JP5202676B2 - Amplifying optical component, optical fiber amplifier using the same, and fiber laser device - Google Patents

Abstract

The purpose is to provide an optical component for use in amplification, an optical fiber amplifier using the same, and a fiber laser device. This optical component (AOP) for use in amplification is provided with: an amplifying optical fiber (30) containing a core (31) to which an active element is added, and a cladding (32) subjected to incidence of excited light for exciting the active element; and a loop propagation optical fiber (50) that causes some of the excited light for propagating the cladding (32) to travel along the loop thereof, and is joined optically to a cladding section (61) between one end (36) and another end (37) of the amplifying optical fiber (30).

Description

  The present invention relates to an amplification optical component that can efficiently absorb pumping light with a simple configuration by using an amplification optical fiber, an optical fiber amplifier using the amplification optical component, and a fiber laser device.

  A fiber laser device using an optical fiber for amplification has excellent light condensing performance, a small beam spot with a high power density is obtained, and non-contact processing is possible. Used in various fields. In particular, fiber laser devices used in the processing field and the medical field have high output.

  An amplification optical fiber used in a fiber laser device includes a core to which an active element is added and a clad that covers an outer peripheral surface of the core. When the excitation light propagating through the cladding is absorbed by the active element, the active element is in an excited state, so that the amplified light propagating through the core of the amplification optical fiber is amplified. Therefore, it is desirable that the active element absorb the excitation light without waste. However, the excitation light incident on the amplification optical fiber includes one that propagates while being absorbed by the active element added to the core, and one that propagates without passing through the core. In general, the excitation light that propagates without passing through the core is called skew light.

  As an amplification optical fiber that suppresses such skew light, the following Patent Document 1 or Patent Document 2 has been proposed. In the amplification optical fiber of Patent Literature 1, the outer shape of the cross section of the clad (described as the second core) through which the excitation light propagates is a quadrangle. In the amplification optical fiber of Patent Document 2, a small bend is formed in a part of the clad by the compression element provided in a part of the amplification fiber. In these amplification optical fibers, the skew light is suppressed by disturbing the propagation mode of the excitation light.

Japanese Patent No. 3479219 Japanese Patent Laid-Open No. 2002-237637

  However, in the amplification optical fiber described in Patent Document 1 or Patent Document 2, it is necessary to form the cladding in a special shape as described above, and the skew light from the base material production stage for manufacturing the amplification optical fiber. It is necessary to make a special design to suppress Further, in the amplification optical fiber of Patent Document 2, the pumping light is lost due to the pumping light returning to the input end of the amplification optical fiber in accordance with the compression direction of the compression element. The amplification efficiency of the excitation light will be reduced. Therefore, there is a demand for an amplification optical component having a simple configuration that can be efficiently amplified using the amplification optical fiber.

  Therefore, the present invention provides an amplification optical component capable of improving the amplification efficiency of pumping light in the amplification optical fiber with a simple configuration, an optical fiber amplifier using the amplification optical component, and a fiber laser device. Objective.

  An amplification optical component according to the present invention includes an amplification optical fiber including a core to which an active element is added, and a cladding into which excitation light for exciting the active element is incident, and one end of the amplification optical fiber; And a detour propagation optical fiber that is optically coupled to the clad portion between the other end and that makes a part of the excitation light propagating through the clad travel.

  In this amplification optical component, since the cladding portion of the amplification optical fiber and the light propagation path of the bypass propagation optical fiber are optically coupled, the light propagation condition in the cladding of the amplification optical fiber is optical. The part that is connected to is different from the other part. Accordingly, a change occurs in the propagation mode of the skew light propagating through the clad in the optical coupling portion, and this change improves and reduces the skew light propagating through the clad as passing through the core. In addition, since the optical coupling portion is formed at the intermediate portion of the amplification optical fiber, the core can be used while shortening the propagation distance of the skew light with respect to the cladding as compared with the case where it is formed at the end of the amplification optical fiber. The propagation distance of the excitation light improved so as to pass through can be increased. Therefore, the passing efficiency of excitation light to the core is increased. In addition, since the optical coupling portion can be formed without bending the amplification optical fiber, the intensity distribution of the excitation light in the amplification optical fiber changes, and the excitation light returns to the input end of the amplification optical fiber. It is possible to greatly suppress the loss of excitation light due to the above. Thus, the amplification efficiency of the pumping light in the amplification optical fiber is improved. On the other hand, since the bypass propagation optical fiber may be a commonly used optical fiber, the amplification optical component can be easily configured without requiring a special design for the amplification optical fiber from the base material preparation stage.

  Note that in this specification, “optically coupled” means that light can be propagated.

  Further, the bypass propagation optical fiber has a loop structure that is continuous as a non-end state in the longitudinal direction, and a part of the bypass propagation optical fiber is in a state along the longitudinal direction of the cladding portion, with respect to the cladding portion. And optically coupled.

  In this way, the pumping light that passes through the bypass propagation optical fiber enters the bypass propagation optical fiber from the amplification optical fiber via the optical coupling portion, and the optical coupling portion from the bypass propagation optical fiber. Through the optical coupling portion at least twice when exiting to the amplification optical fiber. Therefore, according to such an optical component for amplification, the efficiency of reducing skew light is further improved.

  In addition, a plurality of bypass propagation optical fibers having the loop structure are provided, and a part of each of the bypass propagation optical fibers includes a plurality of clads that are different from each other between one end and the other end of the amplification optical fiber. It is preferable to be optically coupled to the portion in a state along the longitudinal direction of the cladding portion.

  In this way, since there are a plurality of optical coupling portions of the bypass propagation optical fiber with respect to the cladding of the amplification optical fiber, the opportunity to change the propagation mode of the pumping light propagating through the cladding can be changed. This is an increase compared to the case where the coupling portion is single. Therefore, according to such an optical component for amplification, skew light is further reduced as compared with the case where a single optical coupling portion is used.

