JPH0815563A - Alignment method in coupling part of optical fiber having non-axisymmetrical refractive index distribution and optical waveguide, optical fiber fixing structure and coupling part - Google Patents

Abstract

PURPOSE:To provide an alignment method capable of easily aligning the rotating directions in the coupling part of optical fibers having a non-axisymmetrical refractive index distribution and optical waveguides, an optical fiber fixing structure and the coupling part. CONSTITUTION:The magnified images of the optical fibers are obtd. by photographing the optical fibers 1a, 1b from sideways of the propagating direction of guided light by an image obtaining means 6 and the distribution of the characteristics of the images corresponding to the positions in the radial direction of the optical fiber images from the magnified images obtd. in such a manner. The directions of the rotating directions around the central axes of the optical fibers as the axis of rotation are measured from the distribution of the characteristics of the images. The directions of the rotating directions of the optical fibers 1a, 1b are adjusted by optical fiber rotating members 9a, 9b in accordance with the result of the measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an optical fiber gyro,
An optical modulator, an optical switch having an axisymmetric refractive index distribution used in an optical switch, etc.
The present invention relates to an optical fiber fixing structure and a coupling section.

[0002]

2. Description of the Related Art An example of a coupling portion between an optical waveguide and an optical fiber having a non-axisymmetric refractive index distribution is an optical fiber array using a polarization-maintaining optical fiber. Alignment of the angle of rotation direction of the polarization-maintaining optical fiber, that is, the polarization plane is preserved in the alignment method of the birefringent principal axis, the vibration direction of the electric field propagates linearly polarized light parallel to the birefringent principal axis to the optical fiber, The angle of the birefringent main axis with respect to the optical fiber holding member is adjusted by the angle of the linearly polarized light at the exit end.

For example, as shown in FIG. 15, light emitted from a semiconductor laser 31 is converted into substantially parallel light by a first lens 32 and linearly polarized by a polarizer 33, and then rotated about a central axis of a core. A second lens 34 condenses the polarization plane-maintaining optical fiber 36 held by a possible holder 35 at one end thereof and propagates the light in the optical fiber. On the other hand, the other end of the optical fiber from which the propagating light exits is also provided with a V-shaped groove for embedding the optical fiber previously provided in the optical fiber holding member 37 through the holder 35 rotatable about the core (see FIG. (Not shown) on which the cover member 3 is placed.
8 is mounted.

By the way, since the polarization-maintaining optical fiber has two birefringent principal axes that are orthogonal to each other, if the approximate angle of the birefringent principal axes is not known, which principal axis the oscillation direction of the electric field of the linearly polarized light propagating in the optical fiber is. You cannot know if it is parallel to.

Therefore, if an attempt is made to align the angle of the birefringent main axis only by the vibration direction of the electric field of the linearly polarized light emitted from the optical fiber, the angle may differ from the desired angle by 90 °. It is necessary to perform alignment of the main axis in a substantially desired direction in advance and limit the rotation range of the optical fiber emission end at the time of alignment by the angle of linearly polarized light to the extent of this alignment error.

Therefore, when the elliptic core type optical fiber 42 is used as the polarization-maintaining optical fiber 36, as shown in FIG. 16, the major axis 44 and the minor axis 45 of the elliptical core 43 are the birefringent principal axes, respectively. Therefore, the CCD camera (not shown) mounts it on the holding member while observing the near-field pattern of the emitted light from the optical fiber or the far-field pattern of the emitted light projected on the screen (not shown). The exit end of the optical fiber thus rotated is rotated to align the principal axis of birefringence in a substantially desired direction. Further, when the elliptical jacket type optical fiber 46 is used as the polarization-maintaining optical fiber 36, the major axis 48 and the minor axis 49 of the elliptical jacket 47 become the birefringent principal axes, respectively, as shown in FIG. , The optical fiber emitting end mounted on the holding member so that the shape of the jacket portion can be observed is previously etched with a hydrofluoric acid aqueous solution to form a step between the jacket portion and other portions, CCD
The optical fiber is rotated while observing the magnified image of this end face with the camera, and the birefringent principal axis is aligned in a substantially desired direction.

Next, the emitted light is focused on the photodetector 41 via the third lens 39 and the analyzer 40, and the incident end of the optical fiber and the analyzer 40 are rotated while monitoring the output of the photodetector 41. When the rotational position of the incident end that minimizes the polarization crosstalk is obtained and one of the birefringent principal axes of the optical fiber at the incident end and the oscillation direction of the optical electric field are matched, the light emitted from the optical fiber is Linearly polarized light whose oscillation direction is parallel to one of the two birefringent principal axes. Therefore, next analyzer 4
In the case of an elliptic core type optical fiber, the azimuth of 0 is aligned with the direction of the desired birefringent main axis. In the case of, the birefringent main axis is rotated by rotating within a range of an alignment error due to a magnified image of the end face, for example, within a range of ± 10 ° so that the output of the light receiver 41 is maximized or minimized. Is being aligned.

[0008]

By the way, when the alignment is performed so that the birefringent main axis of the polarization-maintaining optical fiber 36 is directed in a desired direction by the above-described conventional method, the light beam mounted on the holding member 37 is used. In addition to rotating the fiber 36 about the central axis of its core as a rotation axis, various procedures must be performed.

