JP2024011344A - Method for manufacturing optical fiber preform - Google Patents

Abstract

To provide a method for manufacturing an optical fiber preform, capable of preventing the productivity of an optical fiber from decreasing.SOLUTION: A method for manufacturing an optical fiber preform 1P comprises: an intermediate preform formation step P1 of forming an intermediate preform 1PP consisting of a core glass body 10P formed as a body part and a first glass layer 21 being a part of a clad glass body 11P formed as an outer part; and a glass layer formation step P3 of depositing glass fine particles on the outer peripheral surface of the first glass layer 21 to form a coated porous glass body and sintering the coated porous glass body to form a second glass layer 22 being an other part of the clad glass body 11P. The glass layer formation step P3 comprises depositing the glass fine particles on the outer peripheral surface of the first glass layer 21 so that the ratio of the outer diameter of the second glass layer 22 to the outer diameter of the intermediate preform 1PP is a value to be set on the basis of the refractive index distribution normally measured by a preform analyzer having a reference preform in which the profile of the refractive index distribution is similar to the profile of the refractive index distribution of the intermediate preform 1PP.SELECTED DRAWING: Figure 3

Description

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

2. Description of the Related Art As a method for manufacturing an optical fiber preform used for manufacturing an optical fiber, it is known to manufacture an optical fiber preform from an intermediate preform formed by sintering a porous glass body. In this case, for example, a coated porous glass body surrounding the outer peripheral surface of the intermediate base material is formed, and the coated porous glass body is sintered to form a glass layer surrounding the outer peripheral surface of the intermediate base material, thereby making it possible to Manufacture base material for fiber. Further, the above porous glass body and coated porous glass body are formed by depositing glass fine particles in multiple layers using an OVD method (Outside Vapor Deposition method) or a VAD method (Vapor Phase Axial Deposition method). Ru.

In such a manufacturing method, for example, the intermediate base material is composed of a core glass body serving as a core, and a first glass layer consisting of a glass body serving as a part of the cladding and surrounding the outer peripheral surface of the core glass body; The glass layer surrounding the outer peripheral surface of the base material may be a second glass layer made of a glass body that becomes another part of the cladding. In this case, before forming the coated porous glass body, the ratio of the outer diameter of the core glass body to the outer diameter of the intermediate base material is calculated based on the refractive index distribution of the intermediate base material, and from the ratio etc. The ratio of the outer diameter of the second glass layer to the outer diameter of the base material is set. Then, the coated porous glass body is formed such that the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material becomes a set value. As a method for measuring the refractive index distribution of an intermediate base material, measurement using a preform analyzer is known. The preform analyzer allows laser light to enter the intermediate base material in a direction perpendicular to the longitudinal direction of the intermediate base material and scan it in the radial direction, and measures the angle at which the laser light emitted from the intermediate base material is refracted. Measure the refractive index distribution of

As mentioned above, the intermediate base material is a sintered porous glass body in which fine glass particles are deposited in multiple layers. Therefore, in the refractive index distribution of the intermediate base material, minute fluctuations in the refractive index corresponding to each layer of glass fine particles in the porous glass body occur, and this fluctuation is sometimes called striae. The laser beam from the preform analyzer may be diffracted by the striae, and in this case, the refraction angle of the laser beam cannot be accurately measured, and the measured refractive index distribution is disturbed. If such a measurement abnormality occurs, the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate preform cannot be set, and an optical fiber preform having desired optical characteristics cannot be manufactured.

Patent Document 1 below discloses that by stretching an optical fiber base material formed by sintering a porous glass body, the period of striae is shortened and measurement abnormalities due to striae are suppressed. has been done.

JP2013-56786A

If the measurement result of the refractive index distribution of the intermediate base material is disturbed by striae, as in Patent Document 1, the intermediate base material is stretched to prevent the measurement result of the refractive index distribution from being disturbed by the striae. Therefore, it is conceivable to set the above ratio for the stretched intermediate base material. However, when the intermediate preform is stretched, the diameter of the final optical fiber preform becomes smaller. For this reason, the length of the optical fiber that can be manufactured from the optical fiber preform becomes shorter, and the productivity of the optical fiber decreases.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for manufacturing an optical fiber preform that can suppress a decrease in productivity of optical fibers.

Aspect 1 of the present invention is a method for manufacturing an optical fiber preform including a rod-shaped main body and an outer part having a different refractive index from the main body and surrounding the outer peripheral surface of the main body, the preform being porous. an intermediate base material forming step of sintering the glass body to form an intermediate base material consisting of the main body part and a first glass layer that is a part of the outer part; a glass layer forming step of depositing fine particles to form a coated porous glass body, and sintering the coated porous glass body to form a second glass layer that becomes another part of the outer part. In the step of forming the glass layer, the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material is a reference base whose refractive index distribution profile is similar to that of the intermediate base material. The glass particles are deposited on the outer peripheral surface of the first glass layer so as to have a value set based on the refractive index distribution normally measured with a preform analyzer of the material.

