JP2000349390A - Method and device for controlling drive of semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make smoother the switching of an SHG(second harmonic generation) laser, etc., from ACC(automatic current control) to APC(automatic power control). SOLUTION: The cathode of a laser diode 11 is connected to an ACC amplifier 20a and an APC amplifier 30a so that the summed current of an ACC current IC and an APC current IP may become the whole current ID flowing to an SHG laser 10. At the time of starting a laser 10, only ACC is performed so that the whole current ID may become a steady current amount I0 and, when the light output PD of the laser 10 approaches a reference light output P0, second ACC is performed so that the ACC current IC may become smaller than the steady current amount I0 and, at the same time, first APC is performed so that the light output PD may become the reference light output P0. When a prescribed period of time elapses after the second ACC and first APC are started, the second ACC and first APC are stopped and, at the same time, only second APC is made so that the light output PD may become the reference light output P0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive control method and apparatus for keeping the optical output of a semiconductor laser constant, and more particularly to a laser diode pumped solid-state laser or a master oscillator / power amplifier type semiconductor. The present invention relates to a drive control method and apparatus for maintaining a constant optical output of a semiconductor laser such as a laser capable of obtaining a high output optical output.

[0002]

2. Description of the Related Art A reading light source of a pickup unit such as a compact disk player and a mini disk player, a radiation image reading device (for example, Japanese Patent Publication No. 3-79695, Japanese Patent Application Laid-Open No. 7-191421, etc.), and a fluorescence diagnostic device (for example, JP-A-1-136630, JP-A-7-59783, etc.)
It is well known that a semiconductor laser is used as an excitation light source.

[0003] Semiconductor lasers used as light sources in such various devices are used in place of conventional solid-state lasers, gas lasers and the like because of their small size, low cost, and easy handling. And its demand is rapidly increasing.

As the semiconductor laser, for example, as shown in Japanese Patent Application Laid-Open No. 62-189773, a solid laser crystal to which a rare earth element such as neodymium is added is excited by light (laser beam) emitted from a laser diode. 2. Description of the Related Art A laser diode pumped solid-state laser (hereinafter, simply referred to as a pumped solid-state laser) is known. In this pumped solid-state laser, in order to obtain a shorter-wavelength laser beam, it is widely used to arrange a nonlinear optical crystal in the resonator and convert the wavelength of the solid-state laser beam to a second harmonic or a sum frequency. For example, SHG is used to extract a second harmonic used for obtaining visible light or ultraviolet light by frequency doubling using a nonlinear optical crystal based on near-infrared output light. (Second Harmonic Genera
tion) It is called a laser. This pumped solid-state laser
Since it is suitable for obtaining a high-output optical output, its use as a high-output laser is expanding.

In an excitation solid-state laser (including a wavelength-converting laser as described above; the same applies hereinafter),
In order to suppress fluctuations in the optical output and oscillation wavelength of the laser diode, which is the pump source, and to maintain a predetermined phase matching state in the nonlinear optical crystal in the case of performing the above-described wavelength conversion, a laser diode, a solid-state laser crystal and Generally, the temperature of the portion of the resonator is adjusted to a predetermined temperature. This temperature adjustment is usually carried out by placing the above-mentioned parts on the cooling surface of an electronic cooling element such as a Peltier element (heat-absorbing / absorbing element), detecting the temperature inside the laser diode or the resonator, and based on the detected temperature. This is performed by performing feedback control so that the operation of the electronic cooling element is maintained at the final target temperature value.

In the case where the above-mentioned excitation solid-state laser is used as a light source for various devices, the temperature control is performed in order to keep the optical output (light emission amount) of the semiconductor laser constant in a steady state in order to stabilize reading accuracy and the like. APC (Automati
c Power Control) Control is generally performed.

[0007] This APC control is usually realized by adopting the following configuration. That is, the light output of the semiconductor laser is detected by a photodetector such as a photodiode, and a negative feedback circuit including an operational amplifier is configured so that the output signal of the photodetector has a constant value.

On the other hand, as a semiconductor laser capable of obtaining a high output light output, for example, Electronics Letters Vos
l.28 No.2 p 2011-2013, Optics & Photonics Ne
ws Mch. '93 p11-13, JP-A-6-291400, etc., a master oscillator-power amplifier (Master Oscillator-Power Amplifier; M)
An OPA type semiconductor laser (hereinafter referred to as MOPA laser) has also been proposed. In this MOPA laser, in order to keep the optical output of the MOPA laser constant, an ACC (Automated Motor) that keeps the amount of current flowing in one of the master oscillator section and the power amplifier section constant.
It is common to perform APC (Accient Control) control and APC control to keep the light output constant for the other.
In addition, temperature adjustment for maintaining the MOPA laser at a predetermined temperature is also performed in the same manner as the above-described pumped solid laser.

Further, semiconductor lasers such as the above-mentioned pumped solid-state lasers and MOPA lasers have a characteristic that they are destroyed when an overcurrent flows, so that the semiconductor laser does not exceed the maximum allowable current value (Imax) of the semiconductor laser when used. If the current exceeds the maximum allowable current value, the semiconductor laser will eventually be destroyed due to an excessive current. In any control, a limiter circuit is provided as current limiting means for suppressing the amount of current flowing through the semiconductor laser to the maximum allowable current value or less.

Further, when the semiconductor laser does not reach the predetermined temperature, for example, when the power is turned on, or when the power is turned on, the current value by the ACC control is further reduced when the semiconductor laser does not reach the predetermined temperature. If the value has not been reached, that is, not only in the steady state but also in the transient state, it must be satisfied.

