JP2017135151A - Fiber laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber laser device capable of suppressing damage to an optical element and emitting light of one shot pulse, and to provide a pulse light emitting method of the fiber laser device.SOLUTION: In a standby state, a control unit CP brings an AOM 14, which is a second reflecting unit, into a reflecting state and causes an excitation light source 11 to emit excitation light. When an emission command is input in the standby state, the control unit CP changes the AOM 14 to a non-reflecting state after a first predetermined period T1 from when the emission command is input, and changes the AOM 14 to the reflecting state after a second predetermined period T2 when light does not self-oscillate in an amplification optical fiber 13 from when the AOM 14 is changed to the non-reflecting state.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fiber laser device that emits pulsed output light.

  A fiber laser device that amplifies and emits signal light with a rare-earth-doped fiber is used as one of laser devices used for processing machines that perform processing using laser light and medical devices such as a scalpel using laser light. ing. As one of such fiber laser devices, there is known a MO-PA (Master Oscillator Power Amplifier) type fiber laser device that amplifies and emits seed light. In some cases, the seed light unit, which is an MO unit that emits seed light of the fiber laser device, is also composed of a resonant fiber laser device.

  Patent Document 1 listed below describes such a fiber laser device. In the fiber laser device described in Patent Document 1, the seed light portion is composed of a resonance type fiber laser device as described above, and a first FBG (Fiber Bragg Grating) is formed at one end of the amplification optical fiber. The other end is connected to an acousto-optic element (AOM: Acoustic Optic Modulation), and the side opposite to the amplification optical fiber side of the AOM is connected to the second FBG. The AOM propagates incident light in different directions depending on whether it is on or off. In this fiber laser device, light is propagated to the second FBG in the on state, and light is prevented from propagating to the second FBG in the off state. That is, the light is reflected by the second FBG when the AOM is on, and the light is not reflected when the AOM is off. Therefore, when the AOM is on, a resonator is formed between the first FBG and the second FBG via the amplification optical fiber and the AOM, and when the AOM is off, the resonator is not formed. In the seed light portion of this fiber laser device, since the AOM repeats the on state and the off state, pulsed seed light is emitted each time the AOM is turned on.

Japanese Patent No. 4647696

  In the fiber laser device described in Patent Document 1, the pulsed seed light is emitted continuously in synchronism with AOM on / off as described above. Therefore, when the excitation light enters the amplification optical fiber of the amplifier unit, the pulsed seed light is amplified, and the pulsed emitted light is emitted in a row in synchronization with the ON / OFF of the AOM.

  Incidentally, there is a demand for a fiber laser device that emits only one pulse of emitted light. In order to emit such a one-shot pulse light, it is conceivable that the AOM is on standby in an off state and the AOM is turned on at a timing at which the one-shot pulse emission light is desired to be emitted.

  However, when the AOM is in a standby state, the excitation energy of the rare earth element in the amplification optical fiber becomes too high, and unnecessary oscillation (self oscillation) may occur. When such oscillation occurs, there is a concern that a giant pulse is emitted at an unintended timing and destroys an optical element such as an excitation light source.

  Accordingly, an object of the present invention is to provide a fiber laser device capable of emitting one-shot pulsed light while suppressing damage to an optical element, and a pulsed light emitting method for the fiber laser device.

  In order to solve the above problems, a fiber laser device of the present invention propagates through an amplification optical fiber on which excitation light from an excitation light source is incident and a core of the amplification optical fiber provided on one end side of the amplification optical fiber. A first reflecting portion that reflects the light to be reflected on the core, and a reflection that is provided on the other end side of the amplification optical fiber and reflects the light propagating through the core at a lower reflectance than the first reflecting portion. A second reflection unit capable of switching between a state and a non-reflection state in which light propagating through the core is not reflected by the core, and a control unit. The fiber laser device is used in the pulsed light emission method of the fiber laser device of the present invention. This fiber laser device operates as follows when emitting pulsed light. That is, in the standby state, the control unit causes the second reflecting unit to be in the reflective state and emits excitation light from the excitation light source. When an emission command is input in the standby state, the emission command is input. After the first predetermined period, the second reflecting portion is set in the non-reflecting state, and after the second reflecting portion is set in the non-reflecting state, after the second predetermined period in which light does not self-oscillate in the amplification optical fiber. The second reflecting portion is in the reflecting state.

  In such a fiber laser device and the pulsed light emission method of the fiber laser device, in the standby state, since the excitation light is incident on the amplification optical fiber from the excitation light source, the active element in the amplification optical fiber is in the excitation state. It is said. However, since the second reflecting portion is in a reflecting state, oscillation occurs between the first reflecting portion and the second reflecting portion. While this oscillation is occurring, light with low power is continuously emitted from the second reflecting portion, so that the active element is not brought into a highly excited state by the oscillation. For this reason, even when the standby state is long or when the first predetermined period is long, it is possible to prevent unnecessary light having a high spire value from being emitted due to unintentional self-oscillation. In the second predetermined period, since the oscillation does not occur, the active element of the amplifying optical fiber is in a high excitation state, but the second predetermined period is a period in which self-oscillation does not occur. It is possible to prevent unintentional light having a high spire value from being emitted. Then, after the second predetermined period, the second reflecting portion is brought into a reflecting state, and thus oscillation occurs again. As described above, since the active element is in a high excited state in the second predetermined period, pulsed light having a high spire value can be emitted by the oscillation. Thus, according to the fiber laser device and the pulsed light emission method of the fiber laser device of the present invention, it is possible to emit one-shot pulsed light while suppressing damage to the optical element.