  Further, a plurality of portions in the bypass propagation optical fiber having the loop structure are arranged in a longitudinal direction of the cladding portion with respect to a plurality of different cladding portions between one end and the other end of the amplification optical fiber. It is preferable to be optically coupled in a state along.

  In this way, a plurality of optical coupling portions of the bypass propagation optical fiber exist with respect to the cladding of the amplification optical fiber. In addition, since the bypass propagation optical fiber has a loop structure, the pumping light propagating through the bypass propagation optical fiber loops recursively through various loop paths via one of a plurality of optical coupling portions. , A plurality of light coupling portions will be passed. Therefore, according to such an optical component for amplification, skew light is further reduced as compared with the case where a single optical coupling portion is used.

  Moreover, it is preferable that the optically coupled portions are integrally formed by fusion.

  By doing so, the propagation mode of the excitation light propagating through the clad in the optical coupling portion changes more greatly because the disturbance of the optical coupling portion occurs more than in the case of simply contacting. Therefore, according to such an optical component for amplification, the skew light is further reduced as compared with the case where it simply contacts.

  An optical fiber amplifier according to the present invention includes any one of the above-described amplification optical components and a pumping light source that emits the pumping light to the cladding.

  According to such an optical fiber amplifier, in the amplification optical component, the skew light is reduced as described above, and the amplification optical fiber can efficiently absorb the excitation light. However, a higher amplification factor can be obtained.

  The fiber laser device of the present invention includes any one of the above-described amplification optical components, an excitation light source that emits the excitation light to the cladding, and a seed light source that emits seed light to the core. It is characterized by comprising.

  In such a fiber laser device, in the amplification optical component, the skew light is reduced as described above, and the amplification optical fiber can efficiently absorb the pumping light. A PA (Master Oscillator-Power Amplifier) type fiber laser device can be obtained.

  Alternatively, the fiber laser device of the present invention is provided on one end side of the amplification optical component according to any of the above, an excitation light source that emits the excitation light to the cladding, and the amplification optical fiber, A mirror that reflects at least a part of the light emitted by the active element and a light that is provided on the other end side of the amplification optical fiber and reflects light reflected by the first mirror with a lower reflectance than the first mirror. And a second mirror.

  Such a fiber laser device is a resonance type fiber laser with high amplification efficiency because skew light is reduced as described above in the amplification optical component and the amplification optical fiber can efficiently absorb the excitation light. It can be a device.

  As described above, according to the present invention, the amplification optical component capable of improving the amplification efficiency of the pumping light in the amplification optical fiber with a simple configuration, the optical fiber amplifier using the same, and the fiber laser An apparatus is provided.

1 is a diagram illustrating a fiber laser device according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view perpendicular to the longitudinal direction of the amplification optical fiber of FIG. 1. FIG. 2 is a cross-sectional view perpendicular to the longitudinal direction of the bypass propagation optical fiber of FIG. 1. It is an enlarged view of the optical coupling part of FIG. It is sectional drawing which passes along the VV line of FIG. It is a graph which shows the result of having experimented the excitation light absorption amount according to the length of the optical fiber for amplification with and without the optical coupling part. It is a figure which shows the optical component for amplification which concerns on 2nd Embodiment of this invention. It is an enlarged view of the optical coupling part of FIG. It is a figure which shows the optical component for amplification which concerns on 3rd Embodiment of this invention. It is a figure which shows the optical component for amplification which concerns on 4th Embodiment of this invention. It is a figure which shows the optical component for amplification which concerns on 5th Embodiment of this invention. It is a figure which shows the fiber laser apparatus which concerns on 6th Embodiment of this invention. It is a figure which shows the modification of the optical component for amplification.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of an optical component of the present invention, and an optical fiber amplifier and a fiber laser device using the optical component will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is an equation showing a fiber laser device according to the first embodiment of the present invention.

  As shown in FIG. 1, the fiber laser device 1 is, for example, an MO-PA type fiber laser device, and includes a seed light source 10 that emits seed light and an optical fiber amplifier 5 that amplifies the seed light.

  The optical fiber amplifier 5 includes an excitation light source 20 that emits excitation light, an amplification optical component AOP that receives seed light and excitation light, and a combiner 40 that causes seed light and excitation light to enter the amplification optical component AOP. And as a main configuration. The amplification optical component AOP includes an amplification optical fiber 30 and a bypass propagation optical fiber 50 coupled to an intermediate portion of the amplification optical fiber 30.

  The seed light source 10 is composed of, for example, a laser light source composed of a laser diode, or a Fabry-Perot type or fiber ring type fiber laser device. The seed light emitted from the seed light source 10 is not particularly limited. For example, when ytterbium (Yb) is added to the amplification optical fiber 30 as described later, a laser beam having a wavelength of 1070 nm is used. Is done. The seed light source 10 is connected to a seed light fiber 15 composed of a core and a clad covering the core, and the seed light emitted from the seed light source 10 passes through the core of the seed light fiber 15. Propagate. An example of the seed light fiber 15 is a single mode fiber. In this case, the seed light propagates through the seed light fiber 15 as single mode light.

  The excitation light source 20 is composed of a plurality of laser diodes 21. The excitation light emitted from each laser diode 21 is not particularly limited. For example, when Yb is added to the amplification optical fiber 30 as described later, the laser light has a wavelength of 915 nm. . Further, each laser diode 21 of the excitation light source 20 is connected to the excitation light fiber 22, and the excitation light emitted from the laser diode 21 propagates through the excitation light fiber 22. An example of the excitation light fiber 22 is a multimode fiber. In this case, the excitation light propagates through the excitation light fiber 22 as multimode light.

