JPS6366435A - Structure measuring apparatus - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention, for example, measures the difference between the core center position and the craft center position of a quartz-based optical fiber base material, that is, the eccentricity, by observing the base material from the side. The present invention relates to a structure measuring device for measuring structures.

<Conventional technology and problems> Measuring the eccentricity of an optical fiber with high accuracy requires
This is particularly important for single mode optical fibers with small core diameters from the viewpoint of reducing splice loss.

A conventional method for measuring the amount of eccentricity of an optical fiber is to cut the end face of the optical fiber into a mirror surface and observe the cut surface using a microscope, ITV, or the like. However, the standard outer diameter of the optical fiber is 125/+
1, a measurement accuracy of about 0.1μ or less is required to measure the amount of eccentricity in consideration of the effect on splice loss. Because the value is small compared to the wavelength range (using wavelengths in the range), it has been extremely difficult to perform measurements that satisfy the required accuracy.

Incidentally, silica-based optical fibers are usually obtained by high-temperature fusion drawing of a base material called a preform, which has a structure similar to that of optical fibers. It is considered possible to estimate the structural parameters of optical fibers. Conventionally, the method of measuring base metals is to irradiate measurement light from the side of the base material, find the refraction angle of the light beam caused by changes in the refractive index distribution of the core part, and estimate the refractive index distribution of the core part from this. However, it has not been necessary to accurately measure the difference (eccentricity) between the core center position and the clad center position.

The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a structure measuring device that can measure the eccentricity of an optical fiber base material with high precision.

<Means for Solving the Problems> The structure measuring device of the present invention surrounds a cylindrical transparent body with a cylindrical transparent body having a higher refractive index than that of the cylindrical transparent body; In an apparatus for measuring the structure of a cylindrical object formed by integrating the cylindrical transparent body,
a point light source that illuminates the object from the side; and a boundary of the object in an observation plane that is arranged on the opposite side of the object to the point light source and is closer to the center of the object and perpendicular to the optical axis. an imaging optical system that captures a partial image containing information; a subject holding stage that moves the subject in a direction perpendicular to both the longitudinal direction and the optical axis; and boundary information of the imaging optical system and the subject. The present invention is characterized by comprising a data processing device that determines the eccentricity of the subject by determining the relative position of each boundary from the movement amount information record of the specimen holding stage.

<Embodiment> A structure measuring device according to an embodiment of the present invention will be described with reference to FIG. 1 showing its overall configuration.

As shown in the figure, the object whose eccentricity is measured by this device is a cylindrical optical fiber base material 1 called a preform, and this base material 1 is a cylindrical transparent body whose refractive index is higher than that of a cylindrical transparent body 2. 3 is surrounded by the cylindrical transparent body 2, and these transparent bodies 2 and 3 are integrated.

This base material 1 is placed and held on a V block of a subject holding stage 4, and when the motor 5 is operated to move the stage 4 in the direction of arrow a in the figure, the base material 1 also moves in the same direction. A point light source 6 is disposed on one side of the base material 1, and an image sensor 8 equipped with an imaging lens 7 is disposed on the other side of the base material 1. It is located perpendicularly on the optical axis from to the imaging lens 7. Therefore, by moving the stage 4, the base material 1 can be moved in a direction perpendicular to both the longitudinal direction and the optical axis direction.

The magnification of the imaging lens 7 is set so as to observe a part of the base material 1, for example, the outer edge of the cylindrical transparent body (cladding) 2, the cylindrical transparent body (cladding) 2 and the cylindrical transparent body. A partial image of the base material 1, such as the boundary between the base material 1 and the core 3, is captured by the image sensor 8.

Therefore, for example, the boundary line 2a of the outer edge of the cladding 2 is observed on a monitor television 10 connected to the image sensor 8 as shown in the figure, and the scanning b'A obtained as the stage 4 moves.
The luminance data along line 10a is sent to the CPUI 2, which is a data processing device, via the controller 11. Note that the observation plane is a plane perpendicular to the optical axis, but by adjusting the focus of the imaging lens 7, this observation plane becomes a plane P′ closer to the imaging lens 7 than the plane P passing through the center of the base material 1. is set to . This is because when considering the refraction of light rays at the interface between the core 3 and the cladding 2, this interface is more clearly identified at the plane P' than at the plane P.

Further, a scale 14 is attached to the stage 4, and the amount of movement (position) of the stage 4 is read by the scale 14 and sent to the CPU 12 via a display 15.

