JPH0797064B2 - Optical fiber structure measurement method - Google Patents

Description

The present invention relates to an optical fiber structure measuring method, and more particularly to an optical fiber structure measuring method for measuring an internal structure of an optical fiber without cutting the optical fiber to be measured. is there.

[Prior Art] Conventionally, as a method for measuring the internal structure of an optical fiber,
A technique is used in which the optical fiber to be measured is cut and the cut cross section is observed through a microscope or a television camera to perform measurement.

[Problems to be solved by the invention]

The conventional measuring method has the following problems.

First, in the conventional cutting method, the optical fiber to be measured is always cut and the structural parameter at the cut surface is observed, so that the optical fiber to be measured is always destroyed.

Second, since the conventional method can observe the cross section of the optical fiber only at the cut surface, it is impossible to continuously measure the structural parameters along the optical axis direction of the optical fiber.
Therefore, it is difficult to measure a local variation of the structural parameter that occurs in a part of the optical fiber, and the entire length of the optical fiber cannot be accurately measured.

Thirdly, cutting the optical fiber requires a high degree of precision, but even with this, the measurement accuracy decreases due to scratches and chips on the optical fiber that occur during cutting, and the inclination of the cut surface. It is difficult to measure accurately.

[Means for solving problems]

The present invention solves the conventional problems and provides a method for easily and accurately measuring the structural parameters of an optical fiber. Therefore, an imaging system including a light source, an imaging lens combined with an image processing function, and a television camera is provided. Is placed at a position where the optical axis connecting the light source and the imaging system is orthogonal to the longitudinal direction of the fiber under test and passes through the center of the fiber under test, and the fiber under test is rotated about the axis of the fiber. , Or the optical axis connecting the light source and the imaging system passes through the measurement point on the fiber under test, and is rotated so as to be orthogonal to the axis of the fiber under test, and at least two or more rotation angles when rotated. The relative position of the outer edge of the cladding and the boundary between the core and cladding of the fiber to be inspected is recognized, and the lens effect on the surface of the fiber to be inspected is corrected based on the position information of the observation surface. Determining the true position of the boundary portion, the eccentricity amount, the cladding diameter and the core diameter at the above two or more measurement angles are calculated. The eccentricity amount, the cladding diameter, the core diameter, and the cladding non-circularity that define the structural parameters of the fiber to be inspected are characterized by the addition of the chemical treatment.

[Work]

In the optical fiber structure measuring method according to the present invention, since the fiber to be inspected is observed from the side surface of the fiber, it is not necessary to cut the fiber to be inspected, and the state of the fiber cut end surface does not affect the measured value. Therefore, the structure of the optical fiber can be measured nondestructively with high accuracy and easily.

In addition, it is possible to know the changes in the cladding diameter, core diameter, and eccentricity in the circumferential direction of the test fiber by observing by rotating the test fiber or the light source and the imaging system, and processing these data. By doing so, the true cladding diameter, core diameter, eccentricity, and cladding non-circularity of the fiber to be tested can be accurately measured. In particular, regarding the amount of eccentricity, only the true eccentricity component is extracted from the measured amount of eccentricity at each rotation angle by a method of fitting a sine wave function, so that it is difficult to receive an electrical or mechanical measurement error factor.

For example, if the magnification of the imaging system is different in the vertical direction,
As shown in FIG. 2A, in the conventional measuring method, the measured eccentricity is subject to the distortion of the magnification of the image pickup system, so that the distortion is not affected by the above distortion even for the test fiber having no eccentricity. The corresponding quantity ε is measured as the amount of eccentricity. 20 in Figure 2a
Is a clad, 1 is a core, 22 is a true core, a true clad,
The center of each measured core, 23 is the measured cladding center. In the optical fiber structure measuring method according to the present invention, the eccentricity of the test fiber is obtained based on the change of the eccentricity measurement amount in the circumferential direction of the test fiber, and thus is less likely to be affected by the strain. 2B and 2C show the influence of distortion of the magnification of the imaging system at the observation angles of 0 ° and 180 ° according to the present invention as an example of measuring a test fiber without eccentricity. In the measuring method according to the present invention, since the measured eccentricity amount does not change even if the observation angle is changed, the eccentricity amount of the test fiber is determined to be zero. Even when measuring a test fiber without eccentricity, even if there is distortion in the magnification of the imaging system, there is no effect on the change in the eccentricity of the test fiber in the circumferential direction, and the sine wave function fitting , The amplitude becomes zero, and the eccentricity of the fiber under test is measured as zero. Embodiments will be described below with reference to the drawings.