First, flat end faces must be formed at both ends of the optical fiber for input / output coupling of light. In addition, alignment is required to couple the light that has passed through the first lens 32, the polarizer 33, and the second lens 34 to the optical fiber 36, and the light that propagates in the optical fiber 36 is oscillated by an electric field. In order to obtain linearly polarized light whose direction is parallel to the birefringent main axis, alignment of the incident end of the optical fiber 36 in the rotation direction is required. That is, in order to align the angle of the birefringent principal axis of the exit end of the polarization-maintaining optical fiber 36 mounted on the holding member 37, the angle of the birefringent principal axis of the entrance end must be aligned. Means that.

On the other hand, when the ellipsoidal core type optical fiber 42 is used as the polarization-maintaining optical fiber 36 in order to preliminarily align the birefringent principal axis in a substantially desired direction,
When the elliptical jacket type optical fiber 46 is used, the near-field pattern of the light emitted from the optical fiber 36 must be observed as an enlarged image of the emission end face of the optical fiber.

Therefore, the CCD camera or screen, the third lens 39, the analyzer 40, and the light receiver 41 are moved and rearranged each time one optical fiber array using polarization-maintaining optical fibers is manufactured. Become. Further, when the elliptical jacket type optical fiber 46 is used, it is necessary to etch the end face with a hydrofluoric acid aqueous solution.

As described above, in order to direct the birefringence main axis of the polarization-maintaining optical fiber in a desired direction, many steps must be taken and a lot of time is required. It has been difficult to reduce the number of manufacturing steps and the manufacturing time of the optical fiber array used.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above problems and to perform alignment in the rotational direction at a coupling portion between an optical fiber having a non-axisymmetric refractive index distribution and an optical waveguide easily in a short time. A method, an optical fiber fixing structure and a coupling part are provided.

[0014]

In order to achieve the above object, the present invention provides a method for aligning an optical fiber having a non-axisymmetric refractive index profile and an optical waveguide in a joint portion, in which an optical fiber is guided by an image acquisition means. Obtain a magnified image of the optical fiber by shooting from the side with respect to the wave light propagation direction, and obtain a distribution of image features such as a light intensity distribution corresponding to the radial position of the optical fiber image from the obtained magnified image, Based on the distribution of the characteristics, the orientation of the optical fiber in the direction of rotation about the central axis of the optical fiber is measured, and the orientation of the optical fiber in the direction of rotation is adjusted by the optical fiber rotating member based on the measurement result.

Further, the optical fiber fixing structure of the present invention includes an optical fiber holding member for coupling at least one optical fiber having a non-axisymmetric refractive index distribution and at least one optical waveguide, respectively. In the above, in the image acquisition means, the optical fiber is photographed from the side in the guided light propagation direction to obtain an enlarged image of the optical fiber, and the light intensity distribution corresponding to the radial position of the optical fiber image is obtained from the obtained enlarged image. The distribution of the image features, such as the image, is obtained, and the direction of the rotation direction with the central axis of the optical fiber as the rotation axis is measured from the distribution of the features. The orientation of is adjusted.

Further, in the coupling section of the present invention, in the coupling section in which an optical fiber having a non-axisymmetric refractive index distribution and an optical waveguide are coupled, the optical fiber is photographed from the side in the guided light propagation direction by the image acquisition means. Then, obtain an enlarged image of the optical fiber, obtain the distribution of image features such as the light intensity distribution corresponding to the radial position of the optical fiber image from the obtained enlarged image, and use the distribution of features to determine the center axis of the optical fiber. The direction of rotation of the optical fiber is measured based on the measurement result by measuring the direction of rotation about the rotation axis.

[0017]

By capturing the optical fiber from the side with respect to the guided light propagation direction by the image acquisition means, a magnified image of the optical fiber can be acquired. When the obtained enlarged image is subjected to image processing by the image processing device, the distribution of image features such as the light intensity distribution corresponding to the radial position of the optical fiber image is obtained. The distribution of the features in this image shows a characteristic curve that differs depending on the direction of rotation of the optical fiber and is reproducible. Therefore, it is possible to measure the rotation angle with the central axis of the optical fiber as the rotation axis from the distribution of the image features, and adjust the direction of the optical fiber rotation direction by the optical fiber rotating member based on the measurement result. .

[0018]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a diagram showing an example of an outline of a main part of an apparatus to which an alignment method in a rotation direction of an optical fiber having a non-axisymmetric refractive index distribution of the present invention is applied. Here, a case will be described in which an optical fiber array is manufactured using the elliptic core type polarization-maintaining single-mode fiber 1 as the optical fiber.

As shown in the figure, two optical fibers 1a and 1b from which the coatings on the tip portions 2a and 2b have been removed are used to embed optical fibers preliminarily arranged in parallel on the surface of the optical fiber holding member 3. Two V-shaped grooves 4a,
4b, each of which is coated with an ultraviolet curable adhesive (not shown), and the cover member 5 is mounted thereon. Rear ends 2c and 2d of the polarization-maintaining optical fiber
Is an optical fiber rotating mechanism 9 as an optical fiber rotating member.
Since it is attached to a and 9b, the tip portions 2a and 2b
Can rotate about the central axis of the core of the optical fibers 1a and 1b as a rotation axis.

On the other hand, of the two polarization-maintaining single-mode optical fibers 1a and 1b mounted on the optical axis of the image-capturing camera 6, the optical fiber 1a which is aligned in the angle of the birefringent main axis is imaged. It is arranged so as to be sandwiched between the camera 6 and the illumination light source 8. Illumination light is emitted from the lower side surface of the optical fiber 1a in a direction crossing the core, and the emitted light is transmitted through the optical fiber 1a, and the imaging camera 6 acquires an enlarged image of the optical fiber tip 2a. From the acquired enlarged image, the light intensity distribution corresponding to the radial position of the optical fiber image (not shown) can be calculated by the image processing device 7. This light intensity distribution has different characteristics depending on the angle of the birefringent principal axis. This is because the components of the polarization-maintaining optical fiber such as the core, the clad, and the jacket have different refractive indexes, and the shape of at least one component is non-axisymmetric.

