JP3229756B2 - Semiconductor laser device for optical pickup - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device used in an optical pickup for irradiating an optical recording medium with a laser beam and detecting reflected light.

[0002]

2. Description of the Related Art An optical pickup comprises a laser diode (semiconductor laser), various optical components, an objective lens, a sensor, and the like, and reads a recording signal from an optical recording medium (optical disk) and records an information signal on the optical disk. To this end, the objective lens is always servo-controlled. The servo control of the objective lens is performed based on focus error detection and tracking error detection. Focus error detection includes methods such as an astigmatism method, a beam size method, and a knife edge method. Tracking error detection includes a method such as a three-beam method and a push-pull method.

In the tracking error detection method, the three-beam method is currently most frequently used. In this method, as shown in FIG. 3, a laser beam emitted from a semiconductor laser 101 is separated into a main beam and two sub-beams by a diffraction grating 102, and three focal points are formed on a disk D by an objective lens 103. The tracking error is detected using two of the sub-beams. The main beam is used for recording / reproducing information signals.

As described above, a single semiconductor laser 101
When the laser beam is separated into three beams, the power of each beam is reduced. Therefore, when a large laser power is required, there is a problem that an excessive load is applied to the semiconductor laser 101. In general, the pitch d of the diffraction grating 102
Is given by d = (L × λ × f ₀ ) / (f _C × P). Here, P is the interval between the three beams on the disk D, L is the distance between the semiconductor laser 101 and the diffraction grating 102, f ₀ is the focal length of the objective lens 103, and f _C is the focal length of the collimator lens. For this reason, in an optical pickup in which the semiconductor laser 101, the optical unit, the sensor, and the like are incorporated in a minute package, the above L is very small, and the pitch d of the diffraction grating 102 is also very small, making it difficult to manufacture. A similar problem is caused by shortening the wavelength.

[0005]

For this reason, instead of the method of generating three beams using a diffraction grating as shown in FIG.
A method using a beam laser diode array has been proposed. However, in this method, as many APC circuits as the number of laser diodes are required as shown in FIG. 2 for compensating power fluctuations of the semiconductor laser due to heat generation or the like, which leads to an increase in size and cost of the apparatus. There is a problem. That is, the circuit shown in FIG. 2 receives the emitted laser beams from the three semiconductor lasers 1, 1a, 1b by the monitoring sensors 2, 2a, 2b, respectively.
a, 2b are output from the IV converters 3, 3a, 3b, respectively.
Is converted to a voltage signal, and each voltage signal is converted to an APC (Auto po
wercontroll) input to the circuits 4, 4a, 4b to generate control signals for bringing the output laser power closer to the target value, and input the respective control signals to the VI converters 5, 5a, 5b, and This is a feedback control circuit that generates drive currents for the lasers 1, 1a, and 1b, respectively, and requires the same number of APC circuits as the number of semiconductor lasers (three).

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the number of APC circuits in a device for an optical pickup using a plurality of semiconductor lasers, thereby facilitating miniaturization.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a semiconductor laser device used in an optical pickup for irradiating an optical recording medium with a laser beam and detecting reflected light, comprising a first laser diode and a first laser diode. APC that outputs a signal for controlling a drive current of the first laser diode based on the intensity of the laser beam emitted from the laser diode so that the intensity of the laser beam emitted from the first laser diode becomes a predetermined intensity.
A semiconductor laser device for an optical pickup, comprising: a circuit; an attenuating means for attenuating an output signal of an APC circuit at a predetermined attenuation ratio; and a second laser diode whose drive current is controlled by the attenuated signal. .

In the above, there is further provided means for comparing a value obtained by attenuating the intensity of the laser beam emitted from the first laser diode by the above-mentioned attenuation ratio with the intensity of the laser beam emitted from the second laser diode. The result may be fed back to a signal for controlling the drive current of the second laser diode. Further, a third laser diode whose drive current is controlled by the signal attenuated by the attenuating means may be provided. In addition, the second
Means for comparing the intensity of the outgoing laser beam of the third laser diode with the intensity of the outgoing laser beam of the third laser diode, and the result of the comparison is fed back to a signal for controlling the drive current of the third laser diode. May be.

[0009]

The output signal of the APC circuit which feeds back the intensity of the laser beam emitted from the first laser diode is attenuated at a predetermined attenuation ratio, and the second laser diode is driven and controlled based on the attenuated signal. You. Therefore, when the attenuation ratio is set to a desired value, the intensity of the laser beam emitted from the second laser diode becomes a value obtained by multiplying the intensity of the laser beam emitted from the first laser diode by the attenuation ratio.

[0010]

Embodiments of the present invention will be described below. FIG. 1 is a block diagram of a control circuit of a semiconductor laser device for an optical pickup according to an embodiment. In FIG. 1, reference numeral 11 denotes a laser diode for emitting a main beam for recording / reproducing signals, and reference numerals 11a and 11b denote laser diodes for emitting a sub-beam for tracking error detection. Hereinafter, the subscripts “a” and “b” indicate elements relating to a sub-beam for tracking error detection.

The laser beam emitted from the laser diode 11 is focused on the recording surface of an optical disk (not shown), and the reflected light is received by the monitor sensor 12.
The monitoring sensor 12 outputs a current corresponding to the amount of received light. This current is converted into a voltage signal by the IV converter 13 and input to the APC circuit 14. APC circuit 14
Outputs a control signal based on the input signal so that a driving current for emitting a laser beam having a predetermined intensity from the laser diode 11 is supplied to the laser diode 11. This control signal is input to the VI converter 15,
The drive current is supplied from the VI converter 15 to the laser diode 11. In this way, the intensity of the laser diode 11 is feedback-controlled and maintained at a certain desired value.

