GB1596388A

GB1596388A - Optical fibre connector

Info

Publication number: GB1596388A
Application number: GB53390/77A
Authority: GB
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1976-12-27
Filing date: 1977-12-22
Publication date: 1981-08-26

Description

(54) OPTICAL FIBER CONNECTOR (71) We, WESTERN ELECTRIC COMPANY, INCORPORATED, of 222 Broadway, New York City, New York State, United States of America, a Corporation organized and existing under the laws of the State of New York, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to optical fiber or fiberguide connectors.

Fiber-optic communication channels have larger signal carrying capacity, are lighter in weight, smaller in size and potentially lower in cost than their electrically conductive counterparts. In addition, they are immune to electromagnetic and radio frequency interference and offer advantages in eliminating cross-talk and in assuring privacy.

Recent improvements in fiber-optic transmission lines, both in performance and in mechanical strength, are impressive and promise widespread application in the very near future.

One of the persistent problem areas, however, in the practical application of fiber optics for communications has been that of the optical fiber connector.

In optical communication systems, it is necessary to couple optical fibers end-to-end as well as to devices such as detectors or signal generators. An axial misalignment results in attenuation across the coupling.

The problem of connecting fibers can be simply stated. Adjacent fiber ends must be flat, perpendicular, and polished as well as aligned axially and transversely. The difficulty arises when dimensional tolerances are considered. In order to keep optical loss negligible, i.e., about 0.1 dB, the transverse alignment error must be less than 1/20 the fiber core diameter and the axial separation less than 1/2 the diameter. Practical multi-mode fiber core diameters are likely to be 50 to 250 m (0.002" to 0.010"), and therefore positional errors of the fiber core of even 0.0001" would result in measurable loss. Another requirement not imposed on wire connectors is that of cleanliness.

The making or breaking of the connection must not generate debris that could obstruct the light path or alter the alignment of the fibers.

The necessary alignment could be accomplished by making an adjustable connector, but this procedure would be cumbersome and the apparatus costly. Many designs involving numerous complex parts machined to close tolerances have been shown to operate satis factorily, particularly with the larger fibers or fiber bundles. See, for example, T. Bowen, "Fiber Optics on an Interconnecting Medium", Electronic Packaging and Production, pp.

17-32 (April 1976). Whether or not such designs, if standardized and made in large quantities, would be reasonable in cost is yet to be demonstrated.

It is an object of this invention to provide a simple, precise, low cost optical fiber connector It is another object of the invention to alleviate the need for expensive machining of connector parts to critically tight tolerances, it being possible to assemble the connector largely from inexpensive, off-the-shelf, precision components.

According to the present invention there is provided an optical fiber connector comprising at least three inner cylindrical rods located in tangential contact with each other about an axis and forming an aperture therebetween, an optical fiber located within the aperture formed by the inner rods, at least three outer rods in parallel with and in contact with the inner rods, the diameter of the outer rods being at least 1.5 times that of the diameter of the inner rods, and a tubular resilient sleeve whose inner surface is in contact with, and exerts a radial pressure on the outer rods, the radial pressure being transmitted to the inner rods thereby providing a support for the inner rods and fiber.