  2 is a cross-sectional view perpendicular to the longitudinal direction of the amplification optical fiber 30 of FIG. As shown in FIG. 2, the amplification optical fiber 30 includes a core 31, a cladding 32 that covers the core 31, an outer cladding 33 that covers the cladding 32, and a coating layer 34 that covers the outer cladding 33. The Further, in the present embodiment, the outer shape in the cross section of the core 31, the outer cladding 33, and the coating layer 34 is circular, and the outer shape in the cross section of the cladding 32 is non-circular. In the present embodiment, the outer shape of the cross section of the clad 32 is a substantially regular polygon.

  The refractive index of the cladding 32 is lower than the refractive index of the core 31, and the refractive index of the outer cladding 33 is further lower than the refractive index of the cladding 32. As the material constituting the core 31, for example, an element such as germanium (Ge) that increases the refractive index and an active element such as Yb that is excited by excitation light emitted from the excitation light source 20 are added. Quartz. Examples of the active element include rare earth elements, and examples of the rare earth element include thulium (Tm), cerium (Ce), neodymium (Nd), europium (Eu), erbium (Er), and the like in addition to the above Yb. Furthermore, bismuth (Bi) etc. can be mentioned as an active element other than a rare earth element. Moreover, as a material which comprises the clad | crud 32, the pure quartz to which no dopant is added can be mentioned, for example. In the case where an element such as Ge that increases the refractive index is not added to the material of the core 31, fluorine (F) or the like that decreases the refractive index is added to the material of the cladding 32. On the other hand, the material constituting the outer clad 33 includes, for example, a resin, and specifically, an ultraviolet curable resin. On the other hand, as a material constituting the covering layer 34, for example, an ultraviolet curable resin different from the resin constituting the outer cladding 33 can be cited.

  The combiner 40 connects the seed light fiber 15 and the respective excitation light fibers 22 and the amplification optical fiber 30 at one end 36 of the amplification optical fiber 30. Specifically, in the combiner 40, the core of the seed light fiber 15 is connected to the core 31 of the amplification optical fiber 30, and the core of each of the excitation light fibers 22 is connected to the cladding 32. ing. Therefore, the seed light emitted from the seed light source 10 and the excitation light emitted from the excitation light source 20 are incident on the core 31 and the clad 32 with the one end 36 of the amplification optical fiber 30 as the incident end, respectively. The other end 37 of the amplification optical fiber 30 is an emission end.

  FIG. 3 is a cross-sectional view perpendicular to the longitudinal direction of the bypass propagation optical fiber 50 of FIG. As shown in FIG. 3, the bypass propagation optical fiber 50 includes a core 51 and a clad 52 that covers the core 51. Unlike the clad 32 of the amplification optical fiber 30, the outer shape of the clad 52 in the cross section is circular.

  The refractive index of the core 51 is equal to the refractive index of the cladding 32 of the amplification optical fiber 30 and is higher than the refractive index of the cladding 52 of the bypass propagation optical fiber 50. Examples of the material constituting the core 51 include the same material as the clad 32 of the amplification optical fiber 30 described above.

  Further, as shown in FIG. 1, the bypass propagation optical fiber 50 has a loop structure that is continuous as a non-end state in the longitudinal direction, and a part thereof is integrated with an intermediate portion of the amplification optical fiber 30. The optical coupling portion 61 is formed.

  4 is an enlarged view of the optical coupling portion 61 of FIG. 1, and FIG. 5 is a cross-sectional view taken along line VV of FIG. As shown in FIGS. 4 and 5, in the optical coupling unit 61, the cladding 52 of the bypass propagation optical fiber 50, the outer cladding 33 and the coating layer 34 of the amplification optical fiber 30 are peeled off, and the bypass propagation optical fiber is peeled off. 50 cores 51 and the clad 32 of the amplification optical fiber 30 are exposed.

  With the exposed portion of the core 51 and the exposed portion of the clad 32 aligned, at least a part of the exposed portion is fused and the exposed portions are joined together. Therefore, in the optical coupling part 61, light can propagate between the core 51 and the clad 32. The length L of the exposed portion is selected within a range of several mm to several tens mm, for example. However, it may be outside this range.

  The exposed portions of both the core 51 and the clad 32 are covered with a resin 69. The refractive index of the resin 69 is lower than the refractive index of the clad 32, and examples of such a resin 69 include the same resin as that of the outer clad 33.

  Next, the operation of the fiber laser device 1 will be described.

  First, seed light as amplified light is emitted from the seed light source 10 and excitation light is emitted from the excitation light source 20. As described above, the wavelength of the seed light is, for example, 1070 nm, and the wavelength of the excitation light is, for example, 915 nm.

  The seed light emitted from the seed light source 10 is incident on the combiner 40 via the seed light fiber 15, and is incident on the core 31 from one end 36 of the amplification optical fiber 30 by the combiner 40 and propagates through the core 31. On the other hand, the pumping light emitted from each pumping light source 20 is incident on the combiner 40 via the pumping light fiber 22, and is incident on the cladding 32 from one end 36 of the amplification optical fiber 30 by the combiner 40 and propagates through the cladding 32. .

  As described above, at the intermediate portion of the clad 32, the optical coupling portion 61 is formed in which a part of the core 51 of the bypass propagation optical fiber 50 is optically coupled. Due to this coupling, the light propagation condition of the clad 32 in the optical coupling part 61 is different from the light propagation condition in the clad 32 other than the optical coupling part 61. In particular, the optical coupling portion 61 of the present embodiment is one in which the clad 32 and the core 51 are coupled together by fusion, and therefore, the coupling portion is greatly disturbed. Therefore, the light propagation conditions of the clad 32 in the optical coupling portion 61 and the light propagation conditions in the clad 32 other than the optical coupling portion 61 are further increased as compared with the case where the clad 32 and the core 51 are simply brought into contact with each other. It is very different.

  For this reason, the excitation light propagating through the cladding 32 of the optical coupling portion 61 changes in its propagation mode, and due to this change, the skew light generated between the input end of the cladding 32 and the optical coupling portion 61 is It is improved as excitation light passing through the core 31. As a result, the skew light included in the excitation light propagating through the clad 32 is reduced.

