GB2382883A

GB2382883A - In situ processing optical waveguide in optoelectronic package

Info

Publication number: GB2382883A
Application number: GB0228519A
Authority: GB
Inventors: Michael Osborne; Laurence Frederick Forrest
Original assignee: OpTek Ltd
Current assignee: OpTek Ltd
Priority date: 2001-12-06
Filing date: 2002-12-06
Publication date: 2003-06-11
Also published as: AU2002347363A8; WO2003048824A2; AU2002347363A1; GB0228519D0; GB0129286D0; WO2003048824A3

Abstract

A method of processing optical waveguides, comprises one or more of the steps of stripping of buffer material from the waveguide, cleaning the stripped waveguide, cleaving or otherwise cutting the waveguide, and fusion splicing adjacent waveguides, wherein one or more of said steps is: a) preferably effected using laser radiation, and b) carried out in situ within an optoelectronics package. The waveguide may be an optic fibre held in a V-groove or V-groove array 7 or holes. Optic fibre bundles 3,4, electrical module 2 and erbium doped fibre amplifier (EDFA) package 1 are shown.

Description

IMPROVEMENTS RELATING TO THE COUPLING OF OPTICAL WAVEGUIDES Field of the Invention : This invention concerns improvements relating to the coupling of optical waveguides, particularly though not exclusively optical fibres.

Background of the Invention : In optical communications there often arises the need to couple light from one fibre into another with the minimum of loss. Fusion splicing, in which the ends of two fibres are heated to their softening point and then fused together to provide a permanent low loss joint, is an essential part of building optical communications networks. Several options exist to provide the heat source for the fusing, but the electric arc dominates the market.

The conventional splicing process includes a number of discrete steps, including stripping the buffer from the ends of the (at least) two fibres to be fused, cleaving the two ends, cleaning the bare fibre, fusion splicing the two fibres, and re-covering the splice with a protective coating or sleeve. The processes prior to the splice are collectively known as"fibre prep".

With the exception of the final splice protection step which is sometimes carried out within a separate part of the same machine as the fusion splicing, each of these steps is carried out using discrete pieces of equipment, therefore requiring a significant amount of handling of the

stripped fibre. This can lead to microscopic fibre damage which then results in reduced tensile strength, and to contamination of the fibre which can result in variable splice results.

Historically the strength of the resulting fusion spliced fibre has been typically only 10% of that of the virgin fibre (typical ultimate tensile strength

of fused joint-5N c. f. tensile strength of-50N for the original 125um diameter fibre). Recent demands to increase the strength of spliced fibres have fuelled the development of the process and, with very careful handling of the fibre at all steps in the process, strengths of > 15N can now be achieved at acceptable yields.

Automated fusion splicing systems are being developed which link together the various elements described above. However, even with automation, the complexity of the multi-step process presents challenges in terms of throughput, splice reproducibility and machine reliability. In such automated systems, the effective management of the waste (e. g. the part of the fibre cleaved-off, or the stripped buffer) also presents a challenge.

Fusion splicers have been proposed which use an electric arc to soften the fibre ends and allows them to be effectively fused together. However, the heating effect of the electric arc is amenable to only limited spatial tailoring, resulting in less than perfect heat distribution along the fibre. These leaves residual stresses which compromise the effective tensile strength. Moreover, the arc imposes its own atmosphere in the splice region, which has been claimed to be detrimental, and the process suffers from spallation from and

degradation of the electrodes. Electric arc fusion splicers are known from EP 0 462 893 for example.

In conventional electric arc fusion splicing the demands of the fibre manipulation, the vision and observation systems, and of the arc electrodes dictate that the splicer be a stand-alone unit, and hence that the fibres to be spliced be transported to the splicing machine. This means that at least -1m of fibre must be allowed on each side of each splice in order to take the fibres from the module in build (for example an erbium doped fibre amplifier, EDFA) to the splicer.

