JP4455071B2 - Optical fiber preform processing method - Google Patents

Description

  The present invention relates to a method for processing an optical fiber preform that removes foreign matter buried in a surface layer of an optical fiber preform, and more particularly to a method that can reliably remove foreign matter and can be processed without requiring a large amount of equipment.

  When the optical fiber preform is manufactured, transported, stored, or attached to / detached from the apparatus, foreign matter such as dust or dust may adhere to the surface layer of the optical fiber preform and be buried. When an optical fiber is manufactured by spinning an optical fiber preform in which foreign matter is buried in the surface layer, the foreign matter is mixed into the optical fiber, resulting in a decrease in strength of the optical fiber and a deterioration in transmission characteristics. In particular, the decrease in strength is remarkable, which causes a decrease in yield.

As a typical method for removing foreign matter buried in the surface layer of the optical fiber preform, there is a method of flame polishing the entire surface layer of the optical fiber preform. However, in the flame polishing method, depending on the type and size of the buried foreign matter, the foreign matter may enter the optical fiber preform and the foreign matter may remain.
In addition, as a method for preventing foreign matter from adhering to and burying itself on the surface layer of the optical fiber preform, a method for accommodating and transporting the optical fiber preform in a container supplied with clean air has been proposed. (See Patent Document 1).
However, in order to make all the manufacturing processes including conveyance into a highly clean atmosphere and to avoid the adhesion of foreign matters, a large amount of equipment is required, leading to an increase in the cost of optical fibers.
JP-A-9-110454

When an optical fiber is spun using an optical fiber preform in which foreign matter is buried in the surface layer, foreign matter is mixed into the optical fiber, causing the following problems.
(1) Cracks are generated in the optical fiber due to the mixing of foreign substances, and the strength of the optical fiber is extremely reduced as described above.
(2) The crystal structure of quartz glass around the foreign matter changes due to the foreign matter (for example, crystallization), which causes a decrease in the strength of the optical fiber, and also causes a deterioration in transmission characteristics and an increase in transmission loss. .
(3) Foreign matter itself diffuses into the fiber, resulting in an increase in transmission loss.

The optical fiber preform is roughly divided into the following two types. One is an optical fiber preform immediately before spinning formed so that the core and the clad have an appropriate ratio, and is referred to as a fiber rod in this specification. Moreover, what is manufactured in the intermediate process which manufactures this fiber rod is called an intermediate rod.
When foreign matter is buried in the surface layer of the fiber rod, the problem (1) appears remarkably, and the yield is lowered due to the strength reduction. On the other hand, if a foreign substance is buried in the surface layer of the intermediate rod, the problems (2) and (3) described above appear remarkably and normal signal transmission may not be possible.

  The present invention has been proposed in order to solve the above-described problems, and is to provide an optical fiber preform processing method that can reliably remove foreign substances without requiring a large amount of equipment.

That is, an optical fiber preform processing method according to the present invention is an optical fiber preform processing method for removing foreign matter buried in a surface layer of an optical fiber preform. A partial removal step of removing the foreign matter by partially removing, and subjecting the optical fiber preform having a recess formed by partial removal of the surface layer to a spinning step, and in the partial removal step, The depth of the recess is 0.2% or more and 1% or less with respect to the diameter of the optical fiber preform used in the spinning step .
In the conventional flame polishing method, since the optical fiber preform is softened by the heat of the flame, foreign matter may enter and remain inside the optical fiber preform. On the other hand, in this invention, the foreign material buried in the surface layer can be reliably removed by partially removing the surface layer of the optical fiber preform in the vicinity of the foreign material.
In addition, since foreign matters can be reliably removed, it is not necessary to make all the manufacturing processes including transporting into a highly clean atmosphere in order to completely avoid the adhesion and burying of foreign matters to the surface layer as in the prior art.
Further, when spinning the processed optical fiber preform, it is possible to suppress the strength of the spun optical fiber from being lowered due to the recess, and to suppress problems such as disconnection.

As a method for partially removing the surface layer of the optical fiber preform near the foreign matter, a method for polishing and removing the surface layer of the optical fiber preform near the foreign matter using a polishing jig, or by irradiating a laser beam. A method of heating and removing the surface layer of the optical fiber preform near the foreign matter is preferable.
By polishing and removing the surface layer using a polishing jig, the surface layer of the optical fiber base material near the foreign material can be partially removed in a short time.
Further, by irradiating the surface layer with laser light, the concave portion formed by partially removing the surface layer can be narrowed.
Since the 1.06 μm band laser beam is transmitted through the quartz glass, when the optical fiber preform is made of quartz glass, the laser beam is concentrated on the foreign matter by using the 1.06 μm band laser beam. The foreign matter can be selectively removed by heating. For this reason, the recessed part formed after foreign material removal can be narrowed.