  A part of the pumping light propagating through the clad 32 of the optical coupling part 61 is incident on the core 51 of the bypass propagation optical fiber 50. Since the bypass propagation optical fiber 50 has a loop structure, the excitation light incident on the core 51 circulates at least once or more and then exits from the optical coupling portion 61 to the output end side of the clad 32. Therefore, the excitation light propagating through the core 51 of the bypass propagation optical fiber 50 passes through the optical coupling portion 61 at least twice at the time of incidence and at the time of emission. As a result, the skew light included in the pumping light passing through the bypass propagation optical fiber 50 is further reduced as compared with the non-passing pumping light.

  On the other hand, the seed light propagating through the core 31 of the amplification optical fiber 30 is amplified by stimulated emission of the active element added to the core 31, and is emitted from the other end 37 of the amplification optical fiber 30 as emitted light. . The stimulated emission of the active element is caused by excitation light passing through the core 31.

  As described above, according to the amplification optical component AOP of this embodiment, the core 51 of the bypass propagation optical fiber 50 is integrally bonded to a part of the clad 32 of the amplification optical fiber 30 by fusion. Thus, the optical coupling portion 61 is formed. For this reason, the light propagation condition of the clad 32 in the optical coupling part 61 and the light propagation condition in the clad 32 other than the optical coupling part 61 are different. Therefore, the propagation mode of the excitation light propagating through the clad 32 of the optical coupling portion 61 changes, and this change reduces the skew light generated before reaching the optical coupling portion 61. In addition to this, since the optical coupling portion 61 can be formed without bending the amplification optical fiber 30, the intensity distribution of the excitation light in the amplification optical fiber 30 is changed, or the input end of the amplification optical fiber 30 is excited. Loss of pumping light in the amplification optical fiber 30 due to light returning or the like is prevented in advance. Thus, the amplification efficiency in the amplification optical fiber 30 is improved.

  Moreover, the optical coupling part 61 is formed in the intermediate part. Therefore, compared with the case where the optical coupling portion 61 is formed at the end portion of the amplification optical fiber 30, the pumping light improved to pass through the core 31 while shortening the propagation distance of the skew light with respect to the clad 32. Propagation distance can be increased. In addition to this, the propagation distance of the skew light with respect to the clad 32 and the propagation distance of the excitation light improved so as to pass through the core 31 according to the position of the optical coupling portion 61 to be formed in the amplification optical fiber 30. Can be adjusted.

  Further, the bypass propagation optical fiber 50 that is optically coupled to the intermediate portion of the amplification optical fiber 30 as the optical coupling portion 61 has a loop structure. For this reason, the excitation light propagating through the core 51 of the bypass propagation optical fiber 50 passes through the optical coupling portion 61 at least twice at the time of incidence and at the time of emission. As a result, the skew light included in the pumping light that passes through the bypass propagation optical fiber 50 is further reduced as compared with the non-passing pumping light. This can be realized without making the outer shape of the cladding 32 of the bypass propagation optical fiber 50 special.

  FIG. 6 shows the results of experiments on the amount of pumping light absorbed according to the length of the amplification optical fiber 30 with and without the optical coupling portion 61. In this experiment, the outer diameter of the coating layer 34 in the amplification optical fiber 30 was 650 μm, the diameter of the clad 32 was 400 μm, and Yb was added to the core 31. On the other hand, the diameter of the clad 52 of the bypass propagation optical fiber 50 is 250 μm, and the diameter of the core 51 is 105 μm. The optical coupling portion 61 is formed at a position that is half of the entire length of the amplification optical fiber 30, and the length L of the exposed portion of the core 51 and the exposed portion of the clad 32 in the optical coupling portion 61 is 10 mm. The wavelength of the excitation light was 915 nm. As apparent from FIG. 6, when the optical coupling portion 61 is formed, the skew light is reduced as compared with the case where the optical coupling portion 61 is not formed, and the amount of reduction is significantly larger as the length of the amplification optical fiber is longer. It has been confirmed that

(Second Embodiment)
Next, a second embodiment of the present invention will be described in detail with reference to FIGS. In addition, about the component which is the same as that of the said embodiment, the same description is attached | subjected and the overlapping description is abbreviate | omitted except the case where it demonstrates especially. FIG. 7 is a diagram showing an amplification optical component according to the second embodiment of the present invention, and FIG. 8 is an enlarged view of the optical coupling parts 62A and 62B of FIG.

  The amplification optical component AOP of the present embodiment is provided in place of the amplification optical component AOP of the first embodiment. The amplification optical fiber 30 and the bypass propagation optical fiber 55 are the same as those of the first embodiment. And have. As shown in FIG. 7, the bypass propagation optical fiber 55 is different from the bypass propagation optical fiber 50 of the first embodiment having a loop structure in that it has a non-loop structure.

  One end of the bypass propagation optical fiber 55 is formed as an optical coupling portion 62A integrated with an intermediate portion of the amplification optical fiber 30, and the other end of the amplification optical fiber 30 is more than the optical coupling portion 62A. It is formed as an optical coupling part 62B integrated with another intermediate part on the output end side.

  As shown in FIG. 8, the cladding 32 of the amplification optical fiber 30 in the optical coupling portions 62A and 62B is exposed by peeling off the outer cladding 33 and the coating layer 34, as in the first embodiment. On the other hand, the core 51 of the bypass propagation optical fiber 55 in the optical coupling portions 62A and 62B is different from that in the first embodiment.

  That is, in the optical coupling part 62A, the clad 52 at one end is peeled off and the core 51 is exposed, and in the optical coupling part 62B, the clad 52 at the other end is peeled off and the core 51 is exposed. Both exposed portions are formed with inclined surfaces IFA and IFB that are inclined with respect to the axis AX of the core 51.

