit operates the semiconductor laser 1 so that the average level va of the output modulation signal 11 matches the reference voltage Vr. In this state, when the circumference changes from T1 to T2, the average drive current automatically moves from Ial to Ia2 shown by the dotted line, so the output modulation signal 11 is kept constant. Therefore, when no external input signal is applied to the input terminal 8, that is, when no modulation is performed, the ALPC circuit operates so that the output voltage of the photoelectric conversion circuit 3 matches the reference voltage vr. Therefore, the output power of silence IIvi is the average value of the output power during modulation.

Incidentally, the semiconductor laser device as described above is applied to a high-density recording and reproducing device (referred to as an optical disk device) that uses the semiconductor laser 1 as a light source for recording and reproducing. In an optical disk device, during recording, the power is modulated to high power by a modulation signal to punch a hole in the recording medium to record, and during playback, the signal is read out by emitting light in a silent and low pitched manner. The light beam during playback must be low enough to avoid puncturing the body. However, when using a semiconductor laser as a light source for an optical disk device, when the output power during reproduction is at the average level of the output power during modulation (that is, the duty cycle is 50%), the output power is approximately half of the maximum power. Therefore, due to irregularities in the recording medium, holes may occur and the information may be destroyed. To prevent this, recording and playback (i.e. modulation and silence Im
) It is necessary to switch the reference voltage vr from negative to negative. When the reference voltage is switched, l<
There is a problem that the noise noise may enter the semiconductor laser 1 and destroy the information recorded on the optical disk, resulting in a lack of reliability. Also, (a) and (b) in Figure 4
) and (C), when a signal with a varying duty cycle is input, the ALPG circuit operates at an average level in the conventional semiconductor laser device, so the maximum power Pp varies. As a result, the recording condition of the optical disc (namely, hole size, etc.) fluctuates, resulting in a problem in that information recording quality deteriorates.

Therefore, an object of the present invention is to eliminate the need to switch the value of the reference voltage during recording and playback, to ensure stable and reliable operation, and to maintain maximum power and minimum power even for signals with varying duty cycles. It is an object of the present invention to provide a semiconductor laser device that maintains a constant value.

In summary, this invention detects the peak value of the output of a semiconductor laser, determines the difference between this peak value and a constant reference voltage during recording and playback, and clamps the external input signal based on the difference voltage. However, the semiconductor laser is driven based on the clamped output voltage.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

FIG. 5 is a block diagram of a semiconductor laser device according to an embodiment of the present invention. In terms of configuration, this embodiment differs from FIG. 2 in that a peak detection circuit 12 is used instead of the low-pass filter 4, and the output of the differential amplifier 6 and the signal input to the input terminal 8 are applied to the clamp circuit 13. , the output of the clamp circuit 13 is provided to the drive circuit 7.

This peak detection circuit 12 detects an extremely low level (minimum level).
It is used to detect. The clamp circuit 13 uses the output voltage of the differential amplifier 116 as a clamp level, and clamps the minimum level of the input signal applied from the input terminal 8. It is something. Note that the peak detection circuit 12 detects the input DC level when a DC signal is input. Furthermore, the clamp circuit 13 is assumed to clamp the input DC level when a DC signal is input. The peak detection circuit 12 and clamp circuit 13 are shown in detail in FIGS. 6 and 7, which will be described later.

FIG. 6 is a detailed circuit diagram of the peak detection circuit 12 used in this embodiment. This peak detection circuit 12 detects the minimum level of an input signal using a diode 12a and a capacitor 12b.

A resistor 12c is inserted between the anode of the diode 12a and the voltage II (V+). As a result, the resistor 12c
By passing a minute current through the diode 12a, the diode 12a becomes conductive even when no modulation is being performed, and a detection operation is performed.

FIG. 7 is a detailed circuit diagram of an example of the clamp circuit 13 used in this embodiment. Clamp circuit 1 of this embodiment
3 clamps the minimum level of the input signal to the clamp voltage VC by the capacitor 13a and diode 13b. Further, by freezing a minute current using the resistor 13c, the diode 13b is made conductive even when no modulation is performed, and a clamp voltage is output.

The peak detection circuit and 1117 shown in FIG.
By using the clamp circuit shown in the figure, when an ill low signal is input, the DC input level is detected or clamped.

FIG. 18 is a diagram showing the relationship between duty cycle and power for explaining the operation of this embodiment.

