JP6005033B2 - Optical fiber laser device control method and optical fiber laser device - Google Patents

Description

  The present invention relates to an optical fiber laser device control method and an optical fiber laser device.

  Conventionally, as a method for controlling the power supplied to the laser device, a method aimed at avoiding a failure of the laser device has been disclosed (see, for example, Patent Documents 1 to 3). In these control methods, it is determined whether the driving conditions exceed the upper limit output power that the laser device can output from the set values and monitor values during pulse driving, and the repetition frequency and the amount of current supplied to the excitation light source are controlled. doing.

JP 2005-252149 A JP-A-5-206548 JP 2007-59690 A

  By the way, when using a semiconductor laser element as an excitation light source in an optical fiber laser device, it is applied to the excitation light source in order to improve the modulation frequency characteristics during pulse driving and to operate so that laser light can be output with high peak power. It is preferable to make the driving voltage to be larger than that during continuous wave driving.

  However, if the drive voltage applied to the excitation light source is set to be large so that the maximum peak light power can be obtained during pulse drive, this time, the drive unit of the excitation light source, particularly the excitation light source, is used during continuous wave drive. The load on the current adjustment unit that adjusts the supplied current increases, and the amount of heat generated in the current adjustment unit increases. As a result, there is a possibility that the current adjusting unit may be broken due to heat generation. However, if the drive current supplied to the excitation light source is reduced in order to suppress heat generation during continuous wave drive, the maximum output light power will be smaller than before the drive voltage is increased to be suitable for pulse drive. Furthermore, if the voltage is increased excessively during continuous wave driving, excessive energy is consumed accordingly.

  The present invention has been made in view of the above, and an optical fiber laser device capable of outputting laser light with higher peak power during pulse driving without applying excessive load to the device even during continuous wave driving. It is an object to provide a control method and an optical fiber laser device.

  In order to solve the above-described problems and achieve the object, a control method for an optical fiber laser device according to the present invention is a control method for an optical fiber laser device that uses a semiconductor laser element as a pumping light source. A power application step for applying a drive voltage and a drive current to the device, wherein the drive voltage applied to the semiconductor laser device when the optical fiber laser device is driven in a continuous wave in the power application step is a first drive voltage; When the driving voltage applied to the semiconductor laser element when the fiber laser device is pulse-driven is a second driving voltage, the second driving voltage having a value larger than the first driving voltage at the time of pulse driving is applied to the semiconductor laser element. It is characterized by giving.

  The control method of the optical fiber laser device according to the present invention includes a confirmation step of confirming the driving condition of the optical fiber laser device in the above invention, and the driving condition confirmed in the confirmation step is a continuous wave driving condition In the power application step, the first drive voltage is applied to the semiconductor laser element, and in the confirmation step, when the drive condition is a pulse drive condition, the second drive voltage is applied in the power application step. The semiconductor laser device is characterized by being provided.

  In the control method of the optical fiber laser device according to the present invention, in the above invention, the peak power, repetition frequency, and duty ratio or pulse width of the laser light output from the optical fiber laser device are set as drive conditions. Including a setting step, wherein in the power application step, the driving current and the second driving voltage corresponding to the set value are applied to the semiconductor laser element.

  The method for controlling an optical fiber laser device according to the present invention includes the step of generating or inputting a set value of the power of the laser beam output from the optical fiber laser device and an output start command or an output stop command in the above invention. And a confirmation step of confirming the set value, the elapsed time from the output start, and the elapsed time from the output stop, and in the power application step, the driving current according to the confirmation result of the confirmation step and the A second drive voltage is applied to the semiconductor laser element.

  The method for controlling an optical fiber laser according to the present invention includes a temperature measuring step of measuring a temperature of a current adjusting unit that adjusts the driving current applied to the semiconductor laser element in the above invention, and the temperature measured in the temperature measuring step. The second drive voltage according to the above is applied to the semiconductor laser element.

  An optical fiber laser device according to the present invention includes an optical fiber laser including a semiconductor laser element as an excitation light source, a power applying unit that applies a driving voltage and a driving current to the semiconductor laser element, and a control unit that controls the power applying unit. , Wherein the control unit sets a driving voltage applied to the semiconductor laser element when the optical fiber laser device is driven in a continuous wave as a first driving voltage, and pulses the optical fiber laser device. When the driving voltage applied to the semiconductor laser element in driving is the second driving voltage, the power is applied so that the second driving voltage having a value larger than the first driving voltage is applied to the semiconductor laser element during pulse driving. The application unit is controlled.

  In the optical fiber laser device according to the present invention, in the above invention, the control unit confirms a driving condition of the optical fiber laser device, and when the confirmed driving condition is a continuous wave driving condition, The power applying unit is controlled to apply one driving voltage to the semiconductor laser element, and when the confirmed driving condition is a pulse driving condition, the second driving voltage is applied to the semiconductor laser element. The power supply unit is controlled.

  In the optical fiber laser device according to the present invention, in the above invention, the control unit uses the peak power, repetition frequency, and duty ratio or pulse width set values of the laser light output from the optical fiber laser device as driving conditions. The power supply unit is controlled so as to set the drive current and the second drive voltage according to the set value to the semiconductor laser element.

  In the optical fiber laser apparatus according to the present invention, in the above invention, the control unit generates or inputs a power set value and an output start instruction or an output stop instruction of the laser light output from the optical fiber laser apparatus, The set value, the elapsed time from the output start, and the elapsed time from the output stop are confirmed, and the power application is performed so that the drive current and the second drive voltage according to the confirmation result are applied to the semiconductor laser element. It is characterized by controlling the part.

  In the optical fiber laser device according to the present invention, in the above invention, the power applying unit includes a current adjusting unit that adjusts the driving current applied to the semiconductor laser element, and a temperature measuring device that measures the temperature of the current adjusting unit; The control unit controls the power application unit so as to apply the second drive voltage corresponding to the temperature measured by the temperature measuring device to the semiconductor laser element.

  According to the present invention, it is possible to output laser light with higher peak power during pulse driving without applying an excessive load to the apparatus even during continuous wave driving.