  In the optical coupling portion 62 </ b> A, the inclined surface IFA of the core 51 faces the outer peripheral surface of the exposed portion of the cladding 32, and the propagation direction of the excitation light that propagates the tip of the core 51 through the cladding 32 of the amplification optical fiber 30. At least a part of the exposed portion of the core 51 and the clad 32 is fused in a state of facing the SD. Accordingly, light can propagate from the clad 32 to the core 51 in the optical coupling portion 62A.

  On the other hand, in the optical coupling part 62B, the inclined surface IFB of the core 51 is opposed to the outer peripheral surface of the exposed portion of the cladding 32, and the tip of the core 51 is along the propagation direction SD of the excitation light propagating through the cladding 32. At least a part of the exposed portion of the core 51 and the clad 32 is fused. Accordingly, light can propagate from the core 51 to the clad 32 in the optical coupling portion 62B.

  In addition, although the inclination angle θ of the inclined surface is not particularly limited, it is preferably a shallow angle with respect to the axis AX of the core 51 from the viewpoint of efficiently transmitting light from the clad 32 to the core 51. The exposed portions of the optical coupling portions 62A and 62B are covered with a resin 69 having a lower refractive index than that of the clad 32, as in the first embodiment.

  As described above, according to the amplification optical component AOP of the present embodiment, one end of the core 51 of the bypass propagation optical fiber 55 is integrally bonded to the intermediate portion of the clad 32 of the amplification optical fiber 30 by fusion. Thus, the optical coupling portion 62A is formed. In addition, the other end of the core 51 of the bypass propagation optical fiber 55 is integrally bonded to an intermediate portion between the optical coupling portion 62A and the output end of the amplification optical fiber 30, so that the optical coupling portion 62B Is formed.

  For this reason, the light propagation conditions of the clad 32 in the optical coupling parts 62A and 62B are different from the light propagation conditions in the clad 32 other than the optical coupling parts 62A and 62B, thereby the clad 32 of the optical coupling parts 62A and 62B. The propagation mode of the excitation light propagating through changes. Therefore, skew light is reduced in the optical coupling unit 62A, and skew light that cannot be improved by the optical coupling unit 62A and newly generated skew light are reduced in the optical coupling unit 62B. The excitation light propagating through the core 51 of the bypass propagation optical fiber 55 is included in the excitation light passing through the bypass propagation optical fiber 55 because it passes through the optical coupling portion 62A when incident and passes through the optical coupling portion 62B when emitted. The skew light is further reduced as compared with the non-passing excitation light.

  In addition, since the optical coupling portions 62A and 62B can be formed without bending the amplification optical fiber 30, the intensity distribution of the excitation light in the amplification optical fiber 30 can be prevented from being changed or lost. Thus, the amplification efficiency in the amplification optical fiber 30 is improved.

  Furthermore, one end of the bypass propagation optical fiber 55 that is optically coupled to the intermediate portion of the amplification optical fiber 30 as the optical coupling portion 62A is fused in a state facing the propagation direction SD of the clad 32. In addition, the other end of the bypass propagation optical fiber 55 that is optically coupled to the intermediate portion of the amplification optical fiber 30 is in a state along the propagation direction SD of the clad 32, and one end of the optical coupling portion 62 </ b> B It is fused in a state along the propagation direction SD.

  For this reason, the back propagation of the excitation light in the optical coupling parts 62A and 62B is reduced, and as a result, the loss of the excitation light due to returning to the input end of the optical fiber 30 is reduced.

  Inclined surfaces IFA and IFB that are inclined with respect to the axis AX of the core 51 are formed at one end and the other end of the bypass propagation optical fiber 55 fused to the amplification optical fiber 30, and the inclined surfaces IFA and IFB are formed. Is opposed to the outer periphery of the clad of the bypass propagation optical fiber 55.

  For this reason, the junction area of one end and the other end of the bypass propagation optical fiber 55 with respect to the clad 32 of the amplification optical fiber 30 increases. Therefore, compared with the case where the inclined surfaces IFA and IFB are not formed, the degree of change in the traveling direction with respect to the excitation light propagating through the clad 32 of the optical coupling portions 62A and 62B can be increased. Skew light is reduced. In addition to this, the loss of pumping light due to returning to the input end of the optical fiber 30 is further reduced as compared with the case where the inclined surfaces IFA and IFB are not formed. In the case of the amplification optical component AOP of this embodiment, it has been confirmed that the skew light is reduced to the same extent as in the first embodiment.

(Third embodiment)
Next, a third embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component which is the same as that of the said embodiment, the same description is attached | subjected and the overlapping description is abbreviate | omitted except the case where it demonstrates especially. FIG. 9 is a diagram showing an amplification optical component according to the third embodiment of the present invention.

  The amplification optical component AOP of this embodiment is provided in place of the amplification optical component AOP of the first embodiment. In the amplification optical component AOP of the present embodiment, the formation positions of the optical coupling portions 62A and 62B formed at the intermediate position of the amplification optical fiber 30 are different from those of the amplification optical component AOP of the second embodiment.

  That is, in the amplification optical component AOP of the second embodiment, as described above, the optical coupling portion 62A is formed near the input end of the amplification optical fiber 30, and the optical coupling portion is located near the output end of the amplification optical fiber 30. 62B was formed. In contrast, in the amplification optical component AOP of the present embodiment, as shown in FIG. 9, an optical coupling portion 62 </ b> A is formed near the output end of the amplification optical fiber 30, and near the input end of the amplification optical fiber 30. An optical coupling portion 62B is formed.

