JP2004341448A - Optical device using double clad fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device in which excited light is surely made incident at a high incident efficiency into a first clad 12 of a double clad fiber 1 in which a second clad 13 is composed in a porous structure. <P>SOLUTION: An incident region in which the exciting light propagates is formed, which is connected to a multimode type optical fiber stretched from an external exciting light source, at the incident end of a double clad fiber 2 having a single mode core 21 in which an amplifying medium is doped, a first clad 22 which covers the periphery of the single mode core 21 and a second clad 23 which is composed of a porous structure including a lot of fine pores 23a and covers the periphery the first clad 22. A non-tapered part which is formed with an outer diameter which is the same as the outer diameter of the multimode type optical fiber and a tapered part which is converged to the outer diameter of the first clad of the double clad fiber of the non-tapered part are formed on the incident end side of the incident region. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical device having a double clad fiber used as, for example, a fiber laser device or an ASE light source device.
[0002]
[Prior art]
Conventionally, fiber laser devices, ASE light source devices, and the like have been used in the optical communication field and the optical measurement field. In these devices, an excitation light is incident on an optical fiber having a core doped with an amplification medium, thereby forming a population inversion characteristic and utilizing stimulated emission therefrom.
[0003]
In recent years, the use of a double-clad fiber having a core doped with the amplification medium has been put to practical use. The double-clad fiber has a single mode core doped with an amplification medium, a first clad covering the periphery of the single mode core, and a second clad covering the periphery of the first clad. Further, as one of the double-clad fibers, a fiber in which the second clad has a porous structure including a large number of pores is also known (for example, see Patent Document 1).
[0004]
The refractive index (effective refractive index) of the second clad having the porous structure depends on its porosity, and the larger the porosity, the smaller the effective refractive index of the second clad. For this reason, in the double clad fiber in which the second clad has a porous structure, by adjusting the porosity, the relative refractive index difference between the first clad and the second clad is larger than that of the conventional double clad fiber. can do.
[0005]
As a result, a double-clad fiber having a porous structure in the second clad has an advantage that the numerical aperture (NA) of pump light propagating inside can be increased.
[0006]
As a method of injecting excitation light into the first clad of such a double-clad fiber, a technique of directly connecting a multi-mode optical fiber extended from an excitation light source device to the incident end of the first clad by thermal fusion. Was used.
[0007]
[Patent Document 1]
JP-A-2002-277669
[0008]
[Problems to be solved by the invention]
However, optical devices using double-clad fibers, including those having a porous structure in the second clad layer, have the following problems. That is, when it is desired to output high-power laser light or ASE light using the optical device, it is necessary to increase the output of incident excitation light. In recent years, with the increase in output of the optical device, a multi-mode laser diode (hereinafter, referred to as “MMLD”) excitation light source having a large output exceeding 5 W has been used.
[0009]
As the output of the MMLD pumping light source increases, the core diameter of a multimode optical fiber (hereinafter, also referred to as “light source MMF”) for guiding the pumping light from the light source to the incident end of the optical device also increases. Is becoming For example, the core diameter of the light source MMF used for the MMLD pumping light source having an output of about 5 W reaches about 200 μm.
[0010]
On the other hand, the outer diameter of the first clad of the double clad fiber used in the optical device is usually 100 μm or less, and is relatively thin, for example, about 75 μm. This is because it is advantageous to reduce the cross-sectional area of the first clad as much as possible in order to improve the conversion efficiency of pump light / signal light (output light) of the double clad fiber used.
[0011]
For this reason, as shown in FIG. 9, when the emission end of the light source MMF81 is fusion-bonded to the incidence end of the double clad fiber 80 as it is, the core 82 of the light source MMF81 and the first clad 83 of the double clad fiber 80 are connected. The overlap at the bonding surface is small, and all of the excitation light cannot enter the first clad 83. Therefore, a considerable loss occurs in the excitation light at the fusion joint.
[0012]
Therefore, as shown in FIG. 10, a technique of tapering the light source MMF 91 toward the emission end so that the outer diameter of the core 92 at the emission end matches the outer diameter of the first clad 93 and fusion-spliced. Has also been developed. According to this technique, most of the pumping light propagating through the core 92 of the light source MMF 91 can enter the first clad 93 of the double clad fiber 90.
