JP5918975B2 - MOPA laser source device and MOPA laser control method - Google Patents

Description

  The present invention relates to a MOPA laser source device and a laser control method.

  The MOPA (Master Oscillator and Power Amplifier) system uses a semiconductor laser capable of high-speed modulation control as a seed light source, and a low-power seed laser beam from a seed laser light generation section (hereinafter referred to as an MO section) having the seed light source. Is a high output laser beam generation system that emits a high power laser beam by amplifying the laser beam by an optical amplification unit (hereinafter referred to as a PA unit).

  In the conventional MOPA system laser light source device, when the oscillation mode is configured to be switched between the continuous oscillation state and the pulse oscillation state, the pulse is switched from the continuous oscillation state to the pulse state as will be described in detail later with reference to FIG. The first peak power of the output laser light immediately after switching to the oscillation state may be larger than the power after the second peak power. Thus, if the first peak power increases immediately after switching from the continuous oscillation state to the pulse oscillation state, for example, when the MOPA laser light source device is used as a light source for laser processing, the spot size, depth, etc. However, there is a problem that uniform processing becomes difficult because the processing state differs between the time of first peak irradiation and the time of irradiation after the second peak.

  In Patent Document 1, regarding the control of a Q-switch type laser light source device in a pulse oscillation state, the reflected light is monitored and reflected in order to keep the peak value of the reflected light from the irradiated body of the output laser light constant. A control method for changing the repetition frequency of pulsed light according to the peak intensity of light is disclosed. However, the control method of Patent Document 1 has a problem that complicated control of the repetition frequency of the output laser light is required in order to suppress fluctuations in power for each peak of the output laser light. Further, the control method of Patent Document 1 is only applied to a pulse oscillation laser light source device, and switching of an oscillation mode from a continuous oscillation state to a pulse oscillation state in a MOPA laser light source device and a laser at the time of switching are performed. A method for controlling the light source device is not disclosed. Furthermore, in the control method of the laser light source device described in Patent Document 1, it is possible to control the second and subsequent pulses of the output laser light by monitoring the reflected pulse and feeding it back. There was a problem that the first pulse could not be controlled.

  On the other hand, in Patent Document 2, when switching the oscillation mode of a Q switch type laser light source device having a Q switch and a gain medium from a continuous oscillation state to a pulse oscillation state, the Q switch pause interval is set to the continuous oscillation state duration. A control method for suppressing the first peak power of the output laser light immediately after switching to the pulse oscillation state is disclosed. According to this control method, the spire value of the first peak of the pulsed light immediately after switching from the continuous oscillation state to the pulsed oscillation state and the spire value of the pulsed light after the second peak can be made uniform.

  However, when such a control method of Patent Document 2 is diverted to the MOPA laser light source device, the first peak interval of the output laser light pulse immediately after switching from the continuous oscillation state to the pulse oscillation state (corresponding to the Q switch pause interval). ) May differ by about twice as much as the peak interval after the second peak. In that case, when the MOPA laser light source device is applied to laser processing, the pulse interval must be controlled to match the processing timing on the processing machine side with the emission timing of the output laser light of the MOPA laser light source device. I must. However, such control of the pulse interval has to be complicated, and there is a problem that it takes time and labor to set conditions for obtaining output laser light with uniform peak values.

JP-A-8-43532 JP 2003-110176 A

  Problems of a conventional general MOPA laser control method will be described with reference to FIG. The MO unit and PA unit of this MOPA laser light source device are each provided with an excitation light source. FIG. 6 shows the power of excitation light input to the MO unit and the output of seed laser light from the MO unit. The figure shows the relationship between the average power, the output pattern of the seed laser light from the MO section, the excitation light input to the PA section, the inversion distribution state of the gain medium in the PA section, and the power of the output laser light.

In the conventional MOPA laser control method, the time-averaged power of the seed laser light from the MO unit is always set to a constant value regardless of the oscillation mode of the pulse oscillation state or the continuous oscillation state. .
In this case, as shown in FIG. 6, the inversion distribution rate of the PA section immediately after switching from the continuous oscillation state to the pulse oscillation state is higher than the inversion distribution rate in the steady state in the pulse oscillation state (FIG. 6 (A )). For this reason, the first peak power of the pulse laser beam immediately after switching to the pulse oscillation state becomes larger than the peak power at the steady state in the pulse oscillation state (FIG. 6B). Thereafter, the pulsed laser beam having a peak power larger than that in the steady state is emitted, so that the inversion distribution rate of the PA portion becomes lower than the inversion distribution rate in the steady state (FIG. 6C). The peak power becomes smaller than the peak power at the steady state. Then, after such an operation is performed several times, the inversion distribution state of the gain medium in the PA section becomes the same as the inversion distribution state immediately after the pulse output during steady pulse oscillation (FIG. 6D).
Therefore, in the conventional MOPA system laser light source device, after switching from continuous oscillation to laser oscillation, the inversion distribution state of the gain medium in the PA section becomes the same as the inversion distribution state at the time of steady pulse oscillation, and the peak of the output laser light There was a problem that it took a long time to get power.
In the conventional MOPA laser control apparatus, the power obtained by averaging the output light from the PA unit with time is controlled so as to be always constant regardless of the oscillation mode.

