Method of aligning optical fiber to optical fiber or optical fiber to optical element at junction and optical fiber array

What is claimed is:

1. An optical fiber holding structure having a holding member for holding at least one optical fiber having an axially asymmetric refractive index distribution, wherein said optical fiber is viewed from a direction lateral to the propagating direction of guided light in the optical fiber using an image obtaining means to obtain an enlarged image of said optical fiber, a distribution of image characteristics corresponding to different radial positions of the optical fiber image is obtained from the obtained enlarged image, the image obtaining means is adjusted so that the image characteristics at outer peripheral portions of the optical fiber are maximized in the distribution of image characteristics, an orientation of the rotational direction around the center axis of the optical fiber serving as a rotational axis is measured from the distribution of the image characteristics after said adjusting, and the orientation of the rotational direction of the optical fiber is aligned with an optical fiber rotating member based on the measured result.

2. An arrangement for orienting a junction coupling at least one optical fiber having an axially asymmetric refractive index distribution and at least one optical wave-guide, comprising image obtaining means for viewing said optical fiber from a direction lateral to the propagating direction of guided light in the optical fiber to obtain an enlarged image of said optical fiber, means for obtaining a distribution of image characteristics corresponding to different radial positions of the optical fiber image from the obtained enlarged image, the image obtaining means being positioned with respect to the optical fiber so that the image characteristics at outer peripheral portions of the optical fiber are maximized in said distribution of image characteristics, means for measuring an orientation of the rotational direction around the center axis of the optical fiber serving as a rotational axis from the distribution of the image characteristics, and means for aligning the orientation of the rotational direction of the optical fiber using an optical fiber rotating member based on a measured result produced by said measuring means.

3. An arrangement for orienting an optical fiber array having a plurality of optical fibers and an optical fiber holding member, comprising:

image obtaining means for obtaining an enlarged lateral image of each of the optical fibers, means for obtaining a distribution of image characteristics corresponding to different radial positions of each optical fiber image from the obtained enlarged images, the image obtaining means being positioned with respect to said optical fibers so that the image characteristics at outer peripheral portions of each optical fiber are maximized in each distribution of the image characteristics, means for measuring an axial displacement of the core center with respect to the center of an optical fiber from a distribution of image characteristics after said adjusting, and means for adjusting the pitches of cores or making them uniform by aligning said axial displacement with respect to the optical fiber holding member using an optical fiber rotating mechanism.

4. An arrangement for an optical fiber array according to claim 3, wherein all of said optical fibers are manufactured by continuously cutting one string of optical fiber, and the alignment of the orientation of the rotational direction of the optical fiber is performed by said adjusting means so that the axial displacement is directed to a desired direction.

5. A method of aligning optical fibers having an axially asymmetric refractive index distribution or of aligning an optical fiber to an optical element in a junction, the method comprising the steps of:

viewing said optical fiber from a direction lateral to the propagating direction of guided light in the optical fiber using an image obtaining means to obtain an enlarged image of said optical fiber;

obtaining a distribution of image characteristics corresponding to radial positions of the optical fiber image from the obtained enlarged image;

adjusting the image obtaining means so that the image characteristics at outer peripheral portions of the optical fiber are maximized in said distribution of image characteristics;

measuring an orientation of the rotational direction around the center axis of the optical fiber from said distribution of image characteristics after said adjusting; and

aligning the orientation of the rotational direction of the optical fiber using an optical fiber rotating member based on the measured result.

6. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to claim 5, wherein the direction of a preset specific axis on the cross-sectional surface of the optical fiber is aligned by rotating the optical fiber after said specific axis is once aligned in parallel to the optical axis of the image obtaining means by repeatedly obtaining enlarged images of the optical fiber from various rotational directions around the center axis of the optical fiber, extracting the distributions of image characteristics for each image and, at the same time, detecting the orientation of the rotational direction of the optical fiber based on preset distributions of image characteristics.

7. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to claim 5, wherein the direction of the optical axis of said image obtaining means to an optical element, including at least one of an optical wave-guide or an optical fiber holding member, is determined, so that the direction of a preset specific axis on the cross-sectional surface of the optical fiber is oriented in a desired direction with respect to the optical medium or the optical fiber holding member when the direction of said specific axis is aligned in parallel to the optical axis of the image obtaining means, by repeatedly obtaining enlarged images of the optical fiber from various rotational directions around the center axis of the optical fiber, extracting the distributions of image characteristics for each image and, at the same time, detecting the orientation of the rotational direction of the optical fiber based on preset distributions of image characteristics.

8. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to any one of claim 6 or claim 7, wherein said optical fiber is an elliptical core type optical fiber, said distribution of the image characteristics is a distribution of light intensity, said specific axis is the major axis of the elliptical core, the major axis of the core being aligned in parallel to the optical axis of the image obtaining means by detecting a direction in which the upward peak value of the light intensity is nearly maximized or the downward peak value of the light intensity is nearly minimized in the middle portion of the optical fiber and its vicinity.

9. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to any one of claim 6 or claim 7, wherein said optical fiber is an elliptical core type optical fiber, said distribution of the image characteristics is a distribution of light intensity, said specific axis is the major axis of the elliptical core, the major axis of the core being aligned in parallel to the optical axis of the image obtaining means by detecting a direction in which the difference between the upward peak value and the downward peak value of the light intensities in the middle portion of the optical fiber and its vicinity is maximized.

10. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to any one of claim 6 or claim 7, wherein said optical fiber is an elliptical core type optical fiber, said distribution of the image characteristics is a distribution of light intensity, and said specific axis is the major axis of the elliptical core, the major axis of the core being aligned in parallel to the optical axis of the image obtaining means by detecting a direction in which the upward peak value of the light intensity is nearly maximized or the downward peak value of the light intensity is nearly minimized in the middle portion of the optical fiber and its vicinity, the distribution of the image characteristic being nearly symmetrical to the center of the core forming an axis of symmetry, the difference in at least one pair of downward peak values or upward peak values of light intensities appearing at the nearly symmetrical positions with respect to the center axis of the core in the vicinity of the central portion of the optical fiber being minimized.

11. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to any one of claim 6 or claim 7, wherein said optical fiber is an elliptical jacket type optical fiber, said distribution of the image characteristics is a distribution of light intensity, said specific axis is any one of the major axis and the minor axis of the elliptical jacket of the optical fiber, the distribution of the image characteristics are nearly symmetrical with respect to the center axis of the core serving as an axis of symmetry, any one of the major axis and the minor axis of said elliptical jacket being aligned in parallel to the optical axis of the image obtaining means by detecting a rotational direction of the optical fiber in which the difference in at least one pair of bright portions or dark portions of light intensities, among bright portions and dark portions appearing at nearly symmetrical positions with respect to the center axis of the core in the vicinity of the central portion of the optical fiber, is minimized.

12. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to claim 11, wherein said specific axis is the minor axis of an elliptical jacket, and when the direction of said minor axis is aligned in parallel to the optical axis of said image obtaining means, the distribution of the image characteristics includes a pair of bright portions at positions nearly symmetrical to the center of the core serving as an axis of symmetry, a pair of dark portions in the inner sides of the bright portions of the optical fiber and at positions nearly symmetrical with respect to the center of the core and a pair of clearly dark portions in the vicinity of the outer sides of the bright portions and at positions nearly symmetrical with respect to the center axis of the core having a lower light intensity than that in the outer peripheral sides.

13. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to claim 11, wherein said specific axis is the major axis of an elliptical jacket of the optical fiber, and when the direction of said major axis is aligned in parallel to the optical axis of said image obtaining means, the distribution of image characteristics includes a pair of bright portions at positions nearly symmetrical with respect to the center of the core serving as an axis of symmetry, a pair of dark portions in the inner sides of the bright portions of the optical fiber and at positions nearly symmetrical with respect to the center of the core and, no clearly dark portions in the vicinity of the outer sides of the bright portions having a lower light intensity than portions in the outer peripheral sides.

14. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to claim 5, wherein said image obtaining means is an image pick-up camera.

15. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to claim 5, wherein the resolution limited by an image input means placed at the image forming plane of said image obtaining means is smaller than 1.6 .mu.m.

16. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to claim 5, wherein said optical fiber and a light source are arranged substantially in a plane through the optical axis of said image obtaining means so as to sandwich said optical fiber between said image obtaining means and said light source, light being radiated from a lateral side of said optical fiber in a direction crossing the core of the optical fiber, an image of the optical fiber being obtained with transmitted light passing through the optical fiber.

17. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to claim 5, wherein said optical fiber is an elliptical core type optical fiber, said distribution of image characteristics is a distribution of light intensity, and the distance between the image obtaining means and the optical fiber is adjusted with a resolution smaller than 5 .mu.m.

