Multi-ferrule structure

Abstract: A multi-ferrule structure comprising a plurality of ferrule units(40: 40a, 40b, 40c, 40d) each for a single optical fiber. The ferrule units are disposed in contact with one or more adjacent units in such a way that the respective axes(O₁, O₂, O₃, O₄) of the ferrule units are in parallel with each other in one and the same plane(P). The ferrule units make one multi-ferrule set(42). The maximum deviation of the distance between optical axis of the optical fibers inserted in the respective ferrule units of the multi-ferrule set is very small. When a number of optical fibers are connected with the same number of other photoconductive components by using the multi-ferrule structure, the positioning accuracy for abutting connection is remarkably improved. In addition, the multi-ferrule structure is small in size and compact.

Description: Background of the Invention Field of the Invention The present invention relates to methods of making multi-ferrule structures suitable for use in transmitting light from a plurality of optical fibers into a plurality of other photoconductive components. In systems wherein information is transmitted by means of light, the technique of connecting optical fibers with various optical elements, that is, the optical connection technique, has been under research and development. Thus, a variety of optical connection devices have been proposed. Figs. 1 and 2 are schematic illustrations of the constructions of typical examples of conventional optical connection devices such as optical connectors for use in such optical connection. Fig. 1 is a plan view of an optical connector with two cores, which is disclosed in Japanese Utility Model Application Laid-Open No. 4,406/1989. This optical connector is of such a construction that a pair of assemblies respectively having tips of single optical cables 10a and 10b (the tips usually consist of a core portion and a cladding portion, which are together referred to as a "wire", but without a covering for the wire, and are also referred to as "terminal strands of optical fibers.") inserted into respective ferrule units 12a and 12b (in a cylindrical form) are disposed and fixed in a housing 14 with such a distance therebetween that the ferrule units 12a and 12b cannot come into contact with each other. Fig. 2 is a perspective view of the plug of a multi-core optical fiber connector as disclosed in Japanese Patent Application Laid-Open No.72,912/1983. A number of optical fibers 16a, 16b, 16c and 16d have the terminal strands thereof inserted into respective ferrule units 18a,18b, 18c and 18d, which are attached to a plug body 22 in such a way as to pass through corresponding through-holes 20a, 20b, 20c and 20d provided in a plug base. In this conventional examples as well, the ferrule units are disposed with such a distance therebetween that they cannot come into contact with each other. The core diameter of the cores of optical fibers is usually in the range of about 4 µm to about 50 µm, while the outer diameter of cladding portions around cores is generally about 100 µm. Ferrule units to highly accurately position and fix the terminal strands of optical fibers having such an outer diameter include metallic ferrules, ceramic ferrules, and plastics ferrules, among which ceramic ferrules are now predominantly used since they are especially excellent in strength, final processing accuracy, connection characteristics, etc. Additionally stated, all of such ferrules are usually in a cylindrical form. In every one of these ferrules, a very small through-hole is provided to allow the terminal strand of an optical fiber having an axis in common therewith to be inserted and fixed thereinto. In the case of zirconia ceramic ferrules, an accuracy of about ± 0.5 µmm to about ± 0.1 µm, usually around ± 0.2 µm, is now secured when the outer diameter of the ferrules is usually set to be as small as about 1.5 mm. In a construction wherein such ferrules capable of highly accurately fixing an optical fiber are arrayed apart from each other and in parallel with each other as in the conventional optical connectors described in connection with Figs. 1 and 2, a housing or the like for fixation of the ferrules is provided with holes for such fixation which holes are poor in positioning accuracy, with the result that the accuracy of the distance between the axes of adjacent ferrules arrayed is usually at least ± 10 µm, while the best attainable accuracy is around ± 3 µm. The accuracy is not good for optical connection. When the accuracy of inter-axis distance is of such a degree, connection of optical fibers (represented by reference numeral 32) with an optical element-cum-photoconductive component 30 such as an optical switch, an optical coupler, an optical sensor, an optical gate or other optical integrated circuit, for example, as shown in Fig. 3, entails a poor positioning accuracy of at least ± 3 µm for connection of the optical fibers 32 with, for example, light wave guides (represented by reference numeral 34) formed in the optical element 30; this presents a problem in that the connection loss attributed to deviations of the axes of the light wave guides from the axes of the optical fibers is increased. Reference numeral 36 in Fig. 3 designates optical switch portions. As a result of extensive investigations and experiments, the inventors of the present invention have reached a conclusion that, when use is