JPH026347A - Drawing of optical fiber - Google Patents

Abstract

PURPOSE:To obtain an optical fiber having low transmission loss in high yield, preventing the diffusion of impurities to the core part, by specifying and narrowing a high-temperature heating zone in the drawing of an optical fiber preform melted by heating with a heater through a furnace core tube. CONSTITUTION:A heater 20 for heating and melting an optical fiber preform 40 is provided in a drawing furnace 10 interposing a furnace core tube 3 between the heater 20 and the preform 40. An optical fiber 5 is drawn in drawing furnace 10. In the furnace core tube 3 for heating the optical fiber preform 40 in the drawing furnace 10, the longitudinal length of the high-temperature heating zone H maintained at >=1800 deg.C is controlled to 30-150mm. When the length is <=30mm, the optical fiber preform 40 cannot be sufficiently heated to unable the drawing of the fiber by the breakage of optical fiber. When it is >=150mm, the optical fiber preform is excessively heated to cause the diffusion of the impurities such as H2 from the preform into the core part and increase the transmission loss of the obtained optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application> The present invention relates to an optical fiber drawing method for drawing an optical fiber with low transmission loss.

<Prior art> Optical fibers are produced by feeding an optical fiber base material made of quartz or the like from the top of a drawing furnace and heating and melting its tip.
This molten portion is pulled out from the lower part of the drawing furnace and drawn into a wire by reducing the diameter to a desired diameter.

Also, during this drawing process, foreign matter may be present in the air around the tip of the molten optical fiber in the drawing furnace.

In order to prevent the presence of oxygen and the like, the drawing furnace is usually filled with an inert gas to prevent a decrease in the mechanical strength of the drawn optical fiber.

FIG. 4 shows such a conventional optical fiber drawing apparatus. As shown in the figure, a heater 2 such as a long carbon heater and a furnace core tube 3 are provided in a drawing furnace 1.
The optical fiber preform 4 is inserted through the upper opening 1a of the drawing furnace 1, and the drawn optical fiber 5 is drawn through the lower opening 1b. Furthermore, in order to prevent heat radiation from the heater 2, a heat insulating material 6 surrounding the heater 2 is provided inside the drawing furnace 1. Here, airtight members 7 with gas seals are provided in the upper and lower openings 1a and lb of the drawing furnace 1.
, 7 are provided respectively. These airtight members 7, 7 have an annular space, and the inert gas G is supplied to these spaces from the gas supply pipes 8, 8.
Inward from the inner circumferential surfaces 7a, 7a, that is, the upper and lower openings 1
It is blown onto the outer peripheral surfaces of the optical fiber preform 4 and the optical fiber 5 located near a and lb.

When drawing the optical fiber 5 using the above-mentioned apparatus, generally a long carbon heater having an axial length of 110 m or more is used. Therefore, the furnace core tube 3 in the drawing furnace 1
A high-temperature heating region is formed in the interior over a long range in the axial direction, thereby sufficiently heating the optical fiber preform 4, facilitating drawing, and improving productivity.

<Problems to be Solved by the Invention> However, since the optical fiber preform 4 is exposed to high temperature for a long time while passing through the high 1 heating region, Si and O contained in the preform.

F, other than CI, such as horse or Fe, Cu, N
There is a problem in that impurities such as transition metals such as i are diffused into the core portion which is the light transmission region, and as a result, they adversely affect the transmission loss of the obtained optical fiber 5. or,
When drawing an optical fiber with a core of 5IO2 and a cladding of SiO2-F, F is added to the cladding, which reduces the density of the glass and prevents impurities from diffusing into the core. This is particularly problematic because it becomes easy.

In view of the above-mentioned circumstances, an object of the present invention is to provide an optical fiber drawing method that can produce a low-loss optical fiber with high yield without diffusion of impurities into the core portion.

Means for Solving the Problems> The structure of the present invention for achieving the above object is to provide an optical fiber drawing method in which an optical fiber preform is heated and melted by a heater through a furnace tube and drawn. The length in the axial direction of the above high temperature heating area is 30+m or more.

It is characterized by being 150m or less.

Effect> Since the optical fiber preform to be drawn has a short high-temperature heating region, the heating time is short, and impurities such as lumps in the optical fiber preform are suppressed from diffusing to the core portion. Furthermore, when drawing an optical fiber preform that contains fluorine and has a relatively low glass density and easy diffusion of impurities compared to a conventional optical fiber preform that contains GeO3 in the core, The diffusion of impurities is prevented.

Embodiments Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 schematically shows an optical fiber drawing apparatus according to this embodiment. Incidentally, the same members as those in FIG. 4 according to the prior art are given the same reference numerals, and explanations of duplicate members will be omitted.

