1. Field of the Invention
This invention relates to an optical fiber array comprising a plurality of optical-fiber bare fibers which are disposed in alignment between two opposing plate members and are optically connected to connection elements (e.g., optical fiber lines, optical waveguide lines or optical elements on optical circuit boards) in an end-to-end facing arrangement with each other. More particularly, this invention relates to an optical fiber array which facilitates the optical and mechanical coupling of the bare fibers and the connection elements, and also relates to a method for manufacturing the same.
2. Description of the Related Art
In optical fiber arrays of this type, the alignment intervals between optical-fiber bare fibers are set with high accuracy so that positional matching and optical coupling can be facilitated with ease in relation to the optical fiber lines, optical wave guide lines or the like on optical circuit boards arranged at corresponding alignment intervals.
In conventional optical fiber arrays, optical-fiber bare fiber guide members for accurately setting the alignment intervals between optical-fiber bare fibers are provided as structural members of these optical fiber arrays. The V-groove member a as shown in FIG. 8A is conventionally known as an optical-fiber bare fiber guide member.
More specifically, the above V-groove member a is so configured that a plurality of grooves with substantially V-shaped cross sections (V grooves) a1 are formed lengthwise on its one side. Then, as shown in FIG. 8B, optical-fiber bare fibers c are respectively placed in the V grooves a1 of the V-groove member a. The optical-fiber bare fibers c are secured in place by the two lateral inclined planes of the V grooves a1, and the fixing positions of these optical-fiber bare fibers c are set, by downward pressure from a presser plate d on the upper part.
A plurality of optical-fiber bare fibers c can be aligned at regular intervals by forming a plurality of identically sized V grooves a1 at regular intervals. An optical fiber array e configured as shown in FIG. 8C is obtained by filling the gaps between the optical-fiber bare fibers c (uncovered optical fibers themselves having been stripped of their outer envelopes, i.e., fibers each constituted of a core and a cladding are referred to as “optical-fiber bare fibers”; in a narrow sense, this term applies to portions uncovered by stripping optical-fiber fiber ribbons of their tip outer envelopes), the V-groove member a and the presser plate d with an adhesive and allowing this adhesive to solidify (see Japanese Patent Applications Laid-open No. 5-307129, No. 11-242127, No. 11-326704, No. 2000-275465 and No. 2000-329971).
Now, the optical-fiber bare fiber guide members such as the V-groove member a are required to have high dimensional accuracy, and hence the optical-fiber bare fiber guide members involve a high manufacturing cost.
In addition, conventional optical fiber arrays are provided with the above optical-fiber bare fiber guide members set in as structural members, and hence there has been a problem that the cost of such optical fiber arrays is also proportionally higher.
To solve this problem, a method for manufacturing an optical fiber array by which method the optical-fiber bare fibers can be aligned with high accuracy without setting therein any expensive optical-fiber bare fiber guide members has recently been proposed (see Japanese Patent Application Laid-open No. 6-11625).
More specifically, this manufacturing method entails, as shown in FIG. 9A, installing an optical-fiber fiber ribbon alignment guide g provided on its top surface with a plurality of V grooves formed at an equal pitch, an optical-fiber bare fiber alignment guide h provided on its top surface with a plurality of V grooves formed at an equal pitch (see FIG. 10), and a presser i having trapezoid projections that fit into the V grooves of the optical-fiber bare fiber alignment guide h. The tip portions of optical-fiber fiber ribbons k (portions uncovered by stripping optical-fiber cables j of their jackets j1, i.e., portions covered with ribbon material k1 for fiber ribbons are referred to as “optical-fiber fiber ribbons”) are inserted into the V grooves of the optical-fiber fiber ribbon alignment guide g to support these optical-fiber fiber ribbons k in a parallel formation. The tip portions of optical-fiber bare fibers m (the optical-fiber bare fibers in a narrow sense; refer to portions uncovered by stripping the optical-fiber fiber ribbons k of their ribbon material k1 for fiber ribbons are referred to as “optical-fiber bare fiber”) are inserted into the V grooves of the optical-fiber bare fiber alignment guide h to support the optical-fiber bare fibers m in a parallel formation. Also, the presser i is placed on the optical-fiber bare fiber alignment guide h to prevent the optical-fiber bare fibers m from shifting upward. Thereafter, the external peripheral surfaces of the optical-fiber bare fibers and optical-fiber fiber ribbons k are coated with an adhesive n.
