GB2191598A - Optical fibre connectors - Google Patents

SPECIFICATION Optical fibre connectors This invention relates to optical fibre connectors.

Optical fibre connectors are known. For example connectors for multi-fibre spices are known and sold underthe name Seicor. This device comprises an etched connector having V-grooves for alignment of up to twelve fibres of a first group. A cover is epoxied overthe bare and coated sections of the fibres to form a first multi-fibre splice piece. The same is done for another group of fibres to form a second splice piece. Joining of the splice pieces involves the use of an alignment part and fastener. Index matching fluid is applied to one array piece and the two pieces are slid and butted together on alignment rails. They are then secured in place by snap fasteners.

Such connectors are in the main satisfactory but where space is limited and the fibres need to be coiled or curved in order to fit them in place, then difficulties can be experienced. For example if the fibres are curved by the installer more tightly than the minimum designed bending radius, then they may cause significant losses in the signals to be transmitted, and in the worst case they may become broken. This is particularly so when installing cables which are feed individual users in e.g. a local area network in a building and particularly using ribbon cables.

It is an object of the present invention to provide an optical fibre connector system which simplifies cable installation and overcomes the above mentioned disadvantages.

According to the present invention there is provided an optical fibre connector comprising a sub stantially rigid substrate supporting a pluralityofin- terconnection optical fibres terminated at both ends in respective terminating units to which mateable connectors can be secured or individual cablefibres can be connected whereby optical fibre cables can be interconnected by means of said optical fibre connector.

In one form the connector provides a two-way 900 in-plane curved connector. By in-plane is meanta connector which connects ribbon cables which lie in the same plane.

In another form the connector provides a two-way 90" out-of-piane curved connector. By out-of-plane is meant a connectorwhich connects ribbon cables lying in different planes which are for example at 900 to each other.

In anotherform the connector provides a three way in-plane T-connectorfor connecting three inplane ribbon cables.

Afurtherembodiment provides afour-way inplane connectorforfour ribbon cables.

In order that the invention can be clearly understood reference will now be made to the accompanying drawings, in which: Figure 1 shows a plan view of a 90 in-planetwoway connector according to an embodiment ofthe invention, and Figures 1Ato 1D show details of Figure 1; Figure2 shows a plan view of a three-way in-plane T-connector according to a second embodiment of the invention; Figure3 shows a plan view of a four-way in-plane connector according to a further embodiment ofthe invention; Figure 4 shows diagrammatically a 90" out-ofplane through connector according to an embodi ment of the invention;; Figure5shows diagrammatically a 90" right hand out-of-plane through connector according to an em bodimentofthe invention, and Figure 6shows an alternative arrangement according to an embodiment ofthe invention.

What is proposed is a multiway fibre interconnect system in which preformed elbows, tees and crossovers obviate the need for, and risk in, bending multiple fibre cable at corners of rooms and buildings.

Normally 90" curves are proposed but different angles e.g. 60 or 1200 are also envisaged.

Referring to Figure 1 ofthe drawings the connector there shown is two-way through-connector in-plane providing a curvethrough 90". It comprises a substrate 1 formed with twelve grooves 2 (see Figure 1 A) each locating an optical fibre 3. Less than twelve grooves could be provided if desired. A cover 4 (re movedforclarityin Figure 1) is shown in section in Figure 1Aand 1 Band retains the fibres loosely in the grooves.

On the substrate there is a termination unit 5 at one end and a similar unit 5 at the other end. Each unit5 has an accurately grooved base 6 having V-grooves made for example by etching a sil icon member and having a cover7 epoxied over the silicon member and the bared ends 3' of the fibres 3. Such termination units would be similarto those described in the preamble and secured with the fibre 3 to the sub- strate 1. Thus the substrate 1 extends beneath the termination units 5 and this is shown more clearly in Figure 1 B. The substrate 1 has a shallow end portion 1A, on which is mounted the base 6, and a step 6A wheretheshallowportion meetsthe main curved portion.The cover4, the substrate 1 and the base 6 each have corresponding pairs of lugs 4A, 1 B, 6A lying one on top of the other with the base lugs 6A sandwiched between the other two. This is shown in Figure 1C and a schematic view of the cover showing its lugs is seen in Figure 1D. On assembly, the lugs which are already apertured are secured together by a hollow metal rivet such as 8 which securesthe parts of the connector together in the correct relative positions and act as mounting holes for the connector.

An alternative arrangement for securing the base 6 tothesubstrate 1 would beaclamping arrangement (notshown inthedrawings).

The connectorshown in Figures 1,1A, 1 B, 1 C and 1D can be made asfollows. The substrate 1 of moulded plastics material has the bases 6 placed in position at each end. Optical fibres 3 are then laid in the grooves 2 by hand and into the grooves of the base members6 having previously had end portions3' bared. The cover4 is placed overthe substrate 1 and the fibre ends are epoxied into the grooves in base member 6 with the cover 7. This is done at both ends one afterthe other and the ends are then polished.

The lugs 4A, 6A, 1 B are then secured togetherwith the hollow rivets.

Connection can be made to the ends by mateable connectors 9 at the end of ribbon cable if, the connection 9 being located by e.g. grooves or ribs on the base 6to align with the termination unit 5 and held in place by e.g. clips. The ribbon cables such as 1 F are interconnected by the connector of Figure 1.

As an alternative manufacturing technique it would be possible to place the fibre 3 in a jig similar to the substrate 1, while the termination units 5 are completed, and then the terminated fibres are removed and placed on a flat or grooved substrate and secured in place thereon, either by the cover such as 4 or by epoxying the terminated fibres direct onto the substrate. This would enable the substrate to be more cheaply made.