  The first predetermined period is preferably longer than the second predetermined period.

  Since the first predetermined period is long, another operation can be performed between the emission command and the emission of the one-shot pulsed light. For example, when a one-shot pulsed light emitted from a fiber laser device is incident on an amplifier using an amplification optical fiber and further amplified, the active element of the amplification optical fiber of the amplifier is excited in a first predetermined period. Can do.

  The control unit preferably maintains the reflection state of the second reflection unit after the second predetermined period for a period longer than the first predetermined period.

  The excited state of the active element in the amplification optical fiber immediately after the pulse light is emitted is unlikely to be the same as the predetermined excited state immediately before the second predetermined period starts. However, since the second predetermined period is longer than the first predetermined period, the excited state of the active element in the amplification optical fiber is reduced compared to the case where the second predetermined period is shorter than the first predetermined period. The predetermined excited state can be approached. When the emission command is input, the second reflecting portion is further brought into the reflecting state only for the first predetermined period, and the excited state of the active element in the amplification optical fiber can be brought closer to the predetermined excited state. For this reason, it can suppress that the spiers value and pulse width of one shot pulse light change for every emission.

  In addition, the control unit may be configured such that the second reflecting unit is in the reflecting state after the second predetermined period and that the active element in the amplification optical fiber is in the excited state in the standby state. The second reflecting portion is in the non-reflecting state only for a third predetermined period, and the excited state of the active element is the excited state of the active element in the standby state during the third predetermined period. It is preferable that the period is shorter than the period of the same excited state.

  When the one-shot pulse light is emitted, the active element in the amplification optical fiber is in a low excitation state. This excited state may be lower than the excited state in the standby state. Therefore, the second reflecting portion is set to the non-reflecting state only for the third predetermined period in a state where the excited state of the active element is lower than the excited state of the active element in the standby state. By making the second reflection part non-reflective only for a third predetermined period, which is a short period, the active element in the amplification optical fiber can be brought close to the excited state of the active element in the standby state at an early stage. As described above, the third predetermined period is shorter than the period in which the excited state of the active element is in the same excited state as the excited state of the active element in the standby state. Therefore, even if the second reflecting portion is brought into a non-reflecting state again after the third predetermined period, it is possible to suppress the emission of pulsed light.

  In this case, the first predetermined period is longer than the second predetermined period, and the control unit sets the reflection state of the second reflecting unit after the third predetermined period to the first predetermined period. It is preferable to maintain for a longer period.

  As described above, since the period in which the second reflecting portion is in the reflecting state is longer than the first predetermined period, the one-shot pulse light is compared with the case where the second predetermined period is shorter than the first predetermined period. It is possible to suppress changes in the spire value and pulse width of each time the light is emitted.

  As described above, according to the present invention, there are provided a fiber laser device capable of emitting one-shot pulsed light while suppressing damage to an optical element, and a pulsed light emitting method for the fiber laser device.

It is a figure which shows the MO-PA type fiber laser apparatus which has the fiber laser apparatus which concerns on this invention as a light source. 2 is a timing chart schematically showing the operation of the fiber laser device of FIG. 1. It is a figure which shows the mode of the magnitude | size of the power of the light radiate | emitted from each site | part at the time of the emission of one-shot pulsed light. 6 is a timing chart schematically showing another operation of the fiber laser device of FIG. 1.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a fiber laser device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a fiber laser device according to the present invention.

  As shown in FIG. 1, the fiber laser device 1 includes a seed light unit MO that emits seed light, a preamplifier PR that amplifies seed light emitted from the seed light unit MO, a main amplifier PA, and a seed light unit MO. Controls the wavelength conversion unit RF provided between the preamplifier PR, the wavelength selection filter FL provided between the wavelength conversion unit RF and the main amplifier PA, the seed light unit MO, the preamplifier PR, and the main amplifier PA. A control unit CP is provided as a main configuration. Thus, the fiber laser device 1 is a so-called MO-PA type fiber laser device in which the seed light part MO is a master oscillator and the main amplifier PA is a power amplifier.

<Configuration of seed light part MO>
The seed light unit MO includes an excitation light source 11 that emits excitation light, an amplification optical fiber 13 to which excitation light emitted from the excitation light source 11 is incident and an active element that is excited by the excitation light is added, and an amplification light source The main configuration is an FBG (Fiber Bragg Grating) 12 as a first reflecting portion provided on one end side of the optical fiber 13 and an AOM 14 as a second reflecting portion connected to the other end of the amplification optical fiber 13. Prepare. Thus, the seed light unit MO is composed of a resonant fiber laser device.