  As described above, in the conventional MOPA laser light source device in which the oscillation mode is switched between pulse oscillation and continuous oscillation, the first peak of the output pulse laser beam immediately after switching from the continuous oscillation state to the pulse oscillation state As a result, if the laser light source device is used as a light source for laser processing, for example, the processing state such as spot size and depth is the same as that at the time of the first peak irradiation. Unlike the case of irradiation after the second peak, there is a problem that uniform processing becomes difficult.

The present invention has been made in the context of the above-described circumstances, and in a MOPA laser light source device that can be switched between a pulse oscillation state and a continuous oscillation state at an arbitrary timing, a pulse oscillation state is changed from a continuous oscillation state to a pulse oscillation state. It is an object of the present invention to provide a method and apparatus for appropriately controlling the first peak power of the output laser beam immediately after switching to.

  The present inventors changed the oscillation form of the MOPA laser light source device from the MO unit in the continuous oscillation state according to the pulse oscillation conditions (output power and repetition frequency) when switching the oscillation form from the continuous oscillation state to the pulse oscillation state. The problem was solved by changing the average power of the seed laser beam.

  That is, the MOPA type laser light source device according to the first aspect of the present invention includes a seed laser light source for generating seed laser light, an optical amplifier for amplifying the seed laser light, and control for controlling the seed laser light source. The control unit controls the switching between the pulse oscillation state and the continuous oscillation state in the seed laser light source, and controls the average power of the seed laser light to be different between the pulse oscillation state and the continuous oscillation state. It is characterized by having a configuration.

According to the MOPA-type laser light source device of the first aspect, by controlling the average power of the seed laser light incident on the optical amplifier to be different between the pulse oscillation state and the continuous oscillation state, It is possible to appropriately control the first peak power of the output pulse laser beam immediately after switching to the pulse oscillation state.
However, the MOPA laser light source device of the first aspect is not applied only to output pulsed laser light with uniform peak power immediately after switching from the continuous oscillation state to the pulse oscillation state. In other words, the first peak power immediately after switching from the continuous oscillation state to the pulse oscillation state should also be applied when the peak power in the steady state of the pulse oscillation state needs to be made larger or smaller. In these cases, the average power of the seed laser light in the continuous oscillation state may be controlled according to the target first peak power immediately after switching from the continuous oscillation state to the pulse oscillation state.

  The MOPA laser light source apparatus according to the second aspect of the present invention is the same as the MOPA laser light source apparatus according to the first aspect, except that the optical amplifier immediately after switching from continuous oscillation to pulse oscillation is controlled by controlling the average power of the seed laser beam. The inversion distribution ratio of the gain medium is controlled to be substantially the same as the inversion distribution ratio of the gain medium of the optical amplifier immediately after the pulse output in the steady pulse oscillation state.

  In the MOPA laser light source device of the second aspect, the inversion distribution ratio of the gain medium of the optical amplifier immediately after switching from continuous oscillation to pulse oscillation is the inversion distribution of the gain medium of the optical amplifier immediately after the pulse output in the steady pulse oscillation state. By controlling to be equal to the rate, even if the pulse interval when switching from the continuous oscillation state to the pulse oscillation state is the same as the pulse interval during steady-state pulse oscillation, the continuous oscillation state is changed to the pulse oscillation state. Immediately after switching, pulsed laser light with uniform peak power can be emitted.

  The MOPA laser light source apparatus according to the third aspect of the present invention is the MOPA laser light source apparatus according to the second aspect, wherein the average power of the seed laser light in the continuous oscillation state is higher than the average power of the seed laser light in the pulse oscillation state. It is characterized by having a configuration in which control is performed so as to increase.

