JPH02248835A - Measurement of eccentricity of core for optical fiber base material - Google Patents

Abstract

PURPOSE:To achieve a quicker feedback to a production process with a higher measuring accuracy by measuring an angle of refraction distribution from three directions at the right angle to a center axis of an optical fiber base material to calculate eccentricity from a distance between centers of a core section and a clad section and an angle therebetween. CONSTITUTION:An optical fiber base material 1 is rotated with a center axis of a clad section 3 as center axis of rotation to measure a distribution of angle of refraction from three directions at the right angle to the axis. Then, a distance between centers of a core section 2 and the clad section 3 is determined in three directions. Then, an approximation is made to a sine curve by data at three points indicated by the angle and the distance in the three directions to calculate an amplitude of the curve thereby enabling the determination of eccentricity of the core section 2 with respect to the center axis of the clad section 3. This enables measurement of eccentricity at the stage of the optical fiber base material thereby achieving a higher measuring accuracy while allowing a quicker feedback to a production process.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for measuring the eccentricity of an optical fiber core at the stage of an optical fiber preform that has been sintered and made into transparent glass.

[Conventional technology]

Conventionally, the amount of eccentricity of the core of an optical fiber is usually measured by observing the end face of an optical fiber produced by drawing and spinning an optical fiber preform. That is, the amount of deviation between the center of the core and the center of the cladding at the end face of the optical fiber is measured, and this amount of deviation is taken as the amount of core eccentricity.

[Problem to be solved by the invention]

However, the conventional core eccentricity measurement method lacks measurement accuracy because it measures the optical fiber in its strand state, and the feedback to the optical fiber preform manufacturing process is also slow. That is, in order to observe the end face of an optical fiber having a diameter of 125 μm, various restrictions are imposed, such as the need for a high-precision measuring instrument, and it is difficult to obtain high measurement accuracy. Furthermore, most of the causes of eccentricity in the core of optical fibers are due to the manufacturing process of the optical fiber base material, but measuring it at the optical fiber stage requires drawing the optical fiber base material and forming it into a raw optical fiber. Since the measurement must be carried out after the measurement, feedback to the optical fiber preform manufacturing process will be delayed. The present invention aims to provide a method for measuring the amount of core eccentricity of an optical fiber preform, which can easily measure the amount of core eccentricity with high accuracy, and can also speed up feedback to the optical fiber preform manufacturing process. purpose.

[Means to solve the problem]

In order to achieve the above object, in the method for measuring the core eccentricity of an optical fiber preform according to the present invention, first, the refraction angle of the preform is measured from three different directions on a plane substantially perpendicular to the central axis of the optical fiber preform. The distribution is measured, and then the distance between the center point of the core and the center of the cladding is determined from the refraction angle distribution in these three directions.Furthermore, a sine curve is calculated from the angle and distance in these three directions. It is characterized by approximating and calculating the amplitude of the sine curve.

[For production]

When an optical fiber base material is rotated around its central axis and observed from a certain direction on the side, if the core is eccentric, the center point of this core will be a sine curve with respect to the rotation angle. draw The amplitude of this sine curve corresponds to the amount of eccentricity of the core portion. Since the optical fiber is obtained by drawing the optical fiber preform, the cross-sectional shape of the optical fiber preform can be considered to be similar to the cross-sectional shape of the optical fiber. Therefore,
The amount of eccentricity of the core portion determined at the optical fiber preform stage can be said to be the amount of eccentricity of the core of the optical fiber. Therefore, the distribution of the refraction angle is measured from the side of the optical fiber preform, that is, from one suitable direction on a plane substantially perpendicular to the central axis of the optical fiber preform. From this distribution of refraction angles, the center point of the core portion and the center point of the cladding portion can be determined, and the distance therebetween can be determined. Set this distance to two points on the above plane that are different from the above direction.
Determine from the direction. Then, the points represented by the angles and distances in these three directions will be on the sine curve, so these three
A sine curve can be approximated from the direction angle and distance. If the sine curve is found in this way,
As described above, the amount of eccentricity of the core portion can be determined from the amplitude.

【Example】

Next, an embodiment of the present invention will be described with reference to the drawings. First, using a measuring instrument such as a preform analyzer to examine the optical properties of the optical fiber preform, measure one suitable point on the side of the optical fiber preform, that is, on a plane approximately perpendicular to the central axis of the optical fiber preform. Measure the refraction angle distribution from the direction. Then, this refraction angle distribution becomes as shown in FIG. 3B, which corresponds to the cross-sectional shape of the optical fiber preform 1 shown in FIG. 3A. That is, points P and 8 on the refraction angle distribution correspond to the vicinity of the edge of the cladding portion 3, and points Q and R correspond to the boundary between the core portion 2 and the cladding portion, respectively. Then, the middle point of this P, 8 points is the center point of the cladding part 3,
Since the midpoint between points Q and R becomes the center point of the core portion 2, the respective center points of the core portion 2 and the cladding portion 3 can be determined from these midpoints. If each center point is found in this way, the distance between them can also be found. Such a refraction angle distribution can be obtained by rotating the optical core base material 1 about the central axis of the cladding part 3, in three directions on a plane substantially perpendicular to the central axis of the cladding part 3, in this embodiment. Measurements are taken from the O', 90°, and 180° directions. As a result, FIG. 1A. As shown in B and C, the distances La, Lb, and LC between the center point of the core portion 2 and the center point of the cladding portion 3 in three directions are determined. Next, a sine curve is approximated as shown in FIG. 2 using data at three points represented by the distances La, Lb, and Lc and the angles at which they were obtained. Once the sine curve has been approximated in this way, the amplitude Lm of the sine curve is calculated. Then, this amplitude Lm corresponds to the amount of eccentricity of the central axis of the core section 2 with respect to the central axis of the cladding section 3. Furthermore, if the distances between the center point of the core portion 2 and the center point of the cladding portion 3 at three different angles are determined, one sine curve can be approximated as shown in Figure 2. , the directions for calculating the refraction angle distribution are 0° and 9 as described above.
It is not limited to 0° to 180° and can be arbitrarily selected.

【Effect of the invention】

According to the method for measuring the amount of core eccentricity of an optical fiber preform of the present invention, it is possible to measure the amount of core eccentricity at the stage of a large optical fiber preform, so it is easy to improve the measurement accuracy. Furthermore, since measurement can be performed at the optical fiber preform stage, feedback to the optical fiber preform manufacturing process can be made faster, and non-defective products can be selected at the preform stage.

[Brief explanation of drawings]

Figure 1 A, B, C1 Figure 2, Figure 3 A, B all relate to one embodiment of the present invention, Figure 1 A, B, C shows the three lateral directions of the optical fiber preform. Figure 2 is a diagram showing the approximated sine curve, and Figures 3A and B are the cross-sections of the optical fiber base material and the corresponding refraction angle distribution. FIG. DESCRIPTION OF SYMBOLS 1... Optical fiber base material, 2... Core part, 3... Clad part.

Claims (1)

[Claims] (1) Measure the refraction angle distribution of the optical fiber base material from three different directions on a plane substantially perpendicular to the central axis of the optical fiber base material, and then measure the refraction angle distribution of the optical fiber base material from each of the three directions at the center of the core. and the center point of the cladding part, and further approximates a sine curve from the angles and distances in these three directions, and calculates the amplitude of the sine curve. Eccentricity measurement method.