  The excitation light source 11 of the seed light unit MO is a light source that emits continuous light, and is composed of, for example, a laser diode. The excitation light source 11 emits excitation light having a wavelength for exciting the active element added to the amplification optical fiber 13, for example, light having a wavelength of 915 nm. Further, the excitation light source 11 is connected to the first optical fiber 18, and the light emitted from the excitation light source 11 of the seed light unit MO propagates through the first optical fiber 18.

  The amplification optical fiber 13 of the seed light unit MO has a core and a cladding that surrounds the outer peripheral surface of the core without a gap. In the amplification optical fiber 13, the refractive index of the core is higher than the refractive index of the cladding. Examples of the material constituting the core include germanium and other elements that increase the refractive index, and the excitation light source 11 of the seed light unit MO. And quartz to which an active element such as ytterbium (Yb) that is excited by the light of the seed light part emitted from the substrate is added. Examples of such active elements include rare earth elements, and examples of rare earth elements include thulium (Tm), cerium (Ce), neodymium (Nd), europium (Eu), and erbium (Er) in addition to Yb. Can be mentioned. Furthermore, bismuth (Bi) etc. other than rare earth elements are mentioned as an active element. Moreover, as a material which comprises the clad of the optical fiber 13 for amplification, the pure quartz to which no dopant is added is mentioned, for example.

  The core of the first optical fiber 18 is connected to the core of the amplification optical fiber 13. Further, the FBG 12 is provided in the core of the first optical fiber 18. Thus, the FBG 12 is provided on one end side of the amplification optical fiber 13. The portion of the FBG 12 in which the refractive index increases at a constant period along the longitudinal direction of the first optical fiber 18 is repeated, and the period of the amplification optical fiber 13 in the excited state is adjusted by adjusting this period. Of the light emitted by the active element, the light of a specific wavelength is reflected. As described above, when the active element added to the amplification optical fiber 13 is ytterbium, the FBG 12 has, for example, a reflectance of 100% for light having a wavelength of 1060 nm.

  An AOM 14 is connected to the other end of the amplification optical fiber 13 of the seed light unit MO. The AOM 14 can switch between a reflective state and a non-reflective state. In the reflection state, the light incident on the AOM 14 from the core of the amplification optical fiber 13 propagates in the AOM 14 toward the preamplifier PR, and causes fullel reflection on the end surface of the AOM 14 on the preamplifier PR side. Incident on the core. The reflectance of this Fullel reflection is made lower than that of the FBG 12. In the non-reflecting state, light incident on the AOM 14 from the core of the amplification optical fiber 13 propagates in a direction different from the reflecting state in the AOM 14. For this reason, in the non-reflection state, the light incident on the AOM 14 is not reflected toward the core of the amplification optical fiber 13.

<Configuration of preamplifier PR>
The preamplifier PR includes an excitation light source 21, an amplification optical fiber 23, and a coupler 22 as main components.

  The excitation light source 21 of the preamplifier PR is composed of, for example, a plurality of laser diodes. As will be described later, excitation light having a wavelength for exciting the active element added to the amplification optical fiber 23 of the preamplifier PR, for example, excitation light having a wavelength of 915 nm. Is emitted. The excitation light source 21 is connected to the optical fiber 28, and the excitation light emitted from the excitation light source 21 propagates through the optical fiber 28. An example of the optical fiber 28 is a multimode fiber. In this case, the excitation light propagates through the optical fiber 28 as multimode light.

  The amplification optical fiber 23 of the preamplifier PR has a core, an inner cladding that surrounds the outer peripheral surface of the core without a gap, and an outer cladding that covers the outer peripheral surface of the inner cladding. In the amplification optical fiber 23, the refractive index of the core is higher than the refractive index of the inner cladding, and the refractive index of the inner cladding is higher than the refractive index of the outer cladding. That is, the amplification optical fiber 23 has a double clad structure. In the amplification optical fiber 23, as a material constituting the core, for example, the same material as the core of the amplification optical fiber 13 of the seed light portion MO can be exemplified, and as a material constituting the inner cladding, For example, the same material as the cladding of the amplification optical fiber 13 of the seed light part MO can be mentioned. Examples of the material constituting the outer cladding of the amplification optical fiber 23 include an ultraviolet curable resin.

  In the present embodiment, the AOM 14 of the seed light unit MO is connected to the second optical fiber 29. The coupler 22 connects the second optical fiber 29 and the optical fiber 28 and one end of the amplification optical fiber 23. Specifically, in the coupler 22, the core of the second optical fiber 29 is connected to the core of the amplification optical fiber 23, and the core of the optical fiber 28 is connected to the inner cladding of the amplification optical fiber 23. ing. Accordingly, the light emitted from the AOM 14 of the seed light unit MO enters the core of the amplification optical fiber 23 via the second optical fiber 29 and propagates through the core. The excitation light emitted from the excitation light source 21 enters the inner cladding of the amplification optical fiber 23 and propagates mainly through the inner cladding. Accordingly, the light propagating through the core of the amplification optical fiber 23 causes stimulated emission of the active element excited by the pumping light emitted from the pumping light source 21, thereby amplifying the light propagating through the core.