In the MOPA laser light source device of the third aspect, since the average power of the seed laser light in the continuous oscillation state is controlled to be higher than the average power of the seed laser light in the pulse oscillation state, the pulse is output from the continuous oscillation state. It is possible to output pulsed laser light having the same peak power immediately after switching to the oscillation state.
Here, in carrying out the control described as the third aspect, in practice, the inversion distribution rate in the continuous oscillation state and the inversion distribution rate immediately after the pulse output in the steady pulse oscillation state are approximated in advance. Then, the average power of the seed light in the continuous oscillation state is checked, and the average power of the seed laser light is set based on the average power. Thus, when the average power of the seed laser light is adjusted to a preset power, the inverted distribution immediately before the first pulse of the laser light is emitted when switching from the continuous oscillation state to the pulse oscillation state. Approaches the inversion distribution just before the pulse is emitted in the steady state of pulse oscillation.
Therefore, even when the inversion distribution of the gain medium of the optical amplifier when switching from the pulse oscillation state to the continuous oscillation state is different from the inversion distribution ratio of the gain medium of the optical amplifier immediately after the pulse output at the time of steady pulse oscillation Then, pulsed light with uniform peak power is emitted.

  The MOPA type laser light source device according to the fourth aspect of the present invention is the monitor for detecting spontaneous emission light generated in the optical amplifier and returned to the seed laser light source in the MOPA type laser light source device of the second or third aspect. A seed laser beam so that the difference between the detection level of spontaneous emission at the monitor immediately after pulse output in the steady pulse oscillation state and the detection level of spontaneous emission at the monitor in the continuous oscillation state is reduced. The average power is controlled to be controlled.

According to the MOPA type laser light source device of the fourth aspect, spontaneous emission light (hereinafter referred to as ASE light) generated by the optical amplifier and returning to the seed laser light source is detected, and immediately after the pulse output in the steady pulse oscillation state. The average power of the seed laser light is controlled so that the difference between the detection level of the ASE light and the detection level of the ASE light in the continuous oscillation state is reduced. As a result, laser light with uniform peak power can be emitted even when the pulse oscillation state and the continuous oscillation state are switched.
The MOPA laser light source device of the fourth aspect utilizes the fact that the power of the ASE light increases or decreases according to the inversion distribution rate and gain of the PA section.

  The MOPA laser light source apparatus according to the fifth aspect of the present invention is the MOPA laser light source apparatus according to any one of the first to fourth aspects, wherein the MOPA laser light source apparatus is a fiber laser. It is what.

  According to the MOPA system laser light source device of the fifth aspect, since the MOPA system laser light source device is composed of a fiber laser, it is necessary to stabilize the output laser light particularly in order to perform fine printing and processing in laser processing. Even in such a case, it is possible to provide a laser light source device suitable for a processing light source that has high beam quality and is easy to narrow and narrow the beam.

 Furthermore, the sixth to ninth aspects of the present invention relate to a MOPA laser control method.

  The MOPA laser control method of the sixth aspect of the present invention uses a MOPA laser light source device that amplifies the seed laser light from the seed light generation section by the light amplification section, and switches between pulsed light and continuous light to be emitted. In the enabled laser output, the average power of the seed laser light incident on the optical amplifying unit is switched between a pulse oscillation state and a continuous oscillation state.

  According to the above-described MOPA laser control method of the sixth aspect, the pulse oscillation state is changed from the continuous oscillation state by switching the average power of the seed laser light incident on the optical amplifier between the pulse oscillation state and the continuous oscillation state. The gain of the optical amplifying unit immediately after switching to can be controlled, and the first peak power of the output pulse laser beam can be appropriately controlled.

  The MOPA laser control method according to the seventh aspect of the present invention is the MOPA laser control method according to the sixth aspect, wherein the inversion distribution ratio of the gain medium of the optical amplifying unit immediately after switching from continuous oscillation to pulse oscillation is constant. The average power of the seed laser beam is controlled so as to be substantially the same as the inversion distribution rate of the gain medium of the optical amplification unit immediately after the pulse output in the pulse oscillation state.

  According to the MOPA laser control method of the seventh aspect, the inversion distribution ratio of the gain medium of the optical amplifying unit immediately after switching from continuous oscillation to pulse oscillation is obtained by the gain of the optical amplifying unit immediately after the pulse output in the steady pulse oscillation state. When the pulse interval of the output laser light immediately after switching from the continuous oscillation state to the pulse oscillation state is the same as the pulse interval in the steady-state pulse oscillation state by controlling so that the inversion distribution ratio of the medium is substantially the same (see FIG. 1 (when t0 = t as shown in FIG. 1), it is possible to output pulsed laser light with uniform peak power immediately after switching from the continuous oscillation state to the pulse oscillation state.

  The MOPA system laser control method according to the eighth aspect of the present invention is the MOPA system laser control method according to the seventh aspect, wherein the average power of the seed laser light in the continuous oscillation state is higher than the average power of the seed laser light in the pulse oscillation state. The average power of the seed laser light is switched so as to be high.

