JP2007250951A - Double-clad fiber and fiber laser provided therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber laser providing a higher output than that of prior arts by improving a double-clad fiber with an air clad structure with high heat resistance. <P>SOLUTION: The double-clad fiber 10a is provided with a core 1 to which an optical amplification component is doped, a first clad 2 provided to cover the core 1, and a second clad 3 provided to cover the first clad 2 and formed with a plurality of pores 3a extended along the core 1. An emission side reflection film 12 for reflector of light propagated through the core 1 is provided to one fiber end face; an incident side reflection film 11 reflected in the emission side reflection film 12 and for reflecting the light propagated through the core 1 is provided to the other fiber end face; and each diameter of the core 1, the first clad 2, and the second clad 3 is increased from the one fiber end toward the other fiber end. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a double clad fiber used for a high-power fiber laser.

  A double clad fiber, which is one type of optical fiber, includes a core doped with a rare earth element as an optical amplification component from the center of the fiber, a first clad provided to cover the core and having a lower refractive index than the core, And a second cladding having a refractive index lower than that of the first cladding. In the double-clad fiber, the excitation light incident on the first cladding propagates through the region surrounded by the second cladding while repeating reflection at the interface between the first cladding and the second cladding, and the excitation light passes through the core. In this case, the rare earth element doped in the core is turned into an inversion distribution state excited by the outermost electrons, and the light propagating through the core can be amplified by the stimulated emission.

For example, Patent Document 1 proposes a double clad fiber having an air clad structure in which the second clad is formed by a plurality of pores.
Japanese Patent Laid-Open No. 11-142672

  By the way, in a fiber laser using a double clad fiber, for example, an LD (laser diode) that emits pumping light is disposed at one fiber end, and the pumping light incident on the fiber end face from the LD propagates through the first cladding. In the meantime, when the excitation light passes through the core, the rare earth element in the core is excited. Then, the spontaneous emission light oscillated from the excited rare earth element propagates through the core and is emitted from the other fiber end face.

  The double clad fiber having the air clad structure is superior in heat resistance to the conventional double clad fiber in which the second clad is formed of a resin having a low refractive index, and the first clad and the second clad. It is possible to design a large numerical aperture by increasing the difference in refractive index.

  By the way, in recent years, high-power lasers have become an important technology in production processing in all industries, including space, aviation, and electronics. Also in the used fiber laser, high output of the laser is desired.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a fiber laser having a higher output than the conventional one by improving a double-clad fiber having a highly heat-resistant air-clad structure. is there.

  In order to achieve the above object, according to the present invention, in a double clad fiber having an air clad structure, each fiber end face is provided with a reflection portion and a reflection film, or the core, the first clad, and the second clad. Each diameter expands from one fiber end toward the other fiber end.

  Specifically, a double clad fiber according to the present invention includes a core doped with an optical amplification component, a first clad provided to cover the core, and the core provided to cover the first clad. A second clad formed with a plurality of pores extending along the first clad, and the excitation light incident on the first clad is repeatedly reflected at the interface between the first clad and the second clad and the second clad Propagating in the region surrounded by the core, the optical amplification component of the core is activated when the excitation light passes through the core, and the optical amplification component is configured to amplify the light propagating through the core. A double-clad fiber, wherein one end face of the fiber is provided with an exit-side reflecting portion that reflects a part of the light propagating through the core, and the other end face of the fiber is reflected by the exit-side reflecting section. Above Wherein the incident side reflection film for reflecting light propagating A is provided.

  According to the above configuration, since the exit-side reflecting portion and the incident-side reflecting film are directly provided on each fiber end surface, for example, when optically coupled with an optical element such as a lens constituting a fiber laser or an excitation light source, Adjustment is easy. On the other hand, when the exit-side reflecting portion and the incident-side reflecting film are not directly provided on each fiber end face, the core diameter is usually about 10 to 100 μm, so that it can be coupled to the optical element with high coupling efficiency. Have difficulty.

  Therefore, since optical adjustment with the optical elements constituting the fiber laser becomes easy, it is possible to improve the air clad structure double clad fiber with high heat resistance and provide a fiber laser with higher output than before. become.

  Moreover, as a preferable aspect, both fiber end surfaces may be sealed and polished, and an exit-side reflecting portion and an incident-side reflecting film may be provided on both end surfaces of the sealed and polished fibers. According to this, both the exit side reflection part and the incident side reflection are compared with the case where the exit side reflection part and the incident side reflection film are provided on both end faces of the fiber that are not sealed and polished, that is, each cleaved surface that is cut only. The laser resistance of the film is improved.

