JP2013197371A - Drive circuit, light source device, light amplifier, and driving method - Google Patents

Abstract

An object of the present invention is to suppress a deviation of a transmission wavelength that may occur when adjusting an output of a laser diode.
A drive circuit is a drive circuit that drives a plurality of laser diodes connected in parallel to each other, and the number of laser diodes to be lit is a target output to which a total output of the laser diodes to be lit is given. Is provided with a control unit 11 that controls to match or substantially match.
[Selection] Figure 1

Description

  The present invention relates to a driving circuit and a driving method for driving a plurality of laser diodes. The present invention also relates to a light source device provided with such a drive circuit and an optical amplifier provided with such a light source device.

  BACKGROUND ART Fiber lasers are widely used as laser processing machines that perform cutting and welding with laser light. The fiber laser is a laser oscillator that uses an optical fiber as a laser medium, and includes an amplification fiber to which a rare earth is added and a light source device that emits excitation light to be introduced into the amplification fiber. In a high-power fiber laser used as a laser processing machine, a light source device including a plurality of laser diodes is used, and pumping light is obtained by combining laser beams emitted from these laser diodes by a pump combiner. The configuration is common.

  By the way, in such a fiber laser, it is known that the amplification factor fluctuates due to the fluctuation of the wavelength of the excitation light. For example, when the wavelength of the pumping light deviates from the target wavelength, the absorption rate of the pumping light in the amplification fiber decreases, and as a result, the amplification factor of the fiber laser decreases.

  The wavelength of the laser light emitted from the laser diode depends on the magnitude of the drive current supplied to the laser diode and the temperature of the laser diode. For this reason, if the drive current and temperature of the laser diode used as the excitation light source change, the amplification factor of the fiber laser will change. Therefore, in order to increase the amplification efficiency of the fiber laser, it is necessary to control the drive current and temperature of the laser diode used as the excitation light source so that the wavelength of the excitation light matches the target wavelength.

  For example, in Patent Document 1 below, a part of the output light of the excitation laser diode is extracted and dispersed, the deviation of the oscillation wavelength from the target wavelength is detected, and the result is fed back to the temperature adjustment circuit and the setting is made. A technique for stabilizing the oscillation wavelength by adjusting the temperature is disclosed.

  In Patent Document 2 below, laser resonance occurs between the excitation LD element and the wavelength selective reflection device by reflecting only light of a specific wavelength by the wavelength selective reflection device of the excitation light generated by the excitation LD element. A technology is disclosed that constitutes a laser and oscillates only the light of the specific wavelength. According to this technology, it is possible to provide an optical amplifier in which the wavelength of pumping light does not change with respect to temperature change.

Japanese Patent Laid-Open No. 5-90672 (published on April 9, 1993) Japanese Patent Laid-Open No. 11-186642 (published July 9, 1999)

  However, the technique disclosed in Patent Document 1 requires a mechanism for monitoring the temperature and a mechanism for adjusting the temperature in order to stabilize the laser diode oscillation wavelength. Not only will the cost be increased, but the cost will increase.

  Further, in the technique disclosed in Patent Document 2, since it is necessary to insert an expensive wavelength selective reflection device on the excitation light path, the light emission efficiency of the laser diode is reduced due to the insertion loss. Not only will the cost increase.

  On the other hand, conventionally, a method of adjusting the output of the laser diode by adjusting the magnitude of the driving current of the laser diode has been used. However, as described above, since the wavelength of the excitation light depends on the magnitude of the drive current of the laser diode, in this method, the wavelength of the excitation light changes with the adjustment of the output of the laser diode, and the fiber laser The amplification efficiency will be reduced.

  As described above, conventionally, there are various problems in the technology for stabilizing the output wavelength of the laser diode and the technology for adjusting the output of the laser diode.

  The present invention has been made in view of the above-described problems, and an object thereof is to suppress a deviation in oscillation wavelength that may occur when adjusting the output of a laser diode.

  In order to solve the above-described problems, a drive circuit according to the present invention is a drive circuit for driving a plurality of laser diodes connected in parallel to each other, and for each of the plurality of laser diodes, the laser diode is specified. The magnitude of the output obtained when oscillating at a wavelength is predetermined, and the total output of the laser diodes to be lit gives the number of laser diodes to be lit based on the above-mentioned predetermined output magnitude. And a control unit that controls to match or substantially match the set target output.

