JP2008039536A - Method for measuring cladding outer diameter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for measuring a cladding outer diameter capable of carrying out a user-friendly operation of precise focusing with high repeatability and realizing a precise measurement by which the measurement error of the cladding outer diameter is suppressed to 0.12 μm or less. <P>SOLUTION: A photographing apparatus 11 is provided with a photographing position adjusting means 21 for axially moving an optical fiber 13 to be photographed, and a focus compensating process of fine adjusting a distance between an objective lens 2a and an edge 13a of the optical fiber 13 is previously carried out by the photographing position adjusting means 21, such that a linewidth w2 of a profile line f1 in a focus compensation-use edge image which is photographed at a prescribed photographing position becomes a prescribed specification value or less, and then a regular operation of photographing the edge 13a is carried out to calculate the cladding outer diameter. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cladding outer diameter measuring method for photographing an end face of an optical fiber and analyzing the image to calculate the cladding outer diameter of the optical fiber.

In the produced optical fiber, structural parameters such as cladding outer diameter, cladding non-circularity, and core eccentricity are measured, and the measured structural parameters are used for quality control or product management.
As a method for measuring such a structural parameter, a so-called video analyzer method is known.
In this measurement method, the end face of the optical fiber to be measured is photographed, and the image is analyzed to calculate the outer diameter of the clad of the optical fiber.

FIG. 4 shows an example of the configuration of a photographing apparatus that photographs the end face of an optical fiber.
The photographing apparatus 1 photographs an end face of an optical fiber that is a subject through a sapphire glass 4 disposed in front of the objective lens 2a of the CCD camera 2 on the optical axis. Around the sapphire glass 4 is mounted an LED light source 6 that irradiates the end face of the optical fiber.

  In the CCD camera 2, the objective lens 2a is supported by the tilt adjustment mechanism 2b so that the aspect ratio can be adjusted, and the camera body 2c incorporating the CCD image pickup device and the control circuit and the tilt adjustment mechanism 2b are shielded from light. They are connected by a cylinder 2d.

  Up to now, focusing in the photographing apparatus 1 as described above is performed automatically by setting a calibration plate 7 having a lattice on the surface at a predetermined photographing position H so that the lattice on the calibration plate 7 can be clearly seen. This was done by performing focus or manual focus.

  By the way, with the rapid spread of optical fiber networks in recent years, the quality specifications of optical fibers required from customers to manufacturers have been improved year by year. The required value of the outer diameter of the cladding is becoming stricter, and even if an optical fiber that actually meets the requirements is manufactured, sufficient measurements are not performed at the measurement stage, even if it is a good product and a defective product. Are treated as In terms of measurement reproducibility (variation), there is a limit to cladding outer diameter measurement. If the measurement is repeated many times, it converges to the original value. However, this increases the measurement workload and increases the cost of the fiber. On the other hand, if the number of measurements is not increased, even if the optical fiber originally meets the requirements, the measurement result will be nonconforming. Such a measurement result is expected to increase more and more as the required value becomes more severe in the future.

When the present inventors actually investigated the reproducibility of the measuring device, the measuring device is generally set to prevent reproducibility even though it has the performance to improve the reproducibility. There was found. However, the measuring instrument is a precision instrument in which the main body of the photographing apparatus is made into a black box, and the measuring instrument user cannot freely modify it from the viewpoint of guaranteeing measurement accuracy.
Note that in this reproducibility study, the distance between the end face of the optical fiber and the objective lens so that the width of the contour line of the captured image of the optical fiber is not more than a predetermined specified value as a matter other than the black boxed portion. As a result of investigating the effects of measurement errors, it was found that the clad diameter, clad noncircularity, and core eccentricity had a significant effect only on the clad diameter. Therefore, in the present invention described below, adjustment is performed so that the measurement error in the cladding diameter is equal to or less than a predetermined specified value.
Moreover, the most strict requirement value of recent users is 125 ± 0.2 μm for a standard optical fiber having a cladding diameter of 125 μm. In order to guarantee this, it is necessary that the accuracy is 1/3 to 1/4 of the tolerance of 0.006 μm or less. Therefore, in order to achieve a reproducibility of 0.006 μm or less at 3σ, the measurement error σ needs to be 1/3 of 0.002 μm or less.

  The purpose of the present invention is to achieve highly accurate and highly reproducible focusing without modifying the black box part of the main body of the photographing apparatus, and with high accuracy with a clad diameter measurement error suppressed to 0.002 μm or less. It is to provide a cladding outer diameter measuring method capable of realizing a proper measurement.

