Reusable mechanical connector for optical fibers

Abstract: A reusable mechanical connector (10) for an optical fiber (16,16A) has an elongated mount (11) of substantially uniform elliptical cross section and a straight longitudinal groove (13) extending the full length of the mount (11). The groove (13) has a uniformly shallow central portion and uniformly deep outer portions. A deformable housing (18) surrounds the mount (11). When the housing (18) is undeformed while bare ends (14,14A) of two abutting optical fibers (16,16A) are nesting in said shallow central portion and adjacent buffers of the fibers (16,16A) are nesting in said deep portions, the housing (18) pinches both the bare ends (14,14a) and buffers (16,16A) against the mount (11) simultaneously, thus optically interconnecting the fibers (16,16A). The fibers (16,16A) can be released simply by squeezing the deformable housing (18).

Description: Background of the Invention Field of the Invention The invention concerns optical fiber connectors such as can coaxially interconnect two optical fibers or can connect an optical fiber to an opto-electronic element. The invention is particularly concerned with connecting polarizing or polarization-maintaining optical fibers. Description of the Related Art Prior optical fiber connectors tend to be expensive, often requiring mechanical elements to be secured permanently to the optical fibers, followed by attaching each such element either to a complementary element or to a fixture. Doing so can require special tools. A relatively inexpensive optical fiber connector can be constructed as disclosed in U.S. Pat. No. 4,470,180 (Blomgren). A preferred Blomgren connector includes an elongated mount of substantially uniformly elliptical cross section that is encompassed by a resiliently deformable housing which, in its relatively undeformed state, can pinch a free end of an optical fiber against at least one straight longitudinal groove in the surface of the mount. Upon squeezing to deform the housing, a free end of a second optical fiber can be inserted to become coaxially interconnected with the first as shown in Blomgren Fig. 6C. An optical fiber connector now on the market ("Dorran" mechanical splice from 3M) is constructed as taught in the Blomgren patent and further has a strain-relief chock which grips a buffer layer that protects the optical fiber except at its free end which is bare. Typically, the buffer is in turn covered by a jacket and an intermediate layer of "Kevlar" fibers which can be stripped back to expose the buffer. Summary of the Invention According to the present invention there is provided a reusable mechanical connector for an optical fiber which connector comprises (a) an elongated mount, the surface of which is formed with at least one straight longitudinal groove and (b) a deformable housing surrounding said mount, which housing when undeformed is substantially cylindrical and can pinch a respective bare end of an optical fiber against the groove, said connector being characterized in that:- said connector is adapted for use with an optical fiber having a protective buffer; said groove has a uniformly relatively shallow portion for a bare end of the optical fiber; and said groove has a uniformly relatively deep portion for an adjacent portion of the optical fiber buffer, such that the outermost surfaces of the optical fiber bare end and buffer define a substantially straight line, thus permitting said deformable housing to pinch the optical fiber and buffer against the mount simultaneously. Thus there is disclosed a reusable mechanical connector for an optical fiber that has a protective buffer. Like the connector of the Blomgren patent, the novel connector is inexpensive to construct and includes (a) an elongated mount, the surface of which is formed with at least one straight longitudinal groove, and (b) a deformable housing surrounding said mount, which housing when undeformed is substantially cylindrical and can pinch a bare end of an optical fiber against the groove. Like the elongated mount of the Blomgren patent, that of the invention preferably has a substantially uniform elliptical cross section. The novel optical fiber connector differs from that of the Blomgren patent in that the groove in the mount has uniformly shallow and uniformly deep portions that respectively receive both a bare end of an optical fiber and the adjacent portion of its buffer such that the outermost surfaces of the bare end and buffer lie in a substantially straight line. This permits the deformable housing to pinch the optical fiber and buffer against the mount simultaneously. By a "bare end" is meant the portion of the optical fiber from which the buffer is stripped off, e.g., a core-cladding. When there is a non-strippable protective layer beneath the buffer, that protective layer is part of the bare end. As compared to the "Dorran" mechanical splice, optical fibers may be more quickly and easily assembled into the novel connector, because both the bare end of the optical fiber and its buffer can be secured in a single motion. To employ the novel connector to interconnect two optical fibers, the groove formed in the mount has a central shallow portion and outer deep portions, and said deformable housing can pinch simultaneously the bare ends of both fibers and their buffers when the bare ends abut at the shallow portion of the groove. The novel connector is particularly useful for interconnecting polarizing or polarization-maintaining optical fibers, because the connection can be tested, readjusted by fiber rotation, and retested until the desired transmission is attained. The mount of the novel connector can be a single piece that preferably is a block of ceramic, because (1) ceramic can closely match