18. A method of aligning an optical fiber having an axially asymmetric refractive index distribution according to claim 5, wherein said optical fiber is an elliptical jacket type optical fiber, said distribution of the image characteristics is a distribution of light intensity, the distance between the image obtaining means and the optical fiber is within a range between a position where a upward peak value of the light intensity of the image in the periphery of the optical fiber, excluding the vicinity of the core, is maximized and a position where the image obtaining means and the optical fiber are spaced from said position nearly by 50 .mu.m.

19. A method of aligning orientations of the rotational direction of optical fibers in an optical fiber array having a plurality of optical fibers and an optical fiber holding member, the method comprising the steps of:

obtaining an enlarged image of a lateral view of each of the optical fibers using an image obtaining means;

obtaining a distribution of image characteristics corresponding to different radial positions of the optical fiber images from each of the obtained enlarged images;

adjusting the image obtaining means so that image characteristics at outer peripheral portions of each optical fiber are maximized in each distribution of image characteristics;

measuring an axial displacement of the core center to the center of the optical fiber from said distribution of image characteristics after said adjusting; and

aligning the axial displacement with respect to the optical fiber holding member using an optical fiber rotating mechanism.

20. A method of aligning orientations of the rotational direction of optical fibers in an optical fiber array having a plurality of optical fibers and an optical fiber holding member, the method comprising the steps of:

obtaining an enlarged image of a lateral view of each of the optical fibers using an image obtaining means;

obtaining a distribution of image characteristics corresponding to different radial positions of the optical fiber images from each of the obtained enlarged images;

measuring an axial displacement of the core center to the center of the optical fiber from said distribution of image characteristics; and

aligning the axial displacement with respect to the optical fiber holding member using an optical fiber rotating mechanism.

21. A method of aligning orientations of the rotational direction of optical fibers in an optical fiber array having a plurality of optical fibers and an optical fiber holding member, the method comprising the steps of:

obtaining enlarged images of a lateral view of at least one optical fiber using an image obtaining means;

obtaining a respective distribution of image characteristics corresponding to each of a plurality of radial positions of the optical fiber image from the obtained enlarged images;

adjusting the image obtaining means so that image characteristics at outer peripheral portions of the optical fiber are maximized in said distribution of image characteristics;

measuring an axial displacement of the core center of the optical fiber to the center of the optical fiber for said optical fiber using at least two of said distributions of image characteristics of the optical fiber with varying viewing angles for each of the optical fibers after said adjusting; and

aligning said axial displacement with respect to the optical fiber holding member using an optical fiber rotating mechanism by rotating the optical fiber with respect to the holding member.

22. A method of aligning orientations of the rotational direction of optical fibers in an optical fiber array having a plurality of optical fibers having an axially asymmetric refractive index distribution and an optical fiber holding member, the method comprising the steps of:

obtaining enlarged images of an optical fiber in various rotational directions with respect to the center axis of the optical fiber from a direction lateral to the propagating direction of guided wave in the optical fiber for each of the optical fibers using an image obtaining means;

obtaining a distribution of image characteristics corresponding to the radial positions of the optical fiber image from the obtained enlarged images;

aligning a predetermined specific axis on the cross-sectional plane of the optical fiber to the optical axes of the image obtaining means by detecting an orientation of the rotational direction of the optical fiber which will exhibit a predetermined distribution of image characteristics;

measuring an axial displacement of the core center with respect to the center of the optical fiber from the distribution of the image characteristics; and then

aligning the orientation of the specific axis and the axial displacement with respect to the optical fiber holding member for each of the optical fibers by rotating the optical fiber or the holding member for holding the optical fiber.

23. A method of aligning orientations of the rotational direction of optical fibers in an optical fiber array having a plurality of optical fibers having an axially asymmetric refractive index distribution and an optical fiber holding member, the method comprising the steps of:

obtaining enlarged images of an optical fiber in various rotational directions with respect to the center axis of the optical fiber from a direction lateral to the propagating direction of guided wave in the optical fiber for each of the optical fibers using an image obtaining means;

obtaining a distribution of image characteristics corresponding to the radial positions of the optical fiber image from the obtained enlarged images;

aligning a predetermined specific axis on the cross sectional plane of the optical fiber to the optical axis of the image obtaining means by detecting an orientation of the rotational direction of the optical fiber which will exhibit a predetermined distribution of image characteristics;

measuring an axial displacement of the core center with respect to the center of the optical fiber from the distribution of the image characteristics; and

aligning or presetting the optical axis of the image obtaining means to the holding member for each of the optical fibers so that the orientation of the specific axis of each of the optical fibers is directed in a desired direction with respect to the optical fiber holding member when the specific axes of all the optical fibers are aligned in parallel to the optical axis of the image obtaining means by rotating the optical fibers by 180.degree. to positions of axial displacement which do not agree with the desired positions or with the positions of axial displacement of more than a half-number of the optical fibers.