Therefore, if the APC control is continued while the semiconductor laser is not in a steady state, there is a possibility that the semiconductor laser may be destroyed due to an excessive current. To prevent excessive current by continuing, when not in a steady state, AP
Without operating the C control, ACC control is performed to maintain the amount of current flowing through the semiconductor laser at a current amount substantially equal to the steady current amount corresponding to the reference light output in the steady state. A control drive method for switching to control has been proposed (JP-A-10-178230).
issue).

[0012]

However, in the method described in JP-A-10-178230, A
When switching from the CC control to the APC control, a non-control period in which neither the ACC control nor the APC control operates instantaneously occurs. Therefore, the temperature of the semiconductor laser fluctuates, and the ACC control is stably changed from the ACC control. It is difficult to shift to APC control, that is, JP-A-10-178230.
In fact, in the method described in the above paragraph, the ACC
There is a problem that it is difficult to smoothly switch to the control, and in some cases, an excessive current may flow through the semiconductor laser, leading to deterioration or destruction.

The present invention has been made in view of the above circumstances, and a drive control method capable of maintaining a constant optical output of a semiconductor laser and smoothly performing switching from ACC control to APC control. And an apparatus. It is another object of the present invention to provide a new drive control method and device having a current limiting method and means suitable for the device.

[0014]

The drive control method for a semiconductor laser according to the present invention relates to an ACC control for maintaining a current flowing through a semiconductor laser at a current substantially equal to a steady current corresponding to a reference light output in a steady state. The new control method for controlling the amount of current flowing to the semiconductor laser by combining a different ACC control for maintaining a predetermined current amount equal to or less than the steady-state current amount and an APC control for maintaining the optical output at the reference optical output has been described above. By intervening at the time of switching from ACC control to APC control, the control method can be smoothly switched. That is, the semiconductor laser drive control method according to the present invention is a semiconductor laser drive control method for controlling the optical output of the semiconductor laser by controlling the current flowing through the semiconductor laser. Sometimes, the first ACC control for keeping the current amount substantially constant is performed so that the amount of current flowing through the semiconductor laser becomes close to the steady state current amount corresponding to the reference light output in the steady state. When the output approaches the reference light output, as a second step, the amount of current by the ACC control is:
A second ACC that keeps the current amount substantially constant so that the current amount becomes a value corresponding to a predetermined light output that is equal to or less than the reference light output.
Control, and first APC control for maintaining the optical output of the semiconductor laser at the reference optical output is performed.

Further, in the semiconductor laser drive control method according to the present invention, further, after a predetermined time elapses after the start of the second ACC control and the first APC control, the third control is performed.
As a step, the second ACC control and the first APC
The control may be stopped, and a second APC control for maintaining the light output of the semiconductor laser at the reference light output may be performed.

Here, the first AP in the second step
The C control and the second APC control in the third step both maintain the optical output of the semiconductor laser at the reference optical output, and are controls that perform substantially the same operation. The first APC control compensates for the shortage (50 to 90% of the reference light output) of the light output (for example, 50 to 90% of the reference light output) corresponding to the amount of current by the ACC control of the second ACC control. While the control is performed so as to keep the output at the reference light output, the second APC control is performed only by the second APC control so as to maintain the light output of the semiconductor laser at the reference light output. The operation of both APC controls differs in small points.

That is, the drive control method for a semiconductor laser according to the present invention has the effect of maintaining the optical output of the semiconductor laser near the reference optical output.
Only by control, in the second step, the second A
The shortage caused by the CC control is compensated for by performing the first APC control, and the third step is performed only by the second APC control. In other words, in the first step, only the ACC control is performed, in the first step, the ACC control and the APC control are combined, and in the third step, the light output of the semiconductor laser is set to the reference light output only by the APC control. Is what you do.

In the semiconductor laser drive control method according to the present invention, during the predetermined time, that is, during the second step, the current is limited so that the amount of current flowing through the semiconductor laser is equal to or less than a predetermined value. desirable. Here, the amount of current flowing in the semiconductor laser during a predetermined time is the second amount.
Means the total amount of current flowing through the semiconductor laser, which is the sum of the current component obtained by the ACC control and the current component obtained by the first APC control. Further, "performs current limiting so that the amount of current flowing through the semiconductor laser is equal to or less than a predetermined value" means that the total amount of current flowing through the semiconductor laser does not exceed a predetermined value and flows through the semiconductor laser. This means limiting the amount of current.

As a method of detecting the total amount of current, for example, the amount of current obtained by calculation or the like based on the control voltage of the second ACC control, or the like, is calculated based on the control voltage of the first APC control. The total amount of current may be obtained indirectly by summing the amount of current obtained in step (1), but by directly detecting the current flowing through the semiconductor laser, the amount of current by the second ACC control and the amount of first current can be obtained. It is more efficient to obtain the total current amount at once without distinguishing the current amount from the APC control.

As described above, if the current flowing through the semiconductor laser is detected directly and all at once without distinguishing between the current under the ACC control and the current under the APC control, the current limiting effect in the second step can be obtained. In the first step and the third step, the current can be limited so that the amount of current flowing through the semiconductor laser is equal to or less than a predetermined value by using the same current limiting means as described above.

A semiconductor laser drive control apparatus according to the present invention is an apparatus for realizing the above method, that is, an apparatus for controlling an optical output of the semiconductor laser by controlling a current flowing through the semiconductor laser. At startup,
A first ACC control for performing the first ACC control for keeping the current amount substantially constant so that the current amount flowing through the semiconductor laser becomes close to the steady state current amount corresponding to the reference light output in the steady state.
CC control means, which operates when the light output of the semiconductor laser approaches the reference light output, so that the amount of current flowing through the semiconductor laser becomes an amount corresponding to a predetermined light output equal to or less than the reference light output. A second ACC control means for performing a second ACC control for keeping the current amount substantially constant, and an APC for performing the first APC control for keeping the light output of the semiconductor laser at the reference light output
And control means.