〔Example〕

FIG. 1 is a schematic diagram of the configuration of an embodiment of an optical fiber structure measuring apparatus using the optical fiber structure measuring method of the present invention. Reference numeral 1 is a light source, 3 is a fiber to be inspected, 4 is an imaging lens, 5 is a television camera (abbreviated as TV camera), 6 is a fiber stage with a rotation mechanism for rotating the fiber 3 to be inspected around the axis of the fiber, 2 Is an optical axis connecting the light source 1, the fiber 3 to be inspected, the imaging lens 4 and the TV camera 5, and the optical axis 2 is arranged at a position orthogonal to the axis of the fiber 3 to be inspected. Reference numeral 7 is an image processing apparatus, 8 is a TV monitor, 9 is a host CPU, and 10 is a printer.

FIG. 3 is an example of a monitor image when a single mode optical fiber is observed from the side surface using the optical fiber structure measuring apparatus shown in FIG. Reference numeral 11 indicates the cladding portion of the fiber to be inspected, and 12 indicates the core portion.

FIG. 4 shows the luminance distribution on the straight line (1) of the monitor image shown in FIG. The apparent structural parameters, that is, the cladding diameter, the core diameter, and the eccentricity amount when the fiber to be inspected is viewed from a certain rotation angle are obtained by processing the data of the luminance distribution shown in FIG. In FIG. 4, the positions P ₁ and P ₂ of the outer edge of the cladding are obtained by using the defined slice level, and the position of the center of the cladding is determined.
M ₁ is found as the midpoint between P ₁ and P ₂ . The positions Q ₁ and Q ₂ of the core / clad boundary portion and the position M _{2 of the} core center are obtained by processing the brightness data between R ₁ and R ₂ of the brightness distribution characteristic. The positions Q ₁ and Q ₂ of the core-clad boundary and the position M ₂ of the center of the core are set to the position of the observation surface, that is, the relative position between the focus of the imaging system and the fiber to be inspected due to the lens effect of the fiber to be inspected. It changes, but this is the contrast ratio By adding a correction based on the value of, the true core-clad boundary position is converted into a true core-clad position ▲ Q ^* ₁ ▼ ▲ Q ^* ₂ ▼ and a true core center position ▲ M ^* ₂ ▼. At this time, the cladding diameter, core diameter, and eccentricity at the observation angle are Is represented by.

When the optical axis connecting the light source and the image pickup system is not orthogonal to the axis of the fiber to be inspected, for example, as shown in FIG.
When the position of changes from A to B, the fiber under test 14
Through the objective lens 15, the pattern of the luminance distribution observed by the television camera 16 changes as shown in FIG. In the luminance distribution of FIG. 6, I _A is the light source 13 of FIG.
Is the luminance distribution when there is no light source deviation at the position of A, and I _B
Is a luminance distribution when the light source 13 is displaced at the position B. The structural parameter obtained from this luminance distribution is added with the influence of the positional deviation of the light source, but in the optical fiber structure measuring device according to the present invention, the optical axis connecting the light source and the imaging system is the fiber to be inspected. Since it is orthogonal to the axis, it is not affected by the light source shift.

7 to 9 show the results of measuring the cladding diameter, core diameter and eccentricity of the single mode optical fiber by using the measuring apparatus of FIG. 1 while rotating the fiber to be tested by 30 degrees.

FIG. 7 shows the measurement result of the cladding diameter D. The average of the measured values of the cladding diameter at each observation angle is the cladding diameter of the test fiber. Also, the value obtained by dividing the difference between the maximum and minimum values of the cladding diameter at each observation angle by the average cladding diameter, that is, δ / D × 100, is the cladding non-circularity.

FIG. 8 shows the measurement result of the core diameter d. The average of the measured values of the core diameter at each observation angle is the core diameter of the fiber under test.