In the method for processing an optical fiber preform according to the present invention, after the partial removal step, a post-polishing step of polishing the concave portion and the surface layer in the vicinity thereof can be performed prior to the spinning step.
A recess is formed after the surface layer of the optical fiber preform in the vicinity of the foreign material is partially removed, but the surface of the recess is rough and may have fine irregularities, and burrs are formed around the recess. Sometimes it is done. In such a rough concave portion of the surface state, foreign matter reattaches or abrasives such as grinding stone powder easily adhere, and even if the optical fiber preform is washed after removing the foreign matter, It may be difficult to remove the abrasive.
By polishing the surface layer of the optical fiber preform, the surface of the recess becomes smooth, and burrs and the like formed around the recess can be removed, thereby suppressing the reattachment of foreign matter and the adhesion of abrasives such as abrasive fines. Can do. Further, even if foreign matters are reattached or abrasives are attached, they can be easily removed by washing.

As a method of polishing the surface layer of the optical fiber preform, a method of polishing using a polishing jig or a method of flame polishing is preferable.
By polishing using a polishing jig, the surface layer of the optical fiber base material near the recess can be polished in a short time. As the polishing jig, it is preferable to use a grindstone containing fine grinding powder having a particle size of # 1000 or more. This makes it possible to polish the surface of the optical fiber preform so as not to leave a polishing mark, and to recycle foreign matter. It is possible to prevent adhesion and adhesion of abrasive fines.
In addition, in the flame polishing method, the surface layer of the optical fiber preform is softened by the heat of the flame to make the surface of the recess smooth, so by using the flame polishing method, the surface of the recess is made smooth regardless of the shape of the recess. can do.

In the present invention, in the optical fiber preform processing method for removing foreign matter buried in the surface layer of the optical fiber preform, the foreign matter is removed by partially removing the surface layer of the optical fiber preform in the vicinity of the foreign matter. a partial removal step of removing the surface layer partially removed soot particulates are deposited on the outer surface of the optical fiber preform having a recess formed by the, possess a vitrification step of heating vitrified in said vitrification step the optical fiber preform can be employed a processing method for subjected to spinning step.
In this invention, after the said partial removal process, prior to the said vitrification process, the post-polishing process which grind | polishes the said recessed part and its surface layer of the vicinity can be performed.

According to the processing method of the optical fiber preform of the present invention, it is possible to reliably remove the foreign matter buried in the surface layer without requiring a large amount of equipment as in the prior art.
Further, by using an optical fiber preform from which foreign matter has been removed, an optical fiber can be manufactured with high yield without causing a decrease in the strength of the optical fiber, a deterioration in transmission characteristics, an increase in transmission loss, and the like caused by the foreign matter. For this reason, in the processing method of the optical fiber preform of the present invention, it is possible to obtain an optical fiber preform that can produce an optical fiber with a high yield without requiring a large amount of equipment, and this can contribute to the cost reduction of the optical fiber.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing an example of a state in which foreign matter 2 such as dust or dust is buried in the surface layer 11 of the optical fiber preform 1, and FIG. 2 is a foreign matter surrounded by an alternate long and short dash line A in FIG. It is an enlarged view showing 2 neighborhood.
Here, the optical fiber preform 1 is roughly divided into the following two types. One is formed so that the core and clad have an appropriate ratio (spinnable state), and the other is manufactured in an intermediate process of manufacturing a fiber rod.
In the present specification, a fiber rod in a spinnable state is referred to as a fiber rod, and an intermediate rod manufactured in an intermediate process for manufacturing the fiber rod is referred to as an intermediate rod. In the following description, an optical fiber preform 1 is referred to as a fiber rod. And both intermediate rods.
Further, the surface layer 11 of the optical fiber preform 1 refers to the vicinity of the surface of the optical fiber preform 1.

In the present invention, the foreign matter 2 is removed by partially removing the surface layer 11 of the optical fiber preform 1 near the foreign matter 2.
A method for partially removing the surface layer 11 of the optical fiber preform 1 in the vicinity of the foreign matter 2 is not particularly limited, but the optical fiber preform 1 in the vicinity of the foreign matter 2 can be removed using a polishing jig such as a diamond grindstone. A method of polishing and removing the surface layer 11 or a method of heating and removing the surface layer 11 of the optical fiber preform 1 in the vicinity of the foreign matter 2 by irradiating laser light and heat of the laser light is preferable.

