JP2018037578A - Fiber laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber laser device in which the pulse width of outgoing light can be increased, and tolerance to return light has been improved.SOLUTION: A fiber laser device includes a light source 10, a wavelength conversion part RF performing wavelength conversion of at least a part of pulse light emitted from the light source 10, a first reflection part 51 placed between the wavelength conversion part RF and the light source 10, and a second reflection part 52 placed on the opposite side to the first reflection part 51 of the wavelength conversion part RF. The second reflection part 52 transmits a part of the light subjected to wavelength conversion in the wavelength conversion part and reflects another part to the first reflection part 51 side. The first reflection part 51 transmits the pulse light emitted from the light source 10 and reflects the light subjected to wavelength conversion in the wavelength conversion part to the second reflection part 52 side with higher reflectivity than the second reflection part 52.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fiber laser device that emits pulsed emitted 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 the fiber laser apparatus as described above, there is a desire to increase the pulse width of the emitted light according to the application. In order to increase the pulse width of the emitted light, it is conceivable to weaken the excitation light intensity of the MO. However, when the excitation light intensity of the MO is weakened, the output of the seed light becomes weak and it may be difficult to amplify the seed light.

  As a technique for increasing the pulse width of the pulsed light, for example, there is one disclosed in Patent Document 1 below. Patent Document 1 listed below describes a laser device that includes a laser oscillator and a sub-resonator output mirror that extracts a part of laser light emitted from the laser oscillator and transmits the other part. In this laser apparatus, a part of the laser light emitted from the laser oscillator can be taken out by the sub-resonator output mirror, and the other part can be amplified by returning to the laser oscillator side by the sub-resonance total reflection mirror. As a result, a plurality of pulse lights are emitted from the sub-resonator output mirror with a time shift relative to each other, and the plurality of pulse lights shifted in time overlap each other, thereby reducing the pulse width of the pulse light. growing.

Japanese Patent No. 3002998

  However, in the laser device disclosed in Patent Document 1, the laser beam amplified and emitted is reflected from the surface of the irradiation object and the like, and enters the exit as return light, and a part of the return light is emitted. In some cases, the laser beam propagates to the laser oscillator via the sub-resonator output mirror. When the laser beam amplified in this way returns to the laser oscillator, there is a risk of damaging the optical component.

  Accordingly, the present invention is intended to provide a fiber laser device that can increase the pulse width of outgoing light and has improved resistance to return light.

  In order to solve the above problems, a fiber laser device of the present invention includes a light source, a wavelength conversion unit that converts the wavelength of at least part of pulsed light emitted from the light source, and emits the wavelength conversion unit and the light source. And a second reflection unit disposed on the opposite side of the wavelength conversion unit from the first reflection unit, wherein the second reflection unit is the wavelength conversion unit. And transmits a part of the light whose wavelength has been converted by the light source and reflects the other part to the first reflecting part, and the first reflecting part transmits the pulsed light emitted from the light source and transmits the pulsed light. The light wavelength-converted by the wavelength conversion unit is reflected to the second reflection unit side with a higher reflectance than the second reflection unit.

  According to such a fiber laser device, part of the pulsed light emitted from the light source is wavelength-converted by the wavelength conversion unit. A part of the wavelength-converted light is transmitted through the second reflecting part, and the other part is reflected by the second reflecting part toward the first reflecting part. The light reflected by the second reflecting portion toward the first reflecting portion is reflected by the first reflecting portion toward the second reflecting portion and is incident on the second reflecting portion again. Then, the pulsed light that is incident on the second reflecting portion again is divided into light that is again transmitted through the second reflecting portion and light that is reflected by the second reflecting portion. In this way, a plurality of pulse lights having a temporal shift relative to each other are emitted. A plurality of pulse lights having a temporal shift relative to each other are superimposed on each other, whereby a pulse light having a large pulse width can be generated. Further, when light emitted from the fiber laser device is reflected by the surface of the irradiation object and enters the fiber laser device from the exit as return light, even if the wavelength-converted light enters the fiber laser device The light is reflected by the first reflecting portion or the second reflecting portion provided in front of the light source. Therefore, the return light is prevented from entering the light source, and the resistance to the return light is improved. As described above, the fiber laser device can increase the pulse width of the emitted light, and has improved resistance to return light.

