JPH111340A - Detection of defect part of optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate problems in that an additional device such as a light source or a photodetector device must further be used in a method for measuring the intensity of scattered light due to a defect part in order to detect the defect part of an optical fiber and the actual defect part of the optical fiber does not accurately correspond to a part detected as the defect part in a method for detecting a change in the takeoff speed. SOLUTION: An outside diameter fluctuation pattern in which the outside diameter is increased from a prescribed outside diameter and then reduced from the prescribed outside diameter and the extent of fluctuation to the side for reducing the outside diameter is larger than that to the side for increasing the outside diameter from the prescribed outside diameter is detected from the outside diameter fluctuation patter of an optical fiber by using only an outside diameter measuring instrument conventionally installed in an apparatus for producing the optical fiber to thereby detect the presence of a cavity in the optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a defective portion of an optical fiber, in particular, a cavity in the optical fiber.

[0002]

2. Description of the Related Art Quartz-based optical fibers used for optical transmission are required to control the outer diameter with high precision in order to reduce fusion loss and connection loss at a connector portion. The allowable range of the error with respect to the outer diameter of the fiber of 125 μm is about ± 1 μm. The part where the error of the outer diameter of the optical fiber is out of the allowable range is detected and removed by a known method.

However, even when the outer diameter of the optical fiber fluctuates within a specified allowable range, there is a problem that fusion splicing cannot be performed if a cavity exists in the optical fiber. This is because at the time of fusion splicing, the gas entering the hollow portion expands and expands the fused portion of the optical fiber. If a cavity occurs in the core, this defect can be detected by inspection of optical characteristics such as OTDR. However, if a cavity occurs in the cladding or at the interface between the core and the cladding, it must be detected and removed. Was difficult.

[0004] Conventionally, as a method of detecting a defect portion of an optical fiber which can detect a cladding portion of the optical fiber or a defect portion generated at an interface between the core and the cladding, a take-up speed of the optical fiber is described as follows. (JP-A-6-239641) and a method of measuring the intensity of scattered light from an optical fiber (JP-A-7-2298).
No. 13, JP-A-8-166356).

FIG. 4 shows a method disclosed in Japanese Patent Application Laid-Open No. 6-239641. First, an optical fiber 43 is drawn by heating and melting a preform rod 41 for an optical fiber in a heating furnace 42.
After the outer diameter is measured by an outer diameter measuring device 45 and then the resin is applied by a coating device 46, the resin is cured by a curing furnace 47, passes through the capstan 44, and is wound by a winding device 48. When a change in the outer diameter is detected by the outer diameter measuring device 45, the outer diameter measuring device 4 is moved along a path indicated by a broken line in FIG.
5 sends a control signal to the capstan 44 for controlling the take-off speed. Here, if air bubbles are generated over a certain length during the drawing of the optical fiber 43, the air bubbles may be crushed or the air bubbles may be reduced. In such a case, compared to a case where no air bubbles are generated. Optical fiber 43
Tries to be thinner. When the outer diameter is reduced, a control signal is issued from the outer diameter measuring device 45, and the optical fiber 43
The take-up speed of the capstan 44 is reduced so that the outer diameter of the capstan 44 becomes a predetermined value. This known invention monitors the change in the take-up speed of the optical fiber with the arithmetic processing unit 49,
This is to detect a defective portion of the optical fiber.

FIG. 5 shows a method disclosed in Japanese Patent Laid-Open No. 7-229813. This method utilizes the fact that light traveling inside an optical fiber exhibits a specific scattering pattern due to defects. Specifically, the optical fiber 55 drawn by heating and melting the optical fiber preform rod 51 in the heating furnace 52 is cooled in the cooling device 53, and the coating (resin coating) is performed by the coating device (coating device and curing furnace). Apply. Here, the light receiving element 5 is provided inside the cooling device 53.
4a, 54b are attached, and the optical fiber 5
The scattered light generated due to the air bubbles in the optical fiber of the light traveling in 5 is detected. The known invention analyzes the intensity of the scattered light by comparing the output change of each of the light receiving elements 54a and 54b, and distinguishes between the change in brightness due to bubbles and the change in brightness due to other factors. This is to detect a bubble (defect) portion of.