According to the MOPA laser control method of the eighth aspect, by controlling so that the average power of the seed laser light in the continuous oscillation state is higher than the average power of the seed laser light in the pulse oscillation state, the continuous oscillation state It is possible to output pulsed laser light having the same peak power immediately after switching to the pulse oscillation state.
Specifically, as shown in FIG. 1, the inversion distribution ratio of the gain medium in the optical amplifier is lowered by the amount that the average power of the seed laser light in the continuous oscillation state is increased, and the gain medium of the optical amplifier in the continuous oscillation state is reduced. Can be approximated to the inversion distribution rate immediately before the oscillation of each pulse in the steady state of the pulse oscillation state. As a result, even if the inversion distribution of the gain medium of the optical amplifier when switching from the pulse oscillation state to the continuous oscillation state is different from the inversion distribution ratio of the gain medium of the optical amplifier immediately after the pulse output during steady pulse oscillation, The first peak power of the output pulse laser beam immediately after switching from the oscillation state to the pulse oscillation state can be brought close to the peak power of the output laser beam in the steady state, and the output laser having the same peak power from the MOPA laser light source device Light can be obtained.

  The MOPA laser control method according to the ninth aspect of the present invention is the MOPA laser control method according to the seventh or eighth aspect, wherein the spontaneous emission light generated in the optical amplifying unit and returned to the seed laser light generating unit is detected. The average power of the seed laser beam is controlled so that the power of the spontaneous emission light immediately after the pulse output in the steady pulse oscillation state becomes substantially the same as the power of the spontaneous emission light during continuous oscillation. is there.

According to the MOPA laser control method of the ninth aspect, the ASE light generated in the optical amplifying unit and returned to the seed laser light generating unit is monitored, and the power of the ASE light during continuous oscillation is set to the steady pulse oscillation state. By controlling the average power of the seed laser light during continuous oscillation so as to be the same as the power of the ASE light immediately after the pulse output, the gain of the optical amplification unit monitored indirectly through the power of the ASE light is controlled. The average power of the seed laser beam can be controlled to be a target value.
This control method utilizes the fact that the power level of the ASE light returning from the optical amplification unit to the seed laser light generation unit increases or decreases according to the inversion distribution state of the gain medium of the optical amplification unit.

  According to the MOPA type laser light source device and laser control method of the present invention, the output pulse laser immediately after switching from the continuous oscillation state to the pulse oscillation state as the MOPA type laser light source device that can be switched between the pulse oscillation state and the continuous oscillation state. The peak power of each pulse of light can be adjusted appropriately. Therefore, when the present invention is applied to, for example, laser processing, immediately after switching from processing using continuous light to processing using pulsed light, it is necessary to change the pulse interval in order to stabilize the power of pulsed light. The problem of uneven machining due to power fluctuations in the output pulse light can be solved.

It is a schematic diagram which shows the outline | summary of the MOPA system laser control method of this invention. 1 is a schematic diagram showing an overall configuration of a MOPA laser light source device according to a first embodiment of the present invention. It is a rough solution figure showing composition of a seed laser light source of a MOPA system laser light source device by a 1st embodiment of the present invention. It is a schematic diagram which shows the whole structure of the MOPA system laser light source apparatus by the 2nd Embodiment of this invention. It is a schematic diagram which shows the relationship between the oscillation mode switching signal in the MOPA system laser light source device by the 2nd Embodiment of this invention, the output average power of MO part, and the power of the ASE light from PA part. It is a schematic diagram which shows the outline | summary of the conventional MOPA system laser control method.

  The basic principle of the MOPA laser control method of the present invention will be described with reference to FIG. The MOPA laser light source device of FIG. 1 has a configuration in which the MO unit and the PA unit each include an excitation light source. For easy comparison with the conventional MOPA laser control method, as in FIG. 6, FIG. 1 also shows the power of the pumping light input to the MO unit according to the oscillation mode and the seed laser light from the MO unit. The figure shows the relationship between the average power, the output pattern of the seed laser light from the MO section, the excitation light input to the PA section, the inversion distribution state of the gain medium in the PA section, and the power of the output laser light.

  In this MOPA laser control method, the MO unit employs a Q switching method as shown in FIG. 3, and a diffraction grating is formed on the acoustooptic device while a high frequency voltage is applied to the acoustooptic device, so that diffracted light is formed. It becomes the structure which occurs. Therefore, diffracted light is generated while a high-frequency voltage is applied to the acoustooptic device, and the diffracted light is reflected by the fiber Bragg grating and amplified in the laser resonator. In the present invention, the acousto-optic device performs switching control between the pulsed light and continuous light of the seed laser light emitted from the MO unit, and by changing the power of the excitation light input to the MO unit, Perform switching control.

