Optical connector

Abstract: To realize an optical connector in which the optical connector plugs (411) can be inserted only in a predetermined direction or orientation into a connector housing (416) at which a plurality of optical connector plugs (411) are mounted at the highest possible mounting density, the optical connector comprising (a) an adapter housing formed with a housing cutout (425) and two opposing housing projections (424) and (b) a square cross-section optical plug (411) formed with an axially extending plug projection (419) on one side surface thereof so as to be engaged with the housing cutout (425) and with two axially extending plug grooves (418) on two opposing side surfaces thereof so as to be engaged with the two opposing housing projections (424), an outside contour of said square optical connector plug being symmetrical with respect to a plane including an axial center of said connector plug and a middle portion of the plug projection but asymmetrical with respect to the axial center of said connector plug.

Description: The present invention relates to an optical connector structure for connecting an optical fiber, and more specifically to an optical connector locating structure suitable for a plug-in optical connector used to connect a package board on which optical or electrical parts are mounted to a unit frame or suitable when optical connectors are required to be arranged at high mounting density. Prior to the description of the optical connector, a reference will be made to a prior-art optical connector with reference to the attached drawings. JIS prescribes F04 single-core optical fiber connectors used to connect optical fibers, in which an optical fiber is fixed to the center of a cylindrical ferrule and this ferrule is inserted into a precise cylindrical hollow alignment sleeve so that two opposing ferrule end surfaces can be connected to each other. Fig. 1 shows this optical connector composed of an optical connector plug 401 and a connector housing 402 called adapter. A pair of optical connector plugs 401 are fitted to both the side surfaces of the connector housing 102 for coupling the two optical connector plugs 401. The connector plug 401 is composed of a plug housing 404 for supporting a ferrule 403 attached to one end of the optical fiber 400 and a knob 405. The plug housing 104 is slidable in the axial direction of the ferrule 103 within the knob 405. The connector housing 402 engaged with the optical connector plug 401 is composed of a cylindrical hollow alignment sleeve 406 to which the ferrule 403 is inserted and an insertion hole 407 to which the end portion of the knob 405 is inserted. These optical connector plug 401 and the connector housing 402 are coupled to each other by fitting the ferrule 403 into the alignment sleeve 406 and fitting the knob 405 into the insertion hole 407, respectively. Further, the above engagement is locked when two claw portions 411 of two engage arms 410 of the connector housing 402 are engaged with two engage recessed portions 409 of two grooves 408 formed on two opposing side surfaces of the optical connector 401, respectively. When the optical connector as described above is used to connect a single core optical fiber, generally two mating plugs are coupled to each other in a predetermined orientation so as to eliminate an eccentricity between the ferrule and the optical fiber core, that is, to maintain a required connection characteristics. In the case of the F04 single core optical fiber connector, therefore, a projection 412 is formed on one side surface of the optical connector plug 401, and a groove 413 fittable to this projection 412 is formed in the connector housing 402 so that the optical connector plug 401 having two symmetrical surfaces can be engaged with the connector housing 402 in a predetermined positional relationship. On the other hand, where package boards on each of which various optical modules are mounted are attached to a unit frame and optical signals are transmitted between these package boards and between the package board and an external device, a plug-in optical is used as disclosed in U.S. Patent No. 4,895,425 entitled "Plug-in Optical Fiber Connector". In the case of the plug-in optical connector, a plurality of optical connector plugs are fitted to the respective housings, and two mated optical connector plugs are connected simultaneously when the two housings are coupled with each other. In this usage, it is required to mount a plurality of optical connector plugs on a housing at high mounting density. Further, when a higher mounting density is required for the ordinary single core optical connector, a method of using an adapter is known to simultaneously couple a plularity of plugs. Figs. 2(a) and (b) show a connector housing 420 to which a plurality of optical connector plugs 401 are fitted. In this case, since each groove 421 for receiving a projection 412 formed on the side surface of the optical connector plug 401 is formed at each insertion hole 422 of the connector housing 420, each partition wall 423 for partitioning two adjacent insertion holes 422 is cut away to minimize the mounting pitch, so that two adjacent insertion holes 422 are connected to each other as shown. When the optical connector plug 401 is coupled with the connector housing 420, the optical connector plug 401 is locked by engaging an engage