IE913492A1

IE913492A1 - Optical fibre connector

Info

Publication number: IE913492A1
Application number: IE349291A
Authority: IE
Original assignee: British Telecomm
Priority date: 1990-10-09
Filing date: 1991-10-04
Publication date: 1992-04-22
Also published as: AU8643191A; WO1992006396A1; GB9021956D0

Abstract

A fibre array connector comprises a pair of identical connector halves (A and B). Each connector half (A and B) has a fibre support member (1) and a spring member (2) formed from separate silicon substrates. Each fibre support member (1) defines a plurality of V-grooves (3), and each spring member (2) is constituted by a plurality of cantilever springs (5). Each spring (5) is fixed to the base of a respective V-groove (3), the arrangement being such that, with the two connector halves (A and B) placed together with the V-grooves in alignment, fibres (7) can be resiliently mounted in the diamond-shaped apertures defined by the aligned V-grooves.

Description

OPTICAL FIBRE CONNECTOR This invention relates to an optical fibre connector, and in particular to a connector for an array of parallel optical fibres. The invention also relates to a method of assembling a plurality of fibres to form an array connector.

Fibre array connectors often use accurately defined V-grooves for positioning the fibres. Such an array connector uses removable metal pins to provide accurate mating of the connector with a similar connector. Connectors of this type are described in the specification of our co-pending British patent application No. 9014639.0. Tolerances are such that the fibres can be located within the plane of the array with submicron precision. However, the height (z-coordinate) of a fibre core above its V-groove is dependent on the fibre diameter and fibre concentricity. Deviation from concentricity is often submicron, but the outer diameter typically has a 2pm spread. Since the V-grooves only references the outer diameter of the fibres, these tolerances reflect directly on the core positions, and hence the coupling loss of the fibres.

If all the fibres within an array are the same size, the fibre cores may have an absolute error in y (height), but variations from planarity could be larger than lpm. More importantly, the smaller fibres are free to move within their V-grooves, giving rise to increases in x (transverse) and possibly z (longitudinal) positioning errors.

If a fibre is sandwiched between a pair of identical V-grooves, then the tolerance in the core position will be submicron along all three axes, if the y reference plane is the mid-point between the two groove substrates. If these substrates are fabricated as identical springs with undersized grooves, the fibre will force both springs apart, giving the required submicron precision on the fibre core position, when referenced to a non-sprung part of the assembly. This has been demonstrated to work in single fibre mechanical splices, using micromachined silicon springs. A single pair of substrates is used to hold both fibres (hence a splice, not a - 2 plug and socket). Each device is typically 1 χ 1 x 8mm, and the springs are separated by mechanical sawing. As the devices are spaced by several millimetres, this technique is not suitable for forming array connectors which require fibres to be closely spaced apart by about 25Ομπι.

The aim of the invention is to extend this principle to array connectors.

The present invention provides a fibre array connector comprising a pair of connector parts, each connector part having a fibre support member and a spring member formed from separate substrates, wherein each fibre support member defines a plurality of V-grooves, and each spring member is constituted by a plurality of cantilever springs, each of which is fixed to the base of a respective V-groove, the connector being such that, with the two connector part placed together with the V-grooves in alignment, fibres can be resiliently mounted in the diamond-shaped apertures defined by the aligned V-grooves.

Advantageously, each fibre support member is constituted by a cantilever membrane portion and a rigid support portion, the V-grooves being formed in both the cantilever membrane portion and the rigid support portion. Preferably, each cantilever membrane portion is formed with V-shaped corrugations which define the V-grooves of that portion, and each of the cantilever membrane portions is formed with further corrugations in those portions thereof which join adjacent V-shaped corrugations.

In a preferred embodiment, each of the V-grooves tapers towards the end thereof remote from the rigid support portion of the associated fibre support member. Preferably, the two fibre support members are substantially identical.

Each spring member may be constituted by a plurality of cantilever springs which extend from a rigid support portion. Conveniently, each of the cantilever springs has a generally diamond-shaped cross-section, and each is formed with a cavity which faces that portion of the associated V-groove in the region where that V-groove meets the rigid support portion of the associated fibre support member. - 3 Preferably, the two substrates of each connector part are bonded together, and the two connector parts are bonded together. The substrates may be silicon substrates.

