1、 International Telecommunication Union ITU-T L.12TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (03/2008) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT Optical fibre splices Recommendation ITU-T L.12 Rec. ITU-T L.12 (03/2008) i Recommendation ITU-
2、T L.12 Optical fibre splices Summary Splices are critical points in the optical fibre network, as they strongly affect not only the quality of the links, but also their lifetime. In fact, the splice shall ensure high quality and stability of performance with time. High quality in splicing is usually
3、 defined as low splice loss and tensile strength near that of the fibre proof-test level. Splices shall be stable over the design life of the system under its expected environmental conditions. At present, two technologies, fusion and mechanical, can be used for splicing glass optical fibres and the
4、 choice between them depends upon the expected functional performance and considerations of installation and maintenance. These splices are designed to provide permanent connections. Source Recommendation ITU-T L.12 was approved on 8 March 2008 by ITU-T Study Group 6 (2005-2008) under Recommendation
5、 ITU-T A.8 procedure. ii Rec. ITU-T L.12 (03/2008) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a pe
6、rmanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, estab
7、lishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary sta
8、ndards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Re
9、commendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents
10、are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed I
11、ntellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not re
12、ceived notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/
13、ipr/. ITU 2009 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T L.12 (03/2008) iii CONTENTS Page 1 Scope 1 2 Normative references 1 3 Abbreviations and acronyms 2 4 Types of splices: General descripti
14、on. 2 4.1 Fusion splices . 2 4.2 Mechanical splices 2 5 Splicing procedure steps. 3 5.1 Fibre cleaning and end preparation 3 5.2 Coating stripping 3 5.3 Cleaning of the bare fibre ends. 4 5.4 Fibre cleaving . 4 5.5 Splicing. 4 5.6 Field splice loss measurements 8 6 Functional properties of the splic
15、es 9 6.1 Recommended characteristics for single-mode fibre splices . 9 6.2 Performance criteria for multimode fibre splices. 10 Appendix I Index of refraction matching materials for mechanical optical fibre splices. 11 Appendix II Japanese experience on optical fibre splicing. 12 Bibliography. 15 Re
16、c. ITU-T L.12 (03/2008) 1 Recommendation ITU-T L.12 Optical fibre splices 1 Scope This Recommendation deals with the application of splices of single-mode and multimode optical fibres. It describes a suitable procedure for splicing that shall be carefully followed in order to obtain reliable splices
17、 between optical fibres or ribbons. This procedure applies both to single fibres or ribbons (mass splicing). In addition, this Recommendation advises on the optical, mechanical and environmental testing methods required for the splice system design and equipment qualification. Further information is
18、 provided in b-ITU-T Handbook. The fibres shall be in accordance with ITU-T G.651.1, ITU-T G.652, ITU-T G.653, ITU-T G.654, ITU-T G.655, ITU-T G.656 and ITU-T G.657. 2 Normative references The following ITU-T Recommendations and other references contain provisions which, through reference in this te
19、xt, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition
20、of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.651.1 Recommendation ITU-T
21、 G.651.1 (2007), Characteristics of a 50/125 m multimode graded index optical fibre cable for the optical access network. ITU-T G.652 Recommendation ITU-T G.652 (2005), Characteristics of a single-mode optical fibre and cable. ITU-T G.653 Recommendation ITU-T G.653 (2003), Characteristics of a dispe
22、rsion-shifted single-mode optical fibre and cable. ITU-T G.654 Recommendation ITU-T G.654 (2004), Characteristics of a cut-off shifted single-mode optical fibre and cable. ITU-T G.655 Recommendation ITU-T G.655 (2006), Characteristics of a non-zero dispersion-shifted single-mode optical fibre and ca
23、ble. ITU-T G.656 Recommendation ITU-T G.656 (2006), Characteristics of a fibre and cable with non-zero dispersion for wideband optical transport. ITU-T G.657 Recommendation ITU-T G.657 (2006), Characteristics of a bending loss insensitive single mode optical fibre and cable for the access network. I
24、EC 61300 IEC 61300-x-series (in force), Fibre optic interconnecting devices and passive components - Basic test and measurement procedures. IEC 61755-2-x IEC 61755-2-series (2006), Fibre optic connector optical interfaces. 2 Rec. ITU-T L.12 (03/2008) IEC/TR 62316 IEC/TR 62316 (2007), Guidance for th
25、e interpretation of OTDR backscattering traces. 3 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: IL Insertion Loss or attenuation MFD Mode Field Diameter RH Relative Humidity OTDR Optical Time Domain Reflectometer RL Return Loss 4 Types of splices: Gene
26、ral description All optical fibre splices as mentioned in this Recommendation should be suitable for indoor applications as well as for outdoor environments when stored in an appropriate enclosure. 4.1 Fusion splices Different methods exist to obtain a fusion splice of fibres or ribbons. Electric ar
27、c-fusion is the most widely used method to make reliable single or mass optical splices in the field. The fusion process is realized by using specially-developed splicing machines. To make a fusion splice, all the protective coatings are removed from the fibre, the fibres are cleaved and then positi
28、oned and aligned between two electrodes in the splicing machine. An electric arc heats the silica glass until the “melting“ or softening point is reached and at the same time the fibres are brought together longitudinally in such a way that a geometrically continuous splice is obtained. This process
29、 produces a continuous glass filament. The fibre alignment in these machines can be passive (v-groove alignment) or active (light injection and detection system or core/cladding profile monitoring and alignment system). A suitable protection device is then applied to the splice to protect the bare f