made of a multi-ferrule structure wherein a plurality of ferrule units capable of highly accurately positioning and fixing an optical fiber are juxtaposed and fixed themselves in contact with an adjacent one(s) and in parallel with each other in the case where a plurality of optical fibers are respectively connected with a corresponding number of photoconductive components such as optical fibers for connection therewith or light wave guides formed in an optical element, the accuracy of the distance between the axes of ferrule units respectively disposed on both ends of the structure can be increased, as well as the accuracy of distance between the axes of mutually adjacent ferrule units, as compared with the conventional level of such accuracy, since it depends on the dimensional accuracy of the ferrule units themselves, with the result that the positioning accuracy for connection of the optical fibers with the photoconductive components can also be increased accordingly. Thus, an aim of the present invention is to provide a multi-ferrule structure for optical fibers which is capable of increasing the positioning accuracy for connection of a plurality of optical fibers with a plurality of photoconductive components. Summary of the Invention JP-A-63-85609 discloses a multi-ferrule structure for use in an arrangement for transmitting light between a plurality of optical fibers and respective aligned photoconductive means, comprising a plurality of ferrule units each for a single optical fiber, which are held in contact with one or more adjacent units in such a way that the respective axes thereof are in parallel with each other in one and the same plane. However, the base and the end pieces between which the ferrule units are held form an integral unit. In accordance with the present invention, there is provided a method of making a multi-ferrule structure as defined in claim 1. In carrying out the invention, it is preferable that the end member has an operative surface perpendicular to the flat upper surface of said base member. In a preferred example, the end face of the base member on the side of the abutting end faces (abutting surfaces) of the optical fibers is perpendicular to the flat upper surface of said base member, and said end member has an operative surface extending along a direction perpendicular to said end face of said base member. Preferably, the above-mentioned fixing part further comprises one or more resin layers preferably made of a synthetic resin and integrally fixing all the ferrule units. In every multi-ferrule structure as described above, the ferrule units are preferably made of a ceramic material, most preferably of a zirconia ceramic material. The foregoing multi-ferrule structure of the present invention is of such a construction that a plurality of ferrule units not only capable of being produced with good external dimensional accuracy but also capable of highly accurately fixing strands of optical fibers may be disposed in contact with or in close contact with an adjacent unit(s) in such a way that the axes thereof are arrayed on one and the same plane in parallel with each other within the required tolerance limits. Therefore, the accuracy of distance between the axes of the two outermost ferrule units depends solely on the external dimensional accuracy of the individual ferrule units. Similarly the accuracy of the distance between the axes of mutually adjacent ferrule units also depends solely on the external dimensional accuracy of the individual ferrule units. Accordingly, the accuracy of such inter-axis distance can be increased to a very considerable extent. In addition, the multi-ferrule structure becomes small in size and compact. When a plurality of ferrule units of the same diameter are juxtaposed in contact with an adjacent unit(s) to form a multi-ferrule structure, an end-positioning end member, such as a base block, to serve as a basis of positioning of the ferrule units may be preliminarily fixed on a highly smooth upper surface of a base member, such as a plate, for installation of ferrules, and the ferrule units are juxtaposed on the upper surface of the base plate in contact with an adjacent unit(s), followed by such positioning of the whole groups of the ferrule units that the ferrule unit adjacent the base block is pressed against the base block as well as the upper surface of the base plate with a pressure applied to the outermost ferrule unit on the side opposite to the above-mentioned ferrule unit. Thereafter, the ferrule units are fixed. Insertion and fixation of the terminal strands of the optical fibers into the corresponding ferrule units may be done either before or after assembling of the multi-ferrule structure. Uniform arrangement of the abutting end faces of all the ferrule units to constitute the multi-ferrule structure may be done using a block gauge as usual. Brief Description of the Drawings The present invention will be better understood by reference to the following description taken in connection with the accompanying drawings, in which: Fig. 1 is a schematic plan view of a conventional optical connector; Fig. 2 is a schematic perspective view of another conventional optical connector; Fig. 3 is a schematic perspective illustration, which is illustrative of a conventional method of connecting optical fibers with an optical element; Fig. 4 is schematic enlarged front view of a multi-ferrule set, which is used in