  According to the above configuration, the number of laser diodes to be lit is controlled based on a predetermined value as the magnitude of output obtained when the laser diode oscillates at a specific wavelength as described above. It is. Therefore, it is possible to realize a drive circuit that has a simpler configuration and lower cost than the conventional feedback control.

  Here, that the total output substantially matches the target output means that the total output matches the target output with an accuracy that can be achieved by increasing or decreasing the number of laser diodes to be lit. For example, when the output of each laser diode is 5 W, it can be said that the total output substantially matches the target output if the difference between the total output and the target output is smaller than 5 W.

  When the drive current supplied to the laser diode is determined, the output of the laser diode and the power consumption of the laser diode are determined. When the power consumption of the laser diode is determined, the temperature of the laser diode at a specific environmental temperature is determined, and as a result, the oscillation wavelength of the laser diode is determined (strictly speaking, the oscillation wavelength of the laser diode is It depends on the drive current supplied to the laser diode itself). That is, there is a certain correspondence between the laser diode drive current, output, and oscillation wavelength. Therefore, when the laser diode is oscillated at a specific wavelength, the magnitude of the output obtained by the laser diode is an amount that can be determined in advance by experiments or the like.

  In the drive circuit according to the present invention, the control unit sets, for each of the laser diodes to be lit, the magnitude of the drive current supplied to the laser diode as the magnitude of the drive current that causes the laser diode to oscillate at a specific wavelength. It is preferable to control to a predetermined value.

  According to said structure, the wavelength of the laser beam oscillated from each of said several laser diode can be made to correspond with the said specific wavelength. That is, by combining the laser light oscillated from each of the plurality of laser diodes, it is possible to generate light whose output substantially matches the target output and whose wavelength matches the target wavelength.

  Note that, as described above, there is a certain correspondence between the three of the laser diode drive current, output, and oscillation wavelength. Therefore, in order to oscillate a laser diode at a specific wavelength, the magnitude of the drive current to be supplied to the laser diode is an amount that can be determined in advance by experiments or the like.

  In the drive circuit according to the present invention, the control unit determines the magnitude of the drive current supplied to the laser diode for each of the N-1 laser diodes among the N laser diodes to be lit. The magnitude of the drive current for causing the diode to oscillate at a specific wavelength is controlled to a predetermined value, and the drive current supplied to the laser diode for the remaining one of the N laser diodes Is preferably controlled so that the total output of the N laser diodes matches a given target output.

  According to said structure, the wavelength of the laser beam oscillated from each of the said N-1 laser diode can be made to correspond with the said specific wavelength. In addition, the wavelength of the laser light oscillated from the remaining one laser diode can be made substantially coincident with the specific wavelength. Therefore, by combining the laser light oscillated from each of the plurality of laser diodes, it is possible to generate light whose output matches the target output and whose wavelength substantially matches the target wavelength.

  The drive circuit according to the present invention supplies, for each of the plurality of laser diodes, a predetermined value as the magnitude of the drive current that causes the laser diode to oscillate at the specific wavelength, and a drive current of that magnitude. A laser storing a table in which a predetermined value as a magnitude of the output of the laser diode obtained is stored, and the control unit refers to the table to turn on the laser It is preferable to determine the number of diodes and the magnitude of the drive current supplied to each of the laser diodes to be lit.

  According to the above configuration, the total output of the plurality of laser diodes can be adjusted to the target output without monitoring the intensity and wavelength of the laser light oscillated from the plurality of laser diodes. That is, it is possible to simplify the configuration of the drive circuit and reduce its cost without sacrificing the above-described effects.

  In order to solve the above-described problem, a light source device according to the present invention includes a plurality of laser diodes and the driving circuit that is a driving circuit for driving the plurality of laser diodes. To do.

  Thus, a light source device including the plurality of laser diodes and the driving circuit is also included in the scope of the present invention.

  In the light source device according to the present invention, each of the plurality of laser diodes is preferably attached to a heat sink insulated from each other.

  According to the above configuration, lighting a certain laser diode does not increase the temperature of other laser diodes. Therefore, it becomes possible to determine the drive current supplied to a certain laser diode without referring to whether or not other laser diodes are lit. Therefore, the configuration for determining the drive current supplied to each laser diode is simplified.

