Optical fiber connector terminal and method of making same

Abstract: An optical fiber connector terminal includes a sleeve (6); a plurality of pins (7) disposed equidistance from a center within the sleeve to form a receiving aperture (9); a plurality of inner ridges (8) disposed between the sleeve and the pins; and an optical fiber (10) inserted into and bonded to the receiving aperture.

Description: The present invention relates to an optical fiber terminal connector comprising a sleeve provided with axially extending inwardly projecting ridges, a plurality of pins accommodated side by side in said sleeve equidistantly arranged about the center axis of the sleeve with adjacent pins contacting each other along their full length thereby forming an elongated fiber receiving passageway and elongate V-shaped cross-section grooves being formed between adjacent external surfaces of the pins and an optical fiber bonded into the fiber receiving passageway. Moreover, the present invention also relates to a method of making such an optical fiber terminal connector, the method includes the steps of providing a plurality of inner ridges on an inner wall of a sleeve, placing a plurality of pins side by side in said sleeve so as to form an elongated fiber receiving passageway between the pins and bonding an optical fiber in the fiber receiving passageway. Such optical fiber connector terminals are used for connecting cords or cable of optical fibers within an adapter in the field of communication systems, data transmission systems and other optical systems. An optical fiber terminal connector of this type is known from US-A-4,201,443. In said known optical fiber connector, glass rods form a guide assembly with an elongated fiber receiving aperture. The guide assembly consists of several single glass rods which are connected to each other by thermal fusing and a subsequent drawing process. Then the guide assembly is potted in a housing or a sleeve made of plastic material which forms a protective cover. In said known optical fiber connector, the optic fiber is secured in the guide assembly by fusing or by the use of an adhesive. From US-A-4,773,725 a sleeve of an optical fiber connector is known which has a trifoliate shaped bore. Pins are pressed into said trifoliate shaped bore and crimped onto an optical fiber by means of a crimping ferrule thereby fixing the optical fiber in the connector by clamping. Generally in optical fiber transmission lines, the connection between optical fibers is critical. The connection of optical fibers requires a precise registration of optical fibers. Optical fibers are made from glass and have a diameter of 100 microns. There are two requirements for the connector terminals; protecting and reinforcing the optical fibers and registering optical fibers with high-precisions in the order of micrometers. In an attempt to satisfy such requirements, an optical fiber connector terminal such as shown in Fig. 24 has been proposed. This connector terminal includes a terminal body 40 which is made from zirconia ceramic. The terminal body 40 is made by molding a terminal body which is slightly larger than the finished product, sintering it at high temperatures, and grinding a receiving aperture 41 with a wrapping wire or the like to the desired size. The terminal body 40 is then press fitted into a support member 42. However, it is very difficult to make a long core pin of the mold for the receiving aperture 41 so that it is very difficult to make a thin long receiving aperture 41 which is longer than 10 mm. For this reason, the strength of an optical fiber bonded to the conventional receiving aperture 41 is so small that the finished product is not reliable. The zirconia ceramic materials require sintering at high temperatures, making the manufacturing process complex and difficult, resulting in the low yield. In addition, thin connector terminals between 1.0 and 1.5 mm in diameter have low bending resistance and are easy to break upon connection and disconnection. Even if the connector terminal is made from a metal, it is extremely difficult to make a thin long receiving aperture in the connector terminal. Moreover, the terminal body 40 and the support member 42, which are made from different materials, are not compatible and can break upon forcible connection. The problem underlying the present invention is to provide an optical fiber terminal connector of the type mentioned at the beginning which is easy to make and still allows precise positioning of the optical fiber, and a method for making such a connector. According to the present invention there is provided an optical fiber terminal connector of the type mentioned above, wherein the V-shaped grooves between adjacent pins are each filled by permanently deformed material of the ridges and the sleeve which are pressed into the V-shaped