GB2272658A

GB2272658A - Preparation of optical fibre ribbon ends

Info

Publication number: GB2272658A
Application number: GB9224288A
Authority: GB
Inventors: Paul Stephen Chappell; Neil Macfarlane; Anthony Neville Apperley
Original assignee: York Technology Ltd
Current assignee: York Technology Ltd
Priority date: 1992-11-19
Filing date: 1992-11-19
Publication date: 1994-05-25
Also published as: GB9224288D0

Abstract

A method of preparing an end of an optical fibre ribbon comprises the steps of supporting such a ribbon (1) so that it extends axially through a passageway in a sleeve-form holder (24); introducing a potting compound (28) into one end (25) of the holder, so that the potting compound (28) fills the passageway space around the ribbon (1) at a location adjacent to the said one end; cutting off a portion of the ribbon (1) that projects from the said one end of the holder, so as to leave the remaining ribbon portion in the passageway with a cut end adjacent to the said one end; and polishing the cut end while the said remaining ribbon portion is still held by the potting compound (28) within the holder. In such a method, during polishing the cut end of the fibre ribbon is held firmly and intimately around its outer surface by the potting compound. The potting compound serves to prevent the forces generated during the polishing process from altering the shape of the ribbon or displacing the fibres within the ribbon from their original positions. <IMAGE>

Description

PREPARATION OF OPTICAL FIBRE RIBBON ENDS The present invention relates to preparation of optical fibre ribbon ends, for example in a method of optically examining a section through such a ribbon.

An optical fibre ribbon comprises a number (for example up to 24) of individual coated optical fibres, arranged side by side either within a common outer covering or simply adhered laterally to one another with no such common outer covering. Such a ribbon is capable of transmitting large amounts of information from different sources.

When such an optical fibre ribbon is to be employed as a so-called patch cord to connect two pieces of equipment together, connectors must normally be applied to the opposite ends of the ribbon. To enable the connectors to be applied successfully, it is necessary that after preparation of the ribbon end the core of each individual fibre in the ribbon end should lie accurately on a common centre line passing through all of the fibre cores and at the correct spacing, along that centre line, from the nearest adjacent fibre. It is also necessary to ensure that the fibre coatings (and outer covering of the overall ribbon if present) are of the correct thickness.

It may also be desirable to prepare a ribbon end accurately solely for examination purposes, such as for example when, during testing of a sample of optical fibre, it is required to determine the geometry of a section through the fibre. In one method of optically determining the geometry of such a ribbon section, the ribbon is cut adjacent to the position of the section of interest and the cut end is then prepared so as to produce a flat and highly polished end-face. This endface should also be orthogonal to the axis of the ribbon in order that, during subsequent optical examination of the ribbon end, the separation between an optical source used to direct light onto the endface and the end-face itself is uniform over the entire area of the end-face.

Conventionally, an optical fibre ribbon end is prepared by cutting the ribbon to create a free end and subsequently polishing the free end. Such polishing can, however, lead to undesirable distortion of the ribbon end geometry for example by changing the shapes of the fibre coatings or the relative positions of the core centres. This may render the prepared end unsuitable for connectorisation or, when the end is being prepared for the purpose of examining a section through the ribbon, may make it impossible to derive any reliable information about the geometry of the section due to distortion of the very parameters that are to be measured.

It is desirable to provide a method of preparing the end of an optical fibre ribbon which does not give rise to unacceptably-high distortion of the ribbon geometry.

According to the present invention, there is provided a method of preparing an end of an optical fibre ribbon, comprising: supporting such a ribbon so that it extends axially through a passageway in a support device; introducing a potting compound into one end of the passageway, so that the potting compound fills the passageway space around the ribbon at a location adjacent to the said one end; cutting off a portion of the ribbon that projects from the said one end of the passageway, so as to leave the remaining ribbon portion in the passageway with a cut end adjacent to the said one end; and polishing the said cut end while the said remaining ribbon portion is still held by the potting compound within the passageway.