A method for polishing and removing the surface layer 11 of the optical fiber preform 1 using a polishing jig such as a diamond grindstone will be described below.
FIG. 3 is a schematic diagram showing an example of a state in which the surface layer 11 of the optical fiber preform 1 in the vicinity of the foreign material 2 has been removed by polishing with a polishing jig. A polishing jig harder than the quartz glass base material 1 such as a diamond grindstone is attached to a support such as a hand grinder or an ultrasonic polishing machine. Then, the polishing jig is applied to the surface layer 11 of the optical fiber preform 1 near the foreign material 2 while rotating or reciprocating at a high speed, and the surface layer 11 near the foreign material 2 is polished and removed by the polishing jig.
In the surface layer 11 of the optical fiber preform 1, the recess 3 is formed in the polished and removed portion.
By using a support that rotates or reciprocates at high speed, such as a hand grinder or an ultrasonic grinder, the surface layer 11 of the optical fiber base material 1 near the foreign material 2 can be polished and removed in a short time.

Next, a method of heating and removing the surface layer 11 of the optical fiber preform 1 by irradiating laser light will be described.
FIG. 4 is a schematic diagram showing an example of a state in which the surface layer 11 of the optical fiber preform 1 in the vicinity of the foreign matter 2 is removed by heating with a laser beam of a CO ₂ laser. Since the laser beam has a small spot diameter, the formed recesses 4 can be made narrower than when the surface layer 11 is polished by a polishing jig such as a grindstone.
The laser light to be used is not particularly limited, and laser light whose wavelength, output, etc. are appropriately adjusted according to the application and purpose is used. For example, by using a solid-state laser in which a crystal in which neodymium or the like is added to yttrium aluminum garnet (YAG), yttrium vanadate (YVO ₄ ), or the like is used as a laser medium, the wavelength is 1.06 μm band. Laser light can be emitted. Further, by using a CO ₂ laser using carbon dioxide gas (CO ₂ ) as a laser medium, a laser beam having a wavelength of 10.6 μm can be emitted.
In particular, laser light in the 1.06 μm band has a property of transmitting through quartz glass. For this reason, when the optical fiber preform 1 is made of quartz glass, the laser light can be focused on the foreign matter 2 by using the laser light in the 1.06 μm band, and the foreign matter 2 can be selectively applied. Can be removed by heating. Therefore, as shown in FIG. 5, the concave portion 5 formed after the removal of the foreign matter 2 has substantially the same shape as the foreign matter 2, and the concave portion 5 can be made narrower than when a CO ₂ laser or the like is used. it can.

As described above, the surface layer 11 of the optical fiber preform 1 near the foreign material 2 is partially removed by various methods.
As described above, after the surface layer 11 of the optical fiber preform 1 in the vicinity of the foreign material 2 is partially removed, the recesses 3, 4, and 5 are formed. However, the surface state of the recesses 3, 4, and 5 is usually rough and fine. There may be irregularities. In particular, the concave portion 5 formed by heating and removing the foreign matter 2 by the 1.06 μm band laser beam has almost the same shape as the foreign matter 2 as shown in FIG. There are noticeable fine irregularities.
3 to 5, dotted lines indicate that the surfaces of the recesses 3, 4, and 5 are rough. In addition, burrs (not shown) may be formed around the recesses 3, 4, and 5.
In such concave portions 3, 4, 5 having a rough surface state, the foreign matter 2 is likely to adhere again, or grindstone powder or the like is easily attached. Even if the optical fiber preform 1 is washed after removing the foreign matter 2, the concave portion In some cases, it is difficult to remove the foreign matter 2 or the grindstone powder that has re-attached to the surfaces of 3, 4, and 5.

Therefore, in the present invention, it is preferable to polish the surface layer 11 after partially removing the surface layer 11 of the optical fiber preform 1 near the foreign material 2. As a result, the surfaces of the recesses 3, 4, and 5 are smoothed, and burrs and the like formed around the recesses 3, 4, and 5 can be removed, so that reattachment of foreign matter 2 and adhesion of grindstone powder and the like can be suppressed. it can. Further, even if the foreign matter 2 adheres again or grindstone powder adheres, it can be easily removed by washing.
The method of polishing the surface layer 11 of the optical fiber preform 1 is not particularly limited, but a method of polishing using a polishing jig such as a diamond grindstone composed of diamond polishing fine powder, or a method of flame polishing is preferable. .

