JP3418296B2 - Detecting the amount of misalignment of optical fibers of different diameters - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a method for detecting the amount of misalignment of optical fibers having different diameters. 2. Description of the Related Art As shown in FIGS. 2A and 2B, for example, core layers 1S and 1L and core layers 1S and 1L, respectively.
As an example of a method of fusion-splicing a pair of optical fibers 3S, 3L having clad layers 2S, 2L formed outside of L and having different outer diameters of the clad layers 2S, 2L at their end faces, , These optical fibers 3S, 3
The axis deviation ΔCORE of the L core layers 1S, 1L is detected,
Then, there is a method of aligning the optical fibers 3S and 3L based on the amount of axis deviation ΔCORE and fusion-splicing the optical fibers 3S and 3L. The optical fiber 3S has a small diameter and the optical fiber 3L has a large diameter. [0003] FIG. 3 shows a conventional example of a method of detecting the axial deviation ΔCORE between the core layers 1S, 1L in such optical fibers 3S, 3L having different diameters. x axis, one axis orthogonal to the x axis is y
Axis (the axis perpendicular to the plane of the paper in the drawing), and the axis orthogonal to the x-axis and the y-axis is the z-axis, and the axis shift amount ΔC of the core layers 1S and 1L in the y-axis direction.
The example which detects ORE is shown. In FIG. 3, reference numeral 4 denotes a light source disposed on the side of the optical fibers 3S and 3L (here, the z-axis direction), and reference numeral 5 denotes a light source opposite to the optical fibers 3S and 3L. It is an imaging device arranged on the side. This imaging device 5
Is composed of, for example, a lens and a CCD camera for receiving an image enlarged by the lens, and is capable of reciprocating in the z-axis direction by a direct-acting bearing mechanism or the like.
In this example, the outer diameters of the cladding layers 2S and 2L are 90 μm and 125 μm, respectively, between the optical fibers 3S and 3L.
And the outer diameter of the core layers 1S and 1L is 8 μm.
It shows what is the same as. First, as shown in FIG. 3, optical fibers 3S,
3L are arranged in a state where the end faces face each other. Then, light is emitted from the light source 4 to the two optical fibers 3S and 3L, and the image pickup device 5 is moved in the optical axis direction (z-axis direction) so that one of the two optical fibers 3S and 3L (here, Focus on the optical fiber 3S). Thereafter, with the optical fiber 3S focused, the light from the light source 4 is converted by the image pickup device 5 as shown in FIG.
The transmitted images 6S and 6L formed by transmitting the light beams L are observed. FIG. 4A and FIG.
The transmitted images 6S and 6L shown in (b) will be described with reference to FIG. As shown in FIG. 5, the optical fibers 3S and 3L respectively function as cylindrical lenses for the light emitted from the light source 4, and the atmosphere in which the optical fibers 3S and 3L are placed, the core layers 1S and 1L, and the cladding. Since the refractive indices of the layers 2S and 2L are different from each other, the light is refracted as shown by the lines a to h. Lines denoted by reference numerals a and h indicate light passing through the atmosphere side at the boundary between the optical fibers 3S and 3L and the atmosphere in which the optical fibers 3S and 3L are placed. The lines indicated by reference numerals b and g indicate the limit positions of light passing through the cladding layers 2S and 2L and entering the image pickup device 5. That is, light passing between the line a and the line b and between the line h and the line g does not enter the image pickup device 5 because of a large refraction angle. Therefore, for example, when focusing on the positions indicated by the reference numerals α and β in FIG. 5, the portions between the line a and the line b and the portions between the line h and the line g are respectively shown in FIGS.
