METHOD OF MANUFACTURING OPTICAL FIBER GLASS BASE MATERIAL

Abstract

A method of manufacturing an optical fiber glass base material includes storing a glass particulate deposit prepared through a vapor-phase axial deposition (VAD) method in a storage chamber, wherein a hydrogen chloride concentration in the storage chamber is maintained at 2 ppm or lower, and a humidity in the storage chamber is preferably maintained at 12 g/m.sup.3 or lower. The storage chamber has an air supply port and an exhaust port, and a gas discharged from the exhaust port is re-supplied from the supply port into the storage chamber using a blower fan. A chemical filter is provided between the exhaust port and the blower fan. A dehumidifier is preferably provided between the exhaust port and the blower fan.

Claims

1. A method of manufacturing an optical fiber glass base material, comprising storing a glass particulate deposit prepared through a vapor-phase axial deposition (VAD) method in a storage chamber, wherein a hydrogen chloride concentration in the storage chamber is maintained at 2 ppm or lower.

2. The method according to claim 1, wherein a humidity in the storage chamber is maintained at 12 g/m.sup.3 or lower.

3. The method according to claim 1, wherein the storage chamber has an air supply port and an exhaust port, and a gas discharged from the exhaust port is re-supplied from the supply port into the storage chamber using a blower fan.

4. The method according to claim 3, wherein a chemical filter is provided between the exhaust port and the blower fan.

5. The method according to claim 3, wherein a dehumidifier is provided between the exhaust port and the blower fan.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0015] FIG. 1 is a schematic diagram illustrating an exemplary configuration of a glass particulate deposit storage chamber according to the present invention; and

[0016] FIG. 2 is a schematic diagram illustrating a configuration of a glass particulate deposit storage chamber in a comparative example.

DESCRIPTION OF EMBODIMENTS

[0017] Hereinafter, embodiments of the present invention will be described in details with reference to the accompanying drawings by explaining an example of the present invention and a comparative example. However, the invention is not limited thereto, and various modes may be possible.

[0018] FIG. 1 is a schematic diagram illustrating an exemplary configuration of a glass particulate deposit storage chamber according to the present invention.

[0019] As illustrated in FIG. 1, a manufactured glass particulate deposit 2 is stored in a storage chamber 1 isolated from the outside. The storage chamber 1 has an exhaust port 3 to discharge the air of the storage space. A gas discharged from the exhaust port 3 passes through a chemical filter 4 arranged in the downstream. The chemical filter 4 is formed from a filter medium based on activated carbon, and adsorbs or removes an acidic gas (hydrogen chloride). A dehumidifier 5 is provided in the downstream of the chemical filter 4 to remove moisture in the air. The dehumidifier 5 compresses a refrigerant using a compressor, and condenses and removes (dehumidifies) moisture in the air using latent heat generated in evaporation of the refrigerant. As a result, a hydrogen chloride gas is removed from the air discharged from the exhaust port, and the air is dried. Then, the treated air is re-supplied from the supply port 7 to the storage chamber 1 using the blower fan 6.

EXAMPLES

[0020] A glass particulate deposit 2 prepared through the VAD method was stored in a storage chamber 1 illustrated in FIG. 1. During the storing, the air inside the storage space was discharged from the exhaust port 3 and was filtered through a chemical filter 4 provided in the downstream thereof to absorb or remove an acidic gas (hydrogen chloride). Furthermore, moisture was removed using the dehumidifier 5 provided in the downstream thereof, and the treated gas was returned from the supply port 7 to the storage chamber 1 using the blower fan 6. As a result, a hydrogen chloride gas concentration in the storage chamber was maintained at 2 ppm or lower, and a humidity in the storage chamber was maintained at 12 g/m.sup.3 or lower.

[0021] Then, the glass particulate deposit 2 was stored in the storage chamber for 24 hours and was then introduced into a furnace core tube formed of quartz glass. The internal space of the furnace core tube was maintained in an atmosphere including a chlorine gas of 2.7%. The glass particulate deposit 2 was heated in the heating furnace at a temperature of 1150 C. for dehydration. Then, the furnace core tube was maintained in a helium atmosphere, and the glass particulate deposit 2 was heated in the heating furnace at a temperature of 1500 C. for transparent vitrification. As a result, a transparent glass core base material was manufactured.

[0022] An optical fiber glass base material was prepared by externally attaching a glass cladding layer around the resulting transparent glass core base material, and was drawn to obtain an optical fiber. The transmission characteristics of the manufactured optical fiber were measured. It was found that a single-mode optical fiber having excellent optical characteristics as shown in Table 1 was obtained.

TABLE-US-00001 TABLE 1 Exam- Exam- Exam- ple 1 ple 2 ple 3 Transmission 1310 nm [dB/km] 0.326 0.324 0.325 loss 1383 nm [dB/km] 0.282 0.279 0.279 1550 nm [dB/km] 0.184 0.185 0.184 Mode field 1310 nm [m] 9.22 9.26 9.26 diameter Cut-off wavelength (2 m- [nm] 1266 1265 1268 length fiber) Zero-dispersion wavelength [nm] 1311.2 1312.3 1312.0

Comparative Example

[0023] A glass particulate deposit 9 prepared through the VAD method was stored in a storage chamber 8 illustrated in FIG. 2. During the storing, the air inside the storage space was discharged from the exhaust port 10, and was filtered through a HEPA filter 11 provided in the downstream thereof to remove dust in a gas. The gas filtered through the HEPA filter 11 was classified to Class 10000, and was returned from the supply port 13 to the storage chamber 8 again using the blower fan 12. Note that the HEPA filter is an air filter having a particle collection rate of 99.97% or higher for particles having a particle diameter of 0.3 m at a rated flow rate and an initial pressure loss of 245 Pa (25 mm H.sub.2O) or less as specified in the standard JIS Z 8122:2000.

[0024] After the glass particulate deposit 9 was stored in the storage chamber 8 for 24 hours in this manner, a transparent glass core base material was prepared in the same sequence as that of the Example. An optical fiber glass base material was prepared by externally attaching a glass cladding layer around the transparent glass core base material obtained in this manner, and was drawn to obtain an optical fiber. The transmission characteristics of the manufactured optical fiber were measured. It was found that a single-mode optical fiber having the optical characteristics as shown in Table 2 was obtained.

[0025] Comparing with the Example, the transmission loss at 1310 nm and 1550 nm was higher by approximately 0.01 dB/km. In particular, the transmission loss at 1383 nm based on the OH group was higher by approximately 0.025 dB/km.

TABLE-US-00002 TABLE 2 Comparative example Transmission loss 1310 nm [dB/km] 0.336 1383 nm [dB/km] 0.306 1550 nm [dB/km] 0.195 Mode field diameter 1310 nm [m] 9.04 Cut-off wavelength (2 m-length fiber) [nm] 1262 Zero-dispersion wavelength [nm] 1321

REFERENCE SIGNS LIST

[0026] 1, 8 storage chamber, [0027] 2, 9 glass particulate deposit, [0028] 3, 10 exhaust port, [0029] 4 chemical filter, [0030] 5 dehumidifier, [0031] 6, 12 blower fan, [0032] 7, 13 supply port, [0033] 11 HEPA filter

[0034] Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

[0035] In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

[0036] The entire disclosures of all applications, patents and publications, cited herein and of corresponding Japanese application No. 2019-023188, filed Feb. 13, 2019, are incorporated by reference herein.

[0037] The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

[0038] From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.