U.S. patent application number 12/341324 was filed with the patent office on 2009-04-23 for method of manufacturing optical fiber base material and apparatus of the same.
This patent application is currently assigned to SHIN-ETSU CHEMICAL CO., LTD.. Invention is credited to Dai Inoue, Hiroyuki Koide, Takaaki Nagao.
Application Number | 20090100876 12/341324 |
Document ID | / |
Family ID | 38845539 |
Filed Date | 2009-04-23 |
United States Patent
Application |
20090100876 |
Kind Code |
A1 |
Inoue; Dai ; et al. |
April 23, 2009 |
METHOD OF MANUFACTURING OPTICAL FIBER BASE MATERIAL AND APPARATUS
OF THE SAME
Abstract
A method of manufacturing an optical fiber base material
includes: forming a porous glass base material by depositing glass
particles; providing a synthetic quartz glass vessel at least
partly made of quartz glass which contains aluminum equal to or
less than 0.01 ppm; introducing dehydration reaction gas and inert
gas into the vessel; heating a portion made of quartz glass which
contains aluminum equal to or less than 0.01 ppm in the vessel that
contains the dehydration reaction gas and the inert gas; and
inserting the porous glass base material into the heated vessel to
dehydrate and sinter the porous glass base material.
Inventors: |
Inoue; Dai; (Ibaraki,
JP) ; Koide; Hiroyuki; (Gunma, JP) ; Nagao;
Takaaki; (Ibaraki, JP) |
Correspondence
Address: |
HOGAN & HARTSON LLP
ONE TABOR CENTER, SUITE 1500, 1200 SEVENTEENTH ST
DENVER
CO
80202
US
|
Assignee: |
SHIN-ETSU CHEMICAL CO.,
LTD.
Ibaraki
JP
|
Family ID: |
38845539 |
Appl. No.: |
12/341324 |
Filed: |
December 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2007/062808 |
Jun 26, 2007 |
|
|
|
12341324 |
|
|
|
|
Current U.S.
Class: |
65/424 ; 65/489;
65/530; 65/531 |
Current CPC
Class: |
C03B 37/0146
20130101 |
Class at
Publication: |
65/424 ; 65/530;
65/489; 65/531 |
International
Class: |
C03B 37/07 20060101
C03B037/07; C03C 13/04 20060101 C03C013/04; C03B 37/014 20060101
C03B037/014 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2006 |
JP |
2006-175712 |
Jun 21, 2007 |
JP |
2007-164422 |
Claims
1. A method of manufacturing an optical fiber base material,
comprising: forming a porous glass base material by depositing
glass particles; providing a vessel at least partly made of quartz
glass which contains aluminum equal to or less than 0.01 ppm;
introducing dehydration reaction gas and inert gas into the vessel;
heating a portion made of quartz glass which contains aluminum
equal to or less than 0.01 ppm in the vessel containing the
dehydration reaction gas and the inert gas; and inserting the
porous glass base material into the heated vessel to dehydrate and
sinter the porous glass base material.
2. The method according to claim 1, wherein the portion made of
quartz glass which contains aluminum equal to or less than 0.01 ppm
in the vessel that is formed by melting a soot deposit, the soot
deposit being formed by depositing glass particles which are
produced by hydrolyzing silicide with oxyhydrogen flame.
3. The method according to claim 2, wherein the silicide includes
any of SiCl.sub.4, (CH.sub.3)SiCl.sub.3, (CH.sub.3).sub.2SiCl.sub.2
or a mixed compound thereof.
4. The method according to claim 1, wherein the portion made of
quartz glass which contains aluminum equal to or less than 0.01 ppm
is larger than at least an area heated by a heat source in the
heating.
5. The method according to claim 1, wherein in the dehydrating and
sintering, a total amount of time over which the vessel is
subjected to a temperature exceeding 1,400 degrees Celsius is
within a time period over which a glass layer is entirely
crystallized in a depthwise direction in at least a part of the
portion made of quartz glass which contains aluminum equal to or
less than 0.01 ppm in the vessel.