  In the optical coupling portion 62A, as in the second embodiment, the inclined surface IFA of the core 51 faces the outer peripheral surface of the exposed portion of the cladding 32, and the propagation direction of the excitation light in which the tip of the core 51 propagates through the cladding 32 At least a part of the exposed portion of the core 51 and the clad 32 is fused in a state of facing the SD. On the other hand, also in the optical coupling part 62B, as in the second embodiment, the inclined surface IFB of the core 51 faces the outer peripheral surface of the exposed portion of the cladding 32, and the tip of the core 51 propagates the excitation light propagating through the cladding 32. In a state along the propagation direction SD, at least a part of the exposed portions of the core 51 and the clad 32 are fused.

  As described above, according to the amplification optical component AOP of the present embodiment, one end of the core 51 of the bypass propagation optical fiber 55 is integrally bonded to the intermediate portion of the clad 32 of the amplification optical fiber 30 by fusion. Thus, the optical coupling portion 62A is formed. In addition, the other end of the core 51 of the bypass propagation optical fiber 55 is integrally bonded to an intermediate portion between the optical coupling portion 62A and the input end of the amplification optical fiber 30, so that the optical coupling portion 62B is Is formed.

  For this reason, the light propagation conditions of the clad 32 in the optical coupling parts 62A and 62B are different from the light propagation conditions in the clad 32 other than the optical coupling parts 62A and 62B, thereby the clad 32 of the optical coupling parts 62A and 62B. The propagation mode of the excitation light propagating through changes. Therefore, the skew light generated up to the optical coupling unit 62A is reduced.

  The pumping light propagating through the core 51 of the bypass propagation optical fiber 55 passes from the optical coupling portion 62A of the amplification optical fiber 30 through the optical coupling portion 62B that exists on the input end side of the optical coupling portion 62A. Then, the amplification optical fiber 30 is returned from the output end side to the input end side. Therefore, the excitation light propagating through the core 51 of the bypass propagation optical fiber 55 recursively loops between the optical coupling portions 62A and 62B via the amplification optical fiber 30 and passes through the optical coupling portions over a plurality of times. As a result, not only the skew light generated up to the optical coupling unit 62A is further reduced, but also the skew light newly generated between the optical coupling units 62B to 62A is reduced. This can be realized without making the outer shape of the clad 32 of the bypass propagation optical fiber 55 special. In the case of the amplification optical component AOP of this embodiment, it has been confirmed that the skew light is reduced to the same extent as in the first embodiment.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component which is the same as that of the said embodiment, the same description is attached | subjected and the overlapping description is abbreviate | omitted except the case where it demonstrates especially. FIG. 10 is a diagram showing an amplifying optical component according to the fourth embodiment of the present invention.

  The amplification optical component AOP of the present embodiment is provided in place of the amplification optical component AOP of the first embodiment, and is formed in the amplification optical fiber 30 of the amplification optical component AOP in the first embodiment. A plurality of optical coupling portions 61 are provided.

  That is, as shown in FIG. 10, optical coupling portions 61 </ b> A to 61 </ b> C that optically couple with a part of the core 51 of the bypass propagation optical fiber 50 are fixed at the intermediate portion of the clad 32 of the amplification optical fiber 30. It is formed at every interval. However, the interval at which the optical coupling portion 61 should be formed may be an arbitrary interval.

  According to such an amplification optical component AOP, there are a plurality of opportunities for the propagation mode of pumping light propagating through the cladding 32 of the amplification optical fiber 30 to change until the output end of the amplification optical fiber 30 is reached. become. Therefore, the skew light is further reduced compared to the case of the first embodiment.

  In the case of the amplification optical component AOP of the present embodiment, it has been confirmed that the skew light is significantly reduced as compared with the first embodiment. Specifically, for example, the optical coupling portion 61 is formed at a position 3 m and a position 6 m from the one end 36 of the amplification optical fiber 30 having a total length of 10 m, and the other conditions are the same as in the case shown in FIG. The absorption amount of the excitation light measured at 1 was 20 dB. On the other hand, as shown in FIG. 7, the amount of absorption was 15 dB when one optical coupling portion 61 was formed at an intermediate portion of the amplification optical fiber 30 having a total length of 10 m.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component which is the same as that of the said embodiment, the same description is attached | subjected and the overlapping description is abbreviate | omitted except the case where it demonstrates especially. FIG. 11 is a diagram showing an amplification optical component according to the fifth embodiment of the present invention.

  The amplification optical component AOP of the present embodiment is provided in place of the amplification optical component AOP of the first embodiment, and each of the plurality of optical coupling portions 61A to 61C according to the fourth embodiment has an optical fiber for bypass propagation. 50 is connected to form a single loop structure.

  That is, as shown in FIG. 11, the bypass propagation optical fiber 56 of this embodiment has a loop structure that is continuous in an endless state in the longitudinal direction. The core 51 in the bypass propagation optical fiber 56 and the intermediate portion of the cladding 32 in the amplification optical fiber 30 are exposed at predetermined intervals. And at least one part of each exposed part is melt | fused, and optical coupling part 61A-61C by which each exposed part was couple | bonded integrally is formed. However, the interval at which the optical coupling portions 61 </ b> A to 61 </ b> C should be formed may be an arbitrary interval, and both or one of the exposure interval of the core 51 and the exposure interval of the clad 32 may be an arbitrary interval.

  As described above, according to the amplification optical component AOP of the present embodiment, as in the fourth embodiment, the opportunity for changing the propagation mode of the excitation light propagating through the cladding 32 of the amplification optical fiber 30 is different from the amplification light. There are a plurality of optical fibers 30 until the output end of the fiber 30 is reached. Therefore, the skew light is further reduced compared to the case of the first embodiment.

  Further, as each of the optical coupling portions 61A to 61C, the bypass propagation optical fiber 56 optically coupled to the amplification optical fiber 30 has a single loop structure. For this reason, there are a wide variety of propagation paths of pumping light propagating through the core 51 of the bypass propagation optical fiber 56 through the optical coupling portions 61A to 61C.

