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); and an optical fiber (10) inserted into and bonded to the receiving aperture.

Description: Background of the Invention The present invention relates to optical fiber connector terminals for closely connecting cords or cables of optical fibers within an adapter for communications systems, data transmission systems, and other optical systems. From US-A-4,300,815 there is known a connector end fitting for optical monofibers comprising a deformable cylinder which is placed round the fiber. To said cylinder are applied forces balanced in four perpendicular directions transmitted to a flexible sheath covering the monofiber. In particular, four jaws are provided in the form of cylinders having a circular cross-section said pins are disposed parallel to and equdistantly from a central axis of said cylinders thereby to define a receiving conduit for the monofiber and its sheath. 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 Figure 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. It is an object of the present invention to provide an improved optical fiber connector terminal and to provide a method of making such an optical fiber connector terminal. The above object is achieved by the subject matter of claim 1 and is achieved in terms of the method by the subject matter of claim 5. Further improvements and preferred embodiments are defined in the pending subclaims. The invention will be described in more detail with reference to embodiments illustrated in the drawings of which, Figure 1 is a perspective view of an optical fiber connector having a connector terminal according to an embodiment of the invention; Figure 2 is a perspective view of the connector terminal of Figure 1; Figure 3 is a longitudinal section of the connector terminal of Figure 1; Figure 4 is a rear view of the connector terminal of Figure 1. Figure 5 is a front view of a terminal body of the connector terminal of Figure 1; Figure 6 is a perspective view showing how to grind a pin for making the connector terminal of Figure 1; Figure 7 shows how to cut a pipe for making a sleeve for the connector terminal of Figure 1; Figure 8 shows how to make a specified inner diameter in the sleeve of Figure 7; Figures 9 and 10 show three pins placed in the sleeve; Figures 11 through 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 another 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. Description of the Preferred Embodiment 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. 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 is subjected to a rotary forging process in a rotary swage, for example, to be reduced in diameter so that the sleeve material fills spaces between the sleeve 6 and pins 7 while the three pins 7 are disposed in 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 in equidistance from the center O within the sleeve 6 to form a receiving conduit 9 at the center O. The sleeve 6 is reduced in diameter so that the sleeve material fills spaces between the sleeve 6 and the pins 7, and the optical fiber 10 is bonded in the receiving conduit 9. As a result, the sleeve 6 and the pins 7 are integrated to hold the pins 7 in place, thereby forming a thin long conduit 9. This makes it possible to make a long connector terminal. Consequently, the bonding strength of the optical fiber 10 to the receiving conduit 9 is increased, resulting in the increased connector reliability. A method of making such an optical fiber connector terminal as described above will be described below with reference to Figs. 6-21. In Fig. 6, a pin material 7a 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, an opening 17 of a specified inner diameter is made with a drill 16 or the like. 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 are 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 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 makes the sleeve material collapse to fill spaces between the sleeve 6 and the pins 7, thereby disposing the three pins 7 in equidistance 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 20 of a substantially triangle cross section is formed at the center of the three pins 7. A receiving conduit 9 of a circular cross section into which an optical fiber is to be inserted is made from the triangle aperture 20. In Fig. 16, a wrapping wire 21 is put through the triangle 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 receiving 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 conduit 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 another embodiment of the invention, wherein five pins 7 are disposed within the sleeve 6 such that they contact the adjacent pins 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 sleeve 6 is subjected to a rotary forging in a rotary swage, for example, so that the sleeve material fills spaces between the sleeve 6 and the pins 7 to dispose the five pins 7 equidistance 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 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 is reduced in diameter by a rotary forging in a rotary swage in the above embodiment, but the same results may be obtained by a drawing or press machine.

Claims: An optical fiber connector terminal comprising: a sleeve (6) made from a metal and having a bore of a predetermined diameter; a plurality of laterally contacting pins (7) disposed parallel to and equidistantly from a central axis within said sleeve (6) thereby to define an optical fiber receiving conduit (9); characterized in that the pins (7) are made of hardened steel, and said metal is softer than said hardened steel; and said sleeve (6) having been subjected to a force to be reduced in diameter so that said metal collapses and completely fills the space between said sleeve (6) and said pins (7), while said pins are disposed equidistantly from said central axis, thereby placing said conduit (9) at said central axis and whereby the outer surface of the sleeve has a circular cylindrical surface. The optical fiber connector terminal of claim 1, wherein said plurality of pins are three pins (7). The optical fiber connector terminal of claim 1, wherein said plurality of pins are five pins (7). The optical fiber connector terminal of claim 1, wherein said pins (7) are made from hardened stainless steel while said sleeve (6) is made from stainless steel which is not hardened. A method of making an optical fiber connector terminal, which comprises the steps of: forming a bore of a predetermined diameter in a metal sleeve (6); placing a plurality of hardened steel pins (7) within said metal sleeve, such that said pins are contiguously disposed and are parallel to a central axis of said metal sleeve; reducing the diameter of said metal sleeve (6) so that the material of said metal fills the space between said sleeve and said pins (7), thereby disposing said pins equidistantly from said central axis to form a long, fine receiving conduit (9) and forming a circular cylindrical outer surface on said sleeve; and securing an optical fiber (10) in said receiving conduit (9) to provide an optical fiber connector terminal. The method of claim 5, wherein said plurality of pins are three pins (7). The method of claim 5, wherein said plurality of pins are five pins (7). The method of claim 5, wherein said sleeve (6) is made from stainless steel which is not hardened. The method of claim 5, wherein said diameter reducing step comprises the step of subjecting said sleeve (6) to a rotary forging process. The method of claim 5, wherein said diameter reducing step comprises the step of subjecting said sleeve (6) to a drawing process. The method of claim 5, wherein said diameter reducing step comprises the step of subjecting said sleeve (6) to a press process. The optical fiber connector terminal of claim 1, wherein said metal is tungsten. The optical fiber connector terminal of claim 1, wherein said metal is beryllium. The optical fiber connector terminal of claim 1, wherein said pins (7) are flush with said optical fiber (10) at a front end surface of said connector terminal, thereby not only protecting but also registering said optical fiber (10) at said center. The method of claim 5, which further comprises, after said reducing step, the step of polishing an end surface of said reduced sleeve (6) at right angle with respect to an axis of said reduced sleeve. The method of claim 15, which further comprises, after said polishing step, the step of forming a guiding surface (28) at a rear end of said receiving conduit (9) for facilitating insertion of said optical fiber (10). The method of claim 5, wherein said securing step comprises bonding said optical fiber to said opening with an adhesive, followed by grinding off excess adhesive and a projected part of said optical fiber to provide a finished optical fiber connector terminal.

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