  The double clad fiber according to the present invention includes a core doped with an optical amplification component, a first clad provided to cover the core, and a core provided to cover the first clad. A second clad formed with a plurality of pores extending along the first clad, and the excitation light incident on the first clad is repeatedly reflected at the interface between the first clad and the second clad while being reflected by the second clad. Propagated within the enclosed region, and configured to activate the light amplification component of the core when the excitation light passes through the core, and the light amplification component amplifies the light propagating through the core In the double clad fiber, the diameters of the core, the first clad, and the second clad are increased from one fiber end toward the other fiber end while maintaining the similar shape of the core and the first clad. And said that you are.

  According to the above configuration, the diameters of the core, the first cladding, and the second cladding are increased from one fiber end toward the other fiber end while maintaining the similar shape of the core and the first cladding. In other words, the diameter of the first cladding is reduced along the length direction from the incident side of the excitation light, and the second cladding has an air cladding structure including a plurality of pores. It becomes continuously higher along the length direction from the incident side of the excitation light. Therefore, leakage of the excitation light propagating through the first cladding to the outside is suppressed.

  For example, an emission side reflection part for reflecting a part of the light propagating through the core is provided at one fiber end, and the light propagating through the core after being reflected by the emission side reflection part is provided at the other fiber end. When a resonator is configured by providing an incident-side reflecting film that reflects, the exit-side reflecting portion generates the inside of the core by the excitation light incident on the first cladding from the other fiber end surface. A part of the light propagating toward one fiber end is reflected, and the incident-side reflection film reflects the light propagating from the output-side reflecting portion and propagating in the core toward the other fiber end. Will propagate again towards one of the fiber ends. As a result, the light propagating through the core of the double clad fiber is laser-oscillated by amplification and resonance between the exit-side reflecting portion and the entrance-side reflecting film, and is also emitted from the core at one end of the fiber to be a fiber laser. Is configured.

  Here, since the diameter of the core is tapered from the incident side of the excitation light along the length direction, the high-order mode light among the light propagating in the core propagates in the core. As a result, the low-order mode light mainly resonates between the exit-side reflecting portion and the incident-side reflecting film, and the beam quality of the oscillated laser is improved. On the other hand, when the diameter of the core remains large along the length direction, the light of the higher order mode is also resonated, so that the beam quality may be deteriorated. Further, when the core diameter remains small along the length direction, the absorption coefficient of the excitation light propagating through the first cladding may be reduced.

  Further, since the diameter of the other fiber end on which the excitation light is incident is larger than the diameter of the one fiber end, for example, coupling with an excitation light source that outputs the excitation light is facilitated.

  Therefore, the leakage of the pumping light propagating through the first cladding is suppressed, the beam quality of the laser oscillated when the fiber laser is configured is improved, and the coupling with the pumping light source is facilitated. A highly clad air clad structure double clad fiber can be improved to provide a fiber laser with higher output than the conventional one.

  The surface of the one fiber end is provided with an exit-side reflecting portion that reflects part of the light propagating through the core, and the surface of the other fiber end is reflected by the exit-side reflecting portion and is An incident-side reflection film that reflects light propagating through the core may be provided.

  According to the above configuration, the exit-side reflecting portion provided on one fiber end face generates the inside of the core by the excitation light incident on the first clad from the other fiber end face, and the inside of the core passes through the one fiber end face. A part of the light propagating toward the light is reflected, and the light that is reflected by the output-side reflecting portion by the incident-side reflection film provided on the other fiber end face and propagates in the core toward the other fiber end. Is reflected and propagates again toward one fiber end. As a result, the light propagating through the core of the double clad fiber is laser-oscillated by amplification and resonance between the exit-side reflecting portion and the entrance-side reflecting film, and is also emitted from the core at one end of the fiber to be a fiber laser. Is specifically configured.

  Moreover, as a preferable aspect, both fiber end surfaces may be sealed and polished, and an exit-side reflecting portion and an incident-side reflecting film may be provided on both end surfaces of the sealed and polished fibers. According to this, both the exit side reflection part and the incident side reflection are compared with the case where the exit side reflection part and the incident side reflection film are provided on both end faces of the fiber that are not sealed and polished, that is, each cleaved surface that is cut only. The laser resistance of the film is improved.

  The one fiber end surface is provided with a one-side reflecting film that reflects light propagating through the core, and the other fiber end surface is reflected by the one-side reflecting film and propagates through the core. There may be provided an exit-side reflecting portion that reflects part of the light to be transmitted.

