JP2007165822A - Optical pumping device, optical amplifier, fiber laser, and multi-core fiber for optical pumping device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pumping device for efficiently combining a signal light and an exciting light with an optical pumping double clad fiber. <P>SOLUTION: A multi-core fiber in which a plurality of optical fibers acting as incident ports are banded, and the optical pumping double clad fiber are connected together with a bridge fiber comprising a tapered double clad fiber, in the optical pumping device. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical amplification technique, and more particularly, to an optical pumping device having an efficient coupling structure, an optical amplifier and a fiber laser using the optical pumping device, and more particularly to a technique for combining signal light and pumping light for amplifying the signal light. And a multi-core fiber for an optical pumping device, which is a constituent member of the optical pumping device.

  Conventionally, as a structure for connecting an optical fiber for signal light transmission and a plurality of optical fibers for pumping light transmission to one end side (incident side) of an optical fiber for optical pumping, for example, disclosed in Patent Documents 1 and 2 Devices have been proposed.

  FIG. 2 is a diagram showing an optical fiber device disclosed in Patent Document 1, and this optical fiber device 1 bundles a plurality of pumping light coupling multimode fibers (hereinafter referred to as MMF) 2. At the tip of the fiber bundle 3, a cross-sectional area reducing portion 5 is formed by reducing the cross-sectional area to the cross-sectional area of the clad pumping fiber 4, and the tip and one end of the clad pumping fiber 4 are coupled at the coupling portion 6. ing.

FIG. 3 is a diagram illustrating an amplifying device disclosed in Patent Document 2. An amplifying device 10A illustrated in FIG. 3A includes an optical fiber 11 for signal light transmission and a plurality of optical fibers 12 for pumping light transmission. Each tip portion is inserted and fixed to the first ferrule 13, and one end portion of the amplification optical fiber 14 is inserted and fixed to the second ferrule 15, and the tip surface of the first ferrule 13 and the second ferrule are inserted. 15 has a structure in which the front end surface of 15 is coupled with the gradient index lens 16 interposed therebetween. 3B has a structure in which the front end surface of the first ferrule 13 and the front end surface of the second ferrule 15 are brought into contact with each other.
Japanese Patent No. 3415449 Japanese Patent No. 3353755

However, the above-described conventional technique has the following problems.
In the prior art disclosed in Patent Document 1, in the process of bundling a plurality of MMFs and reducing the cross-sectional area, a force acts to fill the gaps between the MMFs, and the MMFs arranged on the outermost periphery are operated. The cross-sectional shape is easily deformed, and there is a problem that the deformation of the MMF causes a decrease in coupling efficiency in coupling with the clad pumping fiber. In addition, in relation to this problem, as the number of excitation ports is increased, the deformation rate of the cross-sectional shape increases and the coupling efficiency decreases, so that the scalability is poor and it is difficult to meet the higher power pumping requirements. There is.

As described above, the deformation of the MMF is caused by the force trying to fill the gap.
Normally, when fibers are simply bundled, they are arranged in a close-packed structure as shown in FIG. 5 (here, one signal port fiber 48 at the center and six MMFs around it are bundled). As an example). These are integrated by flame melting or the like, and further stretched or the like to reduce the diameter. At this time, the surface tension, that is, the power to fill the voids works to melt the glass. As a result, the cross-sectional shape of the integrated part is closer to a circle than the original shape. As a result of this deformation, the shape of the light guide portion of each fiber is distorted (a schematic diagram of an example of a cross section is shown in FIG. 6).

In general, when reducing the light guide diameter, the relationship between the diameter D _in on the entrance side and the numerical aperture NA _in and the diameter D _out on the exit side and the numerical aperture NA _out can be expressed by the following formula A.

D _in × NA _in = D _out × NA _out (Formula A)

As in this embodiment, the sectional shape after drawing becomes distorted, it is minor when D _out its smallest diameter in the formula A, i.e. for example the cross-sectional shape was elliptical (illustration), the output light NA _out gets bigger.

  As a result, when the numerical aperture NA of the rare earth doped fiber connected to the output side is determined, the NA is exceeded, resulting in a problem that the connection loss with the rare earth doped fiber becomes very large.

