JPH04321532A - Production of optical fiber reform - Google Patents

Abstract

PURPOSE:To uniform the bulk density of silica powder and prevent the outer diameter of an optical fiber preform from fluctuating, by filling the silica powder in a mold while vibrating the mold, when the filled silica powder is compressed and is intered to produce the optical fiber preform. CONSTITUTION:A glass rod 43 for the core of an optical fiber preform or for botht the core and the inner layer of the clad of the optical fiber preform is placed at the center of a clad mold consisting of mold pieces 11, 13, 15, and silica powder 33 for the clad is filled in the clad mold. The clad mold is pressed from outside to form a composite porous molded product, and the molded product is sintered to produce the optical fiber preform. In the process, the filling of the clad silica powder 33 in the clad mold is performed in such a state that at least the lower lid 11 of the mold is vibrated (utilizing e.g. a vibrator 37).

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical fiber preform.

0002

[Prior Art] Conventionally, one known method for manufacturing optical fiber preforms is to compress silica powder to make a porous molded body, and then sinter this to make an optical fiber preform. There is. An example of a compression device used for this is shown in FIG.

In FIG. 6, 11 is a lower lid, 13 is an upper lid,
15 is a cylindrical molding rubber mold, 17 is a lower annular frame body, 19
21 is a pressure-resistant outer cylinder, and 23 is a pressurized rubber type. The pressurized rubber mold 23 is integrated with the pressure-resistant outer cylinder 21, and a pressurized chamber 25 is formed between them. Pressure-resistant outer cylinder 2
1 includes a passage 2 for feeding a pressure medium such as water into a pressurizing chamber 25;
7 is formed. Further, a deaeration hole 29 is formed in the upper lid 13. Here, the lower lid 11, the upper lid 13, the molding rubber mold 15, the lower annular frame 17, and the upper annular frame 19.
constitutes a mold for cladding, which includes a pressure-resistant outer cylinder 21,
The pressurizing rubber mold 23, the lower annular frame 17, and the upper annular frame 19 constitute a pressurizer.

[0004] To manufacture an optical fiber preform using this device, first, with the upper cover 13 removed, a glass for the core (or for the inner layer of the core and cladding) prepared in advance is placed in the center of the lower cover 11. The rod 31 is stood vertically, and then the molded rubber mold 15 is filled with silica powder 33 for cladding. After that, the upper lid 13 is closed. At this time, the upper end of the glass rod 31 is placed on the support 3 so as not to block the exhaust hole 29.
Hold at 5.

In this state, when a pressure medium such as water is injected into the pressurizing chamber 25 and pressure is applied, the silica powder 33 inside
is pressurized via the pressurizing rubber mold 23 and the molding rubber mold 15,
It is compressed to become a porous molded body. After that, the pressure is removed, the upper cover 13 and the lower cover 11 are removed, the composite porous molded body integrated with the glass rod 31 is taken out, and this composite porous molded body is sintered and vitrified. A fiber preform is obtained.

[0006] In the above method, the cladding portion is formed from silica powder, but the core portion may also be formed from silica powder.

[0007]

[Problem to be solved by the invention] In the conventional method, there is a large variation in the packing density when filling the mold with silica powder, resulting in variations in the outer diameter of the resulting composite porous molded body and optical fiber preform. There was a problem. When manufacturing an optical fiber by drawing an optical fiber preform with a variable outer diameter, not only does the cutoff wavelength vary greatly in the longitudinal direction, but it is extremely difficult to obtain the desired designed cutoff wavelength. .

[0008] Furthermore, if the packing density is non-uniform, air bubbles are likely to occur in the optical fiber preform after the composite porous molded body is made into transparent glass, making it difficult to produce a large-sized preform. An object of the present invention is to provide a method for manufacturing an optical fiber preform that solves the above problems.

[0009]

[Means for Solving the Problems] In order to achieve this object, the invention of claim 1 is such that after filling a core mold with silica powder, the core mold is pressurized from the outside to form porous cores. Next, this porous core molded body is placed in the center of a cladding mold, and after filling the cladding mold with silica powder, the cladding mold is removed from the outside. In a method of producing an optical fiber preform by pressurizing a composite porous molded body and sintering the composite porous molded body, the steps include filling the core mold with silica powder and forming the cladding. The silica powder for cladding is filled into each mold while at least the lower lid of the mold is vibrated.

[0010] In order to achieve the above object, the invention of claim 2 provides a glass rod for the core or for the inner layer of the core and cladding in the center of the cladding mold, and a glass rod for the cladding inside the cladding mold. After filling the silica powder, the cladding mold is pressurized from the outside to produce a composite porous molded body, and the composite porous molded body is sintered to produce an optical fiber preform. This method is characterized in that the silica powder for cladding is filled into the mold while at least the lower lid of the mold is vibrated.