24. A method of aligning orientations of the rotational direction of optical fibers in an optical fiber array according to any one of claim 19 to claim 23, wherein said distribution of image characteristics is a distribution of light intensity, and the position of axial displacement is measured from the distance between a bright portion or dark portion corresponding to the outer periphery of the optical fiber and a bright portion or dark portion corresponding to the core or the center of the core.

25. A method of aligning orientations of the rotational direction of optical fibers in an optical fiber array according to any one of claim 22 and claim 23, wherein said optical fiber is a polarization-maintaining optical fiber, and said specific axis is a main axis of birefringence of the optical fiber.

26. A method of aligning orientations of the rotational direction of optical fibers in an optical fiber array according to claim 25, wherein said optical fiber is an elliptical core type polarization-maintaining optical fiber.

27. A method of aligning orientations of the rotational direction of optical fibers in an optical fiber array according to claim 25, wherein said optical fiber is an elliptical jacket type polarization-maintaining optical fiber.

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BACKGROUND OF THE INVENTION

The present invention relates to a method of aligning optical fibers and to an optical fiber array used in a junction of an optical fiber to an optical fiber, or in a junction of an optical fiber to an optical element used in an optical waveguide, such as an optical fiber gyroscope, an optical modulator, and an optical switch.

As an example of a junction between an optical waveguide and an optical fiber with axially asymmetric refractive index distribution, there is an optical fiber array using polarization-maintaining fibers. The method of aligning the angle of the rotating direction of the polarization-maintaining optical fiber, that is, the method of aligning the main axis of birefringence, involves aligning the angle of an optical fiber to an optical fiber holding member using an angle of linear polarized light at the output port of the optical fiber obtained by propagating linear polarized light having the oscillatory direction of its electric field parallel to the main axis of birefringence in the optical fiber.

For example, as seen in FIG. 18, the rays of light emitted from a semiconductor laser 31 are formed into nearly parallel rays of light using a first lens 32, and the parallel rays are formed into linearly polarized light using a polarizer 33. Then, the polarized light is concentrated using a second lens 34 adjacent one end of a polarization-maintaining optical fiber 36 supported by a holder 35, rotatable around the center axis of the core, so the light is propagated inside the optical fiber. On the other end, the optical fiber radiating the propagated light is mounted in a V-shaped groove (not shown) in an optical fiber holding member 37 after passing through a holder 35, which is rotatable around the center axis of the core, and a cover member 38 is placed on the optical fiber holding member 37.

Since the polarization-maintaining optical fiber has two main axes of birefringence intersecting at a right angle, it cannot be determined which main axis the oscillatory direction of the linear polarized light propagating inside the optical fiber is parallel to unless the approximate angle of the main axis of birefringence is known.

For this reason, when the alignment of the angle of the main axis of birefringence is performed using only the oscillatory direction of the electric field of the linear polarized light radiated out of the optical fiber, there is a possibility of selecting a different angle from the desired angle by 90.degree.. Therefore, in any alignment procedure using the angle of linear polarized light, it is necessary to align the main axis of birefringence as nearly as possible with the desired direction and to limit the range of rotation of the output port of the optical fiber within the error range of this alignment.

In a case where an elliptical core optical fiber 42 is used as the polarization-maintaining optical fiber 36, the major axis 44 and the minor axis 45 of an elliptical core 43 become the main axes of birefringence, as shown in FIG. 19. Therefore, the main axis of birefringence can be set nearly to the desired direction by rotating the output port of the optical fiber mounted on a holding member, while a near-field pattern of the output fight from the optical fiber is observed using a CCD camera (not shown) or a far-field pattern of the output light projected on a screen (not shown) is observed. In a case where an elliptical jacket type polarization-maintaining optical fiber 46 is used as the polarization-maintaining optical fiber 36, the major axis 48 and the minor axis 49 of an elliptical jacket 47 become the main axes of birefringence, as shown in FIG. 20. Therefore, the main axis of birefringence can be set to nearly the desired direction by etching the output port of the optical fiber mounted on a holding member using an aqueous solution of hydro-fluoride to form a step between the jacket portion and the other portions, so that the shape of the jacket portion is observable, and by rotating the output port of the optical fiber, while the enlarged image of the optical fiber is observed using a CCD camera.

