JPH02199040A - Wire drawing of optical fiber - Google Patents

Abstract

PURPOSE:To improve mechanical strength and uniformity of outer diameter of optical fiber by equipping an upper inert gas feed part, a storage chamber of parent material, a furnace core tube provided with a small chamber opening downward at an extended part and a specific gas blowing tool and carrying out melt spinning in an inert gas atmosphere. CONSTITUTION:A fixed amount of inert gas is always sent from an upper inert gas feed part 6 to a high-temperature storage chamber 9 of parent material having stored an optical fiber preform 1, flows downward along the outside of the optical fiber preform 1 and the inert gas is gradually expanded by a small chamber 10 opening downward at an extended part 8 of furnace core tube having an inner diameter l2 smaller than an inner diameter l1 of the stor age chamber 9 of parent material and a throttling part 11 having an inner diameter l3 smaller than l2 set between the storage chamber of parent material and the small chamber. An inert gas is introduced upward from an inert gas blowing tool 12 below the extended part 8 of furnace core tube at a given interval so that a fiber drawing furnace to seal an optical fiber 5 sent from the small chamber 10 from the open air until the optical fiber is solidified is constituted to give an optical fiber having small diameter variability.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention involves heating and melting the lower end of an optical fiber preform with a heater in a vertically oriented furnace tube, and melting the lower end of the molten portion of the optical fiber preform. The present invention relates to an optical fiber drawing furnace that spins optical fiber downward from the top.

[Prior Art #4] The transmission characteristics of optical fibers have improved significantly in recent years, and their practical use is progressing in various fields.

However, issues that still need to be improved regarding optical fibers include improvement of the mechanical strength of the optical fiber and uniformity of the outer diameter. In other words, the former is in response to the increasing demand for long n-strength fibers, such as in the field of submarine optical fiber cables, and the latter is in response to the uniformity of optical fibers required to reduce splice loss. It is something to do.

It is known that the quality of each characteristic of such an optical fiber depends mainly on the method of drawing the optical fiber from a heated optical fiber preform.

The drawing of high-quality optical fibers is generally performed in an optical fiber drawing furnace having a cylindrical core tube.

FIGS. 4(a) and 4(b) are cross-sectional views showing the schematic structure of a general optical fiber drawing furnace using a carbon heater and a carbon furnace tube.

As shown in the figure, the optical fiber drawing furnace includes a carbon-like cylindrical core tube 2 facing upward and downward, which accommodates an optical fiber preform 1.
, a carbon heater 3 disposed around the heater 3 for heating the lower end of the optical fiber preform 1, and a furnace body 4 housing the heater 3.

In such an optical fiber drawing furnace, the optical fiber preform 1 is positioned approximately in the same ring shape as the furnace tube 2 so that its lower end is located between the heaters 3, and the lower end of the optical fiber preform 1 is positioned between the heaters 3. is heated and melted by a heater 3, and an optical fiber 5 is spun downward from the lower end of the melting section 1A while keeping the temperature of the melting section 1A constant.

By the way, when the furnace core tube 2 is made of carbon, the h-bond furnace core tube 2 is easily oxidized and consumed when exposed to the atmosphere at high temperatures where the optical fiber base material 1 is softened. This oxidative wear and tear of the furnace core tube 2 induces a decrease in the strength of the optical fiber 5, and naturally shortens the life of the drawing furnace itself.

Therefore, in order to prevent the furnace core tube 2 from being worn out, the
), as shown in FIG. A gas supply section 7 was provided to feed an inert gas into the furnace core tube 2 to create an inert atmosphere inside the furnace core tube 2.

[Problems to be Solved by the Invention] When inert gas is supplied into the furnace core tube 2 in this way, the optical fiber motherboard 1711 is cooled according to the flow rate of (. The temperature of the gas is greatly influenced by the gas flow rate.