Therefore, when the controller 10 determines the angle of the birefringent main axis and drives the rotating mechanism 9a to which the optical fiber 1a on which the angle of the birefringent main axis is aligned is mounted by the controller 10, It can be adjusted by rotating the angle of the birefringent main axis to a desired angle.

Next, the operation of the embodiment will be described.

FIG. 2A is a schematic cross-sectional view when the angle formed by the optical axis of the image pickup camera and the birefringent main axis in the major axis direction of the elliptical core is 0 °, and FIG. It is a figure which shows intensity distribution. FIG. 3A is a schematic cross-sectional view when the angle formed by the optical axis of the image pickup camera and the birefringent main axis in the major axis direction of the elliptical core is 5 °, and FIG. 3B shows the light intensity distribution. FIG. FIG. 4A is a schematic sectional view when the angle formed by the optical axis of the image pickup camera and the birefringent main axis in the long axis direction of the elliptical core is 45 °, and FIG. 4B shows the light intensity distribution. FIG. FIG. 5A is a schematic cross-sectional view when the angle formed by the optical axis of the imaging camera and the birefringent main axis in the major axis direction of the elliptical core is 90 °, and FIG. 5B shows the light intensity distribution. FIG.

Here, the distance between the image pickup camera 6 and the optical fiber 11 was adjusted with a resolution of 0.5 μm so that the maximum values l and r of the light intensity of the image on the outer periphery of the optical fiber were maximized. When the optical axis 14 and the birefringent main axis 15 are parallel (see FIG.
In (a)), as shown in FIG. 2B, the maximum value a of the light intensity at the center of the optical fiber becomes maximum, and the minimum values b and c of the light intensity appear on both sides of the maximum value a. And the difference in light intensity between a and c was the maximum. Further, the light intensity distribution is substantially line-symmetrical with a corresponding to the center of the core 12 as an axis of symmetry, and the difference in light intensity between the minimum values b and c appearing at the substantially line-symmetrical position is minimized.

By rotating the optical fiber 11 clockwise,
When the angle formed by the optical axis 14 and the birefringent main axis 15 is 5 ° (FIG. 3 (a)), the maximum value a is the maximum value shown in FIG. 2 (b) as shown in FIG. 3 (b). The difference in light intensity between a and the minimum values b and c of light intensity was smaller, and the light intensity of c was smaller than that of b. When the optical fiber 11 is rotated clockwise so that the angle formed by the optical axis 14 and the birefringent main axis 15 is 45 ° (FIG. 4A), the maximum value a as shown in FIG. Also, the absolute value of the amount of change with respect to the vicinity of the minimum values b and c is very small as compared with FIGS. 2B and 3B, making it difficult to distinguish, but the light intensity of c is slightly higher than that of b. It got smaller.

On the other hand, when the angle formed by the optical axis 14 and the birefringent main axis 15 is 90 ° (FIG. 5A), FIG.
As shown in (b), it is difficult to distinguish the maximum value a and the minimum values b and c in the case of 45 ° (Fig. 3 (a),
Similar to (b)), but the difference in light intensity between b and c disappeared. Utilizing the fact that the characteristic light intensity distribution is obtained by the angle of the birefringent main axis 15 in this way, the elliptic core type polarization-maintaining optical fiber 1 mounted on the optical fiber holding member 3 shown in FIG. 1 is used. The control device 10 determines the rotation angle difference between the angle of the birefringent main axis and the desired angle, and the rotation mechanism 9 is driven by the control device 10 to rotate the optical fiber 1 by this angle difference. It was possible to perform the alignment so that the birefringent main axis would have a desired angle without propagating the guided light to the fiber 1. Since the minimum value of the interval between the maximum value a and the minimum value b or c is 1 μm, the resolution limited by the image pickup device of the image pickup camera 6 must be 1 μm or better.

The polarization-maintaining optical fiber 1a shown in FIG.
1b is an elliptic core type optical fiber, and its birefringent main axis is rotated to a desired angle by the above-mentioned alignment method, and then the adhesive is cured by irradiation with ultraviolet rays to obtain the optical fibers 1a and 1b, the holding member 3 and the cover member 5. The end face of is polished to prepare a polarization-maintaining optical fiber array used as a coupling part with the optical waveguide.

By the way, in the case where the optical axis 14 and the birefringent main axis 15 are substantially parallel to each other, FIGS.
As shown in (a) and (b), the difference in light intensity near the maximum value a and the minimum values b and c of the light intensity is large, and the change in the light intensity distribution is sensitive to the change in angle. Therefore, while the optical fiber 11 is rotated, acquisition of the enlarged image and calculation of the light intensity distribution of the acquired image are repeated, and the optical axis 14 and the birefringent main axis 15 are repeated.
The alignment error was 5 ° or less, and the accuracy could be improved by temporarily aligning and in parallel with each other and then rotating the optical fiber by an angle difference from the desired direction. Further, when the optical axis 14 and the birefringent main axis 15 are aligned in parallel, the angle of the optical axis 14 with respect to the holding member 3 is determined in advance so that the angle of the birefringent main axis 15 becomes a desired angle with respect to the holding member 3. By doing so, the alignment accuracy can be improved and the time required for alignment can be shortened.