grooves thereby fixing the pins in their positions. In the above connector terminal, the sleeve, the inner ridges, and the pins are integrated so that the pins are fixed to provide a thin long receiving aperture, thereby providing a long connector terminal. This increases the bonding strength of an optical fiber to the receiving aperture and thus the connector reliability. According to the present invention there is also provided a method of making such an optical fiber terminal connector. In the method as defined above, before inserting the optical fiber into the fiber receiving passageway, the pins are fixed in their positions relative to each other equidistantly about a center axis of the sleeve by reducing the diameter of the sleeve by inwardly permanently deforming the sleeve so that deformed material of the ridges and the sleeve is pressed tightly into gaps between the sleeve and the pins, thereby filling these gaps. By the above method it is possible to make a connector terminal having a thin long receiving aperture without difficulty. The above and other features and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings. Fig. 1 is a perspective view of an optical fiber connector having a connector terminal according to a first embodiment of the invention; Fig. 2 is a perspective view of the connector terminal of Fig. 1; Fig. 3 is a longitudinal section of the connector terminal of Fig. 1; Fig. 4 is a rear view of the connector terminal of Fig. 1; Fig. 5 is a front view of a terminal body of the connector terminal of Fig. 1; Fig. 6 is a perspective view showing how to grind a pin for making the connector terminal of Fig. 1; Fig. 7 shows how to cut a pipe for making a sleeve for the connector terminal of Fig. 1; Fig. 8 shows how to make a specified inner diameter in the sleeve of Fig. 7; Figs. 9 and 10 show three pins and three inner ridges placed in the sleeve; Figs. 11-13 show a connector terminal material with a triangular aperture at the center; Fig. 14 shows how to cut off end portions of the connector terminal material; Fig. 15 is a cross section of the connector terminal material; Fig. 16 illustrates how to wrap the triangular aperture to form a circular receiving aperture; Fig. 17 shows how to grind the circumference of the connector terminal material with a cylindrical grinder; Fig. 18 illustrates how to polish an end of the connector terminal material; Fig. 19 shows how to make a guide surface in the receiving aperture; Fig. 20 illustrates how to round a corner of the connector terminal material; Fig. 21 is a longitudinal section of the connector terminal material in which an optical fiber is bonded; Figs. 22 and 23 are end views of a connector terminal according to a second embodiment of the invention before and after the application of a rotary forging process, respectively; and Fig. 24 is a longitudinal section of a conventional connector terminal. In Fig. 1, the optical fiber connector includes a plug 1 and an adapter 2. The plug 1 has a plug housing 3 for housing an optical fiber connector terminal 5 via a retainer fixture 4. As Figs. 2-5 show, the connector terminal 5 consists of a support member 5a with a flange 5c and a terminal body 5b attached to the support member 5a. The terminal body 5b has a sleeve 6 in which three pins 7 are placed with three inner ridges 8 filling in spaces between the sleeve 6 and the pins 7. An optical fiber 10 of a fiber cable 50 is bonded to a receiving aperture 9 defined by the three pins 7. The sleeve 6 with the inner ridges 8 is subjected to a rotary forging process in a rotary swage, for example, to be reduced in diameter so that the inner ridges 8 fills spaces between the sleeve 6 and pins 7 while the three pins 7 are disposed equidistance from a center O, thereby placing the optical fiber 10 at the center O. As has been described above, the three pins 7 are disposed equidistantly from the center O within the sleeve 6 to form a receiving aperture 9 at the center O. The inner ridges 8 are provided in spaces between the sleeve 6 and the pins 7, and the sleeve 6 is reduced in diameter so that the inner ridges 8 fill spaces between the sleeve 6 and the pins 7. The optical fiber 10 is bonded in the receiving aperture 9. As a result, the sleeve 6 with the inner ridges 8 and the pins 7 are integrated to hold the pins 7 in place, thereby forming a thin long aperture 9. This makes it possible to make a long connector terminal. Consequently, the bonding strength of the optical fiber 10 to the receiving aperture 9 is increased, resulting in the increased connector reliability. A method of making such an optical fiber connector terminal 5 will be described below with reference to Figs. 6-21. In Fig. 6, pin material 7a made of stainless steel is cut to a predetermined length (for example, 60mm), subjected to a heat treatment or hardening process, and ground in