[0011]

[Operation] By filling the mold with silica powder while applying vibration in this manner, the packing density of the silica powder is made uniform, and fluctuations in the outer diameter of the composite porous molded body can be suppressed.

0012

EXAMPLES Examples of the present invention will be described in detail below. Example 1 First, silica powder for the core was produced using VAD, which is a vapor phase method.
Manufactured by the method. This silica powder contains GeO2 as a dopant. The synthesis conditions are as follows. GeCl4: 0.4 g/min
SiCl4: 6.0 g/min H2:
12.0 l/min Ar: 5.0 l/m
in O2: 40.0 l/min

0013
FIG. 1 shows a compression apparatus for forming a porous molded body for a core from the silica powder for a core obtained in this manner. Since this compression device is for the core, it is different in size from the compression device shown in FIG. 6 described above, but is structurally the same as the compression device shown in FIG. 6. Therefore, parts corresponding to those in FIG. 6 are given the same reference numerals. Both the molding rubber mold 15 and the pressurizing rubber mold 23 are made of silicone rubber.

[0014] This compression device differs from the conventional one in that the lower cover 11
A vibrator 37 is embedded inside. As the vibrator 37, PZT, which is a type of piezoelectric element, was used. This vibrator 37 has a thickness of 5 mm and an outer diameter of 8 mm, operates with an applied voltage of about 5 V, and has a resonant frequency of about 100 kHz.

The upper lid 13 of this apparatus is removed, and the cavity formed by the lower lid 11 and the molded rubber mold 15 is filled with the core silica powder 39 obtained as described above. When performing this filling, the vibrator 37 was operated to vibrate the lower lid 11 and the molded rubber mold 15. The molding rubber mold 15 has an inner diameter of 10 mm and a length of about 500 mm, and the amount of silica powder 39 for the core to be charged is about 35 g. Although no solvent was used in this example, the use of a solvent facilitates molding.

After filling the silica powder 39, the upper lid 13 was closed. The silica powder 39 had been sufficiently degassed in advance, and after the top lid 13 was closed, a pump (not shown) was connected to the deaeration hole 29 to perform deaeration for about 1 hour. Note that the surfaces of the upper lid 13 and lower lid 11 that come into contact with the silica powder 39 are coated with tetrafluoroethylene resin for the purpose of preventing contamination.

After degassing, the pressure chamber 25 is opened from the passage 27.
Pressure medium (water) is injected into the pressurized rubber mold 23.
A pressure of kgf/cm2 was applied for about 1 minute. Through this operation, pressure was transmitted from the pressurized rubber mold 23 to the molded rubber mold 15, and the core silica powder 39 was compressed. At this time, the depressurization and pressurizing force were adjusted so that the compressed state of the silica powder 39 was uniform. After that, in order to prevent cracks caused by the sudden restoring force of the molded rubber mold 15,
The pressure was slowly reduced over about 1 hour. At this time as well, deaeration was performed to prevent cracks and the like. From the above operations, the outer diameter is 8m.
A porous molded body having a length of 480 mm and free from cracks, cracks, and outer diameter variations was obtained to serve as the core portion of an optical fiber.

Next, a porous molded body for the cladding is formed around this porous molded body for the core, and for this purpose a compression device shown in FIG. 2 is used. This compression device is the same as the compression device shown in FIG. 6 described above except that the vibrator 37 is embedded in the lower lid 11. Therefore, Figure 6
The same reference numerals are given to corresponding parts. The vibrator 37 is a piezoelectric element (PZT) with a thickness of about 30 mm and an outer diameter of about 100 mm, and a resonant frequency of about 300 kHz.

First, the upper lid 13 of the device is removed, and the porous molded body 41 for the core previously manufactured is vertically placed in the center of the lower lid 11, and then fully inserted into the cavity formed by the lower lid 11 and the molded rubber mold 15. is filled with degassed silica powder 33 for cladding. When performing this filling, the vibrator 37 was operated to vibrate the lower lid 11 and the molded rubber mold 15. Molding rubber mold 15
has an inner diameter of 120 mm and a length of about 600 mm, and the amount of silica powder 33 for cladding is about 6.1 kg.

After the filling of the silica powder 33 was completed, the upper lid 13 was closed, and a pump (not shown) was connected to the degassing hole 29 to perform degassing for about 1 hour. After that, pressure medium (water) is injected into the pressurizing chamber 25 from the passage 27, and the pressurized rubber mold 23
A pressure of 1000 kgf/cm2 was applied for about 1 minute. By this operation, the pressurized rubber mold 23 is changed to the molded rubber mold 15.
Pressure was transmitted to the cladding silica powder 33, and the cladding silica powder 33 was compressed. At this time, the depressurization and pressurizing force were controlled so that the compressed state of the silica powder 33 was uniform. Thereafter, the pressure was slowly reduced over about 1 hour. Deaeration was also performed at this time. From the above operations, the outer diameter is 115 mm and the length is 60 mm.
A composite porous molded body having a core portion and a cladding portion with a diameter of 0 mm and no cracks, cracks, or fluctuations in outer diameter was obtained.