Since the maximum width of the position where the maximum value and the minimum value of the light intensity are detected in order to adjust the angle of the birefringent main axis 15 in parallel with the optical axis 14 is 6 μm, this detection range is the core 12 Even if the eccentricity is taken into consideration, it is sufficient to set the half width to 5 μm with respect to the center of the optical fiber, and by doing so, the time required for image processing could be shortened.

The angle of the birefringent main axis 15 is adjusted so as to be parallel to the optical axis 14, and the distance between the image pickup camera 6 and the optical fiber 11 is set to the maximum value l, r of the light intensity of the image on the outer peripheral portion of the optical fiber. 6 and 7 show the light intensity distributions when the distance is made larger than the maximum distance by 5 μm and 10 μm, respectively. As the distance between the imaging camera 6 and the optical fiber 11 is increased, the absolute value of the change amount of the local maximum value a and the local minimum values b and c with respect to the vicinity thereof as shown in FIG.
2 becomes smaller and becomes harder to identify, and then the maximum value a in FIG. 2B becomes the minimum value a in FIG. 7 and the minimum values b and c in FIG. 2B become the maximum values in FIG. The light intensity was inverted to the values b and c.
Therefore, the distance between the imaging camera 6 and the elliptic core type optical fiber is adjusted with a position resolution of 5 μm or better so that the maximum values l and r of the light intensity of the image on the outer peripheral portion of the optical fiber are maximized. It was very effective to align the birefringent principal axes with high accuracy and reproducibility.

Even when the distance between the imaging camera 6 and the elliptic core type optical fiber 11 is adjusted so that the light intensity of the portion corresponding to the center of the core 12 is minimized as shown in FIG. The refraction main axis 15 could be aligned parallel to the optical axis 14.

Next, a case where an elliptic jacket type polarization-maintaining optical fiber is used as the optical fiber having a non-axisymmetric refractive index distribution will be described.

FIG. 8A is a schematic sectional view when the angle formed by the optical axis of the imaging camera and the birefringent main axis in the major axis direction of the elliptical jacket of the ellipsoidal jacket type polarization-maintaining optical fiber is 0 °. 8B is a diagram showing the light intensity distribution. FIG. 9A is a schematic cross-sectional view when the angle formed by the optical axis of the imaging camera and the birefringent main axis in the major axis direction of the elliptical jacket of the elliptical jacket-type polarization-maintaining optical fiber is 5 °. (B) is a figure which shows the light intensity distribution. FIG.
0 (a) is a schematic cross-sectional view when the angle formed by the optical axis of the imaging camera and the birefringent main axis of the elliptical jacket of the elliptical jacket-type polarization-maintaining optical fiber in the long axis direction is 45 °,
FIG. 10B is a diagram showing the light intensity distribution. Figure 11
11A is a schematic cross-sectional view when the angle formed by the optical axis of the imaging camera and the birefringent main axis in the long axis direction of the elliptical jacket of the elliptical jacket-type polarization-maintaining optical fiber is 90 °, and FIG. ) Is a diagram showing the light intensity distribution.

Here, the optical axis 14 and the birefringent main axis 21 are set so that the distance between the image pickup camera 6 and the optical fiber 16 is such that the maximum values l and r of the light intensity of the image on the outer circumference of the optical fiber are maximum. When the and are parallel to each other (FIG. 8 (a)), no conspicuous bright part and dark part appear in the vicinity of the center of the optical fiber, and within this range, the imaging camera 6 is separated by 50 μm from the optical fiber. Appeared.

Therefore, the distance between the image pickup camera 6 and the optical fiber 16 is adjusted with a resolution of 0.5 μm so that the maximum values l and r are larger than the maximum distance by 10 μm.

Here, when the optical axis 14 and the birefringent main axis 21 in the major axis direction of the elliptical jacket are parallel to each other (see FIG. 8).
(A)), as shown in FIG. 8 (b), the light intensity distribution is substantially line-symmetric with respect to the center of the bright portion a corresponding to the center of the core, and further the line-symmetry near the center of the optical fiber. A pair of bright portions d and e appeared at the position of, and the difference in light intensity between them became the minimum. In addition, on the inner circumference side of the optical parts of these bright parts d and e,
A pair of dark portions b and c appear at positions substantially line-symmetric with respect to the center of the bright portion a corresponding to the center of the core, and the light intensity in the vicinity of the outer peripheral side of the bright portions d and e is higher than that in the outer peripheral side. No significant dark areas appeared. When the optical fiber 16 is rotated clockwise and the angle formed by the optical axis 14 and the birefringent main axis 21 is set to 5 ° (FIG. 9 (a)), the light intensity distribution is no longer line-symmetrical. The bright part corresponding to e in 8 (a) was divided into two bright parts d and g as shown in FIG. 9 (b), and the dark part e appeared between them. 10B when the optical fiber 16 is further rotated clockwise so that the angle formed by the optical axis 14 and the birefringent main axis 21 is 45 ° (FIG. 10A).
The light intensity distribution is not line-symmetrical because a new bright part h appears, as shown in FIG. 5, but a set of bright parts d, is formed at a position substantially linearly symmetric with the center of the bright part a corresponding to the center of the core as the axis of symmetry. e appears, and a pair of dark parts b and c appears at positions of the light portions d and e that are substantially line-symmetrical on the inner circumference side of the optical fiber, and at positions near the outer peripheral sides of the bright parts d and e that are substantially line-symmetrical. A remarkable pair of dark parts f and g whose light intensity is lower than that on the outer peripheral side appeared.

