1、 International Telecommunication Union ITU-T L.85TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2010) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT Optical fibre identification for the maintenance of optical access networks Recommendation ITU-
2、T L.85 Rec. ITU-T L.85 (07/2010) i Recommendation ITU-T L.85 Optical fibre identification for the maintenance of optical access networks Summary Recommendation ITU-T L.85 deals with important considerations with respect to the requirements for an optical fibre identification technique by leaky light
3、 waves used for construction and maintenance work in optical access networks. History Edition Recommendation Approval Study Group 1.0 ITU-T L.85 2010-07-29 15 ii Rec. ITU-T L.85 (07/2010) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field o
4、f telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing
5、telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes 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
6、the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate bot
7、h a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when
8、all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents 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
9、RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by
10、 ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that th
11、is may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU
12、-T L.85 (07/2010) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 2 4 Abbreviations and acronyms 2 5 Conventions 2 6 Fundamental requirements for optical fibre identification . 2 7 Measurement methods and procedures
13、 . 2 7.1 Measurement method . 2 7.2 Applicability of optical fibre identification techniques 4 8 Requirements for in-service fibre line identification 4 8.1 Design of bending radius of the optical fibre identifier . 4 8.2 Test light wavelength . 4 8.3 Requirement for in-service monitoring and identi
14、fication equipment . 4 8.4 Monitoring optical power level of the communication light 5 Appendix I Japanese experience Optical fibre identification technology in Japan . 6 I.1 Introduction 6 I.2 Configuration 6 I.3 Procedure for optical fibre identification . 7 I.4 Design of the optical fibre identif
15、ier 7 I.5 Applicable area of optical fibre identification techniques 7 iv Rec. ITU-T L.85 (07/2010) Introduction The demand for broadband access services has increased throughout the world in the recent years. The number of FTTx subscribers is increasing rapidly, and a large number of optical fibre
16、cables are being installed daily to meet the current demand. During the installation and maintenance of optical fibre communication networks, field engineers must first correctly identify a specific fibre from a bundle of fibres to avoid the incorrect cutting and/or connection of an optical fibre at
17、 a worksite. In particular, engineers should distinguish “live“ (signal-carrying) and all dark fibres, since service reliability must be maintained. Therefore, it is very important to employ optical tests that distinguish a fibre for identification in an in-service optical fibre cable with no degrad
18、ation in transmission quality even if the field engineer selects the wrong fibre. Rec. ITU-T L.85 (07/2010) 1 Recommendation ITU-T L.85 Optical fibre identification for the maintenance of optical access networks 1 Scope This Recommendation: describes functional requirements and methods for optical f
19、ibre identification for the construction and maintenance of optical access networks; deals with an optical fibre identification technique that functions by measuring certain optical characteristics. The optical fibre characteristics should comply with ITU-T G.652 and ITU-T G.657, which relate to sin
20、gle-mode optical fibres. It also considers the procedures and requirements for optical fibre identification, including in-service fibre lines, without interfering with optical communication signals in access networks; describes the optical fibre identification technology that can be applied to diffe
21、rent topologies of optical access networks. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations
22、 and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published
23、. 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.652 Recommendation ITU-T G.652 (2009), Characteristics of a single-mode optical fibre and cable. ITU-T G.657 Recommendation ITU-T G.657 (2009), Characteristic
24、s of a bending-loss insensitive single-mode optical fibre and cable for the access network. ITU-T G.671 Recommendation ITU-T G.671 (2009), Transmission characteristics of optical components and subsystems. ITU-T G.987.1 Recommendation ITU-T G.987.1 (2010), 10-Gigabit-capable passive optical networks
25、 (XG-PON): General requirements. ITU-T G.Sup39 ITU-T G-series Recommendations Supplement 39 (2008), Optical system design and engineering considerations. ITU-T L.25 Recommendation ITU-T L.25 (1996), Optical fibre cable network maintenance. ITU-T L.40 Recommendation ITU-T L.40 (2000), Optical fibre o
26、utside plant maintenance support, monitoring and testing system. ITU-T L.41 Recommendation ITU-T L.41 (2000), Maintenance wavelength on fibres carrying signals. ITU-T L.50 Recommendation ITU-T L.50 (2003), Requirements for passive optical nodes: Optical distribution frames for central office environ
27、ments. ITU-T L.53 Recommendation ITU-T L.53 (2003), Optical fibre maintenance criteria for access networks. 2 Rec. ITU-T L.85 (07/2010) ITU-T L.66 Recommendation ITU-T L.66 (2007), Optical fibre cable maintenance criteria for in-service fibre testing in access networks. 3 Definitions 3.1 Terms defin
28、ed elsewhere This Recommendation uses the following term defined elsewhere: 3.1.1 optical distribution frame (ODF) ITU-T L.50. 3.2 Terms defined in this Recommendation This Recommendation does not define any terms. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and
29、 acronyms: FTTx Fibre to the x, where “x“ indicates the final location on the user side of any one of a variety of optical fibre architectures, e.g., FTTB, FTTC, FTTH, FTTP. ODF Optical Distribution Frame PD Photo Detector 5 Conventions None. 6 Fundamental requirements for optical fibre identificati
