Optical connector

Abstract: An optical connector according to the present invention is comprised of a ferrule having at least one optical fiber and a plurality of guide holes, and a plurality of guide pins each being inserted in each of the holes. The guide pin is capable of being attached into and detached from the hole. At least one of an inner diameter of the guide hole and an outer diameter of the guide pin change the longitudinal direction thereof, and at least a part of the guide pin is in contact with the guide hole.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to so-called fit plug type optical connectors in which optical coupling is performed -through guide pins. 2. Description of the Related Art Heretofore, MF optical connectors and MT optical connectors are known as conventional optical connectors having guide holes. Such optical connectors provide optical coupling in a manner that guide pins are inserted into guide holes of respective optical connectors and optical fibers are made to abut on each other at their end surfaces while positioning the optical connectors. In such a conventional optical connector, however, the inner diameter of a guide hole is generally formed so as to be slightly larger (about 1 to 3 µm) than the diameter of a guide pin in order to facilitate an attaching/detaching operation. As a result, optical connector may move by a clearance between the inner diameter of the guide hole and the outer diameter of the guide pin when the optical connector is coupled with another optical connector, so that there is a problem that the coupling loss varies at the time of attachment/detachment of the optical connectors. For example, if there is a displacement by 1 µm in a direction perpendicular to the axial line of the optical fibers when optical connectors having a coupling loss of 0.2dB are coupled with each other, the coupling loss increases to about 0.8dB. Further, when the ferrule is produced by molding with a plastic material, the guide holes cannot be always straight but they may be curved because of the unevenness of shrinkage, the warp, or the like, of the molding material. In such a case, the position in which the guide hole is in contact with the guide pin varies correspondingly to the individual ferrule, so that there is a problem that the fitting state of the guide pin is not determined but varies. Furthermore, the position in which the guide pin is located in the guide hole in the longitudinal direction is not fixed, so that there is a problem that the coupling state of the connectors varies correspondingly to the location of the guide pin. JP 2205809 describes a connector for optical fiber with a guide pin to eliminate connection loss due to the inclusion of extremely small foreign matter. This disclosure shows a guide pin where annular or spiral grooves in the outer peripheral surface of a guide pin are formed. EP 0271721 describes an optical connector comprising an optical fiber connector ferrule which comprises a substrate plate having at least one optical fiber groove and pin grooves, each being formed at one surface thereof in the cover plate joined to the substrate plate to form at least one optical fiber groove hole into which an optical fiber is inserted. Summary of the Invention It is an object of the present invention to provide an optical-connector which improves the positioning precision of the guide pin and makes the inserting and extracting of the guide pin easier. The object is achieved by an optical connector as defined in claim 1. Preferred embodiments are defined by the dependent claims. In the optical connectors according to the present invention, the problem of the increase of optical loss caused by the displacement of the axes of the optical fibers at the time of coupling of the optical connectors hardly occurs because the guide pins are always accurately held in predetermined positions of the guide holes, and extraction/insertion of the guide pins can be smoothly performed because each of the guide pins is held only at one portion thereof. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, Fig. 1 is a perspective view showing the outline of optical connectors to which the present invention is applied; Fig. 2 is a sectional view showing a first embodiment of the present invention; Fig. 3 is a sectional view showing a second embodiment of the present invention; Fig. 4 is a sectional view showing a third embodiment of the present invention; Fig. 5 is a sectional view showing a first illustrative example Fig. 6 is a sectional view showing a second illustrative example; Fig. 7 is a sectional view showing a third illustrative example; Fig. 8 is a sectional view showing a fourth illustrative example; and Fig. 9 is a sectional view showing a fifth illustrative example. PREFERRED EMBODIMENTS OF THE INVENTION Preferred embodiments of an optical connector according to the present invention will be described below in detail with reference to the accompanying drawings. Fig. 1 shows the outline of conventional MT optical connectors as an example of optical connectors to which the present invention is applied. In each of the optical connectors 1, a group of optical fibers 3 are embedded in a ferrule 2 thereof so as to be arranged laterally in parallel with each other at intervals of an equal distance. Incidentally, the number of optical fibers may be only one. On opposite sides in the direction of arrangement of the optical fiber group 3, two guide holes 4 are provided substantially in parallel to the center axis line of the optical fiber group 3 and in positions separated at an equal distance from the center axis line of the optical fiber group 3 so as to pierce the optical connector 1. The reference numeral 5 designates guide pins which are fitted into guide holes 4 of the optical connectors 1 coupled with each other. Incidentally, the center axis line of the optical fiber group 3 used herein means a line which is located in the middle of two center ones of the optical fibers of the optical fiber group 3 when the optical fiber group 3 is constituted by an even number of optical fibers, and which is coincident with the center axis line of the center one of the optical fibers when the optical fiber group 3 is constituted by an odd number of optical fibers. Further, because a pair of ferrules 2 to be coupled with each other have the same shape and are symmetric with respect to the connector end surface, only one side will be described below in order to make understanding easy. Incidentally, illustration of the optical fibers 3 are omitted in embodiments shown in Fig. 2 et seq. for the sake of simplification of the drawing, and the shapes of the guide hole and guide pin are shown exaggeratingly in order to make understanding easy. In a first embodiment of the present invention, as shown in Fig. 2, the inner diameter of each of the guide holes 4 is made so as to change in the longitudinal direction thereof and a minimum portion 41 is formed substantially in the center portion. Each of the guide pins 5 is a straight pin the diameter of which is not changed. Further, in a second embodiment of the present invention shown in Fig. 3, the minimum inner diameter portion 42 of the guide hole 4 is formed on the connector end surface side. The ferrule 2 is generally formed through transfer molding with a plastic material such as an epoxy resin, or the like, and the guide pin 5 is formed of stainless steel, or the like. The basic shape of the guide pin 4 in a third embodiment of the present invention shown in Fig. 4 is the same as that in the second embodiment of the present invention, except that the guide hole 4 having the minimum inner diameter portion 42 on the connector end surface side is formed in a tubular member 6 made of ceramics such as zirconia, or the like, and that the tubular member 6 is formed so as to be embedded in the ferrule 2 in the aforementioned molding process. In the first to third embodiments, the ratio of the length of the small diameter portion or minimum inner diameter portion of the guide holes is in the range of from 20% to 70%, more preferable in the range of from 35% to 65%, based on the whole length of the ferrule. If the ratio is less than 20%, the contact area is so small that an effect for holding the guide pin is lost. Accordingly, the optical axis of the optical fiber may be shifted at the time of optical coupling. On the other hand, If the ratio is more than 70%, the contact area is so large that the guide pin is influenced by curve of the guide hole, variation of the diameter of the guide hole or the like. Consequently, it is difficult to reduce the variation of coupling loss at the time of attachment/detachment of the optical connectors. In the following, a first illustrative example is shown in Fig. 5. In this example, the guide hole 4 is a straight hole without any change in its diameter whereas the outer diameter of the guide pin 5 is changed in the longitudinal direction thereof and maximum portions 51 are formed near opposite end portions thereof, respectively. Further, in a second illustrative example shown in Fig. 6, the guide hole 4 has no change in its diameter, and a maximum portion 52 of the guide pin 5 is formed in the longitudinally center portion thereof, that is, near the connector end surface. In the foregoing