[0013]
However, the following problem also occurs in the technique of performing the taper processing on the light source MMF91. That is, the tapered light source MMF 91 needs to be cut at a portion having an appropriate outer diameter in order to join the light source MMF 91 to the first clad 93 of the double clad fiber 90. However, when cutting a tapered fiber using a normal fiber cutter, there is a problem that it is very difficult to cut the cut surface so as to be perpendicular to the axis.
[0014]
Further, even if the cut surface can be cut perpendicular to the axis, the outer diameter of the light-emitting end of the light source MMF 91 that has been subjected to the taper processing and the incident end of the double-clad fiber 90 in the first place. Because of the large difference from the outer diameter, it was difficult to align the axes of both fibers. Furthermore, when both optical fibers having a large difference in outer diameter are fused, a deviation in surface tension occurs due to the difference in outer diameter, and an axial deviation may occur.
[0015]
Further, the second clad 94 may be crushed near the incident end due to heat at the time of fusion. As a result, a region where the second clad 94 does not exist is formed near the incident end of the double clad fiber 90. When the second clad 94 is crushed in the vicinity of the incident end, a part of the excitation light emitted from the emission end of the light source MMF 91 does not enter the first clad 93 and leaks to the outside of the second clad 94. There was a problem of light leaking.
[0016]
Furthermore, since the vicinity of the tip of the light source MMF 91 which has been tapered is very thin, it is bent when the light source MMF 91 is brought into contact with the incident end of the double clad fiber 90, resulting in a problem that the yield is extremely deteriorated due to poor connection.
[0017]
Therefore, the present invention has been made in view of the above problems, and eliminates the need for tapering of the large-diameter light source MMF, thereby eliminating the difficulty of cutting the front end face and aligning the axis. It is an object of the present invention to realize an optical device capable of reliably causing the excitation light emitted from the excitation light source to enter the first clad of the double clad fiber.
[0018]
[Means for Solving the Problems]
An optical device according to the present invention includes a single mode core doped with an amplification medium, a first clad that covers the periphery of the single mode core, and a porous structure including a large number of pores. And a second clad covering the periphery. The input end of the double clad fiber is connected to a multi-mode optical fiber extending from an external pump light source to form an input region for transmitting the pump light. A non-tapered portion formed in a shape connectable to the multi-mode optical fiber on the incident end side of the incident region, and converged from the non-tapered portion to the outer diameter of the first clad of the double clad fiber. A tapered portion is formed. The output end side of the tapered portion is optically connected to the first clad of the double clad fiber.
[0019]
According to this configuration, the multimode optical fiber extended from the external pumping light source can be satisfactorily connected to the double clad fiber of the optical device without tapering the emission end. That is, an incident region is formed in the double clad fiber, and a non-tapered portion formed in a shape connectable to the multi-mode optical fiber is formed on the incident end side of the incident region. Connect with By forming the incident end side of the incident region in accordance with the multi-mode optical fiber, it is not necessary to taper the exit end of the light source MMF, so that the exit end face of the light source MMF can be easily cut.
[0020]
Furthermore, since the tapered portion is formed so as to converge to the outer diameter of the first clad of the double-clad fiber from the emission end side of the non-tapered portion, the excitation light incident on the non-tapered portion from the light source MMF is The laser beam is narrowed down while propagating in the tapered portion, and is reliably incident on the first clad. Excitation light that has entered the first cladding from the tapered portion propagates through the first cladding while repeating total reflection. Each time the pumping light passes through the single mode core in the first cladding, it stimulates the doped amplification medium to generate stimulated emission, and as a result, obtains a desired laser beam from the emitting end of the double cladding fiber. Can be.
[0021]
Further, the optical device according to the present invention is configured by a single mode core doped with an amplification medium, a first clad covering the periphery of the single mode core, and a porous structure including a large number of pores. A double clad fiber having a first clad and a second clad surrounding the periphery is used. The input end of the double clad fiber is connected to a multi-mode optical fiber extending from an external pump light source to form an input region for transmitting the pump light. A non-tapered portion having the same diameter as the outer diameter of the multi-mode optical fiber is formed on the incident end side of the incident region, and converges from the non-tapered portion to the outer diameter of the first clad of the double clad fiber. Is formed with a tapered portion. The output end side of the tapered portion is optically connected to the first clad of the double clad fiber.