  If the excitation light of the PA part is incident on the gain medium in the PA part, the inversion distribution ratio in the gain medium of the PA part is increased, and if the pulsed seed laser light is incident on the PA part from the MO part, the PA part A high output pulsed light is emitted from. After the pulse light is emitted, the inversion distribution rate of the gain medium returns to the inversion distribution rate before emission of the high-power pulse light by the incidence of the excitation light.

In the MOPA laser control method shown in FIG. 1, the peak level of the first pulse of the output laser light after the control of the output laser light is switched from continuous oscillation to pulse oscillation, and the pulse level of the output laser light in the steady pulse oscillation state. In order to match the peak level, when the control of the seed laser light is switched from pulse oscillation to continuous oscillation, the power of the excitation light of the MO unit is increased by a certain amount. Due to the increased pumping light power, the inversion distribution ratio of the gain medium in the PA section immediately before the first peak emission of the output laser light is substantially the same as the inversion distribution ratio immediately before the peak emission in the steady state of pulse oscillation. Adjusted.
This control method uses the fact that the output average power of the seed laser beam of the MO unit increases and the inversion distribution rate of the gain medium of the PA unit decreases by increasing the power of the excitation light of the MO unit.
The setting value of the pumping light power necessary to match the peak level of the first pulse of the output laser beam with the peak level of the pulse of the output laser beam in the steady state is a continuous control of the seed laser beam emitted from the MO unit. Assuming that the time interval from the oscillation to the pulse oscillation is t0 and the time interval of the seed laser light pulse in the steady state is t, a value corresponding to the time difference between t0 and t is stored in advance in the built-in memory. It is set appropriately according to

  By using such a MOPA system laser light source device, as shown in FIG. 1, the inversion distribution ratio in the gain medium of the PA section immediately after switching from the continuous oscillation state to the pulse oscillation state is the first after the pulse oscillation. An output laser beam in which the peak is very close to the peak after the second peak and the peak power is uniform from the first peak can be obtained.

  The output average power of the PA unit is controlled so as to be always constant regardless of the oscillation mode such as pulse oscillation or continuous oscillation.

  Embodiments of the present invention will be described below with reference to FIGS.

FIG. 2 shows a MOPA laser light source apparatus according to the first embodiment of the present invention. This MOPA laser light source device includes a seed laser light source 1 for generating seed laser light, an optical amplifier 10 for amplifying the seed laser light, a control unit 20, a memory 22, and an external controller 24. doing.
Next, each component of the MOPA laser light source device will be described.

  The seed laser light source 1 functions as an MO unit of the MOPA laser control method in this embodiment, and an example thereof is shown in FIG. As shown in FIG. 3, the seed laser light source 1 includes a rare earth-doped optical fiber 5 connected to the excitation light source 2 and a first fiber Bragg grating (hereinafter referred to as FBG) as an element for constituting a resonator. 3), a second FBG 4, and an acousto-optic device (hereinafter referred to as AOM) 6 for performing a Q-switching operation.

  The optical amplifier 10 functions as a PA unit of the MOPA laser control method in this embodiment. As shown in FIG. 2, the optical amplifier 10 includes an amplification optical fiber 12 and a pumping LD (Laser Diode) 11 for making the pumping light incident on the amplification optical fiber 12. The excitation LD 11 is optically connected to the amplification optical fiber 12.

  The control unit 20 is connected to the excitation light source 2 of the seed laser light source 1 in order to perform the average power control of the seed laser light and the switching control of the oscillation mode between the pulse oscillation state and the continuous oscillation state. The control unit 20 is also connected to the pumping LD 11 of the optical amplifier 10 in order to perform switching control of the ON / OFF state of the output laser light. Further, the memory 22 and the external controller 24 are also connected.

  The memory 22 stores data such as all parameters and schedules relating to the pulse oscillation state and continuous oscillation state of the components of the MOPA laser light source device of FIG. Further, the memory 22 outputs parameters and data necessary for control according to the instruction to the control unit 20 to which the instruction from the user is input via the external controller 24.

Necessary parameters are called from the memory 22 at an arbitrary timing, and control is performed so that the average power of the output laser light in the pulse oscillation state from the optical amplifier 10 is equal to the average power of the output laser light in the continuous oscillation state. Parameters relating to components in the pulse oscillation state and the continuous oscillation state are stored in the memory 22 in advance.
Here, when the user switches from the continuous oscillation state to the pulse oscillation state, information on the repetition frequency of the pulse oscillation state is received from the user during continuous oscillation, and the seed laser light is received according to the frequency. It is desirable to set the average power. The higher the repetition rate, the closer to the inversion distribution during CW oscillation, so the higher the repetition rate, the smaller the difference between the average power during CW oscillation and the average power during pulse driving. It is desirable to control the average power during CW oscillation. Considering the time for switching the average power of the seed laser light, the timing at which the oscillator receives the frequency information is desirably 100 μsec or more before switching to pulse oscillation.

