Optical fiber connector terminal

Abstract: An optical fiber connector terminal includes a sleeve (6); a plurality of collet members (7) disposed around 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 Field 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. Description of the Prior Art 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. 23 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. A further example is found in GB-A-2 096 348 disclosing a termination for fibre optic monofilaments. 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. Summary of the Invention The invention is defined in claim 1. Accordingly, it is an object of the invention to provide an optical fiber connector terminal having a fine long aperture in which an optical fiber is bonded, thereby providing a reliable optical fiber connector terminal. According to an aspect of the invention there is provided an optical fiber connector terminal which includes a sleeve; a plurality of collet members disposed equidistance from a center within the sleeve to form a receiving aperture; and an optical fiber inserted into and bonded to the receiving aperture. In the above connector terminal, the sleeve and the collet members are integrated so that the collet members form 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. The above and other objects, features, and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings. Brief Description of the Drawings Fig. 1 is a partially cutaway perspective view of an optical fiber connector having a connector terminal according to an 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. 2; Fig. 4 is a rear view of the. connector terminal of Fig. 2; Fig. 5 is a front view of a terminal body of the connector terminal of Fig. 2; Fig. 6 is a perspective view of a collet member useful for the connector terminal of Fig. 2; Fig. 7 is a perspective view showing how to grind a pin useful for the connector terminal of Fig. 2; Fig. 8 is a perspective view of a collet for the connector terminal of Fig. 2; Fig. 9 is a perspective view of a collet member for the connector terminal of Fig. 2; Fig. 10 shows how to cut a pipe for making a sleeve for the connector terminal of Fig. 2; Fig. 11 shows how to make a specified inner diameter in the sleeve; Figs. 12 and 13 show three collect members placed in the sleeve; Fig. 14 shows how to cut off end portions of the connector terminal material; Fig. 15 illustrates how to wrap the triangular aperture to form a circular receiving aperture; Fig. 16 shows how to grind the circumference of the connector terminal material with a cylindrical grinder; Fig. 17 illustrates how to polish an end of the connector terminal material; Fig. 18 shows how to make a guide surface in the receiving aperture; Fig. 19 illustrates how to round a corner of the connector terminal material; Fig. 20 is a longitudinal section of the connector terminal material in which an optical fiber is bonded; Figs. 21 and 22 are end views of connector terminals according to embodiments of the invention; and Fig. 23 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 collet members 7 are placed around the center 0. These collet members 7 are made by dividing into three equal circular portions a pin member which has a diameter substantially equal to the inside diameter of the sleeve 6. As best shown in Fig. 6, the collet member 7 has a groove 7a so that the three collet members 7 disposed around the center O form a receiving aperture 9 for an optical fiber 10 as shown in Fig. 5. The collet members 7 are made from tempered or hardened stainless steel such as SUS 305 while the sleeve 6 is made from stainless steel which is not hardened. Consequently, the hardness of the sleeve 6 is less than that of the collet members 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 collet members 7 are disposed equidistance from a center O, thereby placing the receiving aperture 9 at the center O. An optical fiber 10 of an optical cable 50 is inserted and bonded to the receiving aperture 9. A method of making such an optical fiber connector terminal 5 will be described below with reference to Figs. 7-20. In Fig. 7, a pin material 8a 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 member 8 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 8a and a pair of grinding rollers 13 and 14, which rotate in opposite directions shown by arrows to grind the pin material 8a. Thus, the pin member 8 is made from a hardened stainless steel material (for example, SUS 305). In Fig. 8, the pin member 8 is divided into three equal segments of a circle, forming three collet materials 40. In Fig. 9, a groove 7a is formed at the inner ridge of each collet member to provide a collet member 7. Alternatively, a circular aperture is made in the pin member 8 and, then, the pin member 8 is divided into three collet members 7. In Fig. 10, a stainless steel pipe 15 is cut to a predetermined length. In Fig. 11, 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 collet members 7. In Figs. 12 and 13, three collet members 7 are disposed within the sleeve 6 so that the grooves 7a form a substantially circular aperture 20 at the center for receiving an optical fiber. The sleeve 6 having the three collet members 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 reduces the sleeve 6 in diameter to compress the collet members 7 toward the center O, thereby disposing the three collet members 7 equidistance from the center O and the receiving aperture 9 at 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 wrapping wire 21 is put through the substantially circular 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. 16, the outside of the connector terminal material A is polished with a cylindrical grinder 25 to provide the desired degree of concentricity. In Fig. 17, 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. 18, 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. 19, 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. 20, 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. In Fig. 21, two collet members 7 replace the three collet members 7 in the above embodiment to form a receiving aperture 9 which is substantially the same as that of the above embodiment. In Fig. 22, four collet members 7 replace the three collet members 7 in the embodiment of Fig. 5 to provide a receiving aperture 9 which is substantially the same as that of the embodiment of Fig. 5. 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 collet members 7 which are made from hardened stainless steel such as SUS 305. The sleeve 6 having the collet members 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 for pressing the collet members 7 toward the center O. It is noted that the number of collet members are not limited to two, three, and four as shown in the above embodiments.

Claims: An optical fiber connector terminal comprising: a sleeve (6), a plurality of separate segment-shaped collet members (7) formed and arranged within the sleeve so as to define an optical fiber receiving or inserting aperture (9,20) extending along the axial direction of said sleeve, and an optical fiber (10) being inserted into and secured to said optical fiber receiving aperture (9,20), characterized in that said sleeve has been reduced in diameter by rotary forging so as to urge said collet members (7) towards the centre of the sleeve, thereby rendering the center of said optical fiber receiving aperture (9,20) concentric with the central axis of said sleeve (6),wherein said collet members (7) are made of a material of a hardness higher than that of the sleeve. The optical fiber connector terminal according to claim 1, wherein three collet members (7) are provided. The optical fiber connector terminal according to claim 1, wherein two collet members are provided. The optical fiber connector terminal according to claim 1, wherein four collet members are provided. The optical fiber connector terminal according to claim 1, wherein said collet members are made of hardened stainless steel and said sleeve is made of stainless steel which is not hardened.

Inventors: KAWANAMI NORIHIDE C O HIROSE E, KOBAYASHI NOBUAKI C O ORGAN NE, MASUDA KIMIO C O ORGAN NEEDLE, OADA KINJIRO C O HIROSE ELECTR, KAWANAMI, NORIHIDE, C/O HIROSE ELECTRIC CO., LTD., KOBAYASHI, NOBUAKI, C/O ORGAN NEEDLE CO.,LTD., MASUDA, KIMIO, C/O ORGAN NEEDLE CO.,LTD., OADA, 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