  In consideration of the above-described deformation, the fiber bundle needs to have a close-packed structure as much as possible. Therefore, as shown in FIG. 5 and FIG. 7, the shape other than the shape in which the seventeen pieces and the nineteen pieces are bundled is greatly deformed, and there is a problem in practical use. Further, even in the case of 19 pieces, the deformation amount is large, and in many cases, there are problems that it is difficult to use or manufacture is difficult.

  Further, even with the arrangement of the close-packed structure due to this deformation problem, this structure cannot be applied to 37 or more, and there is a problem that the number of ports is insufficient to obtain a large output.

Furthermore, even when only 10 pumping port fibers (MMF) 49 are required, 18 pumping port fibers (MMF) 49 and one signal port fiber 48 are required due to the conditions of the closest packing structure. next, therefore, would be D _in the formula a is unnecessarily increases, as a result, it takes constrained D _out and NA _out, also be a problem when connecting to the rare earth-doped fiber that connects to the output side there were.

  In the prior art disclosed in Patent Document 2, since the spatial propagation is included in the coupling portion between the lens system and the optical fiber, a polishing and antireflection film is provided on the optical fiber end and the lens both ends of the coupling portion, and further on the amplification optical fiber end. Necessary. This increases the manufacturing cost. In addition, if there is a slight amount of dirt or dust on each end face, the light is absorbed when high-power light is incident, and there is a risk that it will generate heat and break down. Furthermore, since the bundle fiber and the amplification optical fiber are not directly connected, there is a concern that the long-term mechanical reliability is poor and a failure is likely to occur. A mechanical failure in this part not only has a great influence on the characteristics of the system, but must also be avoided for safety reasons. Therefore, it can be said that a more reliable structure is essential.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical pumping device for efficiently coupling signal light and pumping light to a double clad fiber for optical pumping.

  In order to achieve the above object, the present invention provides a multi-core fiber in which a plurality of optical fibers serving as incident ports are combined and a double-clad fiber for optical pumping via a bridge fiber made of a double-clad fiber having a tapered shape. And an optical pumping device characterized by being connected.

  In the optical pumping device of the present invention, the multi-core fiber is formed by inserting a plurality of optical fibers into an alignment member for three-dimensionally aligning the optical fibers and contracting the gap portion, and the tip thereof is one end of the bridge fiber. It is preferable to have a structure connected to.

  In the optical pumping device of the present invention, the alignment member is preferably a porous capillary having a plurality of holes.

  In the optical pumping device of the present invention, the porous capillary is preferably made of quartz glass.

  In the optical pumping device of the present invention, the number of holes of the porous capillary is preferably 8 or more, and it is preferable that the holes of the porous capillary are not arranged in a close-packed structure.

  In the optical pumping device of the present invention, it is preferable that all the connection points are fusion-connected.

  The present invention also provides an optical amplifier comprising the above-described optical pumping device according to the present invention and a pumping light source coupled to the incident port.

  The present invention also provides a fiber laser comprising the above-described optical pumping device according to the present invention and a pumping light source coupled to the incident port.

  The present invention also provides a multi-core fiber for an optical pumping device, in which a plurality of optical fibers to be incident ports are inserted into a porous capillary and heated to be integrated.

  In the multi-core fiber for an optical pumping device of the present invention, the number of holes in the porous capillary is preferably 8 or more, and it is preferable that the holes in the porous capillary are not arranged in a close-packed structure.

  In the multi-core fiber for an optical pumping device of the present invention, the porous capillary is preferably made of quartz glass.

In the optical pumping device of the present invention, a multi-core fiber in which a plurality of optical fibers serving as incident ports are combined and a double-clad fiber for optical pumping are connected via a bridge fiber made of a double-clad fiber having a tapered shape. Therefore, the three-dimensional alignment of the optical fibers is facilitated and the incident ports can be connected without being deformed, so that the signal light and the pumping light can be efficiently coupled to the double-clad fiber for optical pumping.
Further, since the plurality of incident ports can be connected without being deformed, the number of incident ports can be easily increased.
In addition, since the entire optical path is mechanically coupled, the long-term mechanical reliability is excellent, the optical characteristics do not change with time, and stable optical pumping characteristics can be obtained for a long time.

  In addition, optimization of the bridge fiber profile increases design freedom.