The invention also provides a method of making a fibre 5 array connector, the method comprising the steps of forming a pair of connector parts each of which is formed with a plurality of V-grooves, and fixing the two connector parts together with the V-grooves in alignment to form diamond-shaped fibre-receiving apertures, wherein each of the connector halves is formed by:a) forming said plurality of V-grooves in a first substrate, b) forming a plurality of V-shaped grooves in a second substrate, and c) fixing the first and second substrates together so that the bases of the V-grooves are aligned with the portions of the second silicon substrate positioned between the V-shaped grooves.

Advantageously, the substrates are silicon substrates and the V-grooves and the V-shaped grooves are formed by anisotropic etching.

Preferably, prior to the formation of the V-grooves, a series of closely-spaced corrugations are formed in each of the first substrates in positions such that each subsequently-formed V-groove has a series of corrugations on either side thereof.

The method may further comprise the step of forming further V-shaped grooves in each of the second substrates after the connector parts have been fixed together, the further V-shaped grooves being formed in those surfaces of the second substrates which are opposite to the surfaces in which the first-mentioned V-shaped grooves are formed, and the further V-shaped grooves being so positioned that, together with the first-mentioned V-shaped grooves, they form diamond-shaped cantilever spring members in the second substrates.

Advantageously, the method further comprises the step of forming further V-grooves in each of the first substrates, the further V-grooves being offset from the first-mentioned V-grooves so as to form V-shaped corrugations in the first substrates. The further V-grooves may be formed by anisotropic etching.

The invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of part of an array connector constructed in accordance with the invention; Figure 2 is a cross-section taken on the line II - II of Figure 1; Figure 3 is a cross-section taken through the entire array connector, and includes a cross-section taken on the line III - III of Figure 1; and Figure 4 shows various stages in the method of forming an array connector of the type shown in Figures 1 to 3.

Referring to the drawings, Figure 1 shows one half A of a fibre array connector. The other half B of the connector is shown, in Figure 3, in position against the connector half A.

The two connector halves A and B are identical, so only the connector half A will be described in detail.

As shown in Figure 1, the connector half A is constituted by two (100) silicon wafers 1 and 2. The wafer 1 has a cantilever membrane portion la and a solid support portion lb.

Similarly, the wafer 2 has a cantilever spring portion 2a and a solid support portion 2b. The two wafers 1 and 2 are bonded together. In order to complete the connector, the two connector halves A and B are fixed together by bonding the two portions lb together.

The wafer 1 is formed with three V-grooves 3, the V-grooves being formed by etching into the cantilever portion la and into the support portion lb. Thin membranes 4 extend between adjacent pairs of V-grooves 3 in the cantilever portion la, the membranes being corrugated - at 4a (see Fig. 3) - to allow independent vertical flexing of the V-grooves.

The cantilever spring portion 2a is constituted by three diamond-shaped cantilever springs 5, each of which is bonded to the base of a respective V-groove 3. - 5 As shown in Figure 2, each V-groove 3 is tapered (as indicated by the reference numeral 6) so that the cavity formed by that groove and the corresponding groove of the connector half B is oversize with respect to a fibre 7 held therein in the rigid region of the connector (that is to say in the region defined by the wafer support portions lb and 2b) but is undersize in the sprung region (that is to say in the region defined by the cantilever portions la and 2a). This facilitates insertion of the fibres 7.

Each cantilever spring 5 is formed with a cavity 5a (see Figure 2). The cavities 5a ensure that the springs 5 and the associated V-grooves 3 form a parallel action device, thereby ensuring that each fibre end at the open end of the finished connector is clamped rigidly so as to remain in an accurate position with respect to the central axis of its aligned V-grooves. This, in turn, ensures that the fibres 7 are accurately positioned within the connector.

The V-grooves are dimensioned so as to be slightly undersized with respect to the dimensions of the fibres 7 in the sprung region, thereby ensuring that a fibre array can be positioned in the connector with the fibre cores positioned to submicron precision in the y and z axes. Submicron control of the fibres in the x axis (pitch) is achieved by the accurate positioning of the V-grooves 3. Thus, assuming the pitch (separation of fibre core axes) is 250pm and the fibres 7 have an outer diameter of 125pm, a V-groove width of just less than 140pm is required for an undersized groove. The thin membranes 4 are assumed to be just under 5μιη thick - a size which can be well controlled with an etch stop process. The corrugations 4a, which allow concentration of the flexure, need a minimum corrugation length of 30μιη. If the minimum contact between the two wafers 1 and 2 at the tips of the springs 5 is set to 20μιη, this limits wafer thickness to 145μπι for the wafer 1. This is much thinner than normal wafers, but there is minimal processing before it is bonded onto the wafer 2. If necessary, a standard wafer could be used, being thinned after the bonding has been performed. - 6 When the springs 5 are etched from both sides (in the manner described below with reference to Fig. 4), the perpendicular distance (wall thickness) will then be 40/( 2)μιη (or typically 30μιη). The registration error between the two sides should be better than 5μιη, giving 3. 5pm worst case reduction in this wall thickness. Using these dimensions, each of the cavities 5a in the wafer 2 has a maximum depth of 160μιη, giving a maximum wafer thickness of say 310pm, again smaller than standard.