FIG. 1 is a diagram illustrating a configuration of an optical fiber laser device according to the first embodiment. FIG. 2 is a diagram showing a configuration of the excitation light source shown in FIG. FIG. 3 is a flowchart showing a control example 1. FIG. 4 is a diagram illustrating setting conditions in the control example 1. FIG. 5 is a flowchart showing a control example 2. FIG. 6 is a diagram illustrating the relationship between the drive current and the output optical power. FIG. 7 is a diagram illustrating setting conditions in the control example 2. FIG. 8 is a flowchart showing a control example 3. FIG. 9 is a diagram illustrating setting conditions in the control example 3. FIG. 10 is a diagram illustrating setting conditions in the control example 3. FIG. 11 is a diagram illustrating an example of a time chart of the set value of the drive voltage in the control example 3. FIG. 12 is a flowchart showing a control example 4. FIG. 13 is a diagram illustrating a configuration of an optical fiber laser device according to the second embodiment.

  Embodiments of an optical fiber laser device control method and an optical fiber laser device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Moreover, in each drawing, the same code | symbol is attached | subjected suitably to the same or corresponding element.

(Embodiment 1)
FIG. 1 is a diagram showing a configuration of an optical fiber laser device according to Embodiment 1 of the present invention. As shown in FIG. 1, an optical fiber laser device 100 includes a pumping light source unit 110 including a plurality of pumping light sources 111, an optical multiplexer 102 connected to the pumping light source 111, and a fiber Bragg grating (connected to the optical multiplexer 102). FBG (Fiber Bragg Grating) 103, amplification optical fiber 104 connected to FBG 103, FBG 105 connected to amplification optical fiber 104, output side optical fiber 106 connected to FBG 105, and control unit connected to excitation light source 111 120. The excitation light source 111, the optical multiplexer 102, the FBGs 103 and 105, the amplification optical fiber 104, and the output side optical fiber 106 constitute an optical fiber laser FL. The optical fiber laser FL is a so-called QCW (Quasi Continuous Wave) type optical fiber laser.

  The optical multiplexer 102 is composed of, for example, a TFB (Tapered Fiber Bundle). The optical multiplexer 102 combines the excitation lights output from the plurality of excitation light sources 111 and outputs them to the amplification optical fiber 104. The pumping light has a wavelength of, for example, 915 nm, but is not particularly limited as long as it is a wavelength that can optically pump the amplification optical fiber 104.

  Amplifying optical fiber 104 is made of ytterbium (Yb) ion, which is a kind of rare earth element, added to a core portion made of silica-based glass, and is formed of an inner clad layer made of silica-based glass and a resin on the outer periphery of the core portion. A double clad ytterbium-doped optical fiber (YDF) in which an outer clad layer is sequentially formed.

  The FBG 103 has a center wavelength of, for example, 1084 nm, has a reflectivity of about 100% in the wavelength band of about 2 nm in the center wavelength and its surroundings, and almost transmits light having a wavelength of 915 nm, which is the wavelength of the excitation light. The FBG 105 has a center wavelength that is substantially the same as that of the FBG 105, for example, 1084 nm, the reflectance at the center wavelength is about 10% to 30%, the full width at half maximum of the reflection wavelength band is about 1 nm, and the light with a wavelength of 915 nm Is almost transparent.

  Therefore, the FBGs 103 and 104 constitute an optical fiber resonator with the optical fiber for amplification 104 sandwiched with respect to light having a wavelength of 1084 nm. The center wavelengths of the FBGs 103 and 105 are not limited to 1084 nm, and may be within the range of the emission wavelength of the amplification optical fiber 104.

  The output side optical fiber 106 is composed of a single mode optical fiber made of, for example, quartz glass.

  Next, the control unit 120 includes a calculation unit 121, a storage unit 122, a storage unit 123, and an external input unit 124.

  The arithmetic unit 121 performs various arithmetic processes for controlling the excitation light source 111 and is configured by, for example, a CPU (Central Processing Unit). The storage unit 122 stores various programs and data used for the calculation unit 121 to perform calculation processing, and is configured by a ROM (Read Only Memory), for example. The storage unit 123 is used to store a work space when the calculation unit 121 performs calculation processing, a result of calculation processing of the calculation unit 121, and the like. For example, the storage unit 123 is a RAM (Random Access Memory). Composed. The external input unit 124 can accept an external control signal S from the outside of the optical fiber laser device 100. The external control signal S may be an analog signal such as an analog voltage signal or a digital signal such as an 8-bit signal. When an analog signal is input, it is preferable that the external input unit 124 has a noise cut function or the like to prevent malfunction due to noise input.

  Next, the excitation light source 111 will be described. FIG. 2 is a diagram illustrating a configuration of the excitation light source 111. As shown in FIG. 2, the excitation light source 111 is a semiconductor laser element 111a, which is a semiconductor laser diode (LD), a resistor 111b connected to the anode terminal side of the semiconductor laser element 111a, and a resistor 111b. A voltage adjusting unit 111c, a current adjusting unit 111d connected to the cathode terminal side of the semiconductor laser element 111a, and a temperature measuring device 111e provided in the current adjusting unit 111d are provided. The current adjustment unit 111d includes a field effect transistor (FET) 111da having a drain terminal connected to the anode terminal side of the semiconductor laser element 111a and a source terminal grounded, and a gate voltage adjustment unit 111db connected to the gate terminal of the FET 111da. Consists of. The temperature measuring device 111e is, for example, a thermistor. The resistor 111b, the voltage adjusting unit 111c, the current adjusting unit 111d, and the temperature measuring device 111e constitute a power applying unit 111f. The voltage adjustment unit 111c, the current adjustment unit 111d, and the temperature measuring device 111e are connected to the control unit 120.

  The voltage adjustment unit 111c is constituted by a stabilized power source that outputs a voltage with an analog voltage value and can change the output voltage, and is controlled by a DAC instruction value from the control unit 120, for example. Further, the voltage adjusting unit 111c may be configured by a regulator that can vary the output voltage according to a resistance value, and a resistor unit using a digital potentiometer. In this case, the output voltage of the regulator can be changed by controlling the digital potentiometer with a digital control signal from the control unit 120.

  The gate voltage adjustment unit 111db is composed of, for example, an operational amplifier, and controls the voltage applied to the gate terminal of the FET 111da based on the DAC instruction value from the control unit 120.