<Configuration of wavelength converter RF and wavelength selection filter FL>
The wavelength converter RF is connected to the amplification optical fiber 23 of the preamplifier PR. The wavelength converter RF converts light having a power greater than a predetermined power out of incident light into a light having a longer wavelength than the incident light, and emits light having a power smaller than the predetermined power. The light is emitted with the wavelength of the incident light.

  Examples of such a wavelength conversion unit RF include a Raman optical fiber that causes stimulated Raman scattering. Examples of the Raman optical fiber include an optical fiber in which a dopant that increases the nonlinear optical constant is added to the core. Examples of such a dopant include germanium and phosphorus. When the wavelength conversion unit RF is a Raman optical fiber, the threshold value of the intensity of light for wavelength conversion can be changed depending on the diameter of the core, the dopant concentration, the length, and the like.

  Light emitted from the preamplifier PR enters the wavelength selection filter FL via the wavelength conversion unit RF. When the wavelength-converted light in the wavelength conversion unit RF enters the wavelength selection filter FL, the wavelength selection filter FL transmits the wavelength-converted light toward the main amplifier PA, and the wavelength conversion unit RF performs wavelength conversion. When light that has not been made enters the wavelength selection filter FL, the wavelength selection filter FL suppresses transmission of the light that is not wavelength-converted toward the main amplifier PA. Examples of such a wavelength selection filter FL include a WDM coupler and a dielectric multilayer filter.

<Configuration of main amplifier PA>
The main amplifier PA is different from the preamplifier PR in that the incident light is amplified at a higher amplification factor than the preamplifier PR, and includes a plurality of excitation light sources 31, an amplification optical fiber 33, and a coupler 32 as main components.

  Each of the excitation light sources 31 of the main amplifier PA is composed of, for example, a plurality of laser diodes. As described later, excitation light having a wavelength for exciting the active element added to the amplification optical fiber 33 of the main amplifier PA, for example, having a wavelength of Excitation light of 915 nm is emitted. Each excitation light source 31 is connected to an optical fiber 38, and excitation light emitted from each excitation light source 31 propagates through each optical fiber 38. Each optical fiber 38 is, for example, the same as the optical fiber 28 connected to the excitation light source 21 of the preamplifier PR. In this case, the excitation light propagates through the optical fiber 38 as multimode light.

  The amplification optical fiber 33 of the main amplifier PA has the same configuration as the amplification optical fiber 23 of the preamplifier PR.

  In the present embodiment, the wavelength selection filter FL is connected to the third optical fiber 39. The coupler 32 connects the third optical fiber 39 and each optical fiber 38 to one end of the amplification optical fiber 33. Specifically, in the coupler 32, the core of the third optical fiber 39 is connected to the core of the amplification optical fiber 33, and the core of each optical fiber 38 is connected to the inner cladding of the amplification optical fiber 33. It is connected. Accordingly, light emitted from the wavelength selection filter FL toward the main amplifier PA enters the core of the amplification optical fiber 33 through the third optical fiber 39, propagates through the core, and exits from the respective excitation light sources 31. The excitation light enters the inner cladding of the amplification optical fiber 33 and propagates mainly through the inner cladding. Accordingly, the light propagating through the core of the amplification optical fiber 33 causes the active element excited by the pumping light emitted from the pumping light source 31 to cause stimulated emission, thereby amplifying the light propagating through the core.

  A fourth optical fiber 40 is connected to the other end of the amplification optical fiber 33 of the main amplifier PA. The fourth optical fiber 40 is an optical fiber that propagates the light emitted from the amplification optical fiber 33 to a predetermined location and emits it, and is sometimes called a delivery optical fiber.

<Other configurations>
The control unit CP includes a logic gate, a CPU (Central Processing Unit), and the like, and controls the seed light unit MO, the preamplifier PR, and the main amplifier PA. Specifically, it has a configuration for receiving an instruction from the outside, and the excitation light source 11 and AOM 14 of the seed light unit MO, the excitation light source 21 of the preamplifier PR, and the excitation light source 31 of the main amplifier can be controlled by the instruction. .

<Operation of Fiber Laser Device 1>
Next, the operation of emitting one-shot pulsed light from such a fiber laser device 1 will be described.

  FIG. 2 is a timing chart schematically showing the operation of the fiber laser device of FIG. Specifically, each state of the control unit CP, the excitation light source 11 of the seed light unit MO, the excitation light source 21 of the preamplifier PR, the excitation light source 31 of the main amplifier PA, and the AOM 14, and the light emitted from the seed light unit MO It is a figure which shows a mode. Note that FIG. 2 shows a high level state in which light having a large power is emitted from each of the excitation light sources 11, 21, 31 and the seed light unit MO.