As there can be many splices per module (typically 20-40 in an EDFA package, often more in splitters), this results in a significant excess of fibre which all needs to be coiled (observing minimum bend radii) and repackaged within the module. In addition to the fibre, it is usual to fix a"splice protector"around the splice. This, often rigid, component must also be "handled"back into the package. This excess of fibre and protectors complicates the module build, hinders re-work, can have deleterious optical effects, and makes automation of the process difficult.

The use of a CO2 laser as the heat source for splicing has been known for some time. JP 50-10934 & US 4,263, 495 describe CO2 laser splicing using a focused beam applied either directly or via plane or shaped mirrors to the splice region, and include moving the fibres together (stuffing) during the process. US 5,016, 971 adds the possibility of moving the focus during the splice process in order to distribute the heating, and US 5,299, 274 adds

feedback control to the laser power in response to the optical luminescence from the heated fibre (s). Other laser based fusion splicers are described in WO 01/32348, EP 0 292 146 and GB 2 180 369.

Objects and Summary of the Invention: In order to overcome or at least substantially reduce the aforementioned problems, the present invention proposes to carry out the fibre prep (or prep and splice) without the need to move the fibre between the various processes, and also proposes to do some or all of this in-situ within the confined space of an optoelectronics module package. These features of the present invention reduce the fibre handling (and hence potential for damage) and can obviate the need for excess fibre, simplifying automated assembly.

In accordance with a first aspect of the present invention the stripping and cleaning, and preferably also cleaving, of the fibre are all carried out without moving the fibre, contrary to the conventional procedure described below, and all with the use of a laser.

Conventional stripping methods are either mechanical or thermomechanical and hence require access and movement to physically remove the stripped buffer, or are chemical which requires immersion of the fibre in a liquid solvent. In all such cases the access needed to the fibre is such that a separate machine is required to carry out the stripping.

Mechanical and thermo-mechanical stripping leave residues on the fibre which must be removed before splicing. This requires an additional

instrument, often either an ultrasonic bath or a wipe (manual or automated) with a material soaked in solvent. The chemical stripping methods require the solvents to be washed off before proceeding, again a separate exercise.

Conventional cleaving requires that the fibre be clamped either side of the cleave point, tensioned, and then a stress-raising mark produced with a hard material (typically diamond) or with an ultrasonic tip in very close proximity. Again, the access requirements dictate that this is carried out on a separate instrument. As the fibre has been clamped in the cleaver, it is usual to clean the fibre once again before splicing in order to remove any decontamination which may have been picked-up, again a separate process.

Contrary to conventional techniques, the present invention proposes to effect laser stripping of the buffer (as is known in the art) which results in a fibre which does not require additional cleaning to remove deposits.

Moreover, the process does not require physical contact with the fibre, allowing it to be carried out in various geometries. The only access requirements are for the laser beam to approach and leave the fibre, and for an extract to remove the vapourised buffer material.

Again, contrary to conventional techniques, laser cleaving does not require physical contact with the fibre, and has access requirements similar to the laser stripping above. An aspect of the present invention is therefore to combine both the stripping and the cleaving in the same physical location.

The need for handling and movement of the fibre during such a preparation is considerably reduced as compared to conventional processes, offering superior performance in terms of fibre strength and integrity.

Further to the above fibre prep, the present invention also permits that laser splicing of two fibres can be carried out with only a minimal axial movement of the two laser stripped/cleaned and cleaved fibres. This further reduces the overall fibre handling.

The above summarises how a complete prep and splice can be carried out without significant movement of the fibres to be spliced. In another aspect of the present invention, this capability may be used to beneficial effect to perform splices in-situ, within the confines of an optoelectronics package, as will now be explained.

