JP2012129264A - Fiber laser oscillation method and fiber laser oscillation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber laser oscillation method and device, capable of stably obtaining high output power of oscillation light with easy control.SOLUTION: A fiber laser oscillation device includes an optical fiber 1 and a control device 10. Since the control device 10 performs control so that excitation light L2 having the lowest absorption rate by the optical fiber 1 among a plurality of the excitation light L2, L3, L4 with a different wavelength is made incident into the optical fiber 1 at first, the intensity of the excitation light L2 is maintained at a value exceeding a threshold value which enables oscillation of oscillation light over an entire length of the optical fiber. Thereby, the entire length of the optical fiber is put in an inverting distribution state, which can prevent an optical fiber break due to a giant pulse that tends to occur in the presence of an optical fiber portion not to be put in the inverting distribution state. Subsequently, the remaining excitation light L3, L4 are made incident into the optical fiber, which makes oscillation light L1 generated and amplified. Thus, high output power of the oscillation light can be stably obtained with easy control.

Description

  The present invention relates to a fiber laser oscillating method and a fiber laser oscillating device for making excitation light incident on an optical fiber having a core member containing a laser active substance therein, generating and amplifying oscillation light inside the core member, and emitting it.

  For example, Patent Document 1 discloses a pattern generator that generates a predetermined pattern signal, a plurality of semiconductor lasers that receive the pattern signal and emit laser light, and amplifies the laser light incident from one end surface. A fiber laser oscillation device (fiber laser modulation device) including an optical fiber emitting from the other end surface is disclosed. In this fiber laser oscillation device, the pattern signal is formed with output levels of four periods of a low output period, an output increase period, a high output period, and an output decrease period, so that it becomes rectangular pulse light without a surge pulse. Laser light can be emitted.

  Patent Document 2 discloses an optical fiber containing a laser active substance, two mirrors that are disposed at both ends of the optical fiber and reflect only light of a predetermined wavelength, and two excitations having different wavelengths from one end face of the optical fiber. There has been disclosed a fiber laser oscillation device (optical fiber laser) that includes two excitation light sources that enter light, generates and amplifies oscillation light inside the optical fiber, and emits the light from the other end surface of the optical fiber. In this fiber laser oscillation device, an atom at a predetermined energy level in a laser oscillation state is shifted to a lower energy level by one excitation light source, and oscillation light is excited by the other excitation light source. Oscillation can be sustained.

  Patent Document 3 discloses a double-clad optical fiber, a signal light source that makes signal light incident on a core member from one end face of the optical fiber, and signal light that enters the core member or inner clad member from one end face of the optical fiber. Discloses a fiber laser oscillation device (fiber laser) that includes a pumping light source that receives pumping light having different wavelengths, amplifies signal light using the pumping light, and emits the light from the other end surface of the optical fiber. In this fiber laser oscillation device, when the emission of the signal light is set to the standby state, the power of the incident excitation light is set to 0 after being held for a certain period of time with a power larger than 0. The emission state can be improved.

  Patent Document 4 includes an optical fiber containing a laser active substance, and two excitation light sources that respectively enter excitation light from one end face and the other end face of the optical fiber, and generates oscillation light inside the optical fiber. A fiber laser oscillation device (fiber laser oscillator) that amplifies and emits light from the other end surface of the optical fiber is disclosed. In this fiber laser oscillation device, the other end surface of the optical fiber, which is the emission surface of the oscillation light, is partially transmissive to the oscillation light, and the one end surface of the optical fiber is highly reflective to the oscillation light. Since it is formed, high-power oscillation light can be emitted.

  Patent Document 5 includes two optical fibers connected via a return light prevention unit, and two excitation light sources that receive two excitation lights having different wavelengths from one end face of the optical fiber, A fiber laser oscillation device (fiber laser device) that generates and amplifies two oscillation lights inside an optical fiber and emits the light from the other end surface of the optical fiber is disclosed. In this fiber laser oscillation device, the light of one wavelength includes the light of the other wavelength so that a resonance state does not occur. Therefore, two oscillation lights can be reliably emitted.

JP 2007-142380 (paragraphs 0010, 0021, FIG. 4) Japanese Patent No. 2905251 (page 2, left column, lines 29-34, FIG. 1) JP 2008-91773 A (paragraphs 0010, 0012) JP 2009-253075 A (paragraphs 0011 and 0022, FIG. 1) JP 2004-165396 A (paragraphs 0017 to 0022, FIG. 2)

  In the fiber laser oscillation device described in Patent Document 1 described above, the pattern signal needs to be formed at the output levels of four periods of the low output period, the output increase period, the high output period, and the output decrease period. It tends to be expensive. Further, in the fiber laser oscillation device described in Patent Document 2, one excitation light source transitions atoms at a predetermined energy level in a laser oscillation state to a lower energy level, and only the other excitation light source oscillates. Since it excites light, it is not possible to obtain higher output oscillation light.