By using this structure, it is possible to realize the following optical pumping device, which is impossible with the conventional structure or extremely difficult to implement.
(1) An optical pumping device in which the deformation of the pumping light is small, the spread of the numerical aperture NA can be suppressed, and the pumping light can be efficiently guided to the rare earth-doped fiber.
(2) An optical pumping device that has 19 or more excitation ports and can be used at high output.
(3) It is not an arrangement of a close-packed structure, for example, it has nine, ten, twelve, etc. pumping ports, the incident side diameter is smaller than the conventional structure, and pumping light is efficiently converted into a rare earth doped fiber. Optical pumping device that can guide light.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1A and 1B are diagrams showing an embodiment of an optical pumping device according to the present invention. FIG. 1A is a side view of the optical pumping device 20, and FIG. 1B is a cross-sectional view taken along line AA ′ in FIG. FIG. In the optical pumping device 20 of the present embodiment, a signal port 21 that is a distal end portion of a signal light optical fiber and a plurality of excitation ports 22 that are distal end portions of an excitation light optical fiber are inserted into a porous capillary 23 as incident ports. Then, the multi-core fiber 24 formed by shrinking the gap portion and the double clad fiber 25 having a rare earth-doped core for optical pumping are connected via a bridge fiber 27 made of a double clad fiber having a taper portion 26. Configured.

The multi-core fiber 24 is connected to the signal port 21 and the porous capillary 23 made of quartz glass having a large number of pores arranged so that the incident ports (the signal port 21 and the plurality of excitation ports 22) are three-dimensionally aligned. A plurality of excitation ports 22 are inserted and a part thereof is heated so that the gap portion is contracted to form an integrated contracted portion 28.
In the illustration of FIG. 1B, a cylindrical porous capillary 23 is formed with 19 port insertion pores in a dense state. Then, a signal port 21 is inserted into the pore of the porous capillary 23, and a total of 18 excitation ports 22 are inserted around the first layer, six on the first layer and twelve on the second layer. In the portion 28, the porous capillary 23 and each incident port are integrated. Although not shown, the other end of each pumping port 22 is connected to the emitting end of a pumping light source such as a laser diode (LD), and pumping light of a specific wavelength from the pumping light source is sent to the optical pumping device 20. It can be propagated toward.

  The bridge fiber 27 only needs to be able to efficiently propagate the light propagated through the multi-core fiber 24 to the double-clad fiber 25 for optical pumping. For example, a double-clad fiber having an outer diameter equivalent to the tip surface of the multi-core fiber 24 is used. It is done. The tapered portion 26 formed in the bridge fiber 27 is formed by heating and stretching one end side of the bridge fiber 27 to gradually reduce the outer diameter of the fiber. The outer diameter of the end face of the taper portion 26 is desirably equal to the outer diameter of the double clad fiber 25 connected thereto.

The connection point 29 between the multi-core fiber 24 and the bridge fiber 27 and the connection point 30 between the bridge fiber 27 and the double clad fiber 25 are connected by fusion connection in order to ensure long-term mechanical reliability. As a result, an antireflection film or the like is not required at the connection portion, the number of manufacturing steps can be reduced, and resistance to high power light can be improved. Furthermore, stable optical characteristics with little change over time can be obtained. Examples of the heat source used for fusion connection of the connection points 29 and 30 include arc discharge, CO ₂ laser, and oxyhydrogen flame.

  In the optical pumping device 20 of the present embodiment, the pumping light is incident on the double clad fiber 25 through the plurality of pump ports 22 of the multicore fiber 24 via the bridge fiber 27, and the rare earth element added to the core of the double clad fiber 25. When ions are excited and signal light is incident from the signal port 21, optical pumping occurs in the double clad fiber 25, and amplified light is emitted from the other end (exit end) side of the double clad fiber 25 (not shown). The The optical pumping device 20 can be applied to an optical amplifier (fiber amplifier), a fiber laser, and the like. In particular, pumping light from a large number of pumping ports 22 can be efficiently incident on a double-clad fiber 25 for optical pumping. Therefore, it is possible to provide an optical amplifier or a high power fiber laser capable of high-amplification optical amplification.

