JPS6020333B2 - Manufacturing method of optical fiber base material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in the manufacturing method of an optical fiber base material.

Silicon tetrachloride (SIC14) mixed with germanium tetrachloride (QC14), which is the source of a dopant for controlling the refractive index, and oxygen (02) gas are introduced into a reaction tube made of quartz, and the outer wall of the reaction tube is aligned in the direction of the tube. A method for producing an optical fiber base material is well known, in which the glass forming raw material gas SIC14 and the like is heated by a moving heating burner and then deposited as a glass layer in a reaction tube. [Prior Art] Conventionally, when manufacturing an optical fiber base material by such an internal CVD method, as shown in FIG. A heating burner 3 is reciprocated in the tube axis direction to heat the outer wall of the reaction tube and deposit a glass layer 4 inside the reaction tube.

Here, 6 is an exhaust pipe connected to the gas exhaust end 5 of the reaction tube 1 and having an inner diameter larger than that of the reaction tube for depositing unnecessary glass-forming oxide 7. However, when the optical fiber base material is manufactured using this method, the oxides of the raw material gas that are formed are deposited with a trail in the downstream direction of the gas flow, and the oxides are gradually vitrified by the movement of the heating burner. Therefore, the glass layer 4 formed is thick enough to reach the terminal end of the reaction tube, that is, the gas discharge end 5, and the glass layer thus formed is used as a core glass to form an optical fiber base material, When an optical fiber is manufactured from the mother fiber, there arises a drawback that the core diameter of the optical fiber is not uniform in the longitudinal direction of the optical fiber.

In order to eliminate the above-mentioned drawbacks, as shown in FIG. Improvement of the optical fiber base material in which at least a uniform glass layer 4 is formed in the movable reaction tube L of the main burner 3 by heating the introduced gas near the gas introduction end at predetermined time intervals. The manufacturing method was previously proposed by the present inventors.

[Problem that the invention seeks to solve]

However, when the fiber base material is manufactured using the above-mentioned improved optical fiber base material manufacturing method, the oxide deposited at the distance X between the auxiliary burner 8 and the starting point B of the main heating burner 3 is not heated sufficiently. The oxide is not vitrified and is sequentially deposited in the state of soot 9.

Since this soot 9 is not vitrified, its volume increases, and as a result, soot is formed in the glass layer 4 of the reaction tube 1 due to the reciprocating movement of the main burner 3, the rotational movement of the reaction tube 1, the flow rate of the reaction gas G, etc. There is a disadvantage that when the lump 10 flows into the lump 10 and the main burner 3 next reaches this lump, it is not sufficiently vitrified and becomes foamy, making it impossible to obtain a homogeneous optical fiber base material. Ta. [Means for Solving the Problems] The present invention eliminates the above-mentioned drawbacks by introducing a raw material gas for glass formation into a reaction tube, and repeatedly heating the outer wall of the reaction tube with a main heating burner moving in the direction of the tube. In the method of manufacturing an optical fiber matrix in which a plurality of glass layers are deposited in the reaction tube by heating the reaction tube, a semi-fixed auxiliary device is movably attached to the gas introduction end of the reaction tube separately from the main heating burner. A burner is provided, and for a predetermined period of time until the main burner returns from the terminal end 5 of the reaction tube to the gas introduction end B, the auxiliary burner heats the gas introduction part of the reaction tube to form a frit oxide layer in the reaction tube. As the main heating burner reaches the gas introduction section, the auxiliary burner is moved, the heating of the reaction tube by the auxiliary burner is weakened, and the main heating burner is used instead of the auxiliary burner to heat the reaction tube. A glass layer is formed inside the reaction tube by heating the outer wall.

〔Example〕

Embodiments of the present invention will be described below with reference to FIG.

In the drawings, the same functional parts as in FIGS. 1 and 2 are designated by the same reference numerals and will be explained. In the following explanation, the reaction tube 1 used had an outer diameter of 28 mm, an inner diameter of 25 mm, and a length of 85 mm.

Further, a quartz tube with an outer diameter of 35 mm and an inner diameter of 25 mm is connected to both ends of the reaction tube, and this portion is held by a chuck of a glass lathe, which is not shown in FIG.

Now, while the main heating burner 3 starts from the starting point B and moves to the end pupil of the reaction tube 1 to deposit the glass layer 4, the auxiliary burner 8 starts from the starting point B of the main heating burner 3. The auxiliary burner 8 is moved and held vertically by the auxiliary burner moving means 11, and during this period, the thermal power of the auxiliary burner 8 is kept low so that the reaction gas is not decomposed.