In (b), dark portions indicated by reference numerals 8S and 8L are obtained. These dark portions are referred to as outer dark portions 8S and 8L. In addition, the outer dark portion 8
S and 8L can be seen two each. In FIG. 5, lines indicated by reference numerals c and f indicate light passing through the cladding layers 2S and 2L at the boundaries between the core layers 1S and 1L and the cladding layers 2S and 2L. Lines indicated by reference numerals d and e indicate light passing through the core layers 1S and 1L at the boundaries between the core layers 1S and 1L and the cladding layers 2S and 2L. Since there is a portion through which light does not pass between the line c and the line d and between the line e and the line f, for example, when focusing on the position indicated by the symbol α or β in FIG.
The portions between the lines c and d and between the lines e and f are:
In FIG. 4A and FIG. 4B, they are dark portions indicated by reference numerals 7S and 7L, respectively. These dark areas are respectively defined as inner dark areas 7S,
7L. Note that the inner dark portions 7S and 7L are also the outer dark portions 8.
As with S and 8L, two can be seen each. As described above, the inner dark portions 7S and 7L indicate the boundary between the core layer 1S and the cladding layer 2S and the boundary between the core layer 1L and the cladding layer 2L, respectively. Therefore, when both transmission images 6S and 6L are observed as shown in FIG. 4A in a state where the optical fiber 3S is focused as described above, the focused optical fiber 3S is shown. In the transmission image 6S, the midpoint position CORE _SS between the inner dark portions 7S and 7S is set as the position of the core layer 1S.
Is measured. However, in this state, the other optical fiber 3
Since L is not focused, the inner dark portions 7L and 7L indicating the position of the core layer 1L cannot be clearly seen, and it is difficult to accurately measure the position of the core layer 1L. For this reason, after measuring the position CORE _SS of the core layer 1S in one optical fiber 3S as described above, the other optical fiber 3L is also focused as shown in FIG. inner dark portion 7L, on which is be able to see 7L to clearly measure the inner dark portion 7L, a midpoint cORE _LL of 7L between the position of the core layer 1L. Thereafter, these two optical fibers 3S, 3L
From the positions of the core layers 1S, 1L, the axis shift amount ΔCORE of the core layers 1S, 1L is determined by the following equation (1). ΔCORE = CORE _SS −CORE _LL (1) Now, the optical fiber 3 having the different diameter is thus obtained.
Axis shift ΔCOR of core layers 1S and 1L in S and 3L
In the device for detecting E, the moving axis of the imaging device 5 and the light source 4
It is better to make the optical axis as parallel as possible. In practice, however, it is very difficult to configure these units so that they are completely parallel. As shown in FIG. 6, the moving axis of the image pickup device 5 (the thick double arrow in FIG. 6) Line) and the optical axis from the light source 4 (the thin arrow line in FIG. 6) are not almost parallel in most cases. Therefore, in such a case, when the imaging device 5 is moved in the z-axis direction to focus on the respective optical fibers 3S and 3L, the imaging device 5 The observed transmission images 6S and 6L move and shift in the screen, and therefore, the axial shift Δ of the core layers 1S and 1L.
An error occurred in the value of CORE. For this reason, for example, the optical fiber 3 is determined on the basis of the axial deviation ΔCORE of the core layers 1S and 1L including the error.
When the S and 3L are fusion-spliced, the optical fibers 3S and 3L
Optical transmission loss at the fusion spliced part increases,
There was a problem. Such a problem is caused by both optical fibers 3S and 3S.