In intermediate base materials whose refractive index distribution profiles are similar to each other, the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material is approximately the same. Therefore, the refractive index distribution profiles of the respective intermediate base materials on which the second glass layer is formed are similar to each other. Therefore, the refractive index distribution profiles of the obtained optical fiber preforms can be similar to each other, and the optical properties of the manufactured optical fibers are also similar. In aspect 1, as described above, the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material is a value set based on the refractive index distribution of the reference base material successfully measured with a preform analyzer. Glass fine particles are deposited on the outer peripheral surface of the first glass layer so that The refractive index distribution profile of this reference base material is similar to the refractive index distribution profile of the intermediate base material. Therefore, according to aspect 1, even if the intermediate base material is such that the measurement result of the refractive index distribution measured by the preform analyzer is disturbed by striae, the intermediate base material is stretched such that this disturbance does not occur. You can set the above ratio without doing this. Therefore, according to aspect 1, it is possible to suppress the diameter of the manufactured optical fiber preform from becoming small, and it is possible to suppress a decrease in the productivity of the optical fiber. Note that the profile similar to the profile of the refractive index distribution of the intermediate base material includes, for example, a profile that is approximately the same as the profile of the refractive index distribution of the intermediate base material reduced in the radial direction. In addition, as a reference base material having such a profile, for example, a glass member obtained by stretching another intermediate base material formed on the same day under the same conditions and with the same equipment as the intermediate base material forming step, or a glass member formed on a different day. A glass member obtained by stretching an intermediate base material formed under the same conditions as the intermediate base material forming step but using a different device, a glass member obtained by stretching a part of the intermediate base material separated from the intermediate base material. Examples include glass members made of Since these glass members have a smaller outer diameter than the intermediate base material, the period of striae is shorter than that of the intermediate base material, and disturbances due to striae may not occur.

Aspect 2 of the present invention is the method for manufacturing an optical fiber preform of Aspect 1, in which the reference preform is drawn from another intermediate preform formed under the same conditions and with the same apparatus as the intermediate preform forming step. It is characterized by being a glass member.

The refractive index distribution profile of a glass member obtained by stretching another intermediate base material formed under the same conditions and with the same equipment as the intermediate base material is that the refractive index distribution profile of the intermediate base material is reduced in the radial direction according to the stretching magnification. It will be roughly the same as the profile you created. In other words, the refractive index distribution of a glass member whose horizontal axis is the radial position normalized by dividing the radial distance from the center by the outer diameter of the glass member, and the intermediate matrix where the radial distance from the center is the horizontal axis. The refractive index distribution of the intermediate base material, whose horizontal axis is the normalized radial position by dividing by the outer diameter of the material, becomes approximately the same. In aspect 2, such a glass member is the reference base material. Therefore, according to aspect 2, even if the intermediate base material is such that the measurement result of the refractive index distribution is disturbed by striae, the above-mentioned method is applied without stretching the intermediate base material so that this disturbance does not occur. You can set the ratio. Furthermore, according to the second aspect, the reference base material can be easily prepared.

Aspect 3 of the present invention is that in the method for manufacturing an optical fiber preform according to Aspect 1, the reference preform is a glass member obtained by stretching a part of the intermediate preform separated from the intermediate preform. Features.

Similar to the second aspect, the profile of the refractive index distribution of the glass member obtained by stretching a part of the intermediate base material is approximately the same as the profile obtained by reducing the profile of the refractive index distribution of the intermediate base material in the radial direction. In aspect 3, such a glass member is the reference base material. Therefore, according to aspect 3, even if the intermediate base material is such that the measurement result of the refractive index distribution is disturbed by striae, the entire intermediate base material is not stretched so that this disturbance does not occur. You can set the ratio above. In addition, the refractive index distribution profile of a glass member obtained by stretching a part of the intermediate base material is the refractive index distribution profile of a glass member obtained by stretching another intermediate base material formed under the same conditions and with the same equipment as the intermediate base material. Therefore, the profile of the refractive index distribution of the intermediate base material tends to closely resemble a profile that is reduced in the radial direction according to the stretching ratio. This is because, for example, even if another intermediate base material is formed under the same conditions and with the same equipment as the intermediate base material, there will be slight differences in the way the glass particles are deposited. Therefore, according to aspect 3, the above ratio is set more appropriately than when the reference base material is a glass member obtained by stretching another intermediate base material formed under the same conditions and with the same apparatus as the intermediate base material. It can be a value.

Aspect 4 of the present invention is the method for manufacturing an optical fiber preform according to Aspect 1, in which in the glass layer forming step, the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate preform is The glass fine particles are deposited on the outer peripheral surface of the first glass layer so as to have a value set based on the correlation obtained from the refractive index distribution of the reference base material, and the glass particles are deposited on the outer peripheral surface of the first glass layer, and The refractive index distribution of the material includes a feature having a predetermined characteristic based on a change in refractive index, and the feature of the intermediate base material is located in a range that can be normally measured by the preform analyzer, and the feature has a predetermined characteristic based on a change in refractive index. The relationship is set based on the ratio of the distance from the center of the reference base material to the feature in the reference base material to the radius of each of the reference base materials, and the refractive index distribution of each of the reference base materials. It is characterized in that it is a correlation between the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material.