  The optical pumping device 20 of the present embodiment includes a multi-core fiber 24 in which tip portions of incident ports (a signal port 21 and a plurality of excitation ports 22) are combined by a porous capillary 23, and a double clad fiber 25 for optical pumping. Since the connection is made via the bridge fiber 27 having the taper portion 26, the three-dimensional alignment of the respective incident ports is facilitated, and the incident ports can be connected without being deformed. Therefore, the signal light and the pump light are efficiently used for optical pumping. Can be coupled to the double clad fiber 25.

  In the present embodiment, in order to easily integrate the incident ports (the signal port 21 and the plurality of excitation ports 22), the porous capillaries 23 are used, and the respective ports are made into individually opened pores of the porous capillaries 23. After the insertion, the vicinity of the end portion was heated, and the multicore fiber 24 was formed by being shrunk and integrated by the gap between the pores of the porous capillary 23 and each incident port. Thereby, it becomes easy to align a plurality of optical fibers in a three-dimensional manner. Furthermore, since each incident port is inserted into the pore, a substantially uniform force is exerted during contraction, and therefore the incident port, particularly the excitation port 22 can be connected without being deformed. Can be improved and the slope efficiency can be improved.

  If such a structure in which the incident port is integrated using the porous capillary 23 is adopted, the number of the pores formed in the porous capillary 23 and the arrangement thereof are appropriately set, so that future excitation port increase requests can be met. It can be easily handled, and deformation of the excitation port can be suppressed even during contraction and integration. Furthermore, the profile of the bridge fiber 27, for example, the cladding outer diameter, core diameter, taper length, taper outer diameter, mode field diameter, relative refractive index difference, etc. can be separately optimized. Can be handled relatively easily.

  Instead of the perforated capillary 23, a ferrule having a single hole having a circular cross section or a hexagonal shape can be used. However, by using the perforated capillary 23 as described above, the contraction / integration process can be performed. Since the force acting on each port becomes substantially uniform, it is possible to prevent deformation of the port arranged on the outermost periphery, and therefore it is advantageous in terms of characteristics to use a porous capillary.

  The material of the porous capillary 23 is preferably quartz glass. Normally, optical fibers are made of quartz glass, so using a quartz glass capillary prevents mechanical distortion due to differences in the linear expansion coefficient when the gaps shrink or are fused. There is no concern of losing strength. Furthermore, the pore diameter of the porous capillary 23 used when using an optical fiber having an outer diameter of 125 μm as the incident port is preferably about 130 μm to 200 μm. If it is less than 130 μm, it becomes very difficult to insert an optical fiber. When it exceeds 200 μm, the gap portion becomes large, and there is a concern that the eccentricity of the center port becomes large at the time of contraction.

  Further, the advantages of using a porous capillary will be described. In Patent Document 1, the only possible arrangement of the excitation port is a close-packed structure of the excitation port optical fiber. Therefore, when the number of pumping ports is 6 or less, pumping light can be efficiently injected into the clad pumping fiber. However, when the number of excitation ports exceeds 7, the close-packed structure is damaged, and a structure equivalent to the 18-port structure is unavoidable. Further, as described above, the 18-port structure has a large deformation of the excitation port, and is accompanied by manufacturing difficulties.

  On the other hand, the optical pumping device 20 according to the present invention employs a multi-core fiber using a porous capillary and appropriately designs the porous structure, thereby realizing an excitation structure with any number of ports. FIG. 4 illustrates an excitation port arrangement structure of a multi-core fiber using a porous capillary having eight or more holes according to the present invention. In FIG. 4, reference numerals 40A to 40E are multi-core fibers, 41A to 41E are porous capillaries, 42 is a signal port, 43 is a signal port core, 44 is a signal port cladding, 45 is an excitation port, 46 is an excitation port core, and 47 is an excitation port cladding. It is. In the example of FIG. 4, a single mode optical fiber is used for the signal port 42, and MMF is used for the pumping port 45.

  A multi-core fiber 40A shown in FIG. 4 (a) uses a 19-hole porous capillary 41A having a close-packed structure, and a signal port 42 is inserted into a central hole. It has an excitation port arrangement structure in which excitation ports 45 are inserted into a total of 18 holes of 12 eyes.

  The multi-core fiber 40B shown in FIG. 4 (b) uses a 9-hole perforated capillary 41B in which one hole is provided in the center and eight holes are provided slightly apart from the periphery, and the signal port 42 is inserted into the center hole. The excitation port arrangement structure in which the excitation ports 45 are inserted into the eight holes around the holes.