a grinder 11 to form a pin 7 which has a predetermined degree of circularity and a predetermined degree of surface smoothness. The grinder 11 consists of a support member 12 for supporting the pin material 7a and a pair of grinding rollers 13 and 14, which rotate in opposite directions shown by arrows to grind the pin material 7a. Thus, the pin 7 is made from a hardened stainless steel material (for example, SUS 305). In Fig. 7, in order to make a sleeve 6, a stainless steel pipe 15 is cut to a predetermined length. In Fig. 8, this sleeve 6 is made from stainless steel by a drawing process to provide three inner ridges 8 which extend toward the center of the sleeve 6. Unlike the pin 7, the resulting sleeve 6 is made from stainless steel which is not hardened so that its hardness is less than that of the pin 7. In Figs. 9 and 10, three pins 7 and three inner ridges 8 are alternatingly disposed within the sleeve 6. The pins 7 are dimensioned such that they form a substantially triangular cross section, each apex of which contacts the inside of the sleeve 6. In Figs. 11-13, the sleeve 6 having the three pins 7 and the three inner ridges 8 therein is subjected to a rotary forging process, for example, in a rotary swage to reduce the diameter. The rotary forging process is a process by which the sleeve 6 is struck by one or two pairs of forging dies under continuous or intermittent rotation about its axis, thereby forming a connector terminal material A. The rotary forging process causes the inner ridges 8 to collapse and thereby fill spaces between the sleeve 6 and the pins 7, thereby disposing the three pins 7 equidistantly from the center O. In Fig. 14, opposite end portions of the connector terminal material A are cut off with a pair of fine cutters 19. The cutting surfaces are smoothed and cleaned. In Fig. 15, a receiving aperture of substantially triangular cross section is formed at the center of the three pins 7. A receiving aperture 9 of a circular cross section into which an optical fiber is to be inserted is made from said substantially triangular aperture 20. In Fig. 16, a wrapping wire 21 is put through said substantially triangular aperture 20. Grinding diamond granules 22 are put on the wrapping wire 21. A pair of reels 23 and 24 are turned back and forth to reciprocate the wrapping wire 21 to grind the wall of the substantially triangular aperture 20. In Fig. 17, the outside of the connector terminal material A is polished with a cylindrical grinder 25 to provide the desired degree of concentricity. In Fig. 18, an end surface of the terminal material A is polished with a grinder 27 while being held in place with a holder 26 to provide a right angled end surface. In Fig. 19, a guiding surface 28 is made at an end of the receiving aperture 9 by an electric discharge process using an electrode 29. Alternatively, the guiding surface 28 may be made by a cutting process. In Fig. 20, an end of the terminal material A is ground with a grinder 30 to provide a rounded corner. The terminal material A is then cleaned and press fitted into a support member 5a for integration. In Fig. 21, an adhesive 33 is put in the receiving aperture 9, and an optical fiber 10 is put through the receiving aperture 9, thereby building up the adhesive 33 at the end surface so that the projected portion of the optical fiber 10 is also bonded. The built up adhesive 33 and the projected optical fiber 10 are ground off with a grinder to provide a connector terminal 5. Figs. 22 and 23 show a second embodiment of the invention, wherein five pins 7 and five inner ridges 8 are disposed within the sleeve 6 such that they contact the adjacent pins, the inner ridges, and the inside of the sleeve 6. An optical fiber 10 is inserted and bonded in a receiving aperture 9 defined by the five pins 7. The inner sleeve 6 with the ridges 8 is subjected to a rotary forging in a rotary swage, for example, so that the inner ridges 8 fill spaces between the sleeve 6 and the pins 7 to dispose the five pins 7 equidistantly from the center O, thereby disposing the receiving aperture 9 at the center O for the optical fiber 10. By using the five pins 7, it is possible to provide a connector terminal with a receiving aperture having a diameter greater than that of the three pin connector terminal. The five pin connector terminal is made in the same way as that of the three pin connector terminal. Alternatively, the sleeve 6 and the inner ridges 8 made from stainless steel which is not hardened may be made from tungsten or beryllium as far as their hardness is less than that of the pins 7 which are made from hardened stainless steel such as SUS 305. The sleeve 6 having the pins 7 and the inner ridges 8 were reduced in diameter by a rotary forging in a rotary swage in the above embodiments, but the same results may be obtained by a drawing or press machine.

