JP3001016B2 - Semiconductor laser driver - 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 driving apparatus for supplying a driving current to a semiconductor laser to emit laser light.

[0002]

2. Description of the Related Art A semiconductor laser can directly modulate light intensity by changing a driving current, and has a feature of being small and light. Used in dynamic recording and reproducing devices. In recent years, in response to demands for improved performance of semiconductor lasers, mass information processing such as optical transmission and optical recording, and demands for higher speeds and higher densities, higher speed modulation drive of semiconductor lasers and higher densities of drive circuits have been implemented. It is being done. For this reason, Japanese Unexamined Patent Publication No.
By disposing a drive circuit of a semiconductor laser close to the semiconductor laser as disclosed in Japanese Patent Application Laid-Open No. 2-5676, the occurrence of EMF noise and the like due to high-speed pulse transmission is reduced, and the load on the drive circuit is reduced. In addition, there has been proposed a semiconductor laser driving device which eliminates disturbance applied to peripheral circuits.

In a device equipped with the above-described semiconductor laser driving device, for example, an optical recording / reproducing device, a deterioration test of the semiconductor laser for determining whether the semiconductor laser has deteriorated at the time of assembly or repair. Is performed.
In the deterioration test of the semiconductor laser, the drive current IOP of the semiconductor laser for a certain laser emission amount Po is, for example, 5
When the percentage changes, it is determined that the battery is in a deteriorated state. For this reason,
It is necessary to accurately measure the drive current IOP of the semiconductor laser.

[0004]

However, it is difficult to directly drive a semiconductor laser with a conventional semiconductor laser driving apparatus, and a semiconductor laser driving circuit (hereinafter referred to as L
The semiconductor laser must be driven via a D drive circuit. For this reason, an error occurs between the actual drive current IOP of the semiconductor laser and the current supplied to the LD drive circuit due to a temperature change inside the LD drive circuit, variation in elements, or the like. Also, since the output from the PIN photodetector for detecting the laser light emission amount PO normally passes through an amplifier, the actual PIN may vary due to variations in the amplifier.
Light quantity received by the photodetector and light quantity detection signal I PIN
And an error occurs. Therefore, since the drive current IOP of the semiconductor laser cannot be measured with high accuracy, there is a problem that it is difficult to accurately perform a deterioration test of the semiconductor laser.

In order to accurately measure the drive current IOP of the semiconductor laser, it is conceivable to turn off the drive transistor inside the LD drive circuit and detect the current flowing through the bias power supply line. Is possible only when the bias power supply line is directly connected to the semiconductor laser. However, the LD drive circuit is not limited to such a configuration. For example, there are many cases where a current flowing through a bias power supply line is amplified 40 times and used as a drive current for a semiconductor laser. In such a case, It is difficult to accurately measure the drive current IOP of the semiconductor laser.

SUMMARY OF THE INVENTION The present invention has been made in view of these circumstances, and it is possible to accurately measure a driving current of a semiconductor laser with respect to a constant laser light emission amount, and to accurately and efficiently perform a deterioration test of a semiconductor laser. It is an object of the present invention to provide a semiconductor laser driving device capable of performing the above.

[0007]

According to the present invention, there is provided a semiconductor laser driving apparatus comprising: a semiconductor laser which emits laser light; and a light receiving element which receives at least a part of the laser light and detects a light emission amount of the semiconductor laser. A driving unit that supplies a driving current to the semiconductor laser and sets an output to a high impedance state, and supplies a driving current to the semiconductor laser without passing through the driving unit to detect an output of the light receiving element. And a terminal section.

[0008]

The driving means supplies a driving current to the semiconductor laser to emit laser light. A light receiving element receives at least a part of the laser light and detects a light emission amount of the semiconductor laser. An output of the driving unit is set to a high impedance state, and a driving current is supplied to the semiconductor laser from a terminal unit without passing through the driving unit, and an output of the light receiving element is detected.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 relate to a first embodiment of the present invention. FIG. 1 is a circuit diagram showing a configuration of a semiconductor laser driving device, FIG. 2 is an explanatory diagram showing a configuration in a semiconductor laser deterioration test, and FIG. 2 is a block diagram showing the configuration of the measuring apparatus in FIG. 2, FIG. 4 is an explanatory diagram showing a modification of the configuration in the deterioration test of the semiconductor laser shown in FIG. 2, and FIG. 5 is a characteristic showing the relationship between the drive current of the semiconductor laser and the amount of light emission FIG.