In order to achieve the above object, a cladding outer diameter measuring method according to claim 1 according to the present invention photographs an end face of an optical fiber through an objective lens of a photographing apparatus, analyzes the image, and analyzes the image of the optical fiber. A cladding outer diameter measuring method for calculating a cladding outer diameter,
The photographing apparatus includes photographing position adjusting means for adjusting a distance between the objective lens and an end face of the optical fiber by moving the optical fiber from a predetermined position in an axial direction thereof,
At the time of photographing, the end face of the optical fiber is photographed at the predetermined position, and the photographing position adjusting means adjusts the optical fiber so that the width of the contour line of the optical fiber end face in the photographed end face image is equal to or less than a predetermined specified value. A fine adjustment step of finely adjusting the distance between the end surface and the objective lens;
A cladding outer diameter calculating step of calculating a cladding outer diameter from the image of the end face of the optical fiber after fine adjustment.

  In order to achieve the above object, the cladding outer diameter measuring method according to claim 2 according to the present invention is characterized in that, in the cladding outer diameter measuring method according to claim 1, the specified value is 0.12 μm. And

  According to the cladding outer diameter measuring method of the present invention, it is possible to focus with high reproducibility and high accuracy without performing modification of the black box portion of the photographing apparatus body by performing the focus correction process. As a result, it is possible to perform highly accurate measurement with the clad diameter measurement error calculated by analyzing the captured image being suppressed to 0.002 μm or less.

Hereinafter, preferred embodiments of a cladding outer diameter measuring method according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a photographing apparatus main body which is a main part of one embodiment of a measuring apparatus for measuring an optical fiber by a cladding outer diameter measuring method according to the present invention.

  The imaging device 11 shown in FIG. 1 images the end face 13a of the optical fiber 13 that is a subject through a sapphire glass 4 arranged on the optical axis front of the objective lens 2a of the CCD camera 2. Around the sapphire glass 4, an LED light source 6 that irradiates the end face 13a of the optical fiber 13 is mounted.

  In the CCD camera 2, the objective lens 2a is supported by the tilt adjustment mechanism 2b so that the aspect ratio can be adjusted, and the camera body 2c incorporating the CCD image pickup device and the control circuit and the tilt adjustment mechanism 2b are shielded from light. They are connected by a cylinder 2d.

The basic configuration of the photographing apparatus 11 is the same as that of the conventional photographing apparatus 1 shown in FIG.
However, in the case of the photographing apparatus 11 according to the embodiment shown in FIG. 1, a focus correction unit 15 that realizes focusing independently is additionally provided in addition to the autofocus function and the manual focus function of the photographing apparatus 11. .
The focus correction means 15 moves the optical fiber 13 to be photographed from the photographing position H at a fixed position in front of the objective lens 2a in the axial direction of the fiber (in the direction indicated by the arrow A in the drawing), and the objective lens 2a and the light. A photographing position adjusting unit 21 that adjusts the distance between the end face 13a of the fiber 13 and a video processing / control unit 23 that controls the operation of the photographing position adjusting unit 21 based on a video photographed by the camera body 2c are provided. ing.

In the case of the present embodiment, the imaging position adjusting means 21 advances and retracts the optical fiber 13 in the direction of arrow A by rotating and driving a pair of rollers 21a and 21b that sandwich the optical fiber 13 by a rotation driving means (not shown). Let me.
The photographing position adjusting means 21 finely adjusts the position of the end face 13a of the optical fiber 13 by controlling the rotation amount of the rollers 21a and 21b.

The image processing / control unit 23 acquires an image of the end face 13a of the optical fiber 13 taken by the camera body 2c for focus correction (hereinafter referred to as an end face image for focus correction) from the camera body 2c, and performs the focus correction. The distance between the end face 13a of the optical fiber 13 and the objective lens 2a is finely adjusted by the photographing position adjusting means 21 so that the width of the contour line of the optical fiber end face 13a in the end face image is equal to or smaller than a predetermined specified value.
In the case of this embodiment, the specified value is 0.12 μm.
The video processing / control unit 23 includes a display unit (display) 25 that depicts a focus correction end surface image processed by the video processing / control unit 23, and a focus correction end surface image displayed on the display unit 25. An operation input unit 26 is connected to designate a contour line to be corrected and to input a predetermined default value of the width of the contour line to be corrected.

  The measuring device having the photographing device 11 uses a so-called video analyzer method for analyzing an image of the end face 13a of the optical fiber 13 photographed by the CCD camera 2 with an analysis processing device (not shown) connected to the camera body 2c. The clad outer diameter of 13 is calculated.

Next, a method for measuring the outer diameter of the optical fiber clad performed by the measuring apparatus having the photographing apparatus 11 will be described.
In the cladding outer diameter measuring method according to the present embodiment, the focus by the autofocus function provided in the CCD camera 2 is applied to the end face 13a of the optical fiber 13 positioned at the fixed position H before starting the regular measurement process. After performing the alignment, after performing the focus correction process by the focus correction unit 15 to realize the high-precision focus adjustment, the process shifts to a regular measurement process for measuring the clad diameter.