  According to the above configuration, the one-side reflecting film provided on one fiber end face generates the inside of the core by the excitation light incident on the first clad from the other fiber end face, and the inside of the core passes through the one fiber end face. Part of the light propagating in the core is reflected by the exit-side reflection part provided on the other fiber end face and reflected by the one-side reflection film and toward the other fiber end. Is reflected and propagates again toward one fiber end. As a result, the light propagating through the core of the double clad fiber is laser-oscillated by amplification and resonance between the exit-side reflecting portion and the one-side reflecting film, and is emitted from the core at the other fiber end. . Further, since the laser beam is emitted from the fiber end side having a large fiber diameter and the diameter of the core at the fiber end on the emission side is increased, the power density of the laser is lowered, and the laser resistance of the emission side reflection portion is improved. As a result, a fiber laser with improved laser resistance at the exit-side reflecting portion is specifically configured.

  Moreover, as a preferable aspect, both fiber end surfaces may be sealed and polished, and an exit-side reflecting portion and an incident-side reflecting film may be provided on both end surfaces of the sealed and polished fibers. According to this, both the exit side reflection part and the incident side reflection are compared with the case where the exit side reflection part and the incident side reflection film are provided on both end faces of the fiber that are not sealed and polished, that is, each cleaved surface that is cut only. The laser resistance of the film is improved.

  The said exit side reflection part may be comprised with the reflecting film.

  According to said structure, the output side reflection part is specifically comprised by the reflecting film which reflects the light of a predetermined wavelength with a low reflectance, for example.

  The double clad fiber as described above is effective particularly in the fiber laser in the operation of the present invention.

  According to the present invention, in a double-clad fiber having an air-clad structure, each fiber end face is provided with a reflective portion and a reflective film, or each of the core, the first clad, and the second clad has one diameter. Since the diameter increases from the end toward the other fiber end, the double-clad fiber having an air-clad structure with high heat resistance can be improved, and a fiber laser with higher output than before can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment.

Embodiment 1 of the Invention
1 to 5 show Embodiment 1 of a double clad fiber and a fiber laser including the same according to the present invention. Here, FIG. 1 is a cross-sectional view of the double clad fiber 10a of the present embodiment, and FIG. 2 is an observation photograph of the cross section of the double clad fiber 10a. FIG. 3 is a schematic configuration diagram of a fiber laser 30a including the double clad fiber 10a.

  As shown in FIGS. 1 and 2, the double clad fiber 10 a includes a core 1 that is the center of the fiber, a first clad 2 provided around the core 1, and a first clad 2 provided around the first clad 2. 2 clad 3, support layer 4 provided around second clad 3, low refractive index resin layer 5 provided around support layer 4, and protection provided around low refractive index resin layer 5 Layer 6. In FIG. 2, the low refractive index resin layer 5 and the protective layer 6 are omitted.

  Further, as shown in FIG. 3, the double clad fiber 10a has an output side reflection film that is an output side reflection part that reflects a part of light propagating through the core 1 on one end face of the fiber (right side in FIG. 3). 12 and an incident-side reflecting film 11 that reflects the light reflected by the emitting-side reflecting film 12 and propagating through the core 1 is provided on the other fiber end face (left side in FIG. 3).

  Further, as shown in FIG. 3, the double clad fiber 10a has a core 1 and a first clad 2 substantially from one fiber end (right side in FIG. 3) to the other fiber end (left side in FIG. 3). The diameter is increased while maintaining a similar shape, in other words, the diameter is reduced in a tapered shape from the incident-side reflecting film 11 toward the emitting-side reflecting film 12.

  The core 1 is made of quartz, doped with a rare earth element such as ytterbium (Yb) as an optical amplification component, and has a higher refractive index than the first cladding 2. The diameter of the core 1 is, for example, about 150 μm at the incident side end face and about 60 μm at the emission side end face. Further, the numerical aperture (NA) of the core is about 0.06 on the end face on the incident side and the both end faces on the outgoing side.

  The first cladding 2 is also called a pump guide and is made of quartz. The diameter of the first cladding 2 is, for example, about 1500 μm at the incident side end face and about 600 μm at the outgoing end face. Furthermore, the NA of the first cladding 2 is about 0.2 at the incident-side end face and about 0.5 at the exit-side end face.

  Each of the second clads 3 has a plurality of pores 3a extending along the core 1 and is made of quartz. The refractive index of the second cladding 3 is a composite of the refractive index of air in the plurality of pores 3a and the refractive index of quartz in portions other than the pores 3a. That is, it is lower than the refractive index of quartz.

  The support layer 4 is made of quartz. The diameter of the support layer 4 is, for example, about 2500 μm at the incident side end face and about 1000 μm at the emission side end face.

  The low refractive index resin layer 5 is made of, for example, silicon resin, and has a refractive index lower than that of the support layer 4.

  The protective layer 6 is made of, for example, ETFE (ethylene tetrafluoroethlene copolymer) resin.

