JP3514289B2 - Method of manufacturing optical fiber having enlarged mode field diameter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber having a mode field diameter enlarged portion, and more particularly,
The present invention relates to a method for manufacturing an optical fiber having a mode field diameter enlarged portion for facilitating optical coupling with an optical component such as a light emitting element or an optical fiber.

[0002]

2. Description of the Related Art An optical fiber communication network is constructed by connecting a plurality of optical fibers. Further, in a long-distance optical fiber communication network, an optical amplifier may be provided in the middle of the communication network to compensate for the attenuation of light generated in the propagation process. An optical fiber used inside an optical amplifier usually has characteristics different from those of an optical fiber forming a communication network. In this case, a connection portion of optical fibers having different characteristics is formed inside the optical amplifier.

Some of the characteristics of the optical fiber can be grasped from the mode field diameter. The mode field diameter is a diameter of a region in the optical fiber where a light intensity satisfying a predetermined condition is obtained. At the connecting portion of the optical fibers, the mode mismatch loss is likely to occur as the mode field diameters of the connected optical fibers differ. Therefore, if optical fibers having different mode field diameters are connected to each other inside the optical amplifier, an optical signal is attenuated at the connection portion, which is not preferable for obtaining a large gain.

A pump laser diode module is used in the optical amplifier. Some pump laser diodes used in this pump laser diode module emit an elliptical beam.
Since an ordinary optical fiber has an axially symmetrical shape, a circular beam propagates instead of an ellipse. Therefore, when a pump laser diode that emits an elliptical beam and an optical fiber are coupled to each other, the beam shape is different, and thus mode mismatch loss occurs. In the optical amplifier, it is desired that the amplification factor, that is, the gain is large, and the optical output power of the pump laser diode module is large. As described above, when the mode mismatch loss between the pump laser diode and the optical fiber is large, the pump laser diode must be driven with a large current in order to increase the optical output of the pump laser diode module. As a result, there is a problem that the life of the pump laser diode is shortened. Also in this case,
There is also a problem that the power consumption of the optical amplifier increases.
Therefore, it is necessary to form a connecting portion that can efficiently take in the light of the pump laser diode into the optical fiber.

As a technique to meet the above-mentioned problems and requirements, there is known a technique for connecting optical fibers after enlarging the mode field diameter of the optical fibers. For example, "as a circuit element for hybrid integration
Characteristics of TEC Fiber "(IEICE Technical Report OPE
96-125, 1996, Ohtera et al.), A TEC (Thermally-Ex) machined to have the same mode field diameter at the ends.
It is disclosed that the loss of the connecting portion of the optical fiber can be effectively reduced by using the panded core) fiber.

The TEC fiber is an optical fiber in which a mode field diameter enlarged portion is formed by heating a predetermined portion of the optical fiber and diffusing a refractive index control dopant contained in the core of the predetermined portion. Is. above
According to the TEC fiber, an optical fiber having a mode field enlarged portion at its end can be obtained by cutting the mode field enlarged portion. And like this
By using the TEC fiber for one or both of the optical fibers to be connected, the mode field diameters of the two optical fibers can be made to substantially match at the connecting portion.

In addition, "980 nm using a constant polarization TEC fiber
"Coupling system of band pump LD module" (1997 Society of Shinkai Society C-3-102, Yamaguchi et al.) Has demonstrated that 980 nm band pump LD (laser diode) module and high efficiency by heat treatment of polarization maintaining fiber. It is disclosed that an optical fiber that can be optically coupled is obtained. The polarization-maintaining fiber is an optical fiber having a stress generating axis on each of both side surfaces of the core. The 980 nm band pump LD is an LD that emits an elliptical beam.

In the polarization maintaining fiber, the dopant contained in the core and the dopant in the stress generating axis are
The heat treatment causes thermal diffusion, and the region having a high refractive index has an elliptical shape. Therefore, heat treatment of the polarization-maintaining fiber has a mode field suitable for efficiently receiving the elliptical beam.
TEC fiber can be obtained.

As described above, the mode field diameter of the optical fiber can be expanded to an appropriate size and an appropriate shape by subjecting a predetermined portion of the optical fiber to heat treatment. When the mode field diameter is increased by such a method, the accuracy of the mode field diameter after the expansion is greatly influenced by the execution time of the heat treatment and the like.

A method of subjecting an optical fiber to an appropriate heat treatment is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-98203. FIG. 15 shows a block diagram of a system for implementing the method disclosed in the above publication. As shown in FIG. 15, the conventional system includes a light source 10. The light source 10 is provided with a connector 12. One end of an optical fiber 14 is connected to the connector 12. The light source 10 supplies predetermined light to the optical fiber 14 from one end thereof.

The conventional system includes a light output measuring section 16. A connector 18 is provided in the light output measuring unit 16. The other end of the optical fiber 14 is connected to the connector 18. The optical output measuring unit 16 includes a connector 18
The output of the light emitted from the other end of can be detected.

The conventional system also includes a pair of gas burners 20, 22 arranged in place. A heating controller 24 is connected to the gas burners 20 and 22. Further, the light output measuring unit 16 is connected to the heating control unit 24. The heating control unit 24 receives the output signal MS representing the output of the emitted light from the optical output measuring unit 16, and
The stop signal ST is supplied to the gas burners 20 and 22 at a predetermined timing.

In the conventional system, the optical fiber 14
Is set so that the predetermined portion 25 thereof is located within the flame reaching range of the gas burners 20 and 22. When the above-mentioned setting is completed, a predetermined light is made incident on the optical fiber 14 from the light source 10, and the output of the emitted light is measured by the light output measuring section 16, while the heating process of the predetermined portion 25 by the gas burners 20, 22 is started. To be done.

The intensity and distribution of the light passing through the predetermined portion 25 are such that the distribution of the dopant contained therein changes as the predetermined portion 25 is heated, that is, the mode field diameter at the predetermined portion 25 is changed. It changes by changing. Therefore, the output of the emitted light reaching the light output measuring unit 16 also changes as the heating process of the predetermined portion 25 progresses.