6. The method according to claim 1, wherein in the dehydrating and
sintering, a total amount of time over which the vessel is
subjected to a temperature exceeding 1,400 degrees Celsius is
within a time period obtained by multiplying a thickness (mm) of
the quartz glass which contains aluminum equal to or less than 0.01
ppm in the vessel by 1,500 hours.
7. The method according to claim 1, wherein a pressure in the
vessel is adjusted in the heating and the dehydrating and
sintering.
8. The method according to claim 7, wherein the heating and the
dehydrating and sintering further includes alerting when the
pressure in the vessel is out of a predetermined range.
9. The method according to claim 7, wherein the heating and the
dehydrating and sintering further includes measuring a pressure in
the vessel and controlling an outlet flow in order that the
pressure in the vessel be within a predetermined range.
10. The method according to claim 7, wherein the heating and the
dehydrating and sintering further includes alerting when a
difference in pressure between the inside of the vessel and a
portion adjacent to a heat source outside the vessel.
11. The method according to claim 7, wherein the heating and the
dehydrating and sintering further includes measuring a difference
in pressure between the inside of the vessel and a portion adjacent
to a heat source outside the vessel and controlling an outlet flow
in order that the measured difference in pressure be within a
predetermined range.
12. An apparatus for dehydrating and sintering a porous glass base
material for an optical fiber, comprising: a heat source; a furnace
tube at least partly made of quartz glass which contains aluminum
equal to or less than 0.01 ppm; a gas introducing port that
introduces gas to the furnace tube; and a gas discharging port that
discharges gas from the furnace tube.
13. The apparatus according to claim 12, wherein the part made of
quartz glass which contains aluminum equal to or less than 0.01 ppm
in the furnace tube is formed by melting a soot deposit, the soot
deposit being formed by depositing glass particles which are
produced by hydrolyzing silicide with oxyhydrogen flame.
14. The apparatus according to claim 13, wherein the silicide
includes any of SiCl.sub.4, (CH.sub.3)SiCl.sub.3,
(CH.sub.3).sub.2SiCl.sub.2 or a mixed compound thereof.
15. The apparatus according to claim 12, wherein an area heated by
at least a heat source is larger than the portion made of quartz
glass which contains aluminum equal to or less than 0.01 ppm.
16. The apparatus according to claim 12 further comprising: an
intra-furnace tube pressure measuring unit that measures a pressure
in the furnace tube; and a pressure control mechanism that adjusts
a pressure in the furnace tube.
17. The apparatus according to claim 16, wherein the pressure
control mechanism includes an alarm unit that alerts when the
pressure measured by the intra-furnace tube pressure measuring unit
is out of a predetermined range.
18. The apparatus according to claim 16, wherein the pressure
control mechanism include: an automatic valve provided on the gas
discharging port; and a control unit that controls a flow rate of
the automatic valve in order that the pressure measured by the
intra-furnace tube pressure measuring unit be within a
predetermined range.
19. The apparatus according to claim 16 further comprising an
extra-furnace tube pressure measuring unit that measures a pressure
around a heat source outside the furnace tube, wherein the pressure
control mechanism includes an alarm unit that alerts when a
difference between the pressure measured by the intra-furnace tube
pressure measuring unit and the pressure measured by the
extra-furnace tube pressure measuring unit is out of a
predetermined range.
20. The apparatus according to claim 16 further comprising an
extra-furnace tube pressure measuring unit that measures a pressure
adjacent to a heat source outside the furnace tube, wherein the
pressure control mechanism includes: an automatic valve provided on
the gas discharging port; and a control unit that controls a flow
rate of the automatic valve in order that a difference between the
pressure measured by the intra-furnace tube pressure measuring unit
and the pressure measured by the extra-furnace tube pressure
measuring unit be within a predetermined range.
21. The apparatus according to claim 12 further comprising: a shaft
that supports a porous glass base material; and a convection
preventing plate that is mounted adjacent to a porous glass base
material mounting part of the shaft.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation in-part of
PCT/JP2007/062808 filed Jun. 26, 2007, which claims priority from
Japanese Patent Application No. 2006-175712 filed Jun. 26, 2006,
and Japanese Patent Application No. 2007-164422 filed Jun. 21,
2007, the contents of which are incorporated herein in their
entireties by this reference.