In one embodiment of the invention, the optical fiber connector comprises a resilient, hollow, cylindrical sleeve and three parallel cylindrical members (outer rods) affixed to the inner surface of the sleeve. The outer rods are spatially separated with centers on radial axes 120 degrees apart and extend parallel to the cylinder axis of the sleeve. The fibers to be connected each have end portions mounted in male half-connectors which are insertable into the sleeve. Each half-connector comprises a second set of three parallel cylindrical members (inner rods) is mutual contact with one another along their length so as to form as inscribed cylindrical aperture therebetween. The fiber is secured within the aperture to the inner rods, and the inner rods and the fiber end portion terminate in a planar surface substantially perpendicular to the cylinder axis. The diameters of the outer rods are at least 1.5 times that of the inner rods, and are positioned so that, when a half-connector is inserted into one end of the sleeve, each outer rod makes contact with two adjacent inner rods. A second halfconnector is inserted into the other end of the sleeve until the planar surfaces of the inner rods are in contact, thereby aligning the end portions of the fibers. The ends of the rods are preferably curved to facilitate insertion of the half-connectors. The sleeve can be a metal tube and the outer rods are welded to its inner surface. Alternatively, the sleeve can be of rubberlike material into which the outer rods are molded. The sleeves can be mounted in a plurality of holes in a rigid support member to provide mechanical strength and to fix the configuration of the array. It is advantageous that the outer rods are arranged so that they do not contact one another. This arrangement, in conjunction with the resiliency of the sleeve, permits the automatic self-aligning of the halfconnectors. For example, in the case where the inner rods are slightly undersized, the outer rods, under the urging of the sleeve, contract around the inner rods to effect alignment, and conversely expand for slightly oversized inner rods. The diameters of the inner and outer rods are such that the force imparted by the sleeve through the outer rods tends to keep the inner rods in contact with one another. An advantage is that the well developed technology of the roller bearing industry can be exploited by employing inexpensive, precise, uniform cylindrical needle bearings as the inner and outer rods of the connector. These standard rollers are commercially available at a cost of approximately one cent each.

In another embodiment of the invention, there is provided an optical fiber connector having a male connector portion having at least three cylindrical inner rods held in tangential contact with each other forming an opening which contains an optical fiber. A female connector portion has at least three and preferably six, cylindrical outer rods arranged to form a nest to accommodate the inner rods. Nesting of the inner rods within the outer rods positions the fiber, with a high degree of accuracy, within the female connector portion. The nest formed by the outer rods accommodates end-to-end the inner rods of two substantially identical male connector portions, thereby permitting accurate positioning and axial alignment in the end-toend coupling of the fibers held by the two male connector portions. Each outer rod contacts at least one inner rod to thereby fixedly position the optical fiber. Each inner and outer rod is a precision bearing roller, which is a low cost, commercially available item. The outer rods are in tangential contact with each other. This arrangement permits precise control of the size of the nest formed by the outer rods.

In a further embodiment of the invention, there is provided an optical fiber connector which axially aligns two fibers end-to-end and protects the end of a fiber from damage before the connector is assembled.

Thus further optical fiber connector has a housing having a cylindrical opening extending axially therethrough. A plurality of inner rods and a plurality of outer rods are disposed within the opening. The inner rods are held in tangentia contact with each other forming an aperture for receiving a fiber. A fiber disposed in the aperture and the inner rods terminate in a planar surface substantially perpendicular to the longitudinal axis of the fiber. The outer rods are secured between the inner rods and the housing and extend past the planar surface protecting the end of the fiber from damage. The outer rods of one connector are spaced apart to accommodate between them the outer rods of a duplicate mating connector. The outer rods of the two duplicate mating connectors form a nest to accommodate the inner rods of both connectors thereby accurately positioning and axially aligning both fibers.

The invention can be readily understood frorr the following more detailed description taken in conjunction with the accompanying drawings, in which: Figure 1 is a cross-sectional view of an optical fiber connector in accordance with an illustrative embodiment of the invention; Figure 2 is an exploded pictorial view showing how the connector of Figure 1 is used to align a pair of optical fibers; Figure 3 is a pictorial view of an array of outer rod-sleeve assemblies mounted in a rigid support member in accordance with another embodiment of the invention; Figure 4 is a cross-sectional view of a typical optical fiber; Figure 5 is a perspective view of the said other embodiment showing an optical fiber connector, and Figure 6 is a cross-sectional view of the connector shown in Figure 5, with the inner rods of the male connector portion nested within the outer rods of the female connector portion.

Figure 7 is a perspective view of two optical fiber connectors illustrating the said further embodiment of the present invention; Figure 8 is an exploded perspective view of one of the connectors shown in Figure 7; Figure 9 is a perspective view of a connector body shown in Figure 8; Figure 10 is a sectional view of the connector body as shown generally along plane 4-4 of Figure 9; Figure 11 is a sectional view of the connector body as shown generally along plane 5-5 of Figure 9.