[0021] Next, this composite porous molded body was dehydrated and vitrified in a He atmosphere and a Cl2 atmosphere, similarly to those produced by a gas phase method such as the VAD method. The optical fiber preform obtained in this way has an outer diameter of 105 m.
m, length 550 mm, and relative refractive index 0.35%, and no bubbles due to non-uniformity of packing density were observed. Finally, when this optical fiber preform was drawn by a conventional method, characteristics equivalent to those produced by a vapor phase method such as the VAD method were obtained. The cutoff wavelength of the optical fiber was 1.30 μm, which matched the design value.

Example 2 In this example, a glass rod in which the core portion and the cladding inner layer portion were integrally formed was used. This glass rod is V
Manufactured using the AD method, with a core/cladding ratio of 1:4.
It has an outer diameter of 10.6 mm and a length of 500 mm. Approximately 1,600 g of commercially available silica powder (particle size: approximately 1 μm) was prepared for use as a cladding material, and was sufficiently degassed.

The compression device used is as shown in FIG. 3, and is the same as the compression device shown in FIG. 6 described above except that the vibrator 37 is embedded in the lower lid 11. Therefore, parts corresponding to those in FIG. 6 are given the same reference numerals. The vibrator 37 is a piezoelectric element (PZT) with a thickness of about 10 mm and an outer diameter of about 50 mm, operates at a voltage of about 10 V, and has a resonant frequency of about 200 kHz.

Remove the upper lid 13 of the device, place the aforementioned glass rod 43 vertically in the center of the lower lid 11, and then remove the lower lid 11.
The above-mentioned silica powder 33 for cladding is filled into the cavity formed by the molding rubber mold 15. When performing this filling, the vibrator 37 was operated to vibrate the lower lid 11 and the molded rubber mold 15.

After filling the silica powder 33, the upper lid 13 was closed and a pump was connected to the degassing hole 29 to perform degassing for about 1 hour. In addition, the silica powder 3 of the upper lid 13 and lower lid 11
The surface in contact with 3 is coated with tetrafluoroethylene resin for the purpose of preventing contamination.

After that, water is injected into the pressurizing chamber 25 from the passage 27 and pressurized, and the pressurized rubber mold 23 is heated to 500 kgf/c.
A pressure of m2 was applied for about 1 minute. Through this operation, the silica powder 33 for cladding was compressed. At this time, the depressurization and pressurizing force were controlled so that the compressed state of the silica powder 33 was uniform. Thereafter, the pressure was slowly reduced over about 1 hour. Deaeration was also performed at this time. Through the above operations, a composite porous molded body having an outer diameter of 42 mm and a length of 480 mm was obtained, which had a glass rod in the center and was free from cracks, cracks, and outer diameter fluctuations.

Next, this composite porous molded body was dehydrated and vitrified in a He atmosphere and a Cl2 atmosphere. The optical fiber preform thus obtained had an outer diameter of 36 mm and a length of 480 mm, and no air bubbles were observed. An optical fiber was manufactured by drawing this optical fiber preform in a conventional manner, and the cutoff wavelength was measured, and it was found that λc
= 1.28 μm, which matched the design value. Furthermore, regarding the fluctuation of the cutoff wavelength in the longitudinal direction, it had the same characteristics as those obtained by the VAD method.

Example 3 In this example as well, a glass rod in which the core portion and the cladding inner layer portion were integrally formed was used. This glass rod is V
It was manufactured using the AD method and has a core/cladding ratio of 1:5.8, an outer diameter of approximately 7.8 mm, and a length of approximately 160 mm. Further, about 57 g of commercially available silica powder (particle size of about 10 μm) was prepared for use as a cladding material, and was sufficiently degassed.

The compression device used can be separated into a cladding mold 45 shown in FIG. 4 and a pressurizer 47 shown in FIG. 5. The mold 45 is composed of a lower lid 11, an upper lid 13, a molded rubber mold 15, etc., and the molded rubber mold 15 has an inner diameter of 25 mm and a length of 150 mm. The pressurizer 47 is
It is composed of a pressure-resistant outer cylinder 21, a pressurized rubber mold 23, a lower frame 49, an upper frame 51, and the like. The molding rubber mold 15 and the pressurizing rubber mold 23 are made of silicone rubber.

Silica powder 33 for cladding is placed in the mold 45.
When filling, the mold 45 is placed on a vibrator 53, the upper cover 13 is removed, and the glass rod 43 is vertically placed in the center of the lower lid 11. In this state, the entire mold 45 is moved by the vibrator 53. Silica powder for cladding 33 while vibrating
Fill it. The vibrator 53 used here is a commercially available orbital shaker, and the vibration frequency is 20 kHz.