the present invention; Fig. 5 is a schematic enlarged front view of an embodiment of a multi-ferrule structure, which is used in the present invention; Fig. 6 is a schematic enlarged perspective view of an essential part of the multi-ferrule structure of Fig. 5; and Fig. 7 is a schematic perspective illustration, which is illustrative of an optical connection method of connecting optical fibers with the light wave guides of an optical element by using a preferred multi-ferrule structure according to the present invention. Preferred Embodiment of the Invention Examples of the multi-ferrule structure of the present invention will now be described while referring to the accompanying drawings. All the figures are schematically drawn with respect to the sizes and shapes of constituents and the positional relationship therebetween to merely facilitate the understanding of the present invention, while numerical conditions exemplified in the following description are merely preferred ones. Thus, it should be understood that the following description should not be construed as limiting the scope of the present invention. Figs. 4 and 5 are respectively enlarged schematic front views of examples of the multi-ferrule structure of the present invention, when viewed from the side of the abutting end faces of optical fibers. In the following description, preferred examples of the multi-ferrule structure, constituted of ceramic ferrule units, will be described, since the ceramic ferrules are now predominantly used as already described. First, the multi-ferrule structure according to the first embodiment of the present invention will be described while referring to Fig. 4. A plurality of (for example, four) zirconia ferrules 40a, 40b, 40c and 40d (represented by reference numeral 40) as ferrule units each for a single optical fiber can be disposed in contact with an adjacent one(s) in such a way that the respective axes O₁, O₂, O₃ and O₄ thereof are juxtaposed in parallel with each other in one and the same plane P. The diameter of the core portions in these ferrule units 40 is 9 µm and the diameter of the clad portions including the respective core portions is 100 µm, while the outer diameter of the ferrule units is 1.5 mm ± 0.5 µm ( accuracy: ± 0.5 µm). Here, the group of these ferrule units 40 is referred to as a "multi-ferrule set 42" and the multi-ferrule structure of the present invention is constituted either only of the multi-ferrule set 42 itself or mainly of the multi-ferrule set in this example. In the figure, the individual ferrule units 40 constituting the multi-ferrule set 42 are shown to have the terminal strands of respective optical fibers inserted thereinto to fix the terminal strands of the optical fibers, which have respective core portions 44a, 44b, 44c and 44d, and respective cladding portions 46a, 46b, 46c and 46d. Thus, the accuracy of the distance between the axes of the two outermost ferrule units is 0.5 X 4 = 2 µm in the worst case, while the accuracy of the distance between the axes of mutually adjacent ferrule units, for example, 40a and 40b, is 1 µm in the worst case. These accuracies are remarkably high, as compared with 3 µm in the best case of the prior art. When the optical fibers are made to abut against respective photoconductive components, the tolerance of the distance between such axes must be at most ± 3 µm in order to heighten the positioning accuracy for such abutment to keep the connection loss at a low level. It is especially preferable that the accuracy of distance between the axes of mutually adjacent ferrule units be within the range of ± 0.5 µm. The following description will be made while mainly referring to Figs. 5 and 6. Fig. 5 is a schematic enlarged front view of a multi-ferrule structure, wherein ferrule units are actually positioned highly accurately to constitute a multi-ferrule set 42 as described above. Fig. 6 is a perspective view of the multi-ferrule structure of Fig. 5 but excluding a fixing part therefrom. These figures show the ferrule units 40 not having the respective terminal strands of the optical fibers inserted thereinto. This multi-ferrule structure is of a construction comprising a base plate 50 with a flat upper surface for installation of ferrules, an end-positioning base block 54 fixed on the upper surface 50a of the base plate 50, a plurality of ferrule units 40 (40a, 40b, 40c and 40d) of the same outer diameter each for a single optical fiber, and a fixing part 56 fixing the ferrule units 40 (corresponding to a multi-ferrule set 42). In this case, the upper surface 50a of the base plate 50 has been subjected to abrasive finishing to form a highly smooth flat surface as free of unevenness as possible. The base plate 50 is usually made of a ceramic material. It is preferable that the end face 50b of the base plate 50 on the side of the abutting end faces of the optical fibers be perpendicular to the upper surface 50a thereof. The base block 54 is fixed on the upper surface 50a of the base plate 50. This base block 54 serves as a basis for determining the extending directions as well as positions of the ferrule units. Accordingly, the base block 54 is preferably made to have a flat side surface of a certain length on the side of the ferrule units 40. The base block 54 is preliminarily positioned and fixed on the upper surface 50a of the base plate 50 in such a direction as to juxtapose the axes O₁ - O₄ of the ferrule units 40 