Glass manufacturing – Fiber making apparatus – With means for heating newly formed filament – fiber – or preform
Reexamination Certificate
2001-03-19
2003-02-18
Derrington, James (Department: 1731)
Glass manufacturing
Fiber making apparatus
With means for heating newly formed filament, fiber, or preform
C065S500000, C065S537000, C065S540000, C065S427000, C065S385000, C248S317000, C432S253000, C432S258000
Reexamination Certificate
active
06519977
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber preform suspending and supporting apparatus for suspending and supporting a porous optical fiber preform at its upper end, and an optical fiber preform processing apparatus using the optical fiber suspending and supporting apparatus, in a process of producing a porous optical fiber preform on a starting preform by a VAD method or an OVD method or in a process after the above one for vitrifying (dehydrating and sintering) the porous optical fiber preform.
2. Description of the Related Art
An optical fiber comprised of a core and a cladding is formed by heating and drawing a vitrified optical fiber preform.
The method for producing such an optical fiber preform will be described below. First, a core portion porous optical fiber preform is deposited and formed at the lower end of a starting preform (a seed rod) by the VAD method. Then, this core portion porous optical fiber preform is heat treated in a vitrification (dehydration and sintering) step to obtain a transparent core use optical fiber preform. Next, using this transparent core use optical fiber preform as a starting preform, a cladding portion porous optical fiber preform is deposited and formed by the OVD method. Next, the cladding portion porous optical fiber preform is heated in a vitrification (dehydration and sintering) step to obtain a transparent optical fiber preform.
The resultant transparent vitrified optical fiber preform is heated and drawn to form an optical fiber comprised of for example a core of a diameter of 10 &mgr;m and a cladding of a diameter of 125 &mgr;m at the circumference of the core.
When producing such a core portion porous optical fiber preform and cladding portion porous optical fiber preform, the porous optical fiber preforms are suspended and supported at the upper end by an optical fiber preform suspending and supporting apparatus. As known optical fiber preform suspending and supporting apparatuses, there are a pin supporting type, a chuck supporting type, and a combined type of the two.
FIG. 1
is a vertical sectional view of the structure of a pin supporting type optical fiber preform suspending and supporting apparatus
5
A. Specifically, the optical fiber preform suspending and supporting apparatus
5
A shown in
FIG. 1
is configured to be housed in a dehydration and sintering furnace, as an example of an optical fiber preform processing apparatus, used when vitrifying a porous glass layer
8
for cladding to make it transparent in a vitrification (dehydration and sintering) step of a porous optical fiber preform
6
comprising a core use optical fiber preform, that is, a starting preform
7
, and a porous glass layer
8
for cladding produced on the starting preform
7
by the OVD method.
In the dehydration and sintering furnace schematically illustrated in
FIG. 1
, a pin supporting type optical fiber preform suspending and supporting apparatus
5
A is provided so that a main shaft
4
passes through a hole
3
in the upper lid
2
of a furnace tube
1
made of silica-based glass or the like. A not illustrated rotation and support mechanism is provided at the upper portion of the main shaft
4
. The rotation and support mechanism supports the main shaft
4
from which the porous optical fiber preform
6
is suspended and rotates the porous optical fiber preform
6
by rotating the main shaft
4
.
In this way, the porous optical fiber preform
6
is supported and suspended by the main shaft
4
at the upper end of the starting preform
7
by the optical fiber preform suspending and supporting apparatus
5
A.
In this case, the starting preform
7
is the transparent core use optical fiber preform formed on a seed rod. A porous glass layer
8
for cladding is deposited at the circumference of the starting preform
7
.
The optical fiber preform suspending and supporting apparatus
5
A is structured so that the upper end of the starting preform
7
is inserted inside a supporting cylinder
9
at the lower end of the main shaft
4
and a pin
12
is inserted into through holes
10
and
11
formed horizontally in the supporting cylinder
9
and starting preform
7
at the portion where they are fit together so that the starting preform
7
can swing around the pin
12
.
At the circumference of the furnace tube
1
, a heater
13
for heating and vitrifying the porous optical fiber preform
6
is provided.
Such an optical fiber preform suspending and supporting apparatus
5
A is housed at the inside of the high temperature furnace tube
1
to vitrify the porous optical fiber preform, so it is made of heat resistant silica-based glass or the like so as to prevent the invasion of impurities into the porous optical fiber preform
6
.
In the pin supporting type optical fiber preform suspending and supporting apparatus
5
A shown in
FIG. 1
, since the through holes
10
and
11
are formed in the supporting cylinder
9
and the upper portion of the starting preform
7
and the pin
12
is passed through the through holes
10
and
11
to support the porous optical fiber preform
6
by the main shaft
5
, it suffers from the disadvantage of a degraded mechanical strength of the starting preform
7
in which the through hole
11
is formed. In particular, recently large-sized porous optical fiber preforms
6
have been formed. Thus, the porous optical fiber preforms
6
have become heavier too, so the decline of the mechanical strength of the starting preform
7
becomes a problem.
Furthermore, due to the restriction of the mechanical strength of the starting preform
7
, the diameter of the through hole
11
formed in the porous optical fiber preform
6
through which the pin
12
is passed cannot be made too large. Therefore it suffers from another disadvantage that since the diameter of the pin
12
is therefore also small, when placed in the high temperature furnace tube
1
for vitrification, the pin
12
is liable to deform due to the heat from the heater
13
.
In order to overcome these disadvantages, for example, Japanese Patent No. 2683757 proposed to provide a gas passage along the axial line of the main shaft
4
and supply a cooling gas through the gas passage to cool the pin
12
and therefore prevent a decline of the mechanical strength of the pin supporting type optical fiber preform suspending and supporting apparatus
5
A. In such a configuration, however, it is needed to provide means for controlling the flow rate of the cooling gas, preventing reverse flow by controlling the internal pressure of the reaction vessel in the furnace tube, and preventing leakage at the rotating connecting portion of a gas joint of the tube for conducting the cooling gas. Consequently, it suffers from another disadvantage that the operation and maintenance of the dehydration and sintering furnace become rather expensive.
FIG. 2
is a vertical sectional view of the structure of a chuck supporting type optical fiber preform suspending and supporting apparatus
5
B. In the same way as
FIG. 1
,
FIG. 2
shows an example of the case where an optical fiber preform suspending and supporting apparatus
5
B is housed in a dehydration and sintering furnace for vitrifying a cladding portion porous optical fiber preform produced by the OVD method in a vitrification (dehydration and sintering) step.
In the chuck supporting type optical fiber preform suspending and supporting apparatus
5
B, a holding portion
14
comprising a chuck is integrally provided at the lower end of the main shaft
4
. The holding portion
14
is provided with an insertion space
15
open at one side and with a slit
16
for insertion of a starting preform at a supporting portion
14
a
at the bottom of the insertion space
15
.
Such an optical fiber preform suspending and supporting apparatus
5
B, as described previously with reference to
FIG. 1
, is also made of silica-based glass to prevent the invasion of impurities into the porous optical fiber preform
6
.
When using the chuck supporting type optical fiber preform suspendi
Kohmura Yukio
Mikami Toshihiro
Derrington James
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
The Furukawa Electric Co. Ltd.
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