JPH0439045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an inspection method for inspecting the axial misalignment of a multi-core optical fiber by observing it from two directions.

<Prior art> When fusion splicing multi-core optical fibers, each core of a pair of multi-core optical fibers to be spliced is tapped out to form a bare optical fiber, and this tapped pair is used to connect multiple fibers. After fitting the bare optical fiber array from the left and right sides into a V-groove block in which V-grooves corresponding to the number of fibers are precisely formed, and checking whether each part is set accurately in the V-groove, Performing fusion splicing.

These confirmation inspections and observations are performed to detect if the optical fiber is not fully fitted into the V-groove, or if the opening is incomplete and there is residue on the optical fiber, or if there is any residue in the V-groove. This is because if foreign objects such as dust come into contact with the connector, axis misalignment will occur, making it impossible to achieve a perfect connection. Such inspections and observations are the most important cause of high connection loss if axis misalignment remains even after connection, so when evaluating the quality of the connection, it is important to has become indispensable.

Conventionally, for such inspection and observation, in the case of a single-core optical fiber, a method of observing the transmitted light image of the optical fiber from one direction or a method of observing from two directions has been considered.

<Problems to be Solved by the Invention> In the case of multicore optical fibers, the conventional observation method described above from one direction can also be applied, but in this method, observation in a direction perpendicular to the illumination optical axis (perpendicular direction) is applicable. Although axis misalignment can be detected with considerable accuracy, it has the disadvantage that the detection error is large for axis misalignment in the same direction as the illumination optical axis, making it difficult to employ.

On the other hand, although high detection accuracy can be obtained with the above two-direction observation method, in the case of multi-core optical fibers, it is natural that the incident light is I can't enter it. Therefore, the two-way illumination light for observation needs to be at a special angle with respect to the bare optical fiber array.

The present invention has been made in view of these circumstances.

<Means for Solving the Problems> The gist of the present invention is basically as follows:
This is a method of inspecting the axis misalignment by observing the transmitted light image of the connecting part of multi-core optical fibers from two directions that intersect with each other. When removing and butt-connecting, or in a method of inspecting a connection after butt-connecting, illumination light is irradiated from two directions that intersect with each other in the vicinity of this butt-connection, and each transmitted light obtained by these illumination lights is measured. The video signal of the optical image is A/D converted to obtain each corresponding brightness distribution signal, and from each brightness distribution signal, the outer diameter center position of each bare optical fiber row of the multi-core optical fiber is determined, and the axis deviation is detected. The present invention provides a method for inspecting the joints of multi-core optical fibers.

<Operation> With this configuration, the axis deviation of each bare optical fiber row of the multi-core optical fiber can be detected from both two-direction components, so that it can be detected with high precision. Furthermore, since a type of graphical (graphed) brightness distribution signal is used to detect the axis deviation, simple inspection is possible.

<Example> FIGS. 1A and 1B show the general principle of each example according to the method of the present invention.

In the figure, 1 is an imaging device consisting of an objective lens, a TV camera, etc., and in the case of this example, both are 2
In the case of Fig. 1A, _the exposed bare optical fibers f of the multi-core optical fiber F are arranged horizontally in the figure, and in the case of Fig. 1B The surfaces formed by the exposed bare optical fibers f1 _{to 5} of the optical fibers F are arranged vertically in the figure. In addition,
Although the case of five cores will be described here, it is not limited to these five cores.

And in any case, the bare optical fiber
Illumination lights l ₁ and l ₂ are applied from two directions across the f _{1 to 5} columns. In each embodiment, the illumination lights l ₁ and l ₂ are orthogonal to each other (intersect at 90°) and are irradiated from a direction that is 45° to the normal direction of the plane formed by the rows of bare optical fibers f 1 to f ₅ . However, the present invention is not limited to this, and they may intersect at an appropriate angle as described later. Above 2
The imaging devices 1 and 1 of the stand are located at the portion where the transmitted light images X and Y of the illumination lights l ₁ and l ₂ are formed. It is also possible to install one imaging device 1 in a movable manner.

