JP2021110898A - Method for manufacturing optical device - Google Patents

Abstract

To provide a method for manufacturing an optical device, capable of reducing the loss of light in a fusion connection part.SOLUTION: A method for manufacturing an optical device 10 comprises: a bump step of bumping the end surfaces of first and second optical fibers F1 and F2 having different effective cross sectional areas and having a dopant added to a core 11 or a cladding 12 and capable of changing a refractive index; and a heating step of heating a surface P bumped by the first and second optical fibers and fusing and connecting the first and second optical fibers. In the heating step, a difference between the effective cross-sectional areas of the first and second optical fibers in the bumped surface is reduced by diffusing and migrating at least one of the dopants of the first and second optical fibers.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing an optical device.

Patent Document 1 discloses a method of fusing and connecting two optical fibers to each other to integrate them. Two optical fibers (hereinafter referred to as optical devices) integrated by fusion splicing are used in a laser device or the like.

JP-A-2017-194497

When manufacturing such an optical device, it is not easy to prepare two optical fibers having exactly the same effective cross-sectional area (Aeff). If the effective cross-sectional areas of the two optical fibers are different, the loss of light at the fusion splicer becomes large.

The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a method for manufacturing an optical device capable of reducing light loss at a fusion splicer.

In order to solve the above problems, in the method for manufacturing an optical device according to one aspect of the present invention, the first optical fiber and the first optical fiber in which effective cross-sectional areas are different from each other and a dopant for changing the refractive index is added to the core or clad. The abutting step of abutting the end faces of the two optical fibers and the abutting surface of the first optical fiber and the second optical fiber are heated to fuse the first optical fiber and the second optical fiber. It has a heating step of connecting, and in the heating step, by diffusing and moving at least one dopant of the first optical fiber and the second optical fiber, the first optical fiber and the said Reduce the difference in effective cross-sectional area from the second optical fiber.

According to the above aspect, in the heating step, by reducing the difference in the effective cross-sectional areas of the two optical fibers at the fusion splicing portion, the light loss at the fusion splicing portion can be reduced.

Here, in the method for manufacturing an optical device according to the above aspect, a light source is connected to one of the first optical fiber and the second optical fiber, a measuring instrument is connected to the other, and the light is emitted from the light source. It may include a confirmation step of confirming the beam quality of the light passing through the 1 optical fiber and the 2nd optical fiber by the measuring instrument.

Further, the abutting surface and the heating point in the heating step may be deviated in the longitudinal direction.

Further, the dopant for reducing the refractive index is added to the clad of the first optical fiber and the clad of the second optical fiber, and the abutting of the first optical fiber and the second optical fiber is made. The heating point may be shifted to the side where the effective cross-sectional area on the surface is smaller.

Further, the dopant that increases the refractive index is added to the core of the first optical fiber and the core of the second optical fiber, and the abutting of the first optical fiber and the second optical fiber is made. The heating point may be shifted to the side where the effective cross-sectional area on the surface is smaller.

Further, the dopant that lowers the refractive index is added to the clad of the first optical fiber and the clad of the second optical fiber, and the abutting of the first optical fiber and the second optical fiber is made. The amount of the dopant added to the clad having the smaller effective cross-sectional area on the surface may be larger than the amount of the dopant added to the other clad.

Further, the effective cross-sectional area of the first optical fiber before the heating step is smaller than the effective cross-sectional area of the second optical fiber, and the heating step increases the effective cross-sectional area of the first optical fiber. , The effective cross-sectional area of the second optical fiber may be reduced.

Further, a dopant that increases the refractive index is added to the core of the first optical fiber, a dopant that decreases the refractive index is added to the clad of the first optical fiber, and the core of the second optical fiber is refracted. Dopants that reduce the rate may be added.

Further, when the dopant for reducing the refractive index added to the core of the second optical fiber is used as the first dopant, the second dopant for increasing the refractive index is added to the core of the second optical fiber. Therefore, the rate of diffusion movement of the second dopant due to heat may be higher than that of the first dopant.

Further, one of the first optical fiber and the second optical fiber may be an amplification optical fiber in which rare earths are added to the core.