With reference now to Figures 1 and 2, an optical fiber connector 10 comprises a resilient, hollow cylindrical sleeve 12 and three parallel cylindrical members 14 (outer rods) affixed to the inner surface of sleeve 12. The outer rods 14 are spatially separated from one another with centers on radial axes 16 which are substantially 120 degrees apart. The fibers 18 to be connected each have end portions mounted in male half-connectors 20 which are insertable into sleeve 12. Each half-connector 20 comprises a second set of three parallel cylindrical members 22 (inner rods) which contact one another along their length so as to form an inscribed cylindrical aperture 19. Fiber 18 is secured within the aperture 19 to inner rods 22 as, for example, by filling the space 24 between the fiber 18 and rods 22 with epoxy or other suitable cement. The inner rods 22 and the end portion of fiber 18 terminate in a planar surface substantially perpendicular to the cylinder axis of sleeve 12; i.e., perpendicular to the longitudinal axis of fiber 18. The diameters of the inner rods 22 and outer rods 14 are mutually adapted so that, when a half -connector 20 is inserted into one end of sleeve 12, each outer rod 14 makes contact substantially along its entire length with two adjacent inner rods 22.

A second half-connector 20 is inserted into the other end of the sleeve until the planar surfaces formed by the ends of the inner rods 22 abut, thereby aligning the end portions of the fibers.

Preferably the ends of the rods are curved or spherical to facilitate insertion of the halfconnectors.

The particular nested configuration of the inner and outer rods is important in achieving automatic self-alignment of the fibers. More specifically, the outer rods are spatially separate, i.e., not in contact with one another, so that, when the inner rods are inserted, the resilient sleeve can expand slightly and then contract to force the inner rods into alignment. In addition, this configuration allows accommodation of dimensional deviation of the rods, especially if one or more of the inner rods is undersized in diameter.

Another feature of the nested rods is the provision of larger diameter outer rods 14 adapted to force the inner rods 22 together. To this end, it has been found that the ratio of the diameters of the outer to inner rods should be 1.5:1 or greater. With smaller ratios the force transmitted by the sleeve 12 through the outer rods 14 tends to separate the inner rods 22 and may cause misalignment errors or may even crack the epoxy or other cement which secures the fiber 18 to rods 22.

An exemplary fiber 18 is shown in Figure 4.

It comprises a core 18.1 surrounded by a cladding 18.2. Both are typically glass. A nylon coating 18.3 surrounds the cladding and a PVC protective sleeve 18.4 surrounds the coating.

As shown in Figure 2, the half-connectors 20 include heat shrinkable tubing 26 to provide strain relief to the assembly, especially at the back end of the half-connector. The tubing 26 covers only the portion of rods 22 rearward of the planar surfaces, leaving the proximate portion of the rods 22 exposed for ready insertion into sleeve 12. The tubing 26 adheres to the PVC sleeve 18.4 of fiber 18 and to an epoxy anchor 32 which surrounds inner rods 22.

In addition, it will be noted that the nylon coating 18.3 which surrounds the cladding 18.2 is compressible under the force of the inner rods 22. Consequently, as discussed hereinafter, this coating acts as a variable self-centering member.

In a specific exemplary embodiment of the optical connector, the inner and outer rods were cylindrical needle bearings commercially available from the Torrington Bearing Co. of Torrington, Conn. The precision of the bearings was adequate: the overall tolerance of the diameter was +0.0001", but if necessary could be selected to a tolerance of 0.000025 . The standard rollers cost about one cent each, were made of chrome steel, and were lapped and polished on their ends.

These precision rollers (rods), as off-the-shelf items, are graded in increments of 1/64 of an inch, with a wide choice of lengths. The standard rod has a spherical end which is effective in guiding the half-connectors 20 into sleeve 12.