FIG. 9 shows the measurement results of the amount of eccentricity. The solid line shows the result of fitting the sine wave function to the measured value of the eccentricity amount at each observation angle. Amplitude A of this sine wave function
Is the amount of eccentricity of the fiber to be inspected, and the initial phase is the direction angle θ of the eccentricity of the fiber to be inspected.

The following table shows the results of comparison between the reproducibility of measured values measured using the measuring device of FIG. 1 and the reproducibility of measured values by the conventional measuring method. Here, the measured value reproducibility is a value indicated by the standard deviation at 20 repetitions. As can be seen from the following table, according to the present invention, the standard deviation of the measured values when the repeated measurement is performed is higher than that of the conventional method for all the items of the cladding diameter, the core diameter, the core / clad eccentricity, and the cladding non-circularity. Small, reliable measurements are made.

[Effects of the Invention] As described above, in the optical fiber structure measuring method according to the present invention, there are two reasons described below: firstly, the side surface is used instead of the cut surface of the optical fiber. Since the measurement is performed, it is not necessary to cut the fiber to be inspected, and the measurement error due to the irregularity and the inclination of the cut surface of the fiber to be inspected does not occur.

Second, the structure of the fiber to be inspected is measured by rotating the fiber to be inspected or the light source and the imaging system, and averaging and fitting the sine wave function to the measured values obtained at each observation angle. Since it is a method of obtaining parameters, data with excellent reproducibility can be obtained.

For this reason, it is possible to measure the internal structure of the optical fiber in a nondestructive, highly accurate and simple manner, and the effect is great.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an optical fiber structure measuring device used for performing the measuring method of the present invention, and FIGS. 2a to 2c are distortions of magnification of an image pickup system when measuring a fiber without eccentricity. FIG. 2A is a diagram for explaining the influence of
Figures b and c show the observation results by the measuring method of the present invention at the observation angles of 0 ° and 180 °, respectively, and Figure 3 shows the monitor images when the single mode optical fiber is observed using the measuring device of Figure 1. , FIG. 4 shows the line a of the monitor image of FIG.
-A 'on the luminance distribution, FIG. 5 is a diagram for explaining the displacement of the light source, FIG. 6 is a diagram showing a change in the pattern of the luminance distribution due to the displacement of the light source in FIG. 5, FIGS. The figures are the results of measuring the cladding diameter, core diameter and eccentricity of the single mode optical fiber by using the measuring device of FIG. 1, respectively. 1 ... Light source, 2 ... Optical axis, 3 ... Fiber to be inspected, 4 ...
Imaging lens, 5 ... TV camera, 6 ... Fiber stage with rotation mechanism, 7 ... Image processing device, 8 ... TV monitor, 9 ... Host CPU, 10 ... Printer, 11 ...
… Clad part, 12 …… Core part, 13 …… Light source, 14 …… Fiber to be tested, 15 …… Objective lens, 16 …… TV camera, 20
…… Clad, 21 …… Core, 22 …… True core center, true cladding center and measured core center, 23 …… Measured cladding center

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-60-85350 (JP, A) JP-A-58-213225 (JP, A) JP-A-53-11082 (JP, A)

Claims (1)

[Claims] 1. A method for measuring an internal structure of an optical fiber, wherein a light source and an image pickup system including an image pickup lens and a television camera combined with an image processing function are provided, and an optical axis connecting the light source and the image pickup system is a fiber to be inspected. Is arranged at a position orthogonal to the longitudinal direction of the fiber and passing through the center of the fiber to be inspected, and the fiber to be inspected is rotated around the axis of the fiber, or the optical axis connecting the light source and the image pickup system is located in the object to be inspected. It passes through the measurement point on the inspection fiber and is rotated so as to be orthogonal to the axis of the inspection fiber, and the outer edge portion of the cladding and the core of the inspection fiber at at least two or more rotation angles when the rotation is performed. The relative position of the cladding boundary is recognized, the lens effect of the fiber surface under test is corrected based on the position information of the observation surface, and the true position of the core-clad boundary at the observed angle is obtained. By determining the eccentricity amount, the cladding diameter and the core diameter at the two or more measurement angles, by fitting the sine wave function for the eccentricity amount and adding the averaging process for the cladding diameter and the core diameter, The amount of eccentricity that defines the structural parameters of the test fiber
An optical fiber structure measuring method characterized by finding the cladding diameter, core diameter and cladding non-circularity.