Here, the first ACC control means and the second A
As the CC control means, a common ACC control means is used, and by changing a current set value when acting as the first ACC control means, it operates as the second ACC control means. Is preferred.

Further, in the semiconductor laser drive control device according to the present invention, the second ACC control means includes a second AC control means.
After the start of the C control and the first APC control, the control may be stopped after a predetermined time has elapsed. When the second ACC control means stops after a predetermined time has elapsed, the APC
Unlike the first APC control, the control means automatically performs the second APC control for keeping the light output of the semiconductor laser at the reference light output only by the APC control means. The means for performing the second APC control may be provided separately from the means for performing the first APC control, and the two may be switched.

In the semiconductor laser drive control device according to the present invention, current detecting means for detecting the amount of current flowing through the semiconductor laser during the predetermined time, and the amount of current becomes equal to or less than a predetermined value based on the detected amount of current. It is desirable to provide a current limiting means for limiting the current as described above.

The current detecting means should detect the current flowing in the semiconductor laser directly and at once without distinguishing the current amount by the second ACC control from the current amount by the first APC control. desirable.

When the device is provided with a current limiting means, it is desirable that the current limiting means is connected to the semiconductor laser so that the entire current flowing through the semiconductor laser flows through the current limiting means. .

Further, when the apparatus is provided with a current limiting means, the current detecting means has a current / voltage converting function of converting a current value to a voltage value such as a resistor, and the current limiting means is provided with a current limiting means. A transistor in which the total current flows between the collector and the emitter, a voltage value representing the value of the total current converted by the current detecting means, and a reference voltage value representing the predetermined value, and the value of the total current is determined to be a predetermined value. It is desirable to have a means for inputting a voltage to the base of the transistor so that the voltage between the collector and the emitter of the transistor when the value is equal to or more than the value is increased. That is, a configuration in which a total current flows between the collector and the emitter of the transistor, a configuration in which the total current is converted into a voltage value, and the result of comparing the voltage value with the reference voltage value is negatively fed back to the base of the transistor. And When the value of the total current is equal to or less than a predetermined value, it is preferable that the collector and the emitter of the transistor be substantially short-circuited.

[0028]

According to the semiconductor laser drive control method and apparatus of the present invention, ACC control for maintaining the amount of current flowing through a semiconductor laser at a predetermined amount of current equal to or less than the steady-state current corresponding to the reference light output in a steady state, "ACC control +" which is combined with APC control to keep the light output at the reference light output.
Introducing a new control method called "APC control"
Instead of immediately switching from CC control to conventional APC control, conventional ACC control → ACC control + APC control →
Since the control method is shifted according to the procedure of the conventional APC control, there is no possibility that an uncontrol period in which neither the ACC control nor the APC control operates will occur. That is, when switching from the conventional ACC control corresponding to the first ACC control of the first step according to the present invention to the conventional APC control corresponding to the second APC control of the third step according to the present invention, the first step As a second step between the first step and the third step, a new drive control method called “ACC control + APC control” combining the ACC control and the APC control is interposed. When switching, ACC control continues to operate,
In addition, when switching from the second step to the third step, the APC control continues to operate.
There is no possibility that a non-control period in which neither the control nor the APC control operates will occur.

Therefore, it is possible to stably shift from the ACC control to the AP.
The control can be shifted to the C control, so that an excessive current does not flow through the semiconductor laser, and deterioration and destruction of the semiconductor laser due to the excessive current can be prevented.

Further, if the total amount of current flowing through the semiconductor laser is detected and the current is limited so that this amount of current becomes equal to or less than a predetermined value, the second step, ie, ACC
Even when both the control and the APC control are operating, the current limiting action can be exerted so that the current flowing through the semiconductor laser does not exceed the maximum allowable current.

At this time, the circuit can be simplified if the current limiting means and the semiconductor laser are connected such that the entire current flowing through the semiconductor laser flows through the current limiting means.

In addition, a total current flows between the collector and the emitter of the transistor, the total current is converted into a voltage value, and the result of comparing the voltage value with the reference voltage value is fed back to the base of the transistor. With this configuration, an extremely simple current limiter circuit can be configured.

[0033]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a semiconductor laser drive control method and apparatus according to an embodiment of the present invention;

FIG. 1 is a basic block diagram showing the configuration of an embodiment of a semiconductor laser drive control device according to the present invention.
FIG. 3 is a timing chart showing the relationship between the drive control method and the amount of current flowing through the semiconductor laser and the light output, FIG. 3 is a diagram showing another example of the current limitation, and FIG. 4 is a concrete block diagram of FIG. FIG. 5 is a functional block diagram of the circuit shown in FIG. In FIG. 1 and the like, the same elements are denoted by the same reference numerals, and description thereof will be made only in one of the drawings, and will be omitted in other drawings unless necessary.

The semiconductor laser drive control device 1 shown in FIG.
Is a laser beam L output from the resonator 12 by controlling the amount of current ID flowing through the laser diode 11 of the SHG laser 10, which is an embodiment of a laser diode-pumped solid-state laser including the laser diode 11 and the resonator 12.
This is configured to control the light output (light emission amount). Instead of the SHG laser 10, another semiconductor laser such as a MOPA laser may be used.

The anode of the laser diode 11 is connected to the positive power supply 13 and the cathode thereof is connected to the ACC control means 20.
And an APC control amplifier 30a forming the APC control means 30. The output of the ACC control amplifier 20a and the output of the APC control amplifier 30a are connected to the addition circuit 19. Thus, when both the ACC control amplifier 20a and the APC control amplifier 30a are in an operable state, the total current ID flowing through the laser diode 11 once becomes the ACC current IC and the APC
The current is shunted to the APC current IP by the control amplifier 30a,
Thereafter, the signals are combined by the adder circuit 19 and reproduced into the total current ID. On the other hand, when one of the ACC control amplifier 20a and the APC control amplifier 30a is in an inactive state, the entire current ID flows through the active control amplifier without being divided.