Figure 4 shows the various stages of a stylised process of forming an array connector of the type shown in Figures 1 to 3, Figures 4a to 4c showing the process stages of forming individual connector halves A and B, and Figures 4d and 4e showing the remaining stages of the process. Initially, the two silicon wafers 1 and 2 are separate, and mask layers Ila and lib are deposited or grown on the wafer 2. Windows 12 are then opened up in the mask 11a, and V-grooves 13 are formed in the wafer portion 2a by anisotropic etching using ethylene diamine pyrocatechol and water (EDP) or KOH. This etching step also opens up the cavities 5 (not shown in Figure 4). An etch stop layer 14 is then diffused into the grooves 13. An etch stop layer 15 is also diffused, through a suitable mask 16, into the wafer 1, this etch stop layer being positioned along the line which will form the regions at which the cantilever springs 5 are bonded to the bases of the corresponding V-grooves 3. The layer 15 prevents subsequent etching steps applied to the wafer 2 etching into the wafer 1 through the cavities 5. This stage of the process is shown in Figure 4a.

The two wafers 1 and 2 are then bonded together. If necessary, the wafer 1 is thinned either before or after the bonding step. The corrugations 4a are then etched into the wafer 2 through a suitable mask (not shown). An isotropic etch step (using, for example, HF and HNO3 with CH3COOH) is preferably used for corrugation formation, as this results in corrugations which are more symmetrical than those which result from an anisotropic etch. An etch stop layer 17 is - 7 then diffused into the regions surrounding the corrugations 4a. This stage of the process is shown in Figure 4b.

The V-grooves are then etched into the wafer 1 through carefully-defined windows using an anisotropic etchant such as EDP or KOH. A new mask layer may be required for this etching step, though it is possible that the existing mask defined by the etch stop layer 17 could be used. In either case, the window openings for the V-grooves 3 require plasma etching for linewidth control. This stage of the process is shown in Figure 4c.

The wafer pair 1, 2 is then bonded to an identical wafer pair 1, 2 with the V-grooves 3 in alignment. Windows are then opened up in the mask layers lib on the wafers 2, and V-grooves 18 are formed by using an anisotropic etchant such as EDP or KOH. This etching step terminates at the etch stop layers 14. The stage of the process is shown in Figure 4d.

The layers 14 are then plasma etched to the bases of the V-grooves 13 so as to join the grooves 13 with the associated grooves 18. A further anisotropic etching step, using an etchant such as EDP or KOH, is then carried out to separate the springs 5 and to form grooves 19 complementary to the V-grooves 3 in the wafer portions la. This etching step terminates at the etch stop layers 17. This stage, shown in Figure 4e, completes the process.

The etch stop layer 14 between the two sets of grooves 13 and 18 in each of the wafers 2 prevents undercutting at the mesa corners formed by the reflex angles between the two sets of grooves. If this layer 14 were not present, the fast etching silicon planes (i.e. the (211) and (311) planes) would be exposed along the vertices, resulting in narrowing of the cantilever springs 5. This etch stop layer 14 also passivates the flat inner surfaces of the springs 5.

The four wafers 1 and 2, which are bonded together during the fabrication process to form several tens or hundreds of connectors during one step, are diced to form individual array connectors. Pre-cleaved fibres can then be threaded into each channel of a given connector, the fibres being pushed in against the radial spring forces. The insertion forces will be - 8 small, as the open ends of the channels can be significantly larger than the fibres. Once all the fibres are inserted, they can be secured more permanently with UV epoxy.

A similar procedure can be used to form sprung V-grooves 5 for a pair of metal alignment pins, these V-grooves being positioned outboard of the fibre V-grooves. These additional V-grooves are larger than the fibre V-grooves so as to accommodate the metal alignment pins, and so are formed through the pairs of wafers 1 and 2 of each connector half. 10 A third wafer is then added to each connector half, the cantilever springs for the pin V-grooves being formed in these wafers.