The incident-side reflection film 11 is configured by laminating thin films such as Ta ₂ O ₅ and SiO ₂ , and is an optical thin film that reflects, for example, 99.8% of 1080 nm light.

The emission side reflection film (emission side reflection part) 12 is configured by laminating thin films such as Ta ₂ O ₅ and SiO ₂ , and is an optical thin film that reflects, for example, 5% of 1080 nm light.

  The double clad fiber 10a having the above-described configuration is manufactured by heating and stretching a preform to draw a fiber, and then depositing a thin film on both end faces of the fiber. Specifically, an example will be described below.

  First, a cylindrical support tube made of quartz, a cylindrical clad rod made of quartz and doped with a predetermined amount of Yb along the central axis, and a plurality of cylindrical capillaries made of quartz And prepare.

  Subsequently, a clad rod and a plurality of capillaries are filled in a support tube in a penetrating state to form a preform. At this time, the support tube is filled with a plurality of capillaries, and the cladding rod is arranged at the position of the central axis of the support tube.

  Further, the formed preform is heated and drawn in a drawing furnace to form a fiber. At this time, the fiber is formed in a tapered shape by adjusting the stretching speed. Here, the preform clad rod is formed in the core 1 and the first clad 2 of the double clad fiber 10a, the plurality of preform capillaries are formed in the second clad 3 of the double clad fiber 10a, and the preform support tube is doubled. It becomes the support layer 4 of the clad fiber 10a.

  Subsequently, each end face of the fiber formed in a tapered shape is heated to seal the pores 3a on the end face of each fiber, and then the end face of each sealed fiber is polished with a grindstone or the like.

  Thereafter, a plurality of thin films are deposited on the thick end and polished end face of the tapered fiber by using an electron beam deposition apparatus or an ion assist electron beam deposition apparatus, and the incident side reflection film 11 is formed.

  Further, a plurality of thin films are vapor-deposited on the narrow end and polished end face of the tapered fiber by using an electron beam vapor deposition apparatus or an ion-assisted electron beam vapor deposition apparatus, and the output side reflection film 12 is formed.

  Finally, a low refractive index resin layer 5 is formed by applying and curing a silicone resin on the surface of the fiber support layer 4 on which the incident side reflection film 11 and the emission side reflection film 12 are formed. The protective layer 6 is formed by applying and curing EFTE resin on the surface of the layer 5.

  As described above, the double clad fiber 10a of this embodiment can be manufactured.

Next, a fiber laser 30a provided with the double clad fiber 10a of this embodiment will be described with reference to FIG. 3. As shown in FIG. 3, this fiber laser 30a has an LD (laser diode) 20, a lens 21, and the above-described configuration. This is an optical device in which the double clad fibers 10a are arranged in order.

  For example, the LD 20 is an excitation light source that outputs excitation light in which two wavelengths of 915 nm and 940 nm are synthesized.

  The lens 21 has an NA of about 0.2, and condenses the excitation light 26 from the LD 20 to, for example, a spot diameter of 1500 μm.

  In this fiber laser 30 a, the excitation light 26 from the LD 20 is incident on the first cladding 2 of the double clad fiber 10 a through the lens 21, and the incident excitation light 26 is incident between the first cladding 2 and the second cladding 3. Propagating in the region surrounded by the second cladding 3 while repeating reflection at the interface, when the excitation light 26 passes through the core 1, the rare earth element in the core 1 is activated to generate spontaneous emission light. Then, spontaneously emitted light generated in the core 1 propagates through the core 1 and reaches the exit-side reflection film 12. Here, among spontaneously emitted light, light having a wavelength (about 1080 nm) included in the reflection wavelength band of the exit-side reflection film 12 is reflected and propagates inside the core 1 again. Further, the light reflected by the exit-side reflecting film 12 and propagating through the core 1 is reflected by the incident-side reflecting film 11 and propagates through the core 1 again. In the fiber laser 30a, the incident-side reflecting film 11 and the emitting-side reflecting film 12 form a resonator, so that resonance occurs between the incident-side reflecting film 11 and the emitting-side reflecting film 12, and repeated stimulated emission is performed. As a result, laser oscillation occurs and the laser 27 is extracted.

  As described above, according to the double clad fiber 10a and the fiber laser 30a of the present embodiment, the diameters of the core 1, the first clad 2 and the second clad 3 are from one fiber end (the right side in FIG. 3). The diameter of the core 1 and the first cladding 2 is increased toward the other fiber end (left side in FIG. 3) while maintaining a similar shape, in other words, the incident side of the excitation light 26 (left side in FIG. 3). Since the second clad 3 has an air clad structure including a plurality of pores 3a, the numerical aperture of the first clad 2 is made incident on the excitation light 26. It continuously increases along the length direction from the side (left side in FIG. 3). Therefore, leakage of the excitation light 26 propagating through the first cladding 2 to the outside can be suppressed.