The maximum diameter cylinder (i.e., fiber core plus cladding diameter) which will fit in the aperture 19 formed by inner rods 22 is directly related to the roller diameter. The relationship is 1 to 6.4641. Therefore for off-theshelf roller dimensions, the apertures 19 available to position an optical fiber are 4.8, 7.2, 9.7 etc. thousandths of an inch (mils) in diameter. For example, a large core fiber developed for use with incoherent light sources in an electronic switching system is well suited to the 9.7 mil diameter opening. This fiber, shown in Figure 4, consists of a 5 mil glass core 18.1 surrounded by 1.5. mil thick glass cladding, 18.2 giving a core-cladding diameter of about 8.25 mils. A thin nylon protective coating 18.3 about 1 mil thick brings the diameter to 11 mils. When this fiber is clamped by the three inner rods 22, (the PVC sleeve 18.4 is first stripped back), the nylon coating is slightly deformed or extruded into the available space but the glass core-cladding remains unstressed and centered well within j 0.5 mil. It should be noted that no stripping of the protective nylon coating is required, and in fact the coating actually permits a wider tolerance on the core-cladding diameter than if it were not used.

In an illustrative specification for the optical fiber, the core-cladding diameter was controlled to between 8.1 and 9.3 mils. Of the approximately 100 fiber ends prepared, using inexperienced personnel and first generation tooling, about 80% were centered within 0.5 mil. These results indicate that an acceptable yield can be obtained with a specification requiring centering of the fiber core and cladding to this tolerance.

The diameter of the rollers (rods) themselves are extremely uniform as purchased, but the three assembled inner rods 22 were checked for size to within 0.1 mil by means of hole gauges. It would appear, that the centering error will in large part depend on the fiber to be centered, with considerable latitude permitted because the nylon coating acts as a variable selfcentering sleeve for the core-cladding portion of the fibers. The following table lists the permissible combinations of uncoated optical fibers and standard rollers. Dimensions are in inches, and the diameter tolerance of all Torrington rods was + .0000 and - .0002.

diameter of the circle inscribed by the outer rods. The diameter of the outer and inner rods was 3/32 inch and 1/16 inch, respectively.

In a second embodiment adapted for mounting an array of connectors shown in Figure 3, the sleeve comprised an annular or tubular rubber-like member 12.1 carried by a rigid support member or panel 30. In practice, the outer rods 14 were molded into the rubber sleeve and the panel 30 comprised polystyrene.

The advantage of the rubber sleeve is that the outermost diameter of the sleeve may now be interfaced with a rigid body, whereas in the previous embodiment the steel tubing should be free to provide resiliency. The use of a rubberlike sleeve enables a plurality of sleeves to be assembled to form a jack field simply by drilling holes in an appropriate panel.

The tensioning provided by this embodiment is a function of the rubber-like material, the size of the hole that receives the sleeve-outer rod assembly, and the design of the core used in the molding operation. The core should be made such that the outer rods 14 assume a slightly smaller inscribed circle than the circum Opening for Uncoated Standard Inner Suggested Outer Cylindrical Fiber Rod (Roller) Dia. Rod (Roller) Dia.

0.00483 0.0312 0.0469 0.00726 0.0469 0.0781 0.00967 0.0625 0.0938 0.0121 0.0781 0.1250 0.0145 0.0938 0.1562 0.0169 0.1094 0.1875 As noted previously, sleeve 12 functions to guide the precise half-connectors 20 when making a connection. An economical way to achieve this guidance to the required precision was, once again, to use standard rollers for the outer rods 14. The outer rods 14, which are at least 1-5 times that of the inner rods 22, acted as self-aligning rails along which the inner rods 22 glide. Outer rods of at least 1.5 times the diameter of the inner rods provide a net compressive force on the half-connectors.

The positioning of the outer rods 14 in the sleeve 12 should permit easy insertion of the inner rod assembly on the one hand, and yet apply sufficient tension to bring about the selfalignment of the whole connector assembly on the other. The tensioning action should also be great enough to overcome stress which might be externally applied to the connector e.g., from the weight of optical cables or the method of routing the cables.

In one embodiment of the foregoing connector, sleeve 12 comprised thin-walled stainless steel tubing. The tension of the sleeve is controlled by the wall thickness and the shape of the tubing. For example, it has been found that a 0.300" diameter tube with an 0.006" wall could be inelastically distorted using a three jaw chuck to provide a fine adjustment of the scribed circle required to hold the inner rods 22, yet provide clearance for free travel along the outer rods of the sleeve 12. Polyurethane of Shore A hardness 50 is one rubber-like material that has been found to be adequate.