  In order to solve the above-described problems, an optical amplifier according to the present invention is combined by the light source device, a pump combiner that combines the laser beams oscillated from the plurality of laser diodes, and the pump combiner. And a laser medium using the laser light as excitation light.

  According to said structure, since the said laser beam by which the shift | offset | difference of the oscillation wavelength was suppressed can be utilized as said excitation light, the optical amplifier with the high amplification efficiency can be provided.

  In order to solve the above-described problem, a driving method according to the present invention is a driving method for driving a plurality of laser diodes connected in parallel to each other, and each of the plurality of laser diodes includes the laser diode. The size of the output obtained when the laser is oscillated at a specific wavelength is determined in advance, and the number of laser diodes to be lit is determined based on the predetermined output size, and the total number of laser diodes to be lit It includes a control step of controlling the output so as to match or substantially match a given target output.

  According to said structure, there can exist an effect similar to the said drive circuit.

  According to the present invention, with a relatively simple configuration, it is possible to suppress the deviation of the transmission wavelength that may occur when adjusting the output of the laser diode.

It is a block diagram which shows the outline of the laser apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the outline of the fiber laser which concerns on one Embodiment of this invention. (A) is a figure which shows the drive current dependence of the oscillation wavelength in the some laser diode which concerns on one Embodiment of this invention. (B) is a figure which shows the drive current dependence of the output power in the said several said laser diode. It is a figure which shows the look-up table which concerns on one Embodiment of this invention. It is a perspective view which shows the structure of the laser diode which concerns on one Embodiment of this invention, and a heat sink. (A) is a figure which shows the drive current dependence of the oscillation wavelength in the laser diode which concerns on 1 aspect of this invention. (B) is a figure which shows the drive current dependence of the output power in the said laser diode. (C) is a figure which shows the outline of each oscillation wavelength spectrum of each said diode, and the combined oscillation wavelength spectrum.

  An embodiment of the present invention will be described below with reference to the drawings.

(Fiber laser 100)
First, a fiber laser 100 according to an embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing an outline of a fiber laser according to an embodiment of the present invention. As shown in FIG. 2, the fiber laser 100 includes a laser device 40, a laser beam multiplexer 50, and an amplification fiber 60.

  The laser device 40 includes n laser diodes LD1 to LDn arranged in parallel and a drive circuit 10 for driving the diodes LD1 to LDn, and each laser diode oscillates a laser beam having a predetermined wavelength λp. . Each laser beam oscillated from each laser diode is introduced into an optical fiber corresponding to each laser diode.

  The n optical fibers are combined into one optical fiber in the pump combiner 50 (laser light multiplexing unit). That is, the laser light oscillated by the n laser diodes is multiplexed in the pump combiner 50.

  The combined laser light is introduced into an amplification fiber 60 that is a gain medium (laser medium). Rare earth ions such as ytterbium and erbium are added to the core of the amplification fiber 60. The combined laser beam functions as pump light that excites rare earth ions.

  When signal light is incident on the amplification fiber 60 in a state where the rare earth ions are excited, the signal light is amplified and then emitted as output light.

(Laser device 40)
Next, the configuration of the laser device will be specifically described with reference to FIG. FIG. 1 is a block diagram showing an outline of a laser apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the laser device 40 includes a drive circuit 10, a power source 21, a user interface 22, and n laser diodes LD1 to LDn. The laser diodes LD1 to LDn are electrically arranged in parallel. The laser diodes LD1 to LDn are installed in heat sinks 31a to 31n for the laser diodes LD1 to LDn to insulate each other (that is, to break the thermal contact). In the present embodiment, the power source 21 is a constant voltage power source.

  In the laser device 40 configured as described above, the target output of the laser light oscillated by the laser device 40 is input by the user via the user interface 22. The drive circuit 10 controls the number of laser diodes to be lit so that the total output of the lit laser diodes matches or substantially matches the given target output.

  In particular, the drive circuit 10 controls the magnitude of the drive current supplied to each laser diode that is lit to a value that causes the laser diode to oscillate at a specific wavelength.

  As a result, each laser diode oscillates a laser beam having a specific wavelength (that is, a laser beam in which the wavelength shift is suppressed). Then, the total output of the laser light oscillated from each laser diode matches or substantially matches the given target output.

