JPH02212328A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To obtain an optical fiber preform having a specified ratio of outer diameter/core diameter and a uniform outer diameter and to facilitate the control of the outer diameter after drawing by grinding the periphery of an optical fiber preform, and then drawing the preform to a fixed diameter. CONSTITUTION:An optical fiber preform having a specified core diameter when the preform is drawn to a specified outer diameter is produced. However, the ratio of the outer diameter of the preform to the core diameter is not always consistent. Accordingly, the periphery of the preform is ground to allow the changes in the preform outer diameter to conform to the fluctuations in the core diameter. Consequently, a preform having a uniform outer diameter-to-core diameter ratio in the longitudinal direction is obtained by the grinding. The preform is then drawn to obtain an optical fiber having a uniform outer diameter and core diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing an optical fiber preform, and particularly to a method for strictly controlling the core diameter of a single mode optical fiber preform.

[Conventional technology]

In order to obtain a desired cutoff wavelength and dispersion characteristics in an optical fiber, particularly a single mode optical fiber (base material), it is necessary to control the core diameter within a predetermined range. Among them, the optical soliton method, which is desired to be realized as a conventional long-distance, high-capacity optical communication method, has a dispersion value of -
It has been reported that the controllability of the dispersion value is insufficient even at ±0.5 psec/km/n- when assuming that the dispersion value is 'l psec/ks/nm. ” paper, pp. 117-122, published in 1988).

- Considering the step-type refractive index distribution, the controllability of the dispersion value is approximately ±0, 5 psec, which is approximately ±1% in terms of the controllability of the core diameter. This value is close to the limit that can be achieved using a normal manufacturing method for optical fiber preforms.

On the other hand, as a means to improve the controllability of the core diameter, for example, optical fiber In the so-called rod-in-tube method, in which a base material for optical fiber corresponding to the central part is made and inserted into a commercially available quartz pipe for drawing, the cross-sectional area of the quartz pipe to be used is measured and rigorously selected. There is a method.

[Problem to be solved by the invention]

However, in the latter rod-in-tube method, the number of quartz tubes that can be used is severely limited due to strict selection of the quartz tube diameter, resulting in increased costs and the refractive index distribution of the optical fiber base material in the center. If there is a change in the core diameter in the longitudinal direction, no measures can be taken at all.

[Means to solve the problem]

The present inventors have discovered that when thinning an optical fiber preform by drawing, in order to obtain an optical fiber preform with a predetermined outer diameter/core diameter ratio and a uniform outer diameter, They discovered that it is essential to grind the outer periphery of the material and then stretch it, leading to the completion of the present invention.

Therefore, the present invention, as a means for solving the above-mentioned problems, includes; , provides a method for manufacturing an optical fiber, which is characterized in that the optical fiber is stretched to have a constant outer diameter and then drawn.

In addition, in order to smooth out minute irregularities on the surface of the optical fiber base material after grinding, the surface of the optical fiber base material is etched in advance with a corrosive solution, and then subjected to the stretching and drawing process. This is a method of manufacturing fiber.

The present invention will be explained in detail based on the drawings.

Figures 1 and 2 show the outer diameter/core diameter of the optical fiber base material (hereinafter simply referred to as the base material) by the conventional method (drawing only... - solid line) and the method of the present invention (grinding/drawing). Processing and/or etching + line drawing...chain line, - point vA
FIG. 2 is an enlarged schematic diagram of a cross section of an optical fiber (base material), explaining IIm).

For example, 5.1u when drawn with an outer diameter of 125μmΦ
When preparing an optical fiber preform with a core diameter of mΦ as the target, the outer diameter and core diameter of the prepared preform are as shown in Figure 1 (a).
Assume that the fluctuation is as shown by the solid line in ~(c). If such a base material is drawn as it is to have an outer diameter of 125 μmΦ, the resulting fiber usually has a core diameter of 5.0 μm, which is the target value, as shown by the solid line in FIG. 1(d). ltI
It deviates by about m and also fluctuates considerably in the longitudinal direction.

Therefore, in the present invention, as shown by the chain lines in FIGS. 1(a) and 1(b), the change in the outer diameter of the base material matches the core diameter variation in the base material shown in FIG. 1(C). First, at least a portion of the outer periphery of the base material is ground by a known grinding means used for processing glass fibers, such as a rotary grinding plate or a grinding wheel with abrasive particles, to obtain a uniform outer diameter/core in the longitudinal direction. Process into a base material with a diameter ratio.

On the other hand, if the wire is simply ground like this, the outer diameter will be uneven and non-uniform, so even if the wire is thinned later in the wire drawing process, it will be extremely difficult to control the outer diameter as mentioned above. It is necessary to make the outer diameter of the base material uniform.

In the method of the present invention, the base material is further heated by any heat source used for processing glass fibers, such as an acid/hydrogen burner, and stretched by an appropriate stretching means (controlling the winding speed, etc.). It is characterized by having a predetermined diameter.

In addition, as a heat source for heating the preform, laser heating, induction heating, a belt-shaped heating plate, etc. can be used.

