GB1572502A

GB1572502A - Optical waveguide couplings

Info

Publication number: GB1572502A
Application number: GB3281776A
Authority: GB
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1976-08-06
Filing date: 1976-08-06
Publication date: 1980-07-30

Description

(54) OPTICAL WAVEGUIDE COUPLINGS (71) We, SMITHS INDUSTRIES LIMITED, a British Company of Cricklewood, London NW2 6JN, 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 couplings, and, more particularly, to couplings and terminals for optical waveguides.

In such couplings it is common practice to provide a pair of lenses, for example, biconvex or planar-convex lenses, for optically coupling the ends of the optical waveguides.

However, in order to provide optimum optical coupling between the waveguides it is necessary accurately to position the waveguides at focal points of the respective lenses.

This accurate positioning of the ends of the waveguides tends to be rather difficult and time consuming and it is an object of the present invention to provide couplings and terminals for optical waveguides in which the mounting of the waveguides is considerably simplified.

According to one aspect of the present invention there is provided a terminal for an optical waveguide, including a connector having a longitudinal bore in which an end of an optical waveguide is to be anchored, a lens for transmitting light from one end of the waveguide, and a housing in which the connector and the lens are mounted, wherein the terminal includes an elongate optical member mounted in the connector for optically coupling a said waveguide to the lens, one end of the said optical member extending partially through the connector while the other end thereof is disposed at a focal point of the lens, and wherein the connector includes means for maintaining the said one end of the optical member and a said end of an optical waveguide in alignment with one another.

With such a terminal the mounting of a said optical waveguide in the terminal is considerably simplified, it being necessary merely to insert the end of the optical waveguide into the connector until it engages and is spliced to the said one end of the elongate optical member.

The longitudinal axis of the bore may pass through the said focal point of the lens.

The other end of the optical member may project from the connector.

The said alignment maintaining means may be resilient means.

The connector may include a tubular body and the alignment maintaining means may comprise a multiplicity of flexible elongate members mounted on the body and extending longitudinally through the body, the flexible elongate members being spaced apart around the body and resiliently engaging the said elongate optical member.

The ends of each of the said flexible elongate members may be displaced with respect to one another about the longitudinal axis of the tubular body.

The ends of each of the flexible elongate members may be displaced in the same sense about the longitudinal axis of the tubular body, and, in such a case, the ends of each of the flexible elongate members may be displaced by the same angular extent.

The lens may comprise a biconvex lens.

Alternatively, the lens may comprise a planar-convex lens. In such a case, the elongate optical member may extend into a recess in the planar-convex lens.

The elongate optical member may comprise an optical fibre.

The terminal may include means for engaging an end of a said optical waveguide to anchor the optical waveguide in the said connector.

According to a further aspect of the present invention there is provided a coupling for a pair of optical waveguides comprising a pair of terminals as aforesaid.

Various forms of couplings for optical waveguides including terminals therefor in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a sectional side view of a first form of the coupling for a pair of optical fibres; Figure 2 is a sectional side view of a connector for the coupling; Figure 3 is an end view of the connector; Figure 4 is a sectional side view of an alternative form of connector for the coupling; Figures 5 and 6 are side views partly in section showing a modification of the coupling of Figure 1; Figure 7 is a sectional side view of a second form of the coupling, and Figure 8 is a sectional side view of a third form of the coupling.

Referring to Figure 1, the coupling comprises a pair of optical terminals for optical fibres and includes a tubular housing 10 having two parts 11 and 12. These parts 11 and 12 have, respectively, an annular projection 30 at an end of one part and an annular recess 31 on the other part to receive the annular projection and permit coupling and decoupling of the two parts.

The terminal parts 11 and 12 each house a biconvex lens 13, and a connector 14 for receiving the end of an optical fibre 15 which is to be optically coupled to the lens 13. The connectors 14 are each of the form shown in Figures 2 and 3 and include a tube 16 of brass on which is mounted five wires 17 of resilient metal, such as, for example, stainless steel, copper alloy or phosphor bronze, that extend longitudinally through the bore of the tube 16 and are equally spaced around the tube.