On the other hand, when the angle formed by the optical axis 14 and the birefringent principal axis 21 is 90 ° (FIG. 11A), that is, the optical axis 14 and the birefringent principal axis 22 in the minor axis direction of the elliptical jacket.
When the and are aligned in parallel to each other, as shown in FIG. 11B, the light intensity distribution is substantially line symmetric with the center of the bright portion a corresponding to the center of the core as the axis of symmetry, and A pair of bright parts d and e appear in the vicinity of substantially line-symmetrical positions.
A pair of dark parts b and c appearing at positions of line e on the inner circumference side of the optical fiber, and a pair of remarkable dark parts in which light intensity is lower near the outer circumference side of the bright parts d and e than the outer circumference side. f and g appeared. Utilizing the fact that a characteristic light intensity distribution is obtained depending on the angle of the birefringent principal axis 21 or the birefringent principal axis 22 in this manner, an elliptic jacket type polarization plate mounted on the optical fiber holding member 3 shown in FIG. 1 is utilized. In the wavefront-maintaining optical fiber as well, as in the case of the elliptic core-type polarization-maintaining optical fiber, it was possible to perform alignment so that the principal axis of the birefringence was at a desired angle without propagating the guided light to the optical fiber. still,
Since the minimum value of the center distance between the bright portion and the dark portion except the outer peripheral portion of the optical fiber was 1.6 μm, the resolution limited by the image pickup device of the image pickup camera 6 should be 1.6 μm or better. I had to do it. Further, by aligning the birefringent principal axis 21 or the birefringent principal axis 22 and the optical axis 14 in parallel, it is possible to improve the alignment accuracy even in the elliptical jacket type polarization-maintaining optical fiber. As shown in FIGS. 8B and 11B, this is because the light intensity distribution is substantially line-symmetrical with the center of the core as the axis of symmetry, and bright portions d and e, dark portions b and c, and further FIG. In b), in addition to these, by detecting the rotation angle of the optical fiber 16 that minimizes the difference in the light intensity of at least one of the sets of the dark parts f and g, the birefringent main axis 21
Alternatively, it is possible to align the birefringent main axis 22 in parallel with the optical axis 14. At that time, the vicinity of the center of the optical fiber where the bright parts d and e, the dark parts b and c, and the dark parts f and g were detected was within a range of a half width of 20 μm centered on the core, so this detection range was determined by the core 17 Even if the eccentricity of the clad 18 and the jacket 19 is taken into consideration, it is sufficient that the half width is 25 μm with respect to the center of the optical fiber, and by doing so, the time required for image processing can be shortened.

Although the elliptic core type polarization-maintaining optical fiber and the elliptic jacket type polarization-maintaining optical fiber have been described above as the optical fibers having the non-axisymmetric refractive index distribution, the present invention is not limited to these. , So-called PANDA type, Bow-Tie type, side pit type,
The polarization-maintaining optical fiber or the absolute single-polarization optical fiber or the multi-core optical fiber of which the refractive index distribution is not axially symmetric, such as the side tunnel type, can obtain the characteristic image processing result depending on the rotation angle. Is possible.

Although the optical fiber array of two cores is taken as an example, the number of cores is not limited to two, and the number of cores may be larger or one. The groove shape of the optical fiber holding member 3 may be U-shaped, arc-shaped, rectangular or polygonal.
The optical fiber array may have a structure in which optical fibers 25a and 25b having a non-axisymmetric refractive index distribution are fitted into two small holes 24a and 24b formed in the holding member 23 as shown in FIG. 12, The cross-sectional shape of the small holes 24a and 24b may be circular, elliptical or polygonal.

Here, in the case of an optical fiber array having two or more cores, the excessive connection loss with the optical waveguide due to the positional displacement is 0.1.
In order to make it equal to or less than dB, the diameter of at least the portion of the inscribed circle of the small holes 24a, 24b where the end face of the optical fiber is exposed is 2 μm larger than the outer diameter of the coating removed portion of the optical fiber.
It is desirable to be large in the range of m or less.

Further, as shown in FIG. 13, two optical waveguides 2
The optical waveguide 2 is formed on the substrate 27 on which 6a and 26b are arrayed.
Optical fibers and optical waveguides in which optical fibers 25a and 25b having a non-axisymmetric refractive index distribution are fitted in V-shaped grooves 29a and 29b arranged so that end surfaces 28a and 28b of 6a and 26b are exposed. Even at the joint portion of the above, the rotation angles of the optical fibers 25a and 25b can be aligned by the method of the present invention. In this case as well, as in the case of the optical fiber array, the number of cores is not limited to two, and may be more or more than one, and the groove shape formed on the substrate is U-shaped, arc-shaped, rectangular or polygonal. May be

As shown in FIG. 14, two optical waveguides 26 are provided.
An optical fiber 25a having a non-axisymmetric refractive index distribution is formed in a concave portion 30a, 30b having a circular cross section formed in an array so that the end faces 28a, 28b of the optical waveguide are exposed in a substrate 27 in which a, 26b are arrayed. Even in the coupling portion between the optical fiber and the optical waveguide in which 25b is fitted, the rotation angle of the optical fiber can be aligned by the method of the present invention. In this case as well, as in the case of the optical fiber array, the number of cores is not limited to two, and may be more or more than one, and the cross-sectional shape of the recesses 30a and 30b formed in the substrate 27 is elliptical, rectangular or It may be polygonal.

Here, in order to reduce the excess connection loss between the optical fiber and the optical waveguide due to the positional displacement to be 0.1 dB or less, the diameter of at least the portion where the optical fiber end face is located in the inscribed circles of the recesses 30a and 30b is set. It is desirable that the diameter is larger than the outer diameter of the coating removed portion of the optical fiber in the range of 2 μm or less.