In such a method, during polishing the cut end of the fibre ribbon is held firmly and intimately around its outer surface by the potting compound. The potting compound serves to prevent the forces generated during the polishing process from altering the shape of the ribbon or displacing the fibres within the ribbon from their original positions.

Moreover, during polishing the support device, rather than the fibre ribbon itself, can be clamped in the polishing machine, so avoiding possible damage to the fragile fibre ribbon by such clamping. Also, once the support device is so clamped the potting compound serves to maintain the axis of the ribbon accurately aligned perpendicularly to the plane of a polishing disc or the like used to perform the polishing, ensuring that the polished end of the fibre ribbon will be orthogonal to the ribbon axis.

Preferably, during curing of the potting compound the ribbon is supported under tension, at least in the portion thereof within the passageway, so as to remove any natural curve in the ribbon portion within the passageway. This helps to ensure orthogonality of the eventual polished ribbon end with respect to the ribbon axis.

The potting compound is preferably so formulated as to permit axial displacement of the fibre ribbon in the passageway, relative to the support device, after curing of the potting compound has taken place. Such axial displacement may be required after preparation of the end in order to enable the support device to be removed from the cut ribbon end.

In one embodiment of the invention, lubricant is applied to the ribbon, prior to introduction of the potting compound, so as to cover outer surface portions of the ribbon to which potting compound will be applied, thereby to permit axial displacement of the fibre ribbon in the passageway, relative to the support device, after curing of the potting compound has taken place.

In such an embodiment it may be advantageous to displace the fibre ribbon axially relative to the support device, in the direction from the said one end to the other end of the passageway, after curing of the potting compound but before cutting of the fibre ribbon, so as to ensure that the point of cutting on the fibre ribbon is free of lubricant. This can prevent the eventual prepared end from being contaminated by lubricant which might hamper subsequent manipulation or optical examination thereof.

The potting compound is preferably a quick-setting epoxy acrylic mix which undergoes low shrinkage during curing so as to avoid the possibility of the compound separating from the ribbon and/or support device during the curing process. The potting compound preferably also has a weak exothermic reaction during curing, so as to avoid significant heating of the fibre ribbon which might soften the ribbon outer covering and allow relative displacement of the fibres in the ribbon.

In a preferred embodiment of the invention the said support device comprises a sleeve-form holder which defines the said passageway. Such a holder permits convenient manipulation of the ribbon end during preparation (and possible subsequent optical examination) thereof, and is a low cost item suitable for disposal after use.

Preferably the internal peripheral form of the sleeve-form holder is such that the said passageway is constricted at an intermediate location therealong between its two ends, thereby to define a receptacle for the said potting compound at the said one end of the passageway. Such a receptacle contains the potting compound at the said one end of the passageway, preventing remaining portions of the ribbon further away from the one end from being contacted by the potting compound.

The receptacle is preferably formed on its inside with protrusions (for example the receptacle may have a cruciform internal cross-section) that reduce the volume of the receptacle available for the potting compound. By reducing the volume of potting compound used, heating of the fibre ribbon by the exothermic curing reaction can be reduced.

Apparatus for carrying out a method as described above advantageously includes means for simultaneously supporting a plurality of fibre ribbons relative to respective such holders during curing of potting compound around the ribbons in those holders. This can enable respective ends of a plurality to fibre ribbons to be prepared quickly and conveniently in the same apparatus, for example up to 12 ribbon ends can be prepared in 30 to 40 minutes.

The supporting means may comprise a plate-form member formed with a plurality of receptacles for receiving respectively the said holders, the receptacles being arrayed across the plate-form member and being adapted to retain their respective holders such that an end portion of each holder, which portion is at the said one end of the passageway defined by the holder, projects from a main face of the plate-form member, and the plate-form member being adapted to be mounted in a polishing machine, of the kind having a planar polishing surface, in parallel with the polishing surface, thereby to enable the polishing surface to contact all of the cut ends of the fibre ribbons simultaneously.

