JP2000146751A - Method for observing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate the presence or absence and the size of cracks by adjusting the focusing position of an optical system for flattening the brightness distribution of an optical fiber image and obtaining the brightness distribution of an end part for the optical fiber image. SOLUTION: An area value when there are cracks at a level for influencing a connection loss in the end face of an optical fiber is examined in advance. More specifically, a focusing position is kept as it is, an observation position is shifted to the end part of an optical fiber image, a window is set in a range where the crack parts can be fully accommodated, and a brightness distribution as shown in figure (c) is obtained for a plurality of cursors in the window. A, B, and D indicate a portion with lower brightness than a lower-limit threshold, while C indicates a portion with higher brightness than an upper-limit threshold. A and D indicate a portion with a low brightness even without any cracks. Therefore, the number of pixels included in B and C becomes that of pixels in the brightness distribution. By obtaining the total area value of the pixels of cracks in the brightness distribution of all cursors in the window, a connection loss after the fusion connection of a normal optical fiber is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for observing an optical fiber at the time of fusion splicing of an optical fiber.
And a method for observing.

[0002]

2. Description of the Related Art When an optical fiber is fusion spliced, if the state of the end face of the fiber is poor, the splice loss is affected. The following are examples of the judgment items of the end face state. Cutting angle (see Fig. 4) Dirt adhering to the end face (see Fig. 5) Chipping of the end face (see Fig. 6)

[0003] Of these, the cutting angle can be measured by image processing, so that it is easy to determine the quality.

The quality of the dust is determined based on the size and position, but it is difficult to quantify the dust. However, the presence of garbage is easy to visually recognize,
The judgment by the operator is not so difficult.

[0005]

However, the following problems arise with respect to chipping.

Prior to fusion splicing of the optical fiber, alignment and the quality of the core end face are determined. At this time, the focal position of the optical system is usually set to a position suitable for observing the core. . FIGS. 4 to 6 show optical fiber images at that time. The vicinity of the center including the core is bright, and both ends are dark. Regarding the dust having the above-mentioned cutting angle, observation and measurement are easy in this state.

However, the situation is different in the case of the lack. That is, referring to FIG. 6, it can be visually recognized that there is a chip in a bright part of the fiber image, but cannot be visually recognized even if there is a chip in a dark part.

In the above-mentioned fiber image, it is very difficult to quantify the size of the chip by image processing.
The reason is described below. Image processing most commonly utilizes differences in brightness (brightness). In the case of FIG. 6, the chip in the bright part can be recognized by human eyes. However, there is almost no difference in luminance. Also, in the dark part, the difference in luminance is not known (although there may be chipping). For the reasons described above, it is difficult to determine a chip in image processing.

When fusion splicing is performed with a chipped state,
Connection loss worsens, resulting in poor connection.

[0010]

Means for Solving the Problems The present invention according to claim 1 is characterized by the following: When light transmitted through an optical fiber is received by an optical system to obtain an optical fiber image and image processing of the optical fiber image is performed, The focus position of the optical system is adjusted so that the luminance distribution of the optical fiber image becomes substantially flat. The luminance distribution at the end of the optical fiber image is obtained.

In the above description, “the focal position of the optical system is adjusted to make the luminance distribution substantially flat”
As shown in FIG. 1B, the luminance distribution does not have an extreme height, that is, a distribution state in which the difference between the maximum value and the minimum value is small.

On the other hand, the luminance distribution in the case of normal core observation has a remarkably high (bright) portion as shown in FIG. 7 (fiber images are shown in FIGS. 4 to 6).

FIG. 1A shows a fiber image when the brightness distribution is as shown in FIG. 1B. The brightness of the core portion is much lower than that in the normal core observation, and the fiber image is obtained. But dim as a whole.

If a chip is present, the refractive index of the transmitted light in that portion changes, so that the portion looks brighter or darker than the other portions as shown in FIG. You can see. That is, since the brightness of the portion is different, if a brightness distribution is obtained by performing image processing on a portion having a chip (the end of the optical fiber image), a curve as shown in FIG. 1C is obtained, for example. B is a dark part and c is a light part (more on this later). From this, it is possible to estimate the presence or absence of a chip and its size.

The mechanism for adjusting the focal position is usually provided in the optical fiber fusion splicer, so that the mechanism is used to move the focal point only at the time of chipping observation, and to set the other focal points to the normal focal position. Therefore, it is not necessary to add a special mechanism for implementing the present invention.

The focus position can be adjusted while observing the change in the optical fiber image. As described in claim 2, the maximum value and the minimum value in the luminance distribution shown in FIG. If the focal position is adjusted so that the difference between them becomes a certain "predetermined luminance value" or less, the focal position can be automatically adjusted.

The above-mentioned "certain predetermined brightness value" is a value which is determined and set in advance as a value which can be determined to be optimal for discriminating a chip as the fusion device.

Since there may be a chip near the end face, the maximum and minimum values of the internal brightness of the fiber are not stable and cannot be used for adjusting the focal position. Therefore, the above-mentioned adjustment of the focal position utilizes a luminance distribution at a position as far as possible from the end face.

Further, the area of the chip is defined in claim 2,
As shown in FIG. 2, at the end of the optical fiber image 10,
If the sum of the area of the portion having a higher luminance than the upper threshold and the area of the portion having a lower luminance than the lower threshold is obtained, and the sum of the areas is compared with the `` predetermined area value '', the quality of the end face based on the chipping is determined. Automatic identification becomes possible.

The method for determining the area will be described later. The upper threshold value is, for example, the maximum value in FIG. 1B, and the lower threshold value is, for example, the maximum value * 0.2 + the minimum value * 0.8 in FIG. 1B.