The heating control section 24 stores an output signal MS obtained when the state of the predetermined portion 25 is in a desired state. When the output signal MS supplied from the optical output measuring unit 16 matches the stored value, the gas burners 20, 22
The stop signal ST is output to. Gas burner 20,22
Stops the heating process of the optical fiber 14 immediately after receiving the stop signal ST. According to the above process, the execution period of the heating process can be accurately controlled so that the predetermined portion 25 is in a desired state.

[0016]

By the way, in the predetermined portion 25 of the optical fiber 14, the propagation mode of the optical signal is caused by the diffusion of the dopant accompanying the execution of the heat treatment, and hence the fundamental wave (hereinafter, referred to as a single mode component). There is a case where a single mode that propagates only (referred to as) propagates to a multimode that involves the propagation of a higher-order wave (hereinafter, referred to as a multimode component). Therefore, in the above-described conventional system, the light that has passed through the predetermined portion 25 in the multimode may reach the optical output measuring unit 16 during the heat treatment of the optical fiber 14.

When the predetermined portion 25 is cut and used as a connecting portion with another optical fiber, the predetermined portion 25 is processed so as to exhibit desired characteristics when propagating light in a single mode. Is desirable. Therefore, the predetermined portion 25
In order to accurately process the workpiece into the desired state,
It is appropriate to control the execution period of the heat treatment based on the output of light passing through 5 in the single mode.

The multimode component propagating in the optical fiber 14 has a characteristic that the curved the optical fiber 14 is, the more easily it is attenuated, that is, the characteristic that it is difficult to propagate. Therefore,
In order to process the predetermined portion 25 into a desired state with high accuracy, the multi-mode component that has passed through the predetermined portion 25 is almost completely removed under constant conditions before reaching the optical output measurement unit 16. It is desirable that the heat treatment of the optical fiber 14 be performed under the circumstances.

However, in the above-mentioned conventional system, the heat treatment of the predetermined portion 25 is executed without strictly controlling the extension path of the optical fiber 14. More specifically, in the above-mentioned conventional system, a measure for removing the multimode component generated in the predetermined portion 25 before reaching the optical output measurement unit 16, and the multimode component reaching the optical output measurement unit 16 No measures have been taken to stabilize the impact of the.

Therefore, in the conventional system, after the heat treatment of the optical fiber 14 is started, the sum of the outputs of the multi-mode component and the single-mode component passing through the predetermined portion 25 matches the predetermined value. In this case, the heat treatment is terminated, and as a result, a situation may occur in which desired characteristics cannot be imparted to the predetermined portion 25. As described above, the above-mentioned conventional system is not necessarily an optimum system for manufacturing an optical fiber having a mode field diameter enlarged portion showing stable characteristics with a high yield.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method capable of producing an optical fiber having a mode field diameter enlarged portion showing stable characteristics with a high yield. And

[0022]

According to a first aspect of the present invention, there is provided a method of manufacturing an optical fiber having a mode field diameter enlarging portion, in which a predetermined light is incident on an incident surface formed by one end surface of the optical fiber. An incident step, a light output detection step of detecting an output of light emitted from an emission surface composed of the other end surface of the optical fiber, a predetermined portion where a mode field diameter enlarged portion is formed, and the emission surface. in between, multimode
A winding part forming step of forming a winding part of a predetermined shape by winding at least one turn of the optical fiber so that the optical component can be almost completely removed ; and the exit surface passing through the winding part. A heating step of heating the predetermined portion until the output of light emitted from the device reaches a desired value.

According to a second aspect of the present invention, there is provided a method for manufacturing an optical fiber having a mode field diameter enlarged portion, wherein a step of injecting predetermined light into an incident surface constituted by one end surface of the optical fiber, The optical output detection step of detecting the output of the light emitted from the emission surface composed of the other end surface of the fiber, the predetermined portion where the mode field diameter enlarged portion is formed, and the emission surface, the optical fiber Has a diameter of 1 cm
A step of forming a curved portion that is curved to have a predetermined shape with a curvature of 10 cm or less, and the predetermined value until the output of the light passing through the curved portion and emitted from the emission surface reaches a desired value. And a heating step of heating the part.

A method of manufacturing an optical fiber having a mode field diameter enlarged portion according to a third aspect of the present invention comprises an optical fiber cutting step of cutting the predetermined portion after the heating step.

According to a fourth aspect of the present invention, in the method for manufacturing an optical fiber having a mode field diameter enlarged portion, the light incident step uses the laser diode module or the light emitting diode module as a light source to apply the predetermined light to the incident surface. It is incident.

According to a fifth aspect of the present invention, in a method of manufacturing an optical fiber having a mode field diameter enlarged portion, a light source for making the predetermined light incident on the incident surface and an output of light emitted from the emitting surface are provided. Between the output detection unit to detect,
An optical isolator that allows only the flow of light from the incident surface to the exit surface is provided.

According to a sixth aspect of the present invention, in the method of manufacturing an optical fiber having a mode field diameter enlarged portion, the emitting surface is inclined with respect to the axial direction of the optical fiber in the vicinity of the emitting surface. Is.

According to a seventh aspect of the present invention, in the method of manufacturing an optical fiber having a mode field diameter enlarged portion, a refractive index adjusting member having a refractive index substantially equal to that of the optical fiber is arranged on the exit surface. It is a thing.

According to the eighth aspect of the present invention, in the method of manufacturing an optical fiber having a mode field diameter enlarging portion, the optical fiber is a single mode fiber or a polarization maintaining fiber.

According to a ninth aspect of the present invention, in the method of manufacturing an optical fiber having a mode field diameter enlarged portion, the optical fiber comprises a first optical fiber having a first mode field diameter, and the first mode field. A second optical fiber having a second mode field diameter larger than the diameter, the first optical fiber and the second optical fiber having their one end surfaces in contact with each other, and The optical fiber arranging step is arranged so that the vicinity of these contact portions forms the predetermined portion.

According to a tenth aspect of the present invention, in the method of manufacturing an optical fiber having a mode field diameter enlarged portion, in the winding portion forming step or the bending portion forming step, the optical fiber is attached to a side surface of a predetermined circular member. And a molding step of deforming along.