As described above, the present invention provides a predetermined outer diameter/core diameter ratio by adding a process of controlling and adjusting the outer diameter/core diameter ratio of the base material prior to the drawing process of the optical fiber. It is possible to obtain an optical fiber preform having a uniform outer diameter.

In addition, if the surface of the base material is severely uneven due to grinding, it is difficult to melt and smooth out the microscopic irregularities even if the base material is heated and stretched. - Once the base material is etched in a corrosive solution, for example, an aqueous solution containing hydrofluoric acid as a main component such as HF, or a mixed acid aqueous solution in which a small amount of a strong acid such as hydrochloric acid or sulfuric acid is mixed with the aqueous solution, the surface of the base material can be etched. preferable.

By performing etching treatment in this way, microscopic irregularities on the surface of the base material can be smoothed to some extent, and therefore, if this base material is further heated and stretched using an oxygen or hydrogen flame, an even smoother outer surface can be obtained. The base material is obtained.

Here, ya! 4! The conditions for etching treatment with a neutral solution depend on the glass composition of the optical fiber base material and the surface condition after grinding, but generally, for example, 10% of HF is used.
It is sufficient to immerse it in the aqueous solution for about 1 to 3 hours.

Above, the present invention has been described in detail with reference to FIG. 1 in the case where the outer periphery of the optical fiber preform is ground accurately in accordance with the variation in the core diameter. Furthermore, in the present invention, there is an advantage that even if the grinding process is performed in accordance with the variation in the approximate core diameter, the precision of the predetermined core diameter can be obtained for the container in combination with the subsequent heating and stretching process.

The manufacturing technology of the optical fiber preform of the present invention is particularly used in large-capacity optical communication systems using optical solitons (light waves that do not cause deformation or distortion in the pulse waveform on the time axis even when propagating through an optical fiber with dispersion). It can be suitably applied to precision design of the core diameter of an optical fiber preform.

〔Example〕

The present invention will be specifically explained by examples, but these are not intended to limit the scope of the present invention.

The core is Gear 5ift and the cladding is FS
Two preforms for optical fibers (base material A and base material B) having an outer diameter of about 25 mΦ and a length of about 500 m and having a refractive index distribution shown in FIG. 3 and having a composition of iOx were prepared.

The results of measuring the core diameter and outer diameter over the entire length at intervals of 50 ava for both base materials are shown in Figures 4 (base material A) and 5.
Both base materials shown in the figure (base material B) show similar fluctuations in core diameter and outer diameter.

Regarding the Example base material A, the outer diameter was adjusted by grinding as shown by the chain line in FIG. Then, add 1 to 10% HF aqueous solution.
After being immersed for a period of time and performing HF etching treatment on the surface of the base material, it was heated and stretched using an acid/hydrogen burner so that the outer diameter was 24.0Φ.

Furthermore, this base material A was wire-drawn to have an outer diameter of 125 μmΦ. After drawing, the fiber was divided into 4 pieces each corresponding to the positions of the base material indicated as a, b, c, and d in FIG.
The dispersion value at 55 μm was measured. The results are also shown in Table 1.

In base material A to which the method of the present invention is applied, all four fibers obtained have a dispersion value of +2.0±0°1 psec
/km/n-, demonstrating the effectiveness of the method of the present invention.

(Comparative example) On the other hand, this base material B has 125
The wire was drawn to an outer diameter of pmΦ. After drawing, a and b are shown in Figure 5.
The fiber was divided into 4 pieces each corresponding to the positions of the base material shown as , c, and d, and the dispersion value at 1°55 pm was measured. The results are shown in Table 1.

Variance value 2, 0 psec/ks8-±0, 5
There is only one fiber (a) that satisfies psec/lv/nm, and it can be seen that the core diameter of that fiber also varies in the longitudinal direction.

In this example (comparative example), the core diameter of the base material was measured using a commercially available non-destructive refractive index distribution measuring device (PIOI type manufactured by York).

Table 1 [Effects of the Invention] As explained above, in the present invention, by grinding the outer periphery of the optical fiber base material and then stretching it to a constant diameter, the core diameter is uniform in the longitudinal direction and has a predetermined diameter. This method is effective as a method for manufacturing optical fibers that require close control of the core diameter.

[Brief explanation of the drawing]

FIGS. 1 and 2 are enlarged schematic diagrams of a cross section of an optical fiber (base material) for explaining the effects of the method of the present invention and the conventional method. FIG. 3 is a graph schematically showing the refractive index distribution of the optical fiber preform used in the example. FIG. 4 is a graph showing actual measurement results of the longitudinal outer diameter/core diameter of the optical fiber preform of Example (base material A). FIG. 5 is a graph showing actual measurement results of the longitudinal outer diameter/core diameter of the optical fiber preform of the comparative example (base material B).

Claims (2)

[Claims] (1) Regarding the outer circumference of the optical fiber preform, at least a portion thereof is ground in the longitudinal direction of the optical fiber preform to reduce the outer diameter, and then stretched so that the outer diameter is constant, A method of manufacturing an optical fiber, the method comprising drawing the optical fiber. (2) The method for manufacturing an optical fiber according to claim (1), wherein the surface of the optical fiber base material after grinding is etched in advance with a corrosive solution and then subjected to stretching and drawing steps.