  In addition, the fiber laser device transmits light that has been wavelength-converted by the wavelength converter on the side opposite to the light source of the wavelength converter, and suppresses transmission of the pulsed light that is not wavelength-converted by the wavelength converter. Preferably, the first filter is provided.

  According to the fiber laser device, by providing the first filter, it is possible to suppress the pulsed light that is not wavelength-converted in the wavelength conversion unit from being emitted from the fiber laser device.

  In the fiber laser device, it is preferable that the first filter reflects the pulsed light that is not wavelength-converted by the wavelength converter to the wavelength converter.

  The pulsed light that has not been wavelength-converted is reflected by the first filter toward the wavelength conversion unit, so that the pulsed light is incident on the wavelength conversion unit again. Then, a part of the pulsed light is wavelength-converted in the wavelength conversion unit, and the pulsed light that is emitted from the light source is reflected by the first reflection unit to the second reflection unit side. Efficiency can be improved.

  Further, the fiber laser device includes a second filter that transmits light from the light source side and suppresses transmission of light from the first reflection unit side between the light source and the first reflection unit. It is preferred that

  By providing such a second filter, it is possible to further suppress the return light from entering the light source, and thus the resistance to the return light is further improved.

  As described above, according to the present invention, it is possible to provide a fiber laser device that can increase the pulse width of emitted light and has improved resistance to return light.

It is a figure which shows the fiber laser apparatus which concerns on embodiment of this invention. It is a figure which shows typically the mode of the magnitude | size of the power of the pulsed light radiate | emitted from the fiber laser apparatus which concerns on embodiment of this invention.

  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 embodiment. As shown in FIG. 1, the fiber laser device 1 includes a light source 10 having a seed light part MO that emits seed light and a preamplifier PR that amplifies the seed light emitted from the seed light part MO, a main amplifier PA, A wavelength conversion unit RF disposed between the optical unit MO and the preamplifier PR, a first reflection unit 51 disposed between the wavelength conversion unit RF and the light source 10, and a first reflection unit 51 of the wavelength conversion unit RF. Between the light source 10 and the first reflection part 51, the second reflection part 52 arranged on the opposite side of the light source 10, the first filter 61 arranged on the opposite side of the second reflection part 52 from the light source 10. The second filter 62 is provided as a main configuration. As described above, the fiber laser device 1 is a so-called MO-PA type fiber laser device in which the seed light unit 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 of the present embodiment includes an excitation light source 11 that emits excitation light, and an amplification optical fiber 13 into which excitation light that is emitted from the excitation light source 11 is incident and an active element that is excited by the excitation light is added. And an FBG (Fiber Bragg Grating) 12 provided on one end side of the amplification optical fiber 13 and an acousto-optic element (AOM) 14 connected to the other end of the amplification optical fiber 13 as main components. 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. The pumping light source 11 is connected to the optical fiber 18, and the light emitted from the pumping light source 11 of the seed light unit MO propagates through the 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 optical fiber 18 is connected to one end of the amplification optical fiber 13, and the core of the optical fiber 18 and the core of the amplification optical fiber 13 are optically coupled. Further, the FBG 12 is provided in the core of the optical fiber 18. Thus, the FBG 12 is provided on one end side of the amplification optical fiber 13. In the FBG 12, a portion where the refractive index increases at a constant period along the longitudinal direction of the optical fiber 18 is repeated, and the active element of the amplification optical fiber 13 in an excited state is adjusted by adjusting this period. Is configured to reflect light of a specific wavelength. In the FBG 12, as described above, when the active element added to the amplification optical fiber 13 is ytterbium (Yb), for example, the reflectance of light having a wavelength of 1035 nm is set to 100%.