  In the present embodiment, in the excitation light source unit 110, a plurality of excitation light sources 111 are connected to a common voltage adjustment unit 111c and gate voltage adjustment unit 111db. For example, the semiconductor laser elements 111a of each pumping light source 111 are connected in series to form a plurality of series connection groups, and the plurality of series connection groups are connected in parallel to each other and connected to one common voltage adjustment unit 111c. Has been. Further, one common gate voltage adjustment unit 111db is connected for each series connection group. However, the configuration of the excitation light source unit 110 is not limited to this, and one common voltage adjustment unit 111c may be connected for each series connection group, or each excitation light source 111 may be connected to the voltage adjustment unit 111c and the gate voltage adjustment. The structure provided with the part 111db may be sufficient.

  Next, an example of a basic operation of the optical fiber laser device 100 will be described. First, the external input unit 124 of the control unit 120 receives an external control signal S as a command signal. The control unit 120 sets driving conditions for the optical fiber laser device 100 in accordance with the external control signal S. For example, the calculation unit 121 uses a predetermined program and data (for example, table data) stored in the storage unit 122 to set the optical fiber laser device 100 to a predetermined driving condition (for example, output peak power at the time of pulse driving, repetition frequency, And the duty ratio (duty ratio or pulse width). Here, the duty ratio is the ratio of the time during which laser light is output in one cycle to the time of one cycle of the pulse. The repetition frequency and duty ratio or pulse width are set so that the pulse width is several μs to several hundred ns in consideration of the time constant of the amplification optical fiber 104 and the like.

  When the driving condition is set, the control unit 120 controls the power applying unit 111f so as to apply a predetermined driving voltage and driving current to the semiconductor laser element 111a based on the setting of the driving condition. At this time, the drive current is, for example, a pulse current having a predetermined peak current value, repetition frequency, duty ratio, or pulse width. In the current adjusting unit 111d of the power applying unit 111f, the driving current supplied to the semiconductor laser element 111a can be adjusted by adjusting the gate voltage supplied from the gate voltage adjusting unit 111db to the gate terminal of the FET 111da.

  The semiconductor laser element 111a outputs pumping light having a predetermined optical power when given a driving voltage and a driving current. The optical multiplexer 102 multiplexes the pumping lights output from the semiconductor laser elements 111 a of the respective pumping light sources 111 and outputs them to the amplification optical fiber 104.

  In the amplification optical fiber 104, the Yb ions in the core portion are optically excited by the excitation light, and emit light in a band including a wavelength of 1084 nm. Light emission with a wavelength of 1084 nm is laser-oscillated by the optical amplification action of the amplification optical fiber 104 and the action of the optical resonator constituted by the FBGs 103 and 105. The oscillated laser beam L is output from the output side optical fiber 106. At this time, the output laser light L has a set peak power, repetition frequency, and duty ratio or pulse width.

  Note that the optical fiber laser device 100 is configured to be capable of continuous wave drive if it is set to drive continuously. The driving condition during continuous wave driving is, for example, average output light power. However, the optical fiber laser device 100 may not actually be driven in a continuous wave.

  Next, a control example when the control unit 120 controls the power applying unit 111f will be described.

(Control example 1)
FIG. 3 is a flowchart showing a control example 1. FIG. 4 is a diagram illustrating setting conditions in the control example 1. In FIG. 4, the horizontal axis indicates the drive current applied to the semiconductor laser element 111a, and the vertical axis indicates the drive voltage VLD.

  In the control example 1, as shown in FIG. 3, first, the driving condition of the optical fiber laser device 100 is confirmed (step S1). If the drive condition is pulse drive (step S2, Yes), the drive voltage (VLD) is set to the drive voltage of condition B (step S3) and the process returns to step S1. If the drive condition is continuous wave drive (step S2, No), the drive voltage (VLD) is set to the drive voltage of condition A (step S4), and the process returns to step S1. The VLDs for condition A and condition B are stored in the storage unit 122, respectively.

  Condition A and condition B will be described with reference to FIG. In FIG. 4, a line L <b> 1 is a line indicating an upper limit of a settable range of drive current / drive voltage allowed in consideration of a load applied to the current adjustment unit 111 d when the optical fiber laser device 100 is driven in a continuous wave. is there. Similarly, the line L2 indicates the upper limit of the drive current / drive voltage settable region allowed in consideration of the load applied to the current adjusting unit 111d when the optical fiber laser device 100 is pulse-driven. That is, if the drive current and drive voltage are set in the lower left region from the line L1 during continuous wave driving and the lower left region from the line L2 during pulse driving, the load applied to the current adjusting unit 111d can be suppressed within an allowable range. it can. When the load applied to the current adjusting unit 111d is caused by heat generated by supplying power to the semiconductor laser element 111a, the lines L1 and L2 are curves that are substantially inversely proportional to the drive current. The line L3 is a line indicating the conditions of the drive current and drive voltage that allow the semiconductor laser element 111a to oscillate. If the drive current and drive voltage are in the region on the upper left side of the line L3, the semiconductor laser element 111a can oscillate.

  Here, as indicated by the lines L1 and L2, the upper limit of the allowable setting range of the driving current and driving voltage is larger in the pulse driving than in the continuous wave driving. The reason is that during pulse driving, the semiconductor laser element 111a is intermittently supplied with power at a predetermined repetition rate and duty ratio (or pulse width), so the drive conditions are set to drive current / drive voltage with higher load. Even if it does, it is because it can be made comparable as the load at the time of a continuous wave drive if the load concerning the current adjustment part 111d is time-averaged.

  The line L2 coincides with the line L1 when the duty ratio is 100%, and is further away from the line L1 as the duty ratio becomes lower. Accordingly, a lower drive ratio / drive voltage can be set when the duty ratio is lower.

  Therefore, in this control example 1, when the optical fiber laser device 100 is driven in a continuous wave, the driving voltage applied to the semiconductor laser element 111a is the first driving voltage (VLD of condition A), and the optical fiber laser FL is pulse-driven. If the driving voltage applied to the semiconductor laser element 111a is the second driving voltage (VLD of condition B), the second driving voltage having a value larger than the first driving voltage is applied to the semiconductor laser element 111a. As a result, the optical fiber laser device 100 is driven with a higher driving voltage (driving voltage of the semiconductor laser element 111a) in pulse driving than in continuous wave driving, and thus can output laser light with higher peak power. . On the other hand, since the first driving voltage is applied during continuous wave driving, it is possible to prevent an excessive load from being applied to the device (particularly, the current adjusting unit 111d).

