JPH04275935A - Production of optical fiber preform by discontinuous pulling-up method - Google Patents

Abstract

PURPOSE:To produce the optical fiber preform so that the shape of a cross section is nearly made to a circle and also to keep irregularity in density distribution in the circumferential direction. CONSTITUTION:In the case of producing the optical fiber preform 5 by respective burners 3, 4 by discontinuously pulling up a supporting rod 2 by a pulling-up mechanism 10 while rotating this supporting rod around the axial center thereof by a rotary mechanism 11, the motor 13 of the rotary mechanism 11 gives rotational force to the supporting rod 2 and this rotational force is asynchronously stopped by a rotary clutch 14 which is driven asynchronously and discontinuously. This rotary clutch 14 is driven by a rotary clutch driver 15. This rotary clutch driver 15 is controlled by an asynchronous clutch driving signal generator 16.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical fiber preform by intermittent pulling, in which a porous optical fiber preform is produced by a VAD method while performing intermittent pulling.

0002

[Prior Art] In the VAD method, it is preferable to produce a porous optical fiber preform by continuously pulling the support rod of the optical fiber preform at a low speed while rotating it around its axis at a low speed. .

However, since it is technically difficult to continuously pull up the support rod at a low speed, the support rod is currently pulled up intermittently.

A specific example of such an interrupted pulling type optical fiber preform manufacturing apparatus will be explained with reference to FIG.

In the figure, 1 is a reaction vessel, 2 is a support rod suspended and inserted into the reaction vessel 1, and 3 and 4 are penetrating through the reaction vessel 1 so that each tip is at a predetermined position within the reaction vessel 1. A core burner and a cladding burner 5 are positioned so that the support rod 2 is
A porous optical fiber preform 6 is formed at the bottom of the reaction vessel 1, and 6 is an exhaust pipe provided through the reaction vessel 1.

Reference numeral 7 denotes a light emitter, and 8 a light receiver. These are arranged so that the light beam 9 emitted by the light emitter 7 detects the lower end of the optical fiber preform 5. 10 is a pulling mechanism that pulls up the optical fiber preform 5 via the support rod 2, and 11 is a rotation mechanism that rotates the optical fiber preform 5 via the support rod 2. The pulling mechanism 10 starts pulling up the optical fiber preform 5 when the light beam 9 emitted by the light emitter 7 is blocked by the lower end of the optical fiber preform 5, and starts pulling up the optical fiber preform 5 when the light beam 9 is no longer blocked by the optical fiber preform 5. The intermittent lifting is controlled by a lifting signal from the light receiver 8 so as to stop.

In such an optical fiber preform manufacturing apparatus, the optical fiber preform 5 is manufactured by pulling it up while continuously rotating at a steady rotational speed Nx, so the finished optical fiber preform 5 is as shown in FIG. It has a layered structure as shown in FIGS. 4(a) and 4(b), in which the soot layer 12 consisting of a core portion 12a and a cladding portion 12b as shown is continuously wound downward in a spiral manner.

[0008]

However, in the intermittent pulling method, since the optical fiber preform 5 is pulled intermittently as described above, the thickness and density of the soot layer 12 vary between when pulling and when pulling is stopped. It makes a difference. That is, when the optical fiber preform 5 is stopped, the soot layer 1 is formed as it rotates steadily.
No. 2 is thick and has high density because glass fine particles adhere well to it and it is baked. However, the soot layer 1 formed as the optical fiber preform 5 is constantly rotated while being pulled up
In case 2, the glass particles are less likely to be attached than in the former case, so it is thinner and has a lower density.

For this reason, the rotation period N of the optical fiber preform 5
There is an integer multiple relationship (Nx
/Ny = 1, 2, 3...), (a) (
b) As shown in (c), there is a problem in that the cross-sectional shape of the optical fiber preform 5 is deformed.

It should be noted that the solid lines like annual rings shown in FIGS. 5(a), 5(b), and 5(c) are formed as the optical fiber preform 5 rotates when the optical fiber preform 5 stops being pulled up. The circumferential range of the high-density region is shown.

