GB1579027A

GB1579027A - Fibre optic waveguide connectors

Info

Publication number: GB1579027A
Application number: GB2165676A
Authority: GB
Original assignee: Combined Optical Industries Ltd
Current assignee: Combined Optical Industries Ltd
Priority date: 1976-05-25
Filing date: 1976-05-25
Publication date: 1980-11-12
Also published as: FR2353069A1; DE2722367A1

Description

(54) FIBRE OPTIC WAVEGUIDE CONNECTORS (71) We, COMBINED OPTICAL INDUS TRIES LIMITED, a British Company, of 200 Bath Road, Slough, Berkshire, SL1 4DW, 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 is concerned with optical fibre waveguides and, more particularly, with lens elements useful for connection with the ends of fibre waveguides, with receivers and connectors comprising such an element, and with a method of connecting longitudinally together optical fibre waveguides.

It is well known that the transmission of data by fibre optics has significant advantages for many purposes over conventional electrical systems. Among the advantages are a greater data-carrying capacity, the avoidance of the interference problems associated with electrical systems, the substantial absence of fire risk and the possibility of very low signal losses over long runs.

Whilst it is, in principle, desirable to provide a continuous length of fibre waveguide between the signal input end of a system and the output end, this is not always practicable.

For example, on very long runs fibre waveguides of sufficient length may not be available. In other cases, it may be desirable to be able to extend a system by attaching a further length of fibre waveguide, or to be able to connect and disconnect waveguides as circumstances require.

Connectors have been proposed in the past for these purposes. In these connectors, the waveguide ends to be joined are located coaxially and held with their end faces in contacting abutment. To improve the connection, the end faces of the waveguides are usually polished to an optical finish before the connection is made.

Whilst it is possible in this manner to achieve reasonably acceptable connections, the heavy reliance on accurate alignment and abutment of the waveguide ends is unsatisfactory. For example, if two end faces are not in contact but are separated by an air space of as little as half the fibre diameter, signal losses of at least 50 ( can occur. If the two fibre ends are out of exact longitudinal alignment by as little as 50, a 30% signal loss can arise. If the end faces are laterally displaced by 0 4 times the fibre diameter, a loss of 50 % can occur.

The criticality of accurate alignment and abutment of the waveguides becomes very important where the connection, when made, is to be subjected to vibration or other movement, and also in the case of demountable connections. It will be appreciated that if the end faces of the waveguides become damaged, or if foreign matter becomes lodged between the end faces when a connection is made, significant signal losses will occur.

Not only have problems arisen in the past in connecting together the ends of fibre optic waveguides to provide efficient light transmission therebetween, but also there have been problems in providing a receiver for the end of a waveguide or waveguide bundle, whereby the transmitted light can be satisfactorily received and displayed or reemitted.

We have now found many of the problems associated with prior proposals can be reduced or overcome by the use of a lens element having therein a recess for receiving the end of the fibre optic waveguide or waveguide bundle, and a lens surface arranged to provide a collimated beam of light.

In one aspect, the invention provides a lens element which comprises a body of translucent material having a pair of opposed faces, one face of the pair being a convex lens surface and the other face having a recess therein for receiving the end of a fibre optic waveguide or bundle of fibre optic waveguides, the recess being so arranged relative to the lens surface that light emitted from the end of a waveguide or waveguide bundle therein passes through the lens element and is emitted from the lens surface as a substantially collimated beam of light, and wherein the said recess comprises an inner portion of a diameter closely similar to that of a waveguide or waveguide bundle to be received therein, and an outer portion of greater diameter.

Preferably, the lens element is a generally solid cylindrical body having one end face shaped to provide the said convex lens surface, and the other end face having the said recess therein.

Preferably, the said recess is coaxial with the lens.

The lens element may conveniently be a one-piece plastics moulding.

In another aspect, the invention provides a receiver for an end of a fibre optic waveguide or bundle of fibre optic waveguides, which comprises a lens element as defined above located within a housing, and means for holding a waveguide or waveguide bundle end in the recess in said lens element.

Preferably, the receiver also includes resilient means arranged to permit the lens element to be displaced thereagainst upon insertion of the waveguide or waveguide bundle end in the recess.