  In order to increase the peak power of the laser beam output during pulse driving and the average power of the laser beam output during continuous wave driving as much as possible, it is preferable to increase the drive current as much as possible. Therefore, in the present control example 1, as shown in FIG. 4, in the continuous wave driving, the region is in the lower left region from the line L1 and the upper left region from the line L3, under the conditions of the driving current and the driving voltage where the driving current is as high as possible. It is preferable to drive under a certain condition A. In pulse driving, it is preferable that the driving is performed under the condition B which is a condition of a driving current and a driving voltage where the driving current becomes as high as possible in the lower left area from the line L2 and the upper left area from the line L3. That is, if the condition A is set during continuous wave driving, the average power of the laser beam to be output can be made as high as possible while keeping the load applied to the current adjusting unit 111d within an allowable range. If the condition B is set during pulse driving, the peak power of the laser beam to be output can be made as high as possible while keeping the load applied to the current adjustment unit 111d within an allowable range.

  However, the second drive voltage / drive current applied to the semiconductor laser element 111a is not limited to the drive voltage / drive current of Condition B. Even if it is a value smaller than the driving voltage / driving current in the condition B, if it is a value existing in the upper right region from the line L1, than the case where the driving current / driving voltage allowed during continuous wave driving is set, Laser light can be output with high peak power.

  When the load applied to the current adjusting unit 111d is mainly caused by heat generated by supplying power to the semiconductor laser element 111a, the optical fiber laser device 100 outputs ideally during pulse driving. The peak power of the laser beam can be about 1 / (Duty ratio) times the average power of the laser beam output during continuous wave driving.

  An example of VLD under conditions A and B will be described. For example, in the excitation light source unit 110, nine semiconductor laser elements 111a are connected in series to form a series connection group. At this time, a VLD as a condition A and a predetermined current value are given to the series connection group. Next, as the VLD of the condition B, a voltage higher than the VLD as the condition A by 4 V (about 0.44 V per element) and a predetermined current value are set in the series connection group, and the duty ratio is 0.625 (= When set to about 1 / 1.6), the peak power of the laser light output from the optical fiber laser device 100 can be made about 1.6 times the average power in the case of condition A. The VLD of the condition B can be a value higher than the VLD of the condition A by about 1V or less, for example, a value higher by 0.3V to 0.4V. However, the drive voltage value and current value of the conditions A and B are not limited to these values, and may be set depending on the forward voltage value of the semiconductor laser element 111a to be used, the resistance value of the resistor 111b, and the like. it can.

  This control example 1 is a control suitable for a case where the driving conditions (output peak power, repetition frequency, and duty ratio or pulse width) when the optical fiber laser device 100 is pulse driven are determined in advance.

(Control example 2)
Next, a control example 2 will be described. This control example 2 is a control suitable for a case where the driving conditions (output peak power, repetition frequency, and duty ratio or pulse width) when the optical fiber laser device 100 is pulse-driven can be arbitrarily set.

  FIG. 5 is a flowchart showing a control example 2. FIG. 6 is a diagram showing the relationship between the drive current of the semiconductor laser element 111a and the output light power of the optical fiber laser device 100. As shown in FIG. FIG. 7 is a diagram illustrating setting conditions in the control example 2.

  First, as shown in FIG. 6, when the output light power of the optical fiber laser device 100 is P and the drive current of the semiconductor laser element 111a is I, P is proportional to I. Here, the drive currents of all the semiconductor laser elements 111a are assumed to be equal to I. However, when the drive currents of the respective semiconductor laser elements 111a are different, the drive current I is, for example, the drive current of each of the semiconductor laser elements 111a. Average value.

The average heat generation amount Wavg in the current adjustment unit 111d at the time of pulse driving of the optical fiber laser device 100 is expressed by the following equation (1).
Wavg = VLD × I × (Duty ratio) = VLD × I × (pulse width) / (repetition frequency) (1)
Here, the current I is determined by the output light power P.

Furthermore, the average drive current Iavg is
Iavg = I × (Duty ratio) = I × (pulse width) / (repetition frequency)
In other words, the upper limit value V_lim of the driving voltage VLD (second driving voltage) at the time of pulse driving is a value represented by the following expression (2) from Expression (1). Here, the upper limit average heat generation amount Wavg_max is an upper limit value of the average heat generation amount Wavg allowed by the current adjustment unit 111d.
V_lim = Wavg_max / Iavg (2)

  V_lim will be described with reference to FIG. FIG. 7 is a diagram in which the horizontal axis represents average energy (Eavg = Wav × (pulse width)) and the vertical axis represents the drive voltage VLD, and a line L4 indicates current adjustment when the optical fiber laser device 100 is pulse-driven. It is a line | wire which shows the upper limit of the setting range of the drive voltage and average energy which are accept | permitted considering the load concerning the part 111d. The line L5 is a line that indicates the upper limit of the settable area of the average energy that is allowed in consideration of the load applied to the current adjusting unit 111d when the optical fiber laser device 100 is pulse-driven. Since this is the average energy, the line L5 indicates the upper limit of the settable area of the average energy that is allowed in consideration of the load applied to the current adjusting unit 111d when the optical fiber laser device 100 is driven in a continuous wave. But there is.

  The line L6 is a line indicating the upper limit of the drive voltage settable region allowed in consideration of the load applied to the current adjustment unit 111d. On the other hand, the line L7 indicates the level of the drive voltage at the intersection of the upper limit line of the drive voltage / average energy settable area indicated by the line L4 and the upper limit line of the average energy settable area indicated by the line L5. It is.

  As indicated by the arrow L8 in FIG. 7, if V_lim is a lower left region than the line L4, the load applied to the current adjustment unit 111d can be suppressed within an allowable range. If V_lim is higher than the drive voltage level (V_min) indicated by the line L6, it can be made higher than the drive voltage (first drive voltage) at the time of continuous wave drive, so that laser light can be emitted with higher peak power. Can output. Furthermore, if V_lim is a value lower than the driving voltage level (V_max) indicated by the line L7, the optical fiber laser device 100 can be pulse-driven with higher energy per time than during continuous wave driving. Driving is performed with the setting of the driving current / driving voltage at the upper right of the line L1, and laser light can be output with higher peak power. The arrow L8 indicates the driving condition under the driving current / driving voltage condition where the driving current is as high as possible as in the control example 1. However, the arrow L8 indicates the region surrounded by the line L4, the line L5, and the line L6. The inner drive voltage and average energy may be satisfied.