Next, as shown in FIG. 9B, a bottom plate r (see FIG. 11) is so set that a flat surface p thereof is disposed underneath the optical-fiber bare fibers m and that an angular groove q is disposed underneath the optical-fiber fiber ribbons k. A top plate s (see FIG. 11) is also so set that a flat surface p thereof is disposed above the optical-fiber bare fibers m and that an angular groove q is disposed above the optical-fiber fiber ribbons k. Thus, the optical-fiber bare fibers m are sandwiched between the top plate s and the bottom plate r, in the state of which the adhesive n is allowed to harden to bond the top plate s and the bottom plate r together. Thereafter, the adhesive n and optical-fiber bare fibers m extending from the integrated top plate s and bottom plate r are removed to obtain an optical fiber array t such as that shown in FIG. 9C.
According to this manufacturing method, the optical-fiber bare fibers m are aligned with the aid of an optical-fiber fiber ribbon alignment guide g, an optical-fiber bare fiber alignment guide h and a presser i, and the completed optical fiber array t is devoid of any optical-fiber bare fiber guide members, making it possible to markedly lower the manufacturing costs of such optical fiber arrays.
This manufacturing method, however, has had a problem that the optical-fiber bare fibers m can not be aligned with high accuracy for the reasons stated below, and has not been a method in which manufacturing costs can be lowered without reducing the accuracy of alignment intervals between the optical-fiber bare fibers.
More specifically, in this manufacturing method, it is possible to align with high accuracy the portions of the optical-fiber bare fibers m sandwiched between the optical-fiber bare fiber alignment guide h and the presser i as shown in FIG. 9A (however, as shown in FIG. 9B, these portions correspond to the portions of the optical-fiber bare fibers m that extend from the integrated top plate s and bottom plate r, and are portions removed together with the uncovered adhesive in the manner described above). However, the optical-fiber bare fibers m may loose their tension as they extend from the optical-fiber bare fiber alignment guide h toward the optical-fiber fiber ribbon alignment guide g, making it difficult to align the optical-fiber bare fibers m at these portions with high accuracy. Applying tension to the optical-fiber bare fibers m between the optical-fiber fiber ribbon alignment guide g and the optical-fiber bare fiber alignment guide h has been suggested as a method for preventing the loosening of the optical-fiber bare fibers m. This approach, however, has had a problem that it may cause breakage of the optical-fiber bare fibers m.
In addition, applying the adhesive n to the external peripheral surfaces of the optical-fiber bare fibers m as shown in FIG. 9A may cause the optical-fiber bare fibers m to move close to each other as a result of the surface tension of the adhesive n. Also, when the top plate s or the bottom plate r is brought into contact from above or below with the optical-fiber bare fibers m coated with the adhesive n as shown in FIG. 9B, the optical-fiber bare fibers m and the top plate s or bottom plate r are brought closer to each other by the surface tension of the adhesive n. These may cause the interval between the optical-fiber bare fibers m to vary, making accurate alignment of the optical-fiber bare fibers m difficult to achieve.
Furthermore, bringing the top plate s or the bottom plate r into contact from above or below with the optical-fiber bare fibers m coated with the adhesive n may cause the optical-fiber bare fibers m to shift their positions because of any slight differences in contact pressure on the optical-fiber bare fibers m between the top plate s and the bottom plate r, making accurate alignment of the optical-fiber bare fibers m difficult to achieve.