In such an apparatus the plate-form member serves to support the holders both during curing of the potting compound in the holders and during subsequent polishing of the cut ends. This makes it unnecessary to remove the holders from one supporting means, used to support them during curing, and replace them in another supporting means used to support them in the polishing machine, which removal and replacement would result in the overall method taking longer to complete.

The use of the same supporting means can also avoid possible orthogonality errors in the polished ribbon ends that might otherwise result, for example, from imprecise fixing of the holders with respect to the polishing surface.

Reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 shows an axial sectional view of an optical fibre ribbon; Figures 2 to 5 show respective schematic side elevational views illustrating different stages in a method of preparing the end of an optical fibre ribbon embodying the present invention; Figure 6 shows a schematic perspective view corresponding to Figure 5; and Figure 7 shows a schematic view of a step in a method of optically determining the geometry of the end of an optical fibre ribbon prepared by the method of Figures 2 to 5.

Figure 1 shows an axial sectional view through a typical optical fibre ribbon.

The ribbon 1 comprises six individual coated fibre cores 2 arranged side-by-side within a common outer covering 3. The diameter d of each fibre core 2 may be, for example, 125 pm, and the spacing a, along a common centre line A-A passing through the fibre cores 1, may be, for example, 0.25 mm.

Figure 2 (see also the perspective view of Figure 6) shows a schematic view of apparatus for carrying out a method of preparing the end of an optical fibre ribbon, such as that shown in Figure 1, in a first stage of the method. In Figure 2, a clamping device, generally denoted at 10, comprises upper and lower clamp plates 11, 12 mounted in parallel with one another on a common frame (not shown). The plates are both substantially circular and have, at regular angular intervals therearound, a number of slots 15 (for example 12 slots) extending axially completely through the plates.As shown in Figure 2, the plates 11, 12 are mounted with their respective arrayed slots in registering pairs so that an optical fibre ribbon 1 can be threaded linearly through the two slots of each pair, a portion of the threaded ribbon extending substantially vertically between the upper and lower plates 11, 12. The clamping device 10 can accordingly support a number of threaded fibre ribbons at the same time to permit parallel processing of the ribbons.

Each of the slots 15 has associated therewith a retaining member 17 that can be brought selectively into gripping contact with the fibre ribbon in its slot 15 by tightening a screw 18.

Connected with the lower clamp plate 12 by means of fixing screws 20 is a generally circular polishing jig 21 having a plurality of circular through-holes 22 extending axially through the plate in register respectively with the registering pair of slots 15 in the upper and lower clamp plates 11, 12. A retaining screw 23 is associated with each of the passageways 22 and serves, when tightened, to retain a sleeve-form holder 24, made for example of moulded acrylic plastics material, within the through-hole 22.

The lower clamp plate 12 and polishing jig 21 together constitute a supporting means capable of simultaneously supporting a plurality of the sleeveform holders 24.

Each holder 24 has, at its upper end in Figure 2, a receptacle 25 of cruciform internal cross-section with a flat base 26. The base 26 is formed with a central slot 27 that is preferably elongate in shape, for example rectangular, and of dimensions slightly greater than the corresponding dimensions of the crosssection of the optical fibre ribbon 1 whose end is to be prepared, so that a ribbon can be threaded through the slot 27.

In a first stage of a method of preparing the end of a fibre ribbon embodying the present invention, before the sleeve-form holders are placed in their respective through-holes in the support device one end of a fibre ribbon 1 to be treated is threaded from below through one of the slots 15 in the lower clamp plate 12 and is fed upwardly through the communicating through-hole 22 in the polishing jig 21 sufficiently far that the ribbon end projects above the upper end of the through-hole 22. The projecting end of the fibre ribbon 1 is then threaded through the slot 27 in its sleeve-form holder 24 such that the receptacle 25 thereof is nearest the ribbon end, whereafter the holder is inserted into the through-hole 22 and clamped therein by tightening retaining screw 23.

The end of the fibre ribbon 1 is then fed upwards further so as to pass through the registering slot 15 in the upper clamp plate 11.