[0045]

In summary, according to the present invention, the following excellent effects are exhibited.

An image of the optical fiber such as a light intensity distribution corresponding to the radial direction of the optical fiber image is obtained from the enlarged image of the optical fiber by photographing the optical fiber from the side with respect to the guided light propagation direction. Is obtained, the rotation angle with the central axis of the optical fiber as the rotation axis is measured from the distribution of the characteristics of the image, and the optical fiber is rotated to the desired angle based on the measurement result. An alignment method, an optical fiber fixing structure, and a coupling portion that can easily perform rotation direction alignment at a coupling portion between an optical fiber having an index distribution and an optical waveguide in a short time without propagating guided light to the optical fiber. Can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an outline of a main part of an apparatus to which an alignment method in a rotation direction of an optical fiber having a non-axisymmetric refractive index distribution of the present invention is applied.

FIG. 2 (a) is a schematic cross-sectional view when the angle formed by the optical axis of the imaging camera and the birefringent main axis in the major axis direction of the elliptical core is 0 °, and FIG. 2 (b) shows its light intensity distribution. FIG.

FIG. 3 (a) is a schematic cross-sectional view when the angle formed by the optical axis of the imaging camera and the major axis birefringent main axis of the elliptical core is 5 °, and FIG. 3 (b) shows its light intensity distribution. FIG.

FIG. 4A is a schematic cross-sectional view when an angle formed by the optical axis of the imaging camera and the birefringent main axis in the long axis direction of the elliptical core is 45 °, and FIG. 4B shows a light intensity distribution thereof. FIG.

5A is a schematic cross-sectional view when the angle formed by the optical axis of the image pickup camera and the birefringent main axis in the major axis direction of the elliptical core is 90 °, and FIG. 5B shows the light intensity distribution. FIG.

FIG. 6 is a diagram showing a light intensity distribution when the distance between the imaging camera and the optical fiber is set to be 5 μm larger than the distance where the maximum values l and r of the light intensity of the image on the outer peripheral portion of the optical fiber are maximum. is there.

FIG. 7 is a diagram showing a light intensity distribution when the distance between the imaging camera and the optical fiber is set to be 10 μm larger than the distance where the maximum values l and r of the light intensity of the image on the outer peripheral portion of the optical fiber are maximum. is there.

FIG. 8A is a schematic cross-sectional view when the angle formed by the optical axis of the imaging camera and the birefringent main axis in the major axis direction of the elliptical jacket of the elliptical jacket-type polarization-maintaining optical fiber is 0 °; (B) is a figure which shows the light intensity distribution.

9A is a schematic cross-sectional view when the optical axis of the imaging camera and the birefringent main axis in the major axis direction of the elliptical jacket of the elliptical jacket-type polarization-maintaining optical fiber is 5 °, FIG. (B) is a figure which shows the light intensity distribution.

FIG. 10A is a schematic cross-sectional view when the optical axis of the imaging camera and the birefringent main axis in the major axis direction of the elliptical jacket of the elliptical jacket-type polarization-maintaining optical fiber are 45 °; (B) is a figure which shows the light intensity distribution.

FIG. 11A is a schematic cross-sectional view when the angle formed by the optical axis of the imaging camera and the birefringent main axis in the major axis direction of the elliptical jacket of the elliptical jacket-type polarization-maintaining optical fiber is 90 °; (B) is a figure which shows the light intensity distribution.

FIG. 12 is a view showing a modified example of the holding member shown in FIG.

FIG. 13 shows a coupling portion between an optical fiber and an optical waveguide, which is formed by fitting an optical fiber into a V-shaped groove formed in a substrate on which the optical waveguide is formed so that an end face of the optical waveguide is exposed. FIG.

FIG. 14 shows a coupling portion between an optical fiber and an optical waveguide, which is formed by inserting an optical fiber into a concave portion having a circular cross section formed on a substrate on which the optical waveguide is formed so that an end face of the optical waveguide is exposed. It is a figure.

FIG. 15 is a schematic side view of a system for aligning the birefringent principal axes of a polarization-maintaining optical fiber by a conventional method.

FIG. 16 is a cross-sectional view showing a birefringent main axis of an elliptic core type optical fiber.

FIG. 17 is a transverse sectional view showing a birefringent main axis of an elliptical jacket type optical fiber.

[Explanation of symbols]

1a, 1b Optical fiber 2a, 2b Tip part 2c, 2d Rear end part 6 Image acquisition means (imaging camera) 7 Image processing device 8 Illumination light source 9a, 9b Optical fiber rotating member (optical fiber rotating mechanism)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Kajioka 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture Hitachi Cable Co., Ltd. Hidaka Plant (72) Inventor Mori Ichimura Komaki City, Aichi Prefecture Address 122 Suntech Co., Ltd. (72) Inventor Tomohiro Murakami 122, Kamishima, Komaki, Aichi Prefecture Suntech Co., Ltd.