Since the preform analyzer scans the laser beam across the intermediate base material in the radial direction, the refractive index distribution measurement result shows a normal refractive index distribution outside the area where the disturbance caused by striae occurs. The refractive index distribution is not normal closer to the center than the location. Therefore, the profile of the refractive index distribution in the normally measured range is similar to the profile of the refractive index distribution in the range corresponding to this range of the reference base material. The present inventor has conducted extensive research on the relationship between these similar profiles and the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material, which is set based on the refractive index distribution of the reference base material. As a result, it was found that when the refractive index distributions of the intermediate base material and the reference base material include a feature portion having a predetermined characteristic based on a change in refractive index, the above correlation is approximately a proportional relationship. Therefore, if the characteristic part of the intermediate base material is located in a range that can be normally measured with a preform analyzer, the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material can be set based on this correlation. . Therefore, according to aspect 4, even if the intermediate base material is such that the measurement result of the refractive index distribution is disturbed by striae, the above correlation can be maintained without stretching the intermediate base material such that the disturbance does not occur. Based on this, the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material can be set. Note that the characteristic portion includes, for example, a portion where the refractive index first reaches a predetermined value from the outside toward the center in the radial direction.

As described above, according to the present invention, there is provided a method for manufacturing an optical fiber preform that can suppress a decrease in the productivity of optical fibers.

1 is a diagram schematically showing a cross section perpendicular to the longitudinal direction of an optical fiber preform according to a first embodiment of the present invention; FIG. FIG. 3 is a diagram schematically showing a cross section perpendicular to the longitudinal direction of the intermediate base material in the first embodiment. It is a flowchart which shows the process of the manufacturing method of the preform for optical fibers based on 1st Embodiment. It is a flowchart of a setting process in a 1st embodiment. It is a figure which shows the refractive index distribution of the measured intermediate base material, and the refractive index distribution of a reference base material. The outer diameter of the intermediate base material is set based on the ratio of the distance from the center of the reference base material to the feature in the reference base material to the radius of each reference base material, and the refractive index distribution of each reference base material. It is a figure which shows the relationship with the ratio of the outer diameter of a 2nd glass layer to.

Hereinafter, a method for manufacturing an optical fiber preform according to the present invention will be illustrated with reference to the accompanying drawings. The embodiments illustrated below are provided to facilitate understanding of the present invention, and are not intended to be interpreted as limiting the present invention. The present invention can be modified and improved without departing from its spirit. Note that in the drawings referred to below, the dimensions of each member may be shown with different dimensions to facilitate understanding.

(First embodiment)
FIG. 1 is a diagram schematically showing a cross section perpendicular to the longitudinal direction of an optical fiber preform according to the present embodiment. As shown in FIG. 1, the optical fiber preform 1P of this embodiment includes a rod-shaped core glass body 10P and a clad glass body 11P. The clad glass body 11P surrounds the outer peripheral surface of the core glass body 10P. The outer shape of the clad glass body 11P in the cross section is approximately circular, and the core glass body 10P is arranged at the center of the clad glass body 11P. Although the outer diameter of the optical fiber preform 1P is not limited, it is, for example, 150 mm.

The refractive index of the core glass body 10P and the refractive index of the clad glass body 11P are different from each other. In this embodiment, the core glass body 10P is made of silica glass doped with a dopant that increases the refractive index, such as germanium (Ge), and the clad glass body 11P is made of silica glass without any additives. Note that the core glass body 10P may be made of silica glass without any additives, and the clad glass body 11P may be made of silica glass doped with a dopant that lowers the refractive index, such as fluorine (F). Further, the core glass body 10P may be made of silica glass doped with a dopant that increases the refractive index, and the clad glass body 11P may be made of silica glass doped with a dopant that decreases the refractive index. Furthermore, the dopant that increases the refractive index and the dopant that decreases the refractive index are not limited.

In such an optical fiber preform 1P, if the core glass body 10P is the main body, the cladding glass body 11P can be understood as an outer part that has a different refractive index from the main body and surrounds the outer peripheral surface of the main body. Although details will be described later, the optical fiber preform 1P is manufactured by forming a second glass layer on the outer peripheral surface of a rod-shaped intermediate preform. Next, the intermediate base material will be explained.

FIG. 2 is a diagram schematically showing a cross section perpendicular to the longitudinal direction of the intermediate base material in this embodiment. As shown in FIG. 2, the intermediate base material 1PP is composed of a core glass body 10P and a first glass layer 21 that is a part of the clad glass body 11P. In addition, in FIG. 1, the outer circumferential surface of the first glass layer 21 is shown by a dashed-dotted line, and the area inside the dashed-dotted line is the intermediate base material 1PP. In the clad glass body 11P, the first glass layer 21 is located inside the dashed line, and the second glass layer 22 is located outside the clad glass body 11P. It is a part other than that. Furthermore, the outer diameter of the intermediate base material 1PP of this embodiment is 60 mm, but is not limited thereto.

Next, a method for manufacturing an optical fiber preform according to this embodiment will be described.

FIG. 3 is a flowchart showing the steps of the method for manufacturing the optical fiber preform 1P according to the present embodiment. As shown in FIG. 3, the method for manufacturing the optical fiber preform 1P of this embodiment includes an intermediate preform forming step P1, a setting step P2, and a glass layer forming step P3.

<Intermediate base material forming step P1>
This step is a step of depositing glass fine particles in multiple layers to form a porous glass body, and sintering the porous glass body to form an intermediate base material 1PP that is a part of the optical fiber base material 1P. It is. In this embodiment, a porous glass body is formed by depositing glass fine particles in multiple layers, and the porous glass body is sintered so that the intermediate base material 1PP shown in FIG. 2 is formed. Examples of methods for depositing glass particles include an OVD method and a VAD method. In this embodiment, glass particles are deposited by the VAD method to form a porous glass body.