[0022]
According to this configuration, the multimode optical fiber extended from the external pumping light source can be satisfactorily connected to the double clad fiber of the optical device without tapering the emission end. That is, an incident area is formed in the double-clad fiber, and a non-tapered portion having the same diameter as the outer diameter of the multi-mode optical fiber is formed on the incident end side of the incident area. Connect to the output end of the fiber. There is no need to taper the exit end of the incident region to the exit end of the multimode optical fiber. Therefore, the cutting process of the emission end face of the multimode optical fiber becomes easy. In addition, since the outer diameter of the emission end of the multimode optical fiber is equal to the outer diameter of the non-tapered portion, uneven heating during fusion can be reduced, and axial misalignment can be reduced.
[0023]
Furthermore, since the tapered portion is formed so as to converge to the outer diameter of the first clad of the double-clad fiber from the emission end side of the non-tapered portion, the excitation light incident on the non-tapered portion from the light source MMF is The laser beam is narrowed down while propagating in the tapered portion, and is reliably incident on the first clad. Excitation light that has entered the first cladding from the tapered portion propagates through the first cladding while repeating total reflection. Each time the pumping light passes through the single mode core in the first cladding, it stimulates the doped amplification medium to generate stimulated emission, and as a result, obtains a desired laser beam from the emitting end of the double cladding fiber. Can be.
[0024]
【The invention's effect】
As described above, according to the optical device of the present invention, the large-diameter light source MMF can be fusion-spliced to the incident region of the double-clad fiber without performing taper processing. This makes it possible to eliminate the difficulty of axis alignment, and to connect the light source MMF and the double clad fiber with high yield.
[0025]
Further, according to the optical device of the present invention, the excitation light incident on the non-tapered portion of the incident region can be surely propagated into the first clad of the double clad fiber via the tapered portion of the incident region. . Therefore, the optical device can be connected to the excitation light source with low loss, and a desired output light can be obtained with high efficiency by effectively using the excitation light.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The optical device 1 according to the present embodiment is used for a fiber laser device, an ASE light source device, and the like.
[0027]
FIG. 1 shows a double clad fiber 1 used in the optical device of the present embodiment. The double-clad fiber 2 includes a single mode core 21 extending in the axial direction at the axis of the fiber, a first cladding 22 covering the periphery of the single mode core 21, and a first cladding 22 covering the periphery of the first cladding 22. A second clad 23, a support layer 24 covering the periphery of the second clad 23, and a covering layer 25 covering the outer periphery of the support layer 24 are provided.
[0028]
In the double clad fiber 2, the propagating light propagates in the single mode core 21, while the pumping light propagates in the first clad 22.
[0029]
In the present embodiment, the single mode core 21, the first cladding 22, the second cladding 23, and the support layer 24 are each made of quartz, while the coating layer 25 is made of resin. As the resin used for the coating layer 25, for example, an ultraviolet curable resin or the like is used.
[0030]
The single mode core 21 is doped with Ge or the like so as to have a refractive index higher than the refractive index of the first clad 22, and is doped with an amplification medium. The amplification medium is excited by the excitation light propagating in the first cladding 22 to form a population inversion, and emits stimulated emission light therefrom. The optical device according to the present invention utilizes stimulated emission light generated in the single mode core 21. The amplification medium is appropriately selected from rare earth elements such as Er, Nd, and Yb.
[0031]
The first cladding 22 is formed so as to extend in the fiber axis direction while surrounding the periphery of the single mode core 21, and has a circular cross section. In the present embodiment, the cross-sectional shape of the first clad 22 is circular, but the cross-sectional shape is not limited to a circular shape, and may be, for example, a hexagonal shape, a triangular shape, a polygonal shape such as a rectangular shape, an elliptical shape, or the like. It may be formed. Further, it is also possible to form a shape in which a part of a circle is cut out.
[0032]
The second cladding 23 extends in the fiber axis direction while surrounding the periphery of the first cladding 22. The second cladding 23 of the present invention has a porous structure including a large number of pores 23a extending in the fiber axis direction. The pores 23a are arranged substantially uniformly in the circumferential direction in the cross section of the fiber.