Next, the output light is collected by a photo-receiver 41 through a third lens 39 and an analyzer 40, and the rotational position of the input port which results in minimum polarization cross-talk is obtained by rotating the input port of the optical fiber and the analyzer 40, while the output of the photo-receiver 41 is monitored. When one of the main axes of birefringence of the optical fiber at the input port agrees with the oscillatory direction of the electric field, the oscillatory direction of the electric field of the output light from the optical fiber becomes linearly polarized light parallel to one of the two main axes of birefringence. Then, the direction of the analyzer 40 is set to the desired direction of the main axis of birefringence, and the main axis of birefringence is aligned with a rotational direction where the output of the photo-receiver 41 becomes a maximum or minimum value by rotating the output port of the optical fiber within the error range of the alignment using the near-field pattern or the far-field pattern in the case of the elliptical core optical fiber, or within the error range of the alignment using the enlarged image of the port in the case of the elliptical jacket type polarization-maintaining optical fiber, for example, within .+-.10.degree..

In the aforementioned conventional method of aligning the main axis of birefringence of a polarization-maintaining optical fiber 36 to a desired direction, it is required to perform various kinds of processing other than rotating the optical fiber 36 mounted on the holding member 37 around the center axis of the core as the approximate rotational axis.

It is required to form flat end planes in the both ends of the optical fiber for input and output coupling of light. The alignment is required to couple the light which passes through the first lens 32, the polarizer 33 and the second lens 34 to the optical fiber 36. The alignment of the rotational direction of the input port of the optical fiber 36 is required to change the fight propagating inside the optical fiber 36 into linearly polarized light having the oscillatory direction of the electrical field parallel to the main axis of birefringence. This means that, in order to perform an alignment of the angle of the main axis of birefringence of the output port of the polarization-maintaining optical fiber mounted on the holding member 37, it is required to perform alignment of the angle of the main axis of birefringence of the input port.

On the other hand, in order to align the main axis of birefringence to the desired direction in advance, it is required to observe the near-field pattern of the output light from the optical fiber 36, in the case of using the elliptical core optical fiber 42 as the polarization-maintaining optical fiber 36, or the enlarged image of the surface of the output port of the optical fiber, in the case of using the elliptical jacket type polarization-maintaining optical fiber 46.

As a result, every time an optical fiber array using a polarization-maintaining optical fiber is produced, it is required to move and rearrange the CCD camera or the screen, the third lens 39, the analyzer 40 and the photo-receiver 41. In addition to these, in a case of using the elliptical jacket type polarization-maintaining optical fiber 46, it is also required to etch the end surface using an aqueous solution of hydro-fluoride. Since directing the main axis of birefringence of the polarization-maintaining optical fiber to a desired direction requires various kinds of processing, as described above, and also requires much time, it has been difficult to decrease the number of man-hours or the time needed to produce an optical fiber array using a polarization-maintaining optical fiber.

Further, if an optical fiber array is produced using plural optical fibers having an axial displacement of 0.5 .mu.m, the error in the distance between the cores of adjacent optical fibers to a desired pitch becomes 1 .mu.m at a maximum. Therefore, it is difficult to decrease the coupling loss due to positional displacement in the junction of the optical fiber array and a plurality of optical waveguides formed in an array.

Since the mode field size of the propagating fight inside an optical waveguide and an optical fiber becomes small as the wavelength of the light propagating inside the optical fiber is short, the increasing amount of coupling loss for the same amount of displacement becomes large. Therefore, in a system using short wavelength light, such as a photo-sensor, it is important to decrease the error due to axial displacement of the core in the core pitch of the adjacent optical fibers in an optical fiber array. Further, in a case of using a low cost elliptical core type polarization-maintaining optical fiber, since the mold field size in the direction of the minor axis of the elliptical core is small in comparison to that in the major axis, it is important to produce agreement between the axial positional displacements in the direction of the minor axis for all of the optical fibers composing the optical fiber array.

However, in the conventional method of aligning the rotational direction of a polarization-maintaining optical fiber, it has been impossible to perform alignment considering the axial positional displacement, since it is required to perform various kinds of processing as described above, and the alignment takes a long time to perform.