In one preferred arrangement, the housing comprises an open-ended tube, and said holding means comprises a cap member arranged to fit over and close one end of the tube, the cap member having an aperture therein through which, in use, the waveguide or waveguide bundle passes to be received in the lens member.

The invention further provides a connector for joining together two fibre optic waveguides or waveguide bundles, which comprises two lens elements as defined above and means for mounting the two lens elements with their respective lens surfaces in face-to-face opposition whereby, in use, a collimated beam emitted from one element will be received by the other element and focussed into the waveguide end(s) therein.

Preferably, the two lens elements are mounted coaxially in a tube having, at each end, a removable cap member, each cap member having an aperture therein through which in use, the respective fibre optic waveguide or bundle passes to be received in the respective lens element.

In a particularly preferred arrangement, the two lens elements are axially slidable in the tube and are held apart by a resilient member disposed therebetween.

The connectors of the invention may be demountable, i.e. they comprise the two lens elements mounted coaxially in a respective open-ended tube, each tube having at one end a removable cap member having an aperture therein through which, in use, the respective fibre optic waveguide or bundle passes to be received in the respective lens element, and a tubular sleeve member for receiving therein the two tubes in axial alignment with the two lens elements having their respective lens surfaces in face-to-face opposition, and means for releasably retaining the two tubes in the sleeve.

In a further aspect, the invention provides a method of connecting two fibre optic waveguides or waveguide bundles for optical transmission therebetween, which comprises placing one end of each waveguide or bundle in a recess in a lens element as defined above, and mounting the two lens elements in face-toface opposition whereby the collimated beam emitted from one element is receivable by the other element and focussed into the waveguide or bundle therein.

In the preferred connectors of the invention, the two lens elements are mounted coaxially in a tube having, at each end, a removable cap member, each cap member having an aperture therein through which in use, the respective fibre optic waveguide or bundle passes to be received in the respective lens element. The tube serves to locate the two lens elements in the desired position which will usually be such that substantially all the collimated light emitted from one lens element enters the other lens element, and is focussed thereby. To avoid any possibility of lateral light loss or entry into the system, the tube will preferably be opaque. It may suitably be of plastics material (although it may be of other materials, such as metal).

Each cap member may serve both to retain the respective lens element in the tube and to guide and support the entering waveguide or bundle end. For this purpose, it is preferred to provide a cushion member in association with each cap, the cushion member being arranged to support and grip the respective fibre waveguide or bundle as the respective cap is mounted onto the end of the tube and to move the respective waveguide or bundle fully into the recess in the respective lens element. A suitable cushion member is, for example, a neoprene (or other material) gland having a central bore to receive the fibre(s) and an outer contour conforming with the inner end of the tube. Pressure on the gland, arising when the cap is moved into place, causes the gland to grip and support the fibre(s). Forward movement of the cap onto the tube causes the gland to urge the fibre(s) forward into the tube to the bottom of the receiving recess in the lens element.

In order to align and position the fibre end(s) with the associated lens and to accommodate dimensional changes arising from changes in temperature, for example, and also to relieve any compressive forces built up in the fibre or bundle as it is pushed into the lens recess by engagement of the cap, it is preferred that the lens elements be axially slidable in the tube. Preferably, the members are held apart by a resilient member disposed therebetween, e.g. a spring.

The connectors of the invention can be of the "permanent" or of the demountable type.

In the latter, the two lens members are each mounted coaxially in a respective openended tube, each tube having a removable cap member at one end. In order to make the connection, the two tubes (with the fibre waveguides attached) are received in a sleeve member with the two lenses in face-to-face opposition, and means are provided for releasably retaining the tubes within the sleeve. The retaining means can be of any sort of releasable catch or, for example, a bayonet fitting. To demount the connection, the catch is released and one (or both) the tubes are withdrawn from the sleeve.

In the connectors and receivers of the invention, the or each lens element preferably comprises a generally solid cylindrical body having one end face shaped to provide a convex lens surface and the other end face having the recess formed therein for receiving the end of the fibre waveguide or bundle.