The output of the adder circuit 19 is connected to the ground via the current limiting means 70 and the current detecting means 80 so that the total current ID flowing through the laser diode 11 flows through the current limiting means 70. The terminal a of the current limiter 70 is connected to the detection terminal a of the current detector 80,
Similarly, a terminal b has a reference voltage VR representing a current limit value.
The EF is configured to be input.

The terminal "a" of the ACC control amplifier 20a is connected to the detection terminal "b" of the current detecting means 80, and the terminal "b" is also configured to receive a current command value.
Is configured to receive an ACC on / off signal. As a result, the ACC control unit 20 obtains the laser diode 11 obtained at the detection terminal b of the current detection unit 80.
While monitoring the voltage signal VFB1 corresponding to the total current ID flowing through the laser diode 11,
A is set so that it corresponds to the input current command value and is constant.
Performs CC control.

On the other hand, the terminal a of the APC control amplifier 30a detects the laser light L and outputs a voltage signal VF corresponding to the light output PD.
It is connected to an APC feedback circuit 31 that outputs B2, and is similarly configured so that a light quantity command value is input to a terminal b and an APC on / off signal is input to a terminal c. Thereby, the APC control means 30
While monitoring the output VFB2 of the APC feedback circuit 31,
APC control is performed so that the light output PD of the HG laser 10 corresponds to the input light amount command value and is constant.

Hereinafter, the basic operation of the semiconductor laser drive control device 1 having the above configuration will be described. First, a drive control method for controlling the amount of current flowing through the semiconductor laser will be described with reference to the flowchart shown in FIG.

In the drive control device 1, when the SHG laser 10 is started, the control method of the first step of performing the first ACC control of the present invention is selected as the drive control method of the SHG laser 10. That is, a signal for operating the ACC control amplifier 20a as an ACC on / off signal is set to A.
In addition to the input to the CC control amplifier 20a, a signal for disabling the APC control amplifier 30a is input to the APC control amplifier 30a as an APC on / off signal. Further, a current command value such that the total current ID flowing through the laser diode 11 becomes substantially equal to the light output in the steady state, that is, the steady current amount I0 corresponding to the reference light output P0 is input to the ACC control amplifier 20a.

Thus, the drive control device 1 allows only the ACC control means 20 to make the total current ID flowing through the laser diode 11 substantially equal to the steady current amount I0 corresponding to the reference light output P0 in the steady state, ACC control is performed so that the amount becomes substantially constant.

Accordingly, as shown in FIG. 2, when the SHG laser 10 is started, the first ACC control is activated,
The ACC current IC1 from the ACC control amplifier 20a becomes the total current ID and flows to the laser diode 11, and the optical output PDC1 corresponding to the ACC current IC1 is
Obtained from This optical output PDC1 is a SHG laser 1
It gradually increases with time t until 0 becomes a steady state.

Next, the SHG laser 10 approaches a steady state, and the light output PD of the SHG laser 10 changes to the reference light output P0.
(T1 in FIG. 2), the second ACC of the present invention is used as the drive control method of the SHG laser 10.
In addition to performing the control, the control method of the second step of performing the first APC control of the present invention is selected. That is, while a signal for turning on the ACC control amplifier 20a is input to the ACC control amplifier 20a as an ACC on / off signal, the AP
A signal for activating the APC control amplifier 30a is input to the APC control amplifier 30a as a C on / off signal. Also, of the total current ID flowing through the laser diode 11,
A current command value such that the current component flowing by the second ACC control is equal to or less than the steady current amount I0 corresponding to the reference light output P0, for example, 50 to 90% of the steady current amount I0 (the current command value in the first step described above). Is input to the ACC control amplifier 20a. Further, a light amount command value such that the light output PD of the SHG laser 10 becomes substantially equal to the reference light output P0 is input to the APC control amplifier 30a.

As a result, the drive control device 1 controls the second A
A current control operation combining the CC control and the first APC control is performed. That is, the ACC control amplifier 20a
ACC by the second ACC control due to activation of
The current IC2 flows through the ACC control amplifier 20a, and the optical output PDC2 corresponding to the ACC current IC2 is SHG
Obtained from laser 10. The APC control amplifier 30
a based on the first APC control
C current IP1 flows through APC control amplifier 30a,
The optical output PDP1 corresponding to this APC current IP1 is SH
Obtained from the G laser 10.

Therefore, as shown in FIG.
Thereafter, for a while, the ACC current IC2 and the APC current IP1
Is the total current ID flowing through the laser diode 11, and the result of adding the optical output PDC2 and the optical output PDP1 is the optical output PD of the SHG laser 10.

Here, the first APC control is to control the light output PD of the SHG laser 10 to be substantially equal to the reference light output P0 and to be constant, but the light output PDC2 by the second ACC control is controlled. As a result, the first APC control, as shown in FIG.
The shortage of light output PDP1 due to the ACC control is compensated by the first APC control so that the SHG laser 10
To maintain the reference light output P0 at the reference light output PD.

Since the ACC control continues to operate when the first step is switched to the second step, there is no possibility that an uncontrol period in which neither the ACC control nor the APC control operates will occur. Also, even if there is a difference in the amount of current flowing through the laser diode 11 before and after switching,
The range in which the APC control operates is, as shown in FIG.
Since the size is reduced by the CC control, the possibility of hunting occurring when the drive control method is switched is reduced as compared with the related art.