According to the above aspect of the present invention, it is possible to provide a method for manufacturing an optical device capable of reducing the loss of light at the fusion splicer.

It is sectional drawing of the optical device which concerns on 1st Embodiment. It is a figure which shows an example of the fusion splicer in 1st Embodiment. The cross section and the refractive index distribution of the first optical fiber are shown. (A) is a state before the heating step, and (b) is a state after the heating step. It is the schematic of the laser apparatus which concerns on 5th Embodiment.

(First Embodiment)
Hereinafter, the optical device of the first embodiment and the manufacturing method thereof will be described with reference to the drawings.
As shown in FIG. 1, the optical device 10 includes a core 11, a clad 12 (first clad), a polymer clad 13 (second clad), a first coating layer 14, and a second coating layer 15. Have. The optical device 10 is configured such that the first optical fiber F1 and the second optical fiber F2 are fused and connected to each other. Although not shown, the first optical fiber F1 and the second optical fiber F2 before fusion splicing are also the core 11, the clad 12, the polymer clad 13, the first coating layer 14, and the second coating layer 15, respectively. And have.

The optical device 10 is a so-called double clad fiber having a clad 12 and a polymer clad 13. However, the optical device 10 does not have to have the polymer clad 13. Further, the optical device 10 of the present embodiment has the first coating layer 14 and the second coating layer 15, but the number of coating layers can be changed as appropriate.

(Direction definition)
In the present embodiment, the longitudinal direction of the optical device 10 is simply referred to as the "longitudinal direction". Further, in the longitudinal direction, the first optical fiber F1 side is referred to as the −Z side, and the second optical fiber F2 side is referred to as the + Z side.

The first optical fiber F1 and the second optical fiber F2 may be of the same type as each other. In addition, in this specification, "the same kind" of two optical fibers means that the kind of dopant contained in a core 11 and a clad 12 is the same.
The first optical fiber F1 and the second optical fiber F2 may be a single mode fiber or a multimode fiber.

The core 11 is made of quartz glass. The clad 12 is made of quartz glass and surrounds the core 11. A dopant (also referred to as a down dopant) that lowers the refractive index of quartz glass is added to the clad 12. As such a dopant, F (fluorine), B (boron), and the like can be adopted. Due to the addition of the down dopant, the refractive index of the clad 12 is lower than that of the core 11 at least at the interface with the core 11. As a result, the light can be confined in the core 11.

If necessary, a dopant other than the purpose of lowering the refractive index (for example, for adjusting the viscosity) may be added to the core 11 or the clad 12. Further, a dopant (also referred to as an updopant) that increases the refractive index, such as Ge (germanium), Cl (chlorine), P (phosphorus), Al (aluminum), and Ce (cerium), may be added to the core 11. ..
The material of the polymer clad 13 may be a UV curable resin or a thermosetting resin. The polymer clad 13 is formed of a material having a refractive index lower than that of the clad 12.

The first coating layer 14 covers the polymer clad 13. The second coating layer 15 covers the first coating layer 14. Resin or the like can be used as the coating layers 14 and 15. For example, urethane acrylate-based, polybutadiene acrylate-based, epoxy acrylate-based, silicone acrylate-based, and polyester acrylate-based UV curable resins may be used as the coating layers 14 and 15.

Here, in order to reduce the loss of light at the fusion splicer, it is preferable that the effective cross-sectional areas (Aeff) of the first optical fiber F1 and the second optical fiber F2 match as much as possible. However, the effective cross-sectional areas of the first optical fiber F1 and the second optical fiber F2 do not always match before the fusion splicing. Therefore, in the present embodiment, the difference in the effective cross-sectional area is reduced by adopting the following steps.

First, the first optical fiber F1 and the second optical fiber F2, which are the sources of the optical device 10, are prepared (preparation step). At this time, the effective cross-sectional area of each optical fiber F1 and F2 is measured in advance. For example, the effective cross-sectional area of two or more optical fibers is measured and grouped into an optical fiber having an effective cross-sectional area larger than the reference value and an optical fiber having an effective cross-sectional area smaller than the reference value. You may. The reference value may be a design target value or an average value for a plurality of optical fibers. In this specification, the case where the effective cross-sectional area of the first optical fiber F1 is smaller than the effective cross-sectional area of the second optical fiber F2 will be described.