Claims (27)

[Claims] 1. An alignment method in a coupling portion between an optical fiber having a non-axisymmetric refractive index distribution and an optical waveguide, wherein the optical fiber is photographed from a side with respect to a guided light propagation direction by an image acquisition means. Obtain a magnified image of the fiber, find the image feature distribution corresponding to the radial position of the optical fiber image from the obtained magnified image, and rotate from the feature distribution of the image with the central axis of the optical fiber as the rotation axis. Of the optical fiber having a non-axisymmetric refractive index distribution, characterized in that the direction of the optical fiber is adjusted by the optical fiber rotating member based on the measurement result. Alignment method in the department. 2. The alignment method at a coupling portion between an optical fiber having a non-axisymmetric refractive index distribution and an optical waveguide according to claim 1, wherein the image acquisition means is an imaging camera. 3. An optical fiber and an optical waveguide having a non-axisymmetric refractive index distribution according to claim 1, wherein the resolution limited by the image input means arranged on the image plane of the image acquisition means is 1.6 μm or less. Alignment method at the joint with and. 4. The optical fiber and the illumination light source are arranged substantially on the optical axis of the image acquisition means so as to be sandwiched between the image acquisition means and the illumination light source with respect to the optical fiber. Illuminating light from the direction across the core,
The alignment method at a coupling portion between an optical fiber having a non-axisymmetric refractive index distribution and an optical waveguide according to claim 1, wherein an image of the optical fiber is acquired by transmitting light transmitted through the optical fiber. 5. The alignment at the coupling portion between the optical fiber having the non-axisymmetric refractive index distribution and the optical waveguide according to claim 1, wherein the protective coating of the portion of the optical fiber imaged by the image acquisition means is removed. Method. 6. The acquisition of a magnified image of the optical fiber and the extraction of the distribution of the image feature are repeated from various rotation directions with the central axis of the optical fiber as a substantially rotation axis, and based on the distribution of the image feature obtained in advance. By detecting the direction of rotation of the optical fiber, the predetermined axis on the cross section of the optical fiber is once aligned in parallel with the optical axis of the image acquisition means, and then the optical fiber or the optical fiber rotating member is rotated. Let
The alignment method in a coupling portion between an optical fiber having a non-axisymmetric refractive index distribution and an optical waveguide according to claim 1, wherein the direction of the specific axis is adjusted. 7. Rotation showing a predetermined image feature distribution by repeating acquisition of an enlarged image of the optical fiber and extraction of image feature distribution from various rotation angles with the central axis of the optical fiber as a substantially rotation axis. When the angle of a predetermined specific axis on the cross section of the optical fiber is adjusted to be parallel to the optical axis of the image acquisition means by detecting the angle, the angle of the specific axis is set to the optical medium on which the optical waveguide is formed or The light having a non-axisymmetric refractive index distribution according to claim 1, wherein the orientation of the optical axis of the image acquisition means with respect to the optical medium or the optical fiber holding member is predetermined so as to face a desired direction with respect to the optical fiber holding member. An alignment method at a coupling portion between a fiber and an optical waveguide. 8. The optical fiber is an elliptical core type optical fiber, and the characteristic distribution of the image is a light intensity distribution.
The alignment method at a coupling portion between an optical fiber having an axisymmetric refractive index distribution and an optical waveguide according to claim 1, wherein the distance between the image acquisition means and the optical fiber is adjusted with a resolution of not more than μm. 9. The optical fiber is an elliptical core type optical fiber, the characteristic distribution of the image is a light intensity distribution, and the specific axis is a major axis of the elliptical core, and the optical fiber central portion is provided. Alternatively, the long axis of the core is aligned in parallel with the optical axis of the image acquisition means by detecting a direction in which the maximum value of the light intensity in the vicinity thereof is substantially maximum or the minimum value thereof is substantially minimum. An alignment method in a coupling portion between an optical fiber having a non-axisymmetric refractive index distribution described and an optical waveguide. 10. The optical fiber is an elliptical core type optical fiber, and the characteristic distribution of the image is a light intensity distribution,
The specific axis is the major axis of the elliptical core, and by detecting the direction in which the difference between the maximum value and the minimum value of the light intensity at the central portion of the optical fiber or in the vicinity thereof is maximized, The alignment method in a coupling portion between an optical fiber having a non-axisymmetric refractive index distribution and an optical waveguide according to claim 6 or 7, wherein the major axis of the core is aligned parallel to the optical axis of the image acquisition means. 11. The optical fiber is an elliptical core type optical fiber, and the characteristic distribution of the image is a light intensity distribution,
The specific axis is the major axis of the elliptical core, the maximum value or the minimum value of the light intensity at the center of the optical fiber or in the vicinity thereof is substantially the minimum, and the distribution of the image features is the center of the core. The difference between the minimum value or the maximum value of at least one pair of light intensities which is substantially line-symmetrical as the axis of symmetry and which appears in the position of substantially line-symmetrical with the center axis of the core as the axis of symmetry near the center of the optical fiber is minimized. By detecting the orientation such that