  When the power of the fiber laser device 1 is turned on, the control unit CP enters a standby state. At this time, the control unit CP controls the AOM 14 and the excitation light source 11 of the seed light unit MO so that the AOM 14 is in a reflection state and the excitation light source 11 is in an emission state. When excitation light is emitted from the excitation light source 11 of the seed light part MO, the excited state of the active element added to the amplification optical fiber 13 of the seed light part MO becomes high. When the excited state of the active element added to the amplification optical fiber 13 becomes high, resonance occurs between the FBG 12 and the end face on the preamplifier PR side of the AOM 14 due to the light emitted from the active element. Oscillation occurs in a state where the gain and loss in the optical fiber 13 are balanced. However, in this oscillation state, this light is not so amplified because the excited state of the active element added to the amplification optical fiber 13 is not so high, and becomes continuous light with low power.

  In the present embodiment, in the standby state, the control unit CP controls the excitation light source 21 of the preamplifier PR and the excitation light source 31 of the main amplifier PA so that the excitation light sources 21 and 31 are in a non-emission state. . Accordingly, the active element added to each of the amplification optical fiber 23 of the preamplifier PR and the amplification optical fiber 33 of the main amplifier PA is not excited. Therefore, even if the continuous light having a small power emitted from the seed light unit MO is incident on the amplification optical fiber 23 of the preamplifier PR, it is not amplified. The continuous light that is not amplified enters the wavelength conversion unit RF from the amplification optical fiber 23, but is not wavelength-converted because the power is small. For this reason, the continuous light is suppressed from entering the main amplifier PA by the wavelength selection filter FL.

  Next, an emission command is input from the outside to the control unit CP. Then, the control unit CP enters the emission state, controls the excitation light source 21 of the preamplifier PR and the excitation light source 31 of the main amplifier PA, and sets the excitation light sources 21 and 31 to the emission state. Accordingly, excitation light is emitted from the respective excitation light sources 21 and 31. Therefore, the active elements added to the amplification optical fiber 23 of the preamplifier PR and the amplification optical fiber 33 of the main amplifier PA are in an excited state. At this time, continuous light having a small power emitted from the seed light unit MO enters the amplification optical fiber 23 of the preamplifier PR, whereby the active element of the preamplifier PR in the excited state causes inductive excitation, and the seed light unit MO. The continuous light incident on the preamplifier PR is amplified. However, since the power of the continuous light is small, the power of the light emitted from the preamplifier PR does not reach a power that can be wavelength-converted by the wavelength converter RF. For this reason, the continuous light emitted from the preamplifier PR is not wavelength-converted by the wavelength converter RF, and is incident on the main amplifier PA by the wavelength selection filter FL as in the standby state.

  In the present embodiment, when the amplification optical fibers 23 and 33 of the pumping light sources 21 and 31 are sufficiently pumped, the control unit CP turns on the pumping light source 21 of the preamplifier PR and the pumping light source 31 of the main amplifier PA. By controlling, each excitation light source 21 and 31 is made into a non-emission state.

  Then, the control unit CP controls the AOM 14 after the first predetermined period T1 after the emission command is input, so that the AOM 14 is in a non-reflective state. Therefore, light incident on the AOM 14 from the amplification optical fiber 13 is not reflected toward the amplification optical fiber 13. For this reason, oscillation stops in the amplification optical fiber 13. At this time, the excitation light source 11 remains in the emission state. Accordingly, since the excitation light from the excitation light source 11 continues to enter the amplification optical fiber 13, the excitation state of the active element in the amplification optical fiber 13 is further increased.

  Next, the control unit CP controls the AOM 14 after the first predetermined period T1 and further after the second predetermined period T2, so that the AOM 14 is brought into a reflective state again. That is, the control unit CP sets the AOM 14 in the reflective state within the first predetermined period T1 after the emission command is input, and sets the AOM 14 in the non-reflective state in the second predetermined period T2 after the first predetermined period T1. To do. The second predetermined period T2 is a period in which light does not self-oscillate in the amplification optical fiber 13. Therefore, it is possible to prevent the unintended giant pulse light from being emitted within the second predetermined period T2. When the AOM 14 is brought into the reflective state again, resonance occurs between the FBG 12 and the end face of the AOM 14 on the preamplifier PR side. This active light causes the active element of the amplification optical fiber 13 to be in a high excitation state as described above. Causes stimulated emission, the resonant light is amplified, pulsed light is emitted from the AOM 14, and pulsed seed light as one-shot pulsed light is emitted from the seed light part MO.

  As described above, during the first predetermined period T1, the active element added to each of the amplification optical fiber 23 of the preamplifier PR and the amplification optical fiber 33 of the main amplifier PA is sufficiently excited by the excitation light. The second predetermined period T2 is a period during which the amplification optical fiber 13 does not self-oscillate. In general, the amplification optical fiber 23 and the main amplifier PA of the preamplifier PR are longer than the time for which the active element added to the amplification optical fiber 13 of the seed light unit MO is excited to be sufficiently excited by the excitation light. It takes a long time for the active element added to each of the amplification optical fibers 33 to be excited by the excitation light so as to be in a sufficiently high excited state. For this reason, in the present embodiment, the first predetermined period T1 is longer than the second predetermined period T2.