in parallel with each other. In this sense, the side surface of the base block 54 itself on the side of the ferrule units may be either perpendicular to the upper surface 50a of the base plate 50 or aslant at a certain angle without any trouble. The extending direction of the base block 54 and hence the extending directions of the axes O₁ - O₄ of the ferrule units 40 are preferably perpendicular to the end face 50b of the base plate 50. However, this is not always necessary. Thus, the base block 54 and hence the axes O₁ - O₄ of the ferrule units 40 may be fixed aslant at a given angle. In the latter case, the abutting end faces of the ferrule units 40 may be subjected to processing such as polishing if necessary after assembling thereof in order to effect even or uniform arrangement of the abutting end faces of the ferrule units 40. The positioning base block 54 is also preferably made of a ceramic material. Subsequently, the ferrule unit 40 (40a, 40b, 40c and 40d) are arrayed on the upper surface 50a of the base plate 50, as shown in Fig. 6. A pressure, for example, from the side of the outermost ferrule unit 40a is applied toward the side of the innermost ferrule unit 40d to press the ferrule units 40 against the upper surface 50a of the base plate 50 and the positioning base block 54 to thereby set the ferrule units 40 constituting the multi-ferrule set 42. Alternatively, the individual ferrule units 40 are each pressed in the lateral direction thereof and/or from above to effect arrangement thereof. Either of the foregoing operations allows the ferrule units 40 to be positioned and juxtaposed in parallel with each other and in contact with an adjacent one(s) by means of the upper surface 50a of the base plate 50 and the base block 54, while at the same time juxtaposing the axes O₁ - O₄ of the ferrule units 40 in parallel with each other in one and the same plane along the extending direction of the base block 54. Subsequently, the multi-ferrule set 42 thus formed are fixed using an adequate fixing part 56 to form the multi-ferrule structure. The fixing part 56 comprises at least a first block 60 provided on the upper surface 50a of the base plate 50 in such a way as to be in contact with the outermost ferrule unit 40a most remote from the base block 54, and a second block 62 pressing the ferrule units 40 from the side opposite to the base plate 50. With such first and second blocks 60 and 62, the ferrule units 40 are pressed under adequate pressure from the blocks 60 and 62 against the base plate 50 and the base block 54 thereby holding the ferrule units 40 in close contact therewith. Either without or in addition to the first and second blocks 60 and 62, a resin layer(s) 64 made of, for example, a synthetic resin may be provided in such a way as to integrally fix the whole of the multi-ferrule set 42. Generally stated, the configuration, material(s), etc. of the fixing part 56 are not particularly restricted, and may be adequately chosen. Insertion and fixation of the terminal strands of the optical fibers into the respective ferrule units 40 of the multi-ferrule set 42 may be done either before or after the assembling of the multi-ferrule structure. The abutting end faces of the ferrule units of the multi-ferrule set 42 may be subjected to the same finishing operation as made for conventional ferrule structures, for example, abrasive finishing to effect the finishing of those end faces. This finishing operation may be effected either before or after the insertion of the terminal strands of the optical fibers. The final abutting end faces of the multi-ferrule set 42 after fixing of the optical fibers into the respective ferrule units 40 may either of a so-called PC (physical contact) type or in the form of a flat surface or other shape. Micro optical elements such as microlenses (not shown in the figure) may be attached to the above-mentioned end faces. While the foregoing examples are concerned with cases where the four ferrule units are juxtaposed in the same plane in such a way that the outer wall faces thereof are in contact with an adjacent unit wall face(s), the number of ferrule units may be two or more. The multi-ferrule set is composed of ferrule units of the same outer diameter in combination. Any configuration will suffice in so far as the axes of ferrule units are juxtaposed in parallel with each other in one and the same plane. As described hereinbefore, the multi-ferrule structure of the present invention is of such a construction as will be suitable for use in a planar parallel arrangement of a plurality of optical fibers to effect optical connection thereof. A case where optical fibers are connected with the light wave guides of an optical element by using such a multi-ferrule structure will now be briefly described while referring to Fig. 7. In Fig. 7, an optical element 70 (only a constituent part of which is shown in the figure) is provided with, for example, four light wave guides (represented by reference numeral 72) according to a customary method. The distance between the optical axes of adjacent light wave guides 72 is set to be, for example, 1.5 mm ± 0.5 µm. A multi-ferrule structure 74 has a construction comprising four ferrule units (represented by reference numeral 76) of 1.5 mm ± 0.2 µm in outer diameter positioned with a base block 80 in cooperation with the flat upper surface 78a of a base plate 78 and fixed on the flat upper surface 78a of the