  Since both end faces of the fiber are sealed and polished, they are provided on the exit-side reflection film 12 provided on one fiber end face (right side in FIG. 3) and on the other fiber end face (left side in FIG. 3). The laser resistance of the incident-side reflection film 11 can be improved.

  Further, since the exit-side reflecting film 12 and the incident-side reflecting film 11 are directly provided on the end faces of the respective fibers, it is easy to make optical adjustments when coupled with optical elements such as the lens 21 and the LD 26 constituting the fiber laser 30a. Can be.

  Furthermore, since the diameter of the core 1 is tapered from the incident side of the excitation light 26 (left side in FIG. 3) along the length direction, the higher-order mode among the light propagating in the core 1 Light leaks to the outside while propagating in the core, and the low-order mode light mainly resonates between the exit-side reflecting film 12 and the incident-side reflecting film 11, so that the oscillated laser Beam quality can be improved.

  Further, the diameter of the other fiber end (left side in FIG. 3) on which the excitation light 26 is incident is larger than the diameter of one fiber end (right side in FIG. 3). Bonding can be facilitated.

  Accordingly, as described above, when the excitation light 26 propagating through the first clad 2 is suppressed from leaking to the outside, the laser resistance of the emission-side reflection film 12 and the incident-side reflection film 11 is improved, and the LD 20 is coupled. Therefore, it is possible to easily adjust the optical quality of the laser 27 and to improve the beam quality of the laser 27 to be oscillated. Can be provided.

  Here, when the difference between the fiber laser 30a of the present embodiment and the conventional fiber laser is clarified, in general, when a fiber laser is configured using a double clad fiber, an FBG (Fiber Bragg Grating) is formed in the core. Thus, it is conceivable to form a resonator. In this case, as the fiber diameter increases, it becomes difficult to fuse the double clad fiber and the grating fiber. In the case of a double-clad fiber having an air-clad structure, the core is shielded by the pores forming the air-clad, so that it is difficult to directly write the FBG into the fiber core.

  Furthermore, when a fiber laser is configured using an external resonator, the beam diameter of the fiber laser is small, so it is difficult to adjust the axis of the fiber and the external resonator, and the return light is weak. Then, the beam may be pulsed, and the pulse may be amplified and maximized to cause end face destruction.

  On the other hand, in the fiber laser 30a of the present embodiment, the resonator is constituted by the incident-side reflection film 11 and the emission-side reflection film 12 formed on both end faces of the double clad fiber 10a, so that the fiber can be easily formed. A resonator can be formed, adjustment of the shaft is unnecessary, and the end face breakage as described above can be suppressed.

  In the present embodiment, the exit-side reflection film 12 is exemplified as the exit-side reflection section. However, in the present invention, the exit-side reflection film 12 is omitted, and the exit-side reflection section is configured by Fresnel reflection of the fiber end face. Also good.

  Next, a specific experiment will be described.

  As an example of the present invention, a double-clad fiber 10a was manufactured by the same method as that of the above-described embodiment, and a fiber laser 30a was configured.

  Specifically, the incident side reflection film 11 was formed with the configurations shown in Tables 1 to 3 below.

Here, Table 1 shows conditions when a reflective film is formed by alternately stacking 30 layers of Ta ₂ O ₅ thin films and SiO ₂ thin films using an electron beam evaporation apparatus, and Table 2 shows ion-assisted electrons. Table 3 shows conditions when a reflective film is formed by alternately stacking 30 layers of Ta ₂ O ₅ thin films and SiO ₂ thin films using a beam vapor deposition apparatus. Table 3 shows TiO 2 using an ion-assisted electron beam vapor deposition apparatus. _This is a condition when a reflective film is formed by alternately laminating _two thin films and 30 SiO ₂ thin films.

  FIG. 4 is a graph showing the spectral characteristics of the respective reflective films formed under the conditions shown in Tables 1 to 3. Here, the solid line curve in the graph is the spectral characteristic of the reflective film according to Table 1, the broken line curve in the graph is the spectral characteristic of the reflective film according to Table 2, and the dashed line curve in the graph is according to Table 3. It is the spectral characteristic of a reflecting film.

  Here, as shown in FIG. 4, the reflective film having the configuration shown in Table 1 was excellent in laser resistance, although the reflectance was lower than that of the reflective film having the structure shown in Tables 2 and 3.

  Moreover, the output side reflection film 12 was formed with the configurations shown in Tables 4 to 7 below.