Such an arrangement is particularly advantageous for several reasons. Firstly, it comprises in a single integral unit (most preferably a one-piece plastics moulding) both the lens surface itself (for providing a collimated beam) and the fibre-end receiving recess. As a result, the latter can be very accurately and definitely positioned (in manufacture) relative to the lens surface, with the result that, in use, the fibre or bundle end is automatically accurately positioned by full insertion into the recess. Thus, the cone of light emitted from the fibre end is precisely collimated by the lens and, vice versa, a collimated beam received by the lens is accurately focussed exactly onto the fibre end and thus enters the fibre. This automatic accurate positioning of the fibre end(s) by the mere act of insertion thereof in a recess is a particularly advantageous feature, since it requires no great on-site skill and is a very simple operation. Thus, some of the major problems (of accurate positioning of the fibre ends) associated with prior art connectors and receivers, is overcome in a simple and elegant manner. The lens elements themselves, with the recess therein, can be formed very accurately and relatively cheaply, by plastics moulding techniques.

A second series of advantages arising from the use of lens elements of this type is in the ease of accurate alignment of two such lens elements. This is most conveniently, and simply, achieved by mounting them in a single tube of accurate straightness. The two lens elements are then automatically aligned, and also protected from soiling or damage.

Furthermore, by mounting the lens elements in a tube, relative axial movement of the elements can easily be accommodated without any risk of non-alignment.

A third advantage arising from the use of lens elements of this type is that substantially all the light emitted from a fibre and can be converted into a collimated beam, i.e. with practically no light loss. This is achieved by providing a lens surface of sufficient diameter for it to be able to receive the whole of the cone of light emitted from the fibre end(s).

Further, and particularly when an optical coupling fluid is used, since the light from the fibre ends enters directly into the lens element and travels therein to the lens surface, there is no possibility of loss of light by, for example, reflection at intervening surface.

The unitary lens member provides a homogeneous continuous light-transmitting medium and so substantially avoids internal light losses which would arise when, for example, a lens is used which is separate from a fibreend receiver, or when there are several interfaces in the light path.

It is preferred to use an optical coupling fluid when the fibre or bundle is inserted into the lens recess. Suitable such fluids are known, for example polyethylene silicone. The use of such a fluid can result in improved transmission, and also avoid the need to polish the end faces of the fibres to an optical finish.

The recess in each lens member comprises an inner portion of a diameter closely similar to that of the waveguide or bundle to be received therein, and an outer portion of greater diameter which will accommodate (in use) any excess optical fluid driven from the inner portion upon insertion of the waveguide or bundle.

The lens elements themselves can be made of glass but it will usually be better to make them of a plastics material such as polystyrene or polymethyl methacrylate. Suitable lens elements can be moulded of these materials.

The receivers of the invention are for coupling to the end of a waveguide or waveguide bundle. As such, they protect the delicate ends and, in use, provide a collimated beam output for use as desired. For example, the output may be fed for display and read-out, or for onward transmission.

In the latter case, the receiver may form one half of a demountable connector of the invention.

In order that the invention may be more fully understood, two embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an axial section of one form of lens element of the invention; Figure 2 shows one form of connector of the invention, with single fibre waveguides in position; Figure 3 shows another form of connector of the invention (in this case a demountable connector), with the single fibre waveguides in position; and Figure 4 shows a receiver of the invention.

Referring to the drawings, Figure 1 shows a lens element comprising a generally cylindrical solid body 1, injection moulded of polystyrene, one end face 2 of which is curved to function as a convex lens. At the other end 3 is a recess formed of a tapering outer portion 4, an intermediate slightly tapering portion 5, and an inner narrow portion 6 terminating in face 7. Face 7 may be, and end face 2 usually is, optically polished, face 7 being planar, perpendicularly bisected by the longitudinal axis of the element. In the case of a bundle of fibres, the dimensions of the portions 5, 6 and 7 would be greater to accommodate the bundle.

Face 7 lies at the focal point of the lens surface 2. The lens surface 2 may be spherical or aspherical, depending on the transmission characteristics required.