A method for polishing the surface layer 11 of the optical fiber preform 1 using a polishing jig will be described below.
FIG. 6 is a schematic diagram showing an example of a state in which the vicinity of the recess 3 of the optical fiber preform 1 shown in FIG. 3 is polished by a polishing jig.
A grinding jig such as a diamond grindstone is attached to a support such as a hand grinder or an ultrasonic grinder. Then, the polishing jig is applied to the surface layer 11 of the optical fiber preform 1 while rotating or reciprocating at a high speed, and the vicinity of the recess 3 is polished by the polishing jig to smooth the surface of the recess 3. 3 Remove the surrounding burrs.
As the polishing jig, it is preferable to use a grindstone composed of fine grinding powder having a particle size of # 1000 or more. This enables polishing so as not to leave a polishing mark on the surface layer 11 of the optical fiber preform 1, and foreign matter. 2 reattachment and adhesion of polishing fine powders can be prevented.
Here, the abrasive fine powder having a particle size of # 1000 or more has a d _s -50 value (particle size of 50% cumulative height) measured by the sedimentation test method as defined in JIS R6001. This refers to abrasive fines of 5 μm or less.
By using a support that rotates or reciprocates at high speed, such as a hand grinder or an ultrasonic polishing machine, the surface layer 11 of the optical fiber base material 1 near the recess 3 can be polished in a short time.
In addition, you may use what was comprised from the cerium oxide type polishing powder as a grinding | polishing jig | tool.

Next, a method for polishing the surface layer 11 of the optical fiber preform 1 by flame polishing will be described.
FIG. 7 is a schematic diagram illustrating an example of a state in which the vicinity of the concave portion of the optical fiber preform 1 illustrated in FIG. 5 is polished by a flame polishing method.
The vicinity of the recess 5 shown in FIG. 5 is heated with a flame such as an oxyhydrogen flame to smooth the surface of the recess 5 and eliminate burrs and the like around the recess 5.
As shown in FIG. 5, when the concave portion 5 having a shape that grooves toward the inside of the optical fiber preform 1 is polished, the concave portion 5 can be uniformly polished by a polishing method using a polishing jig. difficult. On the other hand, in the flame polishing method, the surface layer 11 of the optical fiber preform 1 is softened by the heat of the flame to make the surface of the recess 5 smooth, so that the surface shown in FIG. As shown, the recess 7 can be a smooth surface.

As described above, by polishing the surface layer 11 of the optical fiber preform 1 using various methods, the surfaces of the recesses 3 and 5 are made smooth, and burrs around the recesses 3 and 5 are eliminated. Can do. For this reason, the reattachment of the foreign matter 2 and the attachment of the polishing fine powder and the like can be suppressed, and even if the foreign matter 2 is attached again or the polishing fine powder is attached, it can be easily removed by washing.
As described above, when the surface layer 11 of the optical fiber preform 1 is polished, the recesses 3 and 5 have a smooth shape as shown in FIGS.

However, if polishing is performed until the diameter of the optical fiber preform 1 changes significantly over the entire circumference, the ratio of the core diameter and the cladding diameter of the optical fiber obtained by spinning the optical fiber preform 1 deviates from a desired value. May end up. For this reason, it is preferable not to polish excessively, and the surface layers 11 of the optical fiber preform 1 have the polished recesses 6 and 7 remaining.
When the optical fiber preform 1 from which the foreign matter 2 has been removed is spun, the recesses 6 and 7 may cause scratches such as cracks on the surface of the spun optical fiber, which may reduce the strength.
As a result of intensive studies, the inventors of the present invention have made it possible to spin the optical fiber preform, that is, the fiber rod, so that the depth of the recess is 1% or less of the diameter of the fiber rod. It has been found that the strength reduction of the optical fiber can be suppressed and problems such as disconnection can be suppressed.

Table 1 shows the depth (d) of the recess formed in the fiber rod and the number of breaks of the optical fiber obtained by spinning the fiber rod.
Here, in Table 1, after forming the recesses 8 of various depths in the surface layer of the fiber rod 10 having a diameter of 80 mm as shown in FIG. This shows the result of polishing the surface layer 11 of the fiber rod 10 in the vicinity of the recess 8 with the polishing jig.
Further, the depth (d) of the concave portion 8 hardly changed even after polishing using a polishing jig. Therefore, the depth (d) of the concave portion 8 in Table 1 can be approximated to the depth of the concave portion 8 of the fiber rod 10 after the surface layer 11 is polished (after processing).