  On the other hand, in the fiber laser oscillating devices described in Patent Documents 3 to 5, since the oscillation light is excited using a plurality of excitation light sources, higher output oscillation light can be obtained. Here, as shown in FIG. 9A, the intensity of the excitation light that is incident and transmitted through the incident surface (one end surface) of the optical fiber decreases exponentially as the distance from the incident surface of the optical fiber increases. I will do it. That is, the excitation light is gradually absorbed by the optical fiber as it travels through the fiber from the incident surface of the optical fiber. At the position P1 in the vicinity of the incident surface of the optical fiber, the intensity of the pumping light is a threshold value greater than 0 that can oscillate the oscillating light, that is, the pumping light for making the optical fiber in an inverted distribution state. As shown in FIG. 9B, the inversion has a larger number of electrons e in the excited state of the energy level E3 than the electrons e in the ground state of the energy level E0. It is in the state of distribution. The electron e transitions to the energy level E3 and falls into a lower energy state after a certain relaxation time. At that time, the electron e emits light having an energy equal to the unit energy difference between the excited level and the transitioned light. The light having the longest relaxation time and having the same energy, phase and traveling direction is emitted. Electrons e at the excitation level of the level difference having a long relaxation time are stimulated and emitted, and oscillation light is emitted.

  As shown in FIG. 9C, the energy level is obtained at a position P2 at a predetermined distance from the incident surface of the optical fiber where the intensity of the pumping light is slightly larger than the threshold value at which the oscillation light can be oscillated. The number of electrons e in the excited state of the energy level E3 is slightly higher than that of the electrons e in the ground state at the position E0. Accordingly, stimulated emission is performed by light having a level difference that has been released in the region of FIG. 9B, and oscillation light is emitted.

  On the other hand, at the position P3 further away from the position P2 of the optical fiber, the intensity of the excitation light is smaller than the threshold value at which the oscillation light can be oscillated, as shown in FIG. The number of electrons e in the excited state of the energy level E3 is smaller than the electrons e in the ground state of the energy level E0, and the state of inversion distribution is not reached. Therefore, the light having a long level difference emitted in the region of FIGS. 9B to 9C is absorbed as excitation light and is not stimulatedly emitted. When the excitation light continues to enter in this state, absorption proceeds in the region of FIG. 9D, and when the inversion distribution state is reached, the entire fiber becomes ready to emit oscillation light, and stimulated emission occurs at once. Therefore, a giant pulse that breaks the optical fiber is generated. In the fiber laser oscillators described in Patent Documents 3 to 5, there is a possibility that a giant pulse is generated and the optical fiber is broken due to the above-described reason.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fiber laser oscillation method and a fiber laser oscillation apparatus capable of stably obtaining high-power oscillation light with easy control.

[Fiber laser oscillation method]
(Claim 1) The fiber laser oscillation method of the present invention is a fiber laser oscillation method for generating and amplifying oscillation light by entering a plurality of excitation lights having different wavelengths into an optical fiber containing a laser active substance, Of the plurality of pump lights, the pump light having the lowest absorptance absorbed by the optical fiber is first incident on the optical fiber, and then the remaining pump light is incident on the optical fiber to generate the oscillation light. Are generated and amplified.

  (Claim 2) The pumping light having the lowest absorptance may be incident from one end of the optical fiber, and the remaining pumping light may be incident from one or both of the one end and the other end of the optical fiber.

  (Claim 3) When the pumping light having the lowest absorptance travels inside the optical fiber and reaches the end, the intensity of the pumping light is larger than 0 that can oscillate the oscillating light. It is better not to fall below the threshold value.

[Fiber laser oscillator]
(4) A fiber laser oscillation device according to the present invention includes an optical fiber containing a laser active substance, a plurality of pumping light sources capable of entering a plurality of pumping lights having different wavelengths into the optical fiber, and the pumping light sources. A control device for controlling the emission of the pumping light in the pump, wherein the control device has the lowest absorption rate absorbed by the optical fiber among the plurality of pumping lights Light is first incident on the optical fiber, and then the remaining pump light is incident on the optical fiber to generate and amplify the oscillation light.

  (Claim 5) The pumping light source that emits the pumping light having the lowest absorptance is disposed on one end side of the optical fiber, and the pumping light source that emits the remaining pumping light is on one end side of the optical fiber and It is good to arrange at one or both of the other end side.

  (Claim 6) The fiber length of the optical fiber is such that the intensity of the pumping light oscillates when the pumping light having the lowest absorptance incident from one end reaches the other end. Is set to a length that does not fall below a threshold value greater than 0 possible.

  (7) The intensity of the pumping light having the lowest absorptance when reaching the other end of the optical fiber is 10 to 30% of the intensity of the pumping light on the other end of the optical fiber. It is good to be.

  (Claim 1) According to the present invention, since the pumping light having the lowest absorptance absorbed in the optical fiber among the pumping lights having different wavelengths incident on the optical fiber is first incident on the optical fiber, The intensity of the pumping light is maintained at a value that exceeds a threshold that can oscillate oscillation light over the entire length of the optical fiber. Therefore, the entire optical fiber can be in an inversion distribution state, and damage to the optical fiber due to a giant pulse that easily occurs when there is a fiber portion that does not reach the inversion distribution state can be prevented. After that, the remaining pumping light is incident on the optical fiber, and the oscillation light combined with all the pumping light having different wavelengths including the first incident pumping light is generated and amplified. Output oscillating light can be obtained stably.

  (Claim 2) Since the pump light having the lowest absorptance is incident from one end side of the optical fiber, the leakage light of the pump light can be processed on the other end side of the optical fiber. Further, since the remaining excitation light is incident from one or both of the one end side and the other end side of the optical fiber, the output of the oscillation light can be controlled in a wide range.