Next, when a predetermined time elapses after the time t1 (t2 in FIG. 2), as a drive control method of the SHG laser 10, the second ACC control of the present invention is stopped and the second control of the present invention is performed. The control method of the third step for performing the APC control of No. 2 is selected. That is, a signal for activating the APC control amplifier 30a as an APC on / off signal is transmitted to the AP.
While being input to the C control amplifier 30a, a signal for disabling the ACC control amplifier 20a is input to the ACC control amplifier 20a as an ACC on / off signal. Also, SH
A light amount command value such that the light output PD of the G laser 10 becomes substantially equal to the reference light output I0 is input to the APC control amplifier 30a. Note that this light amount command value may be the same as the light amount command value in the above-described second step.

As a result, the drive control unit 1 controls the light output P of the SHG laser 10 by the APC control means 30 alone.
APC control is performed so that D becomes substantially equal to the reference light output P0 and the light amount becomes substantially constant.

Therefore, as shown in FIG.
Thereafter, only the APC current IP2 by the APC control becomes the total current ID flowing through the laser diode 11, and only the optical output PDP2 corresponding to the APC current IP2 becomes the optical output PD of the SHG laser 10.

When switching from the second step to the third step, the state in which the APC control is activated is maintained, so that there is no possibility that an uncontrol period in which neither the ACC control nor the APC control is activated will occur. .

Next, the current limiting operation of the drive control device 1 having the above configuration will be described.

The total current flowing through the SHG laser 10, specifically, the current ID flowing through the laser diode 11, flows into the ground via the current limiting means 70 and the current detecting means 80 in order. The current detection means 80 has a current-voltage conversion function of converting a current value to a voltage value, and a voltage signal VS corresponding to the value of the current ID is obtained from a terminal a of the current detection means 80, and this voltage signal VS is It is input to the terminal a of the current limiting means 70. On the other hand, the reference voltage VREF is input to the terminal b of the current limiting means 70.

When the voltage signal VS is equal to or lower than the reference voltage VREF, the current limiting means 70 brings the addition circuit 19 side and the current detecting means 80 side of the current limiting means 70 into a short-circuit state between the input and output of the current. I do. On the other hand, when the current ID flowing through the laser diode 11 increases and the voltage signal VS becomes equal to or higher than the reference voltage VREF, a predetermined voltage is generated between the input and output. As a result, the potential on the output side of the adder circuit 19 rises, whereby the ACC control amplifier 20
The potentials on the current limiting means 70 side of both the APC control amplifier 30a and the APC control amplifier 30a increase.

In general, the current limiting means 70 of the ACC control amplifier 20a and the APC control amplifier 30a is configured to be an emitter of a transistor.
It works so that the ACC current IC by the control amplifier 20a and the APC current IP by the APC control amplifier 30a are reduced. As a result, a loop connecting the current limiting means 70 and the current detecting means 80 forms a negative feedback loop so that the value of the current ID flowing through the laser diode 11 never exceeds a predetermined value corresponding to the reference voltage VREF. Act to constitute. Therefore, SHG laser 1
0, the reference voltage VREF
Is set, the current flowing through the SHG laser 10 can be suppressed to the maximum allowable current value or less.

As described above, when the drive control method of the SHG laser 10 is switched, the ACC control and the AP
There is no danger that a non-control period in which none of the C control operates will occur, and the current flowing through the SHG laser 10 can be suppressed to the maximum allowable current value or less even at the time of switching. There is no danger that an excessive current will flow and cause the SHG laser 10 to deteriorate or break down.

The ACC control amplifier 20a and the AP
Even when the current limiting means 70 side of the C control amplifier 30a is not configured to be an emitter of a transistor, the voltage between the input and output of the current limiting means 70 is controlled in accordance with the configuration, so that the laser diode 1
It is possible to prevent the value of the current ID flowing to 1 from becoming more than a predetermined value.

Further, as described above, the configuration in which the entire current flowing through the SHG laser 10 flows through the current limiting means 70 is not employed. For example, as shown in FIG. Input, and according to the detection result by the current detection means 80, the ACC control amplifier 20a
The current command value of the APC control amplifier 3
By providing the current limiting means 70 for changing the light intensity command value of the laser diode 11a, the laser diode 11
The value of the current ID flowing through the power supply may not exceed a predetermined value.

Next, an example in which the basic block diagram shown in FIG. 1 is embodied will be described with reference to FIGS.

As shown in FIG. 4, the drive control device 1 includes:
Temperature control means 18 for keeping SHG laser 10 at a predetermined temperature
Is provided. The temperature control means 18 mounts the SHG laser 10 on the cooling surface of a Peltier element (heat generating / absorbing element) 19 as an electronic cooling element, and detects the temperature of the SHG laser 10 by a temperature detecting element (not shown) such as a thermistor. Then, a control signal D1 corresponding to the detected temperature is input to the Peltier device 19 to drive and control the Peltier device 19, thereby performing feedback control so that the SHG laser 10 is maintained at the final target temperature.

The output of the amplifier 50, which is a part of the ACC control amplifier, is connected to the base (control input terminal) b of the transistor 60 as a current output element. The collector c of the transistor 60 is connected to the cathode of the laser diode 11 constituting the SHG laser 10, and the anode of the laser diode 11 is connected to the positive power supply 13.

The amplification amplifier 50 includes an operational amplifier 501, a non-inverting input terminal (+) of the operational amplifier, and a resistor 803 described later.
A parallel circuit of a resistor 503 and a capacitor 504 connected between the output terminal (O) of the operational amplifier 501 and the base b of the transistor 60;
And a diode 505 connected between the base b and the emitter e of the transistor 60.

The transistor 60 is composed of Darlington-connected transistors 601, 602. The emitter e of the transistor 60 is connected to the collector c of the transistor 71 constituting the current limiting means 70 together with the comparison control means 72. The transistor 71 includes Darlington-connected transistors 711 and 712. The emitter e of the transistor 71 is connected to the terminal 8 of the current detecting means 80.
0a, and is connected to the laser ground LG via the terminal 80b of the current detecting means 80.