  In the present embodiment, “driving a laser diode” means that the laser diode is oscillated. Therefore, “to drive the laser diode” includes supplying a drive current from a state in which no current is supplied to the laser diode, and any current that does not cause laser light to oscillate to the laser diode ( For example, it includes both of supplying a driving current from a state of supplying a standby current).

(Drive circuit 10)
Hereinafter, the configuration of the drive circuit 10 will be specifically described.

  As shown in FIG. 1, the drive circuit 10 includes a control unit 11 (control means) and n drive units 12. The n driving units 12 are electrically arranged in parallel corresponding to the laser diodes LD1 to LDn. In the following, the driving unit 12 corresponding to the laser diode LD1 is the first driving unit 12a, the driving unit 12 corresponding to the laser diode LD2 is the second driving unit 12b, and the driving unit 12 corresponding to the laser diode LDn is the first driving unit 12. This will be referred to as n driving unit 12n.

  Each drive unit 12 controls the drive current supplied to each laser diode. Specifically, each control unit 11 is notified of a current value of a predetermined drive current from the control unit 11. In response to this, each drive unit 12 generates a drive current having the notified current value, and supplies the generated drive current to the corresponding laser diode.

  Each drive unit 12 has the same configuration, and includes a current control element 13, a current control element drive circuit 14, and a current detection resistor 15. For example, the first drive unit 12a includes a current control element 13a, a current control element drive circuit 14a, and a current detection resistor 15a.

  The current control element 13a includes a field effect transistor (FET). The current control element drive circuit 14a inputs a drive signal to the gate portion of the FET. The drain portion of the FET is connected to the current detection resistor 15a, and the source portion of the FET is connected to the laser diode LD1.

  The current control element 13a supplies a current corresponding to the drive signal supplied from the current control element drive circuit 14a to the laser diode LD1.

  The controller 11 outputs the value of the drive current IDL1 to be supplied to the laser diode LD1 to the current control element drive circuit 14a.

  The current control element drive circuit 14a receives the value of the drive current IDL1 to be supplied to the laser diode LD1 from the control unit 11, and also receives the voltage value at both ends of the current detection resistor 15a. The current control element driving circuit 14a calculates a current (denoted as I15a) flowing through the current detection resistor 15a from the input voltage value.

  Further, the current control element drive circuit 14a compares the current I15a with the drive current IDL1. When the current I15a is smaller than the drive current IDL1, a drive signal for increasing the current value is supplied to the current control element 13a. On the other hand, when the current I15a is larger than the drive current IDL1, a drive signal for reducing the current value is supplied to the current control element 13a. By the current control described above, the current I15a and the drive current IDL1 become equal. That is, a predetermined drive current ILD1 is supplied to the laser diode LD1.

  In the second drive unit 12b to the nth drive unit 12n, the same current control as the current control in the first drive unit 12a is performed. As a result, predetermined drive currents ILD2 to ILDn are supplied to the laser diodes LD2 to LDn, respectively.

  The current control means is not limited to the above configuration. Any current control means capable of supplying a desired current can be used as the current control means included in the drive circuit 10.

(Characteristics of laser diode)
Here, the characteristics of the laser diode provided in the laser device 40 will be described with reference to FIGS.

  FIG. 3A is a diagram showing an example of the drive current dependence of the oscillation wavelength in the laser diodes LD1 and LD2. Here, the peak wavelength in the laser beam spectrum emitted from the laser diode is defined as the oscillation wavelength.

  The oscillation wavelength of the laser diode has a positive correlation with the drive current. For example, in the laser diode LD1, as the drive current ILD1 is increased, the temperature of the laser diode rises and the oscillation wavelength is shifted to the longer wavelength side.

  Each laser diode has a unique correlation between oscillation wavelength and drive current. For example, the laser diodes LD1 and LD2 exhibit drive current dependency of different oscillation wavelengths (see FIG. 3A).

  Specifically, the laser diode LD1 oscillates a laser beam having a predetermined oscillation wavelength λp at a drive current of 6.0A. That is, ILD1 = 6.0A. On the other hand, the laser diode LD2 oscillates laser light having a predetermined oscillation wavelength λp at a drive current of 6.2A. That is, ILD2 = 6.2A.