  FIG. 3 is a diagram illustrating a state of the magnitude of the power of light emitted from each portion when the one-shot pulsed light is emitted. Specifically, the power of the light emitted from the seed light unit MO, the light emitted from the preamplifier PR, the light emitted from the wavelength conversion unit RF, the light emitted from the wavelength selection filter FL, and the light emitted from the main amplifier PA It is a figure which shows the time change of the magnitude | size of and the mode of a wavelength. In each figure showing temporal changes in light power, the vertical axis shows the power density of light and the horizontal axis shows time.

  The shape of the temporal change in the power of the pulsed light emitted from the seed light part MO is a Gaussian distribution shape. The wavelength of the seed light emitted from the seed light unit MO is, for example, 1060 nm. As described above, the seed light as the one-shot pulsed light emitted from the seed light unit MO enters the core of the amplification optical fiber 23.

  In the amplification optical fiber 23 of the preamplifier PR, the active element is excited by the excitation light as described above. Therefore, when the pulsed seed light is incident on the amplification optical fiber 23, the excited active element causes stimulated emission by the light from the seed light portion MO, and the power of the light is amplified by this stimulated emission. Pulsed light is emitted from the optical fiber 23. The amplification optical fiber 23 emits light having a Gaussian distribution shape in which the power density is amplified with respect to the incident light when light having a Gaussian distribution shape with respect to time change of power is incident. Therefore, as shown in FIG. 3, the preamplifier PR emits light having a Gaussian distribution shape in which the shape of the power change with time is extended in the power density direction.

  A part of the light emitted from the preamplifier PR has a power density that is wavelength-converted by the wavelength converter RF. Therefore, in the wavelength conversion unit RF, the light component having a power density higher than a specific power density indicated by the broken line in the incident light is regarded as the primary scattered light. The power density of the primary scattered light is set to a power density that is not wavelength-converted. For example, when the wavelength of light emitted from the seed light unit MO is 1060 nm as described above, the wavelength of light having a power larger than a predetermined power is set to, for example, 1120 nm in the wavelength conversion unit RF. Then, the wavelength converter RF emits light that is not wavelength-converted and primary scattered light. Among these, as shown in FIG. 3, the light with a wavelength of 1060 nm that is not wavelength-converted is light having a temporal change shape including a tail portion in a Gaussian distribution shape, and light with a wavelength of 1120 nm that is primary scattered light. Is a light whose shape includes a shape similar to the apex portion of the Gaussian distribution shape in the light emitted from the preamplifier PR.

  The light emitted from the wavelength conversion unit RF is incident on the wavelength selection filter FL. As described above, the wavelength selective filter FL transmits the light toward the main amplifier PA when the light whose wavelength is converted by the wavelength conversion unit RF is incident. The transmission toward the main amplifier PA is suppressed. Therefore, transmission of light having a low power density that is not wavelength-converted among light emitted from the preamplifier PR as shown by a broken line in FIG. 3 is suppressed, and is emitted from the preamplifier PR indicated by a solid line in FIG. The primary scattering of light is transmitted through the wavelength selective filter FL. The pulse width of the primary scattered light is made smaller than the pulse width of the light emitted from the preamplifier PR.

  In the amplification optical fiber 33 of the main amplifier PA, the active element is excited by the excitation light as described above. Therefore, when pulsed light with a reduced pulse width is incident on the wavelength selection filter FL, the excited active element causes stimulated emission by the light, and the power of the light is amplified by the stimulated emission. Pulsed light is emitted from the optical fiber 33. Accordingly, light with a narrower pulse width and amplified power than the light emitted from the seed light portion MO is emitted.

  The light emitted from the main amplifier PA propagates through the fourth optical fiber 40 and is emitted from the fiber laser device 1.

  Thus, pulsed light is emitted after the second predetermined period T2 during which the AOM 14 is in the reflecting state. Note that, after the second predetermined period T2, the control unit CP keeps the reflection state of the AOM 14 longer than at least the first predetermined period T1, and enters the standby state.

  Next, the operation of the present invention will be described.

  The seed light unit MO of the fiber laser device 1 of the present embodiment is composed of a fiber laser device, and the control unit CP causes the AOM 14 that is the second reflection unit to be in a reflection state in the standby state and emits excitation light from the excitation light source 11. When the emission command is input in this standby state, the AOM 14 is set in the non-reflective state after the first predetermined period T1 after the output command is input, and the light is transmitted through the amplification optical fiber 13 after the AOM 14 is set in the non-reflective state. The AOM is brought into a reflective state after a second predetermined period T2 during which no self oscillation occurs.