The current detecting means 80 includes parallel resistances 801 and 8
02 and a resistor 803 in series. Parallel resistance 80
1, 802 are connected to the terminal 2 of the resistor 803.

The current detection signal (voltage value) VFB1 output from the terminal 83 of the current detection means 80 is supplied to an ACC feedback circuit 2 composed of a parallel circuit of a resistor 211 and a capacitor 212.
1 is input to the inverting input terminal (−) of the operational amplifier 501.

The output of the amplification amplifier 51 serving as a part of the APC control amplifier is connected to the base b of the transistor 61 as a current output element. The collector c of the transistor 61 is a laser diode 1 constituting the SHG laser 10.
1 cathode. The amplification amplifier 51 is connected between the operational amplifier 511, the resistor 512 connected to the non-inverting input terminal (+) of the operational amplifier and the terminal 3 of the resistor 803, and the output terminal (O) of the operational amplifier 511 and the base b of the transistor 61. A parallel circuit of a resistor 513 and a capacitor 514, and a diode 515 connected between the base b and the emitter e of the transistor 61. The transistor 61 includes transistors 611 and 612 connected in Darlington. The emitter e of the transistor 61 is connected to the collector c of the transistor 71.

A part of the laser beam L output from the resonator 12 of the SHG laser 10 is configured to be incident on the photodetector 32 constituting the APC feedback circuit 31. AP
The amplifying unit 33 included in the C feedback circuit 31 includes an operational amplifier 331 having an inverting input terminal (-) connected to the light detecting unit 32, a non-inverting input terminal (+) connected to the ground, and an inverting input terminal (-). A parallel feedback circuit including a series circuit of resistors 332 and 333 connected to the output terminal (O) and a capacitor 335; a variable resistor 33 connected in parallel to the resistor 333;
Consists of four.

The laser light L detected by the light detection unit 32 is
After being converted into an electric signal, the signal is input to the amplifier 33, and the voltage output of the amplifier 33 is output from the output VF of the APC feedback circuit 31.
B2 is input to the inverting input terminal (−) of the operational amplifier 511 via a parallel circuit of the resistor 331 and the capacitor 332.

The drive control device 1 is provided with a controller 42 for centrally controlling the operation of the drive control device 1. The controller 42 has a CPU (microprocessor) 429 and an operational amplifier 425 connected to a voltage follower. A capacitor 424 is provided between the non-inverting input terminal (+) of the operational amplifier 425 and the ground.

The control signal AVPS representing the light intensity command value output from the CPU 429 is input to the non-inverting input terminal (+) of the operational amplifier 425. The signal obtained at the output terminal (O) of the operational amplifier 425 is supplied to the C terminal via the resistor 426.
An operational amplifier 511 which is combined with a control signal SP for turning on / off the APC control output from the PU 429 and constitutes the amplification amplifier 51 functioning as an APC control amplifier
Are input to the inverting input terminal (−).

On the other hand, a control signal ACCSIG representing the light intensity command value output from the CPU 429 and the CPU 42
9 and a control signal SC for turning on / off the ACC control are synthesized and input to the inverting input terminal (−) of the operational amplifier 501 constituting the amplification amplifier 50 functioning as the ACC control amplifier.

The controller 42 is provided with the temperature control means 1
8 to determine whether or not the SHG laser 10 is in a steady state, and control the control signals SC and SP in accordance with the result of the determination to control the drive of the SHG laser 10. ACC control → ACC control + AP
The laser diode 1 of the SHG laser 10 is switched by sequentially switching from C control to APC control (to be described in detail later) and by setting the control signal ACCSIG to a predetermined size.
1 is set and the control signal APVS is set.
Is set to a predetermined size to set the light output (light amount) PD of the SHG laser 10.

As can be seen from the above configuration, the SHG laser 1
ACC control means 20 for controlling the current flowing through
Is constituted by a loop composed of the ACC feedback circuit 21, the amplification amplifier 50, the transistors 60 and 71, and the current detection means 80. On the other hand, the feedback control loop by the APC control means 30 is the APC feedback circuit 3.
1, a loop composed of an amplifier 51, a transistor 60 and a laser diode 11.

The inverting input terminal 72a of the comparison control means 72 constituting the current limiting means 70 has a current detection signal (voltage value) V detected at the terminal 80a of the current detection means 80.
S is input, and the reference voltage signal V from the reference voltage generation circuit 73 is applied to the non-inverting input terminal 72b of the comparison control means 72.
REF is input and the output 72 of the comparison control means 72
c is connected to the base b of the transistor 71.

The comparison control means 72 includes transistors 721 and 722 having both emitters differentially connected,
The resistor 7 connected between the collector of the power supply 21 and the positive power supply 13
23, a resistor 724 connected between both emitters and the negative power supply 15, a base of the transistor 722 and the transistor 7
1, a resistor 725 connected between the base and the collector of the transistor 722, a resistor 727 connected between the collector of the transistor 722 and the positive power supply 13, and a transistor 722. And a capacitor 728 connected between the collector and the ground.

The reference voltage generation circuit 73 is connected to the positive power supply 1
6 comprises a series circuit of a resistor 731 and a variable resistor 732 connected between the resistor 6 and the ground, and an operational amplifier 733 connected by a voltage follower. The variable terminal of the variable resistor 732 is input to the non-inverting terminal (+) of the operational amplifier 733,
The output terminal (O) of the operational amplifier 733 is the comparison control unit 72
Is connected to the base of the transistor 721 constituting

Although not shown, each operational amplifier is connected to both positive and negative power supplies.