The wires 17 are tensioned with the ends of the wires being folded over the ends of the tube 16 and clamped to the tube 16 and maintained under tension by rings 18 of, for example, brass or plastics. The wires 17 extend substantially in a straight line with the ends of each wire being angularly displaced with respect to one another about the longitudinal axis of the tube 16 so that intermediate portions of the wires 17 are spaced from the inner surface of the tube 16. This angular displacement of the ends of the wires 17 is in the same sense for each wire 17 and is of the order of 1.5 degrees. The ends of the tube 16 are slotted to receive the wires 17.

With such a connector 14 the portions of the wires 17 within the tube 16 are slightly spaced from the tube, the degree of such displacement gradually increasing towards the centre of the tube 16 and thereafter gradually decreasing towards the other end of the tube 16. Thus the bore defined in the tube 16 by the wires 17 is of smallest diameter at the centre of the tube. This bore diameter at the centre of the tube 16 is arranged to be slightly smaller than the diameter of the optical fibres so that during insertion of the fibre ends into the connectors 14, the intermediate portions of the wires 17 are deformed outwardly towards the wall of the tube 16 and the wires grip the fibres 15 and thereby axially align the fibres with the connectors 14.

It is necessary accurately to position the ends of the optical fibres at the focal points of the respective lenses 13 and this is achieved by mounting within the connectors 14 respective short lengths 20 of optical fibres having dimensions and optical characteristics substantially identical to the dimensions and optical characteristics of the fibres 15. These fibre lengths 20 are accurately positioned in the connectors 14 prior to the connectors being mounted in the housing 10, with one end of the fibre lengths 20 being positioned midway along the length of the respective connectors while the other ends of the fibre lengths 20 project from one end of the respective connectors by the appropriate distance. The fibre lengths 20 are secured in position by an epoxy adhesive. The connectors 14 are then inserted into the respective ends of the housing parts 11 and 12 remote from the lenses 13 and these ends are then turned over to mount the connectors 14 in the housing parts with the said other ends of the fibre lengths 20 being disposed at the focal points of the respective lenses 13.

When it is required to couple a pair of optical fibres 15, it is necessary merely to insert the ends of these fibres into the respective connectors 14 until they abut, and are spliced to, the ends of the respective fibre lengths 20. This simplifies considerably the mounting of the fibres 15.

The fibres 15 are secured in the connectors 14 by an epoxy adhesive.

In order to provide the required degree of coupling between the fibres 15, it may be necessary for the ends of the fibre lengths 20 to be highly polished and in these circumstances the ends of the lengths 20 are polished before these lengths are disposed in the connectors 14.

The ends of the fibres 15 are coated with a fluid having the desired optical characteristics to maximise the optical coupling between these fibres and the fibre lengths 20 before the fibres 15 are inserted into the connectors 14. This fluid is conveniently one which also adhesively bonds the ends of the fibres 15 to the fibre lengths 20.

The single fibres 15 are of very small diameter and in order to assist insertion of these fibres into the connectors 14, the connectors may be shaped to define tapered holes to receive the ends of the fibres. Such a connector is shown in Figure 4, where the ring 18 at the end of the connector 14 for receiving a fibre 15 is replaced by an end piece 32 of metal or plastics having an annular portion 33 which clamps the ends of the wires 17 to the tube 16, and a portion 34 which projects from the end of the tube 16 and is shaped to define a tapered hole to receive the end of a fibre 15.

