JPH05178634A - Method for deciding effective part of optical fiber preform - Google Patents

Abstract

PURPOSE:To improve yield by obtaining the distribution of the diameter ratio of the core to clad in the longitudinal direction of a starting preform by picture processing and using the part within the control values as the effective part. CONSTITUTION:White parallel beams 30 are injected from behind the starting preform 10 of an optical fiber to be measured. The beams are two-dimensionally inputted to an electronic computer 34 by using a TV camera 32 (e.g. CCD camera). The inputted pictures are analyzed by the computer to recognize the preform and as the distribution of brightness in the radial direction of the preform 10. The (a) in the brightness pattern is the boundary point between the clad and air, and the (b) is the boundary point between the core and clad. A certain threshold is imparted to the brightness data by the four points A, B, C and D shown in the figure, and the data are binarized to detect the boundary points (a) and (b) as the edge. The (a-a) and (b-b) distances are then digitized to obtain the diameter ratio of the core to clad at an optional point in the preform. The part within the specified values is found to be the effective part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining an effective portion of a starting base material, and particularly, for measuring a core-clad diameter ratio in a longitudinal direction of the starting base material, and then determining an effective portion of the base material. It is about the method.

[0002]

2. Description of the Related Art At present, when manufacturing an optical fiber preform, as shown in FIG. 2, a part of a core 12 and a clad 14 are simultaneously formed (hereinafter referred to as a starting preform 10), and only an effective portion 16 is taken out. After that, the clad 18 lacking in the effective portion 16 is replaced by
The finished base material 20 is added by an external attachment method or a jacket method.

Conventionally, the effective portion 16 of the starting base material 10 is shown in FIG.
As shown in (a), the part PQ where the outer diameter of the clad 14 is uniform
Was judged by the appearance.

The clad amount (additional clad amount) for the shortage depends on the profile, but the dominant parameter is the core-clad diameter ratio of the starting base material. The lacking clad is divided into several points in the base metal (for example, 2 for A and B).
(Point), and a clad having the same thickness was added in the longitudinal direction of the base material.

[0005]

Problems to be Solved by the Invention As shown in FIG.
The outer diameter of the clad 14 is constant, but the diameter of the core 12 may fluctuate. Core 12 in C and D parts
Since the diameter is large, the core / clad diameter ratio of this portion is small as shown in FIG. 3 (b).

However, conventionally, a portion where the core-clad diameter ratio largely fluctuates is also sent to the completed base material manufacturing process as an effective portion. Therefore, an appropriate clad portion cannot be attached at a portion where the core-clad diameter ratio is largely different from the profile measurement points A and B, such as C and D. That is, the additional clad 18 shown in FIG.
However, in reality, a uniform clad is attached as shown by the solid line. Therefore, the C and D portions are added and the clad is too much. As a result, the transmission characteristic of the completed base material is defective, and the standard is broken.

[0007]

[Means for Solving the Problems]

(1) As shown in FIG. 1A, the starting base material 10 of the optical fiber
Collimated light 30 is incident from the rear of the
The core / clad boundary and the clad diameter are detected by capturing with the V camera 32 and then performing image processing (FIG. 1B), and then the distribution of the core / clad diameter ratio in the longitudinal direction of the starting base material is obtained. (Fig. 1 (c)),
(2) Only the portion where the core-clad diameter ratio is within the specified value is the effective portion.

[0008]

[Operation] By using only the part where the core-clad diameter ratio is within the specified value as the effective part, the above C and D parts are eliminated. Further, in FIG. 3A, the core-clad diameter ratio is small in the right part from Q, and the core-clad diameter ratio is small in the left part from P.
Since the cladding diameter ratio becomes large, both are excluded from the effective portion 16.

[0009]

[Measurement method of core-clad diameter ratio] Fig. 1 shows the measurement configuration.
It shows in (a). White parallel light 30 is incident from the rear of the measured starting base material 10. The TV camera 32 (for example, CCD camera or the like) is used to two-dimensionally take it in the computer 34. The computer 34 analyzes the captured image and captures the ratio measurement base material as a radial luminance distribution of the base material.

In the brightness pattern of FIG. 1B, a is a boundary point between the clad and air, and b is a boundary point between the core and the clad.
Note that in FIG. 1B, only four points A, B, C, and D are shown, but in reality, a luminance pattern of a much larger number of points is obtained.

If a threshold of a certain value is given to this luminance data and binarized, the clad / air boundary point a and the core / clad boundary point b can be detected as edges (FIG. 1 (c)). ).

Thereafter, the distances between the edges aa, bb
By numerically processing, the core
It is possible to know the clad diameter ratio. Since the image data is captured two-dimensionally, the core in the longitudinal direction of the base material can be
The distribution of the clad diameter ratio can be known (FIG. 1 (c) left side).

[0013]

[Judgment of effective portion 16] As described above, after the core-clad diameter ratio in the longitudinal direction is obtained at the stage of the starting base metal, only the portion where the core-clad diameter ratio is within a predetermined value is effective portion. And This makes it possible to eliminate locations where the core-clad diameter ratio varies greatly.

[0014]

The distribution of the core-clad diameter ratio in the longitudinal direction of the starting base material is obtained by image processing, and only the portion where the core-clad diameter ratio is within the specified value is set as the effective portion. The effective portion of the material can be accurately determined, and the defective portion is not sent to the subsequent process. This is effective in improving the yield in the subsequent process and eventually reducing the cost. (2) By feeding back this data to the starting base material manufacturing process, it is possible to study an appropriate core and clad manufacturing method, and improve the production amount and yield of the starting base material manufacturing process.

[Brief description of drawings]

FIG. 1A is an explanatory diagram of a measurement configuration of a core-clad diameter ratio distribution, and FIG. 1B is an explanatory diagram of a luminance pattern obtained by capturing a starting base material and its transmitted light with a TV camera, according to an embodiment of the present invention. , (C) are explanatory diagrams of a binarized pattern of a brightness pattern image and a distribution of core-clad diameter ratios obtained from the pattern.

FIG. 2 is an explanatory view of a conventional state in which an effective portion is taken out from a starting base material and a clad is added to form a completed base material.

FIG. 3 is an explanatory view of a conventional method of determining an effective part 16 and its problems.

[Explanation of symbols]

 10 Starting Base Material 12 Core 14 Clad 16 Effective Part 18 Added Clad 20 Completed Base Material 30 Parallel Light 32 TV Camera 34 Computer

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[Procedure amendment]

[Submission date] November 13, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Fig. 2]

[Figure 3]

[Figure 1]

Claims (1)

[Claims] 1. A core-clad boundary and a clad diameter are detected by injecting parallel light from behind a starting base material of an optical fiber, capturing a transmission pattern thereof with a TV camera, and then performing image processing. Then, a method of determining the effective portion of the optical fiber preform, in which the distribution of the core-clad diameter ratio in the longitudinal direction of the starting preform is obtained, and only the portion where the core-clad diameter ratio is within a specified value is the effective portion.