  (Claim 3) When the pumping light having the lowest absorptance travels through the inside of the optical fiber and reaches the end portion, a threshold value having a value larger than 0 that can oscillate the oscillating light is set. I try not to fall below. This threshold value is the limit intensity of the pumping light for bringing the optical fiber into the inverted distribution state. Therefore, the entire optical fiber can be reliably changed to the inversion distribution state, and the occurrence of a giant pulse can be prevented to prevent the optical fiber from being damaged.

  (Claim 4) The control device controls the pumping light having the lowest absorption rate that is absorbed by the optical fiber among the pumping lights having different wavelengths incident on the optical fiber so as to be incident on the optical fiber first. Therefore, the intensity of the pumping light is maintained at a value that exceeds the threshold that can oscillate the oscillation light over the entire length of the optical fiber. Therefore, the entire optical fiber can be in an inversion distribution state, and damage to the optical fiber due to a giant pulse that easily occurs when there is a fiber portion that does not reach the inversion distribution state can be prevented. Then, the remaining pumping light is incident on the optical fiber, and control is performed to generate and amplify the oscillating light combined by all the pumping light having different wavelengths including the pumping light that is incident first. High-power oscillation light can be stably obtained by simple control.

  (Claim 5) Since the pump light having the lowest absorptance is configured to enter from one end side of the optical fiber, the leakage light of the pump light can be processed on the other end side of the optical fiber. A simple configuration can be obtained. Further, since the remaining excitation light is configured to enter from one or both of one end side and the other end side of the optical fiber, the output of the oscillation light can be controlled in a wide range by the control device.

  (Claim 6) When the pumping light having the lowest absorptance incident from one end side of the fiber length of the optical fiber reaches the other end side, the intensity of the pumping light is less than 0 that can oscillate the oscillation light. Since the length is set so as not to fall below the threshold value of a large value, the entire optical fiber can be reliably changed to the inversion distribution state, and the occurrence of a giant pulse can be prevented to prevent the optical fiber from being damaged. .

  (7) The pumping light intensity of the pumping light having the lowest absorptance when reaching the other end side of the optical fiber is 10 to 30% of the pumping light intensity at the one end side of the optical fiber. Therefore, when the other end side of the optical fiber is used as the oscillation light exit surface, leak light with an appropriate amount of leakage is emitted from the exit surface, increasing the oscillation efficiency and high output. Oscillation light can be obtained.

1 is a diagram illustrating an overall configuration of a fiber laser oscillation device according to a first embodiment of the present invention. It is a figure which shows the change of the absorptivity of the excitation light which injects into and transmits the optical fiber in the fiber laser oscillation apparatus of FIG. It is a figure which shows the change of the absorption factor of the excitation light which injects into and transmits the optical fiber in the modification of the fiber laser oscillation apparatus of FIG. It is a figure which shows the relationship between the wavelength of excitation light, and the absorption coefficient of excitation light in an optical fiber. It is a figure which shows the whole structure of the fiber laser oscillation apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows the change of the absorption factor of the excitation light which injects into and transmits the optical fiber in the fiber laser oscillation apparatus of FIG. It is a figure which shows the whole structure of the fiber laser oscillation apparatus which concerns on the 3rd Embodiment of this invention. It is a figure which shows the change of the absorption factor of the excitation light which injects into and transmits the optical fiber in the fiber laser oscillation apparatus of FIG. It is a figure which shows the change of the intensity | strength of the excitation light which injects into an optical fiber and permeate | transmits.

<First Embodiment>
(Outline of fiber laser oscillator)
An overview of the fiber laser oscillator according to the first embodiment will be described. The fiber laser oscillation device can obtain high-power oscillation light while preventing the generation of a giant pulse.

  Here, as described with reference to FIG. 9, light having a level difference with a long relaxation time is absorbed as excitation light, and the absorption proceeds when the excitation light is continuously incident without being stimulated emission. When the inversion distribution state is reached, the entire fiber becomes ready to emit oscillation light, and stimulated emission occurs at a stretch. Therefore, a giant pulse that breaks the optical fiber is generated. Therefore, when the pumping light incident from one end of the optical fiber reaches the other end, the intensity of the pumping light is a threshold value greater than 0 that can oscillate the oscillation light, that is, the optical fiber is inverted. The fiber length is set so that the length does not fall below the limit intensity of the excitation light for achieving the distribution state, that is, the position P2 spaced apart from the incident surface of the optical fiber shown in FIG. 9 is formed as the exit surface. As a result, the entire optical fiber can be reliably changed to a state of inversion distribution, the occurrence of a giant pulse can be prevented, and the optical fiber can be prevented from being damaged.

  In addition, the optical fiber needs to have a certain length in order to increase the efficiency when oscillating the oscillation light, and in order to obtain a high output oscillation light, a plurality of excitation lights having different wavelengths are incident on the optical fiber. There is a need to. However, as described above, it is not easy to have a configuration in which all of the plurality of excitation lights can prevent the generation of giant pulses.

  Therefore, the pump light having the lowest absorption rate absorbed by the optical fiber among the plurality of pump lights is first incident on the optical fiber having the predetermined length. By doing so, it is possible to maintain the intensity of the pumping light at a value exceeding the threshold that can oscillate the oscillation light over the entire length of the optical fiber, and the entire optical fiber can be in an inverted distribution state.