On the other hand, a method is described in Japanese Patent Application Laid-Open No. 1-147506 (1989), in which a constant-polarization optical fiber is observed with direct view method using a TV camera, and coarse alignment of the core in the .theta.-direction is performed by rotating an optical fiber in the .theta.-direction until the images of the optical fiber in the right and left sides are observed to be the same. A brightness profile of the image of the optical fiber obtained by this method is as shown in FIG. 27. The brightness profile varies depending on the direction of the stress applying portion. Approximate aligning of the angle of the optical fiber is performed by utilizing the changes in the brightness of the upward peak value or the downward peak value in the middle portion or in the portions a at both outer sides of the middle portion b to e.

In this method of utilizing a brightness profile, the brightest portion, which is brighter than portions of the outer peripheral surface, always appears in a middle portion between portions a and e in the optical fiber.

According to an experiment conducted by the inventors, using the above method, identification of the points a to e cannot accurately be performed, because of the difference between the upward peak value and the downward peak value of the brightness in the middle portion a or in the portions at both outer sides of the middle portion b to e. Therefore, the above method may be used in practice only for performing coarse aligning of the core of an optical fiber.

SUMMARY OF THE INVENTION

The first object of the present invention is to solve the above problems and to provide a method and an optical fiber holding structure and a junction which are capable of aligning the rotational direction in a junction between an optical fiber, having an axially asymmetric refractive index distribution, and an optical waveguide easily in a short time.

The second object of the present invention is to solve the above problems and to provide a method and an optical fiber array, which are capable of aligning the orientation of the rotational direction of an optical fiber in an optical fiber array in consideration of axial displacement.

A third object of the present invention is to provide an alignment method which is capable of identifying points of a upward peak value and a downward peak value in a brightness profile with a high accuracy and which is capable of aligning an angle of an optical fiber with a high accuracy.

In order to attain the first object and the third object described above, the present invention is characterized by a method of effecting alignment between optical fibers having an axially asymmetric refractive index distribution or between an optical fiber and an optical element in a junction, the method comprising the steps of viewing the optical fiber from a direction lateral to the propagating direction of light in the fiber using an image obtaining means to obtain an enlarged image of the optical fiber, obtaining a distribution of the image characteristics corresponding to the radial positions of the optical fiber image from the obtained enlarged image, adjusting the image obtaining means so that the image characteristics at outer peripheral portions of the optical fiber are maximized in the distribution of the image characteristics, measuring an orientation of the rotational direction around the center axis of the optical fiber from the distribution of the image characteristic after said adjusting, and aligning the orientation of the rotational direction of the optical fiber with an optical fiber rotating member based on the measured result.

According to the present invention, by viewing an optical fiber from a direction lateral to the propagating direction of guided light using an image obtaining means, an enlarged image of the optical fiber can be obtained. By performing image processing on the obtained enlarged image using an image processor, a distribution of the image characteristics, such as a distribution of the light intensity, corresponding to the radial positions of the optical fiber image, can be obtained. The distribution of the image characteristic is represented by a different characteristic curve depending on the orientation of the rotational direction of the optical fiber, and this has a high reproducibility. Therefore, a rotational angle around the center axis of the optical fiber is measured from the distribution of the image characteristic. Based on the result, the orientation of the rotational direction of the optical fiber using an optical fiber rotating member to achieve alignment can be attained.

In order to attain the second object and the third object, the present invention is characterized by a method of aligning orientations of the rotational direction of optical fibers in an optical fiber array having a plurality of optical fibers and an optical fiber holding member, the method comprising the steps of obtaining an enlarged image of the optical fiber for each of the optical fibers using an image obtaining means, obtaining a distribution of the image characteristics corresponding to different radial positions of the optical fiber image from the obtained enlarged image, adjusting the image obtaining means so that the image characteristics at outer peripheral portions of the optical fiber are maximized in the distribution of the image characteristics, measuring an axial displacement of the core center to the center of the optical fiber from the distribution of the image characteristic after the adjusting, and aligning the axial displacement with respect to the optical fiber holding member using an optical fiber rotating mechanism.