As shown in Table 1, when the depth of the concave portion 8 of the fiber rod 10 after polishing the surface layer 11 (after processing) is 1% or less of the diameter of the fiber rod 10, the spun optical fiber is There is no disconnection.
Based on the above results, the conditions for removing the surface layer of the optical fiber preform near the foreign material and the polishing conditions for the surface layer are adjusted so that the depth of the recess is 1% or less of the diameter of the fiber rod 10. It is preferable to process the fiber preform 1. Thereby, it can suppress that the intensity | strength of the optical fiber spun due to the recessed part falls, and can suppress malfunctions, such as a disconnection.

The foreign matter removal conditions and surface layer polishing conditions for processing the optical fiber preform 1 so that the depth of the recesses is 1% or less of the diameter of the fiber rod will be described in more detail below.
First, the case where a fiber rod is processed will be described.
Since the fiber rod 10 is formed so that the core and the clad have an appropriate ratio, when the fiber rod 10 is processed, it is necessary to prevent the diameter of the fiber rod 10 from changing significantly over the entire circumference. is there.

In the step of partially removing the surface layer 11 of the fiber rod 10 in the vicinity of the foreign matter 2, the surface layer 11 is removed step by step, and after removing the surface layer 11 in each step, the residual foreign matter 2 is removed. By confirming the presence or absence, the surface layer 11 is not excessively removed, and the depth (d) of the recess can be made 1% or less of the diameter of the fiber rod 10.
Then, in the step of polishing the surface layer 11 after partially removing the surface layer 11 of the fiber rod 10 in the vicinity of the foreign matter 2, the diameter of the fiber rod 10 changes significantly over the entire circumference without polishing excessively. It is preferable to suppress this. When polishing is performed until the diameter of the fiber rod 10 changes significantly over the entire circumference, the ratio of the core diameter and the cladding diameter of the optical fiber obtained by spinning the fiber rod 10 deviates from a desired value. This is not preferable because of the above problems.
For this reason, the vicinity of the concave portion is selectively polished, and the surface layer 11 of the fiber rod 10 is observed as much as possible in a short time so that the diameter of the entire fiber rod 10 does not change. Is preferred. Thereby, it can be set as the optical fiber preform (fiber rod 10) which can manufacture the optical fiber which has a desired optical characteristic.

Next, the case where an intermediate rod is processed will be described.
The intermediate rod is manufactured in an intermediate process for manufacturing the fiber rod 10, and after removing foreign matters by the processing method of the present invention, soot particles are sprayed on the surface of the intermediate rod, and heat treatment is performed to vitrify the fiber. It becomes the rod 10.
For this reason, the recess formed by partially removing the surface layer 11 of the intermediate rod in the vicinity of the foreign matter 2 is covered with soot particles sprayed on the surface of the intermediate rod when the intermediate rod is used as a glass rod.
Therefore, since the concave portion formed by partially removing the surface layer 11 of the intermediate rod is filled with soot particles when the intermediate rod is used as a glass rod, the concave portion is almost eliminated when the fiber rod 10 is vitrified.
However, if the recess is too large, when soot particles are sprayed on the surface of the intermediate rod, voids are generated in the recess filled with the soot particles and may remain in the fiber rod 10 as bubbles when vitrified. . For this reason, it is preferable to adjust the conditions for removing the surface layer 11 and the polishing conditions after removing the foreign matter so that the concave portions do not become excessively large.

According to the present invention, by partially removing the surface layer 11 of the optical fiber preform 1 in the vicinity of the foreign material 2, the foreign material 2 buried in the surface layer 11 can be reliably and inexpensively removed in a short time.
In particular, since the foreign matter 2 can be reliably removed, it is not necessary to make all of the manufacturing processes including the conveyance into a high-purity clean atmosphere and to completely avoid the adhesion and burial of the foreign matter 2 as in the past, and a large amount of equipment is required. The manufacturing cost of the optical fiber preform 1 can be suppressed.
Further, compared with the conventional method of flame polishing the entire surface layer of the optical fiber preform, the number of work steps is reduced and the foreign matter 2 can be removed in a short time.

Further, in the conventional flame polishing method, since the optical fiber preform 1 is softened by the heat of the flame, the foreign matter 2 may enter and remain inside the optical fiber preform 1.
On the other hand, as described above, a method for polishing and removing the surface layer 11 of the optical fiber preform 1 near the foreign matter 2 using a polishing jig, or an optical fiber preform near the foreign matter 2 by irradiating laser light. In the method of removing the surface layer 11 by heating, since the surface layer 11 in the vicinity of the foreign matter 2 is removed, the foreign matter 2 does not enter the inside of the optical fiber preform 1 and the foreign matter 2 can be reliably removed.
Further, almost no foreign matter 2 remains in the optical fiber preform processed by the processing method of the present invention. By using this optical fiber preform, the strength of the optical fiber caused by the foreign matter 2 is reduced, or the transmission is reduced. Deterioration of characteristics and increase in transmission loss can be suppressed, and an optical fiber can be manufactured with high yield.

