GB2111240A

GB2111240A - Connector for an optical fiber

Info

Publication number: GB2111240A
Application number: GB08232452A
Authority: GB
Inventors: Klaus Maaz; Werner George Schrott
Original assignee: Allied Corp
Current assignee: Allied Corp
Priority date: 1981-12-10
Filing date: 1982-11-12
Publication date: 1983-06-29
Also published as: GB2111240B; JPS58126511A; FR2518270A1; DE3148954A1

Abstract

A connector (10) for an optical fiber (20) is provided with a fastening device (56) to hold the fiber in place. The fastening device is a sleeve (57) formed of soft metal which is crimped directly onto the fiber without damaging it. The soft metal is preferably formed of a soldering tin alloy of lead, or of another material of equivalent hardness. With this arrangement the optical fiber is not damaged even when very large crimping pressure is applied, as the soft metal will yield laterally, enabling secure fastening onto the fiber. This type of connector is especially suitable for plastic clad silicone (PCS) fibres. <IMAGE>

Description

SPECIFICATION Connector for an optical fiber background of the invention The invention concerns a connector for an optical fiber which is provided with a fastening device to hold the optical fiber in place and to prevent undesirable movement by the optical fiber.

The invention is particularly concerned with a connector for an optical fiber preferably made up of a core made of glass with a silicone coating as well as a plastic protective layer on the silicone coating with a guide element accommodating the optical fiber and a fastening device holding the core, the coating and the plastic protective layer of the optical layer in place by its clamping action, which in turn can be connected to the guide element.

West German Patent Application 29 43 180 describes an optical fiber connector using a fastening device made up of a collet and a clamping sleeve. The clamping sleeve and the colletform a so-called clamping cone connection with pressure applied primarily in a vertical direction on the longitudinal axis of the collet, thus pressing the collet somewhat together and holding the optical fiber sleeve against a plastic coating, since the clamping sleeve is set at the same time in a bore of the rear part of the guide element.

The arrangement and design of this already known fastening device is somewhat complicated.

Particularly in the case of optical fibers with smaller diameters, in the range of 200 micrometers, this already known fastening device is difficult to use.

In the use of a connector pin that is already known, an optical fiber is centered and retained by clamping the fiber tight by means of crimping a crimp zone along an elastic clamping sleeve.

Moreover, the optical fiber is centered by deforming the front end of the clamping sleeve.

Specifically, there is either a light compression provided on the plastic coating or pressure into the plastic coating is used. Two parts are required for this already known connector pin arrangement in order to prevent damage to the optical fiber.

Besides the elastic clamping sleeve, the external plastic, pliable crimp zone must be provided to assure lasting cohesive forces.

It would be desirable to provide a connector for an optical fiber which avoids the drawbacks of the present state of the art. In particular, it would be desirable to provide a connector for an optical fiber in such a way that retention of the optical fiber can be guaranteed with a minimum of components and to provide a fastening device that can be assembled at minimum costs.

Summary of the Invention In accordance with this invention, there is provided a connector for an optical fiber having a core, a coating over the core and a protective layer over the coating, the connector comprising a guide element to receive the optical fiber which is held in place by the clamping effect of a fastening device, characterized in that the fastening device is formed of a sleeve made of soft metal which is crimped directly onto the optical fiber without damaging it.

Preferably the fastening device of this invention will be used with optical fibers having rigid cores, for example, out of glass, with a coating of softer material, for example, silicone, surrounding them.

The use of the fastening device of this invention is especially preferred for an optical fiber with a glass core, a silicone coating and a protective layer, preferably of plastic, surrounding it, with the fastening device of this invention mounted on the aforementioned protective layer and compressed onto it so that any shifting or movement, particularly between the protective layer and the coated glass core, will be prevented.

According to the invention, the fastening device for an optical fiber in a connector is designed in such a way that an element having an axial bore and made of soft metal is provided, which after it is slipped onto the optical fiber, is crimped onto it without damaging it.

Brief Description of the Drawings Fig. 1 shows a cross-section of a connector in accordance with the invention; Fig. 2 shows a cross-section of the fastening device in accordance with the invention; Fig. 3 shows a cross-section of the fastening device of this invention of the optical fiber before the crimping process; Fig. 4 shows a view of the fastening device crimped onto the optical fiber.

Description of the Preferred Embodiments Fig. 1 shows a connector 10 for an optical fiber 20. The optical fiber 20 includes the following: a core 21 of glass, for example, a coating 22 of silicone, for example, a protective layer 23 made of fluorocarbon resin, for example, a cover 24 made of a meshed material to relieve tensile pressure, with the cover 24 surrounded by an outer cover 25.