  An AOM 14 is connected to the other end of the amplification optical fiber 13. The AOM 14 can switch between the first state and the second state. The first state is a state where the AOM 14 is turned on, and the AOM 14 vibrates at a predetermined cycle. In the first state, the light incident from the core of the amplification optical fiber 13 propagates through the AOM 14 toward the preamplifier PR, and a part of the light causes a fullnel reflection on the end surface of the AOM 14 on the preamplifier PR side. Therefore, a part of the light is emitted from the AOM 14 toward the core of the amplification optical fiber 13 and the other part of the light is emitted from the AOM 14 toward the preamplifier PR. The reflectance of this Fullel reflection is made lower than that of the FBG 12. The second state is a state in which the AOM 14 is turned off or a state in which the AOM 14 vibrates at a different period from the first state. In the second state, light incident from the core of the amplification optical fiber 13 propagates in the AOM 14 in a direction different from the first state. For this reason, in the second state, the light incident on the AOM 14 is emitted in a different direction from the amplification optical fiber 13.

  As described above, in the seed light unit MO of the present embodiment, the light reciprocates and resonates on the optical path including the part of the optical fiber 18, the amplification optical fiber 13, and the AOM 14.

<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 optical fiber 29. The coupler 22 connects the 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 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. . 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 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 Second Filter 62>
The second filter 62 is optically coupled to the amplification optical fiber 23 of the preamplifier PR, and is disposed between the light source 10 and the first reflection unit 51. The second filter 62 transmits light from the light source 10 side and suppresses transmission of light from the first reflection unit 51 side. Therefore, even when the return light passes through the first reflection part 51 and is emitted from the first reflection part 51 to the light source 10 side, the second filter 62 suppresses transmission of the return light, and the light source 10 The return light can be prevented from entering. An example of such a second filter 62 is an isolator.

<Configuration of the first reflecting portion 51>
The first reflection unit 51 is provided in an optical fiber 58 having one end optically coupled to the second filter 62 and the other end connected to the wavelength conversion unit RF. That is, the first reflection unit 51 is disposed between the wavelength conversion unit RF and the light source 10. The first reflection unit 51 transmits the pulsed light emitted from the light source 10 and reflects the wavelength-converted light generated in the wavelength conversion unit RF to the first reflection unit side with a higher reflectance than the second reflection unit 52. . The reflectance with respect to the wavelength-converted light of the first reflection unit 51 is, for example, 99% or more. Therefore, the light that has been wavelength-converted by the wavelength conversion unit RF and then is reflected by the second reflection unit 52 and returns to the first reflection unit 51 side can be reflected again to the second reflection unit 52 side.

  As such a 1st reflection part 51, FBG can be mentioned, for example. When the first reflecting portion 51 is formed of FBG, a portion where the refractive index increases at a constant period is repeated along the longitudinal direction of the optical fiber 58, and the first reflecting portion is adjusted by adjusting this period. Of the light incident on 51, the wavelength-converted light generated by the wavelength converter RF can be reflected.

<Configuration of wavelength converter RF>
The wavelength converter RF is connected to the optical fiber 58. The wavelength converter RF converts the wavelength of at least part of the pulsed light emitted from the light source 10 and emits it. The wavelength converter RF converts the wavelength of the incident light having a power greater than the predetermined power and outputs the light, and the incident light having the power smaller than the predetermined power remains the wavelength of the incident light. Exit.

  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. The wavelength conversion unit RF may be a nonlinear optical crystal that causes harmonic conversion. Examples of the nonlinear optical crystal include periodically poled lithium niobate. When the wavelength conversion unit RF is periodically poled lithium niobate, the intensity of the wavelength-converted light can be changed depending on the polarization inversion period, the incident angle of light on the crystal, and the like.

<Configuration of Second Reflector 52>
The second reflection unit 52 is provided in an optical fiber 59 having one end connected to the wavelength conversion unit RF and the other end connected to the first filter 61. That is, the 2nd reflection part 52 is arrange | positioned on the opposite side to the light source 10 of wavelength conversion part RF. The second reflection unit 52 transmits a part of the light wavelength-converted by the wavelength conversion unit RF and reflects the other part to the first reflection unit 51 side. The reflectance with respect to the wavelength-converted light of the second reflection unit 52 is, for example, 50%. Therefore, the light that is wavelength-converted by the wavelength conversion unit RF and is incident on the second reflection unit 52 is light that is transmitted through the second reflection unit 52 and light that is reflected by the second reflection unit 52 toward the first reflection unit 51. It is divided into.