As the outer diameter difference between the Ls increases, the core layer 1
Since the error of the axis shift amount ΔCORE of S, 1L also becomes large, it becomes serious. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for detecting the amount of misalignment of an optical fiber having a different diameter, which can more accurately measure the amount of misalignment of a core layer. . According to a first aspect of the present invention, there is provided a method of detecting an amount of misalignment of an optical fiber having a different diameter, comprising the steps of: a core layer; a cladding layer formed outside the core layer; And a pair of optical fibers having different outer diameters of the clad layers are arranged in a state where the end faces face each other, and the focus of an image pickup device arranged on both sides of the two optical fibers is focused on one optical fiber. Above, the position of the core layer of this optical fiber is measured by the imager, and the focus of the imager is adjusted to the other optical fiber. Then, the position of the core layer of the optical fiber is measured by the imager. A method for detecting the amount of misalignment of optical fibers of different diameters, which measures and determines the amount of misalignment between the two core layers based on the difference between the positions of the two core layers, wherein each of the optical fibers is focused on an image pickup device. In any one The position of the clad layer is measured with respect to the optical fiber, and the axial deviation between the two core layers is corrected by the positional change amount of the clad layer obtained from the difference between the positions of the clad layers. In the method for detecting the amount of misalignment of optical fibers having different diameters according to the first aspect of the present invention, the position of the cladding layer is determined for any one of the optical fibers in a state where the optical fibers are mutually focused on the imaging device. Is measured, and the amount of axial deviation between the two core layers is corrected by the amount of change in the position of the clad layer obtained from the difference between the positions of the clad layers. When the focal point of the image pickup device is changed from one optical fiber to the other optical fiber, the position change amount of the clad layer is not parallel to the optical axis from the light source and the movement axis of the image pickup device. Specifically, it indicates the amount of movement of the entire transmitted image in the image of the image pickup device, and an error occurs when the amount of axial deviation of the core layer is detected. Therefore, the amount of axis deviation of the core layer can be detected more accurately by correcting with the amount of positional change of the cladding layer. Further, the amount of change in the position of the cladding layer before and after the movement of the imaging device can be measured more accurately than the amount of change in the position of the core layer. This is for the following reason. First, as shown in FIG. 5, light transmitted through the optical fiber (see lines b to g in FIG. 5) becomes refracted light, so that when the focal position of the imaging device is moved, at least the focal position is changed. Image showing the boundary between the cladding layer and the core layer before or after the movement (Fig. 4
In (a) and (b), the inner dark portions 7S and 7L) become unclear, so that the position of the core layer cannot be measured very accurately. On the other hand, the boundary between the atmosphere where the optical fiber is placed and the cladding layer, which indicates the position of the cladding layer, is parallel light (lines a and h in FIG. 5) incident on the imager without passing through the optical fiber.
4 (a) and 4 (b), it is possible to observe clearly even if the focus position of the image pickup device is changed. Can,
The position can be measured more accurately. Second, as shown in FIG. 5, when the focus position is compared with the broken line position indicated by the reference symbol α and the focus position is indicated by the broken line position indicated by the reference character β, The distance between the line a and the line b and the distance between the line g and the line h are wider. Since the interval between these lines indicates the width of the outer dark part, it can be seen that the width of the outer dark part also changes by moving the imaging device in the z-axis direction to change the focal position (FIG. 4A, (B)). Therefore, especially in a small-diameter optical fiber, when the width of the outer dark part is widened, the distance between the outer dark part and the inner dark part becomes narrower (see FIG. 4B), and the position of the inner dark part, that is, the position of the core layer, It becomes difficult to measure the position accurately. In contrast,
For example, when measuring the position of the outer line of the outer dark part as the position of the cladding layer, such a problem does not occur, so that more accurate measurement can be performed. As described above, according to the present invention, it is possible to detect the amount of axial misalignment between core layers of optical fibers of different diameters more accurately than when no correction is performed or when correction is performed using the amount of change in the position of the core layer. Can be. Embodiments of the present invention will be described below in detail with reference to the drawings. The optical fiber 3 shown here
Devices such as S, 3L, the light source 4, and the image pickup device 5 are the same as those described with reference to FIGS. As shown in FIG. 3, first, both optical fibers 3S and 3L are arranged as in the prior art, and light is emitted from the light source 4 to both optical fibers 3S and 3L. And one optical fiber 3S
In this state, as shown in FIG. 1A, in the transmission image 6S showing the optical fiber 3S, the position of the core layer 1S is set to the midpoint between the inner dark portions 7S and 7S. The position CORE _SS (indicated by a dashed line in the drawing) was measured, and the position of the cladding layer 2S was determined as the outer dark portion 8.