Next, at the ends of the first optical fiber F1 and the second optical fiber F2, the polymer clad 13, the first coating layer 14, and the second coating layer 15 are removed to expose the clad 12. Then, at the end where the clad 12 is exposed, the end faces of the first optical fiber F1 and the second optical fiber F2 are abutted against each other (butting step). That is, the cores 11 and the cladding 12 of the first optical fiber F1 and the second optical fiber F2 are abutted against each other. Hereinafter, the end faces of the first optical fiber F1 and the second optical fiber F2 that have been abutted are referred to as "butting surfaces P". After the first optical fiber F1 and the second optical fiber F2 are fused and connected, that is, after the optical device 10 is manufactured, the abutting surface P disappears. Therefore, in FIG. 1, the abutting surface P is virtual. It is represented by a line (one-dot chain line).

The abutting step is preferably performed using the fusion splicer 100 as shown in FIG. The fusion splicer 100 holds the optical fibers F1 and F2 so that the axis of the first optical fiber F1 and the axis of the second optical fiber F2 coincide with each other and the end faces of the optical fibers F1 and F2 abut against each other. Can be positioned. The shape of the fusion splicer 100 shown in FIG. 2 is an example and can be changed as appropriate.

Next, the abutting surface P is heated to fuse and connect the first optical fiber F1 and the second optical fiber F2 (heating step). The specific method of heating can be changed as appropriate, but it is preferable to use arc discharge by the fusion splicer 100. The fusion splicer 100 is configured so that the relative positions of the abutting surface P and the heating point H in the longitudinal direction can be finely adjusted.

Here, in the present embodiment, as shown in FIG. 1, the heating point H in the heating step is shifted to the first optical fiber F1 side (−Z side) from the abutting surface P. Even if the heating point H deviates from the abutting surface P in the longitudinal direction, the abutting surface P is heated by heat transfer, and the optical fibers F1 and F2 are melted and fused. As described above, since the heating point H is deviated from the abutting surface P, the dopant of the deviated optical fiber (first optical fiber F1) can be positively diffused and moved. Then, the difference in the effective cross-sectional area between the first optical fiber F1 and the second optical fiber F2 on the abutting surface P can be reduced. Hereinafter, a more detailed description will be given with reference to FIGS. 3 (a) and 3 (b).

FIG. 3A shows a cross section and a refractive index distribution of the first optical fiber F1 before the heating step is performed. As shown in the lower part of FIG. 3A, the refractive index of the core 11 is larger than the refractive index of the clad 12. This is because a dopant that lowers the refractive index is added to the clad 12.

When the clad 12 is heated in the heating step, the dopant added to the clad 12 diffuses and moves and enters the core 11. Then, in the vicinity of the interface between the core 11 and the clad 12, the amount of the dopant in the clad 12 decreases, and the amount of the dopant in the core 11 increases. As a result, as shown in FIG. 3B, the refractive index of the clad 12 increases and the refractive index of the core 11 decreases in the vicinity of the interface between the core 11 and the clad 12. Comparing the widths W1 and W2 of the portion where the refractive index rises between FIGS. 3 (a) and 3 (b), the width W2 in FIG. 3 (b) is larger. The effective cross-sectional area of the core 11 increases as the rising widths W1 and W2 of the refractive index increase. That is, the effective cross-sectional area of the first optical fiber F1 is increased by the heating process.

In the present embodiment, the effective cross-sectional area of the first optical fiber F1 is smaller than the effective cross-sectional area of the second optical fiber F2 in the state before the heating step is performed. Therefore, by increasing the effective cross-sectional area of the first optical fiber F1 during the heating step, the difference between the effective cross-sectional areas of the optical fibers F1 and F2 can be reduced. Since the heating point H is in the vicinity of the abutting surface P, the diffusive movement of the dopant also occurs in the second optical fiber F2, and the effective cross-sectional area of the second optical fiber F2 can be increased. However, since the heating point H is shifted to the first optical fiber F1, the increase in the effective cross-sectional area in the first optical fiber F1 is larger than the increment in the effective cross-sectional area in the second optical fiber F2. Therefore, even if the effective cross-sectional area of the second optical fiber F2 is increased by the heating step, the difference in the effective cross-sectional area on the abutting surface P can be reduced.