  An example of the second reflecting portion 52 is FBG. When the second reflecting portion 52 is formed of FBG, a portion where the refractive index increases at a constant period is repeated along the longitudinal direction of the optical fiber 59, and the second reflecting portion is adjusted by adjusting this period. Of the light incident on 52, the wavelength-converted light generated by the wavelength converter RF can be reflected.

<Configuration of the first filter 61>
The first filter 61 is optically coupled to the optical fiber 59 and disposed on the opposite side of the wavelength conversion unit RF from the light source 10. The first filter 61 transmits the wavelength-converted light generated in the wavelength conversion unit RF and suppresses transmission of light that is not wavelength-converted by the wavelength conversion unit RF. Pulse light emitted from the light source 10 enters the first filter 61 via the wavelength converter RF. When the wavelength-converted light generated in the wavelength conversion unit RF is incident on the first filter 61, the light that is transmitted toward the main amplifier PA and is not wavelength-converted in the wavelength conversion unit RF is transmitted to the first filter 61. When incident, transmission of the light toward the main amplifier PA is suppressed. Therefore, the light emitted from the light source 10 that is wavelength-converted by the wavelength converter RF and enters the first filter 61 is transmitted from the first filter 61 toward the main amplifier PA. On the other hand, of the light emitted from the light source 10, the light that enters the first filter 61 without being wavelength-converted by the wavelength conversion unit RF is suppressed from being transmitted from the first filter 61 to the main amplifier PA. Examples of the first filter 61 include a WDM coupler and a dielectric multilayer filter.

<Configuration of main amplifier PA>
The main amplifier PA differs 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 first filter 61 is connected to the optical fiber 39. The coupler 32 connects the 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 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. ing. Therefore, the light emitted from the first filter 61 toward the main amplifier PA enters the core of the amplification optical fiber 33 via the optical fiber 39, propagates through the core, and is emitted from each excitation light source 31. 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.

  An optical fiber 40 is connected to the other end of the amplification optical fiber 33 of the main amplifier PA. The 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.

<Operation of Fiber Laser Device 1>
Next, an operation of emitting pulsed light having a large pulse width from the fiber laser device 1 will be described.

  In the fiber laser device 1 of the present embodiment, the excitation light is always emitted from the excitation light source 11 of the seed light unit MO, and the AOM 14 of the seed light unit MO is in the second state in the standby state. Therefore, the light incident on the AOM 14 from the amplification optical fiber 13 is emitted to the outside without entering the amplification optical fiber 13. Therefore, light does not resonate in the optical path between the FBG 12 and the end face of the AOM 14 on the preamplifier PR side. For this reason, the excited state of the active element of the amplification optical fiber 13 is increased. In the present embodiment, the excitation light sources 21 and 31 are in the emission state in the standby state. Therefore, 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 brought into an excited state. The period in which the AOM 14 of the seed light unit MO is in the second state is a period in which the amplification optical fiber 13 does not self-oscillate. In addition, the period in which the excitation light is incident on the amplification optical fiber 23 and the amplification optical fiber 33 is a period in which self-oscillation does not occur. Accordingly, unintended giant pulse light is suppressed from being emitted from the amplification optical fibers 13, 23, and 33 in the standby state.

  Next, the AOM 14 is set to the first state at a timing slightly before the time when the pulsed light is emitted. Then, the light reciprocates through the optical path between the FBG 12 and the end face of the AOM 14 on the preamplifier PR side, that is, the optical path including a part of the optical fiber 18, the amplification optical fiber 13, and the AOM 14. As a result of this resonant light, the active element of the amplification optical fiber 13 in a highly excited state as described above undergoes stimulated emission, the resonant light is amplified, and pulse light is emitted from the AOM 14, and seed light is emitted from the seed light unit MO. The pulsed light is emitted.

  The shape of the time change of the power of the pulsed light emitted from the seed light unit MO is a Gaussian distribution shape. The wavelength of the pulsed light emitted from the seed light unit MO is, for example, 1035 nm. As described above, the 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 pulsed light enters the amplification optical fiber 23 from the seed light part MO, the excited active element causes stimulated emission by the light from the seed light part MO, and the power of the light is amplified by this stimulated emission. Then, pulsed light is emitted from the amplification 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 whose power changes with time is incident. Accordingly, the preamplifier PR emits pulsed light having a Gaussian distribution shape in which the shape of the time change of power is extended in the power density direction with respect to the pulsed light incident on the preamplifier PR.