FIG. 6 shows a method disclosed in Japanese Patent Application Laid-Open No. 8-166356. This method utilizes the fact that light irradiated from the side of an optical fiber exhibits a specific scattering pattern due to defects. Specifically, the optical fiber 62 immediately after drawing the optical fiber preform rod 61 is continuously irradiated with the parallel light beam 63 from the side, and the forward scattered light 64 is continuously detected by the detector 65. I do. In this known invention, a signal processing unit 66 processes the detected pattern light amount of the scattered light to detect a defective portion of the optical fiber 62.

[0008]

However, in the method of detecting a defect in the optical fiber by detecting a change in the take-up speed, the control of the take-up speed may not catch up with a change in the outer diameter of the optical fiber. In some cases, the portion where the take-up speed has changed does not correspond to the defective portion of the optical fiber.

Further, the method of measuring the intensity of scattered light of an optical fiber to detect a defective portion requires additional devices such as a light source and a light receiving device, which need to be incorporated in a manufacturing apparatus.

[0010]

SUMMARY OF THE INVENTION The present invention relates to an outer diameter measuring device conventionally installed in an optical fiber manufacturing apparatus without adding an additional device such as a light source and a light receiving device to the optical fiber manufacturing apparatus. It is an object of the present invention to provide a method of detecting a defective portion of an optical fiber in which an actual defective portion of the optical fiber and a portion detected as the defective portion exactly correspond to each other using only the defective portion.

The present invention is a method for detecting a defect portion of an optical fiber from an outer diameter variation pattern obtained by measuring the outer diameter of an optical fiber drawn by heating and melting a preform rod for an optical fiber, From the obtained outer diameter variation pattern, becomes smaller than the predetermined outer diameter after being larger than the predetermined outer diameter, and is smaller than the predetermined outer diameter compared to the amount of fluctuation to the side larger than the predetermined outer diameter. The method is characterized in that the presence of a cavity in the optical fiber is detected by detecting an outer diameter fluctuation pattern having a large amount of fluctuation to a certain side.

Further, in the above-mentioned solving means, a variation amount of the outer diameter variation pattern to a side smaller than a predetermined outer diameter is 0.4 μm or more.

The variation is a value indicating the degree of deviation of the measured value of the outer diameter of the optical fiber from a predetermined constant value, that is, a predetermined value. The present invention is characterized in that a time-series variation pattern of the measurement result of the outer diameter of the optical fiber is noticed, and a specific variation pattern is found in a portion corresponding to a hollow portion.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a configuration diagram of an optical fiber manufacturing apparatus to which the present invention is applied, and its main components will be described along an optical fiber manufacturing process. The outer diameter of the optical fiber 5 obtained by heating, melting and drawing the optical fiber preform rod 1 in the heating furnace 2 is measured by the outer diameter measuring device 3 and cooled by the cooling device 4. Next, it is coated with a resin by a coating device (not shown) and wound up by a winding device (not shown).

Here, a mechanism for detecting an outer diameter variation caused by a cavity generated when an optical fiber is manufactured by using the apparatus shown in FIG. 1 will be described below. When the optical fiber preform rod 1 is heated in the heating furnace 2, the optical fiber preform rod 1 is formed inside the optical fiber preform rod 1 at the time of manufacturing the optical fiber preform rod 1 such as an interface between a core and a clad. Fine bubbles may precipitate at the interface. Then, the gas in the minute bubbles becomes hot and expands.

Next, in the process of being stretched into the optical fiber 5, the expanded bubbles become elongated cavities and increase the outer diameter of the optical fiber 5. When the tip of the cavity passes through the outer diameter measuring device 3, the outer diameter measuring device 3 detects that the outer diameter of the optical fiber 5 is increased by the gas in the cavity. It is important to detect this portion of the outer diameter variation pattern, and it has not been used in the past.

Thereafter, when the tip of the cavity passes through the cooling device 4, the gas in the cavity is rapidly cooled, and as a result, the pressure of the gas in the cavity decreases, and the pressure from the outside of the optical fiber 5 causes the heating furnace to cool. The outer diameter of the melted portion of the optical fiber 5 in the section from 2 to the cooling device 4 becomes smaller. The variation when the outer diameter becomes smaller is larger than the variation when the outer diameter becomes larger. When all the hollow portions pass through the outer diameter measuring device 3, the outer diameter returns to a predetermined value.