the mechanical and thermal properties of glass, the material of which most optical fibers are made, and (2) a ceramic block can be produced with precision geometry and surfaces. Other materials that have similar characteristics include certain metal alloys and a liquid crystal polymer such is available as "Xydar" from Amoco Performance Products. Because optical fibers of a single size are currently marketed with buffers of several different sizes, it may be desirable to form the mount from separate pieces for each of the optical fibers and their buffers, which pieces can be interconnected in a manner ensuring that their grooves lie in a straight line. Because the buffers do not need to be as precisely aligned as the bare ends of the optical fibers, the buffer-supporting mount portions (here called "chocks") can be formed less expensively, e.g., from synthetic resin. The use of a synthetic resin makes it easy to color-code the novel connector. A preferred synthetic resin is polycarbonate which is a tough, dimensionally stable, and substantially chemically inert thermoplastic resin. Detailed Disclosure To accommodate optical fibers having buffers of differing diameters, the groove of a connector of the invention can have its deep portions formed to permit the outermost portions of mismatched buffers to define a substantially straight line. The central shallow portion of a groove of a novel connector can likewise have two different depths to permit the interconnection of optical fibers having bare ends of differing sizes. Although the novel optical fiber connector is reusable, it can be employed in a manner that prevents it from being reused. For example, when using the novel connector to interconnect two optical fibers, a curable resin can be used to bond the bare fiber ends together permanently. Doing so could provide a hermetic seal and also enhance resistance to pull-out. When the cured resin has a refractive index matching that of the optical fibers, it can enhance the transmission of light across the interconnection. In some instances, it may be desirable to select a resin which cures to a desired mismatch of refractive indices, thus detuning the interconnection to attentuate transmitted signals. Detuning is desirable whenever there is a danger that the light signals being transmitted might be so intense as to cause a detector to go into saturation. Detuning can also be accomplished in the novel connector by maintaining a desired spacing between the interconnected fibers or by forming the longitudinal groove in the mount to have a central discontinuity to position the abutting optical fibers slightly out of perfect coaxial alignment. When transmitted light emanates from a semiconductor laser whose output gradually diminishes, the mount can be quickly and inexpensively changed from time to time to reduce the attenuation, thus keeping the transmitted signal levels substantially constant. Brief Description of The Drawings The invention may be more easily understood in reference to the drawing, all figures of which are schematic. Each figure of the drawing shows an optical fiber connector of the invention that can interconnect two optical fibers, except that the connector of FIG. 2 connects an optical fiber to an opto-electronic element. Some of the illustrated connectors are partly broken away to reveal details. In the drawings: FIG. 1 is an isometric view of a first optical fiber connector of the invention; FIG. 2 is a longitudinal cross section through a second optical fiber connector of the invention; FIG. 3 is an isometric view of a third optical fiber connector of the invention; FIG. 4 is an isometric view of a fourth optical fiber connector of the invention; FIG. 5 is an enlarged cross section along line 5--5 of FIG. 4; FIG. 6 is a cross section through a fifth optical fiber connector of the invention; and FIG. 7 is a cross section through of a sixth optical fiber connector of the invention. The optical fiber connector 10 of FIG. 1 has an elongated mount consisting of a ceramic block 11 of substantially uniform cross section that approximates an ellipse, and its surface is formed with a straight longitudinal V-groove 13 extending the full length of the block at a major axis of the ellipse. The longitudinal groove has a uniformly shallow central portion in which the bare ends 14 and 14A of a pair of optical fibers can nest and uniformly deeper outer portions in which the adjacent buffers 16 and 16A can nest such that the outermost surfaces of both the nested bare ends and the buffers define a substantially straight line that lies in the plane defined by the major axis of the elliptical mount. Surrounding the ceramic block is a deformable housing 18 which is substantially cylindrical when not deformed. When the housing 18 is squeezed in the direction of the minor axis of the block 11, the optical fibers can be freely inserted or removed. At each of its extremities, the groove 13 opens into a bell mouth 19, 19A to enhance threading optical fibers into the groove. After the optical fibers abut, the housing is released to return to its substantially cylindrical state to pinch each of the bare ends 14 and 14A and the buffers 16 and 16A against the longitudinal groove 13. Preferably the deformable housing 18 is sufficiently transparent to permit one to see that each of the bare ends 14 and 14A extends approximately to the center of the connector 10. When one of the optical fibers is inserted to reach the center of the connector, it acts as a stop for the other optical fiber. As seen in FIG. 2, an optical fiber connector 20, which is identical in construction to half of the optical fiber connector 10 of FIG. 1, permits a single optical fiber 25 to be connected to an opto-electronic element 27 while being pinched by