Referring now to Figures 2 and 3 (like numerals in all the Figures indicate like parts), two lens elements 1 (as in Figure 1) are located axially in tube 10, in face-to-face opposition. The elements 1 are axially slidable in tube 10, and are biased apart by a light compression spring 11 disposed therebetween. At each end of tube 10 is a cap 12 having an aperture 13 through which passes the fibre waveguide 16 (or bundle). Each cap 12 fits over an end of tube 10 and may be held in position by, for example, a screw thread (not shown) or other retaining means.

A cushion member 14, in this case a neoprene bland, is provided within each cap, and in the embodiment shown this gland is of frustoconical shape and contoured to correspond with a gland sealing member 15.

In order to assemble the connection, the caps 12 are removed from tube 10, together with the glands 14 and gland seating members 15. The fibre waveguides (or bundles) to be joined are preferably polished to provide an optical end face, and the conventional plastic cover stripped back to expose the fibre itself. The cap, gland and gland seating are threaded onto the fibre, and a spot of optical fluid is placed on the end of the fibre, e.g. by dipping. The end of the fibre is introduced into recess 6 and mounting of the cap (with gland and gland seating) on the tube is initiated. As the cap moves into position, the gland is compressed around the fibre (or bundle) and supports it and tends to urge it further into the lens recess 6 and against face 7. When the end of the fibre contacts face 7, additional inward movement of the fibre causes the lens element 1 to slide axially inwardly against the bias of spring 1. When the cap is finally in position, the fibre is firmly held and seated in the lens recess with its end face immersed in optical fluid and in contact with face 7. Excess fluid is displaced into portions 5 and 4 of the lens recess.

When both cap members are in position, the connection has been made. Light emerging from either fibre end (or bundle end) extends into the respective lens element in a well-defined cone and is emitted as a collimated beam. This beam passes along tube 10 and into the other lens element where it is focussed onto the end of the fibre (or bundle therein.

Referring now to Figure 3, each lens element 1 is received in a tube 20 corresponding generally to half the tube 10 in Figure 2, except that each tube 20 has an annular gland seating member 21 at one end formed integrally therewith. The neoprene gland 22 is accordingly slightly dinerently shaped (as shown) from gland 14 in Figure 2. The two tubes 20 are snugly received in a sleeve 23 and releasable fastening means 24 (in this case bayonet fasteners) are provided to hold the tubes in place.

Caps 12 are provided, which engage gland seating member 21. At the inner end of each tube 20, a resilient washer 25 is provided to allow for axial movement of each lens member 1 during insertion of the fibre waveguide and, after assembly, to take up dimensional changes due, for example to temperature fluctuation.

The assembly of the connector of Figure 3 is as follows. The fibre waveguides (or bundles) are mounted in the lens members and held by the caps, in essentially the same manner as described above with reference to Figure 2. Each tube 20 is then inserted in the sleeve 23 and locked in place by the bayonet fitting. The connection is thus made. Disconnection is effected simply by removing one or both tubes 10 from sleeve 23.

Figure 4 shows a receiver of the invention which is essentially one half of the demountable connector shown in Figure 3. The numerals have the meaning indicated with reference to Figure 3.

In the connectors and receivers according to the invention, the prior art requirement for precision in many components is avoided and the difficulties and disadvantages associated therewith are thus avoided. In contrast with the prior art connectors, the distance between the ends of the fibres or fibrebundles being connected, is not critical in the connectors of the invention.

In the connectors of this invention, the axially slidable lens members centre the fibre waveguides and take up dimensional variations in use and manufacture.

The connectors of the invention are very easily assembled and the accurate location of the fibre ends is automatically achieved.

The connectors thus have very substantial advantages over prior known connectors.

Furthermore, they can be made relatively cheaply and easily.

WHAT WE CLAIM IS 1. A lens element which comprises a body of translucent material having a pair of opposed faces, one face of the pair being a convex lens surface and the other face having a recess therein for receiving the end of a fibre optic waveguide or bundle of fibre optic

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Claims

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3 is a recess formed of a tapering outer portion 4, an intermediate slightly tapering portion 5, and an inner narrow portion 6 terminating in face 7. Face 7 may be, and end face 2 usually is, optically polished, face 7 being planar, perpendicularly bisected by the longitudinal axis of the element. In the case of a bundle of fibres, the dimensions of the portions 5, 6 and 7 would be greater to accommodate the bundle.