  The multi-core fiber 40C shown in FIG. 4 (c) has a 9-hole porous capillary with one hole in the center, four holes in the first layer adjacent to the periphery, and four holes in the second layer slightly away from the center. 41C is used, and a signal port 42 is inserted into a central hole, and an excitation port arrangement structure is formed in which excitation ports 45 are inserted into eight holes in the first and second layers.

  A multi-core fiber 40D shown in FIG. 4 (d) has a 10-hole perforated capillary 41D in which one hole is provided in the center, three layers in the first layer adjacent to the periphery thereof, and six holes in the second layer on the outer periphery thereof. It has an excitation port arrangement structure in which the signal port 42 is inserted into the central hole, and the excitation ports 45 are inserted into the nine holes in the first and second layers.

  A multi-core fiber 40E shown in FIG. 4 (e) includes a 13-hole perforated capillary 41E having one hole in the center, six first layers adjacent to the periphery thereof, and six holes in the second layer on the outer periphery thereof. It has an excitation port arrangement structure in which the signal port 42 is inserted into the central hole, and the excitation ports 45 are inserted into the 12 holes in the first and second layers.

  The optical pumping device having the structure shown in FIG. 1 was manufactured by the following procedure.

  At the center of the 19-core insertion porous capillary, the mode field diameter (hereinafter referred to as MFD) is approximately 6 μm (wavelength 1.55 μm) as the optical fiber for the signal port, the outer diameter is 125 μm, and the relative refractive index difference Δ is 1. % Single-mode optical fiber was used, and 18 MMFs with a core diameter of 110 μm and an outer diameter of 125 μm were used as optical fibers for the pumping port around it. The outer diameter of the porous capillary was about 1.2 mm and the pore diameter was 150 μm.

  Each of the optical fibers led out was inserted into a hole of a porous capillary and abutted against a flat plate to form an end face. In order to lower the air pressure in the void after forming the end face, heating was performed while sucking with a vacuum pump, and a multi-core fiber having an outer diameter of 725 μm was produced.

  A bridge fiber having an MFD of 6 μm and an outer diameter of 725 μm and a multi-core fiber were fused and connected, and the other end of the bridge fiber was stretched to form a tapered portion. The outer diameter of the tip of this tapered portion was 400 μm. Thereafter, this tip and one end of an optical pumping double clad fiber having an MFD of 20 μm and an outer diameter of 400 μm were fused and connected.

  The coupling efficiency of the pumping port is designed so that the MFD is 20 μm when the bridge fiber is extended to an outer diameter of 725 μm, an MFD of 6 μm, and an outer diameter of 400 μm, considering only NA matching.

Excitation light was incident from each excitation port of the obtained optical pumping device, and connection loss at each connection point was measured. As a result, the connection loss between the multi-core fiber and the bridge fiber is 0.6 dB, the connection loss between the bridge fiber and the double clad fiber is 0.3 dB, and the light from each port is efficiently double-clad for optical pumping with low loss. It has been demonstrated that it can be incident on a fiber.
When an MMF with NA of 0.15 was used, the NA on the exit side was 0.30, which was not significantly different from the theoretical output NA of 0.27 obtained from Equation A.

(Comparative Example 1)
Next, as a comparative example, a device of Patent Document 1 was manufactured. As the fiber, the same fiber as in Example 1 was used. At this time, considering the MFD matching described in Patent Document 1, the reduced diameter was set to 300 μm. The NA on the exit side is 0.38, which is very large as compared with 0.29 which is the theoretical output NA obtained from Formula A, and as a result, the coupling loss of the pumping light is as large as 12 dB.

  The optical pumping device having the structure shown in FIG. 4B was manufactured by the following procedure.

  A single mode fiber with an MFD of about 6 μm (wavelength: 1.06 μm), an outer diameter of 125 μm, and a relative refractive index difference of 0.45% is used as a signal port optical fiber at the center of the 9-core porous capillary. Eight MMFs having a core diameter of 110 μm and an outer diameter of 125 μm were used as excitation fibers. The outer diameter of the porous capillary was 440 μm, and the pore diameter was 135 μm.

  Each of the above-described optical fibers was inserted into a hole of a porous capillary, and the fiber and the capillary were melted and integrated with a flame to produce a multi-core fiber. Thereafter, the integrated part was cut to form an end face.