Here, the longer the heating time, the greater the amount of diffusion movement of the dopant, and the larger the effective cross-sectional area of the first optical fiber F1. Therefore, if the heating time is excessive, the effective cross-sectional area of the first optical fiber F1 becomes larger than the effective cross-sectional area of the second optical fiber F2, and the difference in the effective cross-sectional area may become larger. Conceivable. Therefore, as shown in FIG. 2, the light source 101 may be connected to one of the first optical fiber F1 and the second optical fiber F2, and the measuring instrument 102 may be connected to the other. Then, light is emitted from the light source 101, beam quality of light passing through the first optical fiber F1 and the second optical fiber F2 (e.g. M ^2: M Square), and may be verified by measuring device 102 (checking step ).

The greater the difference in the effective cross-sectional area of the abutting surface P, the lower the beam quality measured by the measuring instrument 102. Conversely, when the beam quality measured by the measuring instrument 102 is within the predetermined range, the difference in the effective cross-sectional area at the abutting surface P is also within the predetermined range. Therefore, by performing the above confirmation step, it is possible to confirm whether or not the difference in the effective cross-sectional area between the first optical fiber F1 and the second optical fiber F2 is within a predetermined range. As a result of the confirmation step, if the difference in the effective cross-sectional area is within the predetermined range, the heating step may be terminated, and if the difference in the effective cross-sectional area is not within the predetermined range, the heating step may be continued. When the effective cross-sectional area of the first optical fiber F1 becomes too large, the heating point H can be shifted to the second optical fiber F2 side to continue the heating process, and the effective cross-sectional area of the second optical fiber F2 can be increased. Is.

Considering the diffusion rate in the quartz glass, F (fluorine) is suitable as the dopant for lowering the refractive index. By using F, the dopant can be moved from the clad 12 to the core 11 and the effective cross-sectional area of the first optical fiber F1 can be increased.

After the heating step and the confirmation step, the portion where the clad 12 is exposed may be recoated with the resin. In this case, the outer peripheral surface of the clad 12 can be protected by the re-covered coating (re-covering portion). However, if there is no concern about heat generation due to leaked light, for example, the recovering portion may not be provided.

(Second Embodiment)
Next, the second embodiment according to the present invention will be described, but the basic configuration is the same as that of the first embodiment. Therefore, the same reference numerals are given to the same configurations, the description thereof will be omitted, and only the different points will be described.

In the first embodiment, the effective cross-sectional area of the first optical fiber F1 is increased by diffusing and moving the dopant added to the clad 12 to reduce the refractive index. On the other hand, in the second embodiment, the effective cross-sectional area of the first optical fiber F1 is increased by diffusing and moving the dopant added to the core 11 to increase the refractive index.

Also in this embodiment, the heating point H in the heating step is shifted to the −Z side with respect to the abutting surface P. That is, the heating point H is shifted to the side of the first optical fiber F1 and the second optical fiber F2 where the effective cross-sectional area on the abutting surface P is small. In the present embodiment, the heating step causes the dopant contained in the core 11 of the first optical fiber F1 to increase the refractive index to diffuse and move toward the clad 12. As a result, the refractive index of the core 11 decreases and the refractive index of the clad 12 increases in the vicinity of the interface between the core 11 and the clad 12. Therefore, as in the first embodiment, the effective cross-sectional area of the first optical fiber F1 is increased to reduce the difference in the effective cross-sectional area between the first optical fiber F1 and the second optical fiber F2 at the fusion splicer. can do.

(Third Embodiment)
Next, the third embodiment according to the present invention will be described, but the basic configuration is the same as that of the first embodiment. Therefore, the same reference numerals are given to the same configurations, the description thereof will be omitted, and only the different points will be described.