It is visualised that it may be necessary to grip the ends of the fibres 15 firmly so as to prevent withdrawal of the fibre ends from the connectors 14 and thereby maintain the splicing between these fibre ends and the fibre lengths 20. One form of coupling for this purpose is shown in Figures 5 and 6 where the parts 11 and 12 of the housing 10 are disposed within respective sleeves 35 of heat-shrinkable plastics shaped as shown in Figure 5 to provide tapered apertures 36 to receive the ends of the fibres 15. When the sleeves 35 are heated, they shrink, as shown in Figure 6, to grip the respective parts 11 and 12, and the ends of the fibres 15 to inhibit withdrawal of the fibres 15 from the connectors 14. The sleeves 35 are slidably mounted on the fibres 15 before they are inserted in the connectors 14, and thereafter slid over the ends of the parts 11 and 12 and heat shrunk.

Various other arrangements may be provided to prevent withdrawal of the fibres 15.

For example, the rings 18 (Figure 2) at the ends of the connectors 14 for receiving the fibres 15 may carry respective end-pieces (not shown) which are externally threaded and have pairs of diametrically-opposed projections whose free ends are shaped to define a tapered aperture through which the ends of the fibres 15 are to be inserted into the connectors 14. The end piece carries a nut which when screwed on to the end piece engages the pair of projections to urge their free ends into engagement with the fibre end to grip the fibre and inhibit its withdrawal from the connector 14.

The couplings may include housings of various other shapes. For example, the housings may be as shown in Figure 7 where the connectors 14 are mounted in tapered end portions 36 of the housing parts 11 and 12. Such a housing may be of plastics and in these circumstances the lenses 13 and the connectors 14 may be moulded as inserts in the housing parts 11 and 12.

Referring to Figure 8, there is shown a similar form of coupling to that shown in Figure 1, except that the coupling has planar-convex lenses 21 instead of biconvex lenses. These lenses 21 are moulded of plastics, for example, acrylic resin, and have apertures 23 formed therein in which the fibre lengths 20 are to be mounted with their ends disposed at the focal points of the lenses.

It has been found that if the fibres 15 were inserted into the apertures 23, the fibres may not always be a tight fit in these apertures and thus be accurately positioned at the focal points of the lenses 21. This is because for any given size of optical fibre the external diameters of the fibres may vary consider ably from one fibre to another. It is necessary to provide apertures in the lenses 21 that are capable of receiving the maximum diameter of fibre and thus, when mounting in the lenses 21 fibres having a relatively small external diameter, difficulties may be experienced in accurately aligning the ends of the fibres in the lenses and locating those ends at the focal points of the lenses. This difficulty is overcome by providing the con nectors 14 in the coupling and by accurately mounting the short fibres 20 in the lenses 21 during the assembly of the coupling. Conve niently the fibres selected for providing the short fibres 20 are of the maximum external diameter so that these fibres are a tight fit in the lens apertures 23. In these circumstances the fibre lengths 20 may be inserted less than half-way through the connectors 14 so as to ensure that fibres 15 of minimum external diameter inserted into the other ends of the connectors will be gripped by the wires 17 and be properlyaligned in the connectors with the short fibres 20.

The fibres 20 are secured in the lenses 21 with an adhesive having the desired optical characteristics.

The housing 10 of Figure 8 is provided with sleeves 22 to receive the fibres 15, the holes in the sleeves 22 being tapered to facili tate insertion of the fibres 15 into the connec tors 14. When the fibres 15 have been inserted into the connectors 14, the sleeves 22 are crimped to secure the sleeves of the fibres in position. As before the ends of the fibres in the connectors 14 are adhesively secured to the short fibres 20.

Various modifications may be made to the embodiments described without exceeding the scope of the invention. For example, the single optical fibres 15 and fibre lengths 20 may be replaced by other optical waveguides or bundles of optical fibres. Also the coupl ing may be for coupling an optical fibre to a light-sensitive device instead of another opti cal fibre.

Attention is directed to our co-pending Patent Application No. 11021/76 (Serial No. 1572501) entitled "Optical Waveguide Assemblies".