  The multi-core fiber and a bridge fiber having an MFD of about 5 μm (wavelength: 1.06 μm) and an outer diameter of 425 μm were fusion-bonded, and the bridge fiber was melt-drawn to form a tapered portion. The outer diameter of the tip of this taper portion was 265 μm. Thereafter, this tip and one end of an optical pumping double clad fiber having an MFD of 20 μm, an inner cladding diameter of 300 μm, and an outer diameter of 350 μm were fusion-bonded to produce an optical pumping device.

  At this time, considering the matching with NA in the inner cladding part of the optically pumped double-clad fiber, which is a connected fiber, the outer diameter of the tapered part is 265 μm smaller than NAO.43 of the optically pumped double-clad fiber. To improve the coupling efficiency of excitation light. In the actually fabricated device, the output NA was 0.35. Similarly, the signal light is designed so that the MFD is approximately equal to 20 μm when the outer diameter of the tip of the tapered portion is 265 μm, and a measure is taken to avoid a decrease in coupling efficiency due to MFD mismatch. In the actually fabricated device, the MFD at the tip of the tapered portion was about 15 μm.

  The coupling efficiency of excitation light of the obtained device was 0.2 dB for the entire device, and the coupling efficiency of signal light was 0.8 dB.

(Comparative Example 2)
Consider using the device of Comparative Example 1 for the same purpose as in Example 2. In the case of the structure of Patent Document 1, even if only 8 ports are used, it is necessary to fabricate with an 18-port structure because of the restriction that a close-packed structure is required. As a result, the outer diameter of the bundle on the incident side becomes large (about 650 μm), and as a result, it is necessary to increase the reduction ratio of the taper portion of the device assuming that it is connected to the same optical pumping double clad fiber.
For this reason, NA _out was 0.60, and only an excitation light coupling efficiency as high as 4.8 dB could be produced.

  The optical pumping device having the structure shown in FIG. 8 was produced by the following procedure. Although the structure of FIG. 8 is the same structure as FIG. 4B, one more excitation port 45 is designed. The number of excitation ports and the degree of freedom of arrangement are the advantages of this structure.

  A single mode fiber with an MFD of about 4 μm (wavelength 1.06 μm), an outer diameter of 125 μm, and a relative refractive index difference of 1% is used as a signal port optical fiber at the center of a 10-core porous capillary. Nine MMFs having a core diameter of 110 μm and an outer diameter of 125 μm were used as excitation fibers. The outer diameter of the porous capillary was 730 μm, and the pore diameter was 135 μm.

Each of the above-described optical fibers was inserted into a hole of a perforated capillary, and the fiber and the capillary were melted and integrated with a CO ₂ laser while sucking with a vacuum pump to produce a multi-core fiber. Thereafter, the integrated part was cut to form an end face.

  The multi-core fiber and a bridge fiber having an MFD of about 5.5 μm (wavelength 1.06 μm) and an outer diameter of 680 μm were fused and connected, and the bridge fiber was melt-drawn to form a tapered portion. The outer diameter of the tip of this taper portion was 360 μm. Thereafter, this tip and one end of an optical pumping double clad fiber having an MFD of 18 μm, an inner cladding diameter of 400 μm, and an outer diameter of 430 μm were fused and connected to produce an optical pumping device.

  At this time, considering the matching with NA in the inner cladding part of the optically pumped double-clad fiber, which is a connected fiber, when the outer diameter of the tip of the taper part is 360 μm, it is smaller than NAO.41 of the optically pumped double-clad fiber. To improve the coupling efficiency of excitation light. In the actual prototype device, the output NA was 0.32. Similarly, the signal light was designed so that the MFD substantially matches 18 μm when the outer diameter of the tip of the taper portion is 360 μm, and a measure was taken to avoid a decrease in coupling efficiency due to MFD mismatch. In the actually fabricated device, the MFD at the tip of the tapered portion was about 14 μm.

  The coupling efficiency of excitation light of the obtained device was 0.3 dB for the entire device, and the coupling efficiency of signal light was 1.3 dB.