Furthermore, the ratio of Nx and Ny mentioned above is not an integral multiple, but (Nx /Ny)<1 or 1<(Nx
/Ny)<2, or 2<(Nx/Ny)<3...
In such a case, the cross-sectional shape of the optical fiber preform 5 is close to a circle as shown in FIGS.
When x /Ny ) < 1 or 1 < (Nx /Ny ) < 2, as shown in FIG. It is distributed in a spiral shape with a gradual shift in the circumferential direction in a counterclockwise or clockwise direction.

As described above, in both cases as shown in FIGS. 5 and 6, the density distribution in the circumferential direction within the optical fiber preform 5 becomes periodic due to the correlation between Nx and Ny. This causes the following problems.

(1) Once a crack occurs in the optical fiber base material 5, the crack propagates outward across the layer interface along the locus of regular low-density layers in the circumferential direction, and the optical fiber base material This will result in the material 5 cracking.

(2) If layers with density distribution exist periodically in the circumferential direction in the optical fiber preform 5, the quality of the optical fiber will become non-uniform.

[0015] An object of the present invention is to provide an intermittent pull type optical fiber which can be manufactured so that the optical fiber preform has a substantially circular cross-sectional shape, and which can prevent regularity in the density distribution in the circumferential direction. The object of the present invention is to provide a method for manufacturing a base material.

[0016]

[Means for Solving the Problems] To explain the means of the present invention for achieving the above-mentioned object, the present invention provides a method of rotating a support rod around its axis and intermittently pulling it up into the flame of a burner. In the method for manufacturing an optical fiber preform of an interrupted pulling type, in which a porous, cylindrical optical fiber preform is manufactured by gradually depositing glass particles synthesized in a layer on the tip side of the support rod, the support rod is It is characterized by rotating while stopping periodically.

[0017]

[Operation] When the support rod is stopped and rotated aperiodically in this way, the correlation between Nx and Ny disappears, and the density distribution in the circumferential direction of the optical fiber preform becomes aperiodic. Therefore, the cross-sectional shape of the optical fiber preform can be approximated to a circle. Further, even if a crack occurs in the optical fiber base material, the irregular density distribution makes it difficult for the crack to propagate to the outside, thereby preventing the optical fiber base material from cracking. Furthermore, the quality of the optical fiber becomes uniform.

[0018]

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

FIG. 1 shows an embodiment of an apparatus for carrying out the method of the present invention. Note that parts corresponding to those in FIG. 2 described above are designated by the same reference numerals. In the figure, 13 is a motor that rotates the support rod 2 at a steady speed;
15 is a rotary clutch driver that drives the rotary clutch 14, and 16 is an aperiodic clutch drive signal composed of, for example, an M-series aperiodic signal generator. It is a generator. These motor 13, rotary clutch 14, rotary clutch driver 1
5. The rotation mechanism 11 is composed of the aperiodic clutch drive signal generator 16.

17 is a motor for pulling up the support rod 2;
8 is a screw that is rotated at a steady speed by a motor 17; 19 is a nut-shaped member that is screwed to the screw 18 and converts the rotational force into a pulling force to pull up the support rod 2; 20 is a puller that intermittents the pulling force; Clutch 21 is a pull-up clutch driver that drives the pull-up clutch 20 with a pull-up signal from the light receiver 8. These motors 17,
Screw 18, nut-shaped member 19, pulling clutch 2
0, the pulling mechanism 10 is composed of the pulling clutch driver 21.

[0021] Next, a method of manufacturing the intermittent pulling type optical fiber preform of this embodiment using such an apparatus will be explained. The support rod 2 is rotated by a motor 13 at a steady speed. In this state, the rotational force of the motor 13 is intermittent aperiodically by the rotary clutch driver 15. As a result, the support rod 2 is rotated while being stopped non-periodically.

In this state, the core 12a and the cladding part 12b are attached to the tip of the support rod 2 by both burners 3 and 4 as described above.
The soot layer 12 consisting of the above is successively stacked on the lower side in a tapered spiral shape to sequentially form the optical fiber preform 5.

When the optical fiber base material 5 grows and blocks the light beam 9 from the light emitter 7, a pull signal is output from the light receiver 8 to the pull mechanism 10, and the pull clutch driver 21 is activated. Then, the pulling clutch 20 is brought into contact, and the pulling force is transmitted to the support rod 2, so that the support rod 2 is pulled up.