  Further, in the present control example 2, V_ref indicated by a line L9 is set as a drive voltage VLD between V_max and V_min, which is an optimal VLD value when pulse driving is performed under the set drive conditions. .

  V_ref is set to a value close to V_max, for example, when it is desired to achieve as high a peak power as possible. Further, as V_ref is brought closer to V_min, the margin with respect to V_max increases. Therefore, even when the duty ratio or the repetition frequency is changed, a desired peak power can be obtained more reliably.

  Based on the above description, the flow (flow F1) of the present control example 2 will be described using FIG.

  First, the driving conditions of the optical fiber laser device 100 are confirmed (step S1). If the driving condition is continuous wave driving (No at Step S2), the driving voltage (VLD) is set to the driving voltage of Condition A (Step S4) as in Control Example 1, and the process returns to Step S1. If the drive condition is pulse drive (step S2, Yes), the output frequency (corresponding to the output peak power) under the drive condition is checked for the repetition frequency and the duty ratio (or pulse width) (step S5). Next, V_lim is calculated using the above-described equation (2) based on the confirmed driving condition. Next, V_ref stored in the storage unit 122 is read and V_lim is compared with V_ref. If V_lim is larger than V_ref (step S7, Yes), the drive voltage (VLD) as the second drive voltage is set to V_ref. (Step S8), and the process returns to step S1. If V_lim is less than or equal to V_ref (step S7, No), VLD is set to V_lim (step S9), and the process returns to step S1.

  As described above, this control example 2 is a control suitable for a case where the driving conditions (output peak power, repetition frequency, and duty ratio or pulse width) when the optical fiber laser device 100 is pulse-driven can be arbitrarily set. is there.

  If it is determined in step S7 that V_lim is equal to or less than V_ref, the optical fiber laser device 100 is in a state where the load is greater than when pulse driving is performed under a desired condition. Therefore, in consideration of safety, control may be performed so that the laser light is not output from the optical fiber laser device 100 by shutting down the drive current instead of step S9 described above.

(Modification of Control Example 2)
By the way, in the above control example 2, V_lim is calculated based on the upper limit average heat generation amount Wavg_max. For example, even when the average heat generation amount Wavg is the same, for example, when the duty ratio is small, per pulse High peak light power. As described above, when the peak light power per pulse is large, the load applied to the current adjustment unit 111d may be larger than when the average heat generation amount is considered. In such a case, V_lim may be calculated based on the peak optical power per pulse as in the following equation (4).

First, the heat generation amount W per pulse at the time of pulse driving of the optical fiber laser device 100 is expressed by the following equation (3).
W = VLD × I × (Duty ratio) / (repetition frequency) = VLD × I × (pulse width) (3)
Here, the current I is determined by the output light power P.
The upper limit value V_lim when the heat generation amount W becomes the upper limit heat generation amount W_max is
From equation (3)
V_lim = upper limit heating value W_max / I / (Duty ratio) × (repetition frequency)
= Upper limit heating value W_max / I / (pulse width) (4)
It becomes.

  For example, in step S5 of the flow F1 shown in FIG. 5, it may be determined which V_lim of the expression (2) and the expression (4) is used based on the confirmed driving condition.

  By the way, the control example 2 and the modification thereof receive an external control signal S as a command signal, and according to the external control signal S, the arithmetic unit 121 stores a predetermined program and data (for example, table data) stored in the storage unit 122. ), The optical fiber laser device 100 can be applied to a setting for driving under predetermined driving conditions (for example, output peak power, repetition frequency, and duty ratio or pulse width during pulse driving). In the control example 2 and the modification thereof, the external control signal S includes information on the driving conditions of the optical fiber laser device 100 (for example, output peak power, repetition frequency, and duty ratio or pulse width during pulse driving). It can also be applied to a signal. In this case, the optical fiber laser device 100 is driven according to information on driving conditions input from the outside.

  On the other hand, as an operation mode of the optical fiber laser device 100, the external control signal S may be a set value of the power of the laser light output from the optical fiber laser device 100 and an output start command or an output stop command. For example, when the optical fiber laser device 100 is in the output stop state (OFF state), for example, the power of the laser light to be output from the optical fiber laser device 100 is set to 500 W as the external control signal S and the output is started. There is a case where a signal including a command to turn on (turn on) is input. Alternatively, when the optical fiber laser device 100 is in an ON state, a signal including a command for turning the optical fiber laser device 100 in an OFF state may be input as the external control signal S.

  When the optical fiber laser device 100 is pulse-driven and the output peak power, repetition frequency, duty ratio, or pulse width are all known, the amount of heat generation can be predicted, but the external control signal S is light In the case of a command signal as a trigger signal for turning on or off the fiber laser apparatus 100, the timing of the next command or the content of the command cannot be predicted. Therefore, the control example 2 and its modification are applied. Difficult to do. Therefore, in the following, as Control Example 3, a control example that can be applied when the external control signal S is a command to turn the optical fiber laser device 100 on or off will be described.

(Control example 3)
FIG. 8 is a flowchart showing a control example 3. 9 and 10 are diagrams showing setting conditions in the control example 3. FIG.

First, the heat generation amount W is expressed by the following equation (5).
W = VLD × I × ((output ON time) + (ON time initial value)) (5)
The output ON time is an elapsed time since the optical fiber laser device 100 was most recently turned on. Further, the initial value of the ON time is obtained from equation (9) described later.
Here, the current I is determined by the output light power P.

The upper limit value Von_lim of the drive voltage VLD calculated when the output is ON, where W is the upper limit heating value W_max,
From the equation (5), it is expressed by the following equation (6). The upper limit heat generation amount W_max is an upper limit value of the allowable heat generation amount W.
Von_lim = W_max / I / ((output ON time) + (ON time initial value)) (6)

Further, the average calorific value Wavg is expressed by the formula (7).
Wavg = VLD × I × (output ON time) / ((output ON time) + (output OFF time)) (7)
The output OFF time is an elapsed time since the optical fiber laser device 100 was most recently turned off.