examples, the ratio of the length of the maximum portion of the guide pin is in the range of from 20% to 70%, more preferable in the range of from 35% to 65%, based on the whole length of the ferrule. In the hollowing, third, fourth and fifth illustrative examples will be described with reference to Figs. 7 through 9, respectively. The above-mentioned examples show the case where either the guide hole 4 or the guide pin 5 has a diameter which is not changed whereas these third, fourth and fifth example show the case where a change of diameter is given to both of the guide hole 4 and the guide pin 5 so that the positioning of the guide pin in the longitudinal direction thereof is attained by using a level difference portion between the guide hole 4 and the guide pin 5. In the third illustrative example shown in Fig. 7, a maximum outer diameter portion 52 is formed in the center portion of the guide pin 5 so that a level difference portion 53 between the maximum outer diameter portion 52 and a small diameter portion 54 of the guide pin 5 abuts on a level difference portion 43 between a small diameter portion 41 of the guide hole 4 and a large diameter portion 44 of the same. Further, the maximum outer diameter portion 52 of the guide pin 5 and the small diameter portion 54 of the same are in contact with the large diameter portion 44 of the guide hole 4 and the small diameter portion 41 of the same, respectively. Further, the fourth illustrative example of the present invention shown in Fig. 8 is the same as the third illustrative example thereof, except that the small diameter portion 54 of the guide pin 5 is further reduced so as not to be in contact with the small diameter portion 41 of the guide hole on the contrary with the third illustrative example. Further, the basic shapes of the guide hole 4 and guide pin 5 in the fifth illustrative example shown in Fig. 9 are the same as those in the fourth illustrative example shown in Fig. 8, except that the guide hole 4 in the fifth illustrative example is formed in a ceramic tubular member 6 in the same manner as in the third embodiment. In the third and fifth illustrative examples, the ratio of the length of the maximum portion of the guide pin is in the range of from 20% to 70%, more preferable in the range of from 35% to 65%, based on the whole length of the ferrule. [Test Examples] Test Example 1 Optical connector ferrules 2 in Figs. 2 and 3 were formed through transfer molding with a thermosetting epoxy resin. In the guide hole 4, the minimum inner diameter portion 41, 42 was adjusted to a value so that the insertion force became about 100g when a 698.5µm guide pin 5 which had an outer diameter longitudinally unchanged was inserted into the guide hole 4, and, on the other hand, the large diameter portion of the guide hole 4 was made to be about 710µm. The length of the minimum inner diameter portion was 2mm with respect to the whole length 8mm of the ferrule. Single mode quartz optical fibers 3 were attached and bonded to 10 pieces of each of the above-mentioned optical connector ferrules, the end surfaces were polished, and then the coupling loss therebetween were evaluated. As a result, the average coupling loss in the configuration shown in Fig. 2 was 0.23dB, and the average coupling loss in the configuration in which the minimum portion 42 was located on the connector end surface side as shown in Fig. 3 was 0.18dB. When coupling losses were evaluated in the same manner as described above by using optical connectors of the conventional configuration each of which had a guide hole not changed in its diameter and a guide pin also not changed in its diameter, as a comparative example, the average coupling loss was 0.32dB. Test Example 2 In the same optical connector ferrule 2 as in the test example 1, zirconia tubular members 6 having guide holes 4 formed therein were embedded at the time of transfer molding to thereby produce an optical connector of such a configuration as shown in Fig. 4. Incidentally, the size was made identical with that in the test example 1 and the coupling losses between the optical connectors were evaluated. As a result, the average coupling loss was 0.16dB. First and second Illustrative Examples An optical connector in which the diameter of each of the guide holes was not changed longitudinally was produced. The inner diameter of the guide hole was adjusted to a value so that the insertion force became about 100g when a 698.5µm guide pin was inserted. By using a guide pin 5 having a large diameter portion (51, 52) of 698.5µm and a small diameter portion of 688.5µm as shown in Figs. 5 and 6 in this optical connector, the coupling losses