Claims: An optical fiber terminal connector comprising a sleeve (6) provided with axially extending, inwardly projecting ridges (8), a plurality of pins (7) accommodated side by side in said sleeve (6) equidistantly arranged about the centre axis (0) of the sleeve (6) with adjacent pins (7) contacting each other along their full length thereby forming an elongated fiber receiving passageway (9) and elongate V-shaped cross-section grooves being formed between adjacent external surfaces of the pins and an optical fiber (10) bonded into the fiber receiving passageway (9), characterized in that the V-shaped grooves between adjacent pins (7) are each filled by permanently deformed material of the ridges (8) and the sleeve (6), which are pressed into the V-shaped grooves thereby fixing the pins (7) in their positions. Optical fiber terminal connector according to claim 1, characterized in that three pins (7) are arranged within the sleeve (6) which is provided with three inner ridges (8) on its inner wall. Optical fiber terminal connector according to claim 1, characterized in that five pins (7) are arranged within the sleeve (6) which is provided with five inner ridges (8) on its inner wall. Optical fiber terminal connector according to one of claims 1 to 3, characterized in that the pins (7) have a higher resistance against deformation than the sleeve and its ridges. Optical fiber terminal connector according to one of claims 1 to 4, characterized in that the pins (7) are made of hardened stainless steel whereas the deformable elements (6, 8) are made of non-hardened stainless steel. Method of making an optical fiber terminal connector as claimed in claim 1 including the steps of providing a plurality of inner ridges (8) on an inner wall of a sleeve (6), placing a plurality of pins (7) side by side in said sleeve (6) so as to form an elongated fiber receiving passageway (9) between the pins and bonding an optical fiber (10) into the fiber receiving passageway (9), characterized in that before inserting the optical fiber (10) into the fiber receiving passageway (9) the pins (7) are fixed in their positions relative to each other equidistantly about the centre axis (0) of the sleeve (6) by reducing the diameter of the sleeve (6) by inwardly permanently deforming the sleeve (6) so that deformed material of the ridges (8) and the sleeve (6) is pressed tightly into the gaps between the sleeve (6) and the pins (7) filling these gaps. Method according to claim 6, characterized in that three pins (7) are inserted into the sleeve (6) which is provided with three inner ridges (8) on its inner wall. Method according to claim 6, characterized in that five pins (7) are inserted into the sleeve (6) which is provided with five inner ridges (8) on its inner wall. Method according to one of claims 6 to 8, characterized in that the pins (7) are made of hardened stainless steel whereas the sleeve and its ridges (6, 8) are made of non-hardened stainless steel. Method according to one of claims 6 to 9, characterized in that the diameter reducing process of the sleeve (6) comprises the step of subjecting the sleeve (6) to a rotary forging process. Method according to one of claims 6 to 9, characterized in that the diameter reducing process of the sleeve (6) comprises the step of subjecting the sleeve (6) to a drawing process. Method according to one of claims 6 to 9, characterized in that the diameter reducing process of the sleeve (6) comprises the step of subjecting the sleeve (6) to a pressing process.

Inventors: KAWANAMI NORIHIDE, KOZU YOSHIKAZU, OKADA KINJIRO, KAWANAMI, NORIHIDE, KOZU, YOSHIKAZU, OKADA, KINJIRO, KAWANAMI, NORIHIDE C/O HIROSE ELECTRIC CO.LTD., KOZU, YOSHIKAZU C/O ORGAN NEEDLE CO. LTD., OKADA, KINJIRO C/O HIROSE ELECTRIC CO. LTD.
Applicants: HIROSE ELECTRIC CO LTD, HIROSE ELECTRIC CO., LTD.
Application year: 1991
Main classification: G02B6
IPC codes: G02B6