  For example, the pumping light propagating through the core 51 of the bypass propagation optical fiber 56 is light that is present on the input end side of the optical coupling portion 62C from the optical coupling portion 61C that is closest to the output end of the amplification optical fiber 30. The light is returned to the amplification optical fiber 30 through either the coupling portion 61A or 61B. Therefore, the excitation light propagating through the core 51 of the bypass propagation optical fiber 56 recursively loops through various loop paths via any one of the optical coupling portions 61A to 61C, and passes through the optical coupling portion over a plurality of times. As a result, not only the skew light generated up to the optical coupling unit 62A is further reduced, but also the skew light newly generated between the optical coupling units is reduced. This can be realized without making the outer shape of the clad 32 of the bypass propagation optical fiber 56 special. In the case of the amplification optical component AOP of the present embodiment, it has been confirmed that the skew light is reduced to the same extent or more as in the fourth embodiment.

(Sixth embodiment)
Next, a sixth embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component which is the same as that of 1st Embodiment, or an equivalent component, the overlapping description is abbreviate | omitted except the case where it attaches | subjects the same referential mark and demonstrates in particular. FIG. 12 is a diagram showing a fiber laser device according to the sixth embodiment of the present invention.

  As shown in FIG. 12, the fiber laser device 2 of the present embodiment includes an optical fiber amplifier 5, a first resonance fiber 16 connected to the one end 36 side of the amplification optical fiber 30, and the first resonance fiber 16. A first Bragg Grating (FBG) 81 as a first mirror provided in the first optical fiber 30, a second resonance fiber 17 connected to the other end 37 side of the amplification optical fiber 30, and a second resonance fiber 17 provided in the second resonance fiber 17. A second FBG 82 as a two-mirror is provided as a main configuration. As described above, the fiber laser device 2 of the present embodiment is a resonance type fiber laser device.

  For example, the first resonance fiber 16 has the same configuration as the seed light fiber 15 in the first embodiment, and one end is connected to the amplification optical fiber 30 by the combiner 40 in the same manner as the seed light fiber 15. ing. Further, a non-reflection terminal 19 is provided at the other end of the first resonance fiber 16. Further, a first FBG 81 is formed in the core of the first resonance fiber 16. Thus, the first FBG 81 is provided on the one end 36 side of the amplification optical fiber 30. The first FBG 81 has a portion in which the refractive index increases at a constant period along the longitudinal direction of the first resonance fiber 16, and the first FBG 81 is in an excited state by adjusting this period. The amplifying optical fiber 30 is configured to reflect at least part of the wavelength of light emitted by the active element. When the active element is Yb as described above, the first FBG 81 has a reflectance of 100% at, for example, 1070 nm.

  The second resonance fiber 17 is connected to the other end 37 of the amplification optical fiber 30. For example, the second resonance fiber 17 has the same configuration as the first resonance fiber, and the core of the second resonance fiber 17 is coupled to the core of the amplification optical fiber 30. A second FBG 82 is provided in the core of the second resonance fiber 17. Thus, the second FBG 82 is provided on the other end 37 side of the amplification optical fiber 30. The second FBG 82 has a portion where the refractive index increases at a constant period along the longitudinal direction of the second resonance fiber 17, and reflects light having the same wavelength as the light reflected by the first FBG 81 lower than the first FBG 81. For example, light having the same wavelength as the light reflected by the first FBG 81 is reflected at a reflectance of 50%.

  In such a fiber laser device 2, when excitation light is emitted from each laser diode 21 of the excitation light source 20, this excitation light is incident on the clad 32 of the amplification optical fiber 30 in the combiner 40. In the same manner as in the first embodiment, the active element added to the core 31 of the amplification optical fiber 30 is brought into an excited state. And the active element made into the excited state emits spontaneous emission light of a specific wavelength. The spontaneously emitted light at this time is, for example, light having a constant band with a center wavelength of 1070 nm. The spontaneous emission light propagates through the core 31 of the amplification optical fiber 30 and is reflected by the first FBG 81 formed in the core of the first resonance fiber 16, and the reflected light is reflected from the amplification optical fiber 30. The light propagates to the second FBG 82 formed in the second resonance fiber 17 through the core 31 and is reflected by the second FBG 82, thereby causing light resonance. The light is amplified when propagating through the core 31 of the amplification optical fiber 30, and part of the light is transmitted through the second FBG 82 and emitted from the second resonance fiber 17.

  According to the fiber laser device 2 of this embodiment, skew light is reduced in the amplification optical component AOP of the optical fiber amplifier 5 as described above, and the amplification optical fiber 30 efficiently absorbs excitation light. For this reason, it can be set as the resonance type fiber laser apparatus with high amplification efficiency. In the present embodiment, the first FBG 81 and the second FBG 82 have been described as examples of the first mirror and the second mirror. However, the first mirror and the second mirror are not limited to the FBG. Further, instead of the amplification optical component AOP of this embodiment, any of the amplification optical components AOP of the second to fifth embodiments may be applied.

  As mentioned above, although this invention was demonstrated to the 1st-6th embodiment as an example, this invention is not limited to these.

  For example, different amplification optical components AOP are shown in the first to fifth embodiments, but the amplification optical components of the present invention are not limited to those shown as the first to fifth embodiments. For example, the amplification optical component AOP shown in FIG. 13 is used in both the MO-PA type fiber laser device 1 described in the first embodiment and the resonance type fiber laser device 2 described in the sixth embodiment. Applicable.