Due to the arrangement of these illumination systems and imaging systems, transmitted light images X, Y from two directions of the bare optical fiber f _{1 to 5} rows are
is obtained. With these two transmitted light images X and Y,
It is possible to precisely inspect the two-direction components of the axis deviation of the bare optical fibers f1 _to f5, that is, the abutting portions of the optical fibers F and F to be connected.

In addition, for these illumination systems and imaging systems, it is possible to install two systems each for the illumination light source and imaging device and switch them using a relay switch, etc., or to use one system.
A possible method is to fix the relative position of the illumination light source of the system and the imaging device and rotate it by 90 degrees around the center position of the rows of bare optical fibers f1 _{to f5} as the rotation center.

When the arrays of bare optical fibers f _{1 to 5} are observed simultaneously using this imaging system, the focal positions for each of the bare optical fibers f _{1 to 5} are observed to be different, and the width of the multicore optical fiber F is observed as shown in FIG. Let L be the difference in focal length of each center line image, then L/√2. In addition, in FIG. 2, P is the distance between adjacent core wires, and d is the outer diameter of the core wires.

Next, a method for inspecting axis misalignment using screen processing from this transmitted light image will be described.

The core image of the multi-core optical fiber F obtained by the apparatus system shown in FIGS. 1A and B above is shown in FIG. 3, with rows of bare optical fibers f _{1 to 5} on the left and bare optical fibers f _{1 to The fifth} column corresponds to each fiber of the pair of multi-core optical fibers F, F to be just connected.

From the image in Figure 3, the cursor shown in the figure
A/D the video signal of the TV camera at the positions above C _{1 to 4} .
Upon conversion, the brightness distribution shown in FIG. 4 is obtained. From this brightness distribution, the third
10 intersection _points of A, B, C, . Furthermore, by finding the midpoint positions of A and B, C and D, E and F, G and H, and I and J marked with x in Figure 3, this is the outer diameter center position of each optical fiber f1 _{to f5} . Become. Perform this operation on the left bare optical fiber f1 _~5 .
Repeat this process on cursors C ₁ and C ₂ for the rows, and on cursors C ₃ and C ₄ for the right bare optical fiber f′ 1 _{to 5} columns to find the outer diameter center position, and compare the data of the two points on the left and the right side. Linearly extrapolate the data of the two points to the center of the screen to find the outer diameter axis deviation of each core wire from one direction Δ _x1 ~ Δ _x5 (Δ _y1
~ _Δy5 ) can be obtained. Furthermore, from the intersection of the luminance distribution in Fig. 4 and the luminance threshold value 2,
Extracting only A, B, C, ... I, J is
This is possible because the distances between the intersections of A and B, C and D, E and F, G and H, and I and J correspond to the outer diameters of the bare optical fibers f _{1 to 5} and f' _{1 to 5} being observed. It is.

This outer diameter axis deviation detection operation is repeated for the X image and the Y image, and the outer diameter axis deviations ΔD ₁ to ΔD ₅ of each left and right optical fiber core wire are determined as ΔD _i =√ ² + ² (i=1 to
5).

By using the method of the present invention, it is possible to detect the axis deviations of the bare optical fibers f1 _{to f5} of the multi-core optical fiber F by adjusting the focus position once for each of the two images, the X image and the Y image.

Next, we will describe the conditions under which the axis shift can be determined by this one-time focal position adjustment.

First, the illumination light transmitted through bare optical fibers f1 _~5 is
Draw the trajectory shown in Figure 5. The illumination light E ₀ passing outside the bare optical fibers f _{1 to 5} goes straight to the objective lens 3,
After the illumination light passing inside the bare optical fibers f _{1 to 5} is refracted twice at the boundary between the bare optical fibers f _{1 to 5} and air,
It reaches the objective lens 3. Of the illumination light passing inside the bare optical fibers f _{1 to} f 5 , the angle of the light ray that can enter the objective lens 3 is limited by the effective aperture and the aperture angle φ of the objective lens 3 . When using the objective lens 3 with a sufficiently large effective aperture, the objective lens 3
The angle of the light ray that can be incident on the lens is limited by the aperture angle φ of the objective lens 3, and the light ray indicated by _Ew in the figure is the limiting ray. For example, when focusing on position Q in FIG. 5, ' and ' are dark areas in the optical fiber image, A'B' are bright areas, and A and B are the outer diameter ends of the optical fiber.