  As described above, pulse light having a Gaussian distribution shape is emitted from the light source 10.

  The light emitted from the light source 10 enters the second filter 62. As described above, since the second filter 62 transmits light from the light source 10 side, light incident on the second filter 62 from the light source 10 side passes through the second filter 62 and enters the first reflecting portion 51. Further, as described above, since the first reflection unit 51 transmits the pulsed light emitted from the light source 10, the light incident on the first reflection unit 51 from the light source 10 also transmits through the first reflection unit 51 and is a wavelength conversion unit. Incident to RF.

  In this way, a part of the pulsed light emitted from the light source 10 and incident on the wavelength conversion unit RF has a power density that is wavelength-converted by the wavelength conversion unit RF. Therefore, in the wavelength conversion unit RF, the light component having a power density higher than a specific power density out of the light incident from the light source 10 is wavelength-converted. For example, when the wavelength of light emitted from the seed light unit MO is 1035 nm as described above, the wavelength of light having a power larger than a predetermined power is set to, for example, 1085 nm in the wavelength conversion unit RF. Then, light that has not been converted to wavelength-converted light is emitted from the wavelength conversion unit RF. The shape of the time change in the power of the light emitted from the wavelength conversion unit RF is the same as the shape of the time change in the power of the light emitted from the light source 10. Among these, light having a wavelength of 1035 nm that is not wavelength-converted by the wavelength conversion unit RF is light having a low power density including a tail portion in the Gaussian distribution shape, and light having a wavelength converted to wavelength of 1085 nm includes a vertex portion of the Gaussian distribution shape. Light with high power density.

  The light emitted from the wavelength conversion unit RF enters the second reflection unit 52. As described above, the second reflection unit 52 transmits a part of the light whose wavelength is converted by the wavelength conversion unit RF and reflects the other part to the first reflection unit 51 side. Accordingly, the wavelength-converted light incident on the second reflecting portion 52 is divided into light that is transmitted through the second reflecting portion 52 and light that is reflected toward the first reflecting portion 51 side.

  The light reflected by the second reflecting portion 52 toward the first reflecting portion 51 is again transmitted through the wavelength converting portion RF, but there is little light having a power larger than the predetermined power. Therefore, most of the light reflected by the second reflecting unit 52 toward the first reflecting unit 51 is incident on the first reflecting unit 51 without being wavelength-converted by the wavelength converting unit RF. The wavelength-converted light incident on the first reflecting portion 51 in this way is reflected by the first reflecting portion 51 to the second reflecting portion 52 side. Therefore, the light reciprocates on the optical path between the first reflecting part 51 and the second reflecting part 52.

  As described above, the wavelength-converted light generated in the wavelength conversion unit RF passes through the second reflection unit 52 as it is and the first reflection unit 51 and the second reflection unit 52 after a number of round trips. 2 and the light transmitted through the reflecting portion 52. In this way, a plurality of pulse lights having a relative time shift are emitted. Then, by superimposing a plurality of pulse lights having such a relative time shift, pulse light having a large pulse width is generated as shown in FIG. In FIG. 2, of the light converted in wavelength by the wavelength conversion unit RF, the light emitted without being reflected by the second reflection unit 52 once is emitted after being reflected by W0 and once by the second reflection unit 52. W1 represents the emitted light, and W2 represents the light emitted after being reflected twice by the second reflecting portion 52. The pulsed light whose pulse width is increased in this way has a reduced peak power while suppressing a decrease in the amount of energy per pulse.

  The pulsed light that has passed through the second reflecting portion 52 as described above then enters the first filter 61. As described above, the first filter 61 transmits light that has been wavelength-converted by the wavelength converter RF and suppresses transmission of light that has not been wavelength-converted by the wavelength converter RF. Therefore, the light that has been wavelength-converted by the wavelength converter RF passes through the first filter 61 and enters the main amplifier PA, and the light that is not wavelength-converted by the wavelength converter RF is suppressed by the first filter 61.

