OPTICAL FIBER CONNECTORS

Abstract: The method of making an end connector or splice member (32) for optical fiber arrays (12), utilizes the steps of preparing a metallic master (16) of the member and electroforming on the master the member (32) of the required accuracy, which is then separated from the master and the fibers inserted and fixed in place. In one embodiment (Fig. 9), the connector (47) is electroformed directly onto the spaced fiber array. The invention includes the connectors produced by the disclosed methods (Fig. 12).

Description: OPTICAL FIBER CONNECTOR ' S Technical Field This invention relates to optical fiber connectors and, more particularly, to means for connecting or splicing optical fiber arrays, and of methods of making such connecting means. Background of the Invention In the use of fiber optics for communications purposes, end terminations for the fiber cables, regardless of cable configuration, must be of such accuracy of manufacture and mounting as to be amenable to reliable, low loss connecting and splicing. Inasmuch as single fibers are on the order of fifty to one hundred and fifty microns in diameter, it is obvious that even in the most primitive of end terminations or connectors, extremely close tolerances have to be maintained if accurate, low loss connections are to be made. Among the most successful of connectors in satisfying the above criteria especially in configurations for handling arrays of fibers, has been the photolithographically etched silicon connector. The connector itself comprises a first silicon block having accurately spaced and aligned trapezoidal or V-shaped grooves etched therein, each groove being designed to accommodate a single fiber. A V-shaped groove is in general, a characteristic of the photolithograph process. A second substantially identically grooved block forms a sandwich within the first block and the fibers and they are cemented together by a suitable adhesive, such as epoxy cement. The end face of the sandwich is ground and polished to a flat, mirrorlike finish to insure proper abutment with a similar end terminal on the fiber group to be spliced or joined. The joined sandwiches are enclosed by silicon members which are negative configurations of the grooved members, and the entire assembly is clamped together by spring clips. Such a coupling or splicing OMPI arrangement, properly made and ' assembled, gives low loss, typically in the neighborhood of 0.1 db. The end terminal or coupler as just described is fully disclosed in The Western Electric Engineer, Vo. XXIV, No. 1, Winter, 1980, in a two part article "Interconnection For Lightguide Fibers", pp. 87-101, particularly p. 93. The foregoing silicon chip connector, and variations thereof, have proven to afford low loss connections or splices because of the accuracy achievable in the photolithographic process, which is used to form the grooves. However, there are certain drawbacks or shortcomings to such a connector, which, while not vital to a properly constructed connector, would, nonetheless, be better eliminated or alleviated. Thus, silicon is somewhat fragile, brittle, and susceptible to thermal shock and care must be taken in transporting the optical fiber assembly to the field, where connection is to be made, inasmuch as the wafer itself can be broken, or the grooves damaged, by careless handling. Likewise a problem is the necessity of using cement in order to construct the sandwich. Cements that have proved adequate for this purpose are usually slow in curing, hence the sandwich must remain immobile for an extended time to insure proper cementing. Clearly, a metal termination would eliminate a number of these aforementioned drawbacks. A metal termination would be more likely to stand up under field conditions, being less susceptible to breakage or damage. Further, certain metals adaptable for such use are cheaper in bulk and manufacturing processing than silicon, and hence, in large quantity connectorization, could represent considerable savings. However, the required accuracy and precision for producing the grooves in the metal termination would, in most cases, make the cost of individual terminations prohibitive, negating any cost advantage gained through the use of metal. Summary of the Invention The present invention is a method of making end termination for fiber cables out of metal, in which the necessary precision is achieved, without the prohibitively costly production of the grooves therein and which produces grooves of a cross-sectional shape that are not restricted to the characteristic V-shape. The invention also includes such end termination, both with or without grooves, possessing the accuracy and precision for both vertical and lateral alignment of the fibers therein. The invention relies, to a large extent, on the accuracy that can be achieved from electroforming metal. Electroforming can be performed so accurately and precisely that it's a commonly used method for forming diffraction grating, where tolerances are measured in Angstroms. In electroforming, a master mold that is the negative of the article to be produced, is inserted in a plating bath consisting of, for example, a nickel sulphate solution, to function as a cathode. A block of the metal, such as substantially pure nickel, to be deposited on the master, is inserted as the anode. When the bath is energized, the nickel will be plated on the master which may be, for example, stainless steel. In electroforming, as opposed to electroplating, a relatively thick layer is deposited, sufficiently thick to permit use as an end product, and not as a plated coating. When the process is completed, the plated master is removed from the bath, and the nickel separated from the