30、ibre and to allow handling and storage without adversely affecting the physical integrity of the splice. The cleave quality and the intensity and the duration of the arc as well as the differences between the two fibres to be spliced determine the splice loss. In addition, the quality of coating rem
31、oval, fibre cleaving and splice protection contribute to the long-term mechanical reliability in the field. 4.2 Mechanical splices Mechanical splices have different structures and physical designs, and usually include the following basic components: surface for aligning mating fibre ends; a retainer
32、 to keep the fibres in alignment; an index matching material (gel, grease, adhesive, etc.) placed between the fibre ends. They can be used for single fibres or ribbons. Some designs allow installation on the fibres at the end of a cable in the factory for faster jointing in the field. An optical mat
33、ching material between the ends of the fibres can be used to reduce Fresnel reflections. This material shall be chosen to match the optical properties of the fibre. Common index matching materials include silicon gels, UV-curable adhesive, epoxy resins and optical Rec. ITU-T L.12 (03/2008) 3 greases
34、. The index of refraction of these materials each has a different temperature dependence to the fibre. More detailed information on index matching materials can be found in Appendix I. 5 Splicing procedure steps 5.1 Fibre cleaning and end preparation For jelly-filled cables, the fibres shall be mech
35、anically cleaned of the water-blocking jelly of the cable using lint-free paper tissue or cotton cloth. Commercial solvents are available that can be used to assist in this cleaning. Care shall be taken so that the ribbon matrix material and fibre coatings are not damaged either mechanically or chem
36、ically. Long-term soaking in solvents can damage the fibre coating. In addition, all the safety-related information of these products shall be declared by the solvent supplier. The fusion splicing machine or mechanical splice assembly tool shall be close to the joint closure, so that the fibres are
37、not subjected to excessive bending, tensile or pressure stresses. The ends to be spliced shall be identified on the basis of the cable identification system which denotes the fibres in the cable. If tube-type protection devices are used, they shall be placed over one end of the fibres or ribbons to
38、be spliced before splicing. Clamshell-type protectors can be fitted after splicing is complete. 5.2 Coating stripping Where applicable, secondary coatings (tight buffer or loose tube constructions) shall be removed to the distance recommended by the splice protector manufacturer using an appropriate
39、 tool in order to expose the primary coating. Enough coating shall be removed from the ends so that, after cleaving and splicing, all bare fibre shall be covered by the protection device or mechanical splice. Coating removal could be the most critical operation in the splicing procedure, especially
40、if it has to be performed on fibres that have been in the field for many years, because strippability may get worse due to ageing. Therefore, this step must be performed carefully because the final strength of the completed splice depends on minimizing the exposure that can cause flaws on the bare f
41、ibre. The stripping method could be chemical, thermal or mechanical, depending on the applications and on the desired performance. In the case of a chemical method, all safety-related information of the product shall be supplied by the manufacturer. Typically, for underground, directly buried or aer
42、ial applications mechanical stripping is used. The blade separation and alignment of the semi-circular or v-groove openings shall be controlled to penetrate into the soft inner coating layer without scratching the fibre surface. The blades shall be examined carefully and frequently. The blades shall
43、 be well aligned, clean at all times and replaced if damaged or worn. Where the blades are an integral part of the stripper, the tool shall be replaced. When thermal stripping methods are used, especially for ribbons, the coating shall be heated to the temperature recommended by the ribbon manufactu
44、rer, and then removed by a blade. For submarine applications, the chemical method is more suitable for the higher proof-test levels required. Holders are always used for stripping, cleaving and splicing fibre ribbons and are sometimes used for single fibre splicing systems. The ribbons are held in a
45、 holder prior to stripping and cleaving, and during the fusion process. The holder shall ensure a good alignment of the fibres without damaging them. Only the coated part of the fibre or ribbon shall be put into the holder, so that clamping does not cause damage. The holders shall be kept clean and
46、free of debris. 4 Rec. ITU-T L.12 (03/2008) 5.3 Cleaning of the bare fibre ends When fibre end cleaning is needed, the bare ends shall be cleaned with paper tissue soaked with reagent grade alcohol to eliminate residual coating, paying attention not to break them. Avoid wiping the fibre more than ne
47、cessary to clean off debris. 5.4 Fibre cleaving The bare fibre ends shall be cleaved perpendicularly to the longitudinal axis; the cut surface shall be mirror-like without chips or hackle. For fusion splices, end angles shall be typically less than 1 from perpendicular for single fibres and less tha
48、n 3 to 4 for ribbons (depending on the fibre type) to achieve a satisfactory splice. The cleaving tool shall be capable of achieving these values with a controlled length of bare fibre, compatible with the splicing system and protection device. For mechanical splices, two types can be identified: pe
49、rpendicular cleaved, with typically the same cleave angle as fusion splices; and angle cleaved, with a cleave angle of at least 4. This is done to eliminate reflected light due to the mismatch between fibre glass and index matching material at extreme temperature. When splices are assembled with angled cleaves instead of perpendicular cleaves, the reflected light is no longer completely captured and guided by the fibre core, but is directed to the fibre cladding where it is attenuated. The cleaving tool shall be clean and properly adjusted