FIG. 5 is a functional block diagram of the semiconductor laser drive control device 1 having the configuration shown in FIG. That is, the anode of the laser diode 11 constituting the SHG laser 10 is connected to the positive power supply 13, and the cathode of the laser diode 11 is connected to the transistor 60,
Connected to 61 collectors. ACC control amplifier 2 including ACC feedback circuit 21 and part of amplification amplifier 50
The output of Oa is connected to the base of transistor 60.
The output of the APC control amplifier 30a comprising a part of the APC feedback circuit 31 and the amplification amplifier 50 is a transistor 61
Connected to the base. The emitters of the transistors 60 and 61 are substantially connected by the addition circuit 19, and the output of the addition circuit 19 is connected to the collector of the transistor 71 constituting the current limiting means 70. The emitter of the transistor 71 is connected to the ground via a series circuit of resistors 81 and 82 as current detecting means 80. The inverting input terminal (-) of the comparison control means 72 corresponding to the base of the transistor 722 is connected to the emitter of the transistor 71. A reference voltage signal VREF representing a current limit value is input to a non-inverting input terminal (+) of the comparison control means 72 corresponding to the base b of the transistor 721. The output of the comparison control means 72 is input to the base of the transistor 71.

The signal VFB1 obtained at the connection point between the resistors 81 and 82 corresponding to the terminal 1 of the resistor 803 in FIG. 4, that is, at the terminal 80c of the current detecting means 80 is supplied to the inverting input terminal (-) of the ACC control amplifier 20a. Connected adder circuit 91
Is input to The control signal ACCSIG indicating the current command value output from the controller 42 and the control signal SC for turning on / off the ACC control are added by the adding circuit 90, and the result is input to the adding circuit 91, and the result is input to the adding circuit 91. The signal VFB1 representing the current amount of the laser diode 11 obtained at the terminal 80c is further added to the result, and the result is the inverted input terminal (-) of the ACC control amplifier 20a.
Is input to

On the other hand, the laser light L emitted from the SHG laser 10 is converted into a voltage signal VFB2, and is input to the addition circuit 92 connected to the inverting input terminal (-) of the APC control amplifier 30a. The control signal APVS representing the light amount command value output from the controller 42 and the control signal SP for turning on / off the APC control are added by an adder circuit 93, and the result is input to an adder circuit 92 to further generate a voltage signal VFB2 and a voltage signal VFB2. The result is added to the inverted input terminal (-) of the APC control amplifier 30a.

Hereinafter, the operation of the semiconductor laser drive control device 1 having the above configuration will be specifically described with reference to FIGS. First, a drive control method for controlling the current ID flowing through the SHG laser 10 will be described.

Power is supplied to the drive control device 1 and SH
When the G laser 10 is activated, the laser diode L <b> 0 constituting the SHG laser 10 emits laser light L <b> 0 as excitation light, and the output laser light L wavelength-converted by the resonator 12 is emitted from the resonator 12. .

The temperature of the SHG laser 10 is detected by a temperature detecting element (not shown) such as a thermistor.
The Peltier element 19 is driven and controlled based on the control signal D1 corresponding to 0, and as a result, feedback control is performed so that the SHG laser 10 is maintained at the final target temperature value.

In the drive control device 1, when the SHG laser 10 is started, the first ACC control method of the present invention is selected as the current control method of the SHG laser 10.

In order to select the first ACC control method, first, the controller 42 sets the control signal SP output from the CPU 429 to 0 V, and makes the APC control loop inactive. The control signal ACCSIG as a current command value is supplied to the operational amplifier 501 via the resistor 427 so that the value IC1 of the current ID flowing through the SHG laser 10 becomes substantially equal to the steady current amount I0 corresponding to the reference light output P0.
To the inverting input terminal (-).

The drive control device 1 in such a state
Performs ACC control that keeps the current amount ID substantially constant so that the current amount ID flowing to the SHG laser 10 becomes substantially equal to the steady current amount I0 corresponding to the reference light output P0 in the steady state.

Next, as the SHG laser 10 approaches a steady state, the temperature of the SHG laser 10 is stabilized, and
When the light output of the G laser 10 approaches the reference light output P0, the second ACC control method of the present invention is performed as the current control method of the SHG laser 10 and the first A of the present invention is controlled.
A control method for performing PC control is selected.

In order to select a current control method combining the second ACC control and the first APC control, the controller 42 first sets the control signal SP output from the CPU 429 to a predetermined value (other than 0 V). To make the APC control loop active. Next, in this state, the variable resistor 334 of the amplifier 30 is adjusted so that the voltage of the output terminal (O) of the operational amplifier 331 corresponds to the reference light output P0, and the control signal APVS as the light amount command value is changed. The signal is input to the non-inverting input terminal (-) of the operational amplifier 425. Further, the value IC2 of the current ID flowing to the SHG laser 10 by the second ACC control is equal to or less than the steady current amount I0 corresponding to the reference light output P0, for example, 50 to 90% of the steady current amount I0.
Control signal ACCSI as a current command value
G is input to the inverting input terminal (−) of the operational amplifier 501 via the resistor 427.

The drive control device 1 in such a state
In the first APC control, the shortage of the optical output corresponding to the current amount IC2 by the second ACC control is compensated by the first APC control, so that the optical output PD of the semiconductor laser is kept at the reference optical output P0. Control as follows. Therefore,
The drive control device 1 includes the second ACC control and the first A
"ACC control + APC control" combined with PC control
New current control, and as a result, the second AC
The current I flowing through the SHG laser 10 obtained by adding the current IC2 obtained by the C control and the current IP1 obtained by the first APC control.
D is controlled so as to be substantially equal to and substantially constant to the steady-state current amount I0 corresponding to the reference light output P0 in the steady state.