The respective screws 18 associated with the pair of slots 15 in the upper and lower clamp plates (11, 12) are then tightened while the fibre 1 is under tension. Such tension can assist in removing any natural curve in the portion of the ribbon between the upper and lower clamp plates 11, 12.

Next, as shown in Figure 3 a drop of lubricant, for example PTFE, is applied to the said portion of the ribbon 1 between the clamp plates 11, 12 at a suitable location above the holder so that lubricant flows down the sides of the ribbon 1 and covers both sides thereof between the point of application of the lubricant and the bottom of the receptacle 25 in the sleeve-form holder 24.

Potting compound 28, for example a quick-setting epoxy acrylic mix such as Permabond E01, is then introduced into the receptacle 25 of each holder 24 where it sets so as to fill the receptacle space around the ribbon 1 at least at the upper end of the receptacle. The gaps between the outer surfaces of the ribbon 1 and the inner periphery of the slot 27 are sufficiently small that leakage of the potting compound below the slot 27 is substantially avoided.

The potting compound 28 preferably has low shrinkage so as to avoid separation of the compound from the ribbon and holder that might otherwise result from shrinkage of the compound during curing thereof.

The potting compound 28 also preferably has a weak exothermic reaction when curing so that the fibre ribbon is not heated significantly. Any such heating could soften the outer covering of the ribbon (commonly infrared-setting acrylate) which could permit the relative positions of the fibres in the ribbon to change. The cruciform internal cross-section of the receptacle 25 restricts the volume of the receptacle so that relatively little potting compound is required to fill the receptacle. This can assist in avoiding possible heat build-up in the receptacle during curing.

For reasons that will become clear hereinafter, it is also advantageous for the potting compound to be formulated to allow axial displacement of the'fibre ribbon relative to its holder after curing of the potting compound. In such a case it may be unnecessary to lubricate the ribbon before application of the potting compound, or at least to reduce the amount of lubricant required.

After curing of the potting compound in the receptacle 25 of each of the sleeve-form holders 24 is complete (for example after 3 to 5 minutes), the screws 18 securing the fibre ribbons 1 within their respective slots 15 in the upper clamp plate 11 are all slackened, whereupon the upper clamp plate 11 is removed from the clamping device 10. The screws 18 securing the fibre ribbons 1 in their respective slots 15 in the lower clamp plate are then slackened and each fibre ribbon 1 is axially displaced in its holder 24 a short distance by pulling the ribbon downwards as shown in Figure 4.

Such displacement is not essential, but is desirable to ensure that any part of the ribbon covered by lubricant is withdrawn into the holder 24, leaving exposed above the potted end of the holder only ribbon uncontaminated by lubricant. The screws 18 in the lower clamp plate 12 are then retightened to secure the remaining portions of ribbons l to the lower clamp plate 12.

Using a scalpel, for example, each fibre ribbon 1 is then cut off close to the upper potted end of its holder 24, preferably at less than lmm from the holder end. In some cases, the potting compound 28 may be filled to beyond the level of the upper end of the holder, in which case the protruding potting compound can serve to support the scalpel blade partially during cutting so as to avoid scratching of the ribbon outer surface, for example. After cutting, as shown in Figures 5 and 6 with the holders 24 still in place in the through-holes 22 in the polishing jig 21 the entire supporting means (jig 21 and lower clamp plate 12) is transferred to a polishing machine generally denoted at 30.

The polishing machine 30 comprises, for example, a rotary polishing platen 31 bearing a circular polishing disc 32. The supporting means 21, 12 is mounted with the free front face of the polishing jig 21 substantially parallel to the polishing disc 32, so that the fibre ribbons in the holders 24 extend substantially perpendicularly to the plane of the polishing disc 32.

During polishing the cut end of each fibre ribbon is held firmly and intimately around its outer surface by the potting compound 28. The axis of each ribbon is maintained accurately aligned perpendicularly to the plane of the polishing disc 32 by the support device, ensuring that the polished ends of the fibre ribbons 1 are orthogonal to the ribbon axis. The potting compound serves to prevent the forces generated during the polishing process from altering the shape of the ribbons or displacing the fibres within the ribbons from their original positions.