[0033]
The refractive index (effective refractive index) of the second clad 23 having the porous structure depends on the porosity, that is, the ratio of the volume of the hole 23a to the total volume of the second clad 23 region. The effective refractive index of the two claddings 23 decreases. When the support layer is formed outside the second clad 23, the mechanical strength of the fiber can be ensured by the support layer, so that the porosity can be considerably increased. Therefore, when the second clad 23 has a porous structure, the numerical aperture (NA) for the excitation light can be greatly increased as compared with the case where the second clad 23 has a solid structure.
[0034]
The support layer 24 is formed so as to surround the periphery of the second clad 23. The support layer 24 protects the second clad 23 having a porous structure and improves the mechanical strength of the double clad fiber 2. I am trying to do it.
[0035]
As described above, the double clad fiber 2 in which the second clad 23 has a porous structure is manufactured by heating and stretching a preform and stretching it into a fiber shape. Specifically, the preform is created according to the following procedure.
[0036]
First, one cylindrical support tube having a substantially circular cross section is prepared, one core rod (solid rod), a large number of first clad rods and a second clad capillary (hollow rod) are provided. Prepare each. Each of these members is formed of quartz, and the core rod is doped with the amplification medium.
[0037]
Then, the core rod is arranged at a central position in the support tube, and a plurality of first cladding rods are regularly arranged around the core rod. At this time, it is preferable to dispose the first clad rods approximately densely around the core rods so that the formed first clad portion has a substantially circular cross section.
[0038]
Next, a large number of the second clad capillaries are regularly arranged between the first clad capillary and the inner peripheral surface of the support tube. The order in which the core, the rod for the first cladding, and the capillary for the second cladding are arranged may be changed as appropriate.
[0039]
With the support tube filled with the rods and capillaries, the whole is heated. When the heating temperature is equal to or higher than a predetermined temperature, the rods, capillaries, and support tubes are welded, the gaps between the members are densified, and the preform is completed. The preform is heated and drawn in a drawing furnace to form a fiber.
[0040]
The portion corresponding to the core rod of the preform is the single mode core of the double clad fiber, the portion corresponding to the first clad rod of the preform is the first clad of the double clad fiber, and the second clad of the preform is the second clad fiber. The portion corresponding to each of the capillaries for cladding forms the second clad having the pores of the double clad fiber, and the portion corresponding to the support tube forms the support layer of the double clad fiber. Then, a coating material is applied to the outer periphery of the fiber to form a coating layer of the double clad fiber 2. The formation of the coating layer may be performed at the time of drawing.
[0041]
Thus, the double clad fiber 2 in which the second clad 23 has a porous structure is manufactured.
[0042]
In addition, instead of using the core rod and the first cladding rod, the preform is prepared as a first preform having a core part and a clad part (first clad part). It may be created by using.
[0043]
That is, the first preform is prepared by a known method such as a VAD method, an OVD method, and a rod-in-tube method, and the first preform is disposed at a substantially central position in the support tube. Next, a number of second cladding capillaries are arranged between the first preform and the inner peripheral surface of the support tube. By doing so, a preform having the core portion, the first and second cladding portions can be formed.
[0044]
FIG. 2 shows an optical device 1 according to the embodiment.
[0045]
This optical device 1 has the above-mentioned double clad fiber 2, and an incident area 3 is formed on the incident end 26 side of the double clad fiber 2.
[0046]
The incident area 3 is connected to a light source MMF (not shown in FIG. 2) extended from an external excitation light source (not shown in FIG. 2). The incident area 3 is formed of a quartz material, similarly to the double clad fiber 2.
[0047]
The incident area 3 has a non-tapered portion 3a formed to have the same diameter as the outer diameter of the light source MMF. Further, a tapered portion 3b is formed so as to converge from the non-tapered portion 3a to the outer diameter of the first clad 22 of the double clad fiber 2. Regarding the shape of the tapered portion 3b, it is preferable that the angle of the taper be a smooth tapered shape of about 10 ° or less with respect to the axis. If the angle of the taper is too large, the incident angle of the excitation light propagating through the tapered portion to the inner wall surface of the tapered portion becomes less than the critical angle, and the excitation light may be emitted to the outside without being totally reflected in the tapered portion. There is.