It is commercially available from ML Industries, Heightstown, New Jersey.

One of the more important operations in the fabrication of the connector is the alignment and bonding of the three inner rods 22 to the fiber 18. The three inner rods must be held strictly parallel to each other and in metal inmutual - contact, and then bonded with the fiber in place, A jig was used for this purpose. The jig had a pair of horizontally translatable jaws which formed a trapezoidal opening when closed and a vertically translatable jaw which could be closed over the top of the trapezoidal opening.

Two of the inner rods were first clamped parallel to one another by placing them next to one another at the bottom of the trapezoidal opening and closing the horizontal jaws. Second an end portion of the fiber, after being stripped of the PVC and coated with an epoxy, was laid along the intersection of the two rods.

Next, the third inner rod was put in place on top of the other two and the vertical jaw was lowered to force the fiber into place. The entire assembly was then baked to cure the epoxy. The amount of epoxy used was controlled to slightly overfill the aperture 24 and extrude from the ends, yet not so much as to interfere with the subsequent insertion of the half-connector 20 into sleeve 12. The epoxy was illustratively a one part heat curing structured adhesive, Scotch-Weld #2214, which cures in 40 minutes at 120 degrees C and makes a high strength bond with metals, glass, and some plastics. This epoxy is manufactured by the 3M Company, Minnesota.

At this stage of the fabrication process the fiber extends beyond the ends of the inner rods by a few millimeters or more to allow for proper end preparation and polishing.

As mentioned previously the protective coating 18.4 on the optical fiber should be secured by some appropriate means to the inner rods 22 in order to reduce strain and to prevent an abrupt bend or kink where the fiber enters the inner rods. One method is shown in Figure 2, where the same epoxy which bonds the inner rods was used to form an anchor 32 toward the back of the half-connector 20. Then several layers of heat shrinkable tubing 26 were applied, as required, to form a handle and to provide strain relief. The tubing 26 adhered to the outer jacket 18.4 of the fiber 18. The jacket was typically 100 mil diameter PVC. A simple spring clip (not shown), or other suitable means of securing the half-connectors and sleeve together, may be used to insure that the fiber connection, once made, stays in place.

As stated above, the making of a connection between two optical fibers consists of aligning, axially and transversely, their flat, perpendicular, and polished ends. One simple way to prepare a fiber end is to break the fiber by scribing and bending. However this method does not insure a perpendicular end, and many glass fibers, because of the high internal stresses implicit in their design, do not break cleanly or uniformly.

A more positive approach was to polish the ends. The half-connector with the fiber firmly epoxied to the inner rods was trimmed and polished in two stages by hand, using first a 3,um alumina and finally cerium oxide. The result was a polished end, with the optical core slightly concave.

Finally, a protective coating of silicone rubber compound was placed over the ends of both the fiber and the inner rods 22. Thus, when two half-connectors 20 were brought together, the silicone acted as both a buffer and a seal. The thickness of 0.5 mil for the silicone layers was adequate for this purpose.

Testing of the optical connector was largely one of checking dimensional tolerances. By assuring that mechanical tolerances were met, and that the fiber end was polished, satisfactory optical performance could be obtained.

The inner rod assembly was checked by use of a series of hole gauges, the correct one being 0.1346" for inner rods of 1/16 inch diameter.

Centering of the fiber core was checked by rotating the assembly in the hole gauge, and observing the run-out using a 400X microscope.

Next, light was introduced from the other end of the fiber, and the circularity and uniformity of the light observed. A very high degree of centering, approaching the precision of the roller, can be expected as fiber dimensions come under increasingly better control.

In the said other embodiment of the invention illustrated in Figures 5 and 6 an optical fiber connector 120 comprises a male connector portion 121 and a female connector portion 122. The male connector portion 121 has at least three substantially identical parallel, cylindrical inner rods 123 which are held in tangential contact with each other by heat shrinkable tubing 124. The three inner rods 123 are made of chrome steel and are sold commercially as bearing rollers. The rods are available in various lengths and diameters. The tolerance on each diameter is held, for example, to + .00001 inch.

The three inner rods 123 are held in tangentia contact with each other along their entire length forming an opening 125. The size of the opening 125 is precisely controlled by controlling the diameter D1 of each of the inner rods 123.