According to the above construction, by viewing a plurality of optical fibers from a direction lateral to the propagating direction of light in the fiber using an image obtaining means, a plurality of enlarged images of the optical fiber can be obtained. By performing image processing on each of the plural obtained enlarged images using an image processor, a distribution of the image characteristics, such as a distribution of the light intensity, corresponding to the radial positions of the optical fiber image, can be obtained. The distribution of the image characteristic is represented by a different characteristic curve depending on the orientation of the rotational direction of the optical fiber, and this has a high reproducibility. Therefore, the rotational angle around the center axis of the optical fiber is measured from the distribution of the image characteristic. Based on the result, the axial displacement of the core with respect to the center of the optical fiber can be detected and the pitch between the cores can be set to the pitch of the core of the optical waveguides by rotating any of the optical fibers.

In order to align the main axis of birefringence with a high accuracy and a high reproducibility, it is very effective to adjust the distance between the image pick-up camera and the optical fiber so that the upward peak value of light intensity of the image at the outer periphery of the optical fiber is maximized.

Another aspect of the present invention relates to an optical fiber holding structure in which the optical fiber is held while being viewed from a direction lateral to the propagating direction of the guided light using an image obtaining means to obtain an enlarged image of the optical fiber, distribution of the image characteristics corresponding to the radial positions of the optical fiber image being obtained from the obtained enlarged image, the image obtaining means being adjusted so that the image characteristics at outer peripheral portions of the optical fiber are maximized in the distribution of the image characteristics, an orientation of the rotational direction around the center axis of the optical fiber being measured from the distribution of the image characteristic after adjusting, and the orientation of the rotational direction of the optical fiber being aligned with an optical fiber rotating member based on the measured result.

A further aspect of the present invention relates to a junction in which the optical fiber is viewed from a direction lateral to the propagating direction of light in the fiber using an image obtaining means to obtain an enlarged image of the optical fiber, distribution of the image characteristics corresponding to the radial positions of the optical fiber image being obtained from the obtained enlarged image, the image obtaining means being adjusted so that the image characteristics at outer peripheral portions of the optical fiber are maximized in the distribution of the image characteristics, an orientation of the rotational direction around the center axis of the optical fiber as the rotational axis being measured from the distribution of the image characteristic after the adjusting, and the orientation of the rotational direction of the optical fiber being aligned using an optical fiber rotating member based on the measured result.

A still further aspect of the present invention relates to a method of aligning orientations of the rotational direction of optical fibers in an optical fiber array including a plurality of optical fibers having an axially asymmetric refractive index distribution and an optical fiber holding member, the method comprising the steps of obtaining enlarged images of the optical fiber in various rotational directions with respect to the center axis of the optical fiber from a direction lateral to the propagating direction of a guided wave in the optical fiber for each of the optical fibers using an image obtaining means, obtaining a distribution of the image characteristics corresponding to the radial positions of the optical fiber image from the obtained enlarged images, aligning a predetermined specific axis on the cross sectional plane of the optical fiber to the optical axis of the image obtaining means by detecting that orientation of the rotational direction of the optical fiber which will provide a predetermined distribution of the image characteristic, measuring an axial displacement of the core center to the center of the optical fiber from the distribution of the image characteristic, and aligning or presetting the optical axis of the image obtaining means to the holding member for each of the optical fibers so that the orientation of the specific axis is directed in a desired direction with respect to the optical fiber holding member when the specific axis of all the optical fibers are aligned in parallel to the optical axis of the image obtaining means by rotating the optical fibers, in which the positions of axial displacement do not agree with the desired positions, or in which more than a half-number of the positions of axial displacement do not agree with the desired positions by 180.degree..

A further aspect of the present invention relates to an optical fiber array having a plurality of optical fibers and an optical fiber holding member, wherein an enlarged image of the optical fiber for each of the optical fibers is obtained using an image obtaining means, distribution of the image characteristics corresponding to the radial positions of the optical fiber image being obtained from the obtained enlarged image, the image obtaining means being adjusted so that the image characteristics at outer peripheral portions of the optical fiber are maximized in the distribution of the image characteristics, an axial displacement of the core center to the center of the optical fiber being measured from the distribution of the image characteristic after adjusting, and the pitches of the cores being adjusted or made uniform by aligning the axial displacement to the optical fiber holding member with an optical fiber rotating mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view showing the outline of the main part of an embodiment of an apparatus using a method in accordance with the present invention of aligning the rotational direction of an optical fiber having an axially asymmetric refractive index distribution.

FIG. 2 is a flow chart showing the steps of the method of aligning the rotational direction of an optical fiber using the apparatus of FIG. 1.