In order to accurately determine the outer diameter center position of these bare optical fibers f1 _{to f5} , it is necessary to accurately determine the positions A and B of the outer diameter ends from the brightness distribution of the optical fiber image, and this is possible at a focal point. The position range is shown in Figure 5.
becomes f′. At this time, f' is the outer diameter of the optical fiber, d,
When the aperture angle of the objective lens is ψ, it is given by f'=d/tanψ (1).

On the other hand, the width L of the fiber array of the multi-core optical fiber F is given by L=(n-1)P...(2), where P is the interval between adjacent fibers and n is the number of fibers. The difference f between the focal positions of the respective fibers shown in FIG. 2 is given by f=(n-1)P√2 (3). Therefore, from the optical fiber image,
To accurately determine the two outer diameter ends of each core wire at one focal position, f≦f′...(4) is a necessary condition, and tanψ≦d/{(n-1)P/√2} ...(5) is obtained.

For example, as shown in Figure 1, when n=5, P=250μm, and d=125μm, tanψ=
It becomes 0.176.

Indicated by the numerical aperture NA (=sinφ) of the objective lens,
NA≦0.173, and the inventors used an objective lens with NA=0.1 to convert the bare optical fiber f _{1 to 5} in the above example.
It was confirmed that the center of the outer diameter of the array could be detected at one focal position.

Note that in each of the above embodiments, illumination light from two directions is used.
When l ₁ and l ₂ are orthogonal (intersect at 90°),
Although this has been shown as an optimal example in which the detection error of axis deviation is the smallest, in the present invention, the angle is not particularly limited as long as the illumination light is from two intersecting directions. For example, as shown in FIG. 6, the intersection angle of _the illumination lights l′ ₁ and l′ ₂ may exceed 90°, and as shown _in FIG. The intersection angle may be less than 90°.

<Effects of the Invention> As explained above, according to the multi-core optical fiber joint inspection method according to the present invention, all the bare optical fiber rows of the multi-core optical fiber can be observed within one screen, and at the same time, In addition, the objective lens used in the imaging device system can be of low magnification, and the video signal of the transmitted light image obtained by the imaging device system is graphed as a brightness distribution signal by A/D conversion. The advantage is that it is possible to easily and accurately judge the detection of radial axis misalignment, and it is also possible to detect axis misalignment of a bare optical fiber array from one direction by adjusting the focus position once. There is.

[Brief explanation of drawings]

FIGS. 1A and 1B are principle diagrams showing an outline of the method for inspecting the joints of each multi-core optical fiber according to the present invention, and FIG. 2 is an explanatory diagram showing the bare optical fiber array of the multi-core optical fiber and irradiation light. , Fig. 3 is a diagram showing an observed image of a bare optical fiber array of a pair of multicore optical fibers to be connected, Fig. 4 is a brightness distribution diagram corresponding to the observed image of Fig. 3, and Fig. 5 is a diagram showing the bare optical fiber array of a pair of multicore optical fibers to be connected. Figure 6, which shows the relationship between optical fibers and irradiated light, shows the intersection angle of irradiated light from two directions.
FIG. 7 is a schematic diagram showing a case where the intersecting angle of the irradiated light from two directions is less than 90°. In the figure, F...multi-core optical fiber, f1 _~5 ...bare optical fiber, X, Y...transmitted light image, _l1 , _l2 ...illumination light,
l′ ₁ , l′ ₂ ……Illumination light, l″ ₁ , l″ ₂ ……Illumination light, 1……
Imaging device, 3...objective lens.

Claims (1)

[Claims] 1. In a method for removing the coating of a multi-core optical fiber and performing butt connection, or for inspecting a joint after butt connection, the vicinity of the butt connection is irradiated with illumination light from two directions that intersect with each other. The video signal of each transmitted light image obtained by the illumination light of A multi-core optical fiber connection inspection method characterized by determining the center position and detecting axis misalignment for inspection.