In the first embodiment and the second embodiment, the heating point H is deviated from the abutting surface P in the longitudinal direction, but in the present embodiment, the positions of the heating point H and the abutting surface P are matched in the longitudinal direction.
In the first optical fiber F1 and the second optical fiber F2 in the present embodiment, the amount of the dopant added to the clad 12 for lowering the refractive index is different. More specifically, the amount of the dopant added to the clad 12 of the first optical fiber F1 having a small effective cross-sectional area is larger than the amount of the dopant added to the clad 12 of the second optical fiber F2.

In the case of the present embodiment, since the heating point H and the abutting surface P coincide with each other, both the first optical fiber F1 and the second optical fiber F2 are heated substantially evenly. Therefore, in both the optical fibers F1 and F2, the dopant that lowers the refractive index diffuses and moves from the clad 12 to the core 11, and the effective cross-sectional area increases. Here, since the amount of the dopant added to the clad 12 of the first optical fiber F1 is large, the increase in the effective cross-sectional area of the first optical fiber F1 is larger than that of the second optical fiber F2. Therefore, the difference in the effective cross-sectional area on the abutting surface P can be reduced.

(Fourth Embodiment)
Next, the fourth embodiment according to the present invention will be described, but the basic configuration is the same as that of the first embodiment. Therefore, the same reference numerals are given to the same configurations, the description thereof will be omitted, and only the different points will be described.
In the first to third embodiments, the effective cross-sectional area of both the first optical fiber F1 and the second optical fiber F2 is increased by heating, but the increase amount of the effective cross-sectional area of the first optical fiber F1 is larger. Therefore, the difference in the effective cross-sectional area between the two was reduced. On the other hand, in the fourth embodiment, the effective cross-sectional area of the first optical fiber F1 is increased by heating, and the effective cross-sectional area of the second optical fiber F2 is decreased by heating.

The first optical fiber F1 of the present embodiment is, for example, an FBG (Fiber Bragg Grating) fiber, and an up-dopant is added to the core 11 and a down-dopant is added to the clad 12. The second optical fiber F2 of the present embodiment is, for example, an optical fiber for amplification, and Yb, which is a rare earth element, and B, which is a down dopant, are added to the core 11.

In the present embodiment, when the first optical fiber F1 is heated, the up-dopant of the core 11 diffuses and moves to the clad 12, and the down-dopant of the clad 12 diffuses and moves to the core 11. As a result, the effective cross-sectional area of the first optical fiber F1 is increased. On the other hand, when the second optical fiber F2 is heated, the down-dopant diffuses and moves from the core 11 toward the clad 12, so that the refractive index of the core 11 near the boundary with the clad 12 decreases. As a result, the effective cross-sectional area of the second optical fiber F2 becomes smaller. That is, heating increases the effective cross-sectional area of the first optical fiber F1 and decreases the effective cross-sectional area of the second optical fiber F2. Therefore, even if the effective cross-sectional area of the first optical fiber F1 before heating is smaller than that of the second optical fiber F2, the difference in the effective cross-sectional area between the first optical fiber F1 and the second optical fiber F2 can be reduced by heating. ..

As described above, the method for manufacturing the optical device 10 according to the first to fourth embodiments includes a butt step and a heating step. In the abutting step, the end faces of the first optical fiber F1 and the second optical fiber F2 having different effective cross-sectional areas and having a dopant that changes the refractive index added to the core 11 or the clad 12 are abutted against each other. In the heating step, the abutting surface P between the first optical fiber F1 and the second optical fiber F2 is heated, and the first optical fiber F1 and the second optical fiber F2 are fused and connected. Then, in the heating step, the dopant of the first optical fiber F1 is diffused and moved to reduce the difference in the effective cross-sectional area between the first optical fiber F1 and the second optical fiber F2 on the abutting surface P.

According to the optical device 10 manufactured by such a manufacturing method, the difference in the effective cross-sectional area at the fusion splicing portion becomes small, so that the light loss at the fusion splicing portion can be reduced.