The connector 10 also has a connector element (guide element) made up of a front part 1 and a rear part 2. Starting from a flat polished front surface 33, the front part 1 has a bore 35 with a diameter equal to or somewhat smaller than the outer diameter of the coating 22. The bore 35 is connected to an additional bore 34 with a diameter equal to the outer diameter of the protective layer 23. The core 21 is pressed with the coating 22 into the bore 35 while in the area of the bore 34 a retention of the protective layer 23 with the bore is achieved by adhesion. The front part 1 is basically cylindrical in design and includes a forward plug area 30, a central impact or contact area of a larger diameter 31 and an area 32 with an intermediate diameter.

The rear part (hereinafter called back portion) 2 accommodates the front part 1 (hereinafter called front portion) in a bore 11 inserted into the back portion 2. Bore 11 has a diameter equal to that of area 32. The bore 11 continues along the longitudinal axis of the back portion 2 in a bore 12 having a smaller diameter which equals the outer diameter of the fastening device 56 (hereinafter called mounting device) described below. On its outer surface the back portion 2 has a groove 1 3 which accommodates a locking ring. A coupling nut 3, used for connection with a matching connector (not shown), is retained by the locking ring 4 and the rim area 14 with a larger diameter on the back portion 2.The front portion 1, the back portion 2, the locking ring 4 and the coupling nut 3 can be manufactured in advance as a single unit or can be assembled in its individual parts with the front portion 1 being pressed tightly into the back portion 2 of the connector element.

Primarily in the area of the bore 12, the back portion 2 has a cylindrical area 1 5 which has a smaller diameter equal to that of the crimp sleeve 7 described below and is beveled down at its open end. Details regarding the crimp sleeve 7 and its arrangement are described in the aforementioned German Patent Application 2943180.

The mounting device 56 provided as per the invention is made up of a mounting sleeve 57 of soft metal which is depicted in Figs. 2 to 4. By way of example, soldering tin or lead may be considered as the soft metal. It is also possible to use, for example, a plastic as long as it possesses the characteristics of a soft metal such as, for example, lead or soldering tin. The mounting sleeve 57 is preferably circular and cylindrical in design and has a bore 58 going in the longitudinal direction through which the optical fiber can pass.

Preferably the soft metal sleeve 57 is slipped onto the protective layer 23 and then crimped; this can be done with a tool such as a crimper, for example. Preferably it is crimped in the middle area of the sleeve 57, so that it is possible for the soft metal to yield without difficulty on both sides in an axial direction. By using a mounting device as per the invention, an extraordinarily uniform pressure is applied onto the optical fiber so that the optical fiber is not damaged even when relatively enormous crimping pressure is applied since the soft metal will consistently yield laterally.

Since the mounting sleeve 57 preferably should be made to adhere on its outer surface to the surface of the bore 12, the outer surface of the mounting sleeve 57 is preferably smooth and cylindrical in its crimped state, as shown in Fig. 4, and not deformed with edges.

In Fig. 3 the mounting sleeve 57 is shown positioned on the optical fiber before crimping pressure is applied while in Fig. 4 the crimping process has been carried out and the mounting sleeve 57 makes it impossible from this point on for the optical fiber core 21, the optical fiber coating 22 and the optical fiber protective layer 23 to shift or move with relation to each other. By using a single mounting sleeve 57 of soft metal it is thus possible to assure a principal retention of the optical fiber. For that matter, the protective layer 23, frequently made of a fluorocarbon polymer, is roughened and is made to adhere to the front portion so that a sure retention results: however, despite this, the coating 22 made of silicone continues to provide the protective layer 23 with a sliding capacity.

The mounting device of this invention is especially advantageous when used in conjunction with the so-called PCS (plastic clad silicone) fibers, but it can also be used as a supplementary retaining element with other optical fibers and/or glass fibers.

According to the invention the mounting sleeve 57 is made of soft metal, e.g. a soldering tin alloy or lead. Pure aluminum and copper are not acceptable as the material for the mounting sleeve. As will be explained below, the material for the mounting sleeve 57 must be selected, taking into account its softness (physical adaptability in shape), in such a way that the maximum compression strength of the protective layer of the optical fiber, made for example out of fluorocarbon resin, is not exceeded during the crimping process.

The softness of the material used in the mounting sleeve 57 makes it possible to crimp a large range of fiber diameters. Accordingly, only one single mounting sleeve size is necessary for a variety of fiber strengths. In contrast to this. the design described in the aforementioned application uses various models of clamping sleeves and coilets.

Preferably, the mounting sleeve 57 is crimped using standard hexagonal wedges. but it can also be done with other crimpers that are conventionally used. The softness of the material for the mounting sleeve 57 prevents damage to the optical fiber, particularly a PCS fiber. With regard to the softness or hardness of the material used for the mounting sleeve 57 a compromise is provided insofar as the PCS fibers in particular and the optical fibers in general are not damaged, but on the other hand, the cohesive forces are so great that they are limited by the tearing strength of the protective layer, made of fluorocarbon resin for example, and not by the mounting sleeve per se.