[0048]
The tapered portion 3b is optically connected to the first clad 22 of the double clad fiber 2. The incident region 3 is preferably formed integrally with the first clad 22 by a manufacturing method described later.
[0049]
Around the first cladding 22, a second cladding 23 having a porous structure is formed. Around the second cladding 23, a support layer 24 is formed.
[0050]
Further, a coating layer 25 made of an ultraviolet curable resin or the like is formed around the support layer 24. The other end of the double clad fiber 2 is an emission end 27.
[0051]
Next, a method for manufacturing the optical device according to the present embodiment will be described.
[0052]
As shown in FIG. 3A, a double-clad fiber 2 formed by the above method and uniform over the entire length is prepared. The length of the double clad fiber 1 is not particularly limited, and is determined according to the use of the optical device and required performance.
[0053]
As shown in FIG. 3B, the covering layer 25 is removed over an appropriate length range in the middle part of the double clad fiber 2. The method of removing is not particularly limited, but an appropriate method is selected so as not to damage the internal fiber.
[0054]
As shown in FIG. 3C, the region from which the coating layer has been removed is subjected to a collapse treatment, so that all the pores 23a constituting the second clad 23 are crushed.
[0055]
Specifically, this region is heated by a suitable heating means such as a burner. As a result, the whole quartz material constituting the double clad fiber 2 is brought into a semi-molten state, and the pores 23a are crushed by interfacial tension. As a result, the support layer 24, the portion other than the pores 23a of the second clad 23, and the first clad 22 are integrated. Since the single mode core 21 is solid, it does not change at all.
[0056]
As described above, a region 4 having a single mode fiber type structure (hereinafter, also referred to as a “collapse region 4”) is formed in a part of the double clad fiber 2 by the collapse process. The collapsed region 4 has a slightly tapered region at both ends, but is formed to have substantially the same diameter over the entire region. The collapse region 4 is formed to have the same diameter as the outer diameter of the light source MMF to be connected.
[0057]
Next, as shown in FIG. 3D, a taper process is performed on the emission end side of the collapse region 4. It is preferable that the taper processing be performed by etching using hydrogen fluoride or the like.
[0058]
Specifically, as shown in FIG. 4, the boundary between the collapse region 4 and the emission end side of the double clad fiber 2 is substantially on the axis of the partially cut-out fluororesin tube 5. The fiber is fixed so as to be located substantially at the center of the fluororesin tube 5 in the longitudinal direction. In this state, hydrogen fluoride is injected into the fluororesin tube 5 from the notch 5a. Due to the action of the surface tension, a relatively large amount of hydrogen fluoride is stored in the central portion of the fluororesin tube 5 as compared with both end portions thereof.
[0059]
When left standing in this state, the quartz optical fiber melts from the outer peripheral surface toward the axis. In a state where the movement of the optical fiber and the convection of the hydrogen fluoride are small, the reaction between the hydrogen fluoride and the quartz sequentially reaches a saturated state and stops from both ends having a relatively small storage amount to the center. As a result, in the collapse region, a smooth tapered portion 3b tapering from the incident end side toward the boundary with the double clad fiber 2 is formed. The outer diameter of the tapered portion 3b formed here on the emission end side must be equal to or smaller than the outer diameter of the first cladding 22.
[0060]
As shown in FIG. 3E, in order to form the non-tapered portion 3a, the collapsed region 4 is cut in a region where the taper processing is not performed. Since the outside diameter portion is parallel to the axis in the region where the taper processing is not performed, the cut surface is cut perpendicular to the axis.
[0061]
The emission end of the light source MMF32 is fusion-connected to the incidence area 3 of the optical device 1 thus formed.
[0062]
As shown in FIG. 3 (f), since the outer diameter of the non-tapered portion 3b of the incident area 3 and the outer diameter of the light source MMF32 substantially coincide with each other, it is easy to align the axes and at the time of heating. No torsion occurs due to surface tension caused by the difference in diameter of the shaft, so that there is no axial displacement. The light source MMF 32 also does not need to be tapered, and can solve conventional problems such as difficulty in cutting the emission end.