Further, the manufacturing method according to the first to fourth embodiments may include a confirmation step. In the confirmation step, the light source 101 is connected to one of the first optical fiber F1 and the second optical fiber F2, the measuring instrument 102 is connected to the other, and the first optical fiber F1 and the second optical fiber are emitted from the light source 101. The beam quality of the light passing through the fiber F2 is confirmed by the measuring instrument 102. According to this configuration, it is possible to prevent the difference in effective cross-sectional area from becoming large due to the heating process.

Further, in the manufacturing methods according to the first embodiment and the second embodiment, the abutting surface P and the heating point H in the heating step are displaced in the longitudinal direction.
Further, in the first embodiment, a dopant for reducing the refractive index is added to the clad 12 of the first optical fiber F1 and the clad 12 of the second optical fiber F2, and the first optical fiber F1 and the second optical fiber F2 Of these, the heating point H is shifted to the side where the effective cross-sectional area on the abutting surface P is smaller.
Further, in the second embodiment, a dopant for increasing the refractive index is added to the core 11 of the first optical fiber F1 and the core 11 of the second optical fiber F2, so that the first optical fiber F1 and the second optical fiber F2 Of these, the heating point H is shifted to the side where the effective cross-sectional area on the abutting surface P is smaller.

In this way, by shifting the position of the heating point H in the longitudinal direction with respect to the abutting surface P in the longitudinal direction, the difference in the executed cross-sectional area can be easily reduced.

Further, in the manufacturing method according to the third embodiment, a dopant for reducing the refractive index is added to the clad 12 of the first optical fiber F1 and the clad 12 of the second optical fiber F2, and the first optical fiber F1 and the second optical fiber F1 and the second The amount of the dopant added to the clad 12 having the smaller effective cross-sectional area on the abutting surface P of the optical fiber F2 is larger than the amount of the dopant added to the other clad 12.

According to this configuration, even when the position of the heating point H in the longitudinal direction coincides with the abutting surface P, the difference in the effective cross-sectional area can be reduced.

Further, in the manufacturing method according to the fourth embodiment, the effective cross-sectional area of the first optical fiber F1 before the heating step is smaller than the effective cross-sectional area of the second optical fiber F2, and the first optical fiber F1 is subjected to the heating step. The effective cross-sectional area is increased and the effective cross-sectional area of the second optical fiber F2 is decreased. According to this configuration, the difference in the effective cross-sectional area can be reduced regardless of whether the heating point H is deviated to the + Z side or the −Z side with respect to the abutting surface P.

Further, in the fourth embodiment, a dopant that increases the refractive index is added to the core 11 of the first optical fiber F1, a dopant that decreases the refractive index is added to the cladding 12 of the first optical fiber F1, and the second optical fiber. A dopant that reduces the refractive index is added to the core 11 of F2. With this configuration, it is possible to realize a manufacturing method in which the effective cross-sectional area of the first optical fiber F1 is increased by the heating step and the effective cross-sectional area of the second optical fiber F2 is reduced.

(Fifth Embodiment)
Next, a fifth embodiment according to the present invention will be described. In this embodiment, a laser apparatus using the optical device 10 manufactured by the manufacturing method described in the first to fourth embodiments will be described. The basic configuration of the optical device 10 is the same as that of the first to third embodiments. Therefore, the same reference numerals are given to the same configurations, the description thereof will be omitted, and only the different points will be described.

As shown in FIG. 4, the laser apparatus 1 includes a forward excitation light source 2, a first combiner 3, a first FBG fiber 4, an amplification optical fiber 5, a second FBG fiber 6, a second combiner 7, and a rear. It includes an excitation light source 8 and an output terminal 9. An HR-FBG (High Reflectivity-Fiber Bragg Grating) 4a is formed on the first FBG fiber 4. An OC-FBG (Output Coupler-Fiber Bragg Grating) 6a is formed on the second FBG fiber 6. The amplification optical fiber 5, the first FBG fiber 4, and the second FBG fiber 6 constitute a resonator R that generates laser light by the excitation light emitted by the excitation light sources 2 and 8.
The laser device 1 is a bidirectional excitation type including a front excitation light source 2 and a rear excitation light source 8.