According to the eleventh aspect of the present invention, in the method of manufacturing an optical fiber having a mode field diameter enlarged portion, the heating step heats the predetermined portion by using a burner or a heater as a heat source.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding portions.

Embodiment 1. 1 is a conceptual diagram of a system for carrying out a method of manufacturing an optical fiber having a mode field diameter enlarged portion according to a first embodiment of the present invention. The system shown in FIG. 1 includes a light source 30. The light source 30 is
It is realized by a known laser diode module or the like.

One end of an optical fiber 32 is connected to the light source 30. Hereinafter, this end surface will be referred to as the incident surface 33 of the optical fiber 32. The optical fiber 32 is an optical fiber that propagates an optical signal in a single mode, that is, a single mode fiber. In this embodiment, the optical fiber 32
Is made of quartz having a diameter of 125 μm as a base material. Further, in the center of the optical fiber 32, a core whose refractive index is higher than that of the clad by about 0.5% and has a diameter of about 10 μm is formed.

The system of the present embodiment has a light output measuring unit 3
It is equipped with 4. The optical output measuring unit 34 includes an optical fiber 3
The other end of 2 is connected. Hereinafter, this end face is referred to as the emission face 36 of the optical fiber 32. The optical output measuring unit 34 measures the output of the light emitted from the emitting surface 36 of the optical fiber 32 and outputs a signal P representing the output.

A heating control unit 38 is connected to the light output measuring unit 34. Further, the heating controller 38 includes a burner 40.
Are connected. The heating control unit 38 uses the optical fiber 32.
When the heating command is issued to the burner 40 when the heating process is required, and the signal P supplied from the optical output measuring unit 34 reaches a predetermined value after the heating process by the burner 40 is started. Then, the fire extinguishing command is issued to the burner 40.

The burner 40 has a predetermined portion 4 of the fiber 32.
2 is arranged at a position where it can be heated. Predetermined part 42
Is the position in the optical fiber 32 where the mode field diameter should be increased. In the present embodiment, the path through which the optical fiber 32 extends from the predetermined portion 42 to the light output measuring unit 34 is set to the predetermined path. Further, a winding part 44 formed of a part of the optical fiber 32 is provided between the predetermined portion 42 and the light output measuring part 34.

The winding portion 44 is provided by winding the optical fiber 32 at least once to form a predetermined shape. In the present embodiment, the winding portion 44 is specifically provided by winding the optical fiber 32 twice so that an annular shape having a predetermined radius of curvature is formed.

Next, with reference to FIG. 2, a method of manufacturing the optical fiber having the mode field diameter enlarged portion of the present embodiment will be specifically described. FIG. 2 is a flowchart showing a series of processes executed in the manufacturing method of this embodiment. Figure 2
The series of processes shown in (1) is started from the process of step 50.

In step 50, the process of setting the optical fiber 32 to the state shown in FIG. 1 is executed. In this step 50, specifically, the winding section 4 is wound around the optical fiber 32.
4 is formed, and the process of connecting the entrance surface 33 and the exit surface 36 of the optical fiber 32 to the light source 30 and the light output measurement unit 34, respectively, is executed.

In step 52, the light source 30 is turned on. When the process of step 52 is executed, a predetermined optical signal starts to be supplied to the optical fiber 32 from the incident surface 33.

In step 54, the light output measuring section 34 starts measuring the output of the light emitted from the emitting surface 36.

In step 56, by issuing an ignition command to the burner 40, the burner 40 starts the heating process of the predetermined portion 42.

At step 58, it is judged if the output measured by the light output measuring unit 34 matches the desired value. The process of step 58 is specifically executed by the heating control unit 38 shown in FIG. Optical fiber 3
When the heat treatment is applied to the predetermined portion 42 of FIG.
Diffusion of the dopant occurs inside 2 to increase the mode field diameter. The output of the light reaching the emission surface of the optical fiber 32 changes with the change of the mode field diameter of the predetermined portion 42. Therefore, by monitoring the output of the light that appears on the emission surface, the size of the mode field diameter in the predetermined portion 42 can be detected to some extent.

In the present embodiment, the heating control section 38 stores in advance the optical output corresponding to the mode field diameter to be secured in the predetermined portion 42 by performing the heating process as the above-mentioned desired value. Therefore, when it is determined that the condition of step 58 is satisfied, it can be determined that the mode field diameter of the predetermined portion 42 is expanded to a desired size. When such a determination is made in step 56, the process of step 60 is executed next.

In step 60, a process of ending the heating process of the predetermined portion 42 by the burner 40 is executed. The process of step 60 is specifically realized by the heating control unit 38 issuing a fire extinguishing command to the burner 40. According to the above process, the heating process can be ended when the mode field diameter of the predetermined portion 42 reaches a desired size. Therefore, according to the above process, the optical fiber 32 having a desired mode field diameter can be obtained in the predetermined portion 42.

In step 62, a process of cutting the optical fiber 32 at the predetermined portion 42 is executed. According to the above-mentioned processing, the optical fiber 32 having the part where the mode field diameter is enlarged (mode field diameter enlarged portion) on one end face
Can be obtained. Therefore, with the optical fiber 32 manufactured by the above method, it is possible to realize highly efficient optical coupling with an optical fiber having a mode field diameter larger than the mode field diameter before expansion.

As described above, the optical fiber 32 used in this embodiment has a characteristic of propagating an optical signal in a single mode (a mode in which only a single mode component is propagated). When the predetermined part 42 of the optical fiber 32 is used as a connection part with another optical fiber after the heat treatment, it is desirable that the predetermined part 42 propagates an optical signal in a single mode.

As described above, in the manufacturing method of this embodiment,
When the output of the light appearing on the emission surface of the optical fiber 32 matches a preset desired value, it is determined that the desired mode field diameter is secured in the predetermined portion 42. Here, the above-mentioned desired value is, specifically,
The predetermined portion 42 has a desired mode field diameter and is set to output light that appears on the emission surface 36 when an optical signal is propagated in a single mode.

