U.S. patent application number 11/954269 was filed with the patent office on 2008-04-24 for dehydration-sintering furnace, a manufacturing method of an optical fiber preform utilizing the furnace and an optical fiber preform manufactured by the method.
This patent application is currently assigned to FUJIKURA LTD.. Invention is credited to Manabu SAITOU, Naritoshi YAMADA.
Application Number | 20080092598 11/954269 |
Document ID | / |
Family ID | 34779859 |
Filed Date | 2008-04-24 |
United States Patent
Application |
20080092598 |
Kind Code |
A1 |
SAITOU; Manabu ; et
al. |
April 24, 2008 |
DEHYDRATION-SINTERING FURNACE, A MANUFACTURING METHOD OF AN OPTICAL
FIBER PREFORM UTILIZING THE FURNACE AND AN OPTICAL FIBER PREFORM
MANUFACTURED BY THE METHOD
Abstract
A dehydration-sintering furnace for dehydrating and/or sintering
an optical fiber preform for use in production of an optical fiber
includes a muffle for accommodating the optical fiber preform, a
heater for heating the muffle, and a pressure fluctuation absorbing
apparatus connected to the muffle. Since the pressure fluctuation
absorbing apparatus is thermally insulated from a room temperature
atmosphere or heated, vapor produced in a dehydration-sintering
process is prevented from condensing (liquefying) in a pressure
fluctuation absorbing apparatus, thereby preventing reduced
dehydration effectiveness in the muffle and reduced quality of the
optical fiber preform.
Inventors: |
SAITOU; Manabu; (Chiba,
JP) ; YAMADA; Naritoshi; (Chiba, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
FUJIKURA LTD.
Tokyo
JP
|
Family ID: |
34779859 |
Appl. No.: |
11/954269 |
Filed: |
December 12, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11004966 |
Dec 7, 2004 |
|
|
|
11954269 |
Dec 12, 2007 |
|
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Current U.S.
Class: |
65/426 ;
65/385 |
Current CPC
Class: |
C03B 37/0146
20130101 |
Class at
Publication: |
065/426 ;
065/385 |
International
Class: |
C03B 37/01 20060101
C03B037/01 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 8, 2003 |
JP |
2003-409068 |
Claims
1. A manufacturing method of an optical fiber preform, comprising a
step of utilizing said dehydration-sintering furnace comprising a
muffle for dehydrating and/or sintering an optical fiber preform
for use in production of an optical fiber, wherein a pressure
fluctuation absorbing apparatus is connected to said muffle and
said pressure fluctuation absorbing apparatus is covered with a
thermally insulating material, wherein a gas temperature is 100
degrees Celsius or higher in said pressure fluctuation absorbing
apparatus.
2. A manufacturing method of an optical fiber preform, comprising a
step of utilizing said dehydration-sintering furnace comprising a
muffle for dehydrating and/or sintering an optical fiber preform
for use in production of an optical fiber, wherein a pressure
fluctuation absorbing apparatus is connected to said muffle and
said pressure fluctuation absorbing apparatus is located in a
thermally insulated container, wherein a gas temperature is 100
degrees Celsius or higher in said pressure fluctuation absorbing
apparatus.
3. A manufacturing method of an optical fiber preform, comprising a
step of utilizing said dehydration-sintering furnace comprising a
muffle for dehydrating and/or sintering an optical fiber preform
for use in production of an optical fiber, wherein a pressure
fluctuation absorbing apparatus is connected to said muffle and
provided with heating means configured to heat said pressure
fluctuation absorbing apparatus, wherein a gas temperature is 100
degrees Celsius or higher in said pressure fluctuation absorbing
apparatus.
4. A manufacturing method of an optical fiber preform, comprising a
step of utilizing said dehydration-sintering furnace according to
any one of claims 1-3, wherein said gas temperature is 300 degrees
Celsius or higher in said pressure fluctuation absorbing
apparatus.
5. A manufacturing method of an optical fiber preform according to
any one of claims 1-3, further comprising the steps of flowing of
vapor that contains substances produced in the dehydration and/or
sinter process to said pressure fluctuation absorbing apparatus,
and preventing said vapor from condensing in said pressure
fluctuation absorbing apparatus.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119 to Japanese Patent Application No. 2003-409068,
the entire contents of which are incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a dehydration-sintering
furnace, more particularly, a dehydration-sintering furnace for use
in a dehydration and/or a sinter process of a porous optical fiber
(glass fiber) preform.