As shown in FIG. 1, a plurality of front excitation light sources 2 and rear excitation light sources 8 are arranged with the amplification optical fiber 5 interposed therebetween. The front excitation light source 2 emits the front excitation light toward the amplification optical fiber 5, and the rear excitation light source 8 emits the rear excitation light toward the amplification optical fiber 5. As these excitation light sources 2 and 8, for example, a laser diode can be used.

The first combiner 3 and the second combiner 7 are arranged on both sides of the amplification optical fiber 5 with the amplification optical fiber 5 interposed therebetween. The first combiner 3 combines the excitation light emitted by each forward excitation light source 2 into one optical fiber and directs the excitation light to the amplification optical fiber 5. The second combiner 7 combines the excitation light emitted by each rear excitation light source 8 into one optical fiber and directs the excitation light to the amplification optical fiber 5.

The amplification optical fiber 5 covers a core to which one or more kinds of active elements are added, a clad covering the core (first clad), a polymer clad covering the clad (second clad), and a polymer clad. It has a coating layer and. The amplification optical fiber 5 is a double clad fiber. As the active element added to the core, for example, a rare earth element such as erbium (Er), ytterbium (Yb), or neodymium (Nd) is used. These active elements emit light in the excited state. Quartz glass or the like can be used as the core and clad. As the second clad, a resin such as a polymer can be used. As the coating layer, a resin material such as an acrylic resin or a silicone resin can be used.

The first FBG fiber 4 is fused and connected to the front of the amplification optical fiber 5. The HR-FBG4a is formed in the core of the first FBG fiber 4. The HR-FBG4a is adjusted so as to reflect the light having the wavelength of the signal light among the light emitted by the active element of the excited optical fiber 5 for amplification with a reflectance of almost 100%, and the first FBG fiber. The structure is such that a portion having a high refractive index is repeated at a constant cycle along the longitudinal direction of 4.

The second FBG fiber 6 is fusion-bonded to the rear of the amplification optical fiber 5. The OC-FBG 6a is formed in the core of the second FBG fiber 6. OC-FBG6a has almost the same structure as HR-FBG4a, but is adjusted to reflect light with a lower reflectance than HR-FBG4a.

In the amplification optical fiber 5, the signal light reflected by the HR-FBG4a and OC-FBG6a reciprocates in the longitudinal direction of the amplification optical fiber 5. The signal light is amplified along with this round trip to become laser light. In this way, in the resonator R, the light is amplified and the laser beam is generated. A part of the laser light passes through the OC-FBG6a, reaches the output end 9, and is emitted from the output end 9 to the outside of the laser device 1.

In such a laser device 1, the loss of light generated at the fusion splicing portion between optical fibers may lead to a decrease in the performance of the laser device 1. Therefore, in the present embodiment, the fusion splicing method described in the first to fourth embodiments is used for the fusion splicing portion of the laser device 1. For example, one of the first FBG fiber 4 and the amplification optical fiber 5 may be the first optical fiber F1 in the first to third embodiments, and the other may be the second optical fiber F2. Alternatively, one of the amplification optical fiber 5 and the second FBG fiber 6 may be the first optical fiber F1 in the first to third embodiments, and the other may be the second optical fiber F2. Further, the first FBG fiber 4 or the second FBG fiber 6 may be the first optical fiber F1 in the fourth embodiment, and the amplification optical fiber 5 may be the second optical fiber F2 in the fourth embodiment.

That is, one of the first optical fiber F1 and the second optical fiber F2 may be an amplification optical fiber 5 in which rare earths are added to the core 11. According to such a configuration, the difference in the effective cross-sectional area between the fusion optical fiber 5 and the other optical fiber at the fusion splicing portion becomes small, and the light loss at the fusion splicing portion can be reduced. Therefore, it is possible to improve the performance of the laser device 1.

The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

For example, in the laser apparatus 1 of the fifth embodiment, the fusion splicing method described in the first to third embodiments may be adopted for the fusion splicing portion other than the amplification optical fiber 5.
Further, instead of the excitation light sources 2 and 8 in the fifth embodiment, a MOPA (Master Oscillator Power Amplifier) type laser unit may be adopted.