  Thereafter, the remaining excitation light is incident on the optical fiber. The remaining excitation light can be selected such that when the excitation light reaches the other end side, the intensity of the excitation light falls below a threshold value at which oscillation light can be oscillated. If the remaining excitation light alone is incident on the optical fiber, a giant pulse may be generated. However, before the remaining pump light is incident on the optical fiber, the pump light having the lowest absorption rate is already incident on the optical fiber. Therefore, the entire optical fiber is already in the inversion distribution state. Therefore, even if the remaining excitation light is incident, no giant pulse is generated. And it is possible to stably obtain high-power oscillating light combined by all pumping light having different wavelengths including the first incident pumping light by easy control.

  By the way, if the amount of leakage light from the emission surface is large, the oscillation efficiency is lowered and it is difficult to obtain high-power oscillation light. Therefore, the emission light is emitted when the intensity of the excitation light is set to 100% on the incident surface. The fiber length of the optical fiber is set so that the leakage light has an intensity of 10 to 30% on the surface.

(Detailed configuration of fiber laser oscillator)
Next, a detailed configuration of the fiber laser oscillation device will be described with reference to FIG. As shown in FIG. 1, the fiber laser oscillation device includes an optical fiber 1, first to third excitation light sources 2 to 4, first to third dichroic mirrors 5 to 7, a collimator lens 8, and a condenser lens. 9 and a control device 10 that controls emission of excitation light from the first to third excitation light sources 2 to 4. When the end surface on one end side (the left side in the drawing) of the optical fiber 1 is a light incident surface 1a, the optical fiber A1 extends in the direction perpendicular to the incident surface 1a from the farther side than the incident surface 1a (in order from the left). , A first dichroic mirror 5, a second dichroic mirror 6, a collimating lens 8, and a condensing lens 9 are disposed, and light extending in a direction perpendicular to the end surface (exiting surface 1 b) on the other end side (right side in the drawing) of the optical fiber 1. A third dichroic mirror 7 is disposed on the axis A1.

  The first dichroic mirror 5 is arranged to rotate by θ ° counterclockwise with respect to a plane perpendicular to the optical axis A1 of the optical fiber 1. The second dichroic mirror 6 is rotated by θ ° clockwise with respect to the plane perpendicular to the optical axis A1 of the optical fiber 1. The first excitation light source 2 is arranged so that the optical axis A2 of the excitation light L2 coincides with the optical axis A1 of the optical fiber 1 when the excitation light L2 emitted from the light source 2 is reflected by the first dichroic mirror 5. Has been. The second excitation light source 3 is arranged so that the optical axis A3 of the excitation light L3 coincides with the optical axis A1 of the optical fiber 1 when the excitation light L3 emitted from the light source 3 is reflected by the second dichroic mirror 6. Has been. The third excitation light source 4 is arranged so that the optical axis A4 of the excitation light L4 emitted from the light source 4 coincides with the optical axis A1 of the optical fiber 1. The third dichroic mirror 7 is rotated by θ ° counterclockwise with respect to the plane perpendicular to the optical axis A1 of the optical fiber 1. It is to be noted that a fiber laser oscillation device can be configured in which the cost of mirror coating is kept low by reducing the incident angles (θ °) of the excitation light L2 and L3 from the respective excitation light sources 2 and 3.

  The optical fiber 1 is formed in the center of the cross section, and for example, a core member 1c doped with Yb as a rare earth element which is a laser active material, and is formed around the core member 1c and has a lower refractive index than the core member 1c. This is a double clad type active fiber composed of a first clad member 1d and a second clad member 1e formed around the first clad member 1d and having a lower refractive index than the first clad member 1d. The incident surface 1a of the optical fiber 1 is provided with a total reflection mirror that reflects the oscillation light L1, and the emission surface 1b of the optical fiber 1 reflects low-intensity oscillation light and transmits high-intensity oscillation light L1. An output mirror is provided.

  As the excitation light of the optical fiber 1, for example, it can be efficiently excited at three types of wavelengths of 915 nm, 940 nm, and 976 nm. As shown in FIG. 4, the absorption coefficient of the optical fiber 1 when the wavelength of the pumping light is changed is 0.5 dB / m when the wavelength is 915 nm, 0.2 dB / m when the wavelength is 940 nm, and 976 nm. Sometimes 2.0 dB / m. The optical fiber 1 is assumed to contain, for example, Yb. That is, the absorption coefficient of excitation light having a wavelength of 940 nm is minimum, that is, the absorptance (= 10 ^ (− absorption coefficient / 10 * distance from the incident surface in the optical fiber)) is minimum (see FIG. 2). Therefore, the fiber length of the optical fiber 1 is set to 40 m so that leakage light having an intensity of about 15% at the exit surface is obtained when the intensity of the excitation light is 100% at the entrance surface.

  The first excitation light source 2 is, for example, a light source that can emit excitation light L2 having a wavelength of 940 nm. The second excitation light source 3 is a light source capable of emitting excitation light L3 having a wavelength of 915 nm, for example. The third excitation light source 4 is, for example, a light source that can emit excitation light L4 having a wavelength of 976 nm. The first dichroic mirror 5 is a mirror that can reflect the excitation light L2 having a wavelength of 940 nm and transmit the excitation light L4 having a wavelength of 976 nm. The second dichroic mirror 6 is a mirror that can reflect the excitation light L3 having a wavelength of 915 nm and transmit the excitation light L2 and L4 having wavelengths of 940 nm and 976 nm. The third dichroic mirror 7 is a mirror that can reflect the leakage light La having a wavelength of 940 nm and transmit the oscillation light L1.