[0004] 2. Description of the Related Art
[0005] A porous optical fiber preform produced by Vapor Phase Axial
Deposition (VAD) method, Outside Vapor Deposition (OVD) method and
the like is dehydrated and/or sintered by accommodating the preform
in a muffle of a dehydration-sintering furnace, supplying to the
muffle dehydration agents such as chlorine, thionyl chloride or the
like and an inert gas such as helium or the like, and then heating
the muffle with a heater.
[0006] An example of a dehydration-sintering furnace for
dehydrating and/or sintering the porous optical fiber preform is a
furnace that has a muffle connected to a pressure fluctuation
absorbing apparatus such as a balloon type pressure buffer, a
gas-flow buffering chamber, or a pressure fluctuation absorption
chamber utilizing an electro magneto valve and the like in order to
suppress a rather large pressure fluctuation and swiftly keep the
muffle pressure constant (Refer to, for example, Publication of
Examined Utility Model Application H06-50513 and Japanese Patent
Application Laid-open Publications H05-4828, H06-127964, and
H10-120428).
[0007] While the pressure fluctuation absorbing apparatus connected
to the muffle is advantageous in absorbing a short-term pressure
fluctuation in the muffle, the absorbing apparatus is somewhat
disadvantageous as described below.
[0008] When the pressure in the muffle is raised, the gas therein
is pressed out into the pressure fluctuation absorbing apparatus
from the muffle. On the other hand, when the pressure is lowered,
the gas in the pressure fluctuation absorbing apparatus flows back
to the muffle.
[0009] Since the pressure fluctuation absorbing apparatus is
positioned outside of the furnace and exposed to a room temperature
atmosphere, vapor that includes substances produced during a
dehydration and/or sinter process is condensed (liquefied) in the
pressure fluctuation absorbing apparatus. The larger amount of
moisture exists in the porous optic fiber preform, the larger
amount of condensation takes place.
[0010] The liquid produced by condensation (liquefaction) in the
pressure fluctuation absorbing apparatus will flow back to the
muffle when the pressure in the furnace decreases, thereby
deteriorating the dehydration effectiveness in the muffle.
[0011] In addition, the liquid condensed in the pressure
fluctuation absorbing apparatus may drop on the porous optical
fiber preform and then taint the surface of the preform. Also, the
dropped liquid may make brittle the portion of soot on which the
liquid drops and then the portion may fall apart therefrom. Those
will deteriorate the quality of the optical fiber preform and
reduce the production yield of the same.
[0012] Also, when the liquid condensed in the pressure fluctuation
absorbing apparatus does not flow back to the muffle but stays at a
duct and the like connecting the muffle and the pressure
fluctuation absorbing apparatus, since substances produced in the
dehydration process contain strong acids such as hydrogen chloride
and sulfuric acid, the duct and the like will be eroded, thereby
shortening an operating life of the furnace.
[0013] The objective of the present invention is to provide a
dehydration-sintering furnace having a pressure fluctuation
absorbing apparatus, wherein vapor that contains substances
produced in the dehydration and/or sinter process is prevented from
condensing in the pressure fluctuation absorbing apparatus and
thereby the flowing of condensed liquid back to the muffle of the
dehydration-sintering furnace is essentially prevented.
[0014] Another objective of the present invention is to provide a
manufacturing method of optical fiber preform, utilizing the above
dehydration-sintering furnace, the method enabling a stable
production of a high quality optical fiber preform.
SUMMARY OF THE INVENTION
[0015] A first aspect of the present invention provides a
dehydration-sintering furnace having a muffle for dehydrating
and/or sintering an optical fiber preform for use in production of
an optical fiber, wherein a pressure fluctuation absorbing
apparatus is connected to said muffle and said pressure fluctuation
absorbing apparatus is covered with a thermally insulating
material.
[0016] A second aspect of the present invention provides a
dehydration-sintering furnace having a muffle for dehydrating
and/or sintering an optical fiber preform for use in production of
an optical fiber, wherein a pressure fluctuation absorbing
apparatus is connected to said muffle and said pressure fluctuation
absorbing apparatus is accommodated in a thermally insulated
container.
[0017] A third aspect of the present invention provides a
dehydration-sintering furnace having a muffle for dehydrating
and/or sintering an optical fiber preform for use in production of
an optical fiber, wherein a pressure fluctuation absorbing
apparatus is connected to said muffle and said furnace is provided
with heating means configured to heat said pressure fluctuation
absorbing apparatus.
[0018] A fourth aspect of the present invention provides a
manufacturing method of an optical fiber preform, utilizing any of
said dehydration-sintering furnaces, wherein a gas temperature is
at 100 degrees Celsius or higher in said pressure fluctuation
absorbing apparatus.