30、on With a view to realizing the efficient construction and maintenance of optical fibre cable networks, it is very important for field engineers to identify a particular optical fibre among the many fibres in an optical fibre cable or cord at a worksite. Correct optical fibre identification would ma
31、ke it possible to avoid major problems such as the incorrect cutting and/or connection of an optical fibre. Also, when field engineers handle optical fibre lines in existing cables that accommodate “live“ (signal carrying) fibres, they should avoid any degradation of communication signals in order t
32、o maintain service reliability. Therefore, the fundamental requirements of an optical fibre identification technique are as follows: It must be able to correctly identify a specific fibre from a bundle of fibres by measuring certain optical characteristics. It must not damage an optical fibre and th
33、us degrade its reliability. It should be capable of being performed without degrading optical communication signals in live fibres. It must be capable of identifying a specific fibre even if there is interference from the communication light. 7 Measurement methods and procedures 7.1 Measurement meth
34、od The method specified in this Recommendation uses a non-destructive macrobending technique. Figure 1 shows the configuration for optical fibre identification. An identification light is injected into the target fibre from the end of an optical fibre line (e.g., a central office) or is introduced b
35、y Rec. ITU-T L.85 (07/2010) 3 using optical devices for testing (e.g., an optical coupler). This identification light has a different wavelength from the communication light carrying the data signal. The optical fibre identifier bends the optical fibre, and a photodetector (PD) located at the centre
36、 of the bent part detects the modulated identification light leaking from the bent fibre, as shown in Figure 2. This enables the field technician to identify the fibre that is carrying the identification light. Figure 1 Configuration for optical fibre identification Figure 2 Typical configuration of
37、 bent part of optical fibre identifier This method applies to different topologies of optical access networks. However, it is difficult to use this method to identify a specific fibre in a point-to-multipoint network (described in ITU-T L.53) equipped with external optical splitters. This is because
38、 the optical power of the identification light launched from a central office is distributed equally to the branched optical fibres by the optical splitters, so the optical fibre identifier cannot identify a specific fibre. (Optical branching components (wavelength non-selective) are described in de
39、tail in ITU-T G.671.) If necessary, a specific fibre can be identified in a branched region below the optical splitter by launching the identification light from the far end of the optical fibre line at the worksite. 7.1.1 Identification light source The identification light is usually input at the
40、end of an optical fibre in a central office or in a users premises. If the fibre for identification is an in-service line, the communication signal light is carried in the optical fibre and leaked to a PD at the bent part of the optical fibre identifier. By modulating the identification light with a
41、 special frequency such as 270 Hz, 1 kHz, 2 kHz, etc., it is possible to separate the communication light and the identification light and to detect the identification light with a high optical power level. 7.1.2 Bend applying part of the optical fibre identifier The bending loss of an optical fibre
42、 generally increases as the wavelength increases. The optical fibre is bent by the bend applying part of the optical fibre identifier to make it possible to detect the leaked identification light with high efficiency. The insertion loss for the communication light should be suppressed to avoid sever
43、e deterioration in the BER of transmission systems. Identification lightCommunication lightOptical FibreIdentifierCentral Office Customers PremisesPhotodetector device: InGaAs-PDOptical fibreIncident lightLeaked light4 Rec. ITU-T L.85 (07/2010) Also, to take into account the working efficiency when
44、handling optical fibres in an optical enclosure, an optical cabinet, or an optical distribution frame (ODF) in which many optical fibres are accommodated, it is preferable for the head of the bend applying part of the optical fibre identifier to be compact and thin. If bend insensitive fibres (e.g.,
45、 ITU-T G.657) are used, the radius of the bend applying part should be designed appropriately and additional experience is required. 7.2 Applicability of optical fibre identification techniques Typical applicable areas of optical fibre identification techniques are central offices, indoor areas and
46、outdoor areas. The characteristics of optical fibre and fibre-ribbon in applicable areas should comply with ITU-T G.652 and ITU-T G.657. 8 Requirements for in-service fibre line identification The category of working stages for optical fibre identification is described in ITU-T L.25 and ITU-T L.40.
47、An optical fibre identification function is needed for both “preventative maintenance“ and “post-installation pre-service or post-fault maintenance“. During construction work, there are no “active“ fibres among the bundled fibres in the optical fibre cables. Therefore, optical fibre identification c
48、an be performed without regard to wavelength. However, in-service fibre line identification is necessary during service construction and maintenance work, because there are both “live“ and “dark“ (no signal) fibres in the same optical fibre cables. The requirements for optical fibre identification f
49、or in-service fibre lines are described below. 8.1 Design of bending radius of the optical fibre identifier As described in clause 7.1.2, the bending loss increases when the optical fibre identifier is used in service installation or maintenance work, such as the replacement and repair of optical fibre cables. It is necessary to design the bending radius of the bent part of the optical identifier to minimize the effect on the transmission system. There are trade-offs between the measurement dynamic range and th
