JPS62212240A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To obtain an optical fiber essentially free from core-eccentricity from a preform having core-eccentricity, by partially applying glass to or scraping glass off from the outer circumference of a preform having core-eccentricity to balance the thickness of glass at both sides of the core along the eccentric direction of the core and drawing the preform to an optical fiber. CONSTITUTION:An optical fiber is produced from an optical fiber preform in which core-eccentricity is detected by the measurement of core-eccentricity, by drawing the preform after balancing the amounts of glass (amount of clad and jacket, etc.) at both sides of the core along the eccentric direction of the core either by scraping the circumference at a part where the distance between the core center and the preform circumference is longer or by applying a glass layer to a circumference at a part where the above distance is shorter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for manufacturing an optical fiber having substantially no core eccentricity from a preform having core eccentricity.

[Prior art and its problems]

If an optical fiber preform has an eccentric core, the optical fiber produced by drawing it will also have an eccentric core. For this reason, although optical fiber preforms are manufactured with sufficient care to prevent core eccentricity, it is still extremely difficult to completely eliminate core eccentricity.

Conventionally, preforms whose core eccentricity has been measured before drawing have been disposed of as defective products, but this has been extremely uneconomical due to the large cost involved in manufacturing the preforms.

[Means for solving problems and their effects]

In view of the single intermediate layer of the prior art as described above, the present invention provides a method for manufacturing an optical fiber substantially free of core eccentricity from a preform with core eccentricity.

To achieve this objective, the present invention provides a method for manufacturing optical fibers from preforms whose core eccentricity has been measured by measuring the core eccentricity of an optical fiber preform. The amount of glass on both sides of the core (cladding, jacket, etc.) in the core eccentric direction can be balanced by cutting off a portion of the outer circumferential surface side of the longer distance, or attaching a glass layer to the shorter outer circumferential surface side. The preform is then drawn into an optical fiber.

If a part of the outer peripheral surface of the preform is scraped off or a glass layer is attached to the outer peripheral surface, the cross section of the preform will no longer be a perfect circle, but since the preform is heated and melted during wire drawing, the surface at this time The tension causes the cross section to return to a perfect circle. Therefore, by balancing the amount of cladding and jacket on both sides of the core in the eccentric direction of the core before drawing, it is possible to manufacture an optical fiber without eccentricity.

〔Example〕

Example 1 When the cross section of a single mode optical fiber preform manufactured by the VAD method was measured, as shown in FIG.
．． 8-m, the eccentricity of core 2 is 0.2 naea (
rI=20.2w+tm, rt=19.8mm).

The left end of this preform (that is, the outer circumferential surface side with the longer distance from the core center to the preform outer circumferential surface in the eccentric direction of the core 2) was shaved off to a depth of 1.511N as indicated by diagonal lines.

As a result of drawing this into a 125μ- optical fiber using a conventional method, no core eccentricity was detected in the obtained optical fiber (eccentricity of 0.1μ- or less), which would be expected if the above cutting was not performed. The core eccentricity of the optical fiber is 1.25μ-
It is.

The above scraping depth is determined as follows.

As shown in Figure 2, if the radius of the preform is r, the eccentricity of the core is X, and the depth of scraping is y, then the deviation in area due to eccentricity is S -2r x- (1) The area to be scraped is 2
S=4rx・−・(2)・.

Area of fan-shaped OAB T-πr2・2θ/2πr2θ −
(3) Area of triangle OAB U -< r cos θ) 0 (rsin θ) -- (4) Therefore, the scraped area is: From equations (2) and (5), therefore, θ''m 5 x / r -471 Therefore, For example, if the preform radius is 10 mm and the eccentricity is 0.5 an, θ'-6Xo, 0.3 on 5/10 θ=0.669 rad -38,4 y!r-rcO1lθ-r(1-cosθ) -481
Because it is! -10X (1-cos38.4) -10X (
1-0,784)-2,16 steel- Tonari, purity 2.16@- Just scrape it off.

For example, preform radius 1 (1 mm, eccentricity 0.1 m
In the case of m, θ'-6Xo, 1/10 wealth 0,06 θ''0.39 rad y = 10 x (1-0,924)-0,76-
All you have to do is scrape it off to a depth of 0.76mm.