<Setting process P2>
This step is a step of setting the outer diameter of the second glass layer 22 to be formed in the glass layer forming step P3 described later. FIG. 4 is a flowchart of this process in this embodiment. As shown in FIG. 4, this process includes steps SP21 to SP25.

(Step SP21)
This step is a step of measuring the refractive index distribution of the intermediate base material 1PP formed in the intermediate base material forming step P1 using a preform analyzer. The preform analyzer makes the laser beam enter from the direction perpendicular to the longitudinal direction of the intermediate base material 1PP and scans it in the radial direction of the intermediate base material 1PP, and measures the angle at which the laser light emitted from the intermediate base material 1PP is refracted. By doing so, the refractive index distribution of the intermediate base material 1PP is measured. In this embodiment, the peak wavelength of the power of the laser light in the preform analyzer is 632 nm, and the diameter of the laser light when it enters the intermediate base material 1PP is approximately 30 μm, but the preform analyzer is not limited to this. do not have. In addition, the refractive index distribution in this embodiment is measured with the horizontal axis being the radial position normalized by dividing the radial distance from the center of the intermediate base material 1PP by the outer diameter of the intermediate base material 1PP. It is a graph in which the vertical axis is the relative refractive index Δ (%) normalized by dividing the refractive index obtained by dividing the refractive index by the refractive index at the outer peripheral edge of the intermediate base material 1PP. Note that the refractive index distribution is not limited, and for example, the horizontal axis may be the distance in the radial direction from the center of the intermediate base material 1PP. Further, the vertical axis may be the relative refractive index Δ (%) normalized by dividing the measured refractive index by the refractive index of pure silica glass, or may be the measured refractive index.

(Step SP22)
This step is a step performed after step SP21, and is a step for determining whether the refractive index distribution of the intermediate base material 1PP obtained in step SP21 is normal. As mentioned above, the intermediate base material 1PP is a sintered porous glass body in which glass fine particles are deposited in multiple layers. For this reason, striae occur in the refractive index distribution of the intermediate base material 1PP, and the laser beam of the preform analyzer is diffracted by the striae, causing disturbances in the measured refractive index distribution, which causes the refractive index distribution to become normal. may not be able to be measured. In this step, it is determined whether the refractive index distribution of the intermediate base material 1PP is normal without disturbance due to striae. This determination may be made by an operator or by a device such as a microcontroller.

(Step SP23)
This step is a step performed when it is determined in step SP22 that the refractive index distribution of the intermediate base material 1PP is normal. In this step, based on the refractive index distribution of the intermediate base material 1PP obtained in step SP21, the ratio of the outer diameter of the core glass body 10P to the outer diameter of the intermediate base material 1PP is determined, and the outer diameter of the intermediate base material 1PP is determined. The ratio of the outer diameter of the second glass layer 22 to the outer diameter of the second glass layer 22 is set. In this embodiment, the above ratio is set so that the refractive index distribution of the intermediate preform 1PP on which the second glass layer 22 is formed is the same as the refractive index distribution of the optical fiber preform 1P shown in FIG. .

(Step SP24)
This step is a step performed when it is determined in step SP22 that the refractive index distribution of the intermediate base material 1PP is not normal. In this step, a reference base material whose refractive index distribution profile is similar to that of the intermediate base material 1PP and whose refractive index distribution can be normally measured with a preform analyzer is prepared. Then, the refractive index distribution of the reference base material is measured using a preform analyzer. Note that the profile similar to the profile of the refractive index distribution of the intermediate base material 1PP includes, for example, a profile that is generally the same as the profile obtained by reducing the profile of the refractive index distribution of the intermediate base material 1PP in the radial direction.

In this embodiment, the reference base material is a glass member obtained by longitudinally stretching another intermediate base material formed under the same conditions and with the same apparatus as the intermediate base material forming step P1 described above. This reference base material is composed of a core glass body 10P and a first glass layer 21 similarly to the intermediate base material 1PP. Furthermore, although the outer diameter of the reference base material is smaller than the outer diameter of the intermediate base material 1PP, the refractive index distribution profile of the reference base material is similar to that of the intermediate base material 1PP in the radial direction according to the stretching magnification. It will be roughly the same as the reduced profile. In other words, the refractive index distribution of the reference base material whose horizontal axis is the radial position normalized by dividing the radial distance from the center by the outer diameter of the reference base material, and the radial distance from the center. By dividing by the outer diameter of the intermediate base material 1PP, the normalized radial position becomes approximately the same as the refractive index distribution of the intermediate base material 1PP whose horizontal axis is the horizontal axis. Furthermore, the period of striae in the refractive index distribution of the reference base material is shorter than the period of striae in the refractive index distribution of intermediate base material 1PP, so that the measurement result of the refractive index distribution of the reference base material is not disturbed by the striae. short. That is, another intermediate base material is stretched so that the measurement results of the refractive index distribution are not disturbed by striae. The reference base material of this embodiment is a glass member obtained by stretching the outer diameter of another intermediate base material having an outer diameter of 60 mm to an outer diameter of 30 mm, but the degree of stretching of the other intermediate base material is , without limitation. For example, another intermediate base material is stretched so that the outer diameter is 0.5 times or less to form a reference base material.

