Note: Descriptions are shown in the official language in which they were submitted.
1 BACKGROUND OF THE INVENTION
This invention relates to a method of manufac-turing
an optical transmission fiber. Typically such glass fibers are
used as optical waveguides and the like and have a core with a
refractive index higher than that of the peripheral section or
clad. This invention relates specifically to the formation of
optical fibers by first forming a "preform" of the glass material
from which the fiber is ultimately obtained.
SUI~ARY OF THE INVENTION
It is an object of this invention to define a method
oS manu~acturing optical ~ibers that is low in cost and economic-
al in manufacture.
It is another object of this invention to provide a
method of manufacturing optical fibers using quartz glass as a
cover layer.
These and other objects of this invention are accom-
plished in a method of manufacturing employing the steps of;
forming glass particles by subjecting glass raw material gas to
flame hydrolysis, ~orming a cylindrical glass particle body
by supplying the glass particles thus formed onto a starting
member so that the glass particles are laminated thereon and
- successively grown and sintering the cylindrical glass par-
ticle body to provide a transparent glass cylinder. The trans-
parent glass cylinder is inserted into a quartz glass pipe to
provide the assembly of the transparent glass cylinder and the
quartz glass pipe. The assembly is heated to melt the glass
cylinder and the quartz glass pipe together and the assembly
3~ is drawn into a thin fiber.
In one embodiment, the assembly is heated at one end to
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1 melt the glass cylinder and the quartz glass -together while
drawing the assembly into a fiber. In another embodiment the
assembly ls heated to melt and collapse the quar-tz
pipe. Subsequently, the assembly is subjec-ted to high tem-
perature treatment and drawn.
BRIEF DESCRIPTION OF THE DRAWINGS
-
Figs. 1 and 2 are diagrams showing the sectional
structures and the refractive index distributions of prior art
optical fibers;
Fig. 3 is an explanatory diagram showing a method of
forming a glass particle cylinder;
Fig. 4 is an explanatory diagram showing the nozzle
section of a coaxial multi-pipe burner;
Fig. 5 is a diagram for a description of one method
of providing a dopant distribution;
Figs. 6 and 7 are diagrams showing the sectional
structures of fibers covered with jackets;
Fig. 8 is an explanatory diagram showing a method of
forming a fiber; and
Fig. g is an explanatory diagram showing a method in
which a preform is covered with a jacket, and the assembly of
the preform and the jacket is collapsed. `
DESCRIPTION QF TEIE PREFERRED ~BODIMENTS
In order to propagate light in a glass fiber, it is
essential that its refractive index is variable radially in the
section thereof.
In typical kno~n ~lass fibers, the refractive index of a
central section (or a core) 1 is higher than that of a periphexal
section (or a clad) 2 as shown in Figs. 1 and 2. The refractive
1 index of glass may be changed to be higher than th~t of pure
- silica by dopinc~ an oxide of germanium (Ge) J phosphorous (P)
or titanium (Ti) into silica (SiO2). It may be changed to be
lower by doping an oxide of boron (B) or fluorine ~F) into silica
The glass material from which a glass fiber is obtained by re-
ducing the diameter is called "preform". The section of the
preform has a refractive inde~ distribution as indicated in
Figs. 1 or 2.
In one of the methods of forming the preform, shown in
1~ Fig. 3, a rotary starting member 3 such as a glass bar or a
glass plate is provided, and glass particles 4 whose composition
is distributed radially with the distance from the center are
laminated in a cylindrical direction to form a cylindrical glass
particle body 5. Then, this body 5 is sintered to provide a
transparent glass cylinder (or a preform). This method
is described in United States Patent No. 4,135,901 issued
January 23, 1979 to Fujiwara et al. In laminating
the glass particles whose composition is distributed radially,
the glass raw material gas whose dopant density is distributed
radially, together with oxygen and hydrogen, is supplied by
means of a burner 6 to burn the hydrogen, whereby glass particles
are formed by flame hydrolysis and are deposited. The dopant
density may be distributed radially by using a coaxial multipipe
burner comprising pipes 7, 8, 9 and 10 as shown in Fig. 4. The
pipes 7 and 8 supply glass raw material gases different in com~
position, and the pipes 9 and 10 supply hydrogen gas and oxygen
gas, respectively. The same effect may be obtained by a method
in which, as shown in Fig. 5, a plurality of oxyhydrogen burners
11 are arranged, and glass raw material gases different in
3~
composition are supplied into the centers of -the respective
flames.
In the case where the preform thus provided is formed
into a glass fiber, the Eollowing advantages occur by covering
-the outer surface of the preform with a quar-tz glass jac~et
(or a cover layer) 12:
(1) A dopant such as boron or phosphorous has hygro-
scopicity, which lowers the optical transmission characteristic;
however, the damping absorption can be prevented by the pro-
vision of the jacket.
t2) Since the strength of a pure quartz glass is
greater than that of a quartz glass con~aining a dopant, the
strength of the glass fiber can be increased by covering it with
the quartz glass jacket.
(3) In the case where the outsi~e diameter of the glass
fiber is set to a constant value, the productivit~ is increased
because the amount of preform prepared according to the method
described with reference to Fig. 3 is less.
(4) Even if the preform comprising a core and the clad
layer is covered with the quartz jacket, the jacket is not
related to the transmission of light. Therefore, quartz glass
high in optical transmission loss and accordingly low in cost
can be employed as the jacket material. This results in the
manufacture of optical fibers low in price. Such cross sections
are shown in Figs. 6 and 7.
Now, the method of covering the preform with the
quartz glass jacket 12 will be described with reference to Fig. 8,
A preform 13 prepared in accordance with the method described
with reference to Fig. 3 or Fig. 5 is inserted into a quartz
glass pipe 14 which will later become the jacket. Then, while
O
1 passing through a high temperature furnace (at about 2000C),
the preform 13 and the quartz glass pipe 13 are mel~ed to-
gether, and the preform 13 and the pipe 14 thus molten are
pulled to form a fiber 16.
The same effect may be obtained by employing another
method illustrated in Fig. 9. In this method, the preform 13
formed according to the method shown in Fig. 3 or Fig. 5 is in-
serted into the quartz glass pipe 1~. The assembly of the pre-
form 13 and the pipe 14 is heated at a high temperature (about
1800C) by means o a burner 17 or a furnace until the quartz
glass pipe collapses to join the preform 13 and the pipe 1~. Ina subsequent process, the assembly thus treated is subjected to
a high temperature (about 2000C) beginning at one end thereof,
so that it is e~tended into a thin fiber.
In the above description, the preform having the clad
as shown in Figs. 1 or 2 is formed according to the method
shown in Fig. 3 or 5, and then the preform is covered with the
jacket 12 to have the structure as shown in Fig. 6. However,
the same effect can be obtained in accordance with a method in
2~ which, first only the core shown in Figs. 1 or 2 is formed
according to the method shown in Fig. 3, and then it is covered
with the jacket in accordance with the method shown in Figs.
or 9. In the latter method, the jac~et serves as the clad as
shown in Fig. 7.
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