Example 2 When the cross section of a single mode optical fiber preform manufactured by the VAD method was measured, as shown in FIG. 3, the outer diameter of the preform 1 was 40 m#, the outer diameter of the core 2 was 2.8 mm, The eccentricity of core 2 is 0.1 mm to the right (r
t=20. ll1m, rt = 19.9mm).

The right end of this preform (that is, the outer peripheral surface side that is shorter in distance from the core center to the preform outer peripheral surface in the eccentric direction of core 2) is externally attached to the preform length lO by law.
0.176 H of Sin per a+- was deposited and vitrified. 3 is the attached glass layer.

As a result of drawing this into a 125μ- optical fiber using a conventional method, no core eccentricity was detected in the obtained optical fiber (eccentricity of 0.1μ- or less), which would be expected if the above cutting was not performed. The core eccentricity of the optical fiber is 0.625μm
It is.

The adhesion amount of the glass layer is determined as follows.

As shown in Fig. 4, if the radius of the preform is r, the eccentricity of the core is Just let it happen.

Since it is S-2rx, the density of the glass layer is 2.2μ1g
/111m3, the amount of adhesion y (weight) per unit length is ? -2r x X 2 X2.2 XIQ-88r
x-...((1). In Example 2, "-20, x
=0.1, so y-88X20X0.1-176mg.

Example 3 A large-diameter single-mode optical fiber whose core satisfies the single-mode condition with an outer diameter of 1 was prototyped. In this case, a preform was manufactured by repeating overjacketing three times on a normal single-mode optical fiber preform.

As a result of measuring the cross section of the completed preform, the outer diameter was 50 ma+, the core diameter was 0.44 mm, and the eccentricity was 0.4 mm (
r, = 25.4 mm, r, = 24.6 mm).

The scraping depth is as follows.

θ"= 6 Xo, 4/25 0.096θ-0,45
8rad = 26.3 )' -2sx (1-cos26.3) -25X (
1-0,896) = 2.6 as This preform was shaved off by 2.6 mm from the area corresponding to the shaded area in Figure 1, and this was drawn into an optical fiber with an outer diameter of 1 ms using a conventional method. As a result, the eccentricity of the core was less than L0. Met. Note that the core eccentricity of the optical fiber is assumed to be 1 when no cutting is performed.
It is 6 μm.

Since the single mode optical fiber manufactured as described above has a thick outer diameter of 1 mm, it can be called a single mode optical rod, and is cut into short lengths and passed through to form optical components.

Example 4 By intentionally twisting the preform at the preform manufacturing stage, a preform l having an eccentric core 2 in a spiral shape as shown in FIG. 5 was manufactured. After measuring the helical state using a preform analyzer, a glass layer 3 was attached according to the helical state by the external attachment method as in Example 2.

After that, this preform was drawn to produce an optical fiber, and as a result, a significant improvement in eccentricity was observed over the entire length.

In the method of the present invention, there is a concern that the core may be deformed, but since the core diameter is small in single-mode optical fibers, this is not a problem.Also, if the core is made of pure Sing or something close to it, and the synthetic rad is made of a fluorine-doped material, , even if the fluorine-doped layer deforms slightly, the core does not deform at all, so
Deformation of the core can also be suppressed by selecting the glass compositions of the core and cladding.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to manufacture an optical fiber without core eccentricity from a preform with core eccentricity, which was conventionally considered to be a defective product, so that there is an advantage that the yield is significantly improved.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a preform in one embodiment of the present invention, Fig. 2 is a sectional view for explaining the depth of scraping of the preform, and Fig. 3 is a sectional view of a preform in another embodiment of the invention. FIG. 4 is a cross-sectional view for explaining the amount of glass layer adhered to the preform, and FIG. 5 is a side view of the preform in still another embodiment of the present invention. 1 - preform, 2 - core, 3 - glass layer.

Claims (1)

[Claims] In a method of manufacturing an optical fiber from a preform whose core eccentricity has been measured by measuring the core eccentricity of an optical fiber preform, The amount of glass on both sides of the core in the direction of core eccentricity is balanced by cutting off a portion or attaching a glass layer to the shorter outer peripheral surface, and then drawing the preform to form an optical fiber. Characteristic optical fiber manufacturing method.