As shown in FIG. 1, a heater 20 for heating and melting the optical fiber preform 40 is disposed in the drawing furnace 10 via the furnace tube 3, and draws the optical fiber 5.

In this drawing furnace 10, a core 1 that heats the optical fiber preform 4! ! The high 1 heating region H of 1800° C. or higher in :3 is adjusted to be 30 mm or more and 150 mm or less. This is because if the above-mentioned high-temperature heating area H is 30+m++ or less, the optical fiber base material cannot be sufficiently heated, the optical fiber will break, and drawing will become impossible.
If the high-temperature heating region H is 150+nr* or more, the optical fiber base material will be heated too much, and impurities such as horse particles in the base material will diffuse into the core, reducing the transmission loss of the resulting optical fiber. It is from.

In addition, when a carbon heater for heating a long optical fiber base material is used as the heater 20, the length of the effective heat generating portion in the axial direction I
It is preferable to use one with a length of 10 m or more and 50 m or less.

When using the carbon heater of this example, the length of the effective heat generating part! is less than 10 degrees, it is impossible to increase the number of high-temperature heating regions 11 to more than 30 degrees. However, the present invention is not limited to this, and the optical fiber can be made effective by using a reflector or other heating element. Any heat source for wire drawing may be used.

Further, it is preferable that the optical fiber preform 40 to be drawn has a diameter d of 10 mm or more, 80+n+mJ] or less. This is because if the diameter d is less than 10 mm, the productivity of the obtained optical fiber will not increase, which is undesirable.
is 8 (1++ m or more), the base material will not be sufficiently heated within the high temperature heating region H, and sufficient wire drawing will not be possible.

When the wire drawing method of the present invention is performed using such a wire drawing P10, one part of fluorine is added as an additive to the part where impurities are likely to diffuse particularly into the core part, for example, which constitutes the clad part.
Even when using a material added by about wt%, it is possible to suppress impurities such as pigeons from diffusing into the core portion during heating and melting.

Next, a test example using the drawing furnace of this example will be shown below.

In this test example, a wire drawing furnace]0 was used, which has a heater 20 having the temperature distribution shown in Fig. 2, an effective heat generating part length 4 of 50 m+s, and a high temperature heating area H of 1800°C or higher of 100 m. An optical fiber preform 40 of pure silica core single mode fiber containing % fluorine was drawn.

The transmission loss of the optical fiber obtained is y! ! , the distribution of integrated frequencies was measured. The yield of transmission loss of 0.18 dB/kn or less at 1.55 μm of this cumulative frequency distribution was 70%.

As a comparative example, a similar test was conducted using a conventional drawing furnace 1 shown in FIG. 4. Furthermore, the heater 2 has the temperature distribution shown in Fig. 2, and the length of its effective heat generating part is ! is 110+m,
A high-heating area H of 1800° C. or higher was 170 m+++.

When the cumulative frequency of transmission loss of the obtained optical fiber was measured, the yield of transmission loss of 0.18 a/km or less at 1.55 pm was 40%.

The above results are shown in Table 1 and Figure 3.

Table 1 e: Effective heat generating area H: High temperature heating area As shown in Table 1 and Figure 3, the optical fiber of this test example had a transmission loss of 0.18 dB/++ at 1.55 μm.
It was found that the yield rate was as high as 70%, which was a significant improvement compared to the conventional method.

<Effects of the Invention> As described above in detail in Examples and Test Examples, according to the present invention, since the high-temperature heating region is sandwiched, diffusion of impurities in the optical fiber base material during drawing is suppressed, and transmission is improved. It becomes possible to produce optical fibers with low loss at a high yield.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the optical fiber drawing apparatus according to this example, and FIG. 2 is a temperature distribution diagram in the furnace according to the present test example and the conventional example.
FIG. 3 is a cumulative frequency distribution diagram of transmission loss, and FIG. 4 is a schematic diagram of a conventional optical fiber drawing apparatus. In the drawing, 3 is a furnace tube, 5 is an optical fiber, 10 is a drawing furnace, 20 is a heater, 40 is an optical fiber base material, l is the length of an effective heat generating part, and H is a high temperature heating area. Figure Figure H: 170mm

Claims (1)

[Claims] 1) An optical fiber drawing method in which an optical fiber preform is heated and melted by a heater via a furnace tube and drawn,
A method for drawing an optical fiber, characterized in that the length in the axial direction of a high temperature heating region of 1800° C. or higher is 30 mm or more and 150 mm or less. 2) The optical fiber drawing method according to claim 1, characterized in that an optical fiber preform having a diameter of 10 mm or more and 80 mm or less is drawn. 3) The optical fiber drawing method according to claim 1 or 2, characterized in that an optical fiber preform containing fluorine as an additive is drawn.