Therefore, by determining the absolute scale on the monitor television 1θ in advance, the position data of the boundary can be determined from the position data of the stage 4 and the brightness data from the monitor television 10. That is, these position data and brightness data are processed by the CPTJ 12, and the position coordinates of the outer edge boundaries P'+ and P'a of the cladding 2 on the plane P' are determined as Z.
',.

Z'4. The interface P'' between core 3 and craft 2.

If the position coordinates of P'3 are Z't and Z'x, respectively, then the center Z3. Center of cladding 2 Z&+z'
t+z's Eccentricity ΔZ is each 2. = .

Z'++Z'a Z&=, Δ2=2. -2. It is determined by Furthermore, the base material 1 is rotated around the axis by a predetermined angle step Δθ by a rotation mechanism (not shown) to obtain ΔZ(ixΔθ
) (here i=1.2...) and fitting this to the sine wave curve 1A sin (iXΔθ+ψ), the eccentricity amount is found from the amplitude A.

In addition, in order to obtain the true eccentricity λ from the observed eccentricity A, it is necessary to correct the lens effect at the outer edge of the cladding 2, and proximally λ is λ=A/n (n: refractive index). Obtainable.

In the above observation, since the point light source 6 is used as the light source, the angle of the light ray passing through each point on the observation surface in the base material 1 is almost uniquely determined, and the observation surface of the imaging lens 7 is connected to the plane P' Even so, the outline of the outer edge of the craft 2 on the plane P can be clearly observed. On the other hand, when a diffusive light source is used as the light source, when the observation surface of the imaging lens 7 is set to the plane P', the plane P is out of the focusing range of the imaging lens 7, making it difficult to clearly observe the outer edge of the cladding 2. Furthermore, when the observation plane is set to plane P, the interface between the core 3 and the crund 2 cannot be observed as a clear dark line, and in any case, the accuracy of boundary recognition decreases.

Although it is possible to observe the image by capturing the entire image of the object into the image sensor 8, it is possible to observe a partial image of the object in consideration of the resolution limitations of the image sensor 8. Measurement accuracy has been achieved.

Furthermore, since the eccentricity is measured by rotating the base material l around the axis and each measured eccentricity is fitted to a sinusoidal curve, even more accurate measurement is achieved. Furthermore, by adding the function of moving the base material 1 in the axial direction in addition to the function of rotating the base material 1 around its axis, it is possible to measure the amount of eccentricity of the base material 1 and the distribution of the eccentric direction in the longitudinal direction. be able to.

(Specific Example) Using an LED as a point light source, the eccentricity ΔZ of a single mode optical fiber preform with an outer diameter of φ20 m was measured, and the results shown in FIG. 2 were obtained. An imaging lens with a magnification of 4 times was used, and a linear scale with a resolution of 0.1/* was used to read the position of the subject holding stage. When measurements were performed 10 times on the same cross section of the base material, the standard deviation of the measured value of eccentricity was 1.2μ, which was approximately 0.
．． It was found that the eccentricity can be measured with an accuracy of 0.1%.

It should be noted that the present invention is not limited to the above embodiments, but can be modified in various ways, and can also be applied to structural measurements of objects other than base materials.

:Effects of the Invention> According to the present invention, the amount of eccentricity of a subject can be measured non-destructively with extremely high precision. Furthermore, since the amount of eccentricity can be measured at the optical fiber base material stage, its quality can be inspected in an intermediate process, providing a great advantage in optical fiber manufacturing.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a structure measuring device according to an embodiment of the present invention, and FIG. 2 is a graph showing experimental results. In the drawing, 1 is a base material (subject), 2 is a cylindrical transparent body (cladding), 3 is a cylindrical transparent body (core), 4 is a subject holding stage, 6 is a point light source, 8 is an image sensor, 12 is CPU <data processing device).

Claims (2)

[Claims] (1) A cylindrical transparent body surrounded by a cylindrical transparent body with a cylindrical transparent body having a higher refractive index than that of the cylindrical transparent body, and configured by integrating the cylindrical transparent body and the cylindrical transparent body. In an apparatus for measuring the structure of a subject, there is provided a point light source that illuminates the subject from the side; an imaging optical system that captures a partial image containing boundary information of the subject in orthogonal observation planes; a subject holding stage that moves the subject in a direction perpendicular to both the longitudinal direction and the optical axis direction; A structure measuring device comprising: a data processing device that determines the eccentricity of the object by determining the relative position of each boundary from boundary information of the imaging optical system and movement amount information of the object holding stage. (2) Claim 1, characterized in that the data processing device fits the eccentricity sequentially obtained when the subject is rotated around an axis to a sine wave curve, and calculates the eccentricity from the amplitude thereof. Structure measuring device as described.