By the way, the propagation mode of the optical signal in the predetermined portion 42 changes from single mode to multimode (multimode together with the single mode component when the mode field diameter is expanded due to the heat treatment, as the mode field diameter increases. It may change to a mode in which the mode component is propagated). In such a case, when a multimode component that is not propagated in the single mode reaches the emission surface 36, the sum of the outputs of the single mode component and the multimode component may match a desired value.

In the system of this embodiment, when the above condition occurs, the heating control unit 38 determines that the mode field diameter of the predetermined portion 42 has been expanded to a desired size at that time, and the heating process is ended. . In this case, an optical fiber having a mode field diameter enlarged portion that does not satisfy the condition for propagating an optical signal in a single mode (single mode condition) is manufactured.

As described above, in the manufacturing method of this embodiment, when the heating control unit 38 controls the end timing of the heating control based on the sum of the outputs of the single mode component and the multimode component, the predetermined portion 42 is appropriate. It is difficult to manufacture an optical fiber having excellent characteristics with a high yield. In order to avoid the above-mentioned inconvenience, the manufacturing method of the present embodiment has a condition in which the multimode component is always kept constant in the path connecting the predetermined portion 42 and the optical output measurement unit 34 during the heating process of the optical fiber 32. The feature is that it is almost completely removed by.

The above-mentioned characteristic portion will be described below with reference to FIG. FIGS. 3A to 3D are intensity distributions of light propagating in the optical fiber 32 at the portions shown by adding (A) to (D) in FIG. 1, that is, the optical fiber 32, respectively. The figure which shows the intensity | strength of the light which propagates | transmits the inside is shown with the distance from the center part of a core.

The light source 30 makes a predetermined optical signal incident on the incident surface of the optical fiber 32. The optical fiber 32 propagates the optical signal in a single mode. When the optical signal propagates in the single mode, the light intensity is as shown in FIG.
The shape is the strongest in the central part of the core, and becomes a shape (Gaussian shape) that decreases with distance from the center.

The light having the intensity distribution shown in FIG. 3A is propagated to the predetermined portion 42. The intensity distribution of the optical signal is
As the mode field diameter increases, it tends to expand in the width direction. In addition, the propagation mode of the optical signal is likely to shift from the single mode to the multi mode as the mode field diameter increases.

FIG. 3B shows the intensity distribution obtained when the mode field diameter of the predetermined portion 42 is appropriately enlarged. When the mode field diameter of the predetermined portion 42 is appropriately expanded, the intensity distribution of the optical signal is wider than the distribution shown in FIG. 3 (A) by the width method, as shown in FIG. 3 (B). Becomes

FIG. 3C shows the intensity distribution obtained when the propagation mode of the predetermined portion 42 shifts to the multimode. When the propagation mode of the optical signal shifts to multi-mode,
Due to the multimode component, strong intensity appears at a position away from the center of the core. Therefore, when the optical signal transits to the propagation mode multimode, the intensity distribution having the side lobes 64 is obtained as shown in FIG.

The light having the intensity distribution shown in FIG. 3 (B) or (C) is propagated from the predetermined portion 42 toward the winding portion 44. The optical fiber 32 has a normal mode field diameter in the portion extending from the predetermined portion 42 to the winding portion 44 side. Therefore, the multimode components (waves forming the side lobes 64 shown in FIG. 3C) generated at the predetermined portion 42 pass through the predetermined portion 42 and then the optical fiber 3
Propagate in the region including the cladding in 2.

When the optical fiber 32 is curved, the multimode component propagating in such a region is easily emitted to the outside from the clad and is easily attenuated. As mentioned above
The winding portion 44 is formed in a predetermined ring shape by winding the optical fiber 32 at least once. When an optical signal having the intensity distribution shown in FIG. 3C is incident on the winding section 44, the multimode component from the optical signal is always constant while the optical signal propagates through the winding section 44. It can be removed almost completely under the conditions of.

FIG. 3D shows the intensity distribution obtained inside the optical fiber 32 after passing through the winding portion 44. As described above, the winding unit 44 can almost completely remove the multimode component contained in the optical signal. Therefore, regardless of whether the predetermined portion 42 propagates the optical signal in the single mode or the multimode in the path extending from the winding unit 44 to the optical output measuring unit 34. As shown in FIG. 3D, a Gaussian-shaped intensity distribution having a large intensity always appears at the center of the core.

Therefore, according to the manufacturing method of the present embodiment, even when the predetermined portion 42 propagates the optical signal in the multimode, the single mode which should be always propagated in the single mode to the optical output measuring section 34. Only ingredients can be reached. Therefore, according to the manufacturing method of the present embodiment, the optical fiber 3 is always provided at the time when the predetermined portion 42 is in the state of passing the light of the predetermined output in the single mode.
The heat treatment of 2 can be completed.

As a result, according to the manufacturing method of the present embodiment, the mode field diameter enlarging portion realized by the predetermined portion 42 has a desired characteristic, that is, high efficiency with another optical fiber of a different type. An optical fiber having suitable characteristics for realizing optical coupling can be manufactured with a high yield.

In the above embodiment, the optical fiber 3
The burner 40 is used as a heat source for heat-treating 2. According to the burner 40, a large amount of heat is generated and the required heat treatment can be completed in a short time. When the heat treatment time is shortened, the productivity of the optical fiber having the mode field diameter enlarged portion is improved. In this respect, the manufacturing method of the present embodiment has excellent characteristics in manufacturing the above optical fiber at low cost.

As described above, using the burner 40 as a heat source is effective in inexpensively manufacturing an optical fiber having a mode field diameter enlarged portion. However, in the present invention, the heat source for the heat treatment is not limited to the burner 40, and the above heat source can be realized by an electric heater. According to the heater, it is possible to obtain excellent control accuracy regarding the control of the heat generation amount.
Therefore, by using the heater as the heat source of the heat treatment, it is possible to suppress the variation in the heat treatment and further increase the yield of the optical fibers having appropriate characteristics.