In the three-beam tracking error detection method,
The intensity of the sub-beam for tracking error detection is lower than the intensity of the main beam for recording / reproducing signals, and is, for example, about 1/10 of the intensity of the main beam. For this reason, the current required to drive the sub-beam laser diodes 11a and 11b is limited to the main-beam laser diode 1a.
1 drive current. Further, the intensity of the emitted laser beam from the laser diode is proportional to the drive current. Therefore, a drive current required to obtain a desired laser beam intensity can be easily obtained. Utilizing this, in the present embodiment, the output of the APC circuit 14 is attenuated to a predetermined level (eg, 1/10) by the voltage divider 21 and is input to the VI converters 15a and 15b. Drive current for the laser diodes 11a and 11b, respectively. Thereby, the output laser beam intensities of the laser diodes 11a and 11b are each equal to a value obtained by attenuating the output laser beam intensity of the laser diode 11 to the above-described level (eg, 1/10).

The laser beam emitted from the laser diode 11a is focused on a recording surface of an optical disk (not shown).
The reflected light is received by the monitor sensor 12a. The monitoring sensor 12a outputs a current corresponding to the amount of received light. This current is converted into a voltage signal by the IV converter 13 a and input to the differential amplifier 24. Similarly, a voltage signal corresponding to the intensity of the emitted laser beam from the laser diode 11b is output from the monitor sensor 12b and the IV converter 1
3b, and input to the differential amplifier 24.
In the differential amplifier 24, the difference between the two voltage signals is compared, and the result is input to the VI converter 15b.
As a result, feedback control is performed on the intensity of the emitted laser beam from the laser diode 11b, and even when the ratio between the drive current of the two laser diodes 11a and 11b and the intensity of the emitted laser beam is different, it is possible to emit a laser beam of the same intensity. Become.

Further, a signal obtained by inputting the output of the IV converter 13 to a voltage divider 22 and attenuating it to the same level (eg, 1/10) as that of the voltage divider 21 and the IV converter The output signal of the converter 13a is input to the differential amplifier 23 and compared, and the result is input to the VI converter 15a. As a result, feedback control is performed on the intensity of the emitted laser beam from the laser diode 11a.
That is, the laser diode 11a is
1 to a certain level (eg, 1/1)
The laser beam having the intensity attenuated to 0) is emitted.

With the above configuration, the laser diode 1
1a and 11b indicate that the intensity of the laser beam emitted from the laser diode 11 is at a certain level (for example, 1/10).
It is possible to stably emit a laser beam having a reduced intensity. In the above embodiment, the intensity of the laser beams emitted from the laser diodes 11, 11a and 11b is detected by receiving the reflected light from the optical disk (not shown) by the monitor sensor.
A configuration may be adopted in which a part of the laser beam is taken out in the optical path from 1, 11a, 11b to the optical disk and the intensity is detected.

[0016]

As described above, according to the present invention, the output signal of the APC circuit for feedback-controlling the intensity of the laser beam emitted from the first laser diode is attenuated at a predetermined attenuation ratio.
Since the driving of the second laser diode is controlled based on the signal after the attenuation, two laser diodes can be controlled by one APC circuit. Therefore, in an apparatus for an optical pickup using a plurality of semiconductor lasers, A
The number of PC circuits can be reduced and the size can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a control circuit of a semiconductor laser device for an optical pickup according to an embodiment.

FIG. 2 is a block diagram of a control circuit of a conventional semiconductor laser device for an optical pickup.

FIG. 3 is a schematic diagram showing how three beams are generated by a diffraction grating.

[Description of reference numerals] 11, 11a. 11b Semiconductor laser 12,12a, 12b Monitoring sensor 13,13a, 13b IV converter 14,14a, 14b APC circuit 15,15a, 15b VI converter 21,22 Voltage divider 23,24 Comparator

Continuation of the front page (56) References JP-A-6-290485 (JP, A) JP-A-3-3125 (JP, A) JP-A-63-127441 (JP, A) JP-A-5-342615 (JP) JP-A-6-36329 (JP, A) JP-A-64-21736 (JP, A) JP-A-3-102656 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) G11B 7/12-7/22

Claims (4)

(57) [Claims] An optical recording medium is irradiated with a laser beam.
Semiconductor laser used for optical pickup that detects reflected light
A first laser diode and an intensity of a laser beam emitted from the first laser diode.
The laser beam emitted from the first laser diode is
The driving power of the first laser diode is
An APC circuit that outputs a signal for controlling the flow, and a reduction circuit that attenuates the output signal of the APC circuit at a predetermined attenuation ratio.
Decay means and a second laser whose drive current is controlled by the attenuated signal.
A semiconductor laser device for an optical pickup having the diode . 2. The apparatus according to claim 1 , further comprising: an intensity of a laser beam emitted from said first laser diode.
And the value of the second laser diode
Means for comparing the intensities of the laser beams emitted from the
Is compared with the driving current of the second laser diode.
A semiconductor laser device for an optical pickup that feeds back to a control signal . 3. The driving current according to claim 1, wherein the driving current is further controlled by a signal attenuated by said attenuating means.
A semiconductor laser device for an optical pickup having a third laser diode . 4. The intensity of a laser beam emitted from the first laser diode according to claim 3, further comprising:
And the value of the second laser diode
Means for comparing the intensities of the laser beams emitted from the
Is compared with the driving current of the second laser diode.
Feedback to the control signal, the intensity of the laser beam emitted from the second laser diode
And the intensity of the laser beam emitted from the third laser diode.
Means is provided for comparing the degree of
Feedback signal to control the drive current of the laser diode.
-Clicking, the semiconductor laser device for an optical pickup.