As shown in FIG. 1, a semiconductor laser driving device is provided with a semiconductor laser (LD) 1, and an LD driving circuit 2 as driving means for supplying a driving current to the semiconductor laser 1 is connected. The LD drive circuit 2 is provided with a constant current circuit 3 for low output and a constant current circuit 4 for high output, and the output of the constant current circuit 3 and the output of the constant current circuit 4 via the modulation switch 5 are provided. It is connected to the semiconductor laser 1. The low output constant current circuit 3 has a 40-times amplification factor for low power (read power) light emission, and holds a constant current slightly smaller than the threshold current Ith of the semiconductor laser 1 during recording / erasing. It has become. The high-power constant current circuit 4 has a 50-fold amplification factor for high-power (write / erase power) light emission, and supplies a drive current modulated by the modulation switch 5 to the semiconductor laser 1.
To be supplied.

An automatic output adjustment circuit (hereinafter abbreviated as APC) 8 having an automatic output adjustment unit 6 and a current-voltage conversion unit 7 is connected to the LD drive circuit 2. The current control signals 11 and 12 are input to the constant current circuits 3 and 4, respectively, and the modulation signal 13 is input to the modulation switch 5.

Also, a PIN photodetector (PD) as a light receiving element for detecting the light emission amount of the semiconductor laser 1
16 is provided near the semiconductor laser 1, and the PIN photodetector 16 is connected to the current-voltage converter 7 of the APC 8.
It is connected to the. That is, the light amount detection signal 21 indicating the light emission amount of the semiconductor laser 1 is input to the APC 8. Further, as a terminal unit for supplying a drive current to the semiconductor laser and detecting an output of the light receiving element, a light amount detection terminal 17 connected to an output of the PIN photodetector 16;
A test drive terminal 18 connected to the semiconductor laser 1 is provided. A control signal input terminal 1 for setting the outputs of the constant current circuits 3 and 4 to a high impedance state.
A high impedance state control signal 20 is input to the constant current circuits 3 and 4.

The APC 8 receives an oscillation instruction signal of the semiconductor laser 1 or a semiconductor laser 1 from a control circuit (not shown).
An information signal or the like for oscillating while modulating is input.

Next, the operation of this embodiment will be described.
In an optical recording / reproducing apparatus provided with a semiconductor laser driving device, at the time of reproduction, the constant current circuit 3 for low output amplifies the current control signal 11 by 40 times to generate a driving current for reproduction. The semiconductor laser 1 emits light at the read power to reproduce information recorded on the medium. Further, at the time of recording / erasing, the constant current circuit 3 for low output is used.
Is controlled by the current control signal 11 so as to maintain a constant current slightly smaller than the threshold current Ith of the semiconductor laser 1, and the constant current circuit 4 for high output is controlled by the current control signal 12.
Is amplified 50 times to generate a drive current for recording / erasing. The drive current for recording / erasing is modulated by the modulation signal 13 input to the modulation switch 5 and supplied to the semiconductor laser 1. As a result, the semiconductor laser 1 performs, for example, high-speed pulse oscillation to record information on the medium with write power.

At this time, the PIN photodetector 16 receives at least a part of the laser light from the back surface of the semiconductor laser 1, detects the light emission intensity, and outputs the light amount detection signal 21 to the AP.
Output to C8. The APC 8 adjusts the drive current of the semiconductor laser 1 by adjusting the current control signals 11 and 12 so that the light amount detection signal 21 has a predetermined value, that is, the semiconductor laser 1 emits light at a predetermined light emission amount. Automatically controlled in a closed loop. In this embodiment, the semiconductor laser 1 and the LD drive circuit 2 are arranged close to each other.
Since the transmission line connecting the LD drive circuit 2 and the semiconductor laser 1 is extremely short, EMF noise induced from the transmission line can be reduced, and overshoot generated by the transmission line can be reduced.