Further, in the above embodiment, the laser diode module is used as the light source for making the light incident on the optical fiber 32, but the present invention is not limited to this, and the above light source may emit light, for example. It may be configured with a diode module. These modules have the property of producing a stable output over time. Therefore, when these modules are used as a light source, it is possible to realize a suitable state for manufacturing an optical fiber having a mode field expansion portion showing desired characteristics with a high yield.

In the above embodiment, the heat treatment of the predetermined portion 42 is continued until the output of the light emitted from the optical fiber 32 reaches a desired value.
The present invention is not limited to this, and for example, when a desired output is not obtained within a preset time, the heat treatment may be terminated at that time.
Further, in the above embodiment, the specifications of the optical fiber 32 are defined as an example, but the application of the present invention is not limited to this.

In the above embodiment, the "light incident step" according to claim 1 is performed by the step 52.
However, the "light output detecting step" according to claim 1 is performed by the steps 54 and 58, the "winding portion forming step" according to the claim 1 is performed by the step 50, and the light output detecting step is performed by the steps 56, 58 and 60. The "heating step" described in claim 1 is realized. Further, in the above embodiment, the step 62 realizes the "optical fiber cutting step".

Embodiment 2. Next, a second embodiment of the present invention will be described with reference to FIGS. 4 and 5. In the first embodiment described above, the optical fiber 32 is composed of a single mode fiber. The manufacturing method of this embodiment is realized by changing the optical fiber 32 shown in FIG. 1 to the polarization maintaining fiber 70.

FIG. 4 shows a sectional view of the polarization maintaining fiber 70. The polarization maintaining fiber 70 includes a core 72 and a clad 74 that are made of quartz as a base material, and stress generating members 76 and 78 are provided on both sides of the core 72. The stress generating members 76 and 78 generate stress that compresses the core 72 in the left-right direction in FIG. 4 due to the difference in coefficient of linear expansion from quartz. Hereinafter, the direction parallel to the stress direction (left-right direction in FIG. 4) is called the slow axis direction, and the direction perpendicular to the stress direction (up-down direction in FIG. 4) is called the fast direction.

When the above-mentioned stress acts on the core 72, the core 72 exhibits different refractive indexes in the fast axis direction and the slow axis direction. When the refractive index of the core 72 has such a directivity, when light propagates inside the core 72, the polarization direction of the light is maintained in one direction without rotating. Therefore, according to the polarization maintaining fiber 70, the optical signal can be propagated while maintaining the polarization direction in one direction.

FIG. 5 shows a cross section of the polarization maintaining fiber 70 which has been subjected to the heat treatment. When the polarization maintaining fiber 70 is heat-treated, the dopants added to the core 72 and the stress generating shafts 76 and 78 are thermally diffused, respectively. As a result, in the slow axis, the dopant of the core 72 and the stress generating axis 76,
The dopant of 78 diffuses and the area | region where both dopants overlap is obtained. In this region, the function of increasing the refractive index of the dopant of the core 72 is weakened by the dopants of the stress generation axes 76 and 78, so that a refractive index distribution is formed in the slow axis direction that is almost the same as that before the heat treatment. On the other hand, in the fast axis direction, since there are no stress generating axes 76 and 78, only the dopant added to the core 72 diffuses, and the refractive index distribution obtained is wider than that before the thermal diffusion. Therefore, after thermal diffusion, an elliptical shape is obtained as the shape of the region having a high refractive index. Therefore, according to the polarization maintaining fiber 70, by performing an appropriate heat treatment,
And as shown in FIG. 5, the mode field can be changed from circular to elliptical.

In the system shown in FIG. 1, when the optical fiber 32 is changed to the polarization maintaining fiber 70 and the series of processing shown in FIG. 2 is executed, an appropriate heating process is performed on a predetermined portion of the polarization maintaining fiber 70. Can be given. Therefore, according to the manufacturing method of the present embodiment, it is possible to manufacture, with a high yield, an optical fiber having an end face, which is expanded in an elliptical shape and which has a mode field that satisfies the single mode condition. With such an optical fiber, optical coupling with high efficiency can be realized with a light source that outputs an elliptical beam, such as a 980 nm band pump LD or a 1010 nm band pump LD.

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 3 shows a side view of the circular member 80 used in the manufacturing method of the present embodiment. The circular member 80 is a member having a circular cross section. The manufacturing method of the present embodiment is realized by winding the optical fiber 32 around the circular member 80 to form the winding portion 44 shown in FIG.

In the system shown in FIG. 1, in order to always remove the multimode component from the light passing through the predetermined portion 42 under a constant condition, the path of the optical fiber 32 from the predetermined portion 42 to the optical output detecting section 34. Must be a fixed route. In particular, the shape of the winding portion 44 is an important portion for removing the multimode component. Therefore, in order to remove the multimode component under a constant condition, it is important to make the shapes uniform.

As in the manufacturing method of this embodiment, by forming the winding portion 44 by winding the optical fiber 32 around the circular member, the winding portion 44 having a constant shape.
Can be easily formed. Therefore, according to the manufacturing method of the present embodiment, it is possible to easily manufacture an optical fiber in which the mode field diameter enlarged portion has desired characteristics with a high yield.

Fourth Embodiment Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 7 shows a main part of a system for carrying out the manufacturing method of the present embodiment. In FIG. 7, the same parts as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In the manufacturing method of this embodiment, as shown in FIG. 7, the manufacturing method of Embodiment 1 is performed with the curved portion 90 of the optical fiber 32 formed in the path from the predetermined portion 42 to the optical output measuring portion 34. It is realized by executing a process similar to the method. The curved portion 90 connects the optical fiber 32 to the circular member 9
It is formed by deforming along the side surface of 2. The circular member 92 is a member having a circular cross section with a diameter of 1 cm or more and 10 cm or less.

According to the manufacturing method of this embodiment, the bending portion 9
0 can be molded into a constant shape with a curvature of 1 cm or more and 10 cm or less. The optical fiber 32 is realized by forming a core having a diameter of about 10 μm in quartz having a diameter of 125 μm as described above. When the optical fiber 32 having such specifications is curved with a curvature of 10 cm or less in diameter, the multimode component contained in the optical signal is efficiently removed when the optical signal passes through the curved portion. . Further, according to the above-mentioned optical fiber 32, by securing the diameter of curvature to 1 cm or more, it is possible to reliably prevent local bending.

