Optical connector plug

Abstract: To realize an optical connector plug whose optical connector element can be engaged and disengaged by simple insertion and removal operation and which comprises (a) a plug housing (202) formed with a shoulder portion (253) between a large hollow portion (254) and a small hollow portion (251); (b) a plug ferrule (201) connected to an optical fiber (204) and formed with a flange portion (201B) slidably fitted into the large hollow portion of said plug housing and an end portion (201A) passed through the small hollow portion of said plug housing; and (c) a spring (203) housed within said plug housing to urge the flange portion of said plug ferrule against the shoulder portion (253) of said plug housing (202).

Description: The present invention relates to an optical connector ferrule holding structure for connecting an optical fiber of an optical connector plug, and preferably applied to a plug-in optical connector used to mount a package board on which various optical and electrical parts are mounted is assembled as a unit. Prior to description of the ferrule holding structure, a reference will be made to a prior-art holding structure. (1) JIS C5970 prescribes an F Ol single core optical fiber connector as an example of a prior-art optical connector for connecting optical fibers. In this connector, an optical fiber is fixed at the center of a cylindrical ferrule; the ferrule is inserted into a cylindrical hollow alignment sleeve formed with a precisely formed inner hollow portion so that end surfaces of two ferrules butt against each other. This optical connector is composed of a plug and an adaptor, and a pair of plugs are engaged with each other from both the sides of the adaptor. Fig. 1 shows a one-side plug 211 and an adaptor 212. An optical fiber 224 is bonded to a ferrule 221, and the ferrule 221 is floatingly supported inside a plug housing 222. To push end surfaces of the ferrules 221 against each other, the ferrule 221 is urged by a spring 223 within the plug housing 222. This spring 223 is housed within the plug housing 222 so as to be compressed to a predetermined urging force, the urging force is received when a flange portion 221b of the ferrule 221 is brought into contact with an inner wall 222a formed in the plug housing 222.A sleeve holder 226 is supported in the adaptor 212, and an elastic sleeve 225 for supporting two ferrules 221 is disposed within the sleeve holder 226 as shown in Fig. 1. When two ferrules 221 are supported via the elastic sleeve 225 within the adaptor 212, two optical fibers 224 are connected with the adaptor 212 interposed between the two plugs 211. (2) On the other hand, U.S. Patent No.4,895,425 discloses a plug-in connector used to transmit optical signals between a package board (on which various optical modules are mounted and which is mounted to a unit frame) and another package board or an external device. In the case of the above plug-in optical connector, since a plurality of connectors are mounted on a package board, there inevitably exists an error with respect to the connector mounting location or the unit frame and package board manufacturing process, so that it is required to maintain correct mutual positional relationship among plural connectors by absorbing an engagement error of about 1 mm in the axial direction of the optical connector element (ferrule). Therefore, plug-jack type optical elements different from the optical fiber connector shown in clause (1) above is used. (3) To increase the number of fibers per package board in the plug-in connector as described above, it is necessary to prevent the ferrule urging force from being directly applied to the back panel. In this optical connector, when the package board is inserted into the optical connector, two opposing optical connectors are automatically locked independently, and when the package board is removed from the optical connector, the two opposing optical connectors are automatically unlocked to allow the package board to be removable from the back panel. In this case, since the positional relationship between two optical elements is maintained correctly under locked condition, it is possible to apply the single fiber connector structure (plug-adapter-plug structure) as explained in clause (1) above or to use the single core optical connector and the plug in common. Therefore, in this optical connector, a plug and a jack having a sleeve holder with a slitted sleeve are usable. Figs. 2(a) to 2(c) show a prior-art plug structure and the positional relationship between the plug and jack when the single optical fiber connector is applied to the plug-in optical connector. With reference to these drawings, the ferrule 221 for supporting the optical fiber 224 is urged via the flange portion 221b by a spring 223, and the flange portion 221b is in contact with an inner wall 222a of a plug housing 222. The ferrule 221 and another ferrule 221 A supported by a jack side ferrule (not shown) are butted against each other within the elastic sleeve 225 by inserting a sleeve holder 226 (fitted into the jack side plug) into the plug 211 to couple the two optical fibers. In the