between the guide pin and the guide hole were evaluated. As a result, the average coupling loss in the case of use of the guide pin shown in Fig. 5 was 0.23dB, and the average coupling loss in the case of use of the guide pin shown in Fig. 6 was 0.19dB. Third and Fourth Illustrative Examples In an optical connector having the configuration in which the diameter of each of the guide holes was changed longitudinally as shown in Figs. 7 and 8, the guide hole was formed such that the small diameter portion thereof was adjusted to a value so that the insertion force became about 100g when a 698.5µm guide pin was inserted into the guide hole while the large diameter portion was adjusted to a value so that insertion force became about 100g when a 710.0µm guide pin was inserted into the guide hole. On the other hand, in the case of the configuration shown in Fig. 7, the small diameter portion (54) and large diameter portion (52) of the guide pin were selected to be 698.5 µm and 710 µm respectively, and in the case of the configuration shown in Fig. 8, the small diameter portion (54) and large diameter portion of the guide pin were selected to be 688.5 µm and 710 µm respectively. When the coupling losses between the optical connectors were evaluated, the average coupling loss in the configuration of Fig. 7 was 0.22dB and the average coupling loss in the configuration of Fig. 8 was 0.17dB. Fifth Illustrative Example Optical connectors having the configuration of Fig. 9 in which zirconia tubular members 6 each having guide holes of the same basic shape and the same size as in Fig. 8 were embedded was produced by trial and the coupling losses between the optical connectors were evaluated in the same manner as described above. As a result, the average coupling loss was 0.15dB. As described above, according to the present invention, the variety of the coupling loss between optical connectors at the time of attaching/detaching can be reduced effectively compared with the prior art.

Claims: An optical connector (1) comprising: a ferrule (2) having at least one optical fiber (3) and a plurality of cylindrical guide holes (4); and a plurality of cylindrical guide pins (5) each being partly insertable in a respective one of said holes (4), said guide pins (5) being capable of being inserted into and extracted from said holes (4); characterized in that the outer diameter of said cylindrical guide pins (5) is constant in the longitudinal direction thereof, and said cylindrical guide holes (4) have a first longitudinal portion whose inner, diameter is substantially identical to the outer diameter of said guide pins (5) and a second longitudinal portion whose inner diameter is larger than the outer diameter of said guide pins (5) so that the inner wall of the guide holes (4) does not contact with the guide pins (5) at the second longitudinal portion thereof, whilst it is in contact with said guide pins (5) at the first longitudinal portion of said guide holes (4). An optical connector (1) according to claim 1, wherein said first longitudinal portion of said guide holes (4) is located on a substantially center longitudinal portion of said ferrule (2). An optical connector (1) according to claim 1, wherein said first longitudinal portion of said guide holes (4) is located on a longitudinal end portion of said ferrule (2). An optical connector (1) according to claim 1, wherein said guide holes (4) are formed of metal or ceramic tubular members embedded in said ferrule (2). An optical connector (1) according to claim 4, wherein said ceramic tubular member is zirconia. An optical connector (1) according to claim 1, wherein the ratio of the length of said first longitudinal portion is in the range of 20% to 70% based on the whole length of said ferrule (2). An optical connector (1) according to claim 6, wherein the ratio of the length of said first longitudinal portion is in the range of 35% to 65% based on the whole length of said ferrule (2). An optical connector (1) according to claim 1, wherein said ferrule (2) is made of plastic material.

Inventors: HONJO MAKOTO, KATSURA HIROSHI, NAGASAWA SHINJI, TAMEKUNI YOSHIKYO, YAMANISHI TORU, HONJO, MAKOTO, KATSURA, HIROSHI, NAGASAWA, SHINJI, TAMEKUNI, YOSHIKYO, YAMANISHI, TORU, Honjo, Makoto, Yokohama Works Sumitomo Electr.Ind., Katsura, Hiroshi, Yokohama Works Sumitomo El.Ind., Tamekuni, Yoshikyo, Yokohama Works Sumitomo El.Ind, Yamanishi, Toru, Yokohama Works Sumitomo El.Ind.
Applicants: NIPPON TELEGRAPH & TELEPHONE, SUMITOMO ELECTRIC INDUSTRIES, NIPPON TELEGRAPH AND TELEPHONE CORPORATION, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1996
Main classification: G02B6
IPC codes: G02B6