Therefore, according to the manufacturing method of the present embodiment, when the predetermined portion 42 propagates the optical signal in the multimode, the multimode component contained in the optical signal is always kept constant by the bending portion 90. Can be removed efficiently. Under such conditions, it is possible to manufacture an optical fiber in which the mode field enlarged diameter portion has desired characteristics with a high yield.

In the above embodiment, the curved portion 90 is formed by bending the optical fiber 32,
The "curved portion forming step" described in claim 2 is realized.

Embodiment 5. Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 8 shows a main part of a system for carrying out the manufacturing method of the present embodiment. In FIG. 8, the same parts as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In the manufacturing method of this embodiment, as shown in FIG. 8, the manufacturing of Embodiment 1 is performed with the curved portion 100 of the optical fiber 32 formed in the path from the predetermined portion 42 to the light output measuring portion 34. It is realized by executing a process similar to the method. The bending portion 100 is formed by hooking the optical fiber 32 on the hooking pin 102 to bend the optical fiber 32. The latch pin 102 is sufficiently smaller than 10 cm, and has a diameter equal to or larger than the minimum diameter that allows the optical fiber 32 to bend without bending.

According to the manufacturing method of this embodiment, it is possible to easily form the curved portion 100 having a diameter sufficiently smaller than 10 cm and curved in a constant shape. With such a curved portion 100, the multimode component of the optical signal propagating inside the optical fiber 32 can be almost completely removed.

Therefore, according to the manufacturing method of the present embodiment, when the predetermined portion 42 propagates the optical signal in the multimode, the multimode component contained in the optical signal is always kept constant by the bending portion 100. Can be removed almost completely with. Under such conditions, it is possible to manufacture an optical fiber in which the mode field enlarged diameter portion has desired characteristics with a high yield.

In the above embodiment, the bending portion 100 is formed by bending the optical fiber 32 to achieve the "bending portion forming step". Further, in the above embodiment, the latch pin 100 corresponds to the “circular member” in claim 10.

Sixth Embodiment Next, a sixth embodiment of the invention will be described with reference to FIG. FIG. 9 shows a configuration diagram of a system for carrying out the manufacturing method of the present embodiment.
Note that, of the constituent parts shown in FIG. 9, the same parts as those shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

The system shown in FIG. 9 is characterized in that an optical isolator 110 is provided between the light source 30 and the light output measuring section 34. The optical isolator 110 includes the light source 30.
Has a function of allowing the flow of light from the optical output measuring unit 34 toward the optical output measuring unit 34 and blocking the light flowing in the opposite direction.

A part of the light that has propagated through the optical fiber 32 and reaches the emission surface 36 is reflected by the emission surface 36, and thus travels backward in the optical fiber 32 toward the light source 30. When such reflected light reaches the light source 30, the light source 3
The output stability of 0 may be impaired.

In the system of this embodiment, the optical isolator 110 surely blocks the above-mentioned reflected light from proceeding toward the light source 30. Therefore, in the system of the present embodiment, the light source 30 always maintains a stable output characteristic without being affected by the reflected light. Light source 30
When a stable output characteristic is maintained, 2
On the other hand, stable heat treatment can be performed. Therefore, according to the manufacturing method of the present embodiment, it is possible to manufacture an optical fiber in which the mode field diameter enlarged portion has desired characteristics with a high yield.

Seventh Embodiment Next, referring to FIG.
A seventh embodiment of the present invention will be described. FIG. 10 shows an enlarged view of the vicinity of the emission surface 122 of the optical fiber 120 used in this embodiment. In this embodiment, the optical fiber 120 shown in FIG. 10 is subjected to heat treatment by the same method as in the above-described first embodiment.

The emission surface 122 of the optical fiber 120 is shown in FIG.
As shown in 0, it is inclined with respect to the axial direction of the optical fiber 120. When the emission surface 122 is inclined in this way,
The traveling direction of the reflected light generated on the emission surface 122 can be largely deviated from the axial direction of the optical fiber 120. In this case, the components of the reflected light generated on the emission surface 122 that reach the light source 30 are sufficiently suppressed. Therefore, according to the manufacturing method of the present embodiment, as in the case of the sixth embodiment,
It is possible to manufacture an optical fiber in which the mode field diameter enlarged portion has desired characteristics with a high yield.

Eighth Embodiment Next, referring to FIG.
Embodiment 8 of the present invention will be described. FIG. 11 shows an enlarged view of the vicinity of the emission surface 132 of the optical fiber 130 used in this embodiment. In the present embodiment, the optical fiber 130 shown in FIG. 11 is heat-treated by the same method as in the above-described first embodiment.

The exit surface 132 of the optical fiber 130 is shown in FIG.
As shown in FIG. 1, it is covered with a refractive index adjusting member 134. The refractive index adjusting member 134 has a refractive index substantially equal to the refractive index of the optical fiber 120. The surface of the refractive index adjusting member 134 is formed into an appropriate curved surface.

The light propagating inside the optical fiber 130 enters the refractive index adjusting member 134 without being reflected by the emitting surface 132. When the light reaches the surface of the refractive index adjusting member 134, part of the light is reflected light. Most of the light reflected on the surface of the refractive index adjusting member 134 travels in a direction largely deviated from the axial direction of the optical fiber 130. In this case, the component of the reflected light that reaches the light source 30 through the optical fiber 130 is sufficiently suppressed. Therefore, according to the manufacturing method of the present embodiment, as in the case of Embodiments 6 and 7, it is possible to manufacture an optical fiber in which the mode field diameter enlarged portion exhibits desired characteristics with a high yield.

Ninth Embodiment Next, a ninth embodiment of the present invention will be described with reference to FIGS. FIG. 12 shows an enlarged view of the first optical fiber 140 and the second optical fiber 142 used in this embodiment. The contact portion 144 of the first optical fiber 140 and the second optical fiber 142 is previously fused.
In the present embodiment, the contact portion 144 is subjected to heat treatment by the same method as in the above-described first embodiment.