  The external controller 24 is a user interface for a user of the MOPA laser light source device to directly control the MOPA laser light source device. The external controller 24 is a signal for switching between a pulse oscillation state and a continuous oscillation state, and ON / OFF of the output laser light. A state instruction signal and a signal related to the setting of the power of the output laser beam are output to the control unit 20.

Next, the operation of the MOPA type laser light source device shown in FIG. 2 will be described.
In the MOPA laser light source device of FIG. 2, if an instruction signal for turning on the output laser beam and a switching signal for switching between a pulse oscillation state and a continuous oscillation state are input from the external controller 24 to the control unit 20, These two signals are input to the excitation light source 2 of the seed laser light source 1. Excitation light from the excitation light source 2 is controlled and emitted so as to have a predetermined average power according to the switching signal. The excitation light is absorbed by the rare earth element added to the rare earth-doped optical fiber 5 and excites the rare earth element. The light from the rare earth element in the excited state propagates through the rare earth-doped optical fiber 5 and enters the AOM 6.

  The AOM 6 is configured to be switched between a high loss state and a low loss state by being controlled by the control unit 20 via a driver (not shown). When the AOM 6 is in a high loss state, transmission of light from the rare earth-doped optical fiber 5 is suppressed, and in a low loss state, light is transmitted and enters the second FBG 4. Since the second FBG 4 has a lower reflectance than the first FBG 3, a part of the transmitted light of the AOM 6 is reflected by the second FBG 4 and is incident again on the rare earth-doped optical fiber 5 through the AOM 6, and the rare earth element of the rare earth-doped optical fiber 5 Is amplified by stimulated emission of. The amplified light is reflected by the first FBG 3 having a high reflectivity, is incident on the rare earth-doped optical fiber 5 again, and is further amplified. The light amplified again is incident on the second FBG 4 via the AOM 6, and part of the incident light passes through the second FBG 4.

  The components from the first FBG 3 to the second FBG 4 function as a Fabry-Perot resonator, light is amplified according to the control state of the AOM 6, and the amplified light is used as seed laser light for the MOPA laser light source device from the second FBG 4 Emitted. When the AOM 6 is controlled by the control unit 20 so as to periodically repeat a low loss state and a high loss state, the seed laser light output from the second FBG becomes pulse light, and the low loss state is maintained. When controlled to maintain, the seed laser light becomes continuous light.

  Therefore, the seed laser light source 1 to which the oscillation mode switching signal is input from the control unit 20 sends the switching signal to the driver of the AOM 6 and controls the AOM 6 according to the content of the switching signal, so that pulse light or continuous light is transmitted. Either form of seed laser light is emitted.

  The seed laser light from the seed laser light source 1 is incident on the amplification optical fiber 12 of the optical amplifier 10. The amplification optical fiber 12 is composed of a double clad fiber having a core portion to which an excitation element is added, a clad portion covering the core portion, and a resin clad portion covering the clad portion. The core part propagates the seed laser light incident on the optical amplifier 10 as single mode light, and propagates the excitation light emitted from the core part and the clad part as multimode light. A part of the excitation light from the excitation LD 11 incident on the amplification optical fiber 12 is absorbed by the excitation element when propagating through the core, and the excitation element is excited. In the excitation element having an increased inversion distribution rate, stimulated emission is generated by the seed laser light propagating through the core, and high-power light is emitted from the amplification optical fiber 12 by this stimulated emission.

  The pumping LD 11 of the optical amplifier 10 outputs continuous light with a constant output power regardless of whether the oscillation mode is pulse oscillation or continuous oscillation. That is, the optical amplifier 10 amplifies the seed laser light, which is either pulsed light or continuous light, at a constant amplification factor.

Next, the operation when the oscillation mode of the MOPA laser light source device is switched from pulse oscillation to continuous oscillation will be described.
First, an oscillation mode switching signal is input from the external controller 24 to the control unit 20, and the control unit 20 calls up data necessary for continuous oscillation control from the memory 22. Next, the control unit 20 switches the output power of the excitation light source 2 of the seed laser light source 1 and controls the driver of the AOM 6 so that the AOM 6 maintains a low loss state. As described above, the average power of the seed laser light source 1 is the inversion distribution ratio of the gain medium of the optical amplifier 10 in the continuous oscillation state and the inversion distribution ratio of the gain medium of the optical amplifier 10 immediately before the emission of the pulsed light in the pulse oscillation state. Is determined by the control unit 20 based on the data stored in the memory 22.