[0063]
【Example】
Hereinafter, specific examples of the optical device according to the present invention will be described with reference to the drawings.
[0064]
<Example 1>
FIG. 5 is a configuration diagram of a fiber laser device 30 using the optical device 1 according to the present invention.
[0065]
The fiber laser device 30 according to the present embodiment includes the optical device 1 according to the present invention, an MMLD excitation light source 31, a light source MMF32, an excitation light transmission / return light reflection filter 33, a single mode fiber 34, an isolator 35, and the like. I have.
[0066]
The MMLD 31 supplies excitation light to the optical device 1 via the light source MMF32. The light source MMF32 is a large-diameter multimode fiber having a large core diameter, and the core diameter in this embodiment is about 200 μm. As described above, by using a large-diameter multimode fiber for the light source MMF32, the output of the MMLD excitation light source 31 can be increased.
[0067]
The light source MMF 32 is connected to the incident area of the optical device 1 via an excitation light transmission / return light reflection filter 33. The excitation light transmission / return light reflection filter 33 transmits the excitation light emitted from the light source MMF32 to the incident area 3 of the optical device 1, but returns a specific wavelength emitted from the incident area 3 toward the light source MMF32. Light has a function of reflecting light without transmitting it.
[0068]
In this embodiment, the return light is generated according to the following principle. As shown in FIG. 8, the excitation light 6 incident on the first clad 22 of the double clad fiber propagates while repeating total reflection at the interface with the second clad 23. When the pump light 6 is transmitted across the single mode core 21, electrons are excited in the doped amplification medium. In the fiber laser device 30 according to the present embodiment, since the resonator is formed by the single mode core, the excitation light transmission / return light reflection filter 33 and the fiber grating 36, the signal light is bidirectionally transmitted in the double clad fiber. Stimulated emission of spontaneous emission occurs in both directions.
[0069]
The spontaneous emission light toward the incident end is incident on the MMLD excitation light source 31 as return light, and may adversely affect the MMLD excitation light source 31. Therefore, it is necessary to reflect the spontaneous emission light to the emission end side by the excitation light transmission / return light reflection filter 33.
[0070]
In this embodiment, the excitation light transmission / return light reflection filter 33 has a wide reflection wavelength band in order to completely reflect the light having a wide wavelength band excited in the single mode core 21 of the double clad fiber 2. Is preferred.
[0071]
For example, in the excitation light transmission / return light reflection filter 33 used in the present embodiment, it is desirable that all return light be 1 mW or less, and the excitation light transmission / return light reflection filter 33 transmits It is desirable that the wavelength is about ± 20 nm of the excitation light wavelength. Thus, almost 100% of the return light can be reflected.
[0072]
The incident area 3 of the optical device 1 is connected to the emission end side of the excitation light transmission / return light reflection filter 33. A single mode fiber 34 is connected to the emission end 27 side of the optical device 1. The core of the single mode fiber 34 is optically connected to the single mode core 21 of the double clad fiber 2.
[0073]
A fiber grating 36 is formed in the core of the single mode fiber 34. The fiber grating 36 is formed by periodically changing the refractive index of the core of the single mode fiber 34. The fiber grating 36 has a function of selectively reflecting light having a wavelength corresponding to the modulation period of the refractive index.
[0074]
The fiber grating 36 has a reflection wavelength band narrower than that of the excitation light transmission / return light reflection filter 33. For example, the fiber grating 36 used in the present embodiment is preferably set to be 0.1 to 1.0 (nm). The oscillation wavelength of the output laser light is determined by the reflection wavelength band of the fiber grating 36.
[0075]
An isolator is connected to the end of the fiber grating 36.
[0076]
The isolator 35 transmits the laser light emitted from the emission end 27 of the optical device 1 but blocks light incident from the outside toward the optical device 1, and transmits the excitation light transmission / return light reflection filter 33 and the excitation light. Oscillation due to reflection other than that of the fiber grating 36 is suppressed.
[0077]
The fiber laser device 30 configured as described above generates a laser beam as described below.
[0078]
The excitation light emitted from the MMLD excitation light source 31 propagates through the light source MMF 32, passes through the excitation light transmission / return light reflection filter 33, and enters the incident area 3 of the optical device 1. In the present embodiment, since the outer diameter of the light source MMF32 and the outer diameter of the non-tapered portion 3a of the incident area 3 are substantially the same, almost 100% of the excitation light is incident on the incident area 3 and there is almost no connection loss.