When the optical fiber base material 5 rises and the light beam 9 reaches the light receiver 8 without being blocked by the optical fiber base material 5, the light receiver 8 no longer outputs a pull-up signal, and the support rod 2 is removed by the pull-up mechanism 10. lifting is stopped.

[0025] In this manner, the optical fiber preform 5 is manufactured to a desired length by rotation with non-periodic stops and intermittent pulling. In this case, when the support rod 2 is rotated while stopping non-periodically, the soot layer 1 changes as the rotational speed changes with the stop.
The density of 2 will change.

[0026] If such a manufacturing method is adopted, Nx and N
The ratio (Nx/Ny) with y no longer has a steady proportional relationship, so the cross-sectional shape of the optical fiber preform 5 approaches a circle.

Furthermore, if the optical fiber preform 5 is rotated while being stopped non-periodically, the density distribution of the soot layer in the direction of rotation becomes irregular. Therefore, even if a crack occurs inside the optical fiber preform 5, the crack will not propagate to the outside of the optical fiber preform 5, and cracking of the optical fiber preform 5 can be prevented.

Furthermore, when the cross-sectional shape of the optical fiber preform 5 becomes close to a circle and the density distribution in the circumferential direction becomes irregular,
The quality of the optical fiber preform 5 becomes almost uniform, and the quality of the optical fiber can be made uniform.

In the above embodiment, only two burners are used, but the present invention is equally applicable not only to one burner but also to three or more burners.

[0030]

[Effects of the Invention] As explained above, in the method for manufacturing an optical fiber preform of an intermittent pulling type according to the present invention, since the support rod is rotated while being stopped non-periodically, there is no correlation between Nx and Ny. The density distribution in the circumferential direction of the optical fiber preform can be made non-periodic. Therefore, the cross-sectional shape of the obtained optical fiber preform can be approximated to a circle. Further, when the density distribution in the circumferential direction of the optical fiber preform becomes irregular, even if a crack occurs in the optical fiber preform, it will not propagate to the outside, and cracking of the optical fiber preform can be prevented. Furthermore, when the cross-sectional shape of the optical fiber preform becomes close to a circle and the density distribution in the circumferential direction becomes irregular, the quality of the optical fiber preform becomes almost uniform, and the quality of the optical fiber becomes uniform. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the main part configuration of an apparatus for implementing the method of the present invention.

FIG. 2 is a longitudinal cross-sectional view of the production of an interrupted pull-type optical fiber preform.

FIG. 3 is a perspective view of a soot layer formed in each burner shown in FIG. 2;

FIG. 4(a) is a partially vertical side view of an optical fiber preform formed by each burner, and FIG. 4(b) is a cross-sectional view of the optical fiber preform.

FIGS. 5(a), 5(b), and 5(c) are cross-sectional views of optical fiber preforms obtained when the ratio of the pulling period to the rotation period is changed to an integral multiple using a conventional method.

FIGS. 6A and 6B are cross-sectional views of an optical fiber preform obtained when the ratio of the pulling period to the rotation period is changed to a non-integral multiple using a conventional method.

[Explanation of symbols]

1 Reaction vessel 2 Support rod 3 Burner for core 4 Burner for cladding 5 Optical fiber base material 6 Exhaust pipe 7 Emitter 8 Light receiver 9 Light beam 10 Pulling mechanism 11 Rotating mechanism 12 Soot layer 12a Core part 12b Clad part 13 Motor 14 Rotating clutch 15 Rotary clutch driver 16 Aperiodic clutch drive signal generator 17
Motor 18 Screw 19 Nut-shaped member 20 Pulling clutch 21 Pulling clutch driver

Claims (1)

[Claims] Claim 1: A support rod is rotated around its axis and intermittently pulled up, and glass fine particles synthesized in the flame of a burner are gradually deposited in a layer on the tip side of the support rod to form a porous structure. A method for manufacturing an intermittent pull-type optical fiber preform for manufacturing a cylindrical optical fiber preform, the method comprising rotating the support rod while stopping it non-periodically. .