Next, the operation when the oscillation mode of the MOPA laser light source device is switched from continuous oscillation to pulse oscillation will be described.
First, an oscillation mode switching signal is input from the external controller 24 to the control unit 20, and the control unit 20 calls data necessary for pulse oscillation control from the memory 22. Next, the control unit 20 switches the output power of the excitation light source 2 of the seed laser light source 1 to a value at the time of steady pulse oscillation, and the driver of the AOM 6 so that the AOM 6 periodically repeats a low loss state and a high loss state. To control. As described above, since the output average power of the seed laser light is switched to the continuous oscillation state, the inversion distribution ratio of the amplification optical fiber 12 of the optical amplifier 10 immediately after switching from the continuous oscillation to the pulse oscillation is the pulse oscillation. The inversion distribution rate of the amplification optical fiber 12 immediately after the pulse output at a constant time is very close to the inversion distribution rate immediately before output laser light emission after the first peak and the second peak.
With such a laser control method, the MOPA laser light source device emits pulsed output laser light with uniform peak power immediately after switching from the continuous oscillation state to the pulse oscillation state.

  FIG. 4 shows the configuration of a MOPA laser light source apparatus according to the second embodiment of the present invention. In FIG. 4, the same components as those in the MOPA system laser light source device shown in FIG.

4 is a monitor unit for measuring the amount of ASE light returning to the seed laser light source 1 between the seed laser light source 1 and the optical amplifier 10 of the MOPA laser light source apparatus shown in FIG. 30 is provided via an optical coupler 32. The monitor unit 30 uses a light receiving device such as a PD having a function of measuring the amount of light.
The monitor unit 30 is connected to the control unit 20, and a measurement value of the light amount of ASE light is input to the control unit 20.

Next, the operation and function of the MOPA laser light source device of FIG. 4 will be described.
The ASE light is generated in the amplification optical fiber 12 and propagates from the optical amplifier 10 to the laser emission direction of the MOPA laser light source device and also to the seed laser light source 1. Since the power of the ASE light increases and decreases with a change in the inversion distribution rate of the excitation element in the amplification optical fiber 12, the inversion distribution rate and the gain state of the amplification optical fiber 12 indirectly using the monitor unit 30. Can be monitored. Using this principle, the ASE light returning from the optical amplifier 10 to the seed laser light source 1 is monitored by the monitor unit 30, and the control unit 20 is configured so that the amount of light detected by the monitor unit 30 becomes a predetermined value. To adjust the output average power of the seed laser light of the seed laser light source 1 in the continuous oscillation state.

  FIG. 5 shows the relationship between the pulse oscillation and continuous oscillation oscillation mode switching signal, the average output power of the seed laser light from the seed laser light source 1, and the power of the ASE light from the optical amplifier 10 in the second embodiment. Show. When the MOPA laser light source device is in a pulse oscillation state, pulse light is emitted from the seed laser light source 1 in accordance with the oscillation mode switching signal and is incident on the optical amplifier 10. At this time, the time-averaged output power of the seed laser light source 1 is kept constant. Since the pumping light with a constant power is incident on the amplification optical fiber 12 of the optical amplifier 10 from the pumping LD 11, the gain of the amplification optical fiber 12 increases and becomes very close to the maximum gain in the steady state. In this state, if pulsed seed laser light from the seed laser light source 1 is incident on the amplification optical fiber 12, high-power pulse light is emitted from the optical amplifier 10, and the gain of the amplification optical fiber 12 is steady. Return to the minimum gain in the state. Then, the power of the ASE light also varies as shown in FIG. 5 in proportion to the increase / decrease amount of the gain of the amplification optical fiber 12, and the variation amount is detected by the monitor unit 30.

  Here, when the oscillation mode is switched from pulse oscillation to continuous oscillation, an oscillation mode switching signal is output from the control unit 20 to the seed laser light source 1 and continuous light is emitted from the seed laser light source 1 as shown in FIG. And enters the optical amplifier 10. At this time, since the output average power of the continuous light is controlled to be higher than the output average power of the pulsed light when the pulse oscillation is steady, the gain of the optical fiber for amplification 12 of the optical amplifier 10 is immediately after the emission of the pulsed light when the pulse oscillation is steady. (Fig. 5A).

  As described above, the output average power of the continuous light of the seed laser light source 1 is increased, so that the gain of the amplification optical fiber 12 of the optical amplifier 10 is increased and the power of the ASE light from the optical amplifier 10 is also increased ( FIG. 5 (B)).

  The amount of increase in the power of the ASE light at this time is detected by the ASE light monitor unit 30, and a signal related thereto is output to the control unit 20, and the control unit 20 outputs the signal from the seed light laser light source 1 according to the increase amount. The output average power of the continuous light is controlled (FIG. 5C).