The mounting sleeve can be used effectively and inexpensively not only with PCS fibers but also with all covered optical fibers in order to improve the tensile strengths of the fibers compared to the pure adherence (mounting) used conventionally otherwise.

Moreover, the mounting sleeve is also suitable for solving mounting and retaining problems in other technical equipment, for example in spliced connections.

The invention not only makes possible saving in parts but also a low-cost, problem-free assembly and relatively greater safety, even when assembled by non-proiessionals.

According to the invention, the mounting sleeve 57 is made of a soft metal. The concept of soft metal for the purpose of this invention is defined as follows: Most metals have the capacity of permanent plastic deformation when forces are applied to them. Metals are designated as "soft" when the shaping force required to shape the metal is slight.

The present invention uses such soft metals to mount or fasten optical fibers, particularly optical fibers with a protective layer 23, with the soft metal used in such a way, moreover, that it does not damage, but rather compresses the optical fiber and its protective layer 23 during its plastic cold forming (and even afterwards).

Of the pure metals, lead with a hardness (HB/HV of 1.5 kg/mm2) and an elasticity value (E equals 1600 kg/mm2) is especially taken into consideration. According to the invention, in particular alloys of lead and tin can also be used, such as for example the soldering tin alloys commercially available. Preferably the hardness, (HB/HV) in kg/mm2, should be in the hardness range of lead. But is is also possible to use hardnesses of higher values as long as the optical fiber and/or its protective layer 23 and/or its coating 24 are not damaged.

According to the invention, the reshaping process brought about by crimpoing is the result of cold forming with the mounting sleeve 57 being stressed beyond its elasticity limit, which flows and thus surrounds and retains the optical fiber uniformly without damaging it. Thus, in general the invention provides for the use of a soft metal alloy, particularly of lead and tin. But other alloys can also be used, such as for example alloys of copper and aluminum, as long as their hardness is of a sufficiently low value so there is no possibility of damaging the optical fiber. The following approximate ranges of hardness, given in HB/HV kg/mm2, are preferred: 1.5 to 2.0; 1.5 to 5.0; 1.5 to 10; 1.5 to 20. During the crimping process the mounting sleeve 57 can penetrate the protective layer without destroying it. Preferably the mounting sleeve 57 will penetrate both into the protective layer 23 and into the coating 22 for the purpose of retaining or fastening the optical fiber, without destroying in any way the coating or protective layer, i.e. disrupting them.

Ae VVBS already mentioned, the measures provided for in the invention are especially advantageous in the case of optical fibers with small diameters, for example in the diameter range of 200 micrometers to 600 micrometers, and here again preferably for PCS fibers. A typical example of PCS fiber has, for example, a core diameter of 400 micrometers, a core plus coating diameter of 560 micrometers and a core plus coating plus protective layer diameter of 900 micrometers.

Claims

1. A connector for an optical fiber having a core, a coating over the core and a protective layer over the coating, the connector comprising a guide element to receive the optical fiber which is held in place by the clamping effect of a fastening device, characterized in that the fastening device is formed of a sleeve made of soft metal which is crimped directly onto the optical fiber without damaging it.

2. A connector in accordance with claim 1 wherein said soft metal is selected in such a way that it is deformed primarily in the plastic range so that damage to the optical fiber during the crimping process is prevented.

3. A connector in accordance with claim 2, wherein the optical fiber is made of glass.

4. A connector in accordance with claim 3 wherein the coating is made of a silicone material and the protective layer is made of a plastic material.

5. A connector in accordance with claim 4 wherein the sleeve is pressed directly onto the protective layer of the optical fiber.

6. A connector in accordance with claim 1 wherein said soft metal comprises a soldering tin alloy.

7. A connector in accordance with claim 1 wherein said soft metal comprises lead.

8. A connector in accordance with claim 1 wherein said soft metal comprises a lead-tin alloy.

9. A connector in accordance with claim 1 wherein said soft metal is a copper alloy.

10. A connector in accordance with claim 1 wherein said soft metal is an aluminum alloy.

11. A connector in accordance with claim 1 wherein the hardness of the soft metal (HB/HV) is in the range of 1.5 to 20 kg/mm2.

12. A connector in accordance with claim 1 wherein the sleeve is crimped along its entire length onto the optical fiber.

1 3. A connector in accordance with claim 4 wherein the sleeve is crimped along its entire length onto the optical fiber and, once it is crimped, penetrates into the coating and/or protective layer without disrupting the coating and/or protective layer.

14. A connector in accordance with claim 4 wherein said protective layer is formed of a fluorocarbon resin.