BACKGROUND
[0002] 1. TECHNICAL FIELD
[0003] The present invention relates to a method of manufacturing
an optical fiber base material being capable of constantly
manufacturing an optical fiber base material of high quality by
so-called VAD, and an apparatus of the same.
[0004] 2. Related Art
[0005] VAD is well-known as a method of manufacturing base
materials for optical fibers. This method employs the following
apparatus, for example.
[0006] In this apparatus, glass particles produced with a core
deposition burner and a cladding deposition burner disposed in a
reaction chamber; and the glass particles are deposited onto a tip
of a starter mounted on a shaft which rotatably lifts up, so that a
porous glass base material for optical fiber composed of a core
layer and a cladding layer is manufactured. The core layer may be
SiO.sub.2 with which GeO.sub.2 is doped, and the cladding layer may
be substantially pure SiO.sub.2.
[0007] The porous glass base material 1 manufactured as described
above is dehydrated and sintered in a heating furnace. The heating
furnace has a furnace tube 2 which can be sealed, an electric
furnace 3 which heats a part of or the whole of the furnace tube 2,
a gas introducing port 4 which introduces any gas into the furnace
tube and a gas discharging port 5 which discharges the exhaust gas
as shown in FIG. 1, for example. FIGS. 1A to 1C progressively show
vitrifying the porous glass base material. Here, reference numeral
6 indicates a shaft which supports the porous glass base material
1.
[0008] Dehydrating is performed by heating the base material at
approximately 1,100 degrees Celsius in dehydrating gas composed of
such as chlorine, oxygen and helium. Meanwhile, vitrifying is
performed by heating the base material at approximately 1,500
degrees Celsius in an atmosphere containing such as helium.
[0009] For the furnace tube forming a part of the heating furnace,
conventionally a silica tube made of natural quartz has been
employed as described in Japanese Patent Application Publication
No. 2004-002109. For example, the silica tube may be an
electric-furnace-melted natural quartz glass tube such as HERALUX-E
(trade name), available from Shin-Etsu Quartz Products Co., Ltd.,
which is made by pulverizing natural quartz and melting in an
electric furnace (herein after referred to as a natural quartz
tube).
[0010] The optical fiber base material manufactured as above may be
formed as a complete optical fiber base material by adding a
cladding to the periphery thereof.
[0011] An optical fiber is obtained by drawing the optical fiber
base material manufactured as above, and is provided for optical
signal transmission. For example, light having a wavelength of
1,310 nm and 1,550 nm is modulated and transmitted through a
single-mode fiber.
[0012] Usually, the transmission loss of the optical fiber at the
wavelength of 1,310 nm is about 0.32 to 0.34 dB/km, however, it
could infrequently become higher than usual, such as about 0.34 to
0.36 dB/km. In most cases, the transmission loss of the optical
fiber at the wavelength of 1,550 nm is not very higher than a
normal value. Moreover, when transmission losses for a wide
wavelength range, such as 900 nm to 1,600 nm are examined, the
shorter the wavelength is, the larger the transmission loss is.
Conventionally, such transmission loss has been acceptable,
however, the market strictly requests for an optical characteristic
in recent years, therefore, such transmission loss has come under a
problem.
SUMMARY
[0013] According to an aspect related to the innovations herein, a
method of manufacturing an optical fiber base material being
capable of reducing an occurrence of the situation described above
that the transmission loss for a short wavelength region,
particularly equal to or less than 1,310 nm, is larger, and an
apparatus of the same are provided. This object can be achieved by
combinations of features recited in dependent claims. In addition,
independent claims define further advantageous specific
examples.
[0014] According to an aspect related to the innovations herein,
the method of manufacturing an optical fiber base material is
provided. The method includes: forming a porous glass base material
by depositing glass particles; providing a vessel at least partly
made of quartz glass which contains aluminum equal to or less than
0.01 ppm; introducing dehydration reaction gas and inert gas into
the vessel; heating a portion made of quartz glass which contains
aluminum equal to or less than 0.01 ppm in the vessel containing
the dehydration reaction gas and the inert gas; and inserting the
porous glass base material into the heated vessel to dehydrate and
sinter the porous glass base material.