As can be seen from FIGS. 4(a) and 4(b), the inert gas supplied from the inert gas supply section 6.7 rises inside the core tube 2, that is, towards the upper part of the optical fiber preform 1. There are parts that flow toward the lower part of the optical fiber preform 1 and parts that flow toward the lower part of the optical fiber preform 1. On the other hand, the diameter of the optical fiber preform 1 supplied to the furnace tube 2 is not necessarily constant. When the diameter of the optical fiber preform 1 changes, the distance between the core tube 2 and the optical fiber preform 1 naturally changes, and the cross-sectional area of the inert gas flow path formed between them changes, so the inert gas flow path changes. The average density or flow rate of the gas also changes. As a result, the flow of gas flowing upward in the core tube 2, that is, toward the top of the optical fiber preform 1, changes, and as a result, the amount of inert gas supplied from the inert gas supply sections 6 and 7 becomes constant. Then, the gas flow R flowing to the lower part h of the optical fiber preform 1 also changes. As described above, when the flow rate of the gas flowing toward the lower part of the optical fiber preform 1 changes, the temperature of the melted portion 1A of the optical fiber preform 1 changes significantly.

For example, when the flow of inert gas flowing through the molten part 1A of the optical fiber preform 1 increases, the heat m absorbed by the inert gas and flowing out of the core tube 2 increases, and the 1. In particular, the temperature of the melting zone 1A, which has a large surface area relative to its volume, decreases. As a result, the softened state of the fused portion 1A changes, the filament f1 changes, and the outer diameter of the optical fiber 5 changes.

Therefore, in order to draw a quality optical fiber 5 with small variations in outer diameter, adjusting the gas flow rate fed into the inside of the furnace tube 2 is an essential control element in drawing. be.

It is possible to calculate an inert gas supply vessel so that the flow rate of the inert gas at the gas flow interval for uniformizing the outer diameter of the optical fiber 5, that is, at the melting part 1A of the optical fiber base material 1 is constant. It's easy.

However, if the gas flow rate is controlled by focusing only on making the outer diameter of the optical fiber 5 uniform, the amount of inert gas supplied may become insufficient to prevent the gas from entering the reactor core tube 12. be. When air enters the furnace core tube 2, the carbon core tube 2 becomes wet and the strength of the optical fiber 5 decreases. On the other hand, if the gas flow rate is controlled by focusing only on the mixing of air into the reactor core tube 2, the amount of gas supplied tends to increase, turbulence occurs in the gas flow, and the outer diameter of the optical fiber 5 fluctuates.

That is, in the conventional drawing method, temperature control of the optical fiber preform 1 and shielding of the atmosphere from the furnace tube 2 are not compatible, and it may not be possible to draw an optical fiber 5 having a uniform outer diameter and sufficient strength. there were.

FIG. 5 shows the state of variation in the diameter of a conventional optical fiber 50. That is, the diameter of the conventional optical fiber 50 is 0.
．． It fluctuated within a range of 8 μ■ or less.

An object of the present invention is to provide an optical fiber drawing furnace capable of stabilizing the temperature of the optical fiber base material necessary for drawing the optical fiber, protecting the furnace tube, and suppressing fluctuations in the outer diameter of the optical fiber. Our goal is to provide the following.

[Means for Solving yI Problem 1] To explain in detail the present invention for achieving the above object, the present invention heats and melts the lower part of the optical fiber in a vertically oriented furnace tube with a heater. In the optical fiber drawing furnace that spins the optical fiber downward from the lower end of the molten part of the optical fiber preform, a core tube extension section is provided below the core tube, and the optical fiber is disposed within the core tube. A base metal storage chamber for accommodating the reactor core tube is provided, and a small chamber communicating with the base metal storage chamber and having an inner diameter smaller than the inner diameter of the base metal storage chamber and having a lower end opened downward is provided in the core tube extension. An upper inert gas supply section is provided at the upper part of the core tube to supply an inert gas to the preform storage chamber so as to flow downward along the outer periphery of the optical fiber preform, and the (The light coming out of the chamber below the core tube extension)?
The present invention is characterized in that an inert gas blowing shell for blowing out inert gas in ten directions along the pipe is provided at a predetermined interval with respect to the core tube extension.