a deformable housing 28. The optical fiber connector 30 of FIG. 3 has an elongated mount consisting of a central ceramic block 31 and a pair of plastic chocks 32 and 32A, which mount has a substantially uniform cross section that approximates an ellipse. Formed at the major axis of the elliptical mount is a straight longitudinal V-groove 33 that extends in a straight line over the length of the mount, because the block and chocks are (a) formed to interlock against relative rotation, (b) maintained in alignment by a deformable housing 38, and (c) releasably interlocked by detent means formed in the block and chocks at 37. That portion of the groove 33 that is formed in the block 31 is uniformly shallow, and the portions that are formed in the chocks 32 and 32A are uniformly deep up to bell mouths 39 and 39A, respectively, at the extremities of the mount. When a pair of optical fibers are threaded into the space between the housing 38 and the mount, the outermost surfaces of both the nested bare fiber ends 34 and 34A and buffers 36 and 36A lie in a substantially straight line. Although the length of the housing 38 approximates the length of the mount, it could be shorter for various reasons, e.g., to make it easy to grasp the ends of the chocks 32 and 32A for removal or to permit the ends of the chocks to fit into connector-mounting means (not shown). The optical fiber connector 40 of FIGS. 4 and 5 has an elongated mount consisting of a central ceramic block 41 which nests in a saddle chock 42. When so nested, the block 41 and chock 42 have a substantially uniform cross section that approximates an ellipse. Formed at the major axis of the elliptical mount is a straight longitudinal V-groove 43. The block is held in the illustrated position by a deformable housing 48 that pinches the bare ends 44 and 44A and buffers 46 and 46A of a pair of optical fibers in the same manner as in FIG. 3. The optical fiber connector 60 of FIG. 6 has an elongated mount consisting of a central ceramic block 61 which nests in a saddle chock 62 in a manner similar to the connector 40 of FIGS. 4 and 5. Extending the length of the assembled block 61 and chock 62 is a straight longitudinal V-groove 63. The block is held in the illustrated position by a deformable housing 68 which normally pinches the bare ends (one shown at 64) and buffers (not shown) of a pair of optical fibers. The optical fiber connector 70 of FIG. 7 has an elongated mount consisting of a central ceramic block 71 which nests in a saddle chock 72 and is held there by a deformable housing 78. The assembled block and chock together have a straight longitudinal V-groove 73. A bare end 74 of an optical fiber is shown being pinched by the deformable housing 78. Example A prototype of the connector 30 illustrated in FIG. 3 has been constructed to splice a pair of optical fibers, each having a glass core-cladding 125 µm in diameter and a buffer 250µm in diameter. The block 31 was ceramic, and the chocks 32 were polycarbonate. Key dimensions of the prototype were: The heights were measured with a micrometer. The difference in the heights of the bare end and buffer above the V-groove is due in part to the greater breadth of the V-groove where it receives the buffer. Furthermore, the buffer is resilient and hence slightly compressed by the housing, and because of this, pull-out resistance is enhanced. Upon testing the prototype at 1300 nm, average insertion loss was 0.1 dB. Tensile pull-out was greater than 4.5N.

Claims: A reusable mechanical connector for an optical fiber which connector comprises (a) an elongated mount, the surface of which is formed with at least one straight longitudinal groove and (b) a deformable housing surrounding said mount, which housing when undeformed is substantially cylindrical and can pinch a respective bare end of an optical fiber against the groove, said connector being characterized in that:- said connector is adapted for use with an optical fiber having a protective buffer; said groove has a uniformly relatively shallow portion for a bare end of the optical fiber; and said groove has a uniformly relatively deep portion for an adjacent portion of the optical fiber buffer, such that the outermost surfaces of the optical fiber bare end and buffer define a substantially straight line, thus permitting said deformable housing to pinch the optical fiber and buffer against the mount simultaneously. An optical fiber connector as defined in claim 1 wherein said groove has a central shallow portion and outer deep portions, and said deformable housing can pinch simultaneously the bare ends of two optical fibers and their buffers when the fibers abut at the shallow portion of the groove. An optical fiber connector as defined in claim 1 or claim 2 wherein the mount has a substantially uniformly elliptical cross section, and said groove extends the full length of the mount at the major axis of the elliptical mount. An optical fiber connector as defined in claim 1, 2 or 3 wherein the mount is a single block. An optical fiber connector as defined in claim 1 wherein the mount comprises a block in which said shallow portion is formed and at least one chock in which a deep portion is formed, which block and chock are formed to interlock against relative rotation. An optical fiber connector as defined in claim 5 and comprising a single chock which forms a saddle for said block. An optical fiber connector as defined in claim 5, comprising two chocks, each of which can be secured to one end of said block.

Inventors: BLOMGREN JACK P C O MINNESOTA, MEIS MICHAEL A C O MINNESOTA M, BLOMGREN, JACK P., C/O MINNESOTA MINING AND, MEIS, MICHAEL A., C/O MINNESOTA MINING AND
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1990
Main classification: G02B6
IPC codes: G02B6