An alternative solution bears a close resemblance to the unit described in Figure 1 except with regard to the fibre termination. Referring to Figure 6 it is seen thatthe substrate 61 is the same through the 90 .

However, at the point offibre interconnect, allowance is not made fora "silicon splice" arrangement, butthe grooves 62 are continued at 62A, the idea being thatthe termination of the fibres will comprise a simple "cleave and glue" operation whereby the cable fibre ends are butted against the connector fibre ends in the grooves. Obviously, higher attenua tions will be seen, but, as the units are intended for LAN's, office environments, etc., these losses can be tolerated as system losses are relatively low.

Manufacture will require the end terminating grooves to be made to a very high accuracy, whereas the bend section is onlythere as a guide. Consequently, self-realigning plastic (SRP) is suggested as one substrate material which, when injection moul ded,will be able to provide the required accuracies.

Typical dimensions are shown in the diagrams. The advantages of thins technique are cost, i.e. no additional piece parts to complete a connection, and installation time saving.

This method and arrangement is attractive because it is cheaper. However, it is envisaged that there will be a requirementfor both designs- onefor low loss applications and one for economical shorthaul links where connection costs make a system cost effective or cost ineffective.

Referring now to Figure 2 ofthe drawings there is shown a three-way in-plane T-connector made and constructed exactly the same as previously i.e.

Figure 1 orFigure6.Herehowevertheincoming ribbon cable fibres 1 are connected to a terminating unit9 and two groups ofsixfibres F1 and F2 extend in different directions. F1 extends from termination unit 20 across to the opposite unit 21 whereas group F2 extends through 90"to unit 23. Similarly group F3 ofsixfibresextendsfrom unit 21 to unit 23. Connection of terminated ribbon optical fibre cables to each ofthe units is as previously described and as represented schematically by incoming ribbon cable fibres 1 Fand unit 9.All the fibres are secured to a substrate 24 either in grooves or, as pre-terminated groups offibres, directly onto the substrate surface.

A cover shaped to correspond to the substrate can be used to hold the fibres in place and protectthem and hollow rivets secured to the lugs such as 24A as described previously to hold the substrate, cover and terminating unit together, lugs 24A in this embodi mentcorresponding to lugs 6A in the previous embodiment.

Referring to Figure 3 there is shown a four-way inplane star connector. It is made and constructed in the same way as the previous embodiments and alternatives described. It comprises a moulded plastics substrate 30 carrying fourterminating units 31, 32,33 and 34 each the same as those previously described. Unit 31 has a group F4 of six fibres connected to unit 33, a group F5 of three fibres connected to unit 32, a secured group F6 of three fibres connected to unit34, and unit33 similarly hastwo groups F7 and F8 each ofthree fibres, one going to unit 32 and the otherto unit 34. Units 32 and 34 also have a group F9 of sixfibres connected between them.

A cover shaped to correspond to substrate 30 is also provided and thefibres are either laid in grooves in the substrate or pre-terminated and then laid on and secured to the substrate as described earlier.

Once again the lugs such as 30A correspond to lugs on the terminating bases and on the cover and hollow rivets secure the parts together and provide mounting holes as a means for mounting the complete connector in situ in use.

The invention provides simple and cost effective snap-in fibre optic multiway connectors. They are particularly suitable as distribution nodes and corner connectors in the office environment. The protection inherent in the connectorwill allow under-carpet installation and operation of the units. They can be used in industrial environments as process control distribution nodes.

With a suitable environmental enclosure the connector may be used in distribution manholes.

The embodiments ofthe invention described incorporate in one form splicing units (terminating units 5) the same as orsimilarto commercially avail- able unitstogetherwith injection moulded (or they could be stamped out) substrate structures. The splice units one linked by short length of fibres e.g.

10to 20 cms offibres,thefibres being laid in grooves formed in the substrate, or pre-jigged and pre-sliced (terminated) and then slid and secured to grooved or ungrooved substrates. The substrate can be plastic or metal. Incoming ribbon cables have their ends terminated in mateable splice units which arethen snapped into the connector.

There are other configurations possible. For example a straight-through 90" out-of-plane connector such as illustrated schematically in Figure 4 where the direction of the cable goes around the edge of a room e.g.from underthe carpet to travel up the wall sothatthe ribbon cables lie in planes atrightangles to each other.

Another variant is shown in Fig u re 5 where the cablegoesaroundthecornerasin Figure 4 but also changes direction to the right or left (the right is illustrated in Figure 5).

Other possible variations and combinations are possible although those described can accomodate most interconnection arrangements for ribbon cables where the cable isto be fixed flatto re ctangularlyarrangedsurfacesofa building or room.

A 180" straight-through connector may also be useful.

The connector cover and substrate is of such design that each connector is sufficiently robust to withstand direct abrasion and knocks, high pressure loadings and also be able to maintain operating parameters, such as attenuation, during normal e.g.

office environments.

Although the designs described show the interconnect fibres 3 lying parallel to one another, it would also be possible to have a connector in which the fibres are not necessarily parallel and could for example be formed of a terminated bundle of straight fibres subsequently secured to a rigid substrate sothattheterminations are directed in the required directions e.g. directions at 90" to each other with the fibres secured in place save only that none of them are bent through an arcwhich exceeds their minimum designed bending radius. This would normally involve some of the fibres crossing some other fibres in the case of an elbow for example, and the space between the cover and the substrate would necessarily be somewhat greater than that illustra- ted in Figure 1Ato allowforthe fibres to cross and lie over one another. Silicone rubber can be used to fix the fibres in their final positions within the connector.

Although ribbon cables are referred to herein, other shapes can also be used if desired.