[0079]
The excitation light that has entered the incident area 3 propagates through the incident area from the non-tapered portion 3a to the tapered portion 3b, is narrowed down, and enters the first clad 22 of the double clad fiber 2. In the present invention, since the tapered portion 3b is formed so as to converge from the non-tapered portion 3a to the outer diameter of the first clad 22 of the double clad fiber 2, the excitation light incident on the incident region 3 is The light is reliably incident on the first clad 22 without leaking into the second clad 23 and the support layer 24.
[0080]
As described above, the excitation light that has entered the first cladding 22 propagates while repeating total reflection at the interface with the second cladding 23. When the pumping light 6 passes through the single mode core 21, spontaneous emission light having a wavelength different from that of the pumping light 6 is generated from the amplification medium doped in the single mode core 21.
[0081]
The spontaneous emission light is emitted from the emission end 27 of the double clad fiber 2 of the optical device 1 to the core of the single mode fiber 34. The return light of the stimulated emission light is also reflected by the excitation light transmission / return light reflection filter 33 and enters the core of the single mode fiber 34.
[0082]
The spontaneous emission light incident on the core of the single mode fiber 34 propagates through the core and reaches the fiber grating 36. Of the spontaneous emission light, those having a wavelength included in the reflection wavelength band of the fiber grating 36 are reflected and incident again on the single mode core 21 of the double clad fiber 2.
[0083]
A resonator is formed between the fiber grating 36 and the excitation light transmission / return light reflection filter 33, and stimulated emission is also performed by reflected spontaneous emission light. That is, in the fiber laser device according to the present embodiment, resonance occurs between the fiber grating 36 and the excitation light transmission / return light reflection filter 33, and the laser is oscillated by repeated stimulated emission, and high output laser light is emitted. Taken out.
[0084]
According to the present embodiment, since the pumping light of the MMLD pumping light source 31 can pump the amplification medium with little loss, it is possible to extract high-output laser light with high efficiency.
[0085]
Specifically, in the fiber laser device according to the present embodiment, when the Yb-doped double-clad fiber having a length of 20 m is used and excitation light having a wavelength of 980 nm is incident at an output of 3 W, the output end of the fiber laser device is As a result, a fiber laser output with a wavelength of 1085 nm was obtained at an output of 2 W. Further, in the fiber laser device according to the present example, it was found that the pumping light was used with a high utilization efficiency of about 95%.
[0086]
<Example 2>
FIG. 6 is a configuration diagram of the ASE light source device 40 using the optical device 1 according to the present invention.
[0087]
The ASE light source device 40 according to the present embodiment has basically the same configuration as the fiber laser device according to the first embodiment. The same members as those of the fiber laser device of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The difference from the fiber laser device is that the single mode fiber 34 has no fiber grating and the excitation light transmission / return light reflection filter 33 is inclined at an angle θ with respect to the axis of the fiber. There is something.
[0088]
The pump light generated by the MMLD pump light source 31 is efficiently incident on the first clad of the double clad fiber 2 by the optical device 1 according to the present invention. Excitation light incident on the first cladding generates spontaneous emission light by exciting the doped amplification medium.
[0089]
The excitation light transmission / return light reflection filter 33 is usually installed with an angle θ of 6 ° or more. In other words, this is to prevent oscillation due to the return light being reflected by the excitation light transmission / return light reflection filter 33 and re-entering the single mode core. As a result, only the spontaneous emission light having a wide wavelength band generated in the single mode core can be extracted from the output end of the ASE light source device according to the present embodiment.
[0090]
Specifically, in the ASE light source device according to the present embodiment, when the Yb-doped double-clad fiber 2 having a length of 20 m is used and the pump light having the output of 3 W and the wavelength of 980 nm is incident, the output end of the ASE light source device is In a wavelength band of 1010 to 1130 (nm), 800 mW of spontaneous emission light was obtained. Further, in the ASE light source device according to the present example, it was found that the excitation light was used with a high utilization efficiency of about 95%.