Conventional optical fibre prep and splicing positions or locates the fibres at each step of the process. The positional accuracy required ranges from low for, for example immersion in an ultrasonic bath for cleaning (and post-splice recoating), through moderate for cleaving and thermo-mechanical stripping, to high for the splice itself. The high positional accuracy required during the splice step is more than sufficient to allow the other processes to be carried out effectively using the techniques described herein. Typically conventional splicing tools use vision and alignment techniques to accurately align fibres prior to splicing. By this means, the fibres are aligned to-1 um, and the optical losses for an individual splice are of order 0. 05dB. This is acceptable for almost all applications. However, for processing in-situ, it is

not feasible to use the same fibre grippers and vision systems. In the practice of the present invention, the fibres may be passively aligned, for example using v-grooves. V-grooves represent a well established engineering technique for accurately locating objects (particularly those with cylindrical symmetry) and can be made from a range of materials. Several variations to the basic v-groove design also exist, including, for example means to locate the fibre in the groove such as flexible clips or a second v-groove parallel to but opposing the first v-groove. Silicon V-groove arrays can be fabricated economically and can be used to provide on-axis alignments to tolerances of 0. 3um and better. In these circumstances, the concentricity of the fibre core to cladding becomes the dominant factor. As the laser is a remote heat source, it is possible for such a silicon V-groove array and the fibre ends to be processed to remain within the package at all times. This greatly reduces the quantity of excess fibre, reduces the overall package size, reduces handling of the fibre, and is amenable to automated operation.

The V-groove array can also provide mechanical support to the splice, obviating the need for a separate splice protector. It may supplemented by the application of epoxy to both the splices and the V-groove array.

In order to apply the laser beam to the fibres in the v-groove array, local modifications to the V-grooves may be beneficial. In one modification, a slot or hole is provided in the array which allows any of the laser beam which is not intercepted by the fibres to pass through the array. It also provides a convenient aperture from which any vapourised material can be effectively

extracted. It can also be used to apply the laser beam to the fibres from two opposing directions, which can have beneficial effects on the heat distribution. A blind slot can be used as a window for passage of excess radiation. If a slotted V-groove array is used, it will be beneficial to incorporate a matching aperture or window in the module package.

In an alternative modification of the V-groove array, a deeper and offset v-groove may be employed to act as a local retro-reflector, illuminating the splice from multiple directions.

The above and further features of the present invention are set forth in the appended claims, and the following description is given with reference to the accompanying drawings to assist full understanding of the invention.

Description of the Drawings: Figure 1A shows schematically the six stages of a conventional multistage optical fibre splicing system; Figure IB shows schematically an in-situ system embodying the present invention ; and Figure 2 illustrates the use of a laterally offset V-groove to achieve multidirectional splice irradiation.

Description of the Embodiments: Figures 1A and 1B illustrate the advantages, described hereinbefore, that can be obtained by use of the present invention. Figure 1A shows a conventional multi-stage process in which an EDFA package I including an electrical module 2 having optical fibre bundles 3 and 4 requiring to be

spliced together is first operated upon at a stripper 15 where the buffer material is removed. It is then passed to a cleaning station 16 where strip residues are removed from the fibre. It then passes to a cleaving station 17 where the two (or more) fibre ends are cleaved. It then passes to a splicer 5 - where the individual optical fibres are connected. The package is then provided to a protection stage where the splices are protected by application of protective sheaths 6, and finally the protected spliced optical fibres are carefully repackaged.

In contrast to the conventional process abovedescribed, Figure IB shows an in-situ process in accordance with the present invention where an EDFA package 1 is provided with a multiple V-groove array 7 as hereinbefore mentioned which not only provides location of the optical fibres during all of the processing steps but also provides protection for the spliced fibres, thereby obviating the protection stage of the conventional process. The final stage of the conventional process, namely repackaging, is obviated by the very nature of the in-situ process of the invention.

Figure 2 illustrates schematically how an optical fibre 10 received in a V-groove 11 in a laterally offset manner can receive incident laser radiation substantially all around its circumference as a result of reflections from the wall of the V-groove. This arrangement provides more uniform heating of the optical fibre which, inter alia, reduces thermally induced stresses in the fibre.