master, which is not difficult especially when the metals have material differences in thermal coefficients of expansion. For example, 300 Series stainless steel has a coefficient of thermal expansion of 5.3 micromillimeter per millimeter per degree Celsius, while that of nickel is 3.7 micromillimeter per millimeter per degree Celsius. The resulting nickel member is a substantially exact positive (or negative) of the master. In addition, it is of substantially 99% or better purity since impure ions from the anode fall out naturally. If the master was formed with the desired precision, the nicke O PI_ eletroformed member will also have the desired precision. No. 316 stainless steel has excellent precision machining qualities and is highly resistant to the corrosive effects of the nickel sulfate bath. It may then be ground to the desired thickness and transverse dimensions. While the electroforming process is time consuming, the master may be used indefinitely, and, with a sufficient number of masters, it is obvious that large numbers of nickel end terminations may be electroformed simultaneously and/or in seriatim. It is possible, in accordance with the principles of the methods of the present invention, to produce an end termination that does not require a grooved member, and is of a configuration such that it is not necessary to cement any parts together. In this particular embodiment of the invention, a section of the array of fibers is first coated with a metallizing coating, placed in a mold, and the locating member of the end termination eletroformed thereon. This results in the fibers being embedded in the nickel member, and held in precise location thereby. The surfaces of the member thus serve to locate the fibers within a second member, so that accurate splicing, for example, is accomplished. Description of the Drawings The various features of the present invention will be more readily understood from the following detailed description when read in conjunction with the accompanying drawings, in which* FIG. 1 is a plan view of a twelve fiber array tape, as commonly used FIG. 1A is a plan view of the array of FIG. 1 in which a portion of the tape has been removed in preparation for the attaching of an end termination; FIG. 2 is a perspective view of a master mold for electroforming a plurality of end terminations? FIG. 3 is a view illustrating the electroforming operation; _ OMPI FIG. 4 is a perspective view of an electroformed member containing a plurality of end terminations- FIG. 5 is a partial cross-sectional view of an end termination made in accordance with the process of FIGS. 2 through 4? FIG. 6 is a plan view of a step in the making of a second embodiment of the termination of the invention showing the stripped fibers arranged in a channel of the master mold; FIG. 7 is a plan view of another step in the making of the second embodiment' FIG. 7A is a sectional view along the line A-A of FIG. 7? FIG. 8 shows the arrangement of FIG. 7 after the electroforming step- FIG. 9 shows the electroformed portion of the termination- FIG. 9A is a sectional view along the line A-A of FIG. 9- FIG. 10 is a view of a step subsequent to that in FIG. 9 in the making of the end termination: FIG. 10A is a view along the line A-A of FIG. 10: and FIG. 11 is a cross-sectional view of an end termination of the present invention. Detailed Description In FIG. 1 there is shown a twelve fiber array tape sandwich 11 comprising twelve equally spaced fibers 12, 12 sandwiched between two strips 13, 14 of suitable flexible tape such as, for example, MYLAR. In FIG. 1A the sandwich of FIG. 1 has been prepared for attachment of an end termination thereto by removal of a portion of tapes 13, 14. In FIG. 2 there is depicted in perspective an electroforming master 16 for making a plurality of end terminations. Master 16 is preferably made of a relative corrosion proof, durable, accurately machinable metal OMPI such as, for example, No. 316 stainless steel. Master 16 comprises a rectangular block 17, having a plurality of grooves 18, 18, machined longitudinally therein, and a second plurality of grooves 19 , 19 machined transversely thereacross. Grooves 18, 18 have machined longitudinally therein, for example, parallel lands and grooves which must be machined extremely accurately such as by etching, precision grinding, or by techniques used in manufacturing diffraction gratings. Press-fitted into the transverse slots 19, 19 is a plurality of bars 21 , 21 , so that there is formed on the face of master 16 a plurality of cells 22, 22 each of which in turn defines the negative of an end termination. A hanger bar 23 fits through a hole 24 drilled in member 16, to hold the master 16 within the electroforming bath. FIG. 3 is a diagrammatic rendering of the electro¬ forming operation, which, in its simplest form requires a tank 26 filled with suitable electrolyte 27 , such as a nickel sulfamat or other appropriate nickel electrolytes, in which master 16 hangs. A second hanger 28 holds a nickel anode 29 within the electrolyte, spaced from master 16. For simplicity, the voltage sources, switches, and connections have not been shown, inasmuch as they are well known in the art and would simply complicate the figure. Typical examples of voltage and current are 6-12V and 1 to 20 amperes per square decimeter. After the electroforming process is completed, the electroformed material is removed from the master, as by subjection to a temperature change such as chilling to cause a loosening of the bond between master and electroformed material leaving a nickel member 31, as shown in Fig. 4, having a plurality of accurately formed slotted end termination members 32, 32 thereon which may be removed as by sawing, and then