  In the optical fiber preform (fiber rod 10) processed by the processing method of the present invention, it is preferable that the depth (d) of the formed recess is 1% or less of the diameter of the optical fiber preform. In addition, it is possible to suppress the strength of the spun optical fiber from being lowered due to the concave portion, and it is possible to suppress problems such as disconnection.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.
[Examination example]
In the present invention, a concave portion remains in the fiber rod 10 after the foreign substance 2 is removed. However, the influence of the concave portion on the optical fiber spun from now on was examined in advance.
A fiber rod 10 having a length of 1000 mm was prepared by the following method.
First, a porous base material was manufactured by depositing soot fine particles, which become a part of the core and the clad, below the starting base material by a gas phase axis method. This porous base material was dehydrated and sintered in an electric furnace and then flame polished to produce a glass rod. And this glass rod was extended | stretched so that it might become a diameter of about 25 mm, and it was set as the intermediate rod.
Then, soot particles were deposited on the outer side of the intermediate rod by a gas phase axial method, and then sintered in an electric furnace to produce a fiber rod 10 having a diameter of about 80 mm.

A diamond grindstone of # 400 grain size is attached to a hand grinder as a polishing jig, and this polishing jig is applied to the surface layer 11 of the fiber rod 10 while rotating at a high speed. As shown in FIG. Five grooves having a length of 150 mm and a depth (d) of the deepest portion were formed as the recesses 8 in the ten surface layers 11.
Next, the grain size of the diamond grindstone is sequentially changed to # 800, # 1000, and # 2000, and the surface layer 11 of the fiber rod 10 near the recess 8 is polished while observing the surface state with a microscope, and then the fiber rod 10 is purified. Washed with water.
As a result of observing the surface state with a microscope, when the surface was polished with a diamond grindstone having a particle size of # 800 or less, the polishing marks of the surface layer 11 of the fiber rod 10 could be clearly observed. However, when polished with a diamond grindstone having a particle size of # 1000 or more, no trace of polishing remained on the surface layer 11 of the fiber rod 10. Further, the depth (d) of the recess 8 hardly changed by polishing.

Next, the fiber rod 10 formed with the groove (recessed portion) 8 was spun to produce an optical fiber. This optical fiber was subjected to a 1.1% proof test to examine the number of breaks. The results are shown in Table 1.
From Table 1, when the depth (d) of the deepest part of the recess 8 is 1% or less of the diameter of the fiber rod 10, the spun optical fiber has zero breakage and sufficient strength. I understood it.
Further, the loss, mode field diameter, cut-off wavelength, and dispersion value of the optical fiber after the proof test were measured, and in all the optical characteristics, excellent characteristics at a practical level were obtained.

[Example 1]
While the fiber rod 10 having a length of 1000 mm and an outer diameter of 80 mm was heated with a flame, the foreign matter 2 was sprinkled on the fiber rod 10 and the foreign matter 2 was buried in the surface layer 11 of the fiber rod 10 as shown in FIG. As the foreign material 2, dust, fiber powder, iron powder, aluminum powder or the like was used.
In one fiber rod 10, foreign matters were removed by the processing method of the present invention under different conditions for the upper half and the lower half.
Thereafter, the fiber rod 10 was washed with pure water and then spun to produce an optical fiber. This optical fiber was subjected to a 1.1% proof test to examine the number of breaks.
Table 2 shows the processing conditions of the fiber rod 10 and the results of the 1.1% proof test.

Here, in the step of partially removing the surface layer 11 of the fiber rod 10 in the vicinity of the foreign matter 2, when grinding and removing using a polishing jig, a diamond grindstone having a particle size of # 400 was used as the polishing jig. Then, this polishing jig was attached to a hand grinder and applied to the surface layer 11 of the fiber rod 10 while rotating the abrasive at high speed, and the surface layer 11 of the fiber rod 10 in the vicinity of the foreign matter 2 was removed by polishing.
When the surface layer 11 of the fiber rod 10 near the foreign material 2 is heated and removed by irradiating the laser beam, the laser beam is applied to the foreign material 2 using a CO ₂ laser or a YVO ₄ laser while monitoring the foreign material 2 with a microscope. The area was irradiated and heated. And it confirmed that the foreign material was removed visually.