FIG. 5 is a diagram showing the measured refractive index distribution of the intermediate base material 1PP and the refractive index distribution of the reference base material. In FIG. 5, the refractive index distribution of the intermediate base material 1PP is shown by a solid line, and the refractive index distribution of the reference base material is shown by a dotted line. The horizontal axis is the radial position normalized by dividing the radial distance from the center of the intermediate base material 1PP by the outer diameter of the intermediate base material 1PP, and the vertical axis is the measured refractive index. is the relative refractive index Δ(%) normalized by dividing by the refractive index at the outer peripheral edge of the intermediate base material 1PP. In the refractive index distribution of the intermediate base material 1PP shown in FIG. 5, there is a range EA in which the relative refractive index Δ sharply decreases to a negative value, which is an abnormal refractive index distribution. This is considered to be because the measurement result of the refractive index distribution of the intermediate base material 1PP is disturbed by the striae.

(Step SP25)
This step is a step performed after step SP24. In this step, the ratio of the outer diameter of the core glass body 10P in the reference base material to the outer diameter of the reference base material is determined based on the refractive index distribution of the reference base material measured in step SP24, and The ratio of the outer diameter of the second glass layer 22 to the outer diameter is set. In this embodiment, the refractive index distribution profile of the reference base material on which the second glass layer 22 is formed is the refractive index distribution profile of the optical fiber base material 1P shown in FIG. The above ratio is set so as to be the same as the profile reduced in the radial direction according to the above ratio, and the ratio is set as the ratio in the intermediate base material 1PP.

As described above, in this embodiment, when the refractive index distribution of the intermediate base material 1PP can be normally measured, the outer diameter of the second glass layer 22 relative to the outer diameter of the intermediate base material 1PP is determined based on the refractive index distribution of the intermediate base material 1PP. Set the diameter ratio. In addition, if the refractive index distribution of the intermediate base material 1PP cannot be measured normally, the refraction normally measured with the preform analyzer of the reference base material whose refractive index distribution profile is similar to that of the intermediate base material 1PP. Set the above ratio based on the rate distribution.

<Glass layer forming step P3>
In this step, glass fine particles are deposited on the outer peripheral surface of the first glass layer 21 of the intermediate base material 1PP to form a coated porous glass body surrounding the outer peripheral surface of the first glass layer 21, and the coated porous glass body is sintered. This is a step of forming the second glass layer 22 which becomes another part of the clad glass body 11P. When forming the coated porous glass body, the first glass is coated by the OVD method so that the ratio of the outer diameter of the second glass layer 22 to the outer diameter of the intermediate base material 1PP becomes the value set in the setting step P2. Glass particles are deposited on the outer peripheral surface of layer 21 to form a coated porous glass body.

As described above, in the setting step P2, if the measured refractive index distribution of the intermediate base material 1PP is normal, the intermediate base material on which the second glass layer 22 is formed is determined based on the refractive index distribution of the intermediate base material 1PP. The above ratio is set so that the refractive index distribution of the material 1PP is the same as the refractive index distribution of the optical fiber base material 1P shown in FIG. Therefore, by forming the second glass layer 22, the portion consisting of the first glass layer 21 and the second glass layer 22 becomes the clad glass body 11P of the optical fiber preform 1P, and the optical fiber preform 1P becomes the cladding glass body 11P. can get.

In addition, in the setting step P2, if the measured refractive index distribution of the intermediate preform 1PP is not normal, the profile of the refractive index distribution of the reference preform on which the second glass layer 22 is formed is the optical fiber preform shown in FIG. The above ratio is set so that the profile of the refractive index distribution of 1P is the same as the profile obtained by reducing the profile in the radial direction according to the stretching ratio at the time of producing the reference base material. As described above, the profile of the refractive index distribution of the reference base material is approximately the same as the profile obtained by reducing the profile of the refractive index distribution of the intermediate base material 1PP in the radial direction. Therefore, the ratio of the outer diameter of the core glass body 10P in the reference base material to the outer diameter of the reference base material is the ratio of the outer diameter of the core glass body 10P in the intermediate base material 1PP to the outer diameter of the intermediate base material 1PP. It will be roughly the same. Therefore, the above ratio that is set in the setting step P2 when the measured refractive index distribution of the intermediate base material 1PP is not normal is the ratio that is set when the measured refractive index distribution of the intermediate base material 1PP is normal. is roughly the same. Therefore, also in this case, by forming the second glass layer 22, the portion consisting of the first glass layer 21 and the second glass layer 22 becomes the clad glass body 11P of the optical fiber base material 1P, and the optical fiber A base material 1P is obtained.