Here, Table 4 shows conditions when a reflective film is formed by alternately stacking four layers of Ta ₂ O ₅ thin films and SiO ₂ thin films using an electron beam evaporation apparatus, and Table 5 shows ion-assisted electrons. Table 6 shows conditions when a reflective film is formed by alternately stacking four layers of Ta ₂ O ₅ thin films and SiO ₂ thin films using a beam evaporation apparatus. Table 6 shows TiO 2 using an ion-assisted electron beam evaporation apparatus. is a condition when forming the reflective film ₂ thin film and the SiO ₂ thin film is four layers alternately stacked, Table 7, using an electron beam evaporator, Al ₂ O ₃ 4 thin film and a SiO ₂ thin film alternately This is the condition when the reflective film is formed by laminating the layers.

  FIG. 5 is a graph showing the spectral characteristics of each reflective film formed under the conditions shown in Tables 4-7. Here, the solid line curve in the graph is the spectral characteristic of the reflective film according to Table 4, the broken line curve in the graph is the spectral characteristic of the reflective film according to Table 5, and the dashed line curve in the graph is according to Table 6. It is the spectral characteristic of the reflective film, and the two-dot chain line curve in the graph is the spectral characteristic of the reflective film according to Table 7.

  Here, as shown in FIG. 5, the reflective films having the configurations shown in Tables 4 to 7 did not have much difference in reflectivity, but the reflective films having the configurations shown in Table 4 are shown in Tables 5 and 6 It was more excellent in laser resistance than the reflective film having the structure shown in FIG. Further, the reflective film having the configuration shown in Table 7 showed the same laser resistance as the reflective film having the configuration shown in Table 4.

  A double-clad fiber 10a having an incident-side reflecting film 11 having the structure shown in Table 1 on the thick end face of the fiber and an emitting-side reflecting film 12 having the structure shown in Table 4 on the thin end face of the fiber. The absorption coefficient (loss) of excitation light at 915 nm was 1.0 dB / m.

  In addition, a 2 kW laser 27 was output from the fiber laser 30a including the double clad fiber 10a having a total length of 30 m and the LD 20 having an output of 3 kW.

<< Embodiment 2 of the Invention >>
FIG. 6 is a schematic configuration diagram of a fiber laser 30b including the double clad fiber 10b of the present embodiment. In the following embodiments, the same portions as those in FIGS. 1 to 5 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 6, the fiber laser 30b is an optical device in which an LD 20, an incident side lens unit 21c, a double clad fiber 10b, and an output side lens unit 23c are arranged in this order.

  The double clad fiber 10b is substantially the same as the configuration of the double clad fiber 10a of the first embodiment except that no reflection film is provided on both end faces of the fiber.

  The incident side lens unit 21c includes a first lens 21a and a second lens 21b arranged to face each other, and an incident side reflection unit 22 provided therebetween, and the excitation light 26 from the LD 20 is supplied to the predetermined side. It is an optical element for condensing to the spot diameter.

  The emission side lens portion 23 c is an optical element that includes a lens 23 a and an emission side reflection portion 23 b that are arranged to face each other, and emits a laser 27.

  The incident-side reflecting portion 22 and the emitting-side reflecting portion 23b are each composed of, for example, an optical thin film that reflects 99.8% of 1080 nm light and an optical thin film that reflects 5% of 1080 nm light, and is external to the double clad fiber 10b. It functions as a resonator.

  According to the fiber laser 30b of this embodiment, the diameters of the core 1, the first cladding 2 and the second cladding 3 are changed from one fiber end (right side in FIG. 6) to the other fiber end (left side in FIG. 6). The core 1 and the first cladding 2 are enlarged in diameter while maintaining a similar shape, in other words, from the incident side of the excitation light 26 (left side in FIG. 6) to a taper shape along the length direction. Since the second cladding 3 has an air cladding structure including a plurality of pores 3a, the numerical aperture of the first cladding 2 is a length from the incident side (left side in FIG. 6) of the excitation light 26. It is continuously higher along the direction. Therefore, leakage of the excitation light 26 propagating through the first cladding 2 to the outside can be suppressed.