  Accordingly, the first drive unit 12a supplies 6.0 A as the drive current ILD1 to the laser diode LD1 in order for the laser diode LD1 to oscillate laser light having a predetermined oscillation wavelength λp. The second current control means supplies 6.2 A as the drive current ILD2 to the laser diode LD2 so that the laser diode LD2 oscillates laser light having a predetermined oscillation wavelength λp.

  FIG. 3B is a diagram showing the drive current dependence of the output power of the laser light oscillated from the laser diode. The laser diode does not oscillate until the supplied drive current exceeds a threshold current. In a region where the drive current exceeds the threshold current (hereinafter referred to as a laser oscillation region), the drive current and the output power have a linear relationship. In the laser oscillation region, each laser diode exhibits a drive current dependency of its specific output power.

  As shown in FIG. 3B, when ILD1 = 6.0 A is supplied to the laser diode LD1 as a drive current, the output power of the laser diode LD1 becomes 5.0W. On the other hand, when ILD2 = 6.2 A is supplied as a drive current to the laser diode LD2, the output power of the laser diode LD2 is 5.1W.

  Thus, in the present embodiment, each laser diode is driven by a predetermined drive current that oscillates laser light having a predetermined oscillation wavelength λp, and oscillates laser light with an output determined by the characteristics of each laser diode. In other words, the laser device 40 can be said to be a laser device that can oscillate laser light whose oscillation wavelength is unified to λp.

(Lookup table)
Next, with reference to FIG. 4, a lookup table provided in the drive circuit 10 will be described. FIG. 4 is a diagram illustrating a lookup table according to an embodiment of the present invention. The drive circuit 10 includes a memory 16 that stores a lookup table.

  In this look-up table, for each laser diode, a drive current whose oscillation wavelength is a predetermined oscillation wavelength λp is shown as a predetermined drive current. The control unit 11 of the drive circuit 10 is configured to obtain a current value of a predetermined drive current of each laser diode by referring to this lookup table.

  As shown in FIG. 4, the look-up table (hereinafter referred to as LUT) associates the number of each laser diode with the drive current, output power, and total output power of each laser diode. Yes. The LUT shown in FIG. 4 is an LUT in the case where the laser device 40 includes 10 laser diodes.

  Each laser diode is assigned a number from 1 to 10. That is, it is described in the LUT as LD1 to LD10.

  In each of the laser diodes LD1 to LD10, the drive current dependency of the oscillation wavelength is examined in advance, and predetermined drive currents ILD1 to ILD10 that oscillate a predetermined oscillation wavelength λp are obtained. Predetermined drive currents ILD1 to ILD10 are stored in the drive current column in the LUT.

  Similarly, the output power when each laser diode is driven by a predetermined drive current is also examined and stored in the output power column in the LUT.

  The total output power in the LUT means the sum of output powers of i laser diodes from LD1 to LDi. For example, regarding LUT LD3, since i = 3, the total output power is the sum of the output powers of the three laser diodes LD1, LD2, and LD3.

  Note that the LUT only needs to include at least the drive current and output power for each laser diode, and can have any other configuration. For example, the total output power may not be included in the LUT. Even in this case, the control unit 11 can easily obtain the total output power based on the output power indicated in the LUT. Can do.

(Control unit 11)
The control unit 11 of the drive circuit 10 has the largest difference between the total output of the laser diodes and the target output input via the user interface 22 based on the total output power of each laser diode obtained from the LUT. A combination of laser diodes to be driven is determined so as to be small.

  For example, the control unit 11 calculates the difference between the total output power corresponding to the LD1 and the target output as the first difference. Next, the control unit 11 calculates a difference between the total output power in the LD 2 and the target output as a second difference. The control unit 11 similarly calculates the third difference to the tenth difference. The control unit 11 selects the one having the minimum absolute value from the first difference to the tenth difference. And the control part 11 determines the laser diode corresponding to the selected difference as LDi, and determines LD1-LDi as a combination of the laser diode of a drive object.

  Next, the controller 11 supplies predetermined drive currents to the current control element drive circuits 14 corresponding to the LDs LD1 to LDi. As a result, each of the laser diodes LD1 to LDi oscillates at the wavelength λp, and the laser device 40 oscillates laser light having an output power close to the target output.