WHAT WE CLAIM IS: 1. A terminal for an optical waveguide, including a connector having a longitudinal bore in which an end of an optical waveguide is to be anchored, a lens for transmitting light from one end of the waveguide, and a hous ing in which the connector and the lens are mounted, wherein the terminal includes an

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

Claims

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

connector is shown in Figure 4, where the ring 18 at the end of the connector 14 for receiving a fibre 15 is replaced by an end piece 32 of metal or plastics having an annular portion 33 which clamps the ends of the wires 17 to the tube 16, and a portion 34 which projects from the end of the tube 16 and is shaped to define a tapered hole to receive the end of a fibre 15.

It is visualised that it may be necessary to grip the ends of the fibres 15 firmly so as to prevent withdrawal of the fibre ends from the connectors 14 and thereby maintain the splicing between these fibre ends and the fibre lengths 20. One form of coupling for this purpose is shown in Figures 5 and 6 where the parts 11 and 12 of the housing 10 are disposed within respective sleeves 35 of heat-shrinkable plastics shaped as shown in Figure 5 to provide tapered apertures 36 to receive the ends of the fibres 15. When the sleeves 35 are heated, they shrink, as shown in Figure 6, to grip the respective parts 11 and 12, and the ends of the fibres 15 to inhibit withdrawal of the fibres 15 from the connectors 14. The sleeves 35 are slidably mounted on the fibres 15 before they are inserted in the connectors 14, and thereafter slid over the ends of the parts 11 and 12 and heat shrunk.

Various other arrangements may be provided to prevent withdrawal of the fibres 15.

For example, the rings 18 (Figure 2) at the ends of the connectors 14 for receiving the fibres 15 may carry respective end-pieces (not shown) which are externally threaded and have pairs of diametrically-opposed projections whose free ends are shaped to define a tapered aperture through which the ends of the fibres 15 are to be inserted into the connectors 14. The end piece carries a nut which when screwed on to the end piece engages the pair of projections to urge their free ends into engagement with the fibre end to grip the fibre and inhibit its withdrawal from the connector 14.

The couplings may include housings of various other shapes. For example, the housings may be as shown in Figure 7 where the connectors 14 are mounted in tapered end portions 36 of the housing parts 11 and 12. Such a housing may be of plastics and in these circumstances the lenses 13 and the connectors 14 may be moulded as inserts in the housing parts 11 and 12.

Referring to Figure 8, there is shown a similar form of coupling to that shown in Figure 1, except that the coupling has planar-convex lenses 21 instead of biconvex lenses. These lenses 21 are moulded of plastics, for example, acrylic resin, and have apertures 23 formed therein in which the fibre lengths 20 are to be mounted with their ends disposed at the focal points of the lenses.

It has been found that if the fibres 15 were inserted into the apertures 23, the fibres may not always be a tight fit in these apertures and thus be accurately positioned at the focal points of the lenses 21. This is because for any given size of optical fibre the external diameters of the fibres may vary consider ably from one fibre to another. It is necessary to provide apertures in the lenses 21 that are capable of receiving the maximum diameter of fibre and thus, when mounting in the lenses 21 fibres having a relatively small external diameter, difficulties may be experienced in accurately aligning the ends of the fibres in the lenses and locating those ends at the focal points of the lenses. This difficulty is overcome by providing the con nectors 14 in the coupling and by accurately mounting the short fibres 20 in the lenses 21 during the assembly of the coupling. Conve niently the fibres selected for providing the short fibres 20 are of the maximum external diameter so that these fibres are a tight fit in the lens apertures 23. In these circumstances the fibre lengths 20 may be inserted less than half-way through the connectors 14 so as to ensure that fibres 15 of minimum external diameter inserted into the other ends of the connectors will be gripped by the wires 17 and be properlyaligned in the connectors with the short fibres 20.

The fibres 20 are secured in the lenses 21 with an adhesive having the desired optical characteristics.