  Then, an emission side reflecting portion 23b for reflecting a part of the light propagating through the core 1 is provided at one fiber end (right side in FIG. 6), and at the other fiber end (left side in FIG. 6) A resonator is formed by providing an incident-side reflecting portion 22 that reflects light that is reflected by the emitting-side reflecting portion 23b and propagates through the core 1, and the other end face of the fiber (in FIG. 6) is formed by the emitting-side reflecting portion 23b. A part of the light generated inside the core 1 by the excitation light 26 incident on the first cladding 2 from the left side) and propagating through the inside of the core 1 toward one fiber end (right side in FIG. 6) is reflected. At the same time, the light reflected by the exit-side reflecting portion 23b and reflected by the entrance-side reflecting portion 22 and propagating through the core 1 toward the other fiber end (left side in FIG. 6) is reflected. On the right side of 6) That. Thereby, in the fiber laser 30b, the light propagating through the core 1 of the double clad fiber 10b is laser-oscillated by amplification and resonance between the exit-side reflecting portion 23b and the incident-side reflecting portion 22, and at the end of one fiber The light is emitted from the core 1 (right side in FIG. 6).

  Here, since the diameter of the core 1 is tapered from the incident side of the excitation light 26 (left side in FIG. 6) along the length direction, the higher order of the light propagating through the core 1 The mode light leaks to the outside while propagating in the core, and the low-order mode light mainly resonates between the exit-side reflecting portion 23b and the incident-side reflecting portion 22 and is oscillated. 27 beam quality can be improved.

  Further, since the diameter of the other fiber end (left side in FIG. 6) on which the excitation light 26 is incident is larger than the diameter of one fiber end (right side in FIG. 6), the LD 20 that outputs the excitation light or the incident side Coupling with the lens portion 21c can be facilitated.

  Therefore, leakage of the excitation light 26 propagating through the first cladding 2 to the outside is suppressed, the beam quality of the laser 27 oscillated when a fiber laser is configured is improved, and coupling with the LD 20 or the like is facilitated. Therefore, it is possible to improve the double clad fiber having an air clad structure having high heat resistance and to provide a fiber laser having a higher output than the conventional one.

<< Embodiment 3 of the Invention >>
FIG. 7 is a schematic configuration diagram of the fiber laser 30c of the present embodiment.

  In this fiber laser 30c, a lens 23a, a Q switch 24, and a low reflection mirror 23b are arranged in this order on the right side of the emission side reflection film 12 of the double clad fiber 10a in the fiber laser 30a of the first embodiment. Is substantially the same as that of the fiber laser 30a.

  According to the fiber laser 30c, in addition to the effects of the first embodiment, the laser 27 oscillated by the double clad fiber 10a can be pulsed by the Q switch 24.

<< Embodiment 4 of the Invention >>
FIG. 8 is a schematic configuration diagram of a fiber laser 30d including the double clad fiber 10d of the present embodiment.

  In this fiber laser 30d, the grating fiber 10G is fused to one end face of the fiber laser 30a in the fiber laser 30a of the first embodiment, instead of the emitting side reflection film 12 provided on one end face of the double clad fiber 10a. The other configuration is substantially the same as that of the fiber laser 30a. Here, in the grating fiber 10G, an FBG 14 that functions as an exit-side reflecting portion is formed in the core at the center of the fiber.

  According to this fiber laser 30d, it is possible to prepare a plurality of fiber lasers 30d, bundle the grating fibers 10G at their respective ends, and perform fiber coupling with, for example, other multimode fibers. A high-power laser can be emitted from the fiber end.

<< Embodiment 5 of the Invention >>
FIG. 9 is a schematic configuration diagram of a fiber laser 30e including the double clad fiber 10e of the present embodiment.

  As shown in FIG. 9, the fiber laser 30e is an optical device in which an LD 20, a first lens 21a, a dichroic mirror 25, a second lens 21b, and a double clad fiber 10e are arranged in order.

  The dichroic mirror 25 is configured to transmit 1080 nm light and reflect 900 to 1000 nm light.

  The double-clad fiber 10e is provided with one side reflection film 13 on one fiber end face (right side in FIG. 9) and with an emission side reflection film 12a on the other fiber end face (left side in FIG. 9). Except for the point, it is substantially the same as the configuration of the double clad fiber 10a of the first embodiment.

The one-side reflective film 13 is configured by laminating thin films such as Ta ₂ O ₅ and SiO _2, and is, for example, an optical thin film that reflects 99.8% of 1080 nm light.

The exit-side reflection film 12a is configured by laminating thin films such as Ta ₂ O ₅ and SiO ₂ , and is an optical thin film that reflects 5% of 1080 nm light, for example.

