GB1585766A - Connectors for optical fibres - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO CONNECTORS FOR OPTICAL FIBRES (71) We, THE PLESSEY COMPANY LIMITED, a British Company, of Vicarage Lane, Ilford, Essex, 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 the end-to-end coupling of optical fibres, and is particularly but not exclusively, intended to facilitate the coupling of single glass-fibre filaments. In our co-pending U.K. application No. 39905/76 (Serial No. 1 577 729) (Fibre to sleeve attachment jig) we have proposed to provide, in order to facilitate the end-to-end coupling of such elements, each of the ends to be coupled with a so-called ferrule in the form of a precision-cylindrical body in which the end of the filament or the like is arranged in accurate coaxial alignment.

The present invention has for an object to facilitate the rapid and accurate end-toend coupling of optical waveguide elements equipped with coaxial cylindrical end ferrules. According to the invention a connector, for effecting end-to-end coupling of optical fibres which said fibres are equipped at the ends to be coupled with co-axial cylindrical ferrules comprising guide means arranged to permit the axial insertion of the two ferrules to be coupled from opposite ends and then to retain the two ferrules in co-axial end-to-end contact; in which said guide means comprises four or more cylindrical rollers of equal diameter, each said roller being tapered at both ends, and annular spring means, arranged to hold, in the absence of a ferrule in the connector, the cylindrical rollers in an annular array, in which each roller has its axis parallel to each other roller and to the axis of the connector such that the inner surfaces of each roller project radially towards the axis of the connector such that they penetrate an imaginary cylinder about the axis of the connector whose diameter is smaller Ihan the diameter of the thinnest ferrules for which the connector is intended, in which said rollers are arranged within said annular spring means such that the locus of the points of contact of each roller with its adjacent roller substantially lie on the circumference of a first circle, in which the locus of the axial centres of the rollers substantially lie on the circumference of a second circle and in which the radius of the first circle is smaller than the radius of the second circle.

The spring means may consist of two open-ended ring members of resilient material such as spring wire, each comprising, for example, a single circular turn or a small number of helically adjacent turns, in which case the tapered-end cylindrical rollers may each be formed with two longitudinally spaced circumferential grooves, into which the spring members may be placed to be retained at desired points of the length of the connector and at the same time preventing the individual rollers from moving axially relative to each other. Alternatively the spring means may be constituted by a sleeve of rubber-type resilient material which extends over the greater length of the tapered-end cylinders and may be either bonded to the latter or placed round the cylinders with an interference fit.

According to a preferred form of the invention, however, a single multi-turn helical coil spring is arranged to extend over the greater part of the length of the rollers which is so rated as to resiliently hold the rollers in contact with each other, thus ensuring alignment of the rollers parallel to a common axis without opposing excessive force to the insertion of the probes.

It has been found that the use of a suitable rated coil spring of this kind makes it unnecessary to provide retaining cups or retaining grooves for preventing the spring from slipping along the bundle of rollers.

Figures 1 and 2 of the drawings accompanying the provisional specification and figures 3, 4 and 5 of the drawings filed with the complete specification illustrate various examples of connectors according to the present invention.

Figures 1, 2 and 2 respectively show, each in a perspective view, three forms of connector, a pair of ferrules to be coupled being also shown in axially spaced relation thereto, and Figures 4 and 5 show theoretically the way in which the rollers of the connectors of Figures 1, 2 and 3 remain in equilibrium.

Referring now first to Figure 1, the ends of two lengths 1 of light-guide filament, for example of single-filament glass fibre, which are to be coupled in butted alignment, are each fitted with a ferrule 2 whose outer surface is a precision-made cylinder, in which the end of the filament 1 is held in accurate coaxial alignment, for example in a manner described in our above mentioned co-pending application, so as to present at their mutually facing ends, the end face of the fibre 1 in accurately concentric relation to the circumference of the probe and at right angles to the axis thereof. Between the two ferrules to be coupled, one form of connector according to the present invention is shown in Figure 1. It is made up of six members, each in the form of a precision cylinder 4 having tapered end portions 4a and having two circumferential grooves 5 machined in the precision cylinder each approximately half-way between the centre of the length of the cylinder and one or the other, respectively, of the two ends of the cylinder. The cylinders 4 are resiliently held together, in a substantially circular arrangement about a central axis, by two spring clips 6 located in the grooves 5 and resiliently urging the cylinders 4 towards the said central axis. The diameter of each cylinder 4 is slightly smaller than that of the probes in order to ensure that the cylinders 4 are applied by the spring means, with radial pressure to the surface of the probe without being prevented from doing so by mutual contact between adjacent cylinders 4. In other words, the diameter of the cylinders 4 is so chosen that when the cylinders are in contact with each other, the diameter of a circle about the said central axis in tangential contact with each of the cylinders is somewhat smaller than the diameter of the ferrules 2 which are to be coupled, but large enough to allow the ferrules to be introduced axially into contact with the flanks of the tapered portions 4a.