(Operation of fiber laser oscillator)
The operation of the fiber laser oscillation device having such a configuration will be described. First, the control device 10 emits excitation light L2 having a wavelength of 940 nm from the first excitation light source 2. The excitation light L2 having a wavelength of 940 nm is reflected by the first dichroic mirror 5 and transmitted through the second dichroic mirror 6, converted into parallel light by the collimating lens 8, and condensed by the condensing lens 9 on the incident surface 1a of the optical fiber 1. Then, the light is guided into the optical fiber 1. The excitation light L2 having a wavelength of 940 nm guided into the optical fiber 1 is transmitted through the first cladding 1d while being reflected by the inner surface of the second cladding 1e. At this time, as shown in FIG. 2, the excitation light L2 having a wavelength of 940 nm reaches the emission surface 1b of the optical fiber 1 while being absorbed by the optical fiber 1, so that the entire optical fiber 1 has a uniform inversion distribution state. Can be. Furthermore, when the excitation light L2 having a wavelength of 940 nm is transmitted through the first cladding 1d, the rare earth element in the core member 1c is excited to generate oscillation light.

  Next, the control device 10 emits the excitation light L3 having a wavelength of 915 nm from the second excitation light source 3 and the excitation light L4 having a wavelength of 976 nm from the third excitation light source 4. The excitation light L3 and L4 are emitted at the same time, or one of the excitation lights is emitted first, and then the other excitation light is emitted. The excitation light L3 having a wavelength of 915 nm is reflected by the second dichroic mirror 6 to be collimated by the collimator lens 8, and is collected by the condenser lens 9 on the incident surface 1 a of the optical fiber 1 and guided into the optical fiber 1. Lighted. The excitation light L4 having a wavelength of 976 nm is transmitted through the first dichroic mirror 5 and the second dichroic mirror 6 to be collimated by the collimator lens 8, and is condensed by the condensing lens 9 on the incident surface 1a of the optical fiber 1. It is guided into the optical fiber 1.

  The pumping lights L3 and L4 having wavelengths of 915 nm and 976 nm guided into the optical fiber 1 are transmitted through the first cladding 1d while being reflected by the inner surface of the second cladding 1e. At this time, as shown in FIG. 2, the pumping light L3 having a wavelength of 915 nm is absorbed by the optical fiber 1 in a larger amount than the pumping light L2 having a wavelength of 940 nm to reach the emission surface 1b of the optical fiber 1. 0. The excitation light L4 having a wavelength of 976 nm is absorbed by the optical fiber 1 in a larger amount than the excitation light L3 having a wavelength of 915 nm and becomes substantially zero before reaching the output surface 1b of the optical fiber 1. These two excitation lights L3 and L4 excite the rare earth element in the core member 1c that has been transmitted until the absorption rate reaches 100% to generate oscillation light.

  Oscillation light generated by the above three excitation lights L2, L3, and L4 is combined, reflected between the exit surface 1b and the entrance surface 1a of the optical fiber 1, and amplified to finally become high intensity. Light L1 is emitted from the emission surface 1b. The oscillation light L1 emitted from the emission surface 1b passes through the third dichroic mirror 7, is guided to a laser emission unit (not shown), and is emitted. Further, the leakage light La of the excitation light L2 having a wavelength of 940 nm leaking from the emission surface 1b is reflected by the third dichroic mirror 7 and guided to the leakage light processing unit (not shown) so as not to leak outside the apparatus. The

(Function and effect of fiber laser oscillator)
As described above, according to the fiber laser oscillation device of the first embodiment, the control device 10 uses the three excitation lights L2, L3, and L4 having different wavelengths incident on the optical fiber 1 to the optical fiber 1. Control is performed so that the pumping light L 2 having the lowest absorption rate is first incident on the optical fiber 1. Therefore, the intensity of the pumping light is maintained at a value exceeding the threshold that can oscillate the oscillation light L1 over the entire length of the optical fiber 1, and the entire optical fiber 1 can be in an inverted distribution state. As a result, it is possible to prevent the optical fiber 1 from being damaged by a giant pulse that is likely to occur when there is a fiber portion that does not reach the inversion distribution state. Then, the remaining excitation lights L3 and L4 are incident on the optical fiber 1 thereafter. Therefore, since the oscillation light combined by all the excitation light L2, L3, and L4 having different wavelengths including the first incident excitation light L2 is controlled to be generated and amplified, high output oscillation can be achieved with easy control. The light L1 can be obtained stably.

  Further, since the pumping light L2 having the lowest absorptance is configured to enter from one end side of the optical fiber 1, the leakage light La of the pumping light L2 is processed on the other end side of the optical fiber 1. Therefore, a simple configuration can be obtained. Further, since the remaining pumping lights L3 and L4 are configured to enter from one end side of the optical fiber 1, the control device 10 can control the output of the oscillation light L1 in a wide range.