  In such a seed light unit MO and a pulsed light emission method of the seed light unit MO, the pump light from the pump light source 11 is incident on the amplification optical fiber 13 in the standby state. The active element is brought into an excited state. However, since the AOM 14 is in a reflection state, oscillation occurs between the FBG 12 that is the first reflection unit and the AOM 14. While this oscillation occurs, light with low power is continuously emitted from the AOM, so that the active element is not brought into a highly excited state by the oscillation. For this reason, even when the standby state is long or when the first predetermined period T1 is long, it is possible to prevent unnecessary light having a high spire value from being emitted due to unintentional self-oscillation. In the second predetermined period T2, the oscillation does not occur, so that the active element of the amplification optical fiber 13 is in a high excitation state. However, the second predetermined period T2 is a period in which self-oscillation does not occur. It is possible to suppress unintended light having a high spire value from being emitted during the predetermined period T2. Then, the oscillation occurs again when the AOM 14 is brought into a reflective state after the second predetermined period T2. As described above, since the active element is in a high excited state in the second predetermined period T2, pulsed light having a high spire value can be emitted by the oscillation. Thus, according to the seed light unit MO that is the fiber laser device of the present invention and the pulsed light emission method of the seed light unit MO that is the fiber laser device, one-shot pulse light is emitted while suppressing damage to the optical element. can do.

  In the present embodiment, the first predetermined period T1 is longer than the second predetermined period T2. For this reason, other operations can be performed between the emission command and the emission of the one-shot pulsed light. In the present embodiment, the active elements of the amplification optical fibers 23 and 33 of the preamplifier PR and the main amplifier PA are excited in the first predetermined period T1. The first predetermined period T1 may be shorter than the second predetermined period T2, but in this case, in the fiber laser device 1 of the present embodiment, the amplification optical fibers 23 and 33 of the preamplifier PR and the main amplifier PA are used. The active element must be excited before the emission command. Therefore, as described above, the first predetermined period T1 is preferably longer than the second predetermined period T2.

  In the present embodiment, the controller CP maintains the reflection state of the AOM 14 after the second predetermined period T2 for a period longer than the first predetermined period T1. As described above, the one-shot pulsed light is emitted after the second predetermined period T2. The excited state of the active element in the amplification optical fiber 13 immediately after the one-shot pulse light is emitted is unlikely to be the same as the excited state immediately before the second predetermined period T2 starts. However, since the second predetermined period T2 is longer than the first predetermined period T1, the activity in the amplification optical fiber 13 is greater than when the second predetermined period T2 is shorter than the first predetermined period T1. The excited state of the element can be brought close to the excited state immediately before the start of the second predetermined period T2. When the emission command is input, the AOM 14 is further reflected for the first predetermined period T1, and the excited state of the active element in the amplification optical fiber 13 is changed according to the excited state immediately before the start of the second predetermined period T2. You can get closer. For this reason, according to the fiber laser apparatus 1 of this embodiment, it can suppress that the spiers value and pulse width of one-shot pulsed light change for every emission.

  Further, in the fiber laser device 1 of the present embodiment, of the pulsed light from the seed light unit MO amplified by the preamplifier PR, light having a large power is wavelength-converted by the wavelength conversion unit RF and the wavelength conversion is performed. The light passes through the wavelength selection filter FL. On the other hand, even if the continuous light having a small power emitted from the seed light unit MO is amplified by the preamplifier PR, the wavelength conversion unit RF does not perform wavelength conversion, and transmission through the wavelength conversion filter FL is suppressed. Therefore, it is possible to suppress the light originating from the continuous light having a small power emitted from the seed light unit MO from being emitted from the fiber laser device 1. Note that the preamplifier PR may be omitted depending on the power of the pulsed light emitted from the seed light unit MO. For example, if the power of the pulsed light emitted from the seed light unit MO is equal to the power of the pulsed light emitted from the preamplifier PR, the preamplifier PR can be omitted.

  In the fiber laser device 1 of the present embodiment, light that passes through the wavelength selection filter FL is amplified by the main amplifier PA. As described above, the temporal pulse width of the light transmitted through the wavelength selection filter FL is smaller than the temporal pulse width of the pulsed light emitted from the seed light portion MO. Therefore, the fiber laser device 1 can emit light having a high spire value and a small temporal pulse width.

<Other operations of the fiber laser device 1>
Next, another operation of the fiber laser device 1 will be described.

  FIG. 4 is a timing chart showing the operation of the fiber laser device of FIG. 1 in the same manner as FIG. As shown in FIG. 4, in this operation, after the second predetermined period T2, the AOM 14 is set in the non-reflective state only for the third predetermined period T3 after the AOM 14 is set in the reflective state. In the third predetermined period, after the AOM 14 is brought into the reflective state after the second predetermined period T2, the excited state of the active element in the amplification optical fiber 13 is lower than the excited state of the active element in the standby state. Be started. In the third predetermined period T3, since the AOM 14 is in a non-reflective state as described above, the excited state of the active element in the amplification optical fiber 13 is abruptly increased as in the second predetermined period T2. However, the third predetermined period T3 is set to be shorter than a period in which the excited state of the active element of the amplification optical fiber 13 is the same as the excited state of the active element in the standby state.