As explained above, the method for manufacturing an optical fiber preform according to the present embodiment includes an intermediate preform forming step P1 and a glass layer forming step P3. The optical fiber preform 1P includes a rod-shaped core glass body 10P and a clad glass body 11P surrounding the outer peripheral surface of the core glass body 10P. In the intermediate base material forming step, the porous glass body is sintered to form an intermediate base material 1PP consisting of the core glass body 10P and the first glass layer 21 which is a part of the clad glass body 11P. In the glass layer forming step P3, glass fine particles are deposited on the outer circumferential surface of the first glass layer 21 to form a coated porous glass body, and the coated porous glass body is sintered to form other parts of the clad glass body 11P. A second glass layer 22, which will be a part of the glass layer, is formed. If the preform analyzer cannot normally measure the refractive index distribution of the intermediate base material 1PP, in the glass layer forming step P3, the ratio of the outer diameter of the second glass layer 22 to the outer diameter of the intermediate base material 1PP is Glass fine particles are deposited on the outer peripheral surface of the first glass layer 21 so as to have a value set based on the refractive index distribution of the reference base material normally measured by an analyzer. The refractive index distribution profile of this reference base material is similar to the refractive index distribution profile of the intermediate base material 1PP, and the reference base material is another intermediate base material formed under the same conditions and with the same apparatus as the intermediate base material forming step P1. This is a glass member made of a stretched base material.

Therefore, as described above, the above ratio is approximately the same as the ratio set when the measured refractive index distribution of the intermediate base material 1PP is normal. Therefore, according to the method for manufacturing an optical fiber preform of the present embodiment, even if the intermediate preform 1PP has disturbances due to striae in the measurement results of the refractive index distribution measured by a preform analyzer, the disturbances may occur. The above ratio can be set without stretching the intermediate base material 1PP so that no . Therefore, according to the method for manufacturing an optical fiber preform of the present embodiment, it is possible to prevent the diameter of the manufactured optical fiber preform from becoming small, and it is possible to suppress a decrease in the productivity of the optical fiber. Further, according to the method for manufacturing an optical fiber preform of this embodiment, a reference preform can be easily prepared.

(Second embodiment)
Next, a second embodiment of the present invention will be described in detail. Note that components that are the same or equivalent to those in the first embodiment are given the same reference numerals and redundant explanations will be omitted, unless otherwise specified. In the method for manufacturing an optical fiber preform of this embodiment, step SP24 of the setting process P2 is different from step SP24 in the first embodiment. Therefore, below, step SP24 will be explained, and explanations of other steps will be omitted.

In step SP24 of this embodiment, a reference base material different from the reference base material in the first embodiment is prepared. In step SP24 of the present embodiment, one end of the intermediate base material 1PP in the longitudinal direction is cut, and the other elongated end is used as the intermediate base material 1PP. Therefore, the other short end is a part of the intermediate base material 1PP separated from the intermediate base material 1PP, and a glass member obtained by stretching the part is used as a reference base material. Then, the refractive index distribution of this reference base material is measured using a preform analyzer. The reference base material of this embodiment is composed of a core glass body 10P and a first glass layer 21, similarly to the intermediate base material 1PP. In addition, the outer diameter of the reference base material is smaller than the outer diameter of the intermediate base material 1PP, and the profile of the refractive index distribution of the reference base material is approximately the same as the profile obtained by reducing the refractive index distribution profile of the intermediate base material 1PP in the radial direction. becomes. Furthermore, the period of the striae in the refractive index distribution of the reference base material is shorter than the period of the striae in the refractive index distribution of the intermediate base material 1PP, so that the measurement result of the refractive index distribution of the glass member is not disturbed by the striae. short. That is, a part of the intermediate base material 1PP is stretched so that the refractive index distribution can be normally measured by the preform analyzer. For example, a reference base material is formed by stretching a part of the intermediate base material 1PP so that the outer diameter is 0.5 times or less. Then, the refractive index distribution of the reference base material is measured using a preform analyzer.

According to the method for manufacturing an optical fiber preform of this embodiment, as in the first embodiment, even if the intermediate preform 1PP is such that the measurement result of the refractive index distribution is disturbed by striae, the disturbance is not caused. It is possible to set the ratio of the outer diameter of the second glass layer 22 to the outer diameter of the intermediate base material 1PP without stretching the entire intermediate base material 1PP so as to prevent this from occurring. In addition, the profile of the refractive index distribution of a glass member obtained by stretching a part of intermediate base material 1PP is the refractive index distribution of a glass member obtained by stretching another intermediate base material formed under the same conditions and with the same equipment as intermediate base material 1PP. The profile of the refractive index distribution of the intermediate base material 1PP tends to closely resemble the profile obtained by reducing the profile of the refractive index distribution of the intermediate base material 1PP in the radial direction according to the stretching ratio at the time of production of the reference base material. This is because, for example, even if another intermediate base material is formed under the same conditions and with the same equipment as the intermediate base material 1PP, there will be slight differences in the way the glass particles are deposited. Therefore, according to the method for manufacturing an optical fiber preform of this embodiment, when the reference preform is a glass member obtained by stretching another intermediate preform formed under the same conditions and with the same equipment as the intermediate preform 1PP. The above ratio can be set to a more appropriate value.

(Third embodiment)
Next, a third embodiment of the present invention will be described in detail. Note that components that are the same or equivalent to those in the first embodiment are given the same reference numerals and redundant explanations will be omitted, unless otherwise specified. In the method for manufacturing an optical fiber preform of this embodiment, the setting step P2 is different from the setting step P2 of the first embodiment.

Although explanation with illustrations is omitted, the setting process P2 of this embodiment does not include step SP24. Further, in this embodiment, step SP25 is performed when it is determined in step SP22 that an abnormality has occurred in the refractive index profile of the intermediate base material 1PP, and step SP25 is different from step SP25 in the first embodiment. Therefore, below, step SP25 will be explained, and explanations of other steps will be omitted.