Second Embodiment
Next, a fiber laser oscillation device according to a second embodiment of the present invention will be described with reference to FIG. 5 corresponding to FIG. 1 showing the fiber laser oscillation device according to the first embodiment. In FIG. 5, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

(Configuration of fiber laser oscillator)
As shown in FIG. 5, the fiber laser oscillation device includes an optical fiber 1, first to fifth excitation light sources 2 to 4, 11, and 12, first to fifth dichroic mirrors 5 to 7, 13, and 14, Two collimating lenses 8 and 15, two condenser lenses 9 and 16, and a control device 17 that controls the emission of the excitation light from the first to fifth excitation light sources 2 to 4, 11, and 12 are provided.

  The arrangement of the optical system on the incident surface 1a side of the optical fiber 1 is the same as that of the fiber laser oscillation device according to the first embodiment, but the arrangement of the optical system on the emission surface 1b side of the optical fiber 1 is the first. The configuration is different from that of the fiber laser oscillation device according to the embodiment. That is, the fourth dichroic mirror 13, the fifth dichroic mirror 14, and the third dichroic are arranged in order from the farthest from the exit surface 1b (in order from the right) on the optical axis A1 extending in the direction perpendicular to the exit surface 1b of the optical fiber 1. A mirror 7, a collimating lens 15, and a condenser lens 16 are disposed.

  The fourth dichroic mirror 13 is rotated by θ ° counterclockwise with respect to the plane perpendicular to the optical axis A1 of the optical fiber 1. The fifth dichroic mirror 14 is arranged to rotate θ ° clockwise in the figure with respect to a plane perpendicular to the optical axis A1 of the optical fiber 1. The fourth excitation light source 11 is arranged so that the optical axis A5 of the excitation light L5 coincides with the optical axis A1 of the optical fiber 1 when the excitation light L5 emitted from the light source 11 is reflected by the fourth dichroic mirror 13. Has been. The fifth excitation light source 12 is arranged so that the optical axis A6 of the excitation light L6 emitted from the light source 12 coincides with the optical axis A1 of the optical fiber 1.

  For example, the fourth excitation light source 11 is a light source capable of emitting excitation light L5 having a wavelength of 915 nm. For example, the fifth excitation light source 12 is a light source capable of emitting excitation light L6 having a wavelength of 976 nm. The fourth dichroic mirror 13 is a mirror that can reflect the excitation light L5 having a wavelength of 915 nm and transmit the excitation light L6 having a wavelength of 976 nm. The fifth dichroic mirror 14 is a mirror that can reflect the oscillation light L1 and transmit the excitation lights L5 and L6 having wavelengths of 915 nm and 976 nm.

(Operation of fiber laser oscillator)
The operation of the fiber laser oscillation device having such a configuration will be described. First, the control device 17 emits excitation light L2 having a wavelength of 940 nm from the first excitation light source 2. The excitation light L2 having a wavelength of 940 nm is reflected by the first dichroic mirror 5 and transmitted through the second dichroic mirror 6, converted into parallel light by the collimating lens 8, and condensed by the condensing lens 9 on the incident surface 1a of the optical fiber 1. Then, the light is guided into the optical fiber 1. The excitation light L2 having a wavelength of 940 nm guided into the optical fiber 1 is transmitted through the first cladding 1d while being reflected by the inner surface of the second cladding 1e. At this time, as shown in FIG. 6, the excitation light L2 having a wavelength of 940 nm reaches the emission surface 1b of the optical fiber 1 while being absorbed by the optical fiber 1, so that the entire optical fiber 1 has a uniform inversion distribution state. Can be. Furthermore, when the excitation light L2 having a wavelength of 940 nm is transmitted through the first cladding 1d, the rare earth element in the core member 1c is excited to generate oscillation light.

  Next, the control device 17 emits excitation light L3 having a wavelength of 915 nm from the second excitation light source 3, and emits excitation light L4 having a wavelength of 976 nm from the third excitation light source 4. Further, the control device 17 emits excitation light L5 having a wavelength of 915 nm from the fourth excitation light source 11, and emits excitation light L6 having a wavelength of 976 nm from the fifth excitation light source 12. These excitation lights L3 to L6 are emitted at the same time, or the excitation lights are emitted in any order. The pumping light L3 having a wavelength of 915 nm from the second pumping light source 3 is reflected by the second dichroic mirror 6, collimated by the collimating lens 8, and condensed by the condensing lens 9 on the incident surface 1a of the optical fiber 1. It is guided into the optical fiber 1. Excitation light L4 having a wavelength of 976 nm from the third excitation light source 4 is transmitted through the first dichroic mirror 5 and the second dichroic mirror 6 to be collimated by the collimator lens 8, and is incident on the incident surface of the optical fiber 1 by the condenser lens 9. The light is condensed into 1 a and guided into the optical fiber 1.

  On the other hand, the excitation light L5 having a wavelength of 915 nm from the fourth excitation light source 11 is reflected by the fourth dichroic mirror 13, passes through the fifth dichroic mirror 14 and the third dichroic mirror 7, and is collimated by the collimator lens 15. The light is condensed on the exit surface 1 b of the optical fiber 1 by the condenser lens 16 and guided into the optical fiber 1. The excitation light L6 having a wavelength of 976 nm from the fifth excitation light source 12 is transmitted through the fourth dichroic mirror 13, the fifth dichroic mirror 14, and the third dichroic mirror 7 to be collimated by the collimator lens 15 and is collimated by the condenser lens 16. The light is condensed on the exit surface 1 b of the optical fiber 1 and guided into the optical fiber 1.