In addition, when the surface layer 11 of the fiber rod 10 in the vicinity of the foreign material 2 is partially removed and then polished using a polishing jig in the step of polishing the surface layer 11, first a diamond grindstone having a particle size of # 800 Was then used, and finish polishing was performed using a diamond grindstone having a particle size of # 2000.
Further, when the surface layer 11 of the fiber rod 10 is polished by flame polishing, the surface of the concave portion is made smooth by heating the vicinity of the concave portion with an oxyhydrogen flame, and burrs around the concave portion are eliminated.

As shown in Table 2, when the fiber rod 10 was not processed and the foreign matter 2 was not removed, in the optical fiber obtained by spinning the fiber rod (sample No. 1 (upper half)) 10, The disconnection occurred 20 times due to the remaining foreign matter. The loss at 1.31 μm of the optical fiber was 1.2 dB / km.
On the other hand, the foreign material 2 was able to be removed reliably by partially removing the surface layer 11 of the fiber rod 10 in the vicinity of the foreign material 2. For this reason, in the optical fiber obtained by spinning the fiber rod (sample No. 3) 10 after removing the foreign matter 2 (after processing), the number of breaks is 1 to 3 as a result of the proof test. It has been found that the number of disconnections is reduced and the strength is sufficient.
Further, when the surface layer 11 of the fiber rod 10 in the vicinity of the foreign matter 2 is partially removed and then polished, the fiber rod after processing (sample No. 1 (lower half), No. 2) 10 is obtained by spinning. In the optical fiber strand, no disconnection of the optical fiber strand occurred.

This is considered to be because the foreign matter 2 can be removed by processing the fiber rod 10 by the processing method of the present invention, and the decrease in the strength of the optical fiber caused by the foreign matter 2 can be suppressed. Further, since the depth of the concave portion of the surface layer 11 of the fiber rod 10 after processing is 1% or less of the diameter of the fiber rod 10, the strength of the optical fiber obtained by spinning the fiber rod 10 is reduced. It is thought that this could be further suppressed.
As described above, when the processed optical fiber preform 1 is spun, an optical fiber having excellent strength can be manufactured, and the yield for manufacturing the optical fiber can be improved.

[Example 2]
Before stretching the glass rod, the foreign material 2 was sprinkled on the glass rod in the same manner as in Example 1, and then stretched to obtain an intermediate rod having a diameter of 25 mm with the foreign material 2 buried in the surface.
In one intermediate rod, foreign matters were removed by the processing method of the present invention under different conditions for the upper half and the lower half.
Next, soot particles were deposited on the outside of the intermediate rod, and then sintered in an electric furnace to produce a fiber rod 10 having a diameter of 80 mm.
The inside of the obtained fiber rod 10 was visually observed, and the presence or absence of the foreign matter 2 inside the fiber rod 10 was confirmed. Further, the fiber rod 10 was spun to produce an optical fiber, and loss characteristics were measured on this optical fiber. Here, when measuring the loss characteristic, the measurement was performed by selecting a portion where the foreign matter 2 was present in the optical fiber to be measured. These results are shown in Table 3.

As shown in Table 3, when the intermediate rod was not processed and the foreign matter 2 was not removed, the intermediate rod (sample No. 1 (upper half)) was made into a fiber rod 10 and then spun. The optical fiber has a very high transmission loss of 3.8 dB / km at a wavelength of 1.31 μm and cannot be used as a transmission optical fiber.
On the other hand, an intermediate rod (sample No. 3) after removing the foreign matter 2 is used as a fiber rod 10 and an optical fiber obtained by spinning the fiber rod 10 has a transmission loss of They were 0.33 dB / km and 0.41 dB / km, which were low loss.
Further, when polishing is performed after the surface layer 11 of the intermediate rod in the vicinity of the foreign matter 2 is partially removed, spinning is performed after the processed intermediate rod (sample No. 1 (lower half), No. 2) is used as the fiber rod 10. In the optical fiber obtained in this way, no foreign matter was mixed, and the transmission loss was 0.33 dB / km, which was a low loss.