In this embodiment, the outer diameter of the second glass layer relative to the outer diameter of the intermediate base material 1PP is determined based on the correlation obtained from the refractive index profiles of a plurality of reference base materials similar to the refractive index profile of the intermediate base material 1PP. Set the ratio. As in the first embodiment, the plurality of reference base materials of this embodiment are obtained by measuring the refractive index distribution of each of a plurality of other intermediate base materials formed under the same conditions and with the same apparatus as the intermediate base material forming step P1. A plurality of glass members are stretched in the longitudinal direction so that the result is free from disturbances caused by striae. Therefore, like the intermediate base material 1PP, these reference base materials are composed of the core glass body 10P and the first glass layer 21, and the refractive index distribution profile of these reference base materials is the refractive index of the intermediate base material 1PP. Similar to a distribution profile. Further, the refractive index distribution of these reference base materials can be normally measured using a preform analyzer. In this embodiment, these reference base materials are prepared in advance, and the refractive index distribution of each reference base material is measured using a preform analyzer.

In the preform analyzer, the laser beam is scanned across the intermediate base material 1PP in the radial direction, so as shown in Figure 5, the results of measuring the refractive index distribution are as follows: The refractive index distribution becomes normal, and the refractive index distribution closer to the center of the area becomes abnormal. Therefore, the profile of the refractive index distribution in the normally measured range is similar to the profile of the refractive index distribution in the range corresponding to this range in the reference base material. The present inventor has conducted extensive research on the relationship between these similar profiles and the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material, which is set based on the refractive index distribution of the reference base material. As a result, if the refractive index distribution of the intermediate base material and the reference base material includes a feature having a predetermined characteristic based on a change in refractive index, the reference base material is Correlation between the ratio of the distance to the above feature in the base material and the ratio of the outer diameter of the second glass layer 22 to the outer diameter of the intermediate base material 1PP, which is set based on the refractive index distribution of each reference base material It was found that the relationship is generally proportional. For this reason, if the above-mentioned characteristic portion exists in the normally measured range of the intermediate base material, the ratio of the outer diameter of the second glass layer 22 to the outer diameter of the intermediate base material 1PP can be set based on the above-mentioned correlation. .

In this embodiment, as shown in FIG. 5, in the normally measured range of the refractive index distribution of the intermediate base material 1PP, the relative refractive index Δ increases from the outside toward the center, and from a certain point toward the center. The rate of change in the relative refractive index Δ increases. In view of such characteristics, in this embodiment, the above-mentioned characteristic portion is defined as a portion PT1 where the relative refractive index Δ first becomes a predetermined value from the outside toward the center in the radial direction. Further, the predetermined value is a value such that the portion PT1 is closer to the center than the portion PT2 where the rate of change in the relative refractive index Δ is large, and a dashed dot line indicating the predetermined value is shown in FIG. In this embodiment, the above-mentioned correlation is determined using the above-mentioned region PT1 as the characteristic part.

FIG. 6 shows intermediate base materials set based on the ratio of the distance from the center of the reference base material to the characteristic part of the base material to the radius of each reference base material, and the refractive index distribution of each reference base material. It is a graph showing the relationship between the ratio of the outer diameter of the second glass layer 22 to the outer diameter of 1PP. As shown in FIG. 6, these two ratios have a correlation that is approximately a proportional relationship, and in FIG. 6, a straight line indicating this proportional relationship is shown as a broken line. In this embodiment, the ratio of the outer diameter of the second glass layer 22 to the outer diameter of the intermediate base material 1PP is set based on this correlation. As described above, according to the method for manufacturing an optical fiber preform of the present embodiment, even if the intermediate preform 1PP is such that the measurement result of the refractive index distribution is disturbed by striae, it can be made such that the disturbance does not occur. The ratio of the outer diameter of the second glass layer 22 to the outer diameter of the intermediate base material 1PP can be set without stretching the intermediate base material 1PP.

Note that the feature portion having a predetermined feature based on a change in refractive index is not limited. This characteristic portion is a portion that is uniquely determined based on a change in the refractive index, and it is sufficient that the characteristic portion of the intermediate base material 1PP is located within a measurable range.

Although the present invention has been described above using the above embodiments as examples, the present invention is not limited thereto.

For example, in the embodiment described above, the optical fiber preform 1P including the core glass body 10P as the main body and the clad glass body 11P as the outer side has been described as an example. However, the optical fiber preform 1P only needs to include a rod-shaped main body and an outer part that has a different refractive index from the main body and surrounds the outer peripheral surface of the main body.

For example, the main body portion may include a rod-shaped inner core glass body and an outer core glass body that has a lower refractive index than the inner core glass body and surrounds the outer peripheral surface of the inner core glass body. In this case, it is possible to manufacture an optical fiber in which the refractive index distribution of the core increases stepwise toward the center. Further, in this case, the main body portion may be composed of an inner core glass body, and the outer portion may be composed of an outer core glass body and a clad glass body 11P. In this case, for example, the first glass layer 21 in the intermediate base material 1PP is a part of the outer core glass body, and the second glass layer 22 formed in the glass layer forming step P3 is the remaining part of the outer core glass body and It may also be a clad glass body 11P. Alternatively, the first glass layer 21 may be the entire outer core glass body and a part of the clad glass body 11P, and the second glass layer 22 may be the remaining part of the clad glass body 11P.