For these reasons, the method for manufacturing optical fiber arrays disclosed in Japanese Patent Application Laid-open No. 6-11625 has had a problem that the optical-fiber bare fibers m can not be aligned with high accuracy.
Under such technical backgrounds, the present inventor has already proposed an optical fiber array manufacturing method which can lower the manufacturing cost by saving the setting-in of the expensive optical-fiber bare fiber guide member without lowering the accuracy of alignment intervals in the optical-fiber bare fibers (see Japanese Patent Application Laid-open No. 2000-193844, corresponding to U.S. Pat. No. 6,368,441).
More specifically, in this optical fiber array manufacturing method, as shown in FIG. 12A, optical-fiber bare fibers m are held in V grooves h1 of an optical-fiber bare fiber alignment guide h so that they are aligned one by one.
Next, as shown in FIG. 12B, a plate member A provided with an adhesive layer (not shown) is brought into contact with the respective optical-fiber bare fibers m aligned by the optical-fiber bare fiber alignment guide h, and these are pressed on the back side of the plate member A by a transparent pressing means Z to keep the optical-fiber bare fibers m sandwiched between the optical-fiber bare fiber alignment guide h and the plate member A, in the state of which the respective optical-fiber bare fibers m are fastened onto the plate member A through the adhesive layer. Thereafter, the optical-fiber bare fibers m are separated from the optical-fiber bare fiber alignment guide h.
Next, as shown in FIG. 12C, a plate member B is superposingly fitted to the optical-fiber bare fibers m fastened onto the plate member A. Thereafter, an uncured resin material fed onto the plate member B is made to cure into a cured product and the plate member A is unified with the plate member B.
Finally, the optical-fiber bare fibers m extending outward from ends of the unified plate member A and plate member B are removed. Thus, this optical fiber array is completed.
In the optical fiber array manufactured by this method, the optical-fiber bare fibers m held in the region where they have been aligned by the optical-fiber bare fiber alignment guide h are mounted between the plate member A and the plate member B. Hence, compared with the optical fiber array obtained by the method disclosed in Japanese Patent Application Laid-open No. 6-11625, the alignment intervals in the optical-fiber bare fibers can be set with high accuracy.
Now, there is no problem when the thickness dimension of the plate member A and that of the plate member B are uniformly equal over the length in the direction of alignment of the optical-fiber bare fibers m. However, when as shown in FIG. 13 the flat surface of the plate member B on the side opposite to the side on which the optical-fiber bare fibers m are held serves as a disposition standard surface B1 when the array is set in, the thickness dimension of the plate member B may come non-uniform as shown in FIG. 13 (d1 differs from d2). In such a case, because of this non-uniformity in thickness dimension, the distance from central points of the respective optical-fiber bare fibers m to the disposition standard surface B1 may vary to make it impossible to adjust to a desired preset distance H the distance from the disposition standard surface B1 to the central points of the respective optical-fiber bare fibers m. There has been such a problem.
For example, single-mode optical fibers mounted to an optical fiber array and light rays guided through optical waveguide paths have a diameter of about 10 μm. Hence, if the single-mode optical fibers and the optical waveguide paths are positionally deviated by 10 μm or more, their mutual conduction can not be ensured, so that any operation to make mutual positional adjustment that may make the intensity of guided light maximum can not be started. There has been such a problem.
Since in some cases the thickness dimension of the plate member B conventionally used may vary in a width of 10 μm or more, the guided light can not be ensured however accurately the dimensions of optical guide paths are set. Hence, there has been the problem that any operation to make mutual positional adjustment that may make the intensity of guided light maximum can not be started.
Incidentally, there is another problem that, although the positional accuracy in disposing optical-fiber bare fibers can be kept with high accuracy by keeping to a stated value and with high accuracy the thickness dimension of the plate member B on which the optical-fiber bare fibers are to be mounted, this necessitates techniques of working plate members with high accuracy, resulting in a high cost.