Face 7 lies at the focal point of the lens surface 2. The lens surface 2 may be spherical or aspherical, depending on the transmission characteristics required.

Referring now to Figures 2 and 3 (like numerals in all the Figures indicate like parts), two lens elements 1 (as in Figure 1) are located axially in tube 10, in face-to-face opposition. The elements 1 are axially slidable in tube 10, and are biased apart by a light compression spring 11 disposed therebetween. At each end of tube 10 is a cap 12 having an aperture 13 through which passes the fibre waveguide 16 (or bundle). Each cap 12 fits over an end of tube 10 and may be held in position by, for example, a screw thread (not shown) or other retaining means.

A cushion member 14, in this case a neoprene bland, is provided within each cap, and in the embodiment shown this gland is of frustoconical shape and contoured to correspond with a gland sealing member 15.

In order to assemble the connection, the caps 12 are removed from tube 10, together with the glands 14 and gland seating members 15. The fibre waveguides (or bundles) to be joined are preferably polished to provide an optical end face, and the conventional plastic cover stripped back to expose the fibre itself. The cap, gland and gland seating are threaded onto the fibre, and a spot of optical fluid is placed on the end of the fibre, e.g. by dipping. The end of the fibre is introduced into recess 6 and mounting of the cap (with gland and gland seating) on the tube is initiated. As the cap moves into position, the gland is compressed around the fibre (or bundle) and supports it and tends to urge it further into the lens recess 6 and against face 7. When the end of the fibre contacts face 7, additional inward movement of the fibre causes the lens element 1 to slide axially inwardly against the bias of spring 1. When the cap is finally in position, the fibre is firmly held and seated in the lens recess with its end face immersed in optical fluid and in contact with face 7. Excess fluid is displaced into portions 5 and 4 of the lens recess.

When both cap members are in position, the connection has been made. Light emerging from either fibre end (or bundle end) extends into the respective lens element in a well-defined cone and is emitted as a collimated beam. This beam passes along tube 10 and into the other lens element where it is focussed onto the end of the fibre (or bundle therein.

Referring now to Figure 3, each lens element 1 is received in a tube 20 corresponding generally to half the tube 10 in Figure 2, except that each tube 20 has an annular gland seating member 21 at one end formed integrally therewith. The neoprene gland 22 is accordingly slightly dinerently shaped (as shown) from gland 14 in Figure 2. The two tubes 20 are snugly received in a sleeve 23 and releasable fastening means 24 (in this case bayonet fasteners) are provided to hold the tubes in place.

Caps 12 are provided, which engage gland seating member 21. At the inner end of each tube 20, a resilient washer 25 is provided to allow for axial movement of each lens member 1 during insertion of the fibre waveguide and, after assembly, to take up dimensional changes due, for example to temperature fluctuation.

The assembly of the connector of Figure 3 is as follows. The fibre waveguides (or bundles) are mounted in the lens members and held by the caps, in essentially the same manner as described above with reference to Figure 2. Each tube 20 is then inserted in the sleeve 23 and locked in place by the bayonet fitting. The connection is thus made. Disconnection is effected simply by removing one or both tubes 10 from sleeve 23.

Figure 4 shows a receiver of the invention which is essentially one half of the demountable connector shown in Figure 3. The numerals have the meaning indicated with reference to Figure 3.

In the connectors and receivers according to the invention, the prior art requirement for precision in many components is avoided and the difficulties and disadvantages associated therewith are thus avoided. In contrast with the prior art connectors, the distance between the ends of the fibres or fibrebundles being connected, is not critical in the connectors of the invention.

In the connectors of this invention, the axially slidable lens members centre the fibre waveguides and take up dimensional variations in use and manufacture.

The connectors of the invention are very easily assembled and the accurate location of the fibre ends is automatically achieved.

The connectors thus have very substantial advantages over prior known connectors.

Furthermore, they can be made relatively cheaply and easily.