[0091]
<Example 3>
FIG. 6 is a configuration diagram of an optical amplifier device 50 using the optical device 1 according to the present invention.
[0092]
The optical amplifier device 50 according to the present embodiment has basically the same configuration as the fiber laser device according to the first embodiment. The same members as those of the fiber laser device of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The difference from the fiber laser device is that the fiber laser device is not provided with the fiber grating, and is provided with a circulator 37 having an input port 37a and an output port 37b instead of the isolator.
[0093]
The excitation light generated by the MMLD excitation light source 31 is efficiently incident on the single mode core of the double clad fiber 2 by the optical device 1 according to the present invention.
[0094]
On the other hand, the signal light from the transmission path is incident on the incident port 37a of the circulator 37. The signal light enters the single mode core of the double clad fiber 2 from the single mode fiber 34. The signal light incident into the single mode core is amplified by the action of the doped amplification medium and the pumping light from the MMLD pumping light source 31. The signal light that has been amplified and reached the excitation light transmission / return light reflection filter 33 is reflected and re-enters the single mode core. The signal light re-entered into the single-mode core is amplified again by the action of the amplification medium and the pump light, and is incident on the single-mode fiber 34. The signal light that has been amplified and propagates through the single mode fiber 34 is output from the output port 37b of the circulator 37, and transmitted again through the transmission path. Thus, the optical device 1 according to the present invention can be used as an optical amplifier device.
[0095]
Specifically, in the optical amplifier device according to the present embodiment, when the Yb-doped double-clad fiber 2 having a length of 20 m is used and the pump light having the output of 3 W and the wavelength of 980 nm is incident, the incident port 37a of the circulator 37 is used The input signal light of 0.1 mW was able to be output from the output port 37b of the circulator 37 as signal light amplified to 100W. In addition, in the optical amplifier device according to the present embodiment, it was found that the pumping light was used with a high utilization efficiency of about 95%.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a double clad fiber according to the present invention.
FIG. 2 is a conceptual diagram illustrating a configuration of an optical device according to the present invention.
FIG. 3 is a conceptual diagram showing a manufacturing process of the optical device according to the present invention.
FIG. 4 is a schematic diagram showing an outline of an etching process.
FIG. 5 is a configuration diagram of a fiber laser device according to an embodiment of the present invention.
FIG. 6 is a configuration diagram of an ASE light source device according to an embodiment of the present invention.
FIG. 7 is a configuration diagram of an optical amplifier device according to an embodiment of the present invention.
FIG. 8 is a conceptual diagram illustrating the principle of generation of return light.
FIG. 9 is a conceptual diagram showing a connection state of a conventional double clad fiber.
FIG. 10 is a conceptual diagram showing a connection state of a conventional double clad fiber.
[Explanation of symbols]
1 Optical device
2 Double clad fiber
21 Single mode core
22 First cladding
23 Second cladding
24 Support layer
25 Coating layer
3 Incident area
3a Non-tapered part
3b taper part

Claims (2)

A single mode core doped with an amplification medium;
A first cladding that covers the periphery of the single mode core;
An optical device using a double-clad fiber configured to have a porous structure including a large number of pores and having a second clad covering the periphery of the first clad,
At the incident end of the double clad fiber, an incident region for transmitting the excitation light is formed, which is connected to a multi-mode optical fiber extending from an external excitation light source,
A non-tapered portion formed in a shape connectable to the multimode optical fiber on the incident end side of the incident region;
A tapered portion is formed so as to converge from the non-tapered portion to the outer diameter of the first clad of the double-clad fiber,
The tapered portion is optically connected to a first clad of the double clad fiber. A single mode core doped with an amplification medium;
A first cladding that covers the periphery of the single mode core;
An optical device using a double-clad fiber configured to have a porous structure including a large number of pores and having a second clad covering the periphery of the first clad,
At the incident end of the double clad fiber, an incident region for transmitting the excitation light is formed, which is connected to a multi-mode optical fiber extending from an external excitation light source,
On the incident end side of the incident area, a non-tapered portion formed to have the same diameter as the outer diameter of the multimode optical fiber,
A tapered portion is formed so as to converge from the non-tapered portion to the outer diameter of the first clad of the double-clad fiber,
The tapered portion is optically connected to a first clad of the double clad fiber.

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