[0015] According to an aspect related to the innovations herein, an
apparatus for manufacturing an optical fiber base material that
dehydrates and sinters a porous glass base material for an optical
fiber is provided. The apparatus includes: a heat source; a furnace
tube at least partly made of quartz glass which contains aluminum
equal to or less than 0.01 ppm; a gas introducing port that
introduces gas to the furnace tube; and a gas discharging port that
discharges gas from the furnace tube.
[0016] The summary clause does not necessarily describe all
necessary features of the embodiments of the present invention. The
present invention may also be a sub-combination of the features
described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIGS. 1A to 1C are schematic views progressively explaining
a step of vitrifying a porous glass base material.
[0018] FIG. 2 shows a distribution of transmission losses for
optical fibers at a wavelength of 1,310 nm, which are obtained by
using a furnace tube of synthetic quartz and a furnace tube of
natural quartz.
[0019] FIG. 3 shows an exemplary apparatus for manufacturing an
optical fiber base material.
[0020] FIG. 4 shows an exemplary convection preventing plate 10
that is mounted to a shaft 6 for supporting a glass base
material.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0021] Some aspects of the invention will now be described based on
the embodiments, which do not intend to limit the scope of the
present invention, but exemplify the invention. All of the features
and the combinations thereof described in the embodiment are not
necessarily essential to the invention.
[0022] The conventional furnace tube employs a glass tube made of
natural quartz that is manufactured by melting powdered natural
quartz in an electric furnace (hereinafter referred to as a natural
quartz furnace tube). It has been considered that increase of the
transmission loss is caused by contaminating the optical fiber base
material with impurities such a very small amount of ferrum and
aluminum which are contained in the natural quartz. In addition, it
has been considered that increase of the transmission loss is
caused by contaminating the optical fiber base material in the
furnace tube with a metal forming a furnace or a metal contained in
carbon which diffuses and transmits through the tube wall due to
corrosion.
[0023] More specifically, it is considered that increase of the
transmission loss is caused by the following mechanism. That is,
the natural quartz furnace tube is progressively crystallized (into
cristobalite) while it is used at a high temperature such as
approximately 1,400 degrees Celsius. The crystallization starts
with impurities and crystallite as a core, which are contained in
the natural quartz. After several hundred hours, most of the heated
region is crystallized. Particularly, the electric-furnace-melted
natural quartz contains aluminum equal to or more than 15 ppm, and
the aluminum acts as the core of crystallization. It is considered
that a small amount of impurities such as ferrum contained in the
natural quartz separate out and diffuse in a crystal grain boundary
during the crystallization. The diffusion rate of the impurities in
the crystal grain boundary is very faster than a rate at which the
impurities diffuse in amorphous glass.
[0024] Therefore, in comparison with a state before
crystallization, impurities such as ferrum are easily discharged
from the crystallized natural quartz furnace tube into the interior
thereof. A part of the impurities which were discharged into the
furnace tube is taken into the optical fiber base material and
causes fluctuation of the density of glass, so that Rayleigh
scattering increases. It is known that optical loss due to Rayleigh
scattering is in proportion to 1/.lamda..sup.4, where .lamda.
indicates a wavelength of light. Thus, the phenomenon that the
shorter the wavelength is, the larger the loss is, can be explained
by the above described mechanism.
[0025] Therefore, a furnace tube is produced by so-called CVD
method, that is, using vitrified synthetic quartz, which is
obtained by hydrolyzing silicide such as SiCl.sub.4,
(CH.sub.3)SiCl.sub.3, (CH.sub.3).sub.2SiCl.sub.2 with oxyhydrogen
flame to form a soot deposit, and melting the soot deposit in a
heating furnace.