In the method for detecting a defect such as a cavity in an optical fiber according to the present invention, the variation pattern of the outer diameter becomes larger than a predetermined outer diameter at a rate of 0.02 μm or more per 1 m of drawing length. Thereafter, at a rate of 0.06 μm or more per 1 m of the drawn length and when the variation becomes 0.4 μm or less smaller than a predetermined value, the variation pattern further shows the variation on the side where the outer diameter becomes larger. If the variation amount on the side where the outer diameter is smaller is larger, the detection can be performed with higher reliability.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an outer diameter variation pattern will be described with reference to a characteristic diagram. The characteristic diagram shows 400 m of the variation pattern of the outer diameter, and the variation pattern is recorded from the left side of the drawing to the right side of the drawing.

FIG. 2 shows an example of an outer diameter variation pattern of an optical fiber showing the features of the present invention. In FIG. 2, the outer diameter of the optical fiber first becomes larger than the predetermined outer diameter, then becomes smaller than the predetermined outer diameter, and the fluctuation amount of the outer diameter is 0.3 μm on the side where the outer diameter becomes larger. 0.7μ on the side with smaller diameter
m, the fluctuation amount is larger on the side where the outer diameter is smaller. FIG.
As a result of inspection of the optical fiber showing the fluctuation pattern of the above, generation of a cavity of about 20 m was observed at the portion indicated by the thick line in FIG. Also, as a result of inspecting an optical fiber showing the same fluctuation pattern as in FIG. 2 (however, the absolute value of the fluctuation amount is different),
At the location where the outer diameter fluctuated, cavities were observed in all seven samples. The length of the cavity was 4 m at the minimum and 70 m at the maximum.

FIG. 3 shows an example of an outer diameter variation pattern of an optical fiber which does not exhibit the features of the present invention. In FIG. 3, the variation of the outer diameter of the optical fiber is 0.7 μm on the side where the outer diameter increases.
m is 0.1 μm on the side where the outer diameter is smaller, and the fluctuation amount is larger on the side where the outer diameter is larger. As a result of inspection of the optical fiber having the same variation pattern as that shown in FIG. 3, no cavity was found in any of the five samples including the present sample at the outer diameter variation portion.

[0022]

As described above, according to the present invention,
Without adding additional equipment such as a light source and a light receiving device to the optical fiber manufacturing equipment, only the outer diameter measuring instrument conventionally installed in the optical fiber manufacturing equipment is used to determine the actual defect portion of the optical fiber. In addition, it is possible to provide a method for detecting an optical fiber defective portion that accurately corresponds to a portion detected as a defective portion, and to improve the quality of an optical fiber.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an example of an optical fiber manufacturing apparatus to which the present invention is applied.

FIG. 2 is an outer diameter fluctuation characteristic diagram showing an example of outer diameter fluctuation when a cavity is present in an optical fiber.

FIG. 3 is an outer diameter fluctuation characteristic diagram showing an example of outer diameter fluctuation when there is no cavity in an optical fiber.

FIG. 4 is an explanatory diagram of a conventional method for detecting a defective portion of an optical fiber.

FIG. 5 is an explanatory diagram of a conventional method for detecting a defective portion of an optical fiber, which is different from FIG.

FIG. 6 is an explanatory diagram of a conventional method for detecting a defective portion of an optical fiber, which is different from FIGS. 4 and 5;

[Explanation of symbols]

1, 41, 51, 61 Preform rod for optical fiber 2, 42, 52 Furnace 3, 45 Outer diameter measuring instrument 4, 53 Cooling device 5, 43, 55, 62 Optical fiber (uncoated) 44 Capstan 46 Coating Device 47 Curing furnace (curing device) 48 Winding device 49 Arithmetic processing device 54a, 54b Light receiving element 63 Parallel light beam 64 Forward scattered light 65 Detector 66 Signal processing unit

Claims (2)

[Claims] 1. A method for detecting a defect portion of an optical fiber from an outer diameter variation pattern obtained by measuring an outer diameter of an optical fiber drawn by heating and melting a preform rod for an optical fiber. From the outer diameter variation pattern, the side that becomes smaller than the predetermined outer diameter after becoming larger than the predetermined outer diameter, and that becomes smaller than the predetermined outer diameter in comparison with the fluctuation amount to the side that becomes larger than the predetermined outer diameter. A method for detecting a defect in an optical fiber, comprising detecting an existence of a cavity in an optical fiber by detecting an outer diameter fluctuation pattern having a large amount of fluctuation. 2. The optical fiber defect detecting method according to claim 1, wherein an amount of variation of the outer diameter variation pattern to a side smaller than a predetermined outer diameter is 0.4 μm or more.