FIG. 3 is a diagram showing the relationship among an image pick-up camera, an optical fiber and a light source in the apparatus of FIG. 1.

FIG. 4 is a graph showing the characteristic of light intensity at a distance between an image pick-up camera and an optical fiber of L.sub.M where the upward peak values l and r of the light intensity of the image in the outer peripheral portion of the optical fiber are maximized.

FIG. 5A is a schematic view showing an elliptical core type optical fiber where the angle between the optical axis of an image pick-up camera and the main axis of birefringence in the direction of the major axis of the elliptical core is 0.degree., and FIG. 5B is a graph showing the light intensity distribution under that condition.

FIG. 6A is a schematic view showing an elliptical core type optical fiber where the angle between the optical axis of an image pick-up camera and the main axis of birefringence in the direction of the major axis of the elliptical core is 5.degree., and FIG. 6B is a graph showing the light intensity distribution under that condition.

FIG. 7A is a schematic view showing an elliptical core type optical fiber where the angle between the optical axis of an image pick-up camera and the main axis of birefringence in the direction of the major axis of the elliptical core is 45.degree., and FIG. 7B is a graph showing the light intensity distribution under that condition.

FIG. 8A is a schematic view showing an elliptical core type optical fiber where the angle between the optical axis of an image pick-up camera and the main axis of birefringence in the direction of the major axis of the elliptical core is 90.degree., and FIG. 8B is a graph showing the light intensity distribution under that condition.

FIG. 9 is a graph showing the characteristic of light intensity at the distance L between an image pick-up camera and an optical fiber which is larger by 5 .mu.m than L.sub.M where the upward peak values l and r of the light intensity of the image in the outer peripheral portion of the optical fiber are maximized.

FIG. 10 is a graph showing the characteristic of light intensity at the distance L between an image pick-up camera and an optical fiber which is larger by 10 .mu.m than L.sub.M where the upward peak values l and r of the light intensity of the image in the outer peripheral portion of the optical fiber are maximized.

FIG. 11A is a schematic view showing an elliptical jacket type polarization-maintaining optical fiber where the angle between the optical axis of an image pick-up camera and the main axis of birefringence in the direction of the major axis of the elliptical jacket is 0.degree., and FIG. 11B is a graph showing the light intensity distribution under that condition.

FIG. 12A is a schematic view showing an elliptical jacket type polarization-maintaining optical fiber where the angle between the optical axis of an image pick-up camera and the main axis of birefringence in the direction of the major axis of the elliptical jacket is 5.degree., and FIG. 12B is a graph showing the light intensity distribution under that condition.

FIG. 13A is a schematic view showing an elliptical jacket type polarization-maintaining optical fiber where the angle between the optical axis of an image pick-up camera and the main axis of birefringence in the direction of the major axis of the elliptical jacket is 45.degree., and FIG. 13B is a graph showing the light intensity distribution under that condition.

FIG. 14A is a schematic view showing an elliptical jacket type polarization-maintaining optical fiber where the angle between the optical axis of an image pick-up camera and the main axis of birefringence in the direction of the major axis of the elliptical jacket is 90.degree., and FIG. 14B is a graph showing the light intensity distribution under that condition.

FIG. 15 is a view showing an embodiment of a modified holding member for use in the apparatus shown in FIG. 1.

FIG. 16 is a view showing junctions of optical fibers and optical waveguides in which the optical fiber is engaged in a V-shaped groove formed in a base plate manufactured in such a way that the end surfaces of the optical waveguides are exposed.

FIG. 17 is a view showing junctions of optical fibers and optical waveguides in which the optical fiber is inserted into an indention having a circular cross section formed in a base plate manufactured in such a way that the end surfaces of the optical waveguides are exposed.

FIG. 18 is a schematic view showing a system for aligning the main axis of birefringence of a polarization-maintaining optical fiber in accordance with a conventional method.

FIG. 19 is a diagrammatic view showing the main axis of birefringence of a conventional elliptical core type optical fiber.

FIG. 20 is a diagrammatic view showing the main axis of birefringence of a conventional elliptical jacket type optical fiber.

FIG. 21 is a flow chart showing the process flow in another embodiment of a method of aligning the rotational direction of an optical fiber in accordance with the present invention.

FIG. 22A is a schematic view showing an elliptical core type polarization-maintaining optical fiber where the angle between the optical axis of an image pick-up camera and the main axis of birefringence in the direction of the major axis of the elliptical core is 0.degree., and FIG. 22B is a graph showing