[0026] When ferrum and aluminum are taken as an example, the
concentration of the impurities contained in the synthetic quartz
tube which is produced by using such high-purity material is equal
to or less than 0.01 ppm. Meanwhile, it is difficult for the
conventional natural quartz to completely eliminate impurities in
the material, and the natural quartz contains ferrum of
approximately 0.1 ppm and aluminum of approximately 15 ppm as
impurities. An example of analysis of metal impurities contained in
the raw material is shown in Table 1 below. Table 1:
[0027] The synthetic quartz that is made of a high-purity silicide
as the raw material and made by depositing the high-purity silicide
contains little impurity and crystallite. For example, the
synthetic quartz contains aluminum equal to or less than 0.001 ppm
as the core of crystallization. Accordingly, even if the synthetic
quart is used under a high temperature, the crystallization very
slowly progresses in comparison with the natural quartz.
Consequently, the synthetic quartz contains little impurity, and a
path through which impurities diffuse is not formed therein over
the long term. Therefore, when the synthetic quartz having such
feature is used as a furnace tube, it is considered that discharge
of impurities into the furnace tube scarcely occur. Thus, an
optical fiber base material which is manufactured by using the
furnace tube of synthetic quartz according to the mechanism
described above can significantly reduce a risk of increasing the
transmission loss in comparison with the conventional one.
[0028] Under a use environment intended for the present invention,
crystallization of the synthetic quartz progresses by about 1 mm
for 1,500 hours. Therefore, in a period obtained by multiplying the
thickness of the synthetic quartz by 1,500 hours, a state in which
the glass layer remains is maintained even if the synthetic quartz
are used at a temperature equal to or more than 1,400 degrees
Celsius, so that a risk of contaminating the optical fiber base
material can be reduced.
[0029] In addition, since the synthetic quartz is not easily
crystallized in comparison with the natural quartz, the viscosity
thereof decreases by heating. It is likely that a portion in which
the viscosity reduces is deformed due to a difference in pressure
between the inside and outside of the furnace tube. When the
deformed furnace tube contacts an optical fiber base material
during manufacture, the optical fiber base material damages.
Therefore, it is preferable to monitor the pressure in the furnace
tube and control so as not to result in excess differences between
the inside and outside of the furnace tube.
[0030] For example, it is preferable that an apparatus for
manufacturing an optical fiber base material includes a pressure
control mechanism 7 that controls a pressure in the furnace tube
such that the difference in pressure is within a tolerance when the
pressure of the inside or outside of the furnace tube is out of a
predetermined tolerance. Specifically, the apparatus for
manufacturing an optical fiber base material may include an
intra-furnace tube pressure measuring unit 11 that measures a
pressure in the furnace tube, and an extra-furnace tube pressure
measuring unit 12 that measures a pressure adjacent to the heat
source 3 outside the furnace tube. In addition, in order to
artificially adjust a pressure in the furnace tube, an alarm device
8 may activate when the difference in pressure of the inside or
outside of the furnace tube is out of a predetermined tolerance.
Moreover, the exhaust port may be provided with an automatic valve
9 to automatically adjust a flow rate of the valve in order that
the difference in pressure of the inside or outside of the furnace
tube be within a predetermined tolerance.
[0031] The tolerance of the pressure in the furnace tube may be
such as 0 Pa to 1300 Pa. In addition, since a portion adjacent to
the furnace would be the highest temperature in the furnace tube
and tend to be deformed, it is preferable to employ a pressure in
the furnace as a pressure of the extra-furnace tube in order to
know the difference in pressure between the inside and outside of
the furnace tube. The tolerance of the difference in pressure
between the inside and outside of the furnace tube may be such as
-200 Pa to 450 Pa.
[0032] Moreover, it is considered that the pressure in the furnace
tube is fluctuated because of convecting gas in the furnace tube.
The diameter of a porous glass base material is reduced by
dehydrating and sintering. Therefore, a gap between the base
material and the inner wall of the furnace tube is extended so that
it facilitates to convect the gas in the furnace tube. As shown in
FIG. 4, the convection preventing plate 10 may be provided for
preventing the gas from convecting after the diameter of the base
material reduces. It is preferable that the convection preventing
plate 10 is provided adjacent to a portion of the shaft 6 on which
the porous glass base material is mounted. The diameter of the
convection preventing plate 10 may be approximately equal to the
diameter of the porous glass base material before being reduced by
dehydrating and sintering. It is preferable that the convection
preventing plate is made of quartz.