Further, the outer part may be composed of, for example, an inner clad glass body surrounding the outer circumferential surface of the main body part and an outer clad glass body surrounding the outer circumferential surface of the inner clad glass body, which has a different refractive index from the inner clad glass body. . In this case, for example, the first glass layer 21 in the intermediate base material 1PP is a part of the inner cladding glass body, and the second glass layer 22 formed in the glass layer forming step P3 is the remaining part of the inner cladding glass body and It may also be an outer clad glass body. Alternatively, the first glass layer 21 may be the entire inner clad glass body and a part of the outer clad glass body, and the second glass layer 22 may be the remaining part of the outer clad glass body.

Further, in the above embodiment, the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate preform is such that the optical fiber preform 1P is obtained by forming the second glass layer 22. The setting process P2, in which the settings are made as follows, has been explained as an example. However, the above ratio may be smaller than the ratio that allows the optical fiber preform 1P to be obtained. In this case, for example, the optical fiber preform 1P can be obtained by performing the setting step P2 and the glass layer forming step P3 at least once on the intermediate preform 1PP on which the second glass layer 22 is formed. can.

Further, the reference base material of the first and third embodiments was a glass member obtained by stretching another intermediate base material formed under the same conditions and with the same apparatus as the intermediate base material forming step P1. However, in the first and third embodiments, the refractive index distribution of the reference base material can be normally measured with a preform analyzer, and the refractive index distribution profile is similar to the refractive index distribution profile of the intermediate base material 1PP. It is not limited as long as it is a glass member. As a reference base material, for example, a glass member obtained by stretching another intermediate base material formed on the same day under the same conditions and with the same apparatus as the intermediate base material forming step P1, the glass member formed on a different day, an intermediate base material, etc. Examples include a glass member obtained by stretching an intermediate base material formed under the same conditions as the material forming step P1 but using a different device. Furthermore, the measurement interval in the radial direction when measuring the refractive index distribution of such a reference base material using a preform analyzer may be made wider than that for the intermediate base material 1PP. By doing so, the obtained measurement result of the refractive index distribution of the reference base material becomes rough, and it is possible to make the measurement result less likely to be disturbed by striae.

Furthermore, in the first and second embodiments, the setting process P2 including steps SP21 to SP25 has been described as an example. However, in the first and second embodiments, step SP21, step SP22, and step SP23 may be omitted. That is, the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material may be set based on the refractive index distribution of the reference base material without measuring the refractive index distribution of the intermediate base material 1PP.

Further, the method for manufacturing an optical fiber preform may include a step of stretching the intermediate preform 1PP before the setting step P2.

As described above, according to the present invention, a method for manufacturing an optical fiber preform that can suppress a decrease in productivity of optical fibers is provided, and it is expected that the method will be used in fields such as optical fiber communications.

1P... Optical fiber base material 1PP... Intermediate base material 10P... Core glass body (main body)
11P...Clad glass body (outer part)
21...First glass layer 22...Second glass layer P1...Intermediate base material forming process P2...Setting process P3...Glass layer forming process

Claims (4)

A method for manufacturing an optical fiber preform including a rod-shaped main body and an outer part having a different refractive index from the main body and surrounding an outer peripheral surface of the main body,
an intermediate base material forming step of sintering the porous glass body to form an intermediate base material consisting of the main body portion and a first glass layer that is a part of the outer portion;
A second glass layer is formed by depositing glass particles on the outer peripheral surface of the first glass layer to form a coated porous glass body, and sintering the coated porous glass body to become another part of the outer part. a glass layer forming step to form;
Equipped with
In the glass layer forming step, the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material is such that the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material is determined by the ratio of the outer diameter of the second glass layer to the outer diameter of the reference base material whose refractive index distribution profile is similar to that of the intermediate base material. The glass particles are deposited on the outer peripheral surface of the first glass layer so as to have a value set based on the refractive index distribution normally measured with a preform analyzer. Production method. 2. The optical fiber preform according to claim 1, wherein the reference preform is a glass member obtained by drawing another intermediate preform formed under the same conditions and using the same apparatus as the intermediate preform forming step. manufacturing method. 2. The method for manufacturing an optical fiber preform according to claim 1, wherein the reference preform is a glass member obtained by stretching a part of the intermediate preform separated from the intermediate preform. In the glass layer forming step, the ratio of the outer diameter of the second glass layer to the outer diameter of the intermediate base material is a value set based on the correlation obtained from the refractive index distribution of the plurality of reference base materials. depositing the glass particles on the outer peripheral surface of the first glass layer so that
the refractive index distribution of the intermediate preform and each of the reference preforms includes a feature having a predetermined characteristic based on a change in refractive index;
The characteristic portion of the intermediate base material is located in a range that can be normally measured with the preform analyzer,
The correlation is set based on the ratio of the distance from the center of the reference base material to the characteristic portion in the reference base material to the radius of each reference base material, and the refractive index distribution of each of the reference base materials. 2. The method for manufacturing an optical fiber preform according to claim 1, wherein the ratio is a ratio of an outer diameter of the second glass layer to an outer diameter of the intermediate preform.

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