All that is necessary in order to couple two fibres, is to axially introduce their ferrules 2 into the connector, thereby initially forcing the circular spring clips 6 to expand in diameter, and to continue this movement until the mutually facing ends of the two probes make contact with each other. Due to the resilient pressure of the cylinders of the connector against the circumference of the two ferrules, the latter are now held by friction in their coupled position. Samples, which have been produced for testing purposes, have shown that the connector combines convenience of use with a very satisfactory degree of lighttransmission efficiency.

Figure 2 shows a connector which is very similar to that shown in Figure 1 with the exception that instead of the two circular spring clips 6 retained in grooves 5 machined in each of the cylinders 4 of the Figure 1 embodiment, a single helical multi-turn coil spring 7 is employed for urging the cylinders 4 towards the central axis of the connector. This coil spring is so rated that it will, in the absence of a ferrule 2, resiliently hold the cylinders 4 in line-contact with each other thereby ensuring that the cylinders remain parallel to each other and their respective axes lie in a circular array round a common axis, but will yield without requiring undue force to permit the insertion of ferrules 2 along this common axis, while the friction due to the compressive force of the turns of the spring 7 will prevent the coil spring from slipping along the bundle of cylinders and the individual rollers from slipping away axially. For this reason the grooves 5 of Figure 1 have been omitted. If desired, however, grooves similar to the grooves 5 of Figure 1 and a light spring slip resting in each groove may be added at the two ends of the spring member 7 as a safeguard against axial movement of the latter. To produce a rated spring, spring wire of a chosen diameter is wound on a mandrel of suitable diameter with a tensional pre-load applied to the wire.

The embodiment illustrated in Figure 3, similarly to the embodiments of Figures 1 and 2, comprises a set of six precision cylinders 4, each provided with tapered ends 4a, but the radial force urging the cylinders towards the central axis is provided by a cylindrical sleeve 8 of rubber or similarly resiliently flexible material, which is placed round the cylinders 4. This sleeve 8 may be held in position simply by being made an interference fit with the body constituted by the cylinders 4 when in contact with each other, or it may be moulded on to the cylinders.

It will be readily appreciated that some details of each of the three embodiments so far described may be modified without exceeding the scope of the invention. More particularly, although six cylinders 4 have been shown in each of these embodiments as a convenient number, a similar effect may also be achieved with a different number of cylinders, which may be greater or smaller than six, although it is preferred to use not less than six cylinders, and it will be readily appreciated that the suitable diameter for the individual cylinders forming the connector will vary, for the same probe diameter, according to the number of cylinders employed.

Furthermore, although it has been assumed that the cylinders 4 are of circular cross-section, and this is considered to be generally advisable because of the case with which such bodies can be precisionmanufactured, the invention does not exclude the use of cylinders of non-circular cross-section, for example the cross section may be a circle flattened at, for example, the radially outer side of the connector.

The cylinders used in a practical realisation of figures 1 to 3 were of 3/16 inch diameter and were machined to a tolerance of 1/10 thousands of an inch in their diameter. The steel usea was of grade EN31.

In respect of figure 2 the spring was made from 26 gauge stainless steel on a mandrel with a preload of SKgrammes.

Figures 4 and 5 to which reference is now made show that providing the locus of the contact points of the cylinders, as shown by the dotted line is within the locus of the axes of the cylinders, as shown by the chain dotted line, then the assembly will remain stable when surrounded by a spring such as 7 shown in figure 2.

WHAT WE CLAIM IS:- 1. A connector, for effecting end-to-end coupling of optical fibres which said fibres are equipped at the ends to be coupled with co-axial cylindrical ferrules, comprising guide means arranged to permit the axial insertion of the two ferrules to be coupled from opposite ends and then to retain the two ferrules in co-axial end-toend contact; in which said guide means comprises four or more cylindrical rollers of equal diameter, each said roller being tapered at both ends, and annular spring means, arranged to hold, in the absence of a ferrule in the connector, the cylindrical rollers in an annular array, in which each roller has its axis parallel to each other roller and to the axis of the connector such that the inner surfaces of each roller project radially towards the axis of the connector such that they penetrat e an imaginary cylinder about the axis of the connector whose diameter is smaller than the diameter of the thinnest ferrules for which the connector is intended, in which said rollers are arranged within said annular spring means such that the locus of the points of contact of each roller with its adjacent roller substantially lie on the circumference of a first circle, in which the locus of the axial centres of the rollers substantially lie on the circumference of a second circle and in which the radius of the first circle is smaller than the radius of the second circle.