Further, in addition to the down dopant B (first dopant), the up dopant Al (second dopant) is added to the core 11 of the second optical fiber F2 (Yb amplification fiber) of the fourth embodiment. May be good. Since B has a higher rate of diffusion movement due to heat than Al, when the second optical fiber F2 is heated, the amount of B movement from the core 11 to the clad 12 becomes larger than the amount of movement of Al. Also in this case, since the effective cross-sectional area of the second optical fiber F2 is reduced, the effects described in the fourth embodiment can be obtained. Not limited to Al and B, if the rate of diffusion movement of the second dopant by heat is higher than that of the first dopant, the specific type of dopant may be changed as appropriate. Further, the type of the second optical fiber F2 is not limited to the Yb amplification fiber, and may be changed as appropriate.

In addition, it is possible to replace the components in the above-described embodiment with well-known components as appropriate without departing from the spirit of the present invention, and the above-described embodiments and modifications may be appropriately combined.

For example, in the laser apparatus 1 of the fifth embodiment, the fusion splicing methods described in the first to fourth embodiments may be mixed.

5 ... Optical fiber for amplification 10 ... Optical device 11 ... Core 12 ... Clad 101 ... Light source 102 ... Measuring instrument F1 ... First optical fiber F2 ... Second optical fiber H ... Heating point P ... Abutment surface

Claims (10)

An abutting process in which the end faces of the first and second optical fibers having different effective cross-sectional areas and having a dopant that changes the refractive index added to the core or clad are abutted against each other.
It has a heating step of heating the abutting surface between the first optical fiber and the second optical fiber to fuse and connect the first optical fiber and the second optical fiber.
In the heating step, by diffusing and moving at least one dopant of the first optical fiber and the second optical fiber, the effective cross-sectional area of the first optical fiber and the second optical fiber on the abutting surface is A method of manufacturing optical devices that reduces the difference. A light source is connected to one of the first optical fiber and the second optical fiber, a measuring instrument is connected to the other, and light emitted from the light source and passed through the first optical fiber and the second optical fiber. The method for manufacturing an optical device according to claim 1, further comprising a confirmation step of confirming the beam quality of the above with the measuring instrument. The method for manufacturing an optical device according to claim 1 or 2, wherein the abutting surface and the heating point in the heating step are displaced in the longitudinal direction. The dopant that reduces the refractive index is added to the clad of the first optical fiber and the clad of the second optical fiber.
The method for manufacturing an optical device according to claim 3, wherein the heating point is shifted to the smaller effective cross-sectional area of the abutting surface of the first optical fiber and the second optical fiber. The dopant that increases the refractive index is added to the core of the first optical fiber and the core of the second optical fiber.
The method for manufacturing an optical device according to claim 3, wherein the heating point is shifted to the smaller effective cross-sectional area of the abutting surface of the first optical fiber and the second optical fiber. The dopant that reduces the refractive index is added to the clad of the first optical fiber and the clad of the second optical fiber.
Of the first optical fiber and the second optical fiber, the amount of the dopant added to the clad having the smaller effective cross-sectional area on the abutting surface is larger than the amount of the dopant added to the other clad. The method for manufacturing an optical device according to claim 1 or 2, which is often used. The effective cross-sectional area of the first optical fiber before the heating step is smaller than the effective cross-sectional area of the second optical fiber.
The method for manufacturing an optical device according to claim 1 or 2, wherein the effective cross-sectional area of the first optical fiber is increased and the effective cross-sectional area of the second optical fiber is decreased by the heating step. A dopant that increases the refractive index is added to the core of the first optical fiber,
A dopant that reduces the refractive index is added to the cladding of the first optical fiber,
The method for manufacturing an optical device according to claim 7, wherein a dopant for reducing the refractive index is added to the core of the second optical fiber. When the dopant that reduces the refractive index added to the core of the second optical fiber is used as the first dopant, the second dopant that increases the refractive index is added to the core of the second optical fiber.
The method for manufacturing an optical device according to claim 8, wherein the rate of diffusion movement of the second dopant due to heat is higher than that of the first dopant. The production of the optical device according to any one of claims 1 to 9, wherein one of the first optical fiber and the second optical fiber is an amplification optical fiber in which a rare earth element is added to the core. Method.

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