Next, while the main heating burner 3 returns from the position of the terminal end 5 to the position of the starting point B, the heating power of the auxiliary burner 8 is increased to decompose the reaction gas to form oxide soot, and this soot is transferred to the reaction tube 1. It is deposited in portions B to C near the inlet of the gas flow so that the amount gradually decreases toward the bottom of the gas flow. Next, when the main heating burner returns to the starting point B, the auxiliary burner 8 is moved from the starting point B to the starting point A by the auxiliary burner moving means 11, and the heating power is also reduced so that the reaction gas is not decomposed. do it like this. The moving speed of the main heating burner at this time is
The time of movement from starting point B to end point 5 was 22 arc/min, and the time of movement from end point 5 to starting point B was 360 arc/min.

Starting point B is three skins away from the joint of the quartz tubes,
Movement range 1' was spotty. In addition, the raw material gases include camphorium tetrachloride (SIC14) at 2.5 e/min and phosphorus oxychloride (POC13) at 1.2 e/min, germanium tetrachloride (W
C14) was supplied at 1.2 evenings/min, at a raw material temperature of 3 pi, and with a carrier gas of 02.

The flow rate of oxyhydrogen gas to the main heating burner was 60mm on Day 2.
02 was supplied at a constant rate of 25/min while the main heating burner was moving from starting point B to ending point 5 to B. As explained above, the thickness of the deposited glass layer 4 can be corrected over the entire reaction tube 1 by adjusting the thickness of the deposited glass layer 4 at positions B to C near the gas introduction end 2 of the reaction tube 1. .

The heating time and firepower of this auxiliary burner 8 are adjusted. This adjustment amount is 30/min for the peak while the main heating burner is moving from the starting point B to the terminal 5, 5 so/min for 02, and 5 so/min from the terminal 5 to the starting point while the main heating burner is moving from the starting point B to the terminal 5. B
While moving to , day 2 was set at 60 so/min and Q was set at 5 so/min.

As a result, when collapsing after depositing 50 layers of core glass, the preform with the conventional method had a preform length of 50 cm in the portion where the core diameter was uniform, whereas in the present invention, the preform length was 50 cm. It was 60 years old.

Furthermore, on the terminal end 5 side of the preform, the core diameter is 12.5 mm smaller and the outer diameter is 18.6 mm? Met. [Effects of the Invention] As explained above, in the present invention, at least the auxiliary burner is located apart from the starting position of the main heating burner while the raw material gas G is heated by the auxiliary burner 8 to decompose the raw material gas G and form frit oxide. Because of this structure, there is no non-heating part x between the auxiliary burner 8 and the main heating burner 3 unlike in the secondary burner.

Therefore, during this time, unnecessary extra oxide soot is not deposited, and therefore the extra soot lumps are not scattered onto the glass deposited layer 4 portion of the reaction glass tube 1, and the oxidized soot formed by the auxiliary burner 8 is not deposited. The material soot layer is completely vitrified as the king heating burner 3 moves, and a uniform optical fiber base material can be formed without the disadvantages of the conventional method.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams for explaining a conventional method for manufacturing an optical fiber preform, and FIG. 3 is a diagram for explaining a method for manufacturing an optical fiber preform according to the present invention. 1...Reaction tube, 2...Gas introduction end,
3...Main heating burner, 4...Glass layer, 5...Gas exhaust end (end of reaction tube), 6...
....Discharge end, 7..Unwanted glass-forming oxide, 8.
...Auxiliary burner, 9...Soot, 10...
...Soot mass, 11...Auxiliary burner movement means. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. Production of an optical fiber preform by introducing a raw material gas for glass formation into a reaction tube, repeatedly heating the outer wall of the reaction tube with a main heating burner that moves in the tube axis direction, and depositing multiple glass layers inside the reaction tube. In the method, a semi-fixed auxiliary burner is movably attached to the gas introduction end of the reaction tube, separately from the main heating burner, and it takes a predetermined time for the main heating burner to return from the end of the reaction tube to the gas introduction section. The auxiliary burner heats the gas introduction part of the reaction tube to deposit a frit oxide layer inside the reaction tube, and when the main heating burner reaches the gas introduction end, the auxiliary burner is moved and the auxiliary burner is moved. A method for producing an optical fiber preform, characterized in that the heating of the reaction tube by a burner is weakened, and the outer wall of the reaction tube is heated by a main heating burner instead of an auxiliary burner to form a glass layer inside the reaction tube. .