  In this way, the active element in the amplification optical fiber 13 can be brought closer to the excited state of the active element in the standby state earlier than in the case where the AOM 14 is not in the non-reflective state during the third predetermined period T3. Note that, as described above, the third predetermined period T3 is shorter than the period in which the excited state of the active element is the same as the excited state of the active element in the standby state, so that the AOM 14 again after the third predetermined period T3. Even if it is made into a non-reflective state, it can suppress that pulsed light is radiate | emitted.

  Also in this operation, the first predetermined period T1 is preferably longer than the second predetermined period T2, and the controller CP determines the reflection state of the AOM 14 after the third predetermined period T3 as the first predetermined period. It is preferable to maintain a period longer than the period T1.

  As mentioned above, although this invention was demonstrated to the example for embodiment, this invention is not limited to these.

  For example, in the fiber laser device 1 of the above-described embodiment, the AOM 14 is shown as an example of the second reflection unit of the seed light unit MO, but the present invention is not limited to this. For example, a second FBG having a lower reflectance than that of the FBG 12 is provided between the AOM 14 and the preamplifier PR. When the AOM 14 is turned on and light passes through the AOM 14, the light is reflected by the second FBG, and the FBG 12 and the second It can be configured to cause oscillation with the FBG. Therefore, in this case, the second reflecting portion is formed by the AOM 14 and the second FBG. In this case, it is preferable that the end surface of the AOM 14 on the preamplifier PR side is subjected to antireflection processing.

  The fiber laser device 1 includes a preamplifier PR, a main amplifier PA, a wavelength conversion unit RF, and a wavelength selection filter FL in addition to the seed light unit MO. However, the preamplifier PR, the main amplifier PA, the wavelength conversion unit RF, and the wavelength selection filter FL may not be provided as long as the power of light emitted from the seed light unit MO that is a fiber laser device is large.

  As described above, according to the present invention, there are provided a fiber laser device capable of emitting light of a one-shot pulse while suppressing damage to an optical element, and a pulsed light emission method for the fiber laser device. It can be used in the field of using laser light such as a machine or a medical device.

DESCRIPTION OF SYMBOLS 1 ... Fiber laser apparatus 11, 21, 31 ... Excitation light source 13,23, 33 ... Amplifying optical fiber FL ... Wavelength selection filter MO ... Seed light part (fiber laser apparatus)
PA: Main amplifier PR: Preamplifier RF: Wavelength converter

Claims (6)

An amplification optical fiber into which excitation light from the excitation light source is incident;
A first reflecting portion that is provided on one end of the amplification optical fiber and reflects light propagating through the core of the amplification optical fiber to the core;
A reflection state in which the light propagating through the core provided on the other end side of the amplification optical fiber is reflected by the core with a lower reflectance than the first reflecting portion, and the light propagating through the core is not reflected by the core A second reflective portion that can be switched to a non-reflective state;
A control unit;
With
The controller is
In the standby state, the second reflecting portion is placed in the reflecting state and the excitation light is emitted from the excitation light source,
When an emission command is input in the standby state, the second reflecting portion is set to the non-reflective state after a first predetermined period after the extraction command is input,
A fiber laser device characterized in that the second reflecting portion is set in the reflecting state after a second predetermined period in which light does not self-oscillate in the amplification optical fiber after the second reflecting portion is set in the non-reflecting state. . The fiber laser device according to claim 1, wherein the first predetermined period is longer than the second predetermined period. The fiber laser device according to claim 2, wherein the control unit maintains the reflection state of the second reflecting unit after the second predetermined period for a period longer than the first predetermined period. The control unit is configured such that the second reflecting unit is in the reflecting state after the second predetermined period, and the excited state of the active element in the amplification optical fiber is higher than the excited state of the active element in the standby state. In the low state, the second reflecting portion is set to the non-reflecting state only for a third predetermined period,
3. The fiber laser according to claim 1, wherein the third predetermined period is shorter than a period in which the excited state of the active element is in the same excited state as that of the active element in the standby state. apparatus. The first predetermined period is longer than the second predetermined period,
5. The fiber laser device according to claim 4, wherein the control unit maintains the reflection state of the second reflecting unit after the third predetermined period for a period longer than the first predetermined period. An amplifying optical fiber into which excitation light from an excitation light source is incident; a first reflecting portion that is provided on one end of the amplifying optical fiber and reflects light propagating through the core of the amplifying optical fiber to the core; A reflection state that is provided on the other end side of the amplification optical fiber and reflects the light propagating through the core to the core with a lower reflectance than the first reflecting portion, and non-reflecting the light propagating through the core to the core. A pulsed light emission method for a fiber laser device comprising: a second reflection unit that can be switched to a reflection state; and a control unit,
The controller is
In the standby state, the second reflecting portion is placed in the reflecting state and the excitation light is emitted from the excitation light source,
When an output command is input in the standby state, the second reflecting portion is set to the non-reflective state after a first predetermined period after the output command is input,
A fiber laser device characterized in that the second reflecting portion is set in the reflecting state after a second predetermined period in which light does not self-oscillate in the amplification optical fiber after the second reflecting portion is set in the non-reflecting state. Pulse light emission method.

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