[0019] The dehydration-sintering furnace according to the present
invention is capable of preventing vapor produced in a
dehydration-sintering process from condensing (liquefying) in a
pressure fluctuation absorbing apparatus since the pressure
fluctuation absorbing apparatus is thermally insulated from a room
temperature atmosphere or heated.
[0020] Since the above structure is able to essentially prevent the
liquid condensed in the pressure fluctuation absorbing apparatus
from flowing back to the muffle and/or dropping on the optical
fiber preform accommodated in the muffle, a dehydration
effectiveness in the muffle and a quality of the optical fiber
preform are not deteriorated, thereby enabling a stable production
of an optical fiber preform.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In the accompanying drawings:
[0022] FIG. 1 is an illustration of a dehydration-sintering furnace
according to a first embodiment of the present invention;
[0023] FIG. 2 is an illustration of a dehydration-sintering furnace
according to a second embodiment of the present invention;
[0024] FIG. 3 is an illustration of a dehydration-sintering furnace
according to a third embodiment of the present invention;
[0025] FIG. 4 is an illustration of a dehydration-sintering furnace
according to a fourth embodiment of the present invention;
[0026] FIG. 5 is an illustration of a dehydration-sintering furnace
according to a fifth embodiment of the present invention; and
[0027] FIG. 6 is an illustration of a dehydration-sintering furnace
according to a sixth embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A First Embodiment
[0028] Referring to FIG. 1, a hydration-sintering furnace according
to a first embodiment of the present invention will be described in
the following. The hydration-sintering furnace in FIG. 1 has a
quartz-made, hermetically constructed muffle 11 as the furnace main
body. The muffle 11 accommodates a porous optical fiber preform W
so as to suspend the preform W with a seed rod 100 in the interior
13 of the muffle 11.
[0029] Outside of the muffle 11 is provided a furnace body 17 in
which a heater 15 for heating the interior 13, that is, the optical
fiber preform W in the interior 13 is provided. An inert gas such
as helium, argon and the like as a purge gas is supplied from a
purge gas inlet 19 into the furnace body 17. The purge gas supplied
into the furnace body 17 is discharged out from an outlet 21.
[0030] The muffle 11 has at the bottom thereof a gas inlet tube 23
that allows dehydration agents such as chlorine gas, thionyl
chloride or the like and inert gas such as helium or the like to be
supplied from a gas supplier (not shown) into the interior 13.
[0031] In addition, the muffle 11 has at the top thereof a pressure
adjustment port 25. To the pressure adjustment port 25, a pressure
fluctuation absorbing apparatus 29 is connected via a duct 27. The
pressure fluctuation absorbing apparatus 29 can be a well-known one
such as a balloon type pressure buffer, a gas-flow buffer chamber,
or a pressure fluctuation absorption chamber utilizing an electro
magneto valve and the like, about which a detailed explanation is
eliminated.
[0032] The pressure fluctuation absorbing apparatus 29 is covered
and thermally insulated with a thermally insulating material 31.
Also, the duct 27 connecting the muffle 11 and the pressure
fluctuation absorbing apparatus 29 is covered with a thermally
insulating material 33 to thermally insulate the duct 27.
[0033] The thermally insulating materials 31, 33 are formed of
fibrous insulation material, such as an alumina fiber, having high
heat resisting properties and totally cover the pressure
fluctuation absorbing apparatus 29 and the duct 27 for thermal
insulation.
[0034] In the dehydration-sintering furnace having the above
structure, the optical fiber preform W is dehydrated and/or
sintered in the interior 13 by heating the muffle 11 with the
heater 15.
[0035] When the pressure in the interior 13 is raised during a
dehydration and sinter process, the gas in the interior 13 is
pressed out into the pressure fluctuation absorbing apparatus 29
via the duct 27, while the gas in the pressure fluctuation
absorbing apparatus 29 flows back to the muffle 11 via the duct 27
when the pressure in the interior 13 is lowered, thereby
suppressing the pressure fluctuation in the interior 13.
[0036] The gas flow between the interior 13 and the pressure
fluctuation absorbing apparatus 29 contains vapor that contains
moisture emerging from the optical fiber preform W in the interior
13 and substances produced in the dehydration and sinter process.
Since the pressure fluctuation absorbing apparatus 29 and the duct
27 are insulated from a room temperature atmosphere with the
thermally insulating materials 31, 33, such vapor is prevented from
condensing in the pressure fluctuation absorbing apparatus 29 and
the duct 27.
[0037] Therefore, no liquid is produced by condensation in the
pressure 29 and the duct 27, thereby essentially preventing the
flowing of any liquid by condensation back to the muffle 11. This
is how a reduction in dehydration effectiveness and a phenomenon
such as the liquid by condensation dropping on the optical fiber
preform W are prevented, thereby enabling a stable production of a
high quality optical fiber preform.