An optical fiber 126 is disposed within the opening 125 which accurately positions the fiber 126 within the male connector portion 121. A typical optical fiber comprises a core surrounded by a cladding, both usually made of glass and a protective coating and sleeve, usually made of nylon and PVC respectively.

The end of the fiber 126 to be inserted into the opening 125 is stripped of its protective nylon coating so that the cladding of the fiber 126 is exposed. The stripped end of the fiber 126 is then inserted into the opening 125 until its extends slightly past the planar surface 130 containing the inner rods 123. The diameter D1 of each of the inner rods 123 is related to the diameter d of the stripped portion of the fiber 126, for example, by the following expression: D1 = 6.4627d Once the stripped end of fiber 126 is within the opening 125, an adhesive, such as silicone rubber, is inserted into the spaces of opening 125 not occupied by the fiber 126. After the adhesive sets and fastens the fiber 126 and the three inner rods 123 together, the end of the fiber 126 is polished until it is flush with the ends of the inner rods 123 and lies in a planar surface 130, which is substantially perpendicular to the longitudinal axis of the fiber 126.

As shown in Figures 5 and 6, the female connector portion 122 comprises six substantially identical parallel, cylindrical outer rods 128 held together in tangential contact with each other by a cylindrical spring 131. The outer rods 128 are arranged to form a nest with an opening 129 which accommodates the inner rods 123. When the inner rods 123 are nested within the outer rods 128, each outer rod 128 contacts one of the inner rods 123 thereby fixedly positioning the optical fiber 126. Size of the opening 129 is precisely controlled by controlling the diameter D2 of each of the outer rods 128. The diameter D2 of each of the outer rods 128 is related to the diameter D1 of each of the inner rods 123 for example, by the following: D22 -2D1D2 +.1111D12 =0.

Nesting of the inner rods 123 within the outer rods 128 positions the fiber 126, with a high degree of accuracy, within the female connector portion 122.

The six outer rods 128 are held in tangential contact with each other by a cylindrical spring housing 131. The outer rods 128 are made of chrome steel and are sold commercially as bearing rollers. They are available in various lengths and diameters. The tolerance on each diameter is held, for example, to + .00001 inch.

The cylindrical spring 131 is made from phosphor bronze tubing. The spring 131 has an opening 133 extending axially therethrough and a slit 132 extending the length of the spring 131 parallel to the longitudinal axis of the spring.

The diameter of the opening 133 is made smaller than the major diameter of the nest formed by the six outer rods 128. Thus, when the outer rods 128 are inserted into the opening 133, slit 132 permits the opening 133 to expand to accommodate the outer rods 128. The diameter of the opening 133 and the wall thickness of the spring 131 are such that when the six outer rods 128 are within the opening 133, the spring 131 exerts sufficient radial pressure upon each of the outer rods 128 to keep the outer rods in tangential contact with each other. The outer rods 128 are preferably provided with hemispherical ends to aid in the insertion of the inner rods 123 into the opening 133 formed by the outer rods.

To couple end-to-end the fiber 126 held by the male connector portion 121 and a fiber 127 held by a male connector portion 121', shown in Figure 5, which is substantially identical to the male connector portion 121, the two male connector portions 121 and 121' are inserted from opposite ends into the female connector portion 122. The inner rods 123 of the male connector portion 123 and inner rods 123' of the male connector portion 121' are nested within the opening 129 formed by the outer rods 128. The nesting of the inner rods 123 and 123' within the opening 124 formed by the outer rods 128 accurately positions and thus axially aligns the two fibers 126 and 127 held by the inner rods 123 and 123'. respectively.

The fiber 126 terminating in the planar surface 130 and the fiber 127 terminating in a planar surface 130' are coupled end-to-end by bringing the two fiber ends together within the female connector portion so that the planar surface 130 is superimposed upon the planar surface 130'.