  In this fiber laser 30e, the excitation light 26 from the LD 20 is incident on the first cladding 2 of the double-clad fiber 10e via the first lens 21a, the dichroic mirror 25, and the second lens 21b. Propagating in the region surrounded by the second clad 3 while repeating reflection at the interface between the first clad 2 and the second clad 3, and when the excitation light 26 passes through the core 1, the rare earth element in the core 1 is Activates to generate spontaneously emitted light. The spontaneously emitted light generated in the core 1 propagates through the core 1 and reaches the one-side reflective film 13. Here, among spontaneously emitted light, light having a wavelength (about 1080 nm) included in the reflection wavelength band of the one-side reflective film 13 is reflected and propagates through the core 1 again. Further, a part of the light reflected by the one-side reflection film 13 and propagated inside the core 1 is reflected by the emission-side reflection film 12a and propagates inside the core 1 again. In the fiber laser 30e, since the one-side reflecting film 13 and the emitting-side reflecting film 12a form a resonator, resonance occurs between the one-side reflecting film 13 and the emitting-side reflecting film 12a, and repeated stimulated emission is performed. As a result, laser oscillation occurs, and the laser 27 is extracted from the exit-side reflective film 12a through the second lens 21b and the dichroic mirror 25.

  According to the fiber laser 30e, the laser 27 is emitted from the fiber end side having a large fiber diameter, and the diameter of the core 1 at the fiber end on the emission side is larger than the diameter of the core 1 on the emission side in each of the above embodiments. The laser power density is lowered, and the laser resistance of the exit-side reflective film 12a can be improved.

<< Other Embodiments >>
In each of the above embodiments, a fiber laser including a double-clad fiber formed in a tapered shape is illustrated. However, as shown in FIG. 10, the present invention includes a cylindrical double-clad fiber 10f having a constant fiber diameter. It can be applied to the fiber laser 30f.

  As described above, since the present invention can easily oscillate a high-power laser, it is useful for various laser processing such as welding.

It is a cross-sectional view of the double clad fiber 10a according to the first embodiment. 2 is an observation photograph of a cross section of a double clad fiber 10a according to Embodiment 1. 1 is a schematic configuration diagram of a fiber laser 30a according to a first embodiment. It is the 1st graph which showed the spectral characteristic of the reflective film of an Example. It is the 2nd graph which showed the spectral characteristic of the reflective film of an Example. It is a schematic block diagram of the fiber laser 30b which concerns on Embodiment 2. FIG. It is a schematic block diagram of the fiber laser 30c which concerns on Embodiment 3. FIG. It is a schematic block diagram of the fiber laser 30d which concerns on Embodiment 4. It is a schematic block diagram of the fiber laser 30e which concerns on Embodiment 5. FIG. It is a schematic block diagram of the fiber laser 30f which concerns on other embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core 2 1st clad 3 2nd clad 3a Pore 10a, 10b, 10d, 10e, 10f Double clad fiber 11 Incident side reflective film 12, 12a Outgoing side reflective film (outgoing side reflective part)
13 One side reflection film 14 FBG (outgoing side reflection part)
26 Excitation light 30a-30f Fiber laser

Claims (6)

A core doped with an optical amplification component, a first clad provided so as to cover the core, and a plurality of pores extending so as to cover the first clad are formed A second clad, and the excitation light incident on the first clad propagates in a region surrounded by the second clad while repeating reflection at the interface between the first clad and the second clad. A double-clad fiber configured to activate a light amplification component of the core when light passes through the core, and the light amplification component amplifies light propagating through the core,
One fiber end face is provided with an exit-side reflecting portion that reflects part of the light propagating through the core,
A double-clad fiber, characterized in that an incident-side reflecting film is provided on the other fiber end face to reflect light reflected by the emitting-side reflecting portion and propagating through the core. A core doped with an optical amplification component, a first clad provided so as to cover the core, and a plurality of pores extending so as to cover the first clad are formed A second clad, and the excitation light incident on the first clad propagates in a region surrounded by the second clad while repeating reflection at the interface between the first clad and the second clad. A double-clad fiber configured to activate a light amplification component of the core when light passes through the core, and the light amplification component amplifies light propagating through the core,
Each of the diameters of the core, the first clad, and the second clad is expanded from the one fiber end toward the other fiber end while the core and the first clad have a similar shape while being doubled. Clad fiber. The double clad fiber according to claim 2,
On the surface of the one end of the fiber, an exit-side reflecting portion that reflects a part of the light propagating through the core is provided.
The double-clad fiber is characterized in that an incident-side reflection film is provided on the surface of the other fiber end to reflect the light reflected by the emission-side reflection portion and propagating through the core. The double clad fiber according to claim 2,
On the surface of the one fiber end, a one-side reflecting film that reflects light propagating through the core is provided,
The double-clad fiber is characterized in that an exit-side reflecting portion is provided on the surface of the other fiber end to reflect a part of the light reflected by the one-side reflecting film and propagating through the core. In the double clad fiber according to claim 1, 3 or 4,
The double-side clad fiber, wherein the exit-side reflecting portion is constituted by a reflecting film. A fiber laser comprising the double clad fiber according to any one of claims 1 to 5.