Polishing may be continued until the polished fibre ends are flush with the ends of the holders 24 since, as the holders are disposable after use, polishing of the holder ends is of no consequence.

After polishing is complete, the ribbon 1 is pushed in a direction towards its polished end through its holder 24 as shown in Figure 7, so that the polished end 33 of the ribbon 1 is clear of the polished end 34 of its holder 24. The polished ribbon end 33 may now be examined, for example in a York S200 ribbon fibre geometry measuring instrument denoted schematically at 40, to determine by optical techniques the ribbon end geometry. The holder 24 serves during such optical examination to support the fibre laterally with its polished end 33 orthogonal to the longitudinal axis of the holder 24, making it unnecessary for the ribbon to be clamped directly which could damage it.

If a potting compound having a reflectance which is sufficiently different from that of the materials making up the optical fibre ribbon is used, it is not necessary to displace the polished end 33 of the ribbon from the polished 34 of the holder 24 to achieve a satisfactory optical examination.

Of course if it is desired to apply a connector to the polished end, the holder 24 can simply be slid off the polished end 33 of the ribbon 1 before the connector is fitted.

It will be understood that apparatus for carrying out the end preparation method described hereinbefore can take many different forms from that shown in Figures 2 to 6. In particular, any support device which provides one or more passageways, through which the fibre ribbons can be caused to extend axially for potting, can be used in place of the sleeve-form holder of Figures 2 to 6.

When sleeve-form holders such as those of Figures 2 to 6 are employed to pot the fibre ribbons it is not essential that the cut ends be polished while supported by the same jig in which they were supported during potting.

Claims

1. A method of preparing an end of an optical fibre ribbon, comprising: supporting such a ribbon so that it extends axially through a passageway in a support device; introducing a potting compound into one end of the passageway, so that the potting compound fills the passageway space around the ribbon at a location adjacent to the said one end; cutting off a portion of the ribbon that projects from the said one end of the passageway, so as to leave the remaining ribbon portion in the passageway with a cut end adjacent to the said one end; and polishing the said cut end while the said remaining ribbon portion is still held by the potting compound within the passageway.

2. A method as claimed in claim 1, wherein during curing of the potting compound the ribbon is supported under tension, at least in the portion thereof within the passageway, so as to remove any natural curve in the ribbon portion within the passageway.

3. A method as claimed in claim 1 or 2, wherein the said potting compound is so formulated as to permit axial displacement of the fibre ribbon in the passageway, relative to the support device, after curing of the potting compound has taken place.

4. A method as claimed in any preceding claim, wherein lubricant is applied to the ribbon, prior to introduction of the potting compound, so as to cover outer surface portions of the ribbon to which potting compound will be applied, thereby to permit axial displacement of the fibre ribbon in the passageway, relative to the support device, after curing of the potting compound has taken place.

5. A method as claimed in claim 4, wherein the fibre ribbon is axially displaced relative to the support device, in the direction from the said one end to the other end of the passageway, after curing of the potting compound but before cutting of the fibre ribbon, so as to ensure that the point of cutting on the fibre ribbon is free of lubricant.

6. A method as claimed in a preceding claim, wherein the said potting compound is a quick-setting epoxy acrylic mix which undergoes low shrinkage during curing and has a weakly exothermic curing reaction.

7. A method as claimed in any preceding claim, wherein the said support device comprises a sleeve-form holder defining the said passageway.

8. A method as claimed in claim 7, wherein the holder has an internal peripheral form such that the said passageway is constricted at an intermediate location therealong between its two ends, thereby to define a receptacle for the said potting compound at the said one end of the passageway.

9. A method as claimed in claim 8, wherein the receptacle is formed on its inside with protrusions that reduce the volume of the receptacle available for the potting compound.