[Operation] In this way, a preform storage chamber is provided in the core tube that accommodates the optical fiber preform, a small chamber is provided in the core tube extension located below it, and an upper inert gas supply section is provided at the top of the core tube. established,
Inert gas is supplied from the upper inert gas supply section to the preform storage chamber so as to flow downward along the outer periphery of the optical fiber preform, and is provided at a predetermined interval below the core tube extension. When an inert gas blowing device is provided and the inert gas is supplied upward along the optical fiber from the inert gas blowing device,
It is possible to achieve both the temperature tdlt[] of the optical fiber base material and the popular shielding of the furnace tube, and it is possible to sufficiently suppress fluctuations in the outer diameter of the optical fiber.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings. Note that parts corresponding to those in FIGS. 4(a) and 4(b) described above are designated by the same reference numerals.

FIG. 1 shows an embodiment of an optical fiber drawing furnace according to the present invention. As shown in the figure, in the optical fiber drawing furnace of this embodiment, a core tube extension part 8 is provided below the furnace tube 2 and integrally with the furnace body 4 to a length h. A preform housing chamber 9 for accommodating the optical fiber preform 1 is provided within the furnace tube 2 .

Inside the furnace tube extension 8, a small chamber 10 is provided which communicates with the base material storage chamber 9, has an inner diameter β2 smaller than the inner diameter J2+ of the base material storage chamber 9, and has a lower end opened downward. A constricted portion 11 having an inner diameter a3 smaller than the inner diameter C2 of the small chamber 10 is provided between the base material storage chamber 9 and the small chamber 10. An upper inert gas supply section 6 is provided at the upper part of the furnace tube 2 to supply inert gas to the preform housing v9 so as to flow downward along the outer periphery of the optical fiber preform 1. Below the core tube extension 8 , an inert gas blower 12 is installed at a predetermined distance from the core tube extension 8 and blows inert gas upward along the optical fiber 5 coming out of the small chamber 10 . It is provided.

FIG. 2 is a temperature distribution diagram of the base material storage chamber 9 and the small chamber 10 in FIG. 1.

Next, the operation of such an optical fiber drawing furnace will be explained. The preform storage chamber 9 that accommodates the optical fiber preform 1 includes:
Inert gas is supplied from the upper inert gas supply section 6, and the inert gas flows downward along the outer periphery of the optical fiber mother U1. In this case, the base material storage chamber 9 is at a high temperature of approximately 2000° C., and the inert gas flowing therein expands explosively. Suppression! , II was not possible. Therefore, in the present invention, a certain amount of inert gas is poured from above the base material storage chamber 9, and is gradually expanded in the process of reaching the R high temperature. In addition, the inner diameters of the base material storage chamber 9 and the small chamber 10 are set to 1! in order to eliminate interference as much as possible. ,
2<J2+, and a constricted portion 11 with a smaller inner diameter β3 is provided between the two.

In recent years, the diameter of the optical fiber preform 1 has tended to increase. For example, when attempting to draw an optical fiber preform 1 with an outer diameter of 5041IIIφ, the inner diameter a1 of the preform storage chamber 9 is approximately 80 mm.
It must be s+φ. At this time, if the inner diameter 12 of the small V10 is also set to 80 mφ, the flow rate of the inert gas flowing from the upper inert gas supply section 6 will be approximately 401/min due to the upward air flow from the bottom, which will consume a large amount of inert gas. become. Moreover, at this time, the inflow of air into the base material storage chamber 9 cannot be completely prevented, and oxidation and consumption of carbon occurs.
This causes troubles such as deterioration of the strength of the optical fiber 5.

In such a case, if the inner diameter of the small chamber 10 is set to, for example, a maximum of 60 aemφ and At>λ2 as in the present invention, the flow rate of the inert gas from the upper inert gas supply section 6 can be reduced, and the Inflow of air into the material storage chamber 9 can also be completely prevented. Further, by providing the constricted portion 11 between the base material storage chamber 9 and the small chamber 10, the effect can be more reliably exhibited.