  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 pulse light having a large pulse width is incident on the amplification optical fiber 33, the excited active element causes stimulated emission by the light, and the power of the light is amplified by the stimulated emission, thereby amplifying light. Pulse light is emitted from the fiber 33. Therefore, the light amplified more than the light incident on the main amplifier PA is emitted.

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

  Next, a case where the pulsed light emitted from the fiber laser device 1 is reflected by the surface of the irradiation target and enters the fiber laser device 1 as return light will be described.

  As described above, the pulsed light emitted from the fiber laser device 1 is mainly light that has been wavelength-converted by the wavelength converter RF. When this light is reflected on the surface of the irradiation object and the like and enters the fiber laser device 1 from the exit of the fiber laser device 1 as return light, the return light can pass through the main amplifier PA and the first filter 61. A part of the return light is reflected by the second reflecting portion 52. Further, even if the return light further passes through the second reflection unit 52 and the wavelength conversion unit RF, it is reflected by the first reflection unit 51. Therefore, according to the fiber laser device 1 of the present embodiment, since the return light is suppressed from entering the light source 10, damage to the optical component is suppressed.

  Note that the return light is considered to have the same wavelength as the wavelength-converted light mainly generated in the wavelength conversion unit RF as described above, but may include other light components. Even in such a case, by using the second filter 62 as an isolator as described above, it is possible to suppress the return light from entering the light source 10.

  As described above, the fiber laser device 1 of the present embodiment can increase the pulse width of the emitted light, and has improved resistance to return light.

  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 embodiment, the example in which the light source 10 includes the preamplifier PR has been described. However, the power of the light emitted from the seed light unit MO is sufficiently large because the wavelength conversion is performed in the wavelength conversion unit RF. For example, the preamplifier PR is not an essential component. Further, the preamplifier PR may be provided between the first reflector 51 and the main amplifier PA without being provided in the light source 10. However, since the preamplifier PR is included in the light source 10 as in the fiber laser device 1 of the above embodiment, the power of the pulsed light incident on the wavelength conversion unit RF can be increased. It becomes easy to convert the wavelength of the light emitted from.

  Moreover, although the said fiber laser apparatus 1 is provided with the 1st filter 61, this is not an essential structure. However, when the fiber laser device 1 includes the first filter 61, the resistance of the fiber laser device 1 to the return light is further improved as described below. Since the first reflection unit 51 transmits the pulsed light that is not wavelength-converted by the wavelength conversion unit, when the return light includes pulsed light that is not wavelength-converted by the wavelength conversion unit RF, the pulsed light passes through the first reflection unit 51. May be incident on the light source. However, since the fiber laser device 1 includes the first filter 61, it is possible to suppress emission of pulsed light that is not wavelength-converted by the wavelength conversion unit RF from the fiber laser device 1. Accordingly, since the pulsed light that is not wavelength-converted in the wavelength conversion unit RF is suppressed from being returned light, the return light is further prevented from entering the light source 10 and the resistance of the fiber laser device 1 to the returned light is further improved. Is done. However, the light that is not wavelength-converted in the wavelength converter RF is light with low power density, and even if it is incident on the light source 10, the first filter 61 is not essential.

  In the above embodiment, a WDM coupler or a dielectric multilayer filter is exemplified as the first filter 61. However, the first filter 61 has a structure in which light that is not wavelength-converted by the wavelength converter RF is reflected to the wavelength converter RF side. You may have. As such a 1st filter 61, FBG comprised so that the light which is not wavelength-converted by the wavelength conversion part RF may be mentioned. The pulsed light that has not been wavelength-converted is reflected by the first filter 61 toward the wavelength converting unit RF, so that the pulsed light is incident on the wavelength converting unit RF again. Then, a part of the pulsed light is wavelength-converted in the wavelength converting unit RF, and the pulsed light subjected to wavelength conversion is reflected from the first reflecting unit 51 to the second reflecting unit 52 side, and is emitted from the light source 10. The utilization efficiency of pulsed light can be improved.