The semiconductor laser 1 tends to increase the threshold current and decrease the differential quantum efficiency because the resonator loss increases when the semiconductor laser 1 deteriorates. Accordingly, the current-light output characteristics of the semiconductor laser 1 change from (a) to (c) in FIG. 5, and when the semiconductor laser 1 emits light so that the light emission amount becomes a certain reference value, the semiconductor laser 1 emits light. (Drive current IOP) tends to increase as deterioration progresses. Therefore, it is possible to determine whether or not the semiconductor laser 1 has deteriorated by measuring a change in the drive current IOP of the semiconductor laser 1 when the semiconductor laser 1 emits light with a constant light emission amount.

The deterioration test of the semiconductor laser for measuring the drive current IOP of the semiconductor laser with respect to a constant laser light emission amount P0 is performed as shown in FIG. First, the initial value of the drive current IOP is measured by the measuring device 25 with the semiconductor laser (LD) 1 alone as shown in FIG. The measuring device 2
5 is a drive circuit 26 and an APC for measurement, as shown in FIG.
27, a controller 29 for controlling the measurement driving power supply 28, and a memory 30 for storing measurement data. The memory 30 has an initial value of the driving current IOP. Is stored.

Next, as shown in FIG. 2B, an optical pickup 32 is constructed by incorporating the semiconductor laser 1 and a PIN photodetector (PD) 16 and connecting to an LD drive IC 31 in which the LD drive circuit 2 is integrated. Then, when the adjustment of the optical pickup 32 is completed, a first deterioration test is performed. At the time of assembly / adjustment, the semiconductor laser may be deteriorated due to electrostatic breakdown or the like, and it is necessary to determine the deteriorated semiconductor laser by performing a deterioration test. The measuring device 25 is connected to the light amount detection terminal 17, the test drive terminal 18, and the control signal input terminal 19, and the control signal input terminal 19
From the LD drive I
Input to C31 to set the outputs of constant current circuits 3 and 4 to high impedance state. Then, the light amount detection signal 21 indicating the light emission amount of the semiconductor laser 1 obtained from the light amount detection terminal 17 is monitored, and the test drive is performed so that the light emission amount of the semiconductor laser 1 detected by the PIN photodetector 16 becomes a predetermined reference value. The drive current supplied to the terminal 18 is controlled. At this time, the drive current is measured and compared with the initial value. If the drive current fluctuates by 5% with respect to the initial value, it is determined that the motor has deteriorated and a warning is issued. The initial value and the measured value may be displayed so that the tester can recognize the degree of deterioration.

Then, as shown in FIG.
8 is connected to the LD drive IC 31 to form the semiconductor laser driving device 33. When the adjustment of the semiconductor laser driving device 33 is completed, a second deterioration test is performed. As described above, the measuring device 25 is connected to the light amount detection terminal 17, the test drive terminal 18, and the control signal input terminal 19, and the light emission amount of the semiconductor laser 1 detected by the PIN photodetector 16 becomes a predetermined reference value. The drive current supplied to the test drive terminal 18 at that time is measured, and when the drive current fluctuates by 5% from the initial value, it is determined that the battery has deteriorated and a warning is issued.

As a modification of FIG. 2C, a deterioration test can be performed by a configuration as shown in FIG.
As shown in FIGS. 4A and 4B, the LD drive IC 31
Is connected to a connector section 35. The connector section 35 is provided with a light amount detection terminal 17, a test drive terminal 18, a control signal input terminal 19, and a terminal to which a control signal from the APC 8 is input. First, the APC 8 is connected as shown in (a) to adjust the semiconductor laser driving device. Then, as shown in (b), the measuring device 25 is connected and the deterioration test of the semiconductor laser is performed in the same manner as described above. Do. In this way, by switching the devices to be connected by providing the connector section 35, the operation of the ordinary semiconductor laser driving device and the deterioration test of the semiconductor laser can be easily performed.

The deterioration test of the semiconductor laser as described above may be performed not only at the time of assembling / adjusting the semiconductor laser driving device but also at the time of repair. This makes it possible to grasp the state of deterioration of the semiconductor laser.