  The excitation lights L2 to L6 guided into the optical fiber 1 are transmitted through the first cladding 1d while being reflected by the inner surface of the second cladding 1e. At this time, as shown in FIG. 6, the pumping light L3 having a wavelength of 915 nm of the second pumping light source 3 is absorbed by the optical fiber 1 in a larger amount than the pumping light L2 having a wavelength of 940 nm. By the time it reaches, it becomes almost zero. Excitation light L4 having a wavelength of 976 nm from the third excitation light source 4 is absorbed by the optical fiber 1 in a larger amount than the excitation light L3 having a wavelength of 915 nm, and becomes substantially zero before reaching the output surface 1b of the optical fiber 1. . These two excitation lights L3 and L4 excite the rare earth element in the core member 1c that has been transmitted until the absorption rate reaches 100% to generate oscillation light.

  On the other hand, the change in the absorptance of the excitation light L5 having a wavelength of 915 nm of the fourth excitation light source 11 is symmetrical with the change in the absorptance of the excitation light L3 having a wavelength of 915 nm of the second excitation light source 3 and the longitudinal center of the optical fiber 1. Until the incident surface 1a of the optical fiber 1 is reached. The change in the absorptance of the excitation light L6 having a wavelength of 976 nm of the fifth excitation light source 12 is symmetrical with the change in the absorptance of the excitation light L4 having a wavelength of 976 nm of the third excitation light source 4 and the longitudinal center of the optical fiber 1. Before reaching the incident surface 1a of the optical fiber 1, it becomes substantially zero. These two excitation lights L5 and L6 excite the rare earth element in the core member 1c that has been transmitted until the absorptance reaches 100% to generate oscillation light.

  The oscillation light generated by the above five excitation lights L2 to L6 is combined, reflected between the exit surface 1b and the entrance surface 1a of the optical fiber 1, amplified, and finally becomes the high intensity oscillation light L1. Is emitted from the emission surface 1b. The oscillation light L1 emitted from the emission surface 1b passes through the condenser lens 16, the collimating lens 15, and the third dichroic mirror 7, is reflected by the fifth dichroic mirror 14, and is guided to a laser emission unit (not shown) and emitted. Is done. Further, the leakage light La of the excitation light L2 having a wavelength of 940 nm leaking from the emission surface 1b is transmitted through the condenser lens 16 and the collimating lens 15, reflected by the third dichroic mirror 7, and guided to the leakage light processing unit (not shown). It is processed so that it does not leak and leak outside the device.

(Function and effect of fiber laser oscillator)
As described above, according to the fiber laser oscillator of the second embodiment, the same effect as that of the fiber laser oscillator of the first embodiment can be obtained. Furthermore, since the oscillation light is generated by the five excitation lights L2 to L6, higher output oscillation light L1 can be obtained. Further, since the pumping lights L3 to L6 other than the pumping light L2 are configured to be incident from both one end side and the other end side of the optical fiber 1, the output of the oscillation light L1 can be increased in a wider range by the control device 17. Can be controlled.

<Third Embodiment>
Next, a fiber laser oscillation device according to a third embodiment of the present invention will be described with reference to FIG. 7 corresponding to FIG. 1 showing the fiber laser oscillation device according to the first embodiment. In FIG. 7, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

(Configuration of fiber laser oscillator)
As shown in FIG. 7, the fiber laser oscillator includes the optical fiber 1, the second and third excitation light sources 3 and 4, the first and third dichroic mirrors 6 and 7, the collimator lens 8, and the condenser lens. 9 and a control device 18 for controlling the emission of the excitation light from the second and third excitation light sources 3 and 4. That is, the fiber laser oscillation device according to the third embodiment has a configuration in which the first excitation light source 2 and the second dichroic mirror 6 of the fiber laser oscillation device according to the first embodiment are excluded. In this case, the pump light having the lowest absorption rate is pump light L3 having a wavelength of 915 nm emitted from the second pump light source 3, and the length of the optical fiber 1 is the optical fiber 1 of the fiber laser oscillation device according to the first embodiment. Shorter than the length of. That is, the fiber length of the optical fiber 1 is set to 15 m so that leakage light having an intensity of about 18% at the exit surface is obtained when the intensity of the excitation light is 100% at the entrance surface.

(Operation of fiber laser oscillator)
The operation of the fiber laser oscillation device having such a configuration will be described. First, the control device 18 emits excitation light L3 having a wavelength of 915 nm from the second excitation light source 3. The excitation light L3 having a wavelength of 915 nm is reflected by the second dichroic mirror 6, converted into parallel light by the collimating lens 8, condensed by the condenser lens 9 on the incident surface 1 a of the optical fiber 1, and guided into the optical fiber 1. Is done. The excitation light L3 having a wavelength of 915 nm guided into the optical fiber 1 is transmitted through the first cladding 1d while being reflected by the inner surface of the second cladding 1e. At this time, as shown in FIG. 8, the excitation light L3 having a wavelength of 915 nm reaches the emission surface 1b of the optical fiber 1 while being absorbed by the optical fiber 1, so that the entire optical fiber 1 has a uniform inversion distribution state. Can be. Furthermore, when the excitation light L3 having a wavelength of 915 nm is transmitted through the first cladding 1d and is transmitted through the core member 1c, the rare earth element in the core member 1c is excited to generate oscillation light.