Furthermore, the average drive current Iavg is
Iavg = I × (output ON time) / ((output ON time) + (output OFF time))
In other words, the upper limit value Voff_lim of the drive voltage VLD calculated when the output is OFF is expressed by the following expression (8) from the expression (7). The upper limit average power consumption Wavg_max is an amount represented by an average heat generation amount + average heat release amount during continuous wave (CW) driving. The average heat radiation amount is an amount that varies depending on the arrangement of the semiconductor laser element and the current adjusting unit, the size and heat conductivity of the heat sink, air cooling, and water cooling.
Voff_lim = Wavg_max / Iavg (8)

Further, the initial value of the ON time is obtained from the equation (9).
(ON time initial value) = W_max / Voff_lim / I (9)

  Von_lim will be described with reference to FIG. FIG. 9 is a diagram in which the horizontal axis represents energy (E) corresponding to the driving power given to the output ON time, and the vertical axis represents the driving voltage VLD, and the line L4A represents a case where the optical fiber laser device 100 is pulse-driven. 6 is a line showing the upper limit of the drive voltage / energy settable region allowed in consideration of the load applied to the current adjusting unit 111d.

  Lines L6 and L7 are lines indicating V_min and V_max similar to those in FIG.

  As indicated by an arrow L10 in FIG. 9, Von_lim takes a value that does not exceed V_max as an initial value, but the value decreases as the output ON time increases. The reason for this is that heat accumulates in the current adjusting unit 111d as the output ON time increases, so that the load that can be newly applied decreases accordingly. Under this condition, if Von_lim is set in the lower left region from the line L4A, the load applied to the current adjustment unit 111d can be suppressed within an allowable range. Further, if Von_lim is higher than the drive voltage level (V_min) indicated by the line L6, it can be made higher than the drive voltage (first drive voltage) at the time of continuous wave drive, so that laser light can be emitted with higher peak power. Can output. Furthermore, if Von_lim is equal to or lower than the drive voltage level (V_max) indicated by the line L7, the optical fiber laser device 100 can be pulse-driven with higher energy per time than during continuous wave drive. Driving is performed with the setting of the driving current and driving voltage at the upper right, and laser light can be output with higher peak power. The arrow L10 indicates a condition for driving under the condition of a drive current / drive voltage where the drive current is as high as possible, as in Control Example 1. However, the arrow L10 may be a condition lower than V_max and higher than V_min.

  Further, in the present control example 3, V_ref indicated by a line L11 is set as a drive voltage VLD between V_max and V_min, which is an optimum VLD value when pulse driving is performed under the set drive conditions. .

  V_ref is set to a value close to V_max, for example, when it is desired to realize as high a peak power as possible. Further, since the margin for V_max increases as V_ref approaches V_min, the desired peak power can be more reliably obtained even when the output ON time or the output OFF time changes.

  Next, Voff_lim will be described with reference to FIG. FIG. 10 is a diagram in which the horizontal axis represents the average energy (Eavg) and the vertical axis represents the drive voltage VLD, and the line L4 represents the current when the optical fiber laser device 100 is pulse-driven as in FIG. It is a line which shows the upper limit of the setting area | region which can accept | permit the drive voltage and average energy accept | permitted considering the load concerning the adjustment part 111d.

  Lines L5, L6, and L7 are the same as those in FIG.

  As indicated by an arrow L12 in FIG. 10, Voff_lim takes a value larger than V_min as an initial value, but may take a value smaller than V_min. Thereafter, the value of Voff_lim increases as the output OFF time increases. The reason is that as the output OFF time increases, the heat accumulated in the current adjusting unit 111d is dissipated, so that the load that can be newly applied increases accordingly. Under this condition, if Voff_lim is set to the lower left region from the line L4, the load applied to the current adjustment unit 111d can be suppressed within an allowable range. Further, if Voff_lim is higher than the drive voltage level (V_min) indicated by the line L6, the drive voltage (first drive voltage) at the time of continuous wave drive can be made higher, so that laser light can be emitted with higher peak power. Can output. Furthermore, if Von_lim is equal to or lower than the drive voltage level (V_max) indicated by the line L7, the optical fiber laser device 100 can be pulse-driven with higher energy per time than during continuous wave drive. Driving is performed with the setting of the driving current and driving voltage at the upper right, and laser light can be output with higher peak power. Note that the arrow L10 indicates the driving condition under the driving current / driving voltage condition in which the driving current is as high as possible as in the control example 1, but the region surrounded by the line L4, the line L5, and the line L6. The inner drive voltage and average energy may be satisfied.

  For example, as shown in Equation (5), when calculating the heat generation amount W, the initial value of the ON time shown in Equation (9) is added to the output ON time. The initial value of the ON time takes into account the history of the ON / OFF state before the start time of the most recent output ON time considered in the calculation. For example, as can be seen from equation (9) and FIG. 10, Voff_lim increases as the OFF time increases, so the initial ON time value decreases. The initial value of the ON time initial value is zero.

  Based on the above description, the flow of the present control example 3 will be described with reference to FIG.

  First, it is determined whether or not the external control signal S as a trigger signal is used in the control of the optical fiber laser device 100. When the external control signal S is not used (step S10, No), the flow F1 of the control example 2 shown in FIG. 5 is executed. At this time, the flow of the modified example of the control example 2 may be executed. When the external control signal S is used (step S10, Yes), it is determined whether an output start command is input by the external control signal S and the optical fiber laser device 100 is in an output ON operation state.

  When the output is ON (step S11, Yes), the ON time initial value is calculated from Voff_lim using the equation (9) (step S12). If it is not necessary to consider the history of the ON / OFF state before the latest output ON time, the initial value of the ON time is set to zero.

  Next, the output power and the output ON time are confirmed (step S13), and Von_lim is calculated from equation (6) (step S14). Next, V_ref stored in the storage unit 122 is read and compared with Von_lim and V_ref. If Von_lim is larger than V_ref (step S15, Yes), the drive voltage (VLD) as the second drive voltage is set to V_ref. (Step S16), and the process returns to step S11. If Von_lim is equal to or less than V_ref (step S15, No), VLD is set to Von_lim (step S17), and the process returns to step S11.