As described above, the measuring drive power supply 28 provided in the measuring device 25 has no restrictions on the size, cost and the like as compared with the LD driving circuit 2 used in the semiconductor laser driving device. And the like, or a component with high accuracy can be used, and the driving current of the semiconductor laser can be measured with high accuracy. Therefore, by providing a terminal for supplying a drive current to the semiconductor laser and detecting the output of the light receiving element, a measuring device 25 is connected to this terminal to accurately measure the drive current of the semiconductor laser with respect to a constant laser emission amount. And the deterioration test of the semiconductor laser can be performed accurately and efficiently. The LD driving circuit 2 used in the semiconductor laser driving device includes a semiconductor laser 1
It is only necessary to be able to perform automatic output adjustment so that the light emission amount becomes a predetermined value, and since accuracy is not so much required,
The deterioration test can be accurately performed with a simple configuration as a semiconductor laser driving device.

FIG. 6 is an explanatory view showing a configuration of a semiconductor laser driving device according to a second embodiment of the present invention.

As shown in FIG. 6, a semiconductor laser 1 having a heat sink 42 connected thereto is provided in an IC package 41, and this semiconductor laser 1 is connected to an LD drive circuit 2 integrated by bonding wires 43 via a short transmission path. It is connected. The LD drive circuit 2 has the same configuration as that of the first embodiment. Further, a PIN photodetector 16 for detecting a part of light from the back surface of the semiconductor laser 1 is provided. The IC package 41 has a window 44 for transmitting laser light on the front surface, and the laser light is emitted from the window 44. On the rear end face of the IC package 41, the light quantity detection terminal 17 connected to the output of the PIN photodetector 16, the test drive terminal 18 connected to the semiconductor laser 1, and the outputs of the constant current circuits 3 and 4 are in a high impedance state. Control signal input terminal 19 for setting to
A first current control terminal 45 connected to the constant current circuit 3 for low output, a second current control terminal 46 connected to the constant current circuit 4 for high output, and the modulation switch 5. And a modulation signal terminal 47 extending therefrom.

By connecting the current control terminals 45 and 46 and the modulation signal terminal 47 provided on the IC package 41 to the APC 8, the semiconductor laser 1 emits light at the power for reproduction and recording / erasing while the output is automatically adjusted. I do. When the deterioration test of the semiconductor laser 1 is performed, the measurement device 25 is connected to the light amount detection terminal 17, the test drive terminal 18, and the control signal input terminal 19 as in the first embodiment, and the detection is performed by the PIN photodetector 16. The drive current supplied to the test drive terminal 18 when the light emission amount of the semiconductor laser 1 reaches a predetermined reference value is measured, and the deterioration state is determined based on whether or not the change is 5% from the initial value. .

As described above, in this embodiment, since the semiconductor laser 1, the LD driving circuit 2, and the PIN photodetector 16 are arranged close to the IC package 41, the transmission path for driving current and the like becomes short, and the circuit is small. Therefore, the generation of noise can be suppressed, the load loss as a transmission line can be extremely reduced, and a terminal portion for supplying a drive current to the semiconductor laser and detecting the output of the light receiving element is provided. The deterioration test can be performed accurately. In addition, since the semiconductor laser 1, the LD drive circuit 2, the terminal section, and the like are integrally formed, assembly and a deterioration test of the semiconductor laser can be easily performed.

Other structures, operations and effects are the same as those of the first embodiment.

FIGS. 7 to 9 relate to a third embodiment of the present invention. FIG. 7 is a circuit diagram showing a configuration of a semiconductor laser driving device. FIG. 8 is a diagram showing a configuration of a current-voltage converter in FIG. FIGS. 9A and 9B are explanatory diagrams showing a state where the semiconductor laser driving unit of FIG. 7 is connected to a measuring device.