2. A connector as claimed in claim 1 in which said annular spring means comprises two open ended ring members of resilient material each said ring member being of a single circular turn, in which each tapered end cylindrical roller is formed with two longitudinally spaced circumferential grooves, said ring members being placed in said grooves to be retained at desired points along the length of the connector and thereby preventing the rollers from moving axially relative to each other.

3. A connector as claimed in claim 1 in which said annular spring means comprises a sleeve of rubber-type resilient material which extends over the greater length of the tapered end cylinders.

4. A connector as claimed in claim 1 in which said annular spring means comprises a single multi-turn helical coil spring arranged to extend over the greater part of the length of the cylindrical rollers, said spring being so rated as to resiliently hold the cylindrical rollers in contact with each other, thus ensuring axial alignment of the rollers parallel to a common axis; without imposing excessive force to the insertion of the probes.

5. A connector substantially as described with reference to any one of figs 1 and 2 of the drawings accompanying the provisional specification and Fig 3 of the drawings accompanying the complete specification.

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. probe diameter, according to the number of cylinders employed. Furthermore, although it has been assumed that the cylinders 4 are of circular cross-section, and this is considered to be generally advisable because of the case with which such bodies can be precisionmanufactured, the invention does not exclude the use of cylinders of non-circular cross-section, for example the cross section may be a circle flattened at, for example, the radially outer side of the connector. The cylinders used in a practical realisation of figures 1 to 3 were of 3/16 inch diameter and were machined to a tolerance of 1/10 thousands of an inch in their diameter. The steel usea was of grade EN31. In respect of figure 2 the spring was made from 26 gauge stainless steel on a mandrel with a preload of SKgrammes. Figures 4 and 5 to which reference is now made show that providing the locus of the contact points of the cylinders, as shown by the dotted line is within the locus of the axes of the cylinders, as shown by the chain dotted line, then the assembly will remain stable when surrounded by a spring such as 7 shown in figure 2. WHAT WE CLAIM IS:-

1. A connector, for effecting end-to-end coupling of optical fibres which said fibres are equipped at the ends to be coupled with co-axial cylindrical ferrules, comprising guide means arranged to permit the axial insertion of the two ferrules to be coupled from opposite ends and then to retain the two ferrules in co-axial end-toend contact; in which said guide means comprises four or more cylindrical rollers of equal diameter, each said roller being tapered at both ends, and annular spring means, arranged to hold, in the absence of a ferrule in the connector, the cylindrical rollers in an annular array, in which each roller has its axis parallel to each other roller and to the axis of the connector such that the inner surfaces of each roller project radially towards the axis of the connector such that they penetrat e an imaginary cylinder about the axis of the connector whose diameter is smaller than the diameter of the thinnest ferrules for which the connector is intended, in which said rollers are arranged within said annular spring means such that the locus of the points of contact of each roller with its adjacent roller substantially lie on the circumference of a first circle, in which the locus of the axial centres of the rollers substantially lie on the circumference of a second circle and in which the radius of the first circle is smaller than the radius of the second circle.

2. A connector as claimed in claim 1 in which said annular spring means comprises two open ended ring members of resilient material each said ring member being of a single circular turn, in which each tapered end cylindrical roller is formed with two longitudinally spaced circumferential grooves, said ring members being placed in said grooves to be retained at desired points along the length of the connector and thereby preventing the rollers from moving axially relative to each other.

3. A connector as claimed in claim 1 in which said annular spring means comprises a sleeve of rubber-type resilient material which extends over the greater length of the tapered end cylinders.

4. A connector as claimed in claim 1 in which said annular spring means comprises a single multi-turn helical coil spring arranged to extend over the greater part of the length of the cylindrical rollers, said spring being so rated as to resiliently hold the cylindrical rollers in contact with each other, thus ensuring axial alignment of the rollers parallel to a common axis; without imposing excessive force to the insertion of the probes.

5. A connector substantially as described with reference to any one of figs 1 and 2 of the drawings accompanying the provisional specification and Fig 3 of the drawings accompanying the complete specification.