  Next, the control device 18 emits excitation light L4 having a wavelength of 976 nm from the third excitation light source 4. The excitation light L4 having a wavelength of 976 nm is transmitted through the second dichroic mirror 6 to be collimated by the collimator lens 8, condensed by the condenser lens 9 on the incident surface 1 a of the optical fiber 1, and guided into the optical fiber 1. Lighted. The excitation light L4 guided into the optical fiber 1 passes through the first cladding 1d while being reflected by the inner surface of the second cladding 1e. At this time, as shown in FIG. 8, the excitation light L4 having a wavelength of 976 nm is absorbed by the optical fiber 1 in a larger amount than the excitation light L3 having a wavelength of 915 nm and is substantially reduced until reaching the emission surface 1b of the optical fiber 1. 0. The excitation light L4 having a wavelength of 976 nm excites the rare earth element in the core member 1c that has been transmitted until the intensity becomes 0, thereby generating oscillation light.

  The oscillation light generated by the two pumping lights L3 and L4 is combined, reflected between the exit surface 1b and the entrance surface 1a of the optical fiber 1, amplified, and finally becomes the high intensity oscillation light L1. Is emitted from the emission surface 1b. The oscillation light L1 emitted from the emission surface 1b passes through the third dichroic mirror 7, is guided to a laser emission unit (not shown), and is emitted. In addition, the leakage light La of the excitation light L3 having a wavelength of 915 nm leaking from the emission surface 1b is reflected by the third dichroic mirror 7 and guided to the leakage light processing unit (not shown) so as not to leak outside the apparatus. The

(Function and effect of fiber laser oscillator)
As described above, according to the fiber laser oscillation device of the third embodiment, the same effects as those of the fiber laser oscillation device of the first embodiment can be obtained. Furthermore, since there are two excitation light sources 3 and 4, the number of optical elements is reduced as compared with the fiber laser oscillation device of the first embodiment, and the cost can be reduced.

<Modification of First, Second, and Third Embodiment>
In each of the above-described embodiments, the leakage light La leaking from the emission surface 1b of the optical fiber 1 is reflected by the third dichroic mirror 7 and guided to the leakage light processing unit. Instead of this configuration, the output surface 1b of the optical fiber 1 is formed so as to have a function capable of reflecting the leaked light La, so that, for example, the light is reflected by the output surface 1b of the optical fiber 1 as shown in FIG. The excited excitation light L2 can be absorbed by the optical fiber 1 without leaking. Thereby, the 3rd dichroic mirror 7 becomes unnecessary and can reduce cost. Further, although the active fiber containing Yb as the rare earth element is selected as the optical fiber 1, the same effect can be obtained by selecting an active fiber containing another laser active material. Further, the number and arrangement of excitation light sources in each embodiment are not limited, and an arbitrary number of excitation light sources can be selected, and one or both of one end side and the other end side of the optical fiber 1 can be selected. Can be arranged at any position.

  DESCRIPTION OF SYMBOLS 1: Optical fiber 1a: Incident surface 1b: Outgoing surface 2-4, 11, 12: 1st-5th excitation light source 5-7, 13, 14: 1st-5th dichroic mirror 8,15 : Collimating lens, 9, 16: Condensing lens, 10, 17, 18: Control device

Claims (7)

A fiber laser oscillation method in which a plurality of excitation lights having different wavelengths are incident on an optical fiber containing a laser active material to generate and amplify oscillation light,
The pump light having the lowest absorption rate absorbed in the optical fiber among the plurality of pump lights is first incident on the optical fiber,
Then, the remaining pumping light is incident on the optical fiber to generate and amplify the oscillation light. In claim 1,
The fiber laser, wherein the pumping light having the lowest absorptance is incident from one end side of the optical fiber, and the remaining pumping light is incident from one or both of one end side and the other end side of the optical fiber. Oscillation method. In claim 1 or 2,
When the pumping light having the lowest absorptance travels through the optical fiber and reaches the end, the intensity of the pumping light falls below a threshold value greater than 0 that can oscillate the oscillating light. There is no fiber laser oscillation method. An optical fiber containing a laser active material;
A plurality of pumping light sources capable of respectively entering a plurality of pumping lights having different wavelengths into the optical fiber;
A control device that controls emission of the excitation light in the plurality of excitation light sources, and a fiber laser oscillation device comprising:
The control device first enters the pumping light having the lowest absorption rate absorbed into the optical fiber among the plurality of pumping lights, and then enters the remaining pumping light into the optical fiber. And generating and amplifying the oscillation light. In claim 4,
The pumping light source that emits the pumping light having the lowest absorptance is disposed on one end side of the optical fiber, and the pumping light source that emits the remaining pumping light is one of one end side and the other end side of the optical fiber. Or the fiber laser oscillation device characterized by being arrange | positioned at both. In claim 4 or 5,
The fiber length of the optical fiber is such that the intensity of the excitation light that can oscillate the oscillation light when the excitation light having the lowest absorptance incident from one end side reaches the other end side. A fiber laser oscillator characterized by being set to a length that does not fall below a large threshold value. In claim 6,
The intensity of the pumping light having the lowest absorptance when reaching the other end of the optical fiber is 10 to 30% of the intensity of the pumping light on the one end of the optical fiber. A fiber laser oscillator.

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