  By controlling the average output power of the seed laser light from the seed laser light source 1 as described above, the ASE light from the optical amplifier 10 and the gain of the optical fiber for amplification 12 are in a state immediately after emission of the pulse light at the time of steady pulse oscillation. It becomes the same (FIG. 5D).

  That is, by performing the above-described control, the MOPA laser light source device shown in FIG. 4 has pulse light with extremely uniform peak power immediately after the MOPA laser light source device shown in FIG. 4 is switched from the continuous oscillation state to the pulse oscillation state. It is emitted from.

  The amount of light detected by the ASE light monitoring unit 30 is desirably controlled so as to be the power of the ASE light immediately after pulse emission after a sufficient time has elapsed from the start of pulse oscillation. In the case where a predetermined value is set for the amount of light detected by the ASE light monitor unit 30, the predetermined value may be periodically subjected to active calibration. Alternatively, it may be examined before the start of driving of the MOPA laser light source apparatus, recorded in the memory 22 in the form of a data table or the like, and appropriately called by the control unit 20.

  In any of the above-described MOPA laser light source devices, an LD may be used as a seed laser light source. In that case, the seed laser beam of the MO unit is controlled by directly modulating the LD current.

  Although preferred embodiments of the present invention have been described above, the present invention is of course not limited to these embodiments. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit of the present invention.

  The MOPA laser light source device of the present invention is optimal as a light source for laser processing, but is not limited thereto, and can be applied to all applications where high power pulsed light is required.

  DESCRIPTION OF SYMBOLS 1 ... Seed laser light source, 2 ... Excitation light source, 3 ... 1st fiber Bragg grating, 4 ... 2nd fiber Bragg grating, 5 ... Rare earth addition optical fiber, 6 ... Acoustooptic device, 10 ... Optical amplifier, 11 ... Excitation semiconductor laser , 12 ... Optical fiber for amplification, 20 ... Control unit, 22 ... Memory, 24 ... External controller, 30 ... Monitor unit, 32 ... Optical coupler

Claims (5)

A seed laser light source for generating seed laser light, an optical amplifier for amplifying the seed laser light, a monitor unit for detecting spontaneous emission light generated by the optical amplifier and returning to the seed laser light source, A control unit for controlling the seed laser light source,
Wherein the control unit controls the switching between the pulse oscillation condition in the seed laser light source and the continuous oscillation state, the average power of the seed laser beam in continuous oscillation state than the average power of the seed laser beam in a pulsed state is high In addition, the continuous oscillation state so that the detection level of spontaneous emission light at the monitor unit immediately after the pulse output in the steady pulse oscillation state is substantially the same as the detection level of spontaneous emission light at the monitor unit in the continuous oscillation state Control the average power of the seed laser
The power of the pumping light input to the optical amplifier is constant in the pulse oscillation state and the continuous oscillation state.
A MOPA-type laser light source device characterized by that . The MOPA laser light source device according to claim 1,
By controlling the average power of the seed laser light, the inversion distribution ratio of the gain medium of the optical amplifier immediately after switching from continuous oscillation to pulse oscillation is changed to the inversion distribution of the gain medium of the optical amplifier immediately after the pulse output in the steady pulse oscillation state. A MOPA-type laser light source device that is controlled to be substantially the same as the rate. In the MOPA system laser light source device according to claim 1 or 2 ,
The MOPA type laser light source device is a fiber laser. Using a laser light source device of the MOPA system that amplifies the seed laser light from the seed light generation unit by the optical amplification unit, in the laser output that can be emitted by switching between pulsed light and continuous light ,
Than the average power of the seed laser beam in the pulse oscillation state, such that the average power of the seed laser beam in continuous oscillation state is high, switch the average power of the seed laser beam,
Detecting spontaneous emission light generated in the light amplification unit and returning to the seed light generation unit,
Control the average power of the seed laser light in the continuous oscillation state so that the power of the spontaneous emission light immediately after the pulse output in the steady pulse oscillation state is substantially the same as the power of the spontaneous emission light in the continuous oscillation,
Makes the power of the pumping light input to the optical amplifier constant in the pulse oscillation state and the continuous oscillation state.
MOPA type laser control method characterized by. The MOPA laser control method according to claim 4 ,
The inversion distribution rate of the gain medium of the optical amplification unit immediately after switching from continuous oscillation to pulse oscillation is substantially the same as the inversion distribution rate of the gain medium of the optical amplification unit immediately after the pulse output in the steady pulse oscillation state. A MOPA laser control method for controlling the average power of seed laser light in a continuous oscillation state.

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