  Control performed by the control unit 11 will be described using a specific target output. For example, it is assumed that the control unit 11 receives a target output of 20 W via the user interface 22. The control unit 11 calculates the tenth difference from the first difference. As a result, the first difference is 15.0 W, the second difference is 9.9 W, the third difference is 4.5 W, the fourth difference is -0.3 W, and the fifth difference is -5.3 W. Become. Here, the description after the sixth difference is omitted.

  Therefore, the control unit 11 determines that the minimum difference is the fourth difference. As a result, the control unit 11 drives the laser diodes LD1 to LD4 with respective predetermined current values. That is, the total output of the laser light with the wavelength λp output from the laser device 40 is 20.3 W.

  Here, a configuration is described in which the control unit 11 selects an LD number that minimizes the difference between the target output and the total output power of the LUT regardless of whether or not the total output power exceeds the target output. It was.

  Here, the control unit 11 may be configured to select an LD number that minimizes the difference between the target output and the total output power of the LUT within a range in which the total output power does not exceed the target output. In the case where inconvenience occurs when the total output of the laser light of wavelength λp output from the laser device 40 exceeds the target output desired by the user, such a configuration can be adopted.

  In this case, the control unit 11 selects an LD number that has a positive difference between the target output and the accumulated output power of the LUT and has the smallest difference. For example, if the target output is 20 W, the control unit 11 determines that the third difference is the minimum. As a result, the laser diodes LD1 to LD3 are driven with respective predetermined current values. As a result, the total output of the laser light oscillated by the laser device 40 is 15.5W.

  As described above, the laser device 40 of the present embodiment includes an LUT that associates each laser diode with a drive current for oscillating laser light having a predetermined wavelength in each laser diode. Thereby, the laser apparatus 40 of this embodiment can obtain the drive current of each laser diode with an easy and simple configuration. Further, since the current value of each drive current does not fluctuate, it is possible to stably and reliably oscillate laser light having a predetermined wavelength for each laser diode.

  The laser device 40 of the present embodiment records the output when each laser diode oscillates at the wavelength λp in the LUT, and based on the output of each laser diode, the total output of the laser diode to be driven and the target A combination of laser diodes having the smallest difference from the output is determined as a combination of laser diodes to be driven. Thereby, the laser apparatus 40 of this embodiment can make the output of a laser diode the appropriate thing which approached target output.

  The control unit 11 may select a combination of laser diodes that minimizes the difference between the target output and the total output, and that does not have the LD number consecutive from the top (LD1). Thereby, the difference between the target output and the total output can be further reduced.

  For example, when the target output is 20 W, the control unit 11 may set the total output of the laser light oscillated by the laser device 40 to 20.0 W by selecting a combination of the laser diodes LD2, LD4, LD6, and LD10. it can. That is, the target output and the total output can be made equal.

  Thus, in order to select a laser diode combination that minimizes the difference between the target output and the total output, a program that operates according to a known algorithm may be used. The program may be stored in the memory 16 included in the drive circuit 10.

(Measures against heat of laser device 40)
Next, with reference to FIG. 5, a countermeasure against heat applied to the laser device 40 according to the present embodiment will be described. FIG. 5 is a perspective view showing configurations of a laser diode and a heat sink according to an embodiment of the present invention.

  As already explained, the oscillation wavelength of the laser diode also depends on the temperature of the laser diode. For this reason, in order to stably oscillate a laser beam having a predetermined oscillation wavelength λp from the laser diode, it is preferable that the laser beam is not affected by heat from other laser diodes existing around the laser diode.

  Therefore, as shown in FIG. 5, the n laser diodes LD1 to LDn included in the laser device 40 are preferably fixed to independent heat sinks (heat dissipating parts) 31a to 31n. At this time, each laser diode is preferably fixed to each heat sink in a state of high thermal conductivity. When bonding each laser diode and each heat sink, it is preferable to use an adhesive having high thermal conductivity. Examples of such an adhesive include silver paste. Further, the laser device 40 preferably includes a cooling fan 32 that takes in air outside the device and blows air to each heat sink in order to uniformly cool the laser diodes and the heat sink.

  Thereby, each laser diode and each heat sink can be efficiently cooled and kept in a constant temperature equilibrium state without being affected by the thermal effects of the laser diode and heat sink existing in the vicinity.