FIG. 13 shows a sectional view of the first optical fiber 140. The first optical fiber 140 includes a core 146 and a clad 148. The core 146 is provided in the center of the first optical fiber 140 in a substantially circular shape. FIG. 14 shows a cross-sectional view of the second optical fiber 142. The second optical fiber 142 includes a core 150 and a clad 152. The core 150 is provided in the central portion of the second optical fiber 142 in an elliptical shape and has a larger area than the core 146 of the first optical fiber 140.

The contact portion 14 is manufactured by the manufacturing method of the present embodiment.
When the heat treatment is applied to No. 4, in the vicinity of the contact portion 144,
A dopant added to the first optical fiber 140,
And, the dopant added to the second optical fiber 142 also diffuses to the other optical fiber of each other. As a result, after the appropriate heat treatment, a core having an intermediate shape between the core 146 and the core 150 is formed at the contact portion 144.

In the manufacturing method of this embodiment, the contact portion 1
The heat treatment of 44 is performed while monitoring the output of the single mode component passing through the contact portion 144, as in the case of each of the above-described embodiments. Therefore, according to the manufacturing method of the present embodiment, the core 146 and the core 15 are provided in the contact portion 144.
It is possible to manufacture a mode field diameter enlarged portion having an intermediate shape of 0 and having desired characteristics with a high yield.

According to the manufacturing method of this embodiment, the first
By using the optical fiber 140 and the second optical fiber 142 connected to each other, it is possible to obtain an effect that optical coupling with high efficiency can be realized between different kinds of optical fibers. Further, the first optical fiber 14
By cutting 0 and the second optical fiber 142, an optical fiber provided on an end face suitable for obtaining efficient optical coupling between different types of optical fibers and light sources that output elliptical beams. Can be obtained.

By the way, in the above embodiment, the first optical fiber 140 and the second optical fiber 142 are fused beforehand, and then the heat treatment for expanding the mode field diameter is performed. The present invention is not limited to this, and it is also possible to realize fusion of both and expansion of the mode field diameter by one heat treatment.

In the above embodiment, the first optical fiber 140 and the second optical fiber 142 have cores having different shapes, but the application of the present invention is not limited to this. However, the present invention may be applied to the case where the optical fibers have cores having the same shape but different sizes.

In the above embodiment, the first optical fiber 140 and the second optical fiber 142 are connected to the contact portion 1.
10. The optical fiber of claim 9, wherein the first optical fiber 140 and the second optical fiber 142 are properly positioned so that the contact portion 144 can be heated by the burner 40 after fusion at 44. "Placement step" has been realized.

[0104]

Since the present invention is constructed as described above, it has the following effects. Claim 1
According to the described invention, since the winding portion having a predetermined shape is formed between the predetermined portion of the optical fiber and the emission surface, the multimode component passing through the predetermined portion during the heat treatment is always kept under constant conditions. , Can be almost completely removed. Therefore, according to the present invention, it is possible to manufacture an optical fiber in which the mode field diameter enlarged portion has stable characteristics with a high yield.

According to the second aspect of the present invention, since the curved portion having a predetermined shape having a curvature of 1 cm or more and 10 cm or less in diameter is formed between the predetermined portion and the emission surface, the multi-mode passing through the predetermined portion is formed. The components can be almost completely removed under constant conditions. Therefore, according to the present invention,
It is possible to manufacture an optical fiber having a stable characteristic of the mode field diameter enlarged portion with a high yield.

According to the third aspect of the invention, an optical fiber having a mode field enlarged portion on the end face can be manufactured by cutting a predetermined portion after the heating step.

According to the fourth aspect of the invention, since the laser diode module and the light emitting diode module that generate stable output with time are used as the light source, the light whose mode field diameter expanding portion has stable characteristics is used. Fibers can be manufactured with a high yield.

According to the fifth aspect of the present invention, since the optical isolator for preventing the light reflected by the emission surface of the optical fiber from propagating toward the light source is provided, the output of the light source is stabilized. Can be maintained. Therefore, according to the present invention, it is possible to manufacture an optical fiber in which the mode field diameter enlarged portion has stable characteristics with a high yield.

According to the sixth aspect of the present invention, it is possible to form a state in which the light reflected by the emitting surface is difficult to reach the light source by inclining the emitting surface of the optical fiber with respect to the axial direction of the optical fiber. Therefore, according to the present invention, it is possible to perform the heat treatment for forming the mode field diameter enlarged portion while the output of the light source is stably maintained.

According to the invention described in claim 7, since the refractive index adjusting member is disposed on the exit surface of the optical fiber, the light propagating through the optical fiber is reflected on the surface of the refractive index adjusting member. You can In this case, a state is formed in which the reflected light does not easily travel toward the light source. Therefore, according to the present invention, it is possible to perform the heat treatment for forming the mode field diameter enlarged portion while the output of the light source is stably maintained.

According to the eighth aspect of the invention, since the single-mode fiber or the polarization-maintaining fiber is used as the heat-treated optical fiber, it is possible to realize highly efficient optical coupling between the optical fibers. And an optical fiber having a mode field diameter expanding portion suitable for achieving high-efficiency optical coupling with a light source that outputs an elliptical beam. It can be manufactured with a yield.

According to the ninth aspect of the invention, the heat treatment can be applied to a predetermined portion including the contact portion between the first optical fiber having a small mode field diameter and the second optical fiber having a large mode field diameter. . In this case, the first optical fiber and the second optical fiber can be fused together,
In addition, it is possible to obtain a mode field diameter intermediate between both mode field diameters at the fused portion. For this reason,
According to the present invention, it is possible to manufacture an optical fiber having a mode field diameter enlarged portion suitable for realizing highly efficient optical coupling between different kinds of optical fibers with a high yield.

According to the tenth aspect of the present invention, since the winding portion or the curved portion is formed by deforming the optical fiber along a predetermined circular member, their shape can be easily made into a constant shape. can do. Therefore, according to the present invention, it is possible to easily realize a state in which the multimode component can be removed under the same condition.