The laser beam temporal and/or spatial intensity distribution could also be

controlled to effect tailored thermal cycling of the fibre to reduce residual stresses.

The invention having been described in the foregoing by reference to particular embodiments, it is to be well understood that the embodiments are in all respects exemplary and that modifications and variations could be made without departure from the spirit and scope of the invention. For example, fibre or fibres could be accurately located by means other than a v-groove such as precision holes, some of the processes described may be omitted in a given application as dictated by the specific requirements, the optoelectronic packages need not be an EDFA or a splitter but could be a connector or subassembly, and the Figure 2 arrangement could be modified by provision of other structures and/or reliefs adapted to achieve more uniform irradiation of the interaction region by reflection or by any other optical process.

Claims

CLAIMS: 1. A method of processing optical waveguides, said method comprising one or more of the steps of stripping of buffer material from the waveguide, cleaning the stripped waveguide, cleaving or otherwise cutting the waveguide, and fusion splicing adjacent waveguides, wherein one or more of said steps is: a) effected using laser radiation, and b) carried out in situ within an optoelectronics package
2. A method as claimed in claim 1 in which the optoelectronics package is a module, sub-module or connector or a sub-assembly or sub-component thereof.
3. A method as claimed in claim 1 or 2 wherein the waveguides to be processed are passively retained during the splicing operation.
4. A method as claimed in claim 3 wherein the waveguides comprise optical fibres and the passive retention means comprises a V-groove structure.
5. A method as claimed in claim 4 wherein the V-groove structure comprises a plurality of side-by-side V-grooves.

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6. A method as claimed in claim 4 or 5 wherein the V-groove is adapted to effect multi-directional irradiation of the waveguides.
7. A method as claimed in claim 4 or 5 or 6 wherein the structure defining the V-groove (s) is apertured to permit laser radiation by-passing said waveguides to exit said structure.
8. A method as claimed in claim 4 or 5 or 6 wherein the structure defining the V-groove (s) is apertured for removal of laser ablation debris.
9. A method as claimed in any of claims 3 to 8 wherein the passive retention means comprises part of the optoelectronics package.
10. A method as claimed in any of the preceding claims further comprising a step of providing protection for the spliced optical fibre (s) by use of a protective medium applied after completion of splicing.
11. A method as claimed in claim 10 wherein said protective medium comprises a synthetic resin material.
12. A method as claimed in any of the preceding claims including a laser annealing stage for relieving thermally induced stresses in the spliced waveguides.

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13. A product produced by a method as claimed in any of the preceding claims.
14. An optoelectronics package incorporating means enabling in situ optical waveguide preparation and/or splicing, by laser irradiation or other means.
15. A method of optical waveguide preparation for splicing and/or splicing, wherein the method is carried out within an optoelectronics module.
16. An apparatus for use in preparing optical waveguides for splicing and/or for splicing of prepared waveguides, said apparatus including passive waveguide retention means.
17. An apparatus as claimed in claim 16 wherein said passive waveguide retention means comprises a V-groove structure.
18. An apparatus as claimed in claim 17 wherein said V-groove structure comprises a plurality of V-grooves.
19. An apparatus as claimed in any of claims 16 to 18 adapted for preparation and/or splicing of optical waveguides by laser irradiation of the

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same and wherein said passive waveguide retention means is adapted to achieve multi-directional irradiation of the optical waveguides with uni- directional input radiation from the laser.
20. An apparatus as claimed in any of claims 16 to 19 including means for removal of debris from the preparation and/or splicing site.
21. An apparatus as claimed in any of claims 16 to 20 wherein said passive retention means is adapted for the use of a high energy beam for preparation and/or splicing of the waveguides and incorporates means for accommodating parts of the beam which bypass the waveguides.
22. An apparatus as claimed in any of claims 16 to 21 wherein said passive retention means comprises part of an optoelectronics module.