  Here, if the cooling air after cooling each laser diode and each heat sink hits another laser diode and heat sink, the other laser diode and heat sink cannot be sufficiently cooled.

  Therefore, it is preferable that the laser diodes and the heat sinks are arranged so that the cooling air that has cooled the laser diodes and the heat sink does not hit the other laser diodes and the heat sink. Further, the cooling fan 32 is sent from the cooling fan 32 so that the cooling air that has cooled one laser diode (that is, the cooling air heated by the one laser diode) does not hit another laser diode. It is preferable that they are arranged.

  For example, as shown in FIG. 5, each heat sink 31 preferably includes a plurality of plate-like cooling fins, and the cooling fins are parallel to the cooling air flow path (arrow in FIG. 5). It is preferable to arrange | position. Thereby, the cooling air after cooling each heat sink 31 can pass smoothly along the cooling fin without affecting other laser diodes and the heat sink.

  As described above, in the laser device 40 of this embodiment, each laser diode is fixed to the heat sink 31 that is insulated from each other. For this reason, the laser device 40 of the present embodiment can suppress the mutual thermal effects of the plurality of laser diodes and prevent fluctuations in the output wavelength of each laser diode due to the thermal effects. The output wavelength of the diode can be further stabilized.

  In the above example, one laser diode is installed on one heat sink, but a plurality of laser diodes may be installed on one heat sink.

(Modification)
Hereinafter, modifications of the embodiment will be described.

(Modification 1)
The LUT shown in FIG. 4 correlates drive currents at which each laser diode oscillates laser light having a predetermined oscillation wavelength λp at a certain temperature. When the environmental temperature (outside temperature) in which the laser device 40 is used is always controlled to a constant temperature, the drive circuit 10 only needs to have one LUT corresponding to the constant temperature.

  On the other hand, when it is assumed that the laser device 40 is used in various environments, it is conceivable that the temperatures of the laser diodes and the heat sinks in an equilibrium state change due to changes in the outside air temperature.

  Therefore, it is preferable that the drive circuit 10 includes a plurality of LUTs corresponding to an assumed outside air temperature range. In this case, it is preferable that the laser device 40 further includes a thermometer that detects the outside air temperature. The control unit 11 preferably refers to the LUT corresponding to the outside air temperature detected by the thermometer.

  Thereby, the control part 11 can supply the suitable drive current according to external temperature to a laser diode. As a result, the laser device 40 can oscillate laser light having a predetermined oscillation wavelength λp regardless of the outside air temperature.

(Modification 2)
Next, with reference to FIGS. 6A to 6C, a second modification of the embodiment will be described. FIG. 6A illustrates the drive current dependence of the oscillation wavelength in the laser diode according to one embodiment of the present invention. FIG. 6B is a diagram showing the drive current dependence of the output power in the laser diode. FIG. 6C is a diagram showing an outline of the oscillation wavelength spectrum of each of the diodes and the combined oscillation wavelength spectrum.

  In the embodiment, the control unit 11 may control the drive current supplied to at least one laser diode so that the total output is equal to the target output.

For example, at least one LD (hereinafter referred to as “LD _adj ”) for finely adjusting the total output is installed in the laser device 40. Also, the correspondence between the output power of the LD _adj and the drive current is stored in advance in the LUT or the like for the laser device 40. And when the shortage of the total output with respect to the target output occurs, the control unit 11 controls the output from the LD _adj so as to compensate for this shortage. At this time, the control unit 11 can easily specify the drive current corresponding to the shortage by referring to the correspondence relationship. Thereby, the laser device 40 can make the total output equal to the target output.

  Hereinafter, a specific example of the realization method will be described. First, the control unit 11 determines a laser diode to be driven within a range where the total output of the laser diodes does not exceed the target output. For example, when the target output is 13 W, LD1 and LD2 are selected as laser diodes to be driven. The total output of LD1 and LD2 is 10.1W, which is 2.9W shorter than the target output.

Therefore, the controller 11 compensates for the shortage of 2.9 W by driving the LD _adj . At this time, the control unit 11 determines that the drive current that causes the output power of the LD _adj to be 2.9 W (for example, when an LD similar to the LD3 is used as the LD _adj , according to FIG. _Is determined as a drive current applied to LD _adj . Thereby, the total output of each laser diode becomes 13 W equal to the target output.