Next, the operation of this embodiment will be explained with reference to FIGS. 5 to 8. The output of the semiconductor laser 1 is transmitted to the photoelectric conversion circuit 3
The signal is converted into an electrical signal and applied to the peak detection circuit 12. The peak detection circuit 12 detects the minimum level corresponding to the minimum power Pb. This minimum level voltage is input to the differential amplifier 116. The reference voltage Vr output from the reference voltage generation circuit 5 is input to the differential amplifier 6 as a reference voltage. This reference voltage V" is, when the semiconductor laser device of the present invention is applied to an optical disk device,
Carried by constant armor whether played or recorded.

Differential amplification! I6 determines the difference between the reference voltage ■r and the output voltage of the peak detection circuit 12, and provides it as the clamp level of the clamp circuit 13. The clamp circuit 13 clamps the input signal applied from the input terminal 8 at the clamp level determined by the differential amplifier 6, and outputs the output from the drive circuit 7.
give to The drive circuit 7 drives the semiconductor laser 1 based on the output of the clamp circuit 13.

That is, depending on the function of the clamp circuit 13 when the clamp level is kept constant, the output power of the semiconductor laser 1 has a duty cycle of 50%, more than 50%, or less than 50%, as shown in FIG. However, even if there is a non-modulated region, the minimum power Pb remains constant. The action of the ALPCI circuit causes the output voltage of the peak detection circuit 12 to match the reference voltage Vr.

Incidentally, the slope of the I/P characteristic in the oscillation region of the semiconductor laser 1 shown in FIG. 1 is constant without depending much on the hot water temperature. Therefore, if the amplitude of the input signal is constant, the maximum power Pp will also be constant. As is clear from the above explanation, according to this example, the ALPC circuit does not depend on the duty cycle and works to keep the minimum value of the modulation signal constant (that is, the maximum value constant). The optical output when not modulated works to match the minimum value when modulated. Therefore, if the semiconductor laser device of this embodiment is applied to an optical disk device, the optical output during playback (that is, when not modulated) Since the optical output is automatically reduced to the minimum value during modulation, there is no need to switch the reference voltage, and operation is stable and reliable.Also, constant recording that is independent of the duty cycle can be performed, improving the recording quality of information. It has the advantage of being able to improve

As described above, according to the present invention, the operation of the ALPC circuit becomes stable and reliable, and unique effects such as maximum power and minimum power are constant even for signals with varying duty cycles are achieved. . Further, if the semiconductor laser device of the present invention is applied to an optical disk device, there is no need to switch the reference voltage during recording and reproduction (that is, during modulation and during non-modulation), and the recording quality of information can be improved.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the relationship between drive current and output power of a semiconductor laser. FIG. 2 is a block diagram of a semiconductor laser device including an ALPC circuit. FIG. 3 is a diagram showing the modulation characteristics of a semiconductor laser. FIG. 4 is a diagram showing the power relationship for each duty cycle to explain the operation of FIG. 2. FIG. 5 is a block diagram of a semiconductor laser device according to an embodiment of the present invention. FIG. 6 is a specific circuit diagram of an example of the peak detection circuit used in this embodiment. FIG. 7 is a specific circuit diagram of an example of the clamp circuit used in this embodiment. FIG. 8 is a diagram showing the power relationship for each duty cycle to explain the operation of this embodiment. In the figure, 1 is a semiconductor laser, 3 is a photoelectric conversion circuit, and 5 is a semiconductor laser.
is a reference voltage generation circuit, 6 is a differential amplifier, 7 is a drive circuit,
12 is a peak detection circuit, and 13 is a clamp circuit. Agent Shin Kuzuno - (1 other person) ¥1 Figure 2 Figure 3 ■611a2 Iα1 41st

Claims (1)

[Scope of Claims] A semiconductor laser that generates laser light; a photoelectric conversion means that detects a portion of the laser light generated by the semiconductor laser and converts it into an electrical signal; and detects a peak of an output signal of the photoelectric conversion means. peak detection means for detecting the peak detection means; differential amplification means for amplifying the difference between the output signal of the peak detection means and a constant reference voltage; and an external input for modulating the laser light based on the output voltage of the differential amplification means. A semiconductor laser device comprising: a clamp means for clamping a signal; and a drive means for driving the semiconductor laser according to an output voltage of the clamp means.