After filling the silica powder 33, the upper lid 13 is closed and the entire mold 45 is placed in a pressurizer 47 shown in FIG. Note that the surfaces of the upper lid 13 and the lower lid 11 that come into contact with the silica powder 33 are coated with tetrafluoroethylene resin for the purpose of preventing contamination.

Thereafter, a pump was connected to the deaeration hole 29 to perform deaeration for about 1 hour. Further, while degassing was continued, water was forced into the pressurizing chamber 25 through the passage 27, and a pressure of 1000 kgf/cm2 was applied to the pressurizing rubber mold 23 for about 1 minute. Through this operation, the silica powder 33 for cladding was compressed. At this time, the depressurization and pressurizing force were controlled so that the compressed state of the silica powder 33 was uniform. after that,
The pressure was slowly reduced over about 1 hour. Deaeration was also performed at this time. From the above operations, it was found that the outer diameter was 21 mm and the length was 1 mm, with a glass rod in the center, no cracks, no cracks, and no variation in outer diameter.
A composite porous molded body of 48 mm was obtained.

Next, this composite porous molded body was dehydrated and vitrified in a He atmosphere and a Cl2 atmosphere. The optical fiber preform obtained in this way had an outer diameter of 17 mm,
The length was 145 mm, and no air bubbles were observed. An optical fiber was produced by drawing this optical fiber preform in a conventional manner, and the cutoff wavelength was measured, and it was found that λ
c = 1.30 μm, which matched the design value. Also, VAD
It had the same characteristics as those based on the law.

Comparative Example When the mold 45 shown in FIG. 4 is filled with silica powder without applying vibration, the packing density of the silica powder and the variation width of the packing density were measured, and the results were compared with those in Example 3. The results of the comparison are shown in Table 1.

[0035]

[Table 1]

It is clear that the filling density is higher when the filling is performed by applying vibration, and the fluctuation in the filling density is also smaller.

[0037]

As explained above, according to the present invention, since the silica powder is filled into a mold while being vibrated, the packing density of the silica powder becomes uniform. As a result, the density of the composite porous compact obtained by compression becomes uniform, and it is possible not only to eliminate air bubbles in the optical fiber preform after sintering and vitrification, but also to eliminate defects caused by non-uniform packing density. Diameter fluctuation can be suppressed. In addition, by suppressing variations in the outer diameter, it becomes easier to design the cutoff wavelength, and it also becomes possible to suppress variations in the cutoff wavelength in the longitudinal direction. From the above, it becomes possible to easily mass-produce high-quality and inexpensive optical fibers.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a state in which a core mold is filled with core silica powder in a method for manufacturing an optical fiber preform according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state in which the cladding mold is filled with silica powder for cladding in the post-process of FIG. 1;

FIG. 3 is a sectional view showing a state in which a cladding mold is filled with silica powder for cladding in another embodiment of the present invention.

FIG. 4 is a sectional view showing a state in which a cladding mold is filled with silica powder for cladding in still another embodiment of the present invention.

5 is a sectional view showing a pressurizer that houses the cladding mold of FIG. 4. FIG.

FIG. 6 is a cross-sectional view showing a conventional method for manufacturing an optical fiber preform.

[Explanation of symbols]

11: Lower lid 13: Upper lid 15: Molding rubber mold 17: Lower annular frame 19: Upper annular frame 23: Pressurized rubber mold
25: Pressure chamber 27: Passage 29: Deaeration hole 31: Glass rod 33
: Silica powder for cladding 35: Supporting tool 37: Vibrator 39: Silica powder for core 41: Porous molded body for core 43:
Glass rod 45: Molding mold 47: Pressurizer

Claims (2)

[Claims] Claim 1: After filling a core mold with silica powder, the core mold is pressurized from the outside to produce a porous core mold, and then this core porous mold is clad. After filling the cladding mold with silica powder for cladding, pressurize the cladding mold from the outside to create a composite porous molded body. In the method of manufacturing an optical fiber preform by sintering the core mold, filling the core silica powder into the core mold and filling the clad silica powder into the clad mold with at least one of the molds is performed. A method for manufacturing an optical fiber preform, characterized in that the manufacturing method is performed with a lower lid vibrating. 2. After installing a glass rod for the core or for the core and clad inner layer in the center of the cladding mold, and filling the cladding mold with silica powder for the cladding, the cladding mold is In a method for manufacturing an optical fiber preform by applying pressure from the outside to create a composite porous molded body and sintering this composite porous molded body,
A method for manufacturing an optical fiber preform, characterized in that filling the cladding silica powder into the cladding mold is performed while at least a lower lid of the mold is vibrated.