subsequently cleaned, polished and ground to the desired dimensions. The slots 30, 30 in member 32 are best seen in FIG. 5. In FIG. 5 there is shown a partial view of a OMPI connector or end termination 33, comprising a block 34 of material such as nickel having a recess 36 machined therein to receive slotted member 32, which holds fibers 12, 12 in accurate spaced relationship to each other. One or more spring clips 37 hold the assembly together. As with all such end terminations, it is most desirable that the end face be ground flat so as to abut evenly with the flat end face of the end termination of the fibers which will be spliced to the first fiber array. One of the shortcomings of the end termination depicted in FIG. 5 is the fact that cement must be used to hold fibers 12 securely in place and prevent them from being pulled out. In FIGS. 6 through 10 are shown the steps involved in making an end termination that requires no cement, thus eliminating a time consuming step in the making of an end termination. In FIG. 6, the prepared fiber tape 11 of FIG. 1A has silver-plated thereon an approximately two micron layer 38 of roughly the dimensions of an end termination. The tape thus prepared is laid into a recess 39 of a block 41 , preferably of stainless steel, where the fibers 12, 12 are maintained in accurately spaced relationship by spacers 42 and 43, also of, for example, stainless steel, which are held in place by spring clips 44 and 46, as best seen in FIGS. 7 and 7A. It can also be seen from FIG. 7 that an area of the plated region 38, of a size sufficient to insure coverage of all of the fibers during the electroforming step, is left. After the assembly of FIGS. 7 and 7A is inserted in an electroforming bath, the region 38 has electroformed thereon a member 47 of nickel, for example, of the desired dimensions, as shown in FIGS. 9 and 9A. The electroformed member 47 may be left as it appears in FIG. 9A, with the shoulder 48, naturally formed during the electroforming operation, retained for strength. The member 47 is subsequently removed from the member 41, the fibers 12 extending beyond the member 47 trimmed, and the faces of the member 47 polished, producing the basic end termination 51 shown in FIG. 10 and FIG. 10A. The member 51, shown in cross section in FIG. 10A, has the fibers 12, 12 properly spaced, with their center lines in a single plane, and held firmly in place relative to each other by the electroformed member 51 and, more particularly, by the portions 45 filling the spaces between the fibers and substantially surrounding them. The surface 52 of member 51 , properly polished, may serve as a suitable reference surface for abutting a second member 51 to produce a splice. Likewise surfaces 53 and 54 serve to locate the member 51 laterally. Referring to FIG. 11 it can be seen that when member 51 is slip-fitted into a precision formed groove 56, having locating surfaces " 50, 55, and 60, of a nickel support member 57, and clamped in place by spring clips 58 and 59, the fibers 12, 12 are accurately located both laterally and vertically, and a second member 51 slipped into groove 56 will abut the first member so that the fibers 12, 12 are accurately aligned and a low loss splice, as shown in FIG. 12, is achieved. To improve loss performance, an index matching material may be inserted in the region where the members abut. While the foregoing illustrative embodiments of the method and product of the present invention have called for stainless steel for the master and nickel for the electroformed end termination, it is to be understood that other materials may be used in practicing the invention so long as they meet the criteria set forth in the foregoing.

Claims: Cl aims 1. An end termination for optical fibers CHARACTERIZED BY an electroformed metal member (32,51) for holding a plurality of fibers (12) including means integral therewith for precisely locating and holding each fiber relative to other fibers; a second metal member (34) having a grooved portion (56) for receiving and firmly holding the electroformed metal member (32,51); and means (37) for securing the electroformed metal member and the second metal member together. 2. An end termination in accordance with claim 1 , CHARACTERIZED IN THAT the electroformed metal member (32) comprises a plurality of equidistantly spaced slots (30). 3. An end termination in accordance with claim 1, CHARACTERIZED IN THAT portions of the electroformed metal member (51) substantially surround the fibers (12). 4. An end termination in accordance with claim 1, CHARACTERIZED IN THAT the electroformed metal member consists of substantially pure nickel. 5. A method of making an end termination for optical fibers in accordance with any of the foregoing claims 1-4, CHARACTERIZED BY the steps of; forming a master (16) of a first metal having a first coefficient of expansion, the master having a configuration that is the negative of at least part of the end termination; electroforming on the master a layer of a second metal having a second coefficient of expansion different from the first coefficient of expansion; OMPI subjecting the layer and master to a temperature change sufficient to loosen the layer from the master, removing the layer from the master, and cleaning, polishing, and grinding portions of the layer to the desired dimensions. 6. The method in accordance with claim 5, CHARACTERIZED BY the step of positioning an array of fibers (12) within the negative portion of the master (16) prior to the electroforming step.

Inventors: RAGAN RALPH LAWTON, RAGAN, RALPH, LAWTON
Applicants: AMERICAN TELEPHONE & TELEGRAPH, AMERICAN TELEPHONE & TELEGRAPH COMPANY
Application year: 1984
Main classification: G02B6
IPC codes: G02B6