The position CLAD _SS of the outer line of S is measured. Note that the outer line of the outer dark portion 8S indicates both lines that form the contour on the axial direction side of the transmission image 6S in the outer dark portion 8S. Here, the upper line is particularly selected and measured in the drawing. Next, the imaging device 5 is focused on the other optical fiber 3L, and in this state, as shown in FIG. 1B, in the transmitted image 6L showing this optical fiber 3L, the core layer 1
As the position of L, the midpoint position C between the inner dark portions 7L and 7L
OLE _LL was measured, and in the transmission image 6S showing the other optical fiber 3S, the position of the cladding layer 2S was defined as
The position CLAD _LS of the outer line of the outer dark part 8S is measured. Then, the axial deviation ΔCO of the core layers 1S, 1L
RE is determined by the following equation (2). ΔCORE = [CORE _SS + (CLAD _LS −CLAD _SS )] − CORE _LL (2) where (CLAD _LS −C in the above equation (2))
LAD _SS ) is the transmission image 6 due to the movement of the imaging device 5.
This is a correction term related to the amount of change in the position of S. With this correction term, the axis shift amount ΔCORE of the core layers 1S and 1L can be obtained more accurately. Now, the amount of axis deviation ΔC obtained by the above equation (2)
In the case where the ORE is used, and in the case where the axis shift amount ΔCORE obtained by the conventional equation (1) is used, the ΔCORE is used.
After the optical fibers 3S and 3L are aligned with each other on the basis of the above, fusion splicing is performed, and the amount of optical transmission loss in the fusion spliced portion is examined ten times each, and the results are averaged. The results are shown in Table 1. [Table 1] As can be seen from Table 1, when the axial deviation ΔCORE of the core layers 1S and 1L is corrected by the amount of change in the position of the cladding layer 2S (Equation (2) of the present embodiment), It can be seen that the optical transmission loss at the fusion spliced portions of the optical fibers 3S and 3L is smaller than in the case where the correction is not performed using the position change amount (formula (1)). This is the amount of axis deviation ΔCO of the core layers 1S and 1L.
It is considered that the case where the RE is corrected by the amount of change in the position of the cladding layer 2S can accurately quantify the axis shift amount ΔCORE of the core layers 1S and 1L. As described above, it was confirmed that the method for detecting the amount of axial deviation of the optical fibers 3S and 3L of different diameters of the present invention can more accurately detect the amount of axial deviation ΔCORE of the core layers 1S and 1L as compared with the conventional method. In one example of the present embodiment, the core layer 1
Although the example in which the position detection of S and 1L is performed in the order of the small-diameter optical fiber 3S and the large-diameter optical fiber 3L has been described, the order in which the position detection of the core layers 1S and 1L is performed in the present invention is not limited thereto. Instead, a large-diameter optical fiber 3L may be used first. In the present embodiment, the processing for measuring the position of the cladding layer 2S is performed together with the processing for measuring the positions of the core layers 1S and 1L, but the processing procedure in the present invention is not limited to this. Not the core layer 1S,
The position measurement of 1L and the position measurement of the cladding layers 2S and 2L for correcting the positions of the core layers 1S and 1L may be performed in separate processes. Further, in the example of the present embodiment, an example is shown in which the axis shift amount ΔCORE of the core layer 1 is detected only in the y-axis direction. However, in the case of fusion splicing of ordinary optical fibers 3S, 3L, etc. Detects the axis shift amount ΔCORE of the core layers 1S and 1L in the z-axis direction in addition to the y-axis direction,
Needless to say, it is better to align the optical fibers 3S and 3L based on the measured values. In the example of the present embodiment, the position of the outer line of the outer dark portion 8S is determined as the position of the cladding layer 2S to be measured.