According to the eleventh aspect of the present invention, since the burner or the heater is used as a heat source for the heat treatment, the mode field diameter enlarging portion is shortened or the heat treatment is controlled with high accuracy. Can be manufactured. Therefore, according to the present invention, an optical fiber having a mode field diameter enlarged portion is
It can be manufactured at low cost or with high yield.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a system for carrying out a manufacturing method according to a first embodiment of the present invention.

FIG. 2 is a flowchart of a series of processes executed by the manufacturing method according to the first embodiment of the present invention.

3 (A) to (D) are intensity distributions of the optical signal in (A) to (D) shown in FIG. 1, respectively.

FIG. 4 is a sectional view of a polarization maintaining fiber used in a second embodiment of the present invention.

FIG. 5 is a cross-sectional view of the polarization maintaining fiber after being processed by the manufacturing method according to the second embodiment of the present invention.

FIG. 6 is a diagram showing a main part of a system for carrying out a manufacturing method according to a third embodiment of the present invention.

FIG. 7 is a diagram showing a main part of a system for carrying out a manufacturing method according to a fourth embodiment of the present invention.

FIG. 8 is a diagram showing a main part of a system for carrying out a manufacturing method according to a fifth embodiment of the present invention.

FIG. 9 is a configuration diagram of a system for carrying out a manufacturing method according to a sixth embodiment of the present invention.

FIG. 10 is an enlarged view of the vicinity of the emission surface of the optical fiber used in the seventh embodiment of the present invention.

FIG. 11 is an enlarged view of the vicinity of the emission surface of the optical fiber used in Embodiment 8 of the present invention.

FIG. 12 is an enlarged view of a first optical fiber and a second optical fiber used in a ninth embodiment of the present invention.

13 is a sectional view of the first optical fiber shown in FIG.

FIG. 14 is a cross-sectional view of the second optical fiber shown in FIG.

FIG. 15 is a diagram for explaining a conventional method of applying heat treatment to an optical fiber.

[Explanation of symbols]

30 light source, 32; 120 optical fiber, 33 incident surface, 34 light output measuring section, 36; 122; 132 exit surface, 38 heating control section, 40 burner, 42 predetermined portion, 44 winding section, 70 polarization maintaining fiber, 80;
92 circular member, 90; 100 curved part, 100 retaining pin, 110 optical isolator, 134 refractive index adjusting member, 140 first optical fiber, 142 second optical fiber, 144 contact part.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-7-84142 (JP, A) JP-A-4-98203 (JP, A) JP-A-5-264370 (JP, A) JP-A-4- 214507 (JP, A) JP 2-112737 (JP, A) JP 3-130705 (JP, A) JP 6-222226 (JP, A) JP 58-121001 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 6/00-6/02 G02B 6/10 G02B 6/16-6/22 G02B 6/44

Claims (11)

(57) [Claims] 1. A light incident step of injecting predetermined light into an incident surface formed of one end surface of an optical fiber, and detecting an output of light emitted from an emission surface formed of the other end surface of the optical fiber. The multi-mode component is almost completely removed between the light output detection step, the predetermined portion where the mode field diameter enlarged portion is to be formed, and the emission surface.
A winding part forming step of forming at least one winding of the optical fiber so as to form a winding part having a predetermined shape, and an output of light passing through the winding part and emitted from the emission surface is A method of manufacturing an optical fiber having a mode field diameter enlarged portion, comprising: a heating step of heating the predetermined portion to a desired value. 2. A light incident step of injecting predetermined light into an incident surface formed of one end surface of the optical fiber, and an output of light emitted from an emission surface formed of the other end surface of the optical fiber is detected. The optical fiber has a diameter of 1 cm or more between the light output detecting step, a predetermined portion where the mode field diameter enlarged portion is to be formed, and the emission surface.
a curved portion forming step of forming a curved portion that is curved into a predetermined shape with a curvature of cm or less, and the predetermined portion until the output of the light passing through the curved portion and emitted from the emission surface reaches a desired value. A method of manufacturing an optical fiber having a mode field diameter enlarged portion, comprising: 3. The method of manufacturing an optical fiber having a mode field diameter enlarged portion according to claim 1, further comprising an optical fiber cutting step of cutting the predetermined portion after the heating step. 4. The mode field diameter enlarging portion according to claim 1, wherein in the light incident step, the predetermined light is incident on the incident surface using a laser diode module or a light emitting diode module as a light source. A method of manufacturing an optical fiber having the same. 5. Light traveling from the entrance surface to the exit surface between a light source that enters the predetermined light on the entrance surface and an output detection unit that detects an output of light exiting the exit surface. 5. An optical fiber having a mode field diameter enlarging portion according to claim 1, wherein an optical isolator which allows only the flow of the optical field is provided. 6. The mode field diameter enlargement according to claim 1, wherein the emission surface is inclined with respect to the axial direction of the optical fiber in the vicinity of the emission surface. Of manufacturing an optical fiber having a section. 7. A light having a mode field diameter enlarging portion according to claim 1, wherein a refractive index adjusting member having a refractive index substantially equal to that of the optical fiber is disposed on the emission surface. Fiber manufacturing method. 8. The method of manufacturing an optical fiber having a mode field diameter enlarged portion according to claim 1, wherein the optical fiber is a single mode fiber or a polarization maintaining fiber. 9. The optical fiber comprises a first optical fiber having a first mode field diameter and a second optical fiber having a second mode field diameter larger than the first mode field diameter. And the first optical fiber and the second optical fiber,
9. An optical fiber arranging step for arranging such that their one end surfaces are in contact with each other and the vicinity of these contact portions forms the predetermined portion is provided. Method for manufacturing an optical fiber having a mode field diameter enlarging portion of 1. 10. The winding step or the bending portion forming step includes a molding step of deforming the optical fiber along a side surface of a predetermined circular member. A method of manufacturing an optical fiber having a mode field diameter enlarged portion according to any one of claims. 11. The manufacturing of an optical fiber having a mode field diameter enlarged portion according to claim 1, wherein the heating step heats the predetermined portion using a burner or a heater as a heat source. Method.