As shown in FIG. 7, the semiconductor laser driving unit 5
1, a semiconductor laser 1, an LD drive circuit 2, and a PIN photodetector 16 are provided as in the first embodiment. Further, a current-voltage converter 52 for converting a current flowing through the PIN photodetector 16 into a voltage is provided, and an output of the current-voltage converter 52 is input to the APC 54 as a light amount detection voltage signal 53. On the other hand, the light amount detection terminal 17 that outputs the light amount detection signal 21 is directly connected to the PIN photodetector 16. As shown in FIG. 8, the current-voltage converter 52 has an operational amplifier 56 and a resistor 57, and the operational amplifier 56 has a voltage follower configuration. The resistor 57 has one end connected to Vcc in the semiconductor laser driving unit 51 and the other end connected to PI.
It is connected to the cathode side of the N photodetector 16. Thereby, the voltage generated on the cathode side of the PIN photodetector 16, that is, the PIN photodetector 1
Assuming that the current flowing through 6 is IPIN, a voltage corresponding to VCC-IPIN × R is generated at the output of the operational amplifier 56. This output voltage is input to the APC 54 as the light amount detection voltage signal 53. As described above, by converting the minute light amount detection signal 21 into a voltage immediately after the PIN photodetector 16, the influence of disturbance noise or the like on the APC 8 can be reduced. Otherwise, the configuration is the same as that of the first embodiment.

When performing a deterioration test of the semiconductor laser 1,
As shown in FIG. 9, the measuring device 25 is connected to the light amount detection terminal 17,
A drive current connected to the test drive terminal 18 and the control signal input terminal 19 and supplied to the test drive terminal 18 when the light emission amount of the semiconductor laser 1 detected by the PIN photodetector 16 reaches a predetermined reference value. Measure. Here, the light amount detection voltage signal 53 is a current IPI flowing through the PIN photodetector 16 due to a variation in the operational amplifier 56.
The light intensity detection signal 21 from the light intensity detection terminal 17 directly connected to the PIN photodetector 16 is inappropriate for use in a deterioration test because it does not correspond exactly to the value of N.
Perform the measurement using. Then, the deterioration state is determined based on whether the drive current fluctuates by 5% from the initial value. The light amount detection terminal 17 is connected to the positive input terminal of the operational amplifier 56. However, since the positive input terminal of the operational amplifier 56 having a voltage follower has an extremely high input impedance, an accurate value of I PIN is detected. be able to.

As described above, by providing the current-voltage converter 52 in the semiconductor laser driving unit 51, the influence of disturbance noise and the like in the APC can be suppressed, and a driving current is supplied to the semiconductor laser to By providing a terminal portion for detecting the output of the semiconductor laser, a deterioration test of the semiconductor laser can be accurately performed.

Other functions and effects are the same as those of the first embodiment.

[0033]

As described above, according to the present invention, by providing a terminal for supplying a drive current to a semiconductor laser and detecting the output of a light receiving element, the drive current of the semiconductor laser with respect to a constant laser emission amount is provided. Can be accurately measured, and the deterioration test of the semiconductor laser can be accurately and efficiently performed.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing a configuration of a semiconductor laser driving device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration in a deterioration test of a semiconductor laser.

FIG. 3 is a block diagram showing a configuration of a measuring device in FIG. 2;

4 is an explanatory view showing a modification of the configuration in the deterioration test of the semiconductor laser shown in FIG. 2;

FIG. 5 is a characteristic diagram showing a relationship between a driving current and a light emission amount of a semiconductor laser.

FIG. 6 is an explanatory diagram showing a configuration of a semiconductor laser driving device according to a second embodiment of the present invention.

FIG. 7 is a circuit configuration diagram showing a configuration of a semiconductor laser driving device according to a third embodiment of the present invention.

FIG. 8 is a configuration explanatory view showing the configuration of the current-voltage converter in FIG. 7;

FIG. 9 is an explanatory diagram showing a state where the semiconductor laser drive unit of FIG. 7 is connected to a measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 2 ... LD drive circuit 8 ... APC 16 ... PIN photodetector 17 ... Light amount detection terminal 18 ... Test drive terminal 19 ... Control signal input terminal 25 ... Measuring device Deputy Patent Attorney Susumu Ito

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 3/18 H01S 3/096 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A semiconductor laser that emits a laser beam, a light receiving element that receives at least a part of the laser beam and detects a light emission amount of the semiconductor laser, supplies a drive current to the semiconductor laser, and outputs an output. A semiconductor laser comprising: a driving unit that can be set to a high impedance state; and a terminal unit that can supply a driving current to the semiconductor laser without passing through the driving unit and detect an output of the light receiving element. Drive.