(Comparative Example 3)
Consider using the device of Comparative Example 1 for the same purpose as in Example 3. In the case of the structure of Patent Document 1, even if only 9 excitation ports are used, it is necessary to fabricate with an 18-port structure because of the restriction that a close-packed structure is required.
As a result, the outer diameter of the bundle on the incident side becomes large (about 650 μm), and the deformation of the excitation port is large, so NA _out becomes 0.46 and the coupling efficiency of excitation light is as large as 1.8 dB. However, it was only possible to make it.

Similarly, an optical pumping device having 30 excitation ports having the structure shown in FIG. 9 was produced. The used fiber and the manufacturing method are the same as those in Example 2. However, the outer diameter of the bridge fiber was 880 μm.
The coupling efficiency of excitation light of the obtained device was 0.6 dB for the entire device, and the coupling efficiency of signal light was 2.6 dB.

(Comparative Example 4)
Consider using the device of Patent Document 1 for the same purpose as in Example 4 by the method of Patent Document 1. With the structure of Patent Document 1, even when only 30 excitation ports are used, it is necessary to fabricate with a 36-port structure because of the restriction that the close-packed structure is required. In actual trial production, the pump port was greatly deformed, the coupling efficiency of the pumping light was 5.6 dB, and the coupling efficiency of the signal light was 11 dB.

1 shows an embodiment of an optical pumping device of the present invention, in which (a) is a side view of the optical pumping device, and (b) is a cross-sectional view taken along line A-A ′ in (a). It is a side view which shows an example of the conventional device. It is a side view which shows the other example of the conventional device. It is sectional drawing which illustrates the example of fiber arrangement | positioning of the multi-core fiber of this invention. It is an incident side cross-sectional schematic diagram of a conventional structure. It is a radiation side section schematic diagram of the conventional structure. It is an incident side cross-sectional schematic diagram of a conventional structure. It is sectional drawing which illustrates the example of fiber arrangement | positioning of the multi-core fiber of this invention. It is sectional drawing which illustrates the example of fiber arrangement | positioning of the multi-core fiber of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Optical pumping device, 21 ... Signal port, 22 ... Excitation port, 23 ... Porous capillary, 24 ... Multi-core fiber, 25 ... Double clad fiber, 26 ... Tapered part, 27 ... Bridge fiber, 28 ... Contraction part, 29, 30 Connection point, 40A, 40B, 40C, 40D, 40E, 40F, 40G ... Multi-core fiber, 41A, 41B, 41C, 41D, 41E, 41F, 41G ... Porous capillary, 42 ... Signal port, 43 ... Signal port core, 44 ... Signal port cladding, 45 ... excitation port, 46 ... excitation port core, 47 ... excitation port cladding, 48 ... signal port fiber, 49 ... excitation port fiber.

Claims (13)

  An optical pumping device comprising a multi-core fiber in which a plurality of optical fibers serving as incident ports are combined and a double-clad fiber for optical pumping connected via a bridge fiber made of a double-clad fiber having a tapered shape. .   The multi-core fiber has a structure in which a plurality of optical fibers are inserted into an alignment member that three-dimensionally aligns the optical fibers, the gap portion is contracted, and the tip is connected to one end of the bridge fiber. The optical pumping device according to claim 1, wherein:   The optical pumping device according to claim 1, wherein the alignment member is a porous capillary having a plurality of holes.   4. The optical pumping device according to claim 3, wherein the porous capillary is made of quartz glass.   The optical pumping device according to claim 3 or 4, wherein the number of holes in the perforated capillary is eight or more.   6. The optical pumping device according to claim 5, wherein the holes of the porous capillary are not arranged in a close-packed structure.   The optical pumping device according to claim 1, wherein all connection points are fusion-connected.   8. An optical amplifier comprising: the optical pumping device according to claim 1; and a pumping light source coupled to an incident port thereof.   A fiber laser comprising: the optical pumping device according to claim 1; and a pumping light source coupled to an incident port thereof.   A multi-core fiber for an optical pumping device, wherein a plurality of optical fibers to be incident ports are inserted into a porous capillary and integrated by heating.   The multi-core fiber for an optical pumping device according to claim 10, wherein the number of holes of the porous capillary is 8 or more.   The multi-core fiber for an optical pumping device according to claim 11, wherein the holes of the porous capillary are not arranged in a close-packed structure. The multi-core fiber for an optical pumping device according to claim 10, wherein the porous capillary is made of quartz glass.

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