The “predetermined area value” is defined as
For optical fibers having various sizes of chips, the sum of the areas is checked in advance by the method described later, and the set value is set to the area value at a level that affects the connection loss.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A case where the quality of a chip is automatically determined will be described. First, [0016] [001]
7] is determined in the following manner. That is, the focus position of the optical fiber observation is moved from the position where the normal axis alignment or the like is performed, so that the optical fiber portion of the core is almost eliminated and the core becomes dim as a whole. Then, a bright portion or a dark portion indicating a chip is made to be most visible, and a luminance distribution at a position slightly away from the end of the optical fiber image is obtained (FIG. 1B). Then, a difference between the maximum value and the minimum value of the luminance at that time is obtained, and this value is set as a “predetermined luminance value” of the device. Further, a lower limit threshold and an upper limit threshold are obtained from the maximum value and the minimum value of the luminance at that time.

Further, the area value (predetermined area value) in the case where the end face of the optical fiber has a lack of a level which affects the connection loss as described in the above [0021] is checked in advance. that is,
Do the following: That is, as shown in FIG. 2, while keeping the focus position as described above, the observation position is moved to the end of the optical fiber image 10, and the window 20 is set within an appropriate range so that the chipped portion can be sufficiently accommodated. Then, a luminance distribution as shown in FIG. 1C is obtained for a plurality (for example, 16) of the cursors 22 therein. A, B, D in FIG. 1 (c)
Is a portion where the luminance is lower than the lower threshold, and C is a portion where the luminance is higher than the upper threshold. A and D are portions where luminance is low even if there is no chipping.

Therefore, the number of pixels included in the portions B and C is the number of missing pixels in the luminance distribution. The total area value of the missing pixels in the luminance distribution of all the cursors 22 in the window 20 is obtained. Then, the area values of the ends of a large number of optical fibers having chips of various sizes are determined, and the splice loss after fusion splicing with a normal optical fiber is measured. Find the area value of
This is defined as a “predetermined area value”.

The setting up to now only needs to be performed once for the fusing machine. The following is the automatic determination of chipping performed each time connection is made (see FIG. 3).

An optical fiber is set in the fusion splicer, and the end face interval is set. At a position away from the end of the optical fiber, the difference between the maximum value and the minimum value of the brightness inside the optical fiber is the above-mentioned "predetermined brightness value".
The focus position is adjusted in such a manner as described below (the position of the missing observation). In addition, an upper threshold and a lower threshold are obtained from the maximum and minimum luminance values at that time.

As described above, the observation position is moved to the end of the fiber while the focal position is kept as it is, and the sum of the area of the part having a luminance lower than the lower limit threshold and the area of the part having the luminance higher than the upper threshold (missing part) is obtained. Area). Then, when compared with the above “predetermined area value”, when it is smaller, “no chipping”
It proceeds to the next fusion operation. When it is big,
Judge as "Missing" and display "Missing"
The fusing operation stops. The operator again draws out the optical fiber and restarts the fusion operation from the beginning.

The above-described observation of the chipping may be performed before or after the alignment as long as the fiber interval is set. But,
If it is determined that there is a chip after the alignment, it is necessary to re-start the operation, and the alignment is useless.

The above method can also be used to determine chipping in a performance test of an optical fiber cutting machine.

[0030]

Since the focus is focused on a position where the chip is easy to see, the dark part of the fiber image which is difficult to understand can be found at the normal focus position. Since it is difficult to overlook the chipping of the end face, the possibility of occurrence of connection failure due to the chipping is extremely low. It is possible to make the fusion splicer quantitatively and automatically determine the presence or absence of the chipping of the optical fiber, and to always determine the quality of the end face based on the same determination criterion without relying on the eyes of the operator. When used for a performance test of an optical fiber cutting machine, the time required for end face observation can be reduced.

[Brief description of the drawings]

1 (a) is a photograph of an optical fiber image when a focus position is adjusted so that a chip is easily seen,
(B) is a luminance distribution of a portion without a chip at that time,
(C) is a luminance distribution of a part with a chip.

FIGS. 2A and 2B are diagrams showing a method for obtaining a chipped area according to the present invention, wherein FIG. 2A is a photograph and FIG.

FIG. 3 is a flowchart of chipping determination according to the present invention.

FIG. 4 is a photograph when a cutting angle is large in a normal optical fiber observation.

FIG. 5 is a photograph of a normal optical fiber observation when there is dust on the end face.

FIG. 6 is a photograph showing a case where an end face is chipped in a normal optical fiber observation.

FIG. 7 is a luminance distribution of an optical fiber image in normal optical fiber observation.

[Explanation of symbols]

 10 Optical fiber image 20 Window 22 Cursor

Claims (2)

[Claims] An optical fiber receives light transmitted through an optical fiber, obtains an image of the optical fiber, and adjusts a focal position of the optical system when processing the image of the optical fiber. A method for observing an optical fiber, wherein the luminance distribution of the image is made substantially flat, and the luminance distribution at the end of the optical fiber image is obtained. 2. The optical fiber according to claim 1, wherein the transmitted light of the optical fiber is received by an optical system to obtain an image of the optical fiber, and when the image of the optical fiber is processed, the focal position of the optical system is adjusted. The difference between the maximum and minimum values of the image brightness is
In order to be equal to or less than a predetermined luminance value, the upper threshold and the lower threshold are obtained from the luminance distribution of the optical fiber image in such a manner, and the area of a part having a higher luminance than the upper threshold and the area of a part having a lower luminance than the lower threshold are obtained. An optical fiber observation method, wherein a sum of the area and a predetermined area value are compared with each other.