It will be apparent that modifications could be made to the connector described above. In particular the connector could easily be modified to accommodate a greater (or smaller) number of fibres than the three fibres referred to.

Claims

1. A fibre array connector comprising a pair of identical connector parts, each connector part having a fibre support member and a spring member formed from separate substrates, wherein each fibre support member defines a plurality of V-grooves, and each spring member is constituted by a plurality of cantilever springs, each of which is fixed to the base of a respective V-groove, the connector being such that, with the two connector parts placed together with the V-grooves in alignment, fibres can be resiliently mounted in the diamond-shaped apertures defined by the aligned V-grooves.

2. A connector as claimed in claim 1, wherein each fibre support member is constituted by a cantilever membrane portion and a rigid support portion, the V-grooves being formed in both the cantilever membrane portion and the rigid support portion.

3. A connector as claimed in claim 2, wherein each cantilever membrane portion is formed with V-shaped corrugations which define the V-grooves of that portion.

4. A connector as claimed in claim 3, wherein each of the cantilever membrane portions is formed with further corrugations in those portions thereof which join adjacent V-shaped corrugations.

5. A connector as claimed in any one of claims 2 to 4, wherein each of the V-grooves tapers towards the end thereof remote from the rigid support portion of the associated fibre support member.

6. A connector as claimed in any one of claims 1 to 5, wherein the two fibre support members are substantially identical. - 10

7. A connector as claimed in any one of claims 1 to 6, wherein each spring member is constituted by a plurality of cantilever springs which extend from a rigid support portion.

8. A connector as claimed in claim 7, wherein each of the cantilever springs has a generally diamond-shaped cross-section.

9. A connector as claimed in claim 8, wherein each of the cantilever springs is formed with a cavity which faces that portion of the associated V-groove in the region where that V-groove meets the rigid support portion of the associated fibre support member.

10. A connector as claimed in any one of claims 1 to 9, wherein the two substrates of each connector half are bonded together.

11. A connector as claimed in any one of claims 1 to 10, wherein the substrates are silicon substrates.

12. A connector as claimed in any one of claims 1 to 11, wherein the two connector parts are bonded together.

13. A fibre array connector substantially as hereinbefore described with reference to, and as illustrated by, Figures 1 to 3 of the accompanying drawings.

14. A method of making a fibre array connector, the method comprising the steps of forming a pair of connector parts each of which is formed with a plurality of V-grooves, and fixing the two connector parts together with the V-grooves in alignment to form diamond-shaped fibre-receiving apertures, wherein each of the connector halves is formed by:a) forming said plurality of V-grooves in a first substrate, b) forming a plurality of V-shaped grooves in a second substrate, and - 11 c) fixing the first and second substrates together so that the bases of the V-grooves are aligned with the portions of the second substrate positioned between the V-shaped grooves.

15. A method as claimed in claim 14, wherein the first and second substrates are fixed together by bonding.

16. A method as claimed in claim 14 or claim 15, wherein the two connector parts are fixed together by bonding.

17. A method as claimed in any one of claims 14 to 16, wherein the substrates are silicon substrates and the Vgrooves are formed by anisotropic etching.

18. A method as claimed in claim 17, wherein the V-shaped grooves are formed by anisotropic etching.

19. A method as claimed in any one of claims 14 to 18, wherein, prior to the formation of the V-grooves, a series of closely-spaced corrugations are formed in each of the first substrates in positions such that each subsequently-formed V-groove has a series of corrugations on either side thereof.

20. A method as claimed in any one of claims 14 to 19, further comprising the step of forming further V-shaped grooves in each of the second substrates after the connector parts have been fixed together, the further V-shaped grooves being formed in those surfaces of the second substrates which are opposite to the surfaces in which the first-mentioned V-shaped grooves are formed, and the further V-shaped grooves being so positioned that, together with the first-mentioned V-shaped grooves, they form diamond-shaped cantilever spring members in the second substrates.

21. A method as claimed in claim 20, further comprising the step of forming further V-grooves in each of the first substrates, the further V-grooves being offset from the first-mentioned V-grooves so as to form V-shaped corrugations in the first substrates.

22. A method as claimed in claim 21 when appendant to claim 17, wherein the further V-grooves are formed by anisotropic etching.

23. A method of forming a fibre array connector substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

24. The features described in the foregoing specification, or any obvious equivalent thereof, in any novel selection.