[0038] Optical fibers manufactured by drawing the optical fiber
preform that has been dehydrated and sintered in the
dehydration-sintering furnace having a pressure fluctuation
absorbing apparatus 29 covered with a thermally insulating material
show an average transmission loss of as low as about 0.286 dB/km at
a wavelength of 1385 nm. For comparison, other optical fibers are
manufactured under the same conditions but a use of a
dehydration-sintering furnace having a pressure fluctuation
absorbing apparatus with no thermally insulating material covered.
As a result, the optical fibers for comparison show an average
transmission loss of about 0.292 dB/km at a wavelength of 1385 nm.
From this comparison, it is understood that the
dehydration-sintering furnace according to this embodiment and a
manufacturing method of an optical fiber preform utilizing the same
exert a superior operational effect.
[0039] In addition, since any liquid by condensation in the
pressure fluctuation absorbing apparatus 29 does not flow back to
the muffle 11 or stay in the duct 27, the duct 27 is prevented from
erosion in a short term by strong acids such as hydrogen chloride
and sulfuric acid, thereby lengthening the life of the furnace.
A Second Embodiment
[0040] Referring to FIG. 2, a dehydration-sintering furnace
according to a second embodiment of the present invention will be
described. In FIG. 2, a member or component corresponding to that
in FIG. 1 will be represented by a same reference mark used in FIG.
1 to eliminate an undue repetition of explanation.
[0041] In the second embodiment, a pressure fluctuation absorbing
apparatus 29 is totally housed in a hermetically constructed,
thermally insulated container 35. The container 35 is composed of a
hermetic box 37 and a thermally insulating material 39, such as an
alumina fiber and the like, which covers the hermetic box 37 to
thermally insulate substantially the entire box 37.
[0042] In this embodiment, the pressure fluctuation absorbing
apparatus 29 and a duct 27 are thermally insulated from a room
temperature atmosphere by the hermetic box 37 and the thermally
insulating material 33, thereby preventing vapor that contains
substances produced in a dehydration-sintering process from
condensing (liquefying) in the pressure fluctuation absorbing
apparatus 29 and the duct 27.
[0043] Therefore, since any liquid by condensation is not produced
in the pressure fluctuation absorbing apparatus 29 and the duct 27,
any liquid by condensation does not flow back to the muffle 11,
thereby essentially preventing the flowing of condensed liquid back
to the muffle 11 and enabling a stable production of a high quality
optical fiber preform.
A Third Embodiment
[0044] Referring to FIG. 3, a dehydration-sintering furnace
according to a third embodiment of the present invention will be
described. Also in FIG. 3, a member or component corresponding to
that in FIG. 1 will be represented by a same reference mark used in
FIG. 1 to eliminate an undue repetition of explanation.
[0045] In the third embodiment, a pressure fluctuation absorbing
apparatus 29 is housed in a container 41. Outside of the container
41, a heater 43 is provided as a heating means surrounding the
container 41. Electric power supplied to the heater 43 is regulated
by a heater controlling means 45, which controls the heating value
from the heater 43 to heat the container 41. In this way, the
temperature inside the container 41 is raised and the pressure
fluctuation absorbing apparatus 29 is heated indirectly with the
heater 43.
[0046] The container 41 has a temperature sensor 47 therein that
detects a temperature inside the container 41. The heater
controlling means 45 inputs a signal from the temperature sensor 47
and accordingly regulates electric power to be supplied to the
heater 43 in order to keep the temperature inside the container 41
at a predetermined temperature (a constant temperature) needed to
avoid condensation.
[0047] With the above construction, the pressure fluctuation
absorbing apparatus 29 is kept at a temperature equal to or higher
than the temperature needed to avoid condensation, thereby
preventing a generation of liquid by condensation in the pressure
fluctuation absorbing apparatus 29. Therefore, the flowing of
condensed liquid back to the muffle 11 is essentially prevented,
thereby enabling a stable production of a high quality optical
fiber preform.
[0048] Incidentally, the pressure fluctuation absorbing apparatus
29 may be constructed such that the apparatus 29 is directly heated
by the heater 43. This construction also demonstrates the same
operational advantages as the foregoing construction in this
embodiment. Also, an additional heater can be provided for the duct
27.
A Fourth Embodiment
[0049] Referring to FIG. 4, a dehydration-sintering furnace
according to a fourth embodiment of the present invention will be
described. In FIG. 4, a member or component corresponding to that
in FIG. 3 will be represented by a same reference mark used in FIG.