  Moreover, although the said fiber laser apparatus 1 is provided with the 2nd filter 62, this is not an essential structure. However, the provision of the second filter 62 further suppresses the return light from being incident on the light source 10, thereby further improving the resistance of the fiber laser device 1 to the return light. The second filter 62 is particularly useful when the first filter 61 reflects pulsed light that is not wavelength-converted. Since the first reflection unit 51 transmits the pulse light that is not wavelength-converted by the wavelength conversion unit, when the first filter 61 reflects the pulse light that is not wavelength-converted, if the pulse light is not wavelength-converted by the wavelength conversion unit RF, There is a possibility that the light passes through one reflecting portion 51 and enters the light source 10. By providing the second filter 62, it is possible to suppress the incidence of light that has not undergone wavelength conversion to the light source 10. However, the light that is not wavelength-converted in the wavelength conversion unit RF is light with low power density, and even if it is incident on the light source 10, the influence is small, so the second filter 62 is not essential.

  Moreover, in the said embodiment, although the isolator was illustrated as the 2nd filter 62, as demonstrated below, the 2nd filter 62 transmits the light of a specific wavelength, and suppresses transmission of the light of another wavelength. It may be.

  It is considered that most of the return light does not have enough power to be wavelength-converted by the wavelength conversion unit RF, but the return light is wavelength-converted by the wavelength conversion unit RF, for example, by being amplified by the main amplifier PA. You may get as much power. In this case, the return light emitted from the wavelength conversion unit RF may include light that has been wavelength converted a plurality of times. Thus, even when the return light includes light that has been wavelength-converted a plurality of times, if the second filter 62 is configured to have an FBG that reflects light that has been wavelength-converted a plurality of times, the wavelength conversion is performed. The incident light is suppressed from entering the light source 10. In addition, when the first reflection unit 51 is not configured to reflect 100% of the wavelength-converted light, the wavelength-converted light may pass through the first reflection unit 51 to the light source 10 side. In this case, when the second filter 62 has an FBG that reflects the wavelength-converted light, the wavelength-converted light is suppressed from entering the light source 10. Thus, even if the second filter 62 is an FBG, the second filter 62 can transmit the pulsed light emitted from the light source 10 and can suppress the transmission of light from the first reflecting portion 51 side.

  The fiber laser device 1 includes a main amplifier PA, but this is not an essential configuration. However, the provision of the main amplifier PA makes it easy to increase the power of the pulsed light emitted from the fiber laser device.

  ADVANTAGE OF THE INVENTION According to this invention, the fiber laser apparatus which can enlarge the pulse width of an emitted light and improved the tolerance with respect to a return light is provided, and can be utilized for the field | area of optical fiber communication. It can also be used for fiber laser devices and other devices using optical fibers.

DESCRIPTION OF SYMBOLS 1 ... Fiber laser apparatus 10 ... Light source 11, 21, 31 ... Excitation light source 13,23, 33 ... Optical fiber 51 for amplification 51 ... 1st reflection part 52 ... 2nd reflection part 61 ... 1st filter 62 ... 2nd filter MO ... Seed light part PA ... Main amplifier PR ... Preamplifier RF ... Wavelength conversion part

Claims (4)

A light source, a wavelength converter that converts the wavelength of at least part of the pulsed light emitted from the light source, emits the light, a first reflector disposed between the wavelength converter and the light source, and the wavelength converter. A second reflecting portion disposed on the opposite side of the first reflecting portion of the portion,
The second reflection unit transmits a part of the light wavelength-converted by the wavelength conversion unit and reflects the other part to the first reflection unit side,
The first reflection unit transmits the pulsed light emitted from the light source and reflects the light converted in wavelength by the wavelength conversion unit toward the second reflection unit with a higher reflectance than the second reflection unit. And a fiber laser device. A first filter that transmits light that has been wavelength-converted by the wavelength conversion unit and suppresses transmission of the pulsed light that is not wavelength-converted by the wavelength conversion unit is provided on the opposite side of the wavelength conversion unit from the light source. The fiber laser device according to claim 1. The fiber laser device according to claim 2, wherein the first filter reflects the pulsed light that is not wavelength-converted by the wavelength converter to the wavelength converter. The second filter is provided between the light source and the first reflection part, and transmits a light from the light source side and suppresses a light transmission from the first reflection part side. The fiber laser device according to any one of 1 to 3.

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