case of the plug-in optical connector, an axial engagement error of about 1 mm can be absorbed by a clearance between the inner wall 222a and the sleeve holder 226 when the two ferrules are coupled. After coupled, the two optical connectors are automatically locked independently when the package board is inserted to maintain the two element positional relationship correctly. Fig. 3(a) and 3(b) show the ferrule 221. The ferrule 221 is formed with a flange portion 221b with two key grooves 221c. Therefore, when keys (not shown) provided for the plug housing 222 are engaged with the key grooves 221c, it is possible to prevent the ferrule 21 from being rotated. In the optical connector explained in clause (3) above, since the connector 213 is of plug-in type as in clause (2) above, it is necessary to absorb an axial engagement error of about 1 mm when coupled. Therefore, it is necessary to consider the first extreme coupling position where the plug and jack are close to each other as shown in Fig. 2(b) and the second extreme coupling position where the plug and jack are apart from each other by a clearance between the inner wall 222a and the sleeve holder 226 as shown in Fig. 2(c). To provide this clearance, the elastic sleeve 225 must be shortened or the ferrule 221 must be lengthened. If the elastic sleeve 225 is short, the connection reliability is deteriorated; and if the ferrule 221 is long, the bending strength of the ferrule 221 is reduced and not preferable from the standpoint of interchangeability with other optical connectors. Further, although it may be possible to provide another axial engagement error absorbing mechanism separately from each plug element, this results in another problem in that the size of the plug housing 222 is increased and thus the fiber mounting density is reduced. An optical connector plug having the features of the preamble of claim 1 is known from EP 0 228 063 A2. It is the object of the present invention to provide an optical optical connector plug whose optical connector element can be engaged and disengaged by simple insertion and removal operation and by which an axial engagement positional error of about 1 mm can be absorbed when used as a plug-in optical connector. This object is achieved with an optical connector plug having the features of claim 1. According to the present invention, the ferrule is supported within the plug housing and urged in the axial direction by the spring. When the sleeve holder is inserted from the ferrule support side into the plug housing, the sleeve holder is brought into contact with the flange portion of the ferrule passing through the shoulder portion against the urging force of the spring, so that the ferrule can be inserted deep further from the initial position to absorb the axial positional error. Fig. 1 is a perspective, partially broken view showing a prior art optical connector connected via an adapter; Figs. 2(a) to 2(c) are side cross-sectional views for assistance in explaining the engagement positional relationship between the plug and the sleeve holder when a prior art optical connector is applied to the plug-in optical connector; Fig. 3(a) is a front view showing a prior art ferrule; Fig. 3(b) is a side view showing the same prior art ferrule; Figs. 4 to 6 are views for assistance in explaining the present invention; Fig. 4(a) is a cross-sectional view showing an embodiment of the optical connector plug according to the present invention; Fig. 4(b) is a cross-section view taken along the line A-A in Fig. 1(a); Fig. 4(c) is a cross-sectional iew taken along the line B-B; Figs. 5(a) to 5(b) are cross-sectional views for assistance in explaining the engagement relationship between the optical connector plug and the sleeve holder; Fig. 6(a) is a front view showing the ferrule; Fig. 6(b) is a side view showing the ferrule; With reference to Figs. 4 to 6, a ferrule support structure and an optical connector plug used for the ferrule support structure according to the present invention will be explained hereinbelow. Fig. 4(a) is a cross-sectional view showing an embodiment of the optical connector plug according to the present invention; Fig. 4(b) is a cross-sectional view taken along the line A-A in Fig. 4(a); Fig. 4(c) is a cross-sectional view taken along the line B-B; Fig. 6(a) is a front view showing the ferrule; and Fig. 6(b) is a side view showing the ferrule. As shown in Fig. 4(a), an optical fiber 204 is bonded to a body of a ferrule 201, and the ferrule 201 is floatingly supported within the plug housing 202. The ferrule 201 is formed with a flange portion 201b slidably fitted into the plug housing 202. As shown in Figs. 4(b) and 6(a) the flange portion 201b is formed into a square shape whose corners are chamfered in cross section. Therefore, the plug housing 202 is formed with a square hollow portion to which the flange portion 201b of the ferrule 201 is fitted without rotation. The shape of the flange portion 201b is not limited to a chamfered square shape, and a polygonal (e.g. hexagonal) shape can be applicable. A spring 203 is housed within the plug housing 202 to urge the flange portion 201b of the ferrule 201 