10. Apparatus for carrying out a method as claimed in claim 7, 8 or 9, including means for simultaneously supporting a plurality of fibre ribbons relative to respective such holders during curing of potting compound around the ribbons in those holders.

11. Apparatus as claimed in claim 10, wherein the supporting means comprise a plate-form member formed with a plurality of receptacles for receiving respectively the said holders, the receptacles being arrayed across the plate-form member and being adapted to retain their respective holders such that an end portion of each holder, which portion is at the said one end of the passageway defined by the holder, projects from a main face of the plate-form member, and the plate-form member being adapted to be mounted in a polishing machine, of the kind having a planar polishing surface, in parallel with the polishing surface, thereby to enable the polishing surface to contact all of the cut ends of the fibre ribbons simultaneously.

12. Apparatus for carrying out the method of claim 1, substantially as hereinbefore described with reference to Figures 2 to 6 of the accompanying drawings.

12. A method of preparing an end of a fibre ribbon substantially as hereinbefore described with reference to Figures 2 to 6 of the accompanying drawings.

13. Apparatus for carrying out the method of claim 1, substantially as hereinbefore described with reference to Figures 2 to 6 of the accompanying drawings.

Amendments to the claims have been filed as follows 1. A method of preparing an end of an optical fibre ribbon, comprising: supporting such a ribbon so that it extends axially through a passageway in a support device; introducing a potting compound into one end of the passageway, so that the potting compound fills the passageway space around the ribbon at a location adjacent to the said one end; cutting off a portion of the ribbon that projects from the said one end of the passageway, so as to leave the remaining ribbon portion in the passageway with a cut end adjacent to the said one end; polishing the said cut end while the said remaining ribbon portion is still held by the potting compound within the passageway; and axially displacing the fibre ribbon in the passageway, relative to the support device, so as to expose the cut and polished end beyond the support device or to permit removal of the support device from the ribbon.

3. A method as claimed in any preceding claim, wherein lubricant is applied to the ribbon, prior to introduction of the potting compound, so as to cover outer surface portions of the ribbon to which potting compound will be applied, thereby to facilitate axial displacement of the fibre ribbon in the passageway, relative to the support device, after curing of the potting compound has taken place.

4. A method as claimed in claim 3, wherein the fibre ribbon is axially displaced relative to the support device, in the direction from the said one end to the other end of the passageway, after curing of the potting compound but before cutting of the fibre ribbon, so as to ensure that the point of cutting on the fibre ribbon is free of lubricant..

5. A method as claimed in any preceding claim, wherein the said potting compound is a quick-setting epoxy acrylic mix which undergoes low shrinkage during curing and has a weakly exothermic curing reaction.

6. A method as claimed in any preceding claim, wherein the said support device comprises a sleeve-form holder defining the said passageway.

7. A method as claimed in claim 6, wherein the holder has an internal peripheral form such that the said passageway is constricted at an intermediate location therealong between its two ends, thereby to define a container for the said potting compound at the said one end of the passageway.

8. A method as claimed in claim 7, wherein the container is formed on its inside with protrusions that reduce the volume of the container available for the potting compound.

9. Apparatus for carrying out a method as claimed in claim 6, 7 or 8, including means for simultaneously supporting a plurality of fibre ribbons relative to respective such holders during curing of potting compound around the ribbons in those holders.

10. Apparatus as claimed in claim 9, wherein the supporting means comprise a plate-form member formed with a plurality of receptacles for receiving respectively the said holders, the receptacles being arrayed across the plate-form member and being adapted to retain their respective holders such that an end portion of each holder, which portion is at the said one end of the passageway defined by the holder, projects from a main face of the plate-form member, and the plate-form member being adapted to be mounted in a polishing machine, of the kind having a planar polishing surface, in parallel with the polishing surface, thereby to enable the polishing surface to contact all of the cut ends of the fibre ribbons simultaneously.

11. A method of preparing an end of a fibre ribbon substantially as hereinbefore described with reference to Figures 2 to 6 of the accompanying drawings.