  When it is determined in step S17 that Von_lim is equal to or less than V_ref, the optical fiber laser device 100 is in a state where the load is larger than when pulse driving is performed under a desired condition. Therefore, in consideration of safety, control may be performed so that the laser light is not output from the optical fiber laser device 100 by shutting down the drive current instead of step S17 described above.

  On the other hand, when the output stop command is input by the external control signal S and the output is OFF (step S11, No), the output OFF time is confirmed (step S18), and Voff_lim is calculated from the equation (8). (Step S19). Next, V_ref stored in the storage unit 122 and Von_lim that has been calculated and stored most recently are read out to determine whether or not the condition 1 (V_ref> Von_lim> Voff_lim) is satisfied. If condition 1 is satisfied (step S20, Yes), VLD as the second drive voltage is set to Von_lim (step S21), and the process returns to step S11. If condition 1 is not satisfied (step S20, No), it is further determined whether condition 2 (V_ref> Voff_lim> Von_lim) is satisfied. When the condition 2 is satisfied (step S22, Yes), the VLD as the second drive voltage is set to Voff_lim (step S23), and the process returns to step S11. If condition 2 is not satisfied (step S22, No), VLD is set to V_ref (step S24), and the process returns to step S11.

  FIG. 11 is a diagram illustrating an example of a time chart of the set value of the drive voltage VLD in the control example 3. In FIG. 11, the optical fiber laser device 100 repeats the ON state and the OFF state in the sections T1 to T6 in accordance with the ON / OFF command of the external control signal. The sections T1 to T6 are, for example, several μs to several hundred ms. On the other hand, the control flow shown in FIG. 8 is repeated in a sufficiently short time (for example, several ns) for the section.

  First, in the section T1, the value of Von_lim decreases as the output ON time increases. However, since V_ref is smaller, VLD is set to V_ref (step S16 in FIG. 8). In section T2, the value of Voff_lim increases as the output OFF time increases. However, since neither Condition 1 nor Condition 2 is satisfied, VLD is set to V_ref (step S24 in FIG. 8).

  However, in section T3, Von_lim becomes V_ref or less from the middle of section T3, so VLD is set to Von_lim (step S17 in FIG. 8).

  Note that the time waveforms of Voff_lim and Von_lim shown in FIG. 11 vary depending on the output power of the optical fiber laser device 100.

  As described above, the control example 3 is a control signal particularly suitable for a case where the external control signal S is a command signal as a trigger signal for turning the optical fiber laser device 100 on or off, and the driving conditions are set in real time. As an example, since it is first determined whether or not to use the external control signal S as a trigger signal, the present invention can also be applied to the case where the control example 2 is suitable.

  The application range of the control example 3 is not limited to the case where the external control signal S is used as a trigger signal for turning the optical fiber laser device 100 on or off. For example, a trigger signal for turning on or off the optical fiber laser device 100 is generated inside the control device 120 in response to a command from the external control signal S, and the optical fiber laser device 100 is turned on or off by the trigger signal. The control example 3 can also be applied to the control.

(Control example 4)
Next, a control example 4 will be described. This control example 4 may be used in combination with the above control examples 1 to 3 and modifications thereof. In the present control example 4, a temperature measuring device 111e provided in the current adjusting unit 111d is used.

FIG. 12 is a flowchart showing a control example 4. In the present control example 4, a temperature threshold is set for the temperature of the current adjustment unit 111d. Assuming that the temperature threshold conditions are conditions C and D, the following equation is established.
(Temperature threshold of condition C) ≧ (temperature threshold of condition D)

Further, in the present control example 4, when the conditions for the drive voltage VLD as the second drive voltage are the conditions E and F, the following equations are established.
(Voltage value of Condition E) ≦ (Voltage value of Condition F)

  In this control example 4, first, VLD is set to the voltage value of condition F (step S25). At this time, the voltage value of the condition F may be a voltage value determined by the control examples 1 to 3. Next, the temperature measuring device 111e measures the temperature of the current adjusting unit 111d and confirms it (step S26). The temperature measurement value is input to the control unit 120. Next, it is determined whether or not the confirmed temperature is higher than the temperature threshold value of the condition C. When the confirmed temperature is higher than the temperature threshold value of the condition C (step S27, Yes), the drive voltage VLD is set to the voltage value of the condition E (step S28), and the process returns to S26. On the other hand, when the confirmed temperature is equal to or lower than the temperature threshold value of the condition C (step S27, No), it is determined whether or not the confirmed temperature is higher than the temperature threshold value of the condition D. If the confirmed temperature is lower than the temperature threshold value of the condition D (step S29, Yes), the drive voltage VLD is set to the voltage value of the condition F (step S30), and the process returns to S26. On the other hand, when the confirmed temperature is equal to or higher than the temperature threshold value of condition D (step S29, No), the process directly returns to step S26. When the confirmed temperature is higher than the temperature threshold value of the condition C (Yes in step S27), the optical fiber laser device 100 may be turned off instead of step S28, or the driving voltage at the time of continuous wave driving is used. It may be set.

  In this control example 4, the temperature of the current adjustment unit 111d is confirmed, and if the temperature is higher than the temperature threshold of the condition C, the drive voltage VLD is set to a lower value of the condition E, but becomes lower than the temperature threshold of the condition D. Then, the drive voltage VLD is set to a high value of the condition F. As a result, the load applied to the current adjustment unit 111d can be more reliably suppressed within the allowable range, and when the load is within the allowable range, a higher drive voltage VLD can be set to obtain a higher peak output light power. .

  The above control examples 1 to 4 are not limited to the optical fiber laser device 100 according to the first embodiment, but can be applied to optical fiber laser devices having other configurations that use a semiconductor laser element as a pumping light source.

  FIG. 13 is a diagram illustrating a configuration of an optical fiber laser device according to the second embodiment. An optical fiber laser device 200 shown in FIG. 13 is a so-called MOPA (Master Oscillator Power Amplifier) type optical fiber laser device, for example, a seed light source 107 including a semiconductor laser element having a laser oscillation wavelength of 1084 nm, and a seed light source. An optical isolator 108, an optical multiplexer 109, an amplification optical fiber 104, an optical isolator 108, and a bandpass optical filter 130 are sequentially connected to 107. The optical fiber laser device 200 further includes a pumping light source 111 connected to the optical multiplexer 109.

