Packaging Fibre Optic Components

This invention relates to the packaging of fibre optic components. The invention is described herein with particular reference to the packaging of optical fibre couplers but it will be readily appreciated that the principles of the invention are readily applicable to the packaging of any fibre optic component.

Optical fibre couplers are presently supplied in a package which is designed both to physically, protect the component and to prevent the ingress of moisture and other contaminants to the component. In one known assembly, the coupler is disposed in an inner cylindrical housing formed of two half silica tubes which are machined to tight dimensional tolerances. These half tubes are brought together and attached together with adhesive. The resultant capsule includes respective adhesive deposits which serve to anchor the optical fibre component to the inner surface of the capsule and to seal the ends through which the fibres extend. Additional adhesive may be applied to the ends of the capsule to stabilise the fibres over a wide temperature range. The capsule is placed within a stainless steel outer casing which is in turn filled with an elastomer compound. The stainless steel outer casing is provided to give additional strength and protection to the optical component assembly.

Optical fibre couplers are required to have lifetimes approaching 40 years and to withstand extensive environmental variations. Even though the silica capsule is sealed with adhesive, it has been found through intensive simulated environmental testing that these adhesives are not consistently impervious to moisture over extended periods of time. Test samples have been detected where moisture has ingressed the capsule and affected coupler performance.

It is not possible to provide a hermetic glass-metal seal with the outer metal casing because of a mismatch of thermal expansion coefficients between most metals and silica.

It is accordingly an object of the invention to provide an arrangement for packaging optical fibre components which provides improved sealing against moisture ingress relative to presently known arrangements but which does not unacceptably increase manufacturing costs.

In one aspect, the invention provides a fibre optic component package comprising:

a fibre optic component package comprising:

one or more fibre optic components;

an inner housing supporting the component(s), one or more optical fibres associated with the component(s) extending from the housing; and

a layer which is substantially impervious to moisture including water vapour and which encloses said inner housing, said layer including a sheet of substantially moisture impervious flexible material wrapped about the housing and a substantially moisture impervious sealant adhesive which serves to bond said sheet of flexible material and fills at least those regions at edges of said sheet of flexible material.

The invention further provides, in another aspect, a method of packaging a fibre optic component comprising:

supporting the component in an inner housing, with one or more optical fibres associated with the component extending from the housing; and

enclosing said housing in a layer which is substantially impervious to moisture including water vapour, said layer including a sheet of substantially moisture impervious flexible material wrapped about the housing, and a substantially moisture impervious sealant adhesive which serves to bond said sheet of flexible material and fills at least those regions at edges of said sheet of flexible material.

The sheet is preferably a metal foil of any suitably compliant metal, for example tin, nickel, gold, aluminium, monel or an appropriate alloy. The foil is advantageously of a thickness in the range 0.01 to 50 micron. The foil is preferably wrapped about the inner housing so as to be overlapped longitudinally of the housing.

In a practical embodiment, the inner housing may be of generally tubular form, e.g. a capsule formed from two half robes of silica or other appropriate material.

Adhesive means is preferably provided to maintain the housing and optical fibres as an assembly. Where the inner housing is a robe, this adhesive means preferably includes adhesive. deposits to seal the ends of the tube.

The package may further comprise an outer casing, e.g. a tubular casing, of material such as stainless steel, selected to provide physical protection for the package. The assembly of the inner housing and the surrounding moisture impervious layer may be retained in the casing in a suitable Sing such as silicone elastomer.

The sealant adhesive is preferably an epoxy compound.

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a side elevation, partially axially sectioned, of a fibre optic component package according to an embodiment of the invention;

FIG. 2 is a cross-section on the line 2--2 in FIG. 1;

FIG. 3 is a very schematic representation of an arrangenemt by which the package of FIG. 1 might be formed in accordance with the invention.

The illustrated fibre optic component package 10 includes the component itself 11, an inner housing 12 for supporting the component comprising an elongate tubular capsule of silica, a substantially moisture impervious layer 13 including a metal foil wrap 14 providing a sheet of flexible material about housing 12, and an outer casing 16. Component 11 may be a fused biconical taper fibre optic coupler and respective pairs of optical fibres 18a, 19a and 18b, 19b then extend from the ends of package 10.