base plate 78 by means of an adequate fixing part 88 (consisting of first and second check blocks 82 and 84 in the form of a plate and resin layers 86). Optical fibers are respectively inserted and fixed into the ferrule units 76 to form an optical fiber connector. The abutting end face of the optical fibers (consisting of a core portion 90 and a clad portion 92), the end face 78b of the base plate 78, and the end face 80a of the base block 80 are arranged to be flat. The abutting end faces of the optical fibers are allowed to abut against the optical element 70 in such a way that the core portions 90 of the optical fibers respectively abut the light wave guides 72 of the optical element 70. In such a state, the multi-ferrule structure and the optical element are fixed to each other. While the foregoing examples have been described using zirconia as the material of ferrules, alumina or other suitable ceramic material may for example be used to form ferrule. The wires of optical fibers must be inserted into the respective ferrule units of the multi-ferrule structure according to the present invention. The insertion of the wires into the respective ferrule units may be done either before or after assembling of the multi-ferrule structure. The multi-ferrule structure according to the present invention may be produced through fixation of the ferrule units thereof with a resin layer(s). Examples of resins usable for this include epoxy, resins, ultraviolet-curable resins, cold-setting resins, and thermosetting resins. As will be apparent form the foregoing description, since the multi-ferrule structure of the present invention has a construction comprising ferrule units disposed in contact with an adjacent one(s) in such a way that the axes thereof are juxtaposed in parallel with each other in one and the same plane, the accuracy of the distance between the axes of the ferrule units, and hence the accuracy of the distance between the central axes (optical axes) of the terminal strands of optical fibers, when inserted and fixed into the corresponding ferrule units, depend solely on the dimensional accuracy of the ferrule units (manufacture of the units can be such that any eccentricity of the central bore with respect to the outer dimensions is negligible). Since the outer dimensional inaccuracy of the ferrule units is very small, the maximum deviation of distance between the above-mentioned central axes which is controlled by the multi-ferrule set is very small as compared with those in the case of the conventional optical connection devices. Accordingly, when a number of optical fibers are connected with the same number of other photoconductive components by using the multi-ferrule structure of the present invention, the positioning accuracy for the abutting connection is remarkably improved. Therefore, when the multi-ferrule structure of the present invention is used to form an optical connection device for optical fibers, such as optical connectors, the light connection loss advantageously is remarkably decreased as compared with those in the case of the conventional optical connection devices.

Claims: A method of making a multi-ferrule structure for use in an arrangement for transmitting light between a plurality of optical fibers and respective aligned photoconductive means, comprising: (1) providing a base member (50) having a flat upper surface (50a), and an elongate, side-positioning member (54) fixed on the upper surface of said base member; and holding a plurality of elongate ferrule units of the same outer diameter, each for a single optical fiber, in contact with one or more adjacent units so as to be in parallel with each other on the flat upper surface of said base member and held against the side-positioning member, said ferrules thereby being positioned by the upper surface of said base member and said side-positioning member; and (2) subsequently fixing said ferrule units in position by a fixing arrangement (56), said fixing step comprising: (a) fixing a first member (60) on the flat upper surface of said base member in such a way as to be in contact with the side of the outermost ferrule unit most remote from said side-positioning member; and (b) fixing a second member (62) so as to press said ferrule units on to said flat upper surface. A method as claimed in claim 1, wherein said side-positioning member has an operative surface perpendicular to the flat upper surface of said base member. A method as claimed in claim 1 or 2, wherein an end face (50b) of said base member on a side intended for the optical fiber end faces is perpendicular to the flat upper surface of said base member, and wherein said side-positioning member has an operative surface extending in a direction perpendicular to said end face of said base member. A method as claimed in any one of claims 1-3, wherein said fixing arrangement comprises one or more resin layers (64) integrally fixing said ferrule units. A method as claimed in any one of claims 1-4, wherein said ferrule units are made of a ceramic material. A method as claimed in any one of claims 1-5, wherein said base member, said side-positioning member, said first member and said second member (50, 54, 60 and 62) are in the form of blocks.

Inventors: KOMATSU MASAO C O ADAMANT KOGY, KOMATSU, MASAO, C/O ADAMANT KOGYO CO., LTD.
Applicants: ADAMANT KOGYO CO, ADAMANT KOGYO CO., LTD.
Application year: 1990
Main classification: G02B6
IPC codes: G02B6