In the said further embodiment of the invention illustrated in Figure 7, there are shown two substant nylon. None of the dimensions of the connector body 239 are critical. The connector body 239 has a first cylindrical portion 240 having a diameter which is less than the diameter of cylindrical opening 234 of the connector housing 233. This facilitates easy insertion of the first cylindrical portion 240 into the opening 234. The length of the first cylindrical portion 240 is less than the length of the opening 234 to allow outer rods from connector 230 to fit into the opening 234. The connector body 239 further has a second cylindrical portion 241 which has substantially the same diameter that the first cylindrical portion 240 has. The first and second cylindrical portions are connected by a third cylindrical portion 242 having a diameter smaller than the diameter of both the first and second cylindrical portions 240 and 241.

In Figures 8, 9 and 10, there are shown three equally spaced slots 243 in the cylindrical portion 240. The slots 243 extend from the outer perimeter of the first cylindrical portion 240 towards its center. The width of each slot 243 is less than the diameter of an outer rod 238 to insure an interference fit between each outer rod 238 and a slot 243. The length of each slot 243 is not critical as long as outer rods 238 do not bottom out during the final assembly of the connector 230.

In Figures 9, 10 and 11, there is shown an opening 244 in the connector body 239. The opening 244 extends axially, as shown in Figure 11, from the enclosed ends of slots 243 through the first cylindrical portion 240 and the third cylindrical portion 242. The opening 244 has a cross-sectional shape of an equilateral triangle with rounded corners and is oriented, as shown in Figure 10, in such a way that each of the bisectors 257 of the angles of the equilateral triangle is offset by an angle of 30 degrees from the center line 258 of each slot 243. The crosssectional area of the opening 244 is small enough so that the inner rods 237, when forced into the opening 244, are held in tangential contact with each other. The opening 244 has to be deep enough so that the inner rods 237 are held in contact along their entire length.

In Figure 11, there is shown an opening 245 having a truncated conical and cylindrical section. The opening 245 extends axially from the bottom of the triangular opening 244 through the second cylindrical portion 241. The opening 245 has to be sufficiently large at its narrowest point to accommodate the fiber 231.

Connector 230 is assembled as follows.

First, the three inner rods 237 are inserted into the triangular opening 244, as shown in Figure 8. The three inner rods 237 are substantially parallel to each other and form the aperture 254 for receiving the fiber 231. The diameter D1 of each of the inner rods 237 is related to the diameter d of the fiber 231 by the following expression: D1 = 6.4627d The inner rods 237 have to be long enough so that after one set of ends of the inner rods 237 is inserted into the opening 244, shown in Figure 9, the free ends of the inner rods 237 extend past the first cylindrical portion 240, as shown in Figure 8.

Once the inner rods 237 are in place, the fiber 231 is inserted into the opening 245 of the cylindrical portion 241, shown in Figure 11.

The fiber 231 is pushed through the opening 245 into the aperture 254, shown in Figure 8, until one end of the fiber 231 extends slightly past the ends of the three inner rods 237. The inner rods 237 hold the fiber 231 so that the longitudinal axis of the fiber 231 is substantially parallel to the longitudinal axis of each of the inner rods 237. When the fiber 231 is in place, an adhesive, such as silicone rubber, is inserted into the opening 245, shown in Figure 11, and portions of aperture 254, shown in Figure 8, which are not occupied by the fiber 231. The adhesive anchors the fiber 231 to the second cylindrical portion 242 and fastens the fiber 231 and the three inner rods 237 together.

After the adhesive sets, the end of the fiber 231 held by the three inner rods 237 is polished until it is flush with the ends of the inner rods 237 and lies in the planar surface 255, shown in Figure 8, which is substantially perpendicular to the longitudinal axis of the fiber 231.

As shown in Figure 9, each outer rod 238 is pressed into a different one of the slots 243 located in the first cylindrical portion 240. The outer rods 238 are positioned so that they do not bottom out in the slots. The maximum length of each of the rods 238 is such that if a rod 238 is bottomed out in a slot 243, the free end of the rod 238 extends past the free ends of rods 237 by an amount which is equal to or less than the amount the free ends of the inner rods 237 extend past the end of the first cylindrical portion 240. This is to insure that outer rods 238 will not bottom out against the connector body of connector 230' when connectors 230 and 230' are mated. Each outer rod 238 comes in contact with a different one of the inner rods 237. The diameter D2 of each of the outer rods 238 is related to the diameter D1 of each of the inner rods 237 by the following expression: D22 -2D1D2 +.1111D12 =0.