Inner housing or capsule 12 is formed of two half tubes 12a, 12b of silica glass which are butted at their longitudinal edges and glued along these edges to form a tubular enclosure 17 for the coupler. Silica half tube 12b is slightly longer than half tube 12a and respective deposits of adhesive 20 at the ends of half tube 12b locate fibres 18, 19, and therefore coupler 11, centrally of the capsule. Adhesive deposits 20 also seal the ends of the capsule and provide additional adhesion between the two halves. Capsule 12 is typically formed in a final step on the coupler production machine: the two half tubes, with adhesive along their edges, are brought together about a new coupler and the adhesive deposits 20 applied while the fibres 18, 19 are positioned under tension by adjustable clamp devices. The adhesive is cured before the coupler is removed for further processing.

Foil wrap 14 is substantially moisture impervious and is typically of thickness about 10 to 30 micron, for example 25 micron, and preferably in the range 0.01 to 50 micron. The foil may be formed of any suitably compliant metal, for example tin, nickel, gold, aluminium, monel or an appropriate alloy. The foil is circumferentially overlapped at 15 (FIG. 2). The overlapped portion is sealed by a suitable sealant such as epoxy which may also serve to bond the foil to the inner housing 12. Moisture ingress at the ends of the tubular wrap, defined by edge 25, is resisted by the disposition of sealant epoxy in the region 26. The epoxy compound preferably bonds to the foil 14, housing 12 and adhesive deposits 20.

The package 10 is completed by a filling 28 of a low shear strength silicone elastomer within sleeve 16, according to known practice, and by suitable end caps 30 defining ports 32 for the fibres.

It will be appreciated that the metal selected for foil 14 should not have a galvanic action with the material of sleeve 16 as, over extended periods of time, water may then penetrate the sleeve. Sleeve 16 may be stainless steel or other suitable material. If sleeve 16 is stainless steel, a suitable material for the foil 14 is tin.

The manner in which inner capsule 12 is formed has already been described. According to one method of completing the illustrated package, the capsule 12 might be transported from the coupler production machine and first painted along its exterior cylindrical surfaces with the selected epoxy compound. With reference to the diagram of FIG. 3, the painted capsule might then be placed in foil 14' folded into a U-section in a groove 42 of a wrapping form 40, with one side of the foil projecting slightly higher than the other. Two moving wedges (not shown) would then wrap first the short side and then the long side of the foil onto the painted capsule to complete wrap 14. Excess epoxy compound would be squeezed into the overlap region at the completion of the wrap. Excess epoxy compound would also be squeezed from the ends of the wrap during this two-step motion by pressing down the ends 34 of the wrap, thus forming and retaining end fillings 26. Alternatively, end fillings 26 might be provided by applying additional epoxy compound to each end of the wrap either before or after completion of folding.

In an alternative arrangement, the selected epoxy compound may be applied to the inner surface of the foil before wrapping.

The preferred arrangement is that at least a portion of the sealant adhesive is wrapped by the foil and that the sealant adhesive serves to bond the foil 14 and to provide a barrier against moisture ingress to the fibre optic component 11. Preferably the epoxy, compound fills at least those regions at edges of the foil, for example, at the respective axial ends of the wrap and at the region 15 (FIG. 2) where the longitudinal edges overlap. Preferably, the epoxy compound substantially fills the enclosed volume between the foil wrap and housing 12, ie forms a thin layer between the foil wrap and housing 12.

On the completion of wrapping, the package would be removed from the form and placed in an oven for thermal curing of the epoxy, compound.

After curing, the wrapped capsule is placed in stainless steel sleeve 16, which is then filled with silicone elastomer in the known manner, and provided with end caps 30.

It is believed that the illustrated package arrangement provides a significant improvement in sealing of the inner silica capsule 12 without unacceptably adding to the manufacturing cost of the package, and without significantly increasing its weight. This is achieved without risking problems with thermal coefficient mis-matches: thermal expansion will not be a problem as the metal foil is a very thin metal layer and will be constrained by the much larger mass of the silica capsule. The arrangement provides full epoxy/metal protection around the sealed capsule and allows the metal foil to be added to the silica capsule in a wrapping action which avoids the retention of air bubbles, which would not be the case if a metal tube was brought about the capsule. Furthermore, in use of the coupler, water vapour will need to penetrate reasonable lengths of epoxy material 26 before even reaching the innermost housing 12 which in itself is sealed. The metal foil wrap 14, and its manner of application, is such that any small holes in the adhesive at the longitudinal butt joins between the half tubes 12a, 12b will be sealed up by the foil and by the added epoxy compound. The present applicant has found that, in the long term, such small holes can be the source of moisture breaches.

It will be understood that, in alternative embodiments of the invention, the inner housing 12 might not wholly encircle the fibre optic component(s). For example, it is known to provide an inner housing for supporting the component in the form of a half tube.