WHAT WE CLAIM IS 1. A lens element which comprises a body of translucent material having a pair of opposed faces, one face of the pair being a convex lens surface and the other face having a recess therein for receiving the end of a fibre optic waveguide or bundle of fibre optic

waveguides, the recess being so arranged relative to the lens surface that light emitted from the end of a waveguide or waveguide bundle therein passes through the lens element and is emitted from the lens surface a a substantially collimated beam of light, and wherein the said recess comprises an inner portion of a diameter closely similar to that of a waveguide or waveguide bundle to be received therein, and an outer portion of greater diameter.
2. A lens element according to claim 1 which is a generally solid cylindrical body having one end face shaped to provide the said convex lens surface, and the other end face having the said recess therein.
3. A lens element according to claim 1 or 2 wherein said recess is coaxial with the lens.
4. A lens element according to claim 1, 2 or 3, wherein the end face of the inner portion of the recess is planar and optically polished.
5. A lens element according to any of claims 1 to 4, which is a one-piece plastics moulding.
6. A lens element substantially as herein described with reference to Figure 1 of the accompanying drawings.
7. A receiver for an end of a fibre optic waveguide or bundle of fibre optic waveguides, which comprises a lens element as claimed in any preceding claim, located within a housing, and means for holding a waveguide or waveguide bundle end in the recess in said lens element.
8. A receiver according to claim 7, which also includes resilient means arranged to permit the lens element to be displaced thereagainst upon insertion of the waveguide or waveguide bundle end in the recess.
9. A receiver according to claim 7 or 8, wherein the housing comprises an openended tube, and said holding means comprises a cap member arranged to fit over and close one end of the tube, the cap member having an aperture therein through which, in use, the waveguide or waveguide bundle passes to be received in the lens member.
10. A receiver according to claim 9, wherein a cushion member is provided in association with the cap member, the cushion member being arranged to support and grip the waveguide or waveguide bundle as the cap is mounted on the end of the tube and to move the waveguide or waveguide bundle fully into the recess in the lens member.
11. A connector for joining together two fibre optic waveguides or waveguide bundles, which comprises two lens elements as claimed in any of claims 1 to 6, and means for mounting the two lens elements with their respective lens surfaces in face-to-face opposition whereby, in use, a collimated beam emitted from one element will be received by the other element and focussed into the waveguide end(s) therein.
12. A connector according to claim 11, wherein the two lens elements are mounted coaxially in a tube having, at each end, a removable cap member, each cap member having an aperture therein through which in use, the respective fibre optic waveguide or bundle passes to be received in the respective lens element.
13. A connector according to claim 12, wherein the two lens elements are axially slidable in the tube and are held apart by a resilient member disposed therebetween.
14. A demountable connector according to claim 11, wherein the two lens elements are each mounted coaxially in a respective open-ended tube, each tube having at one end a removable cap member having an aperture therein through which, in use, the respective fibre optic waveguide or bundle passes to be received in the respective lens elements, and a tubular sleeve member for receiving therein the two tubes in axial alignment with the two lens elements having their respective lens surfaces in face-to-face opposition, and means for releasably retaining the two tubes in the sleeve.
15. A connector according to claim 14, wherein the said releaseable retaining means comprises at least one bayonet device.
16. A connector according to claim 14 or 15, wherein each lens element is axially slidable in each tube against resilient means provided at the other end of each tube.
17. A connector according to any of claims 12 to 16, wherein a cushion member is provided in association with each cap member and is arranged to support and grip the respective fibre waveguide or bundle as the respective cap is mounted onto the end of the tube and to move the respective waveguide or bundle fully into the recess in the respective lens element.
18. A connector according to any of claims 11 to 17, wherein each lens element is a plastics moulding.
19. A connector for joining together two fibre optic waveguides or waveguide bundles substantially as herein described with reference to Figures 1 and 2 or Figures 1 and 3 of the accompanying drawings.
20. A method of connecting two fibre optic waveguides or waveguide bundles for optical transmission therebetween, which comprises placing one end of each waveguide or bundle in a recess in a lens element as claimed in any of claims 1 to 6, and mounting the two lens elements in face-toface opposition whereby the collimated beam emitted from one element is receivable by the other element and focussed into the waveguide or bundle therein.
21. A method according to claim 20, substantially as herein described, with reference to Figure 2 or Figure 3 of the accompanying drawings.