  In the focus correction process by the focus correction unit 15, the video processing / control unit 23 displays an end surface image for focus correction received from the camera body 2c on the display unit 25, and the optical fiber end surface 13a in the end surface image for focus correction is displayed. The distance between the end face 13a of the optical fiber 13 and the objective lens 2a is finely adjusted by the photographing position adjusting means 21 so that the width of the contour line is 0.12 μm or less.

The end face image for focus correction received by the image processing / control unit 23 from the camera body 2c is focused by the autofocus on the end face 13a of the optical fiber 13 that the CCD camera 2 is positioned at a predetermined shooting position H. This is a picture taken in the state.
If the focusing by the autofocus of the CCD camera 2 is poor, as shown in FIG. 2A, the outline f1 of the end face 13a in the end face image for focus correction is drawn with a thick line width w1.
When the above-described focus correction processing is performed on the end face image for focus correction, the focus is corrected by the movement of the optical fiber 13 by the photographing position adjusting unit 21, and as shown in FIG. The line f1 has a line width w2 that is equal to or less than a specified value.
Then, after the focus correction processing is completed in this manner, the image of the end face 13a of the optical fiber 13 is re-captured by the CCD camera 2, and the image is analyzed by an analysis processing device (not shown). Measurement becomes possible.

  In the focus correction processing, for example, the prescribed value of the line width of the contour line f1 is set in advance with reference to the line width of the contour line in the end face image when the CCD camera 2 is manually focused with high accuracy. Keep it.

According to the clad diameter measuring method of the optical fiber 13 of the embodiment described above, it is possible to focus with high reproducibility and high accuracy by performing the focus correction process. High-accuracy measurement with a measurement error of the calculated cladding diameter being suppressed to 0.002 μm or less becomes possible.
In addition, the focus correction process performed by the structural parameter measurement method of the present invention is different from the focus operation in the general photographing apparatus 11, and the end surface of the optical fiber 13 to be measured without moving the objective lens 2 a of the photographing apparatus 11. Since the focus is achieved by moving 13a, compared with the case of focusing with the manual focus of the photographing apparatus 11, focusing is less time-consuming and the operability is better.
Therefore, high-precision focusing with high reproducibility can improve the measurement accuracy of the structural parameters, reduce the effort required for focusing, and improve the measurement efficiency of the cladding diameter.

FIG. 3 is a table (a) and a graph (b) showing the relationship between the measurement error and the width of the contour line regarding the reproducibility 3σ of the cladding outer diameter. In addition, the measurement variation σ indicates the variation when the measurement is continuously performed 10 times.
As can be seen from FIGS. 3 (a) and 3 (b), in sample 1 and sample 2 using standard optical fibers having a cladding diameter of 125 ± 0.2 μm, the measurement error for achieving reproducibility 3σ is 0. In order to make it 002 μm or less, the width of the contour line needs to be 0.12 μm or less.

In the present embodiment, the focus correction process is performed by the focus correction unit 15 that is separate from the CCD camera 2, and the focus mechanism itself of the CCD camera 2 does not require remodeling. However, the cladding outer diameter measuring method of the present invention can be implemented only by adding the focus correction means 15.
In the above-described embodiment, the case where the automatic focusing between the objective lens and the end face of the optical fiber is performed in advance has been described.

It is a schematic block diagram of the principal part of one Embodiment of the measuring apparatus which measures an optical fiber with the cladding outer diameter measuring method which concerns on this invention. FIGS. 2A and 2B are explanatory diagrams of focus correction processing in the measuring apparatus shown in FIG. 1, where FIG. 1A is an image of a contour line in a poor focus state, and FIG. is there. Regarding the reproducibility 3σ of the cladding outer diameter, (a) is a table showing the relationship between the measurement error and the width of the contour line, and (b) is a graph showing the relationship between the measurement error and the width of the contour line. It is explanatory drawing of the mechanism of focusing of the imaging device in the conventional measuring device.

Explanation of symbols

2 CCD camera 2a Objective lens 2b tilt adjustment mechanism 2c camera body 2d light shielding tube 13 optical fiber 13a end face 15 focus correction means 21 photographing position adjustment means 23 video processing / control section 25 display section 26 operation input section

Claims (2)

A cladding outer diameter measuring method for photographing an end face of an optical fiber through an objective lens of a photographing device, and analyzing the image to calculate a cladding outer diameter of the optical fiber,
The photographing apparatus includes photographing position adjusting means for adjusting a distance between the objective lens and an end face of the optical fiber by moving the optical fiber from a predetermined position in an axial direction thereof,
At the time of photographing, the end face of the optical fiber is photographed at the predetermined position, and the photographing position adjusting means adjusts the optical fiber so that the width of the contour line of the optical fiber end face in the photographed end face image is equal to or less than a predetermined specified value. A fine adjustment step of finely adjusting the distance between the end surface and the objective lens;
And a cladding outer diameter calculating step of calculating a cladding outer diameter from the image of the end face of the optical fiber after fine adjustment.   2. The cladding outer diameter measuring method according to claim 1, wherein the specified value is 0.12 [mu] m.

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