member 424 formed on an inner surface of each insertion hole 422 of the connector housing 420 with a groove 409 formed in a side surface of the optical connector plug 401, in the same way as shown in Fig. 1. Fig. 2(a) shows a state where an optical connector plug 401 is engaged with the above-mentioned connector housing 420, in which the optical connector plug 401 is fitted to the connector housing 420 by engaging two grooves 409 and a single projection 412 formed in the side surfaces of the optical connector plug 401 with two engage members 424 and a single groove 425 formed in the inner surfaces of the connector housing 420. When the plug locating structure of the F04 optical connector as described above is adopted, the following problems arise: Since the optical connector plug 401 is symmetrical with respect to the center line passing through the middle position of the groove 409, if the projection 412 is assumed to be removed, it is possible to fit the optical connector plug 410 into the insertion hole 422 (No. 3), for instance in two different directions as shown in Figs. 2(a) and (b). In case the optical connector plug 401 is inserted in the direction opposite to the predetermined direction, since the eccentric direction of the fiber core is reversed with respect to the center of the ferrule 403 in the case of the single core optical fiber, there exists a problem in that the eccentricity of fiber axis changes as compared with when the two fibers are coupled under the predetermined (selected) coupling conditions and therefore the coupling loss increases. Further, where one of the optical plug connectors 401 is inserted reversely, there inevitably exists some insertion holes 422 into which other plug connectors will not be inserted. It is the object of the present invention to provide an optical connector locating structure in which the optical connector plugs can be inserted only in a predetermined direction or orientation into a connector housing at which a plurality of optical connector plugs are mounted at the highest possible mounting density. The above-mentioned object is achieved by a connector in accordance with claim 1. In the optical connector according to the present invention, when optical connector plugs are mounted on the connector housing at the highest possible mounting density, since the two opposing side surfaces are symmetrical with respect ot a central plane parallel to the two opposing side surface but asymmetrical with respect to a central axis of the two oposing side surfaces, it is possible to prevent the optical connector plug from being inserted into the insertion hole of the connector housing in the erroneous mismatching direction opposite to the predetermined direction, thus securing a correct insertion of the plug into the housing at all times. Fig. 1 is a perspective view showing a prior art optical connector; Figs. 2(a) and (b) are front view for assitance in explaining the states where the prior art optical connector plug is inserted into the connector housing; Figs. 3 to 7 are views for assistance in explaining the present invention; Fig. 3 is a perspective view showing an embodiment of the optical connector according to the present invention; Figs. 4(a) to (d) are illustrations for assistance in explaining the construction of the optical connector. Fig. 4(a) is a front view showing the same; Fig 4(b) is a top view showing the same; Fig. 4(c) is a side, partially cross-sectional view showing same; Fig. 4(d) is a bottom view showing the same; plug of the present invention; Fig. 5 is a side cross-sectional view showing the state where the optical connector plug is inserted; Fig. 6 is a plan view showing the connector housing of the present invention; Figs. 7(a) to (b) are plan views for assistance in explaining the states where the optical connector plug of the present invention is inserted into the connector housing; A preferred embodiment of the present invention will be explained with reference to the attached drawings. Fig. 3 is a perspective view showing the optical connector according to the present invention, Fig. 4(a) is a front view showing the optical connector plug, Fig. 4(b) and 4(d) are side views thereof, Fig. 4(c) is a side cross-sectional view thereof, Fig. 5 is a side cross-sectional view showing the state where the optical connector plug is inserted into the connector housing, and Fig. 6 is a front view showing the connector housing. As shown in these drawings, an optical connector plug 411 comprises a plug housing 414 for supporting a ferrule 413 into which an optical fiber 412 is bonded, a spring 415 for urging the ferrule 413 and a knob 417 for locking and unlocking the optical connector plug to and from the connector housing 416, in the same way as in the prior-art F04 optical connector. The connector plug 411 is square in cross section thereof and formed with two axially extending grooves 418 on the opposing side surfaces of the knob 417 and with a projection portion 419 axially extending on another side surface thereof. The groove 418 is formed on each of the two opposing side surfaces of the knob 417 so as to be a little offset from the middle portion thereof, in such a way that the width W 1 of one inclined projection portion 420a is wider than that W 2 of the other inclined projection portion 420b. Therefore, both the opposing side surfaces in which the grooves 418 are