  FIG. 13 is a diagram showing a modification of the amplification optical component. As shown in FIG. 13, in the amplification optical component AOP of the present modification, an optical coupling portion 63 is formed at an intermediate portion of the amplification optical fiber 30. In this optical coupling portion 63, a part of the cores 51 of the three bypass propagation optical fibers 50 </ b> A to 50 </ b> C having a loop structure are peeled off, and the exposed portion of each core 51 and the exposed portion of the clad 32 are aligned with each other. The exposed portions are fused together, and the exposed portions are optically coupled together. According to the amplification optical component AOP of the present modified example, each of the bypass propagation optical fibers 50A to 50C has a loop structure. Therefore, the pumping light incident on the core 51 circulates at least once or more and then the optical coupling unit 63. To the output end side of the clad 32. Further, since each of the bypass propagation optical fibers 50A to 50C has a loop structure, there are a wide variety of propagation paths of the excitation light propagating to the bypass propagation optical fibers 50A to 50C via the optical coupling portion 63. Therefore, the number of times the excitation light propagating through the bypass propagation optical fibers 50 </ b> A to 50 </ b> C passes through the optical coupling unit 63 increases. As a result, the skew light included in the pumping light passing through the bypass propagation optical fiber 50 is further reduced. In the case of the amplification optical component AOP of this modification, it has been confirmed that the skew light is reduced to the same extent as in the fourth embodiment.

  The amplification optical component AOP shown as the modified example or the first to fifth embodiments is merely an example. In short, if the amplification optical fiber 30 and the bypass propagation optical fiber optically coupled to a part of the clad 32 which is the middle in the length direction of the amplification optical fiber 30 are provided, the present invention. It can be applied as an amplification optical component.

  Further, in the amplification optical component AOP shown in the embodiment and the modification example, the core 51 of the bypass propagation optical fiber and the clad 32 of the amplification optical fiber 30 are optically coupled by fusion. . However, as long as the core 51 and the clad 32 are optically coupled, a coupling method other than fusion may be applied.

  Further, in the amplification optical component AOP shown in the embodiment and the modification, the clad 32 of the optical amplification optical fiber is non-circular, but it may be circular.

  Further, in the amplification optical component AOP shown in the above embodiment and the above modification, the core 51 of the bypass propagation optical fibers 50, 55, and 56 is circular, but it may be noncircular. Further, the bypass propagation optical fibers 50, 55, and 56 may be replaced with optical amplification optical fibers. In this alternative, the optical propagation path optically coupled to the clad 32 of the amplification optical fiber 30 is not the core of the substituted optical amplification optical fiber but the clad. Further, the clad of the optical fiber for optical amplification substituted in this way is not limited to a non-circular shape as in the above-described embodiment, and may be a circular shape.

  Further, the fiber laser device in the above embodiment is a forward pump type in which pumping light enters from one end 36 of the amplification optical fiber 30 and exits from the other end 37. However, the fiber laser device in the above embodiment may be of a backward pumping type in which excitation light enters from the other end 37 of the amplification optical fiber 30 and exits from one end 36, and the excitation light is transmitted to one end of the amplification optical fiber 30. Alternatively, a dual excitation type in which light enters and exits from both 36 and the other end 37 may be used. Note that an optical isolator may be interposed in the propagation path of such a forward-pumped, backward-pumped, or both-pumped fiber laser device.

  Further, the amplification optical component AOP shown in the above embodiment or the above modification, and the excitation light source 20 and the combiner 40 in the above embodiment may be used as a part of the optical communication amplification device.

  As described above, according to the present invention, an amplification optical component capable of improving the amplification efficiency of pumping light in the amplification optical fiber with a simple configuration, an optical fiber amplifier using the same, and a fiber laser An apparatus is provided.

DESCRIPTION OF SYMBOLS 1, 2 ... Fiber laser apparatus 5 ... Optical fiber amplifier 10 ... Seed light source 15 ... Seed light fiber 16 ... 1st resonance fiber 17 ... 2nd resonance fiber 19. ..Non-reflective termination 20 ... excitation light source 21 ... laser diode 22 ... excitation light fiber 30 ... amplification optical fiber 31 ... core 32 ... cladding 33 ... outer cladding 34 ... Coating layer 40 ... Combiner 50, 50A-50C, 55, 56 ... Detour propagation optical fiber 61, 61A-61C, 62A, 62B, 63 ... Optical coupling part 69 ... Resin 81 ... 1st FBG
82 ... 2nd FBG
AOP: Amplifying optical components AX: Shaft IFA, IFB: Inclined surface

Claims (7)

An amplification optical fiber including a core to which an active element is added, and a cladding into which excitation light for exciting the active element is incident;
A detour propagation optical fiber that is optically coupled to a cladding portion between one end and the other end of the amplification optical fiber, and makes a part of the pumping light propagating through the cladding travel ;
The bypass propagation optical fiber has a loop structure that continues as an endless state in the longitudinal direction,
An amplification optical component , wherein a part of the bypass propagation optical fiber is optically coupled to the clad portion in a state along the longitudinal direction of the clad portion . A plurality of bypass propagation optical fibers having the loop structure,
A part of each of the bypass propagation optical fibers is optically coupled to a plurality of different cladding portions between one end and the other end of the amplification optical fiber in a state along the longitudinal direction of the cladding portions. The amplification optical component according to claim 1 , wherein A state in which a plurality of portions in the bypass propagation optical fiber having the loop structure are along a longitudinal direction of the cladding portion with respect to a plurality of different cladding portions between one end and the other end of the amplification optical fiber. The amplifying optical component according to claim 1 , wherein the amplifying optical component is optically coupled. The amplification optical component according to any one of claims 1 to 3, wherein the optically coupled portions are integrally formed by fusion. An optical component for amplification according to any one of claims 1 to 4 ,
An optical fiber amplifier comprising: an excitation light source that emits the excitation light to the clad. An optical component for amplification according to any one of claims 1 to 4 ,
An excitation light source that emits the excitation light to the cladding;
A fiber laser device comprising: a seed light source that emits seed light to the core. An optical component for amplification according to any one of claims 1 to 4 ,
An excitation light source that emits the excitation light to the cladding;
A mirror that is provided on one end side of the amplification optical fiber and reflects at least part of the light emitted by the active element;
A fiber laser device comprising: a second mirror that is provided on the other end side of the amplification optical fiber and reflects light reflected by the first mirror with a lower reflectance than the first mirror.

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