in the rightward direction in Fig. 4(a). The large-diameter hollow portion 254 of the plug housing 202 communicates with the small-diameter ferrule support portion 252 via a shoulder opening portion 253 to receive the outer circumferential edge of the flange portion 201b by a shoulder portion 253. As shown in Fig. 4(c), an end portion 201a of the ferrule 201 is floatingly supported within a ferrule support portion 252 and fitted to a sleeve holder 206, as described later. The ferrule support structure will be explained with reference to Figs. 5(a) and (b), in which a plug and jack are engaged. The plug includes an elastic slit sleeve 205 and a sleeve holder 206 for supporting the slit sleeve 205. In Fig. 5, no jack side is shown. The sleeve holder 206 is slidably fitted into the ferrule support portion 252, and inserted into the plug housing 202 through the shoulder opening portion 253. In the ferrule support structure as described above, the sleeve holder 206 can be inserted into the plug housing 202, because no inner wall 222a formed in the prior-art structure as shown in Fig. 2 is formed. Therefore, as shown in Fig. 5(a), it is possible to insert the sleeve holder 206 deep from the initial ferrule position beyond the shoulder portion 253 against the urging force of the spring 203, thus absorbing an axial engagement error when used as a plug-in optical connector. Accordingly, as shown in Fig. 5(b), the deepest engagement position can be determined in the state where the ferrule 201 is the most deeply inserted into the slit sleeve 205 in the same way as in the ordinary single fiber optical connector. Further, it is necessary to couple two ferrules in the same angular position, in order to obtain an excellent optical connector coupling and decoupling characteristics. In the ferrule support structure of the present invention, since the ferrule flange portion 201b is formed into chamfered square shape, it is possible to reliably determine the angular position of the ferrule 201 about the axis thereof, thus permitting an excellent ferrule engagement and disengagement characteristics. As described above, in the optical connector ferrule support structure and the optical connector plug according to the present invention, since it is possible to insert the ferrule from the initial position further deep by inserting the sleeve holder 206 into the plug housing 202, the axial engagement error can be easily absorbed, without providing another special parts or mechanism. Further, the structure can be effectively applied to the small-sized and multifiber plug-in optical connector. In addition, since the structure can be applied to the single fiber optical connector, it is possible to reduce the cost of the optical connector plug, because the plug can be used in common for both the single and multifiber plug-in optical connector. Further, the angular position of the ferrule can be determined by the square flange portion of the ferrule, it is possible to further reduce the size of the optical connector, which is effective in particular when a multifiber plug-in optical connector is constructed.

Claims: Optical connector plug, comprising: (a) a plug housing (202) formed with a through passageway having a shoulder portion (253) between a larger diameter hollow portion (254) and a smaller diameter hollow portion (252); (b) a plug ferrule (201) connected to an optical fiber (204) and formed with a flange portion (201 b) slidably fitted into the larger hollow portion of said plug housing and an end portion (201 a) extending into the smaller hollow portion of said plug housing; and (c) a spring (203) housed within said plug housing arranged to urge the flange portion of said plug ferrule against the shoulder portion (253) of said plug housing, characterized in that said shoulder portion (253) is shaped to have no projection between the larger hollow portion (254) and the smaller hollow portion (252) whereby a sleeve holder, in which the end portion of the ferrule can be inserted, can slide along through the smaller hollow portion (252) and is not hindered by any projections such that the inner end of the sleeve holder can travel past the shoulder (253) into the large hollow portion (254) as it pushes the flange portion (201 b) of the plug ferrule (201) against the bias of the spring (203). Optical connector plug of claim 1, characterized by (d) a sleeve holder (206) containing a floating alignment sleeve (205). The optical connector plug of claim 1, wherein the large hollow portion (254) of said plug housing and the flange portion (201 b) of said plug ferrule are both formed into polygonal shape. The optical connector plug of claim 3, wherein the large hollow portion (254) of said plug housing and the flange portion (201b) of said plug ferrule are both formed into chamfered square shape.

Inventors: ANDO YASUHIRO, IWANO SHIN ICHI, KANAYAMA KAZUNORI, NAGASE RYO, SUGITA ETSUJI, ANDO, YASUHIRO, IWANO, SHIN'ICHI, KANAYAMA, KAZUNORI, NAGASE, RYO, SUGITA, ETSUJI
Applicants: NIPPON TELEGRAPH & TELEPHONE, NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Application year: 1990
Main classification: G02B6
IPC codes: H01R13, G02B6