Once the assembly of the connector body 239 is complete, the first cylindrical portion 240 is pressed into the housing 233. The pressing operation is done in a fixture which positions the face of the flange 235 and the ends of the inner rods 237 in the same planar surface 255. The fixture also adjusts the position of each of the outer rods 238 so that the ends of the outer rods 238 extend past the ends of the inner rods 237 the same amount that the ends of the inner rods 237 extend past the end of the first cylindrical portion 240. Tabs 239 are then bent down over the third cylindrical portion 242, anchoring the connector body 239 to the housing 233.

WHAT WE CLAIM IS: 1. An optical fiber connector comprising at least three inner cylindrical rods located in tangential contact with each other about an axis and forming an aperture therebetween, an optical fiber located within the aperture formed by the inner rods, at least three outer rods in parallel with and in contact with the inner rods, the diameter of the outer rods being at least 1.5 times that of the diameter of the inner rods, and a tubular resilient sleeve whose inner surface is in contact with, and exerts a radial pressure on the outer rods, the radial pressure being transmitted to the inner rods thereby providing a support for the inner rods and fiber.

2. A connector according to claim 1, wherein the sleeve comprises a thin walled metal tube, and the outer rods are also metallic and are bonded to the inner surface of the tube.

3. A connector according to claim 1, wherein the sleeve is of rubber like material with the outer rods metallic and bonded thereto, and wherein a rigid support member surrounds the sleeve.

4. A connector according to claim 1, or 2, wherein the outer rods are located in slots in a support arrangement extending between the inner rods and the tubular sleeve.

5. A connector according to any one preceding claim, wherein the inner rods and the fiber terminate in a planar surface substantially perpendicular to the said axis.

6. A connector according to any one preceding claim, further comprising at least 3 second cylindrical rods located in tangential contact with each other about the said axis and forming at least one aperture therebetween, a second optical fiber or fibers located within the or each aperture of the second rods, the second inner rods and the second fiber terminating in a second planar surface substantially perpendicular to the said axis, and wherein the first men- tioned planar surface and the second planar surface are brought into engaging relationship within the outer rods.

7. A connector according to claim 6, wherein the first mentioned inner rods and the first fiber are introduced into one end of the resilient sleeve and outer rod arrangement and the second inner rods and second fiber are introduced into the other end of the resilient sleeve and outer rod arrangement, whereby the said planar surfaces abut intermediate the ends of the sleeve.

8. A connector according to claim 6, wherein the first mentioned inner rods and the first fiber are located within a first resilient sleeve and first outer rod arrangement with the first outer rods extending beyond the first planar surface, wherein the second inner rods and the second fiber are located within a second resilient sleeve and second outer rod arrangement with the second outer rods extending beyond the second planar surface, and wherein connection is effected by engaging the resilient sleeves and the said planar surfaces with the first and second outer rods intermeshing in tangential contact with one another.

9. A connector according to any one pre ceding claim, wherein there are six outer rods.

10. A connector according to any one of the preceding claims, wherein each of the inner and outer rods is a precision bearing roller.

11. A connector according to any one of the preceding claims, wherein each optical fiber includes a malleable coating which is compressible under pressure on respective inner rods.

12. An optical fiber connector substantially as hereinbefore described with reference to Figure 1, 2 or 3 or Figures 5 and 6, or Figures 7, 8, 9, 10 and 11, of the accompanying draw ings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the housing 233. WHAT WE CLAIM IS:

1. An optical fiber connector comprising at least three inner cylindrical rods located in tangential contact with each other about an axis and forming an aperture therebetween, an optical fiber located within the aperture formed by the inner rods, at least three outer rods in parallel with and in contact with the inner rods, the diameter of the outer rods being at least 1.5 times that of the diameter of the inner rods, and a tubular resilient sleeve whose inner surface is in contact with, and exerts a radial pressure on the outer rods, the radial pressure being transmitted to the inner rods thereby providing a support for the inner rods and fiber.