formed, respectively are symmetrical with respect to a plane passing through the center of the ferrule 413 in parallel to both the side surfaces of the square plug 411 and through the middle portion of the projection portion 419, but asymmetrical with respect to a center of the axis of the ferrule 413. On the other hand, in the connector housing 416, the housing body 422 is formed with a plurality of insertion holes 416a into which optical connector plugs 411 are inserted, and with projections 424 and grooves 425 fitted to the grooves 418 and the projection 419 of the optical connector plugs 411, respectively. Further, cylindrical hollow alignment sleeves 425 into each of which the ferrule 413 of the optical connector plug 411 is inserted are provided within the insertion holes 416a of the connector housing 416. Further, two elastic deformable engage arms 426 each having an engage claw 426a are formed within the connector housing 416 so as to be engageable with the recessed portion 418a of the groove 418 of the optical connector plug 411. Further, the engage arm 426 is formed with side projection portions 426b (only one is shown) brought into contact with the inclined projection portions 420a and 420b for locking and unlocking function, when the optical connector plug 411 is inserted into or removed from the connector housing 416. Therefore, when the optical connector 411 is inserted into the insertion hole 416a of the connector housing 416, the grooves 418 formed in both the surfaces of the knob 417 are engaged with the projections 424 formed within the insertion holes 416a, so that the claw portions 426a are engaged with the recessed portion 418a of the grooves 418 and further the projections 424 are engaged deep with the grooves 418 to engage the optical connector plug 411 with the connector housing 416 as shown in Fig.5. Fig. 6 shows an example of the connector housing 416 for supporting a plurality of optical connector plugs, in which four insertion holes 416a are formed as four parts I, II, III and IV. In the above-mentioned structure between the optical connector plug 411 and the connector housing 416, even when only a single optical connector plug is inserted into a part III, for instance as shown in Fig. 7(a), it is impossible to insert the optical connector plug 411 in the reverse direction, because the groove 418 between the projections 420a and 420b having two different widths W1 and W2 of the optical connector plug 411 will not be engaged with the projections 424 of the connector housing 416 with an interference 430 (W1-W2) between the two. Therefore, it is possible to prevent the optical connector plug 411 from being inserted into the connector housing 416 erroneously even when the optical connectors 411 are arranged at the highest possible mounting density. Further, in the above embodiment, the asymmetry with respect to the axial center of the optical connector plug 411 is realized by offsetting the grooves 418 from the longitudinal center of the knobs 417 to obtain two different widths W 1 > W 2 of the two projections 420a and 420b. Without being limited thereto, however, it is possible to obtain the same effect by forming the two opposing surface shapes in symmetry with respect to a plane passing through the axial center of the connector plug and parallel to the two opposing surfaces but in asymmetry with respect to an axial center of the connector plug. As described above, in the optical connector plug locating structure according to the present invention, since the two opposing surfaces are symmetrical in shape with respect to a plane passing through the axial center of the connector plug and a middle portion of the plug projection but asymmetrical in shape with respect to the axial center of the connector plug, it is possible to prevent the optical connector plugs from being inserted into the connector housing erroneously in the reverse direction when the optical connector plugs are mounted at the highest possible arrangement density. Therefore, the structure of the present invention is advantageous in particular when applied to a plug-in optical connector for allowing a plurality of fibers to be connected simultaneously, because the highest possible mounting density is required for the plug-in optical connector.

Claims: An optical connector, comprising: an adapter housing formed with a through passageway having a housing cutout (425) in an internal side thereof and two opposing inwardly directed projections (424) within the passageway; and a square cross-section optical plug (411) formed with an elongate projection axially extending along the plug (419) on a first side surface thereof so as to engage the housing cutout (425) when the plug is inserted in the passageway and with two axially extending grooves (418) on two corresponding opposed second side surfaces thereof each groove engaging a different one of the two opposing housing projections (424) when the plug is inserted, wherein an outside cross-sectional contour of said square optical connector plug is symmetrical with respect to a plane coplanar with the central axis of said connector plug and with the plug projection and characterised in that said grooves are located such that said contour is asymmetrical with respect to a plane coplanar with the central axis and orthogonal to the second side surfaces.

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