After the surface layer 11 of the intermediate rod in the vicinity of the foreign material 2 is partially removed, among the intermediate rods that have not been polished, the surface layer 11 in the vicinity of the foreign material 2 is polished and removed using a polishing jig. In the fiber rod 10 formed from the intermediate rod (No. 3 (upper half)), very fine foreign matters remained in two places.
On the other hand, when the surface layer 11 of the intermediate rod near the foreign material 2 is partially removed and then polished, as described above, from the processed intermediate rod (sample No. 1 (lower half), No. 2). The foreign material 2 was not mixed in the formed fiber rod 10.
It is preferable to polish the surface layer 11 after partially removing the surface layer 11 of the intermediate rod in the vicinity of the foreign matter 2, so that the concave surface formed after the removal of the foreign matter 2 vicinity is smooth and formed around the concave portion. The burr etc. which were done can be removed. For this reason, even if the foreign matter 2 is reattached in the vicinity of the concave portion or the polishing fine powder is attached, it can be easily removed by washing, and the fiber rod 10 in which the foreign matter 2 is not buried is obtained.

In Example 2, when soot particles were deposited on the surface layer 11 of the intermediate rod to form the fiber rod 10, soot particles were deposited in the recesses, and no recesses remained on the surface layer 11 of the fiber rod 10.
Thus, in the fiber rod 10 formed using the processed intermediate rod, the foreign matter 2 does not remain and there is no concave portion. Therefore, when the fiber rod 10 is spun to produce an optical fiber, An optical fiber having excellent strength and low loss can be manufactured without being affected by the foreign matter 2 or the concave portion.
For this reason, after forming the fiber rod 10 using the intermediate rod from which the foreign material 2 has been removed by the processing method of the present invention, the fiber rod 10 is spun to improve the yield for manufacturing the optical fiber. it can.

  In the present invention, foreign matter buried in the surface layer of the optical fiber preform can be reliably removed. By spinning the processed optical fiber, an optical fiber having high strength and low loss can be manufactured. For this reason, the optical fiber preform processing method of the present invention is for optical fibers that require high strength and low loss, such as transmission optical fibers and multimode optical fibers that become high-speed transmission paths and long-distance transmission paths. It can be used for the manufacturing process of the optical fiber preform.

It is a schematic diagram which shows the state in which the foreign material entered into the surface of the optical fiber preform. FIG. 2 is an enlarged view showing the vicinity of a foreign object surrounded by an alternate long and short dash line A in FIG. 1. It is a schematic diagram which shows the state by which the surface layer of the optical fiber preform | base_material of the foreign material vicinity was polished and removed with the jig | tool for grinding | polishing. Surface layer of the optical fiber preform of the foreign object near a schematic diagram showing an example of a state of being removed by heating by a laser beam of a CO ₂ laser. Surface layer of the optical fiber preform of the foreign object near a schematic diagram showing an example of a state of being removed by heating with a laser beam of a YVO ₄ laser. It is a schematic diagram which shows an example of the state where the recessed part vicinity of the optical fiber base material shown in FIG. 3 was grind | polished with the jig | tool for grinding | polishing. It is a schematic diagram which shows an example of the state by which the recessed part vicinity of the optical fiber preform | base_material 1 shown by FIG. 5 was grind | polished by the flame grinding | polishing method. It is a schematic diagram which shows the state by which the groove | channel which becomes a recessed part was formed in the longitudinal direction on the surface of the fiber rod.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,10 ... Optical fiber preform, 2 ... Foreign material, 3, 4, 5, 6, 7, 8 ... Recessed part, 11 ... Surface layer.

Claims (4)

In the processing method of the optical fiber preform that removes foreign matter buried in the surface layer of the optical fiber preform,
Partially removing the foreign matter by partially removing the surface layer of the optical fiber preform in the vicinity of the foreign matter,
While subjecting the optical fiber preform formed with a recess by partial removal of the surface layer to a spinning process ,
In the partial removal step, the depth of the concave portion is 0.2% or more and 1% or less with respect to the diameter of the optical fiber preform used in the spinning step . Processing method. After the partial removal step, prior to the spinning step,
2. The method of processing an optical fiber preform according to claim 1, wherein a post-polishing step is performed to polish the concave portion and the surface layer in the vicinity thereof. In the processing method of the optical fiber preform that removes foreign matter buried in the surface layer of the optical fiber preform,
A partial removal step of removing the foreign matter by partially removing the surface layer of the optical fiber preform in the vicinity of the foreign matter;
Said surface layer partially removed soot particulates are deposited on the outer surface of the optical fiber preform having a recess formed by the, possess a vitrification step of heating,
Method of processing an optical fiber preform, which comprises subjecting the optical fiber preform is vitrified in said vitrification step spinning process. After the partial removal step, prior to the vitrification step,
4. The method for processing an optical fiber preform according to claim 3 , wherein a post-polishing step is performed to polish the recess and the surface layer in the vicinity thereof.

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