The inert gas blowing device 12 is located under the furnace tube extension 8 and blows the inert gas upward along the optical fiber 5 -4.
゜This seals the optical fiber 5 coming out of the small chamber 10 and the atmosphere (air). Here, it is desirable to keep the inert gas blowing tool 12 a certain distance from the small chamber 10 on the premise that the sealing effect is not impaired. The reason for this is to prevent the inert gas flowing out from the small chamber 10 and the inert gas coming out from the inert gas blowing device 12 from interfering with each other, becoming a source of vibration for the optical fiber 5, and causing the wire diameter to be disturbed.

When the IQ diameter variation of the optical fiber 5 obtained by drawing the optical fiber 5 as described above was measured, the results shown in FIG. 3 were obtained. That is, the diameter of the optical fiber 5 drawn using the equipment of the present invention falls within the range of 0.2 μm or less,
It was observed that the wire diameter variation was small in Mf.

[Effects of the Invention] As explained below, the optical fiber drawing furnace according to the present invention has the following advantages:
A preform housing chamber is provided in the core tube that accommodates the optical fiber preform, a small chamber is provided in the core tube extension located below the preform, and an upper inert gas supply section is provided in the upper part of the core tube. Inert gas is supplied from the gas supply section to the base material storage chamber so as to flow downward along the outer periphery of the optical fiber base material, and inert gas is blown out at predetermined intervals below the core tube extension. Since the structure is such that the inert gas is supplied upward along the optical fiber from the inert gas blowing tool, it is possible to simultaneously control the warm claw of the optical fiber base material and block the atmosphere from the reactor core tube. It is possible to sufficiently suppress fluctuations in the outer diameter of the optical fiber, and to reduce fluctuations in the outer diameter of the optical fiber.
construction can be done easily. In particular, in the present invention, a small chamber with an inner diameter smaller than the base material storage chamber in the core tube is formed by the core tube extension, and the inert gas is allowed to flow downward from the top of the core tube through the base material storage chamber. Because of this, the existence of a small chamber with a small inner diameter reduces the consumption of inert gas, and also prevents outside air from entering from below.
In addition, it is possible to avoid collision between the descending gas flow and the ascending gas flow within the base material storage chamber. In addition, by blowing out inert gas upward from the inert gas blowing device installed at a predetermined interval below the core tube extension, the optical fiber coming out of the small chamber is sealed from the outside air until it is sufficiently solidified. Can be done. Furthermore, by providing the inert gas blowing device below the furnace tube extension, interference between the inert gas coming out of the small chamber and the inert gas coming out of this inert gas blowing device can be avoided as much as possible. .

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of an optical fiber drawing furnace according to the present invention!
[A top view, FIG. 2 is a diagram showing the temperature and collapse of each chamber in the drawing furnace shown in FIG. Figures 4 (a) and (b) are longitudinal cross-sectional views of two examples of conventional optical fiber drawing furnaces, and Figure 5 is a measurement diagram of the diameter change of optical fibers obtained with the conventional drawing furnace. It is. 1... Optical fiber base material, 1A... Melted part, 2...-
Furnace tube, 3... Heater, 4... Furnace body, 5... Optical fiber, 6... Upper inert gas supply section, 8... Core tube extension, 9... Base material accommodation. Room, 10... Small room, 11
... Throttle part, 12... Inert gas blowing tool.

Claims (1)

[Claims] In an optical fiber drawing furnace, the lower part of an optical fiber preform is heated and melted by a heater in a furnace tube facing in the vertical direction, and the optical fiber is spun downward from the lower end of the melted part of the optical fiber preform. A core tube extension is provided below.
A preform accommodating chamber for accommodating the optical fiber preform is provided in the furnace core tube, and a preform accommodating chamber is provided in the furnace tube extension portion, communicating with the preform accommodating chamber and having an inner diameter smaller than the inner diameter of the preform accommodating chamber. A small chamber whose lower end is opened downward is provided, and an upper chamber is provided at the upper part of the core tube for supplying an inert gas to the base material storage chamber so as to flow downward along the outer periphery of the optical fiber base material. An active gas supply unit is provided below the core tube extension, and an inert gas blowing device is provided below the core tube extension for blowing an inert gas upward along the optical fiber coming out of the small chamber. An optical fiber drawing furnace characterized in that the optical fiber drawing furnace is provided at a predetermined interval.