The housing 10 of Figure 8 is provided with sleeves 22 to receive the fibres 15, the holes in the sleeves 22 being tapered to facili tate insertion of the fibres 15 into the connec tors 14. When the fibres 15 have been inserted into the connectors 14, the sleeves

22 are crimped to secure the sleeves of the fibres in position. As before the ends of the fibres in the connectors 14 are adhesively secured to the short fibres 20.

Various modifications may be made to the embodiments described without exceeding the scope of the invention. For example, the single optical fibres 15 and fibre lengths 20 may be replaced by other optical waveguides or bundles of optical fibres. Also the coupl ing may be for coupling an optical fibre to a light-sensitive device instead of another opti cal fibre.

Attention is directed to our co-pending Patent Application No. 11021/76 (Serial No. 1572501) entitled "Optical Waveguide Assemblies".

WHAT WE CLAIM IS: 1. A terminal for an optical waveguide, including a connector having a longitudinal bore in which an end of an optical waveguide is to be anchored, a lens for transmitting light from one end of the waveguide, and a hous ing in which the connector and the lens are mounted, wherein the terminal includes an

elongate optical member mounted in the connector for optically coupling a said waveguide to the lens, one end of the said optical member extending partially through the connector while the other end thereof is disposed at a focal point of the lens, and wherein the connector includes means for maintaining the said one end of the optical member and a said end of an optical waveguide in alignment with one another.
2. A terminal according to Claim 1, wherein the longitudinal axis of the said bore passes through the said focal point of the lens.
3. A terminal according to Claim 1 or Claim 2, wherein the said other end of the optical member projects from the connector.
4. A terminal according to anyone of the preceding claims, wherein the said alignment maintaining means is resilient means.
5. A terminal according to any one of the preceding claims, wherein the connector includes a tubular body and wherein said alignment maintaining means comprises a multiplicity of flexible elongate members mounted on the body and extending longitudinally through the body, the flexible elongate members being spaced apart around the body and resiliently engaging the said elongate optical member.
6. A terminal according to Claim 5, wherein the ends of each of the said flexible elongate members are displaced with respect to one another about the longitudinal axis of the tubular body.
7. A terminal according to Claim 6, wherein the ends of each of the flexible elongate members are displaced in the same sense about the longitudinal axis of the tubular body.
8. A terminal according to Claim 7, wherein the ends of each of the flexible elongate members are displaced by the same angular extent.
9. A terminal according to any one of Claims 5 to 8, wherein the flexible elongate members are of circular cross-section.
10. A terminal according to any one of Claims 5 to 9, wherein the flexible elongate members are of metal.
11. A terminal according to any one of Claims 5 to 10, wherein the flexible elongate members are of stainless steel.
12. A terminal according to any one of Claims 5 to 10, wherein the flexible elongate members are of copper alloy.
13. A terminal according to any one of Claims 5 to 10, wherein the flexible elongate members are of phosphor bronze.
14. A terminal according to any one of the preceding claims, wherein the lens comprises a biconvex lens.
15. A terminal according to any one of Claims 1 to 13, wherein the lens comprises a planar-convex lens.
16. A terminal according to Claim 15, wherein the said other end of the elongate optical member extends into a recess in the planar-convex lens.
17. A terminal according to any one of the preceding claims, wherein the elongate optical member comprises an optical fibre.
18. A terminal according to any one of the preceding claims, including means for engaging an end of a said optical waveguide to anchor the optical waveguide in the said connector.
19. A terminal according to any one of the preceding claims, wherein the elongate optical member is adhesively secured in the connector.
20. A terminal for an optical waveguide, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.
21. A terminal according to Claim 20 including an optical waveguide connector substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.
22. A terminal according to Claim 20 modified substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings.
23. A terminal according to Claim 20 modified substantially as hereinbefore described with reference to Figure 7 of the accompanying drawings.
24. A terminal for an optical waveguide, substantially as hereinbefore described with reference to Figure 8 of the accompanying drawings.
25. A coupling for a pair of optical waveguides comprising a pair of terminals as claimed in any one of the preceding claims.