The position of S is not limited to this, and may be, for example, a midpoint position between the outer lines of the outer dark portions 8S, 8S. Further, in one example of the present embodiment, the axial deviation ΔCORE is corrected by the small-diameter optical fiber 3S. However, in the present invention, the axial deviation ΔC is corrected by the large-diameter optical fiber 3L.
The ORE may be corrected, or both optical fibers 3S, 3
The correction value may be obtained by L and the average value may be obtained. In the example of the present embodiment, as shown in the above equation (2), the correction term according to the position change amount of the cladding layer 2 is given by (CLAD _LS -CLAD _SS ). The correction term based on the position change amount of No. 2 is not limited to this. For example, this correction term (CLAD _LS -CLAD
_SS ) may be multiplied by another correction coefficient. In the present embodiment, an example has been shown in which the axis shift amount ΔCORE of the core layers 1S, 1L is detected by numerical values in the y-axis direction. However, in the present invention, for example, the optical fibers 3S,
When the axial directions of the 3L do not coincide with each other, or when the axial directions (x-axis direction) of the optical fibers 3S and 3L do not coincide with the raster direction of the image of the image pickup device 5 (for example, the x'-axis direction). Are the inner dark portions 7S and 7L and the outer dark portions 8
The center axis line and the contour line of S, 8L are represented by a straight line y ′ = ax ′ + b on both axes x ′ axis and y ′ axis of the image of the image pickup device 5.
(A, b: constants determined by the position and inclination of the line in the image), and the correction and detection of the axial deviation ΔCORE of the optical fibers 3S, 3L may be performed using these. Further, in one example of the present embodiment, the core layer 1
Although an example is shown in which the outer diameters of S and 1L are the same, it goes without saying that the optical fibers 3S and 3L of the present invention may have different outer diameters of the core layers 1S and 1L. According to the method for detecting the amount of misalignment of an optical fiber having a different diameter according to the present invention, the optical fiber having a different diameter can be more accurately corrected than when no correction is made or when the positional change of the core layer is used. Of the core layers can be detected.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) and 1 (b) are plan views showing images captured by an image pickup device in a method of detecting an amount of misalignment of an optical fiber having a different diameter according to an embodiment of the present invention; . FIGS. 2A and 2B are side views showing an embodiment of fusion splicing of optical fibers related to the method of detecting the amount of axial deviation of optical fibers of different diameters according to the present invention. FIG. 3 is a side view showing the configuration of an apparatus for detecting the amount of axial deviation of optical fibers of different diameters related to the present invention. FIGS. 4A and 4B are plan views showing images captured by an image pickup device in an example of a conventional method of detecting the amount of axial deviation of optical fibers having different diameters. FIG. 5 is a side view for explaining refraction of light transmitted through the optical fiber from the side. FIG. 6 is a side view showing a relationship between a movement axis of an image pickup apparatus related to the present invention and an optical axis from a light source. [Description of Signs] 1S, 1L Core layer 2S, 2L Cladding layer 3S, 3L Optical fiber 4 Light source 5 Imager 6S, 6L Transmission image 7S, 7L Inner dark portion 8S, 8L Outer dark portion

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Claims (1)

(57) Claims 1. A pair of optical fibers each comprising a core layer and a cladding layer formed outside the core layer, wherein the cladding layers have different outer diameters from each other. Are placed face-to-face with each other, and the focus of an image pickup device arranged on both sides of both optical fibers is adjusted to one optical fiber, and then the position of the core layer of the optical fiber is measured by the image pickup device. Then, after focusing on the other optical fiber of the imaging device,
The imaging device measures the position of the core layer of the optical fiber, and determines the amount of axis deviation between the two core layers from the difference between the positions of the two core layers. In each state in which the image pickup device is focused on the optical fibers, the position of the clad layer is measured for one of the optical fibers, and the position change amount of the clad layer obtained from the difference between the positions of the clad layers is used to measure the position of the clad layer. A method for detecting an amount of misalignment of an optical fiber having a different diameter, wherein the amount of misalignment of a core layer is corrected.