  The optical fiber laser device 200 further includes an optical multiplexer 102, an amplification optical fiber 104, and an output-side optical fiber 106, which are sequentially connected to the bandpass optical filter 130. The optical fiber laser device 200 further includes a pumping light source unit 110 including a plurality of pumping light sources 111 connected to the optical multiplexer 102, and a control unit 120 connected to the pumping light source 111.

  In this optical fiber laser device 200, the amplification optical fiber 104 on the front stage side is optically pumped by pumping light from the pumping light source 111 connected to the optical multiplexer 109. Then, the laser light output from the seed light source 107 is optically amplified by the amplification optical fiber 104 on the front stage side. The amplified laser light is further optically amplified by the subsequent amplification optical fiber 104 that is optically pumped by the pumping light from the pumping light source unit 110 including the plurality of pumping light sources 111 connected to the optical multiplexer 102, and laser light Output as L. The band-pass optical filter 130 cuts ASE (Amplified Spontaneous Emission) light or the like generated in the upstream amplification optical fiber 104, and is output from the seed light source 107 and optically amplified by the upstream amplification optical fiber 104. This is for selectively passing the laser beam.

  In this optical fiber laser device 200, the control unit 120 performs the control in the above control example in the same manner as the control unit 120 in the optical fiber laser device 100, so that the laser beam L can be output with a higher peak power during pulse driving.

  The present invention is not limited to the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

DESCRIPTION OF SYMBOLS 100 Optical fiber laser apparatus 102 Optical multiplexer 104 Optical fiber for amplification 106 Output side optical fiber 107 Seed light source 108 Optical isolator 109 Optical multiplexer 110 Excitation light source part 111 Excitation light source 111a Semiconductor laser element 111b Resistor 111c Voltage adjustment part 111d Current adjustment Part 111da FET
111 db Gate voltage adjustment unit 111 e Temperature measuring device 111 f Power application unit 120 Control unit 121 Calculation unit 122 Storage unit 123 Storage unit 124 External input unit 130 Bandpass optical filter 200 Optical fiber laser device F1 Flow FL Optical fiber laser L Laser light L1 L7, L9, L11 line L8, L10, L12 Arrow line S External control signal T1-T6 section

Claims (10)

A method of controlling an optical fiber laser device using a semiconductor laser element as an excitation light source,
Including a power application step of providing a driving voltage and a driving current to the semiconductor laser element,
In the power application step, a driving voltage applied to the semiconductor laser element when the optical fiber laser device is driven in a continuous wave is a first driving voltage, and is applied to the semiconductor laser element when the optical fiber laser device is pulse-driven. A control method for an optical fiber laser device, wherein a driving voltage is a second driving voltage, and the second driving voltage having a value larger than the first driving voltage is applied to the semiconductor laser element during pulse driving. Including a confirmation step of confirming a driving condition of the optical fiber laser device;
When the driving condition confirmed in the confirmation step is a continuous wave driving condition, the first driving voltage is applied to the semiconductor laser element in the power application step,
2. The optical fiber laser device according to claim 1, wherein when the driving condition is a pulse driving condition in the confirmation step, the second driving voltage is applied to the semiconductor laser element in the power application step. Control method. Including a setting step of setting a peak power of a laser beam output from the optical fiber laser device, a repetition frequency, and a setting value of a duty ratio or a pulse width as a driving condition,
3. The method of controlling an optical fiber laser device according to claim 1, wherein, in the power application step, the drive current and the second drive voltage corresponding to the set value are applied to the semiconductor laser element. 4. A step of generating or inputting a set value and output start command or output stop command of the power of the laser beam output from the optical fiber laser device;
A confirmation step of confirming the set value, the elapsed time from the output start, and the elapsed time from the output stop,
3. The control of the optical fiber laser device according to claim 1, wherein, in the power application step, the drive current and the second drive voltage corresponding to a confirmation result of the confirmation step are applied to the semiconductor laser element. Method. A temperature measuring step of measuring a temperature of a current adjusting unit that adjusts the driving current applied to the semiconductor laser element;
5. The optical fiber laser control method according to claim 1, wherein the second drive voltage corresponding to the temperature measured in the temperature measurement step is applied to the semiconductor laser element. 6. An optical fiber laser comprising a semiconductor laser element as an excitation light source;
A power applying unit for applying a driving voltage and a driving current to the semiconductor laser element;
A control unit for controlling the power application unit;
An optical fiber laser device comprising:
The control unit uses the drive voltage applied to the semiconductor laser element when the optical fiber laser device is driven in a continuous wave as a first drive voltage, and the drive applied to the semiconductor laser element when the optical fiber laser device is pulse-driven. If the voltage is the second drive voltage, the power applying unit is controlled so as to give the semiconductor laser element the second drive voltage having a value larger than the first drive voltage during pulse driving. Fiber laser device. The control unit confirms the driving condition of the optical fiber laser device,
When the confirmed driving condition is a continuous wave driving condition, the power applying unit is controlled to apply the first driving voltage to the semiconductor laser element,
7. The optical fiber according to claim 6, wherein when the confirmed driving condition is a pulse driving condition, the power applying unit is controlled to apply the second driving voltage to the semiconductor laser element. 8. Laser device. The control unit sets the peak power of the laser light output from the optical fiber laser device, the repetition frequency, and the set value of the duty ratio or pulse width as a driving condition,
8. The optical fiber laser device according to claim 6, wherein the power applying unit is controlled so that the driving current and the second driving voltage corresponding to the set value are supplied to the semiconductor laser element. 9. The control unit generates or inputs a power set value and an output start command or output stop command of the laser beam output from the optical fiber laser device,
Check the set value, the elapsed time from the output start, the elapsed time from the output stop,
8. The optical fiber laser device according to claim 6, wherein the power applying unit is controlled so as to apply the driving current and the second driving voltage according to the confirmation result to the semiconductor laser element. 9. The power applying unit includes a current adjusting unit that adjusts the driving current applied to the semiconductor laser element, and a temperature measuring instrument that measures the temperature of the current adjusting unit,
The said control part controls the said electric power provision part so that the said 2nd drive voltage according to the temperature which the said temperature measuring device measured may be given to the said semiconductor laser element, The any one of Claims 6-9 The optical fiber laser device according to one.

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