3 to eliminate an undue repetition of explanation.
[0050] In the fourth embodiment, a heat exchanger 49 as a heating
means is provided so as to surround the outside of the container
41. The heat exchanger 49 has a heat transfer medium such as hot
water, steam, and the like flowing therein.
[0051] With this construction, the container 41 is heated and then
the temperature inside the container 41 is raised, thereby heating
indirectly the pressure fluctuation absorbing apparatus 29 by the
heat exchanger 49.
[0052] Accordingly, the pressure fluctuation absorbing apparatus 29
is kept at a temperature equal to or higher than the temperature
needed to avoid condensation, thereby preventing liquid by
condensation from being produced in the pressure fluctuation
absorbing apparatus 29. Therefore, the flowing of liquid by
condensation back to the muffle 11 is essentially prevented,
thereby enabling a stable production of a high quality optical
fiber preform.
[0053] Incidentally, the pressure fluctuation absorbing apparatus
29 may be constructed such that the apparatus 29 is directly heated
by the heat exchanger 49, which is capable of demonstrating the
same operational advantages as the above-mentioned construction in
this embodiment. In addition, the heat transfer medium supplied to
the heat exchanger 49 can be a hot purge gas exhausted from the
furnace body 17. Furthermore, an additional heat exchanger can be
provided for the duct 27.
A Fifth Embodiment
[0054] Referring to FIG. 5, a dehydration-sintering furnace
according to a fifth embodiment of the present invention will be
described. In the fifth embodiment, a container 41 has an inlet 51
and an outlet 53, through which a heat transfer medium such as
steam is supplied to the container 41. With this construction, the
interior of the container 41 is heated so that the temperature
thereof is raised, thereby heating the pressure fluctuation
absorbing apparatus 29.
[0055] Accordingly, the pressure fluctuation absorbing apparatus 29
is kept at a temperature equal to or higher than the temperature
needed to avoid condensation, thereby preventing liquid by
condensation from being produced in the pressure fluctuation
absorbing apparatus 29. Therefore, the flowing of liquid by
condensation back to the muffle 11 is essentially prevented,
thereby enabling a stable production of a high quality optical
fiber preform.
[0056] In addition, the duct 27 connecting the muffle 11 and the
pressure fluctuation absorbing apparatus 29 may be coaxially
surrounded by an outer pipe 55 to form a double tube. The heat
transfer medium such as steam is also supplied to pass through a
path 57 between the duct 27 and the outer pipe 55, thereby heating
the duct 27. The heat transfer medium flowing through the duct
keeps a temperature of the duct equal to or higher than the
temperature needed to prevent condensation, thereby preventing
liquid by condensation from being produced in the duct. By the way,
the heat transfer medium supplied to the container 41 and the path
57 can just as readily be hot water instead of steam.
A Sixth Embodiment
[0057] Referring to FIG. 6, a dehydration-sintering furnace
according to a sixth embodiment of the present invention will be
described. In the sixth embodiment, a container 41 and a path 57
are connected to a gas purge discharge port 21 of a furnace body 17
via ducts 59, 61, 63. With this construction, the purge gas
discharged from the furnace body 17 is supplied to the container 41
and the path 57 as a heat transfer medium, thereby raising the
temperature inside the container 41 and the path 57, and then also
raising the temperature of the pressure fluctuation absorbing
apparatus 29 and the duct 27.
[0058] Therefore, the pressure fluctuation absorbing apparatus 29
and the duct 27 are kept at a temperature equal to or higher than
the temperature needed to avoid condensation, thereby preventing
liquid by condensation from being produced in the pressure
fluctuation absorbing apparatus 29 and the duct 27. Therefore, the
flowing of liquid by condensation back to the muffle 11 is
essentially prevented, thereby enabling a stable production of a
high quality optical fiber preform.
[0059] The gas temperature inside the pressure fluctuation
absorbing apparatus 29 may be kept at 100 degrees Celsius or
higher, or may be kept at 300 degrees Celsius or higher. When the
temperature is 100 degrees Celsius or higher, moisture in the gas
does not condense. When the temperature is 300 degrees Celsius or
higher, even if the dehydration agents contain sulfur atoms and
oxygen atoms and then sulfuric acid or sulfuric acid gas is
produced by dehydration reaction, sulfuric acid does not condense
in the pressure fluctuation absorbing apparatus 29, thereby
enabling a stable production of a high quality optical fiber
preform.
[0060] Although the above exemplary embodiments of the present
invention have been described, it will be understood by those
skilled in the art that the present invention should not be limited
to the described exemplary embodiments, but that various changes
and modifications can be made within the spirit and scope of the
present invention.
* * * * *