[0033] Here, at least a portion of the furnace tube must be made of
the synthetic quartz. Specifically, the portion which is heated at
a high temperature by a heat source such as an electric furnace
must be made of the synthetic quartz. Even if the other portion is
made of the natural quartz, the effect of the invention is not
hurt.
[0034] In addition, it is not directly related to the object of the
present invention, however, the synthetic quartz used in the
embodiment contains little hydroxy group equal to or less than 1
ppm. Therefore, in view of the description of Patent document 1
that moisture contained in the furnace tube adversely affects the
loss characteristic of the optical fiber around the wavelength of
1,380 nm, the synthetic quartz of the embodiment can be used for
manufacturing the optical fiber containing little hydroxy group of
which demand has rapidly grown in recent years without any problem
although the furnace tube is manufactured by a method different
from that of the above described Japanese Patent Application
Publication No. 2004-002109. The step of eliminating adsorption
moisture described as the above described Japanese Patent
Application Publication No. 2004-002109. is applicable to the
synthetic quartz furnace tube which is used in the present
invention as well.
Embodiment 1
[0035] For the sake of comparison, the porous glass base material
which is deposited by VAD is separated into a first furnace tube of
synthetic quartz and a second furnace tube of natural quartz, each
of which thickness of the wall is 4 mm. Then, each furnace tube is
dehydrated and sintered. Further, a cladding is added to each
dehydrated and sintered base material, and the base material with
the cladding is vitrified, so that an optical fiber base material
is obtained. The obtained optical fiber base materials are drawn
respectively to measure the transmission loss at the wavelength of
1,310 nm, and then, a distribution of losses are compared. The
measured optical fibers are obtained by drawing the optical fiber
base materials which are manufactured around the same time, of
which 177 fibers are manufactured with the furnace tube of
synthetic quartz and of which 1,059 fibers are manufactured with
the furnace tube of natural quartz.
[0036] As shown in FIG. 2, among the optical fibers made by the
furnace tube of natural quartz, 4% of those have the transmission
loss more than 0.34 dB/k. Meanwhile, no optical fiber made by the
furnace tube of synthetic quartz have the transmission loss more
than 0.34 dB/k.
[0037] Here, the furnace tube of synthetic quartz is taken out upon
exceeding 6,000 hours over which the furnace tube of synthetic
quartz is subjected to a high temperature more than 1,400 degrees
Celsius, and the heated portion is examined. The result is that the
glass layer is totally eliminated and entirely crystallized in a
large part.
[0038] The manufacturing method and the manufacturing apparatus
according to the present invention may be provided in another
embodiment. That is, in a manufacturing method and a manufacturing
apparatus for an optical fiber base material, a vessel which
accommodates a porous glass base material is made of synthetic
quartz glass, which contains metal impurities less than those in
the natural quartz glass. It is preferable that the content of
aluminum of the synthetic quartz glass is equal to or less than
one-tenth of the metal impurities of the natural quartz glass.
[0039] While the embodiments of the present invention have been
described, the technical scope of the invention is not limited to
the above described embodiments. It is apparent to persons skilled
in the art that various alternations and improvements can be added
to the above-described embodiments. It is also apparent from the
scope of the claims that the embodiments added with such
alternations or improvements can be included in the technical scope
of the invention. The claims, specification and drawings describe
the processes of an apparatus, a system, a program and a method by
using the terms such as operations, procedures, steps and stages.
When a reference is made to the execution order of the processes,
wording such as "before" or "prior to" is not explicitly used. The
processes may be performed in any order unless an output of a
particular process is used by the following process. In the claims,
specification and drawings, a flow of operations may be explained
by using the terms such as "first" and "next" for the sake of
convenience. This, however, does not necessarily indicate that the
operations should be performed in the explained order.
[0040] As is apparent from the above description, since a synthetic
quartz glass vessel is used as a furnace tube, impurities from a
furnace tube material are not discharged into the furnace tube, so
that an optical fiber base material having an excellent optical
characteristic can be constantly manufactured. Moreover, by drawing
the optical fiber base material, an optical fiber having a low
transmission loss can be obtained.
* * * * *