In the above example, any LD that has not been driven may be used as the fine adjustment LD instead of the LD _adj . For example, in the above example, any one of LD3 to LD10 may be used as the fine adjustment LD instead of the LD _adj .

The total output adjustment method is not limited to the above-described method. For example, in the above example, when the output power of LD _adj or the total output power of LD1, LD2, and LD _adj is detected by the detection unit, and the output power of LD _adj is 2.9 W by the control unit 11, _{Alternatively} , the driving current supplied to the LD _adj when the total output power is 13 W can be determined as the driving current of the LD 3.

In this case, the detection unit may be arranged at a position where at least a detection target (in the above example, the output power of the LD _adj or the total output power) can be detected. For example, as the detection unit, an optical sensor including a photodiode can be used.

When the drive current of the LD 3 is adjusted in this way, as shown in FIG. 6C, the output wavelength λ _LD3 of the LD _adj may deviate from the predetermined output wavelength λp. Since only the drive current of the laser diode of the part is adjusted, the ratio of the wavelength component shifted from the wavelength λp to the total output is small. Further, since the target output power (13 W) can be obtained, this configuration is effective particularly when the accuracy of the output power is important.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be used for a light source device including a plurality of laser diodes, a driving circuit and a driving method for driving such a light source device, an optical amplifier including such a light source device, and the like. The present invention is not limited to a fiber laser but can be used for other optical amplifiers such as an optical amplifier (fiber amplifier).

DESCRIPTION OF SYMBOLS 10 Drive circuit 11 Control part 12 Drive part 13a, 13b, ..., 13n Current control element 14a, 14b, ..., 14n Current control element drive circuit 15a, 15b, ..., 15n Current detection resistor 16 Memory 21 Power supply 22 User interface 31a, 31b, ..., 31n Heat sink 40 Laser device (light source device)
100 Fiber laser (optical amplifier)
LD1, LD2, ..., LDn Laser diode

Claims (8)

A drive circuit for driving a plurality of laser diodes connected in parallel to each other,
For each of the plurality of laser diodes, the magnitude of the output obtained when the laser diode is oscillated at a specific wavelength is determined in advance, and the light is turned on based on the predetermined output magnitude. A control unit that controls the number of laser diodes so that the total output of the laser diodes to be lit matches or substantially matches a given target output;
A drive circuit characterized by that.   The control unit controls the magnitude of the drive current supplied to each laser diode to be lit to a predetermined value as the magnitude of the drive current that causes the laser diode to oscillate at a specific wavelength. The drive circuit according to claim 1, wherein:   The control unit causes the laser diode to oscillate at a specific wavelength for each of N−1 laser diodes among the N laser diodes to be lit, with the magnitude of the drive current supplied to the laser diode. The magnitude of the drive current is controlled to a predetermined value, and the magnitude of the drive current supplied to the laser diode of the remaining one of the N laser diodes is set to the N pieces. The drive circuit according to claim 1, wherein the total output of the laser diodes is controlled to coincide with a given target output. For each of the plurality of laser diodes, a predetermined value as the magnitude of the drive current that causes the laser diode to oscillate at the specific wavelength, and the laser diode obtained when a drive current of that magnitude is supplied. A memory in which a table in which a predetermined value is described as the output size is stored;
The control unit determines the number of laser diodes to be lit and the magnitude of the drive current supplied to each of the lit laser diodes by referring to the table. The driving circuit according to any one of the above. A drive circuit for driving the plurality of laser diodes and the plurality of laser diodes, comprising the drive circuit according to any one of claims 1 to 4.
A light source device characterized by that. Each of the plurality of laser diodes is attached to a heat sink insulated from each other,
The light source device according to claim 5. The light source device according to claim 5, a pump combiner that combines laser beams emitted from the plurality of laser diodes, and a laser medium that uses the laser beam combined by the pump combiner as excitation light With
An optical amplifier characterized by that. A driving method for driving a plurality of laser diodes connected in parallel to each other,
For each of the plurality of laser diodes, the magnitude of the output obtained when the laser diode is oscillated at a specific wavelength is determined in advance, and the light is turned on based on the predetermined output magnitude. Including a control step of controlling the number of laser diodes so that the total output of the laser diodes to be lit matches or substantially matches a given target output.
A driving method characterized by that.

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