Next, after a lapse of a predetermined time, the SHG laser 1
As the drive control method of 0, the second APC control of the present invention is selected. That is, the controller 42 keeps the value of the control signal APVS as the light amount command value, and
The control signal SC output from the control unit 29 is set to 0 V to deactivate the ACC control loop.

The drive control device 1 in such a state
In the second APC control, the light output PD of the SHG laser 10 is changed to the reference light output P0 only by the second APC control.
APC control is performed so that the light amount value becomes substantially constant and the light amount value becomes substantially constant.

Next, the current limiting operation will be briefly described. The current ID flowing through the laser diode 11 flows to the ground via the transistor 71 forming the current limiting means 70 and the resistors 81 and 82 forming the current detecting means 80. The voltage signal VS corresponding to the value of the current ID is the resistance 8
1, 82, and this voltage signal VS
Is the base b of the transistor 722, that is, the comparison control means 72
Is input to the inverting input terminal (−).

The reference voltage VREF is input from the reference voltage generation circuit 73 to the base b of the transistor 721, that is, the non-inverting input terminal (+) of the comparison control means 72. When the voltage signal VS is lower than the reference voltage VREF, The collector and emitter of the transistor 71 are substantially short-circuited. On the other hand, when the current ID flowing through the laser diode 11 increases and the voltage signal VS becomes equal to or higher than the reference voltage VREF, a predetermined voltage is generated between the collector and the emitter of the transistor 71. As a result, transistors 60a,
The potential of both emitters 60b rises, and acts to reduce the ACC current IC by the ACC control amplifier 20a and the APC current IP by the APC control amplifier 30a. Therefore, the transistor 71 and the comparison control circuit 72
In the negative feedback loop so that the value of the current ID flowing through the laser diode 11 never exceeds a predetermined value corresponding to the reference voltage VREF.

In the circuit shown in FIG. 4, a negative feedback loop is formed through differential transistors 721 and 722, and the circuit configuration is extremely simple. It can be good. That is, even when the current flowing through the laser diode 11 becomes pulse-like, the amount of flowing current can be reliably suppressed to the maximum allowable current value or less.

[Brief description of the drawings]

FIG. 1 is a basic block diagram showing a configuration of an embodiment of a semiconductor laser drive control device according to the present invention.

FIG. 2 is a timing chart showing a drive control method of a semiconductor laser according to the present invention and a relationship between an amount of current flowing through the semiconductor laser and an optical output;

FIG. 3 is a diagram showing another example of the current limitation.

FIG. 4 is a diagram showing an example of a circuit embodying the basic block diagram of FIG. 1;

FIG. 5 is a functional block diagram of the circuit shown in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 SHG laser 20 ACC control means 30 APC control means 70 Current limiting means 71 Transistor 73 Comparison control means 80 Current detection means

Claims (8)

[Claims] 1. A semiconductor laser drive control method for controlling an optical output of a semiconductor laser by controlling a current flowing through the semiconductor laser, wherein when starting up the semiconductor laser, an amount of current flowing through the semiconductor laser is in a steady state. Performing a first ACC control that keeps the current amount substantially constant so as to be near a steady-state current amount corresponding to the reference light output; and when the light output of the semiconductor laser approaches the reference light output, the ACC control is performed. A second ACC control for keeping the current amount substantially constant so that the current amount becomes a value corresponding to a predetermined light output equal to or less than the reference light output is performed, and the light output of the semiconductor laser is changed to the reference light output. A semiconductor laser drive control method, comprising: performing first APC control for maintaining output. 2. The second ACC control and a first AP
After a predetermined time has elapsed after the start of the C control, the second AC
2. The semiconductor laser drive control method according to claim 1, further comprising: stopping the C control and the first APC control, and performing a second APC control for keeping an optical output of the semiconductor laser at the reference optical output. 3. The semiconductor laser drive control method according to claim 1, wherein during the predetermined time, the current is limited so that the amount of current flowing through the semiconductor laser is equal to or less than a predetermined value. 4. A semiconductor laser drive control device for controlling an optical output of the semiconductor laser by controlling a current flowing through the semiconductor laser, wherein when the semiconductor laser is started, the amount of current flowing through the semiconductor laser is in a steady state. First ACC control means for performing first ACC control for keeping the current amount substantially constant so as to be close to the steady-state current amount corresponding to the reference light output; A second ACC control that operates when approaching the output and maintains the current amount substantially constant so that the amount of current flowing through the semiconductor laser corresponds to a predetermined light output that is equal to or less than the reference light output is performed. A semiconductor laser drive comprising: a second ACC control means; and an APC control means for performing a first APC control for keeping the light output of the semiconductor laser at the reference light output. Control device. 5. The second ACC control means, wherein:
5. The semiconductor laser drive control device according to claim 4, wherein the device stops after a predetermined time has elapsed after the start of the ACC control and the first APC control. 6. A current detecting means for detecting an amount of current flowing through the semiconductor laser during the predetermined time, and a current limiter for performing a current limit based on the detected amount of current such that the amount of current becomes a predetermined value or less. 5. The semiconductor laser drive control device according to claim 4, further comprising means. 7. The semiconductor laser according to claim 6, wherein said current limiting means is connected to said semiconductor laser such that a total current flowing through said semiconductor laser flows through said current limiting means.
14. A semiconductor laser drive control device according to claim 1. 8. The current detection means has a current-to-voltage conversion function, and the current limiting means includes a transistor through which the entire current flows between a collector and an emitter, and a transistor for detecting the total current converted by the current detection means. By comparing the voltage value representing the value and the reference voltage value representing the predetermined value, when the value of the total current is equal to or more than the predetermined value, a voltage such that the collector-emitter voltage of the transistor increases. 8. The semiconductor laser drive control device according to claim 7, further comprising means for inputting a signal to a base of said transistor.