8. The alignment method in a coupling portion between an optical fiber having a non-axisymmetric refractive index distribution and an optical waveguide according to claim 6, wherein the major axis of the core is aligned parallel to the optical axis of the image acquisition means. 12. The optical fiber has a central portion and its vicinity for detecting a maximum value and a minimum value of the light intensity in order to align the direction of the major axis of the elliptical core in parallel with the optical axis of the image acquisition means. The alignment method in the coupling portion between the optical fiber having the non-axisymmetric refractive index distribution and the optical waveguide according to any one of claims 9 to 11, wherein the half width is within a range of 5 µm with respect to the center of the. 13. The optical fiber is an elliptical jacket type optical fiber, the characteristic distribution of the image is a light intensity distribution, and the distance between the image acquisition means and the optical fiber is in the outer peripheral portion excluding the vicinity of the core of the optical fiber. 2. The non-axisymmetric refractive index distribution according to claim 1, wherein the non-axisymmetric refractive index distribution is within a range between a position where the maximum value of the light intensity of the image is maximum and a position where the image acquisition means and the optical fiber are separated from the position by about 50 μm. An alignment method at a coupling portion between an optical fiber and an optical waveguide. 14. The optical fiber is an elliptical jacket type optical fiber, and the characteristic distribution of the image is a light intensity distribution, and the specific axis is either the major axis or the minor axis of the elliptical jacket. , The image feature distribution is substantially line-symmetrical with the central axis of the core as a symmetry axis, and further, in the vicinity of the center of the optical fiber, at least a bright part or a dark part appearing at a position of substantially linear symmetry with the central axis of the core as a symmetry axis. One of the major axis and the minor axis of the elliptical jacket is set as the optical axis of the imaging acquisition means by detecting the direction of the rotation direction of the optical fiber that minimizes the difference in the light intensity between the pair of bright and dark portions. The alignment method at a coupling portion between an optical fiber having a non-axisymmetric refractive index profile and an optical waveguide according to claim 6 or 7, which are aligned in parallel. 15. The center of the core in the image feature distribution when the specific axis is the major axis of the elliptical jacket and the orientation of the major axis is aligned with the optical axis of the image acquisition means. It has one set of bright parts at positions that are substantially line-symmetrical as an axis of symmetry, and has one set of dark parts at positions that are substantially line-symmetrically on the inner circumference side of the optical part of the bright part and where the central axis of the core is the axis of symmetry. 15. An alignment method in a coupling portion between an optical fiber having a non-axisymmetric refractive index distribution and an optical waveguide according to claim 14, wherein there is no remarkable dark portion having a light intensity lower than the outer peripheral side in the vicinity of the outer peripheral side of the bright portion. . 16. The central axis of the core in the distribution of image features when the specific axis is a minor axis of an elliptical jacket and the orientation of the minor axis is aligned with the optical axis of the image acquisition means. Has a pair of bright parts at positions substantially linearly symmetric with respect to the axis of symmetry, and has a pair of dark parts at positions substantially linearly symmetric with respect to the central axis of the core on the inner circumference side of the optical fiber of the bright parts. In addition, in the vicinity of the outer peripheral side of the bright portion and at a position substantially linearly symmetric with the central axis of the core as the axis of symmetry, a remarkable dark portion whose light intensity is lower than that of the outer peripheral side is
The alignment method in a coupling portion between an optical fiber having a non-axisymmetric refractive index distribution and an optical waveguide according to claim 14, which has a set. 17. The central axis of the optical fiber is located near the central portion of the optical fiber where a bright portion and a dark portion for aligning the directions of the major axis and the minor axis of the elliptical jacket in parallel with the optical axis of the image acquiring means are detected. 15. The alignment method in the coupling portion between the optical fiber having the non-axisymmetric refractive index profile and the optical waveguide according to claim 14, wherein the half width is within the range of about 25 μm. 18. An optical fiber fixing structure including at least one optical fiber having a non-axisymmetric refractive index distribution and a holding member for holding the optical fiber, wherein the optical fiber is guided by an image acquisition means with respect to a guided light propagation direction. Obtain a magnified image of the optical fiber taken from the side, obtain the distribution of the image features corresponding to the radial position of the optical fiber image from the obtained enlarged image, from the distribution of the features of the image of the optical fiber An optical fiber fixing structure characterized in that the direction of rotation is measured with a central axis as a rotation axis, and the direction of rotation of the optical fiber is adjusted by an optical fiber rotating member based on the measurement result. 19. The optical fiber fixing structure according to claim 18, wherein the optical fibers are fitted and arranged in at least one groove formed and arranged in the optical fiber holding member holding the optical fiber. 20. The cross-sectional shape of the groove is V-shaped, U-shaped,
20. The optical fiber fixing structure according to claim 19, which has an arc shape, a rectangular shape, or a polygonal shape. 21. The optical fiber fixing structure according to claim 18, wherein an optical fiber is fitted and arranged in at least one small hole arranged and formed in the optical fiber holding member. 22. The cross-sectional shape of the small hole is circular, elliptical or polygonal, and the diameter of at least the portion of the inscribed circle where the end face of the optical fiber is exposed is larger than the outer diameter of the coating removed portion of the optical fiber. 22. The optical fiber fixing structure according to claim 21, which is also large in the range of 2 μm or less. 23. In a coupling section in which at least one optical fiber having a non-axisymmetric refractive index distribution and at least one optical waveguide are coupled, the optical fiber is laterally arranged with respect to a guided light propagation direction by an image acquisition means. Obtain a magnified image of the optical fiber by shooting, obtain the distribution of the image features corresponding to the radial position of the optical fiber image from the obtained enlarged image, the central axis of the optical fiber from the distribution of the feature of the image A coupling part characterized in that the direction of rotation in the direction of rotation about the axis of rotation is measured, and the direction of rotation of the optical fiber is adjusted by the optical fiber rotating member based on the measurement result. 24. The coupling section according to claim 23, wherein an optical fiber is fitted in a groove formed in an optical medium including the optical waveguide so that an end face of the optical waveguide is exposed. 25. The coupling part according to claim 24, wherein the shape of the groove is V-shaped, U-shaped, arc-shaped, rectangular or polygonal. 26. The coupling section according to claim 23, wherein an optical fiber is fitted in a recess formed in an optical medium including the optical waveguide, the end surface of the optical waveguide being exposed at the bottom thereof. 27. The cross-sectional shape of the recess is circular, elliptical, rectangular or polygonal, and the diameter of at least the portion of the inscribed circle where the end face of the optical fiber is located is larger than the outer diameter of the optical fiber. 27. The joint according to claim 26, which is large in a range of 2 μm or less.