1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T L.41TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (05/2000) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT Maintenance wavelength on fibres carrying signals ITU-T Recommendation L.41 (Formerly CCITT Rec
2、ommendation) ITU-T L.41 (05/2000) i ITU-T Recommendation L.41 Maintenance wavelength on fibres carrying signals Summary This ITU-T Recommendation assigns the wavelengths for fibre identification, fault location and maintenance monitoring that may be used to manage the physical plant. The maintenance
3、 wavelength assignment has a close relationship with the transmission wavelength assignment selected by Study Group 15. Source ITU-T Recommendation L.41 was prepared by ITU-T Study Group 6 (1997-2000) and approved under the WTSC Resolution 1 procedure on 12 May 2000. ii ITU-T L.41 (05/2000) FOREWORD
4、 The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. 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
5、Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topic
6、s. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSC 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 “
7、Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual
8、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 received notic
9、e of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. Ge3 ITU 2001 All rights reserved. No p
10、art of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. ITU-T L.41 (05/2000) iii CONTENTS Page 1 Scope. 1 2 In-service maintenance . 1 Appendix I Remarks on the way
11、for in-service maintenance of optical fibres . 2 Appendix II Japanese consideration for selecting maintenance wavelength 2 II.1 Present Japanese maintenance wavelength. 2 II.2 Reason. 3 II.2.1 Laser diode (LD) market 3 II.2.2 Filter. 3 II.2.3 Fibre identification 3 II.3 Direction for the future . 4
12、II.3.1 LD market 4 II.3.2 Filter. 4 II.3.3 Fibre identification and handling. 4 II.4 Result 5 Appendix III Information of bending loss for considering the wavelength assigned 5 ITU-T L.41 (05/2000) 1 ITU-T Recommendation L.41 Maintenance wavelength on fibres carrying signals 1 Scope This ITU-T Recom
13、mendation deals with maintenance wavelength on fibres carrying signals without in-line optical amplifiers. ITU-T Recommendation L.25 “Optical fibre cable network maintenance“ defines comprehensive guidelines to maintain optical fibre and suitable wavelength should be used for preventive maintenance
14、as defined by this Recommendation. Maintenance systems which use wavelengths in a vacant window of optical fibre carrying signals are being operated currently and it should be taken into account that in-service maintenance of optical fibre should not interfere with the normal operation and expected
15、performance of the information channels. 2 In-service maintenance In-service maintenance of optical fibre should be done in such a way that it does not interfere with the normal operation and expected performance of the information channels. Wavelength for in-service maintenance, as shown in Table 1
16、, should be used. Table 1/L.41 Maintenance wavelength assignment 1310 nm-window 1550 nm-window 1625 nm-windowb)1650 nm-windowa), b)Case 1 Active Vacant or maintenance Vacant or maintenance Vacant or maintenanceCase 2 Vacant or maintenance Active Vacant or maintenance Vacant or maintenanceCase 3 Acti
17、ve Active Vacant or maintenance Vacant or maintenanceCase 4 Active or vacant Active Active Vacant or Maintenance a)When there is no optical light (nominally below 60 dBm) from the OTDR laser at all wavelengths equal to or below the maximum client signal wavelength (see Case 4) at the point “R“, it i
18、s not necessary to consider interference with transmission. b)These OTDR wavelengths are suitable only for systems with client signals at wavelengths less than 1565 nm. Applicability for client signals at longer wavelength is under study. Case 1: This usually applies to single mode fibre. Transmissi
19、on system uses only 1310 nm-window. Case 2: This usually applies to dispersion shifted fibre. Transmission system uses only 1550 nm-window. Case 3: This usually applies to single mode fibre. Transmission system uses two or more wavelengths in 1310 nm-window and 1550 nm-window. 2 ITU-T L.41 (05/2000)
20、 Case 4: The maximum transmission wavelength is under study in Study Group 15, but is limited to less than or equal to 1625 nm. Wavelength is independent of types of fibre (single mode fibre or dispersion shifted fibre). APPENDIX I Remarks on the way for in-service maintenance of optical fibres Loss
21、: The optical interfaces are defined at points S (source) and R (receive). Point of presence should be after the point S and before the point R, therefore, the coupling/filtering function loss will be counted as part of the physical plant. Receive cross-talk: Even with filtering, the special charact
22、eristics of the light source from maintenance equipment are broad enough to allow the possibility of cross-talk or other similar impairment to the service bearing signals. The combination of its spectral characteristic and filter requirements might well be best limited by a requirement to the effect
23、 of: the total amount of residual optical power at point R shall be less than XX dBm at all wavelengths below the maximum operating wavelength of YY. Average optical power: For the time intervals during which OTDR pulses are present, it will contribute to the effective average optical power. It is p
24、resumed, but should be verified, that the OTDR contribution to the total is low enough to avoid concerns about fibre non-linearities, safety concerns, or error detection circuits. Items should correspond with transmission systems characteristics: Optical characteristics of light sources from mainten
25、ance equipment (power, wavelength, FWHM of its spectrum, modulation frequency of the light source, OTDRs pulsewidth and repetition cycle). Allowing for light power at points R and S. APPENDIX II Japanese consideration for selecting maintenance wavelength II.1 Present Japanese maintenance wavelength
26、Trunk networks: Communication Maintenance Case A 1310 nm 1550 nm Case B 1550 nm (Distance 80 km) 1310 nm (Testing and monitoring) 1650 nm (Fibre identification) Case C 1550 nm (Distance 160 km) 1550 nm (Testing for post-fault and after installation) 1650 nm (Fibre identification and monitoring) ITU-
27、T L.41 (05/2000) 3 Access networks: Communication Maintenance Case D 1310 nm 1550 nm Case E 1310 nm and 1550 nm 1650 nm II.2 Reason II.2.1 Laser diode (LD) market 1310 nm and 1550 nm LD markets are big while for other LDs the market is small. Because a lot of transmission systems use 1310 nm or 1550
28、 nm LD, the use of 1310 nm or 1550 nm wavelength for optical fibre maintenance support systems would be economical. II.2.2 Filter In cases A, B and D, the wavelength difference between communication light and maintenance light is 240 nm. Filters have the characteristics as shown in Figure II.1. Ther
29、e is no problem for insulation. Transmission systems use 1310 nm or 1550 nm wavelength. Therefore, the 1550 nm or 1310 nm wavelength for optical fibre maintenance should be used, except fibre identification. In cases C and E, we need 70-100 nm wavelength differences at least, according to the filter
30、 characteristics. For manufacturing, we had better keep the difference 100 nm. In these cases, the popular type specification of the insulation loss is 30 dB. And that of the cheapest type is 20 dB. T0604670-995030151310 1550 1650InsertionlossFilter for 1310 nmtransmissionFilter for 1550 nmtransmiss
31、ionWavelengthFigure II.1/L.41 Characteristics of filter There are a few LDs in a central office but a lot of filters are installed in front of ONU and OLT. Optical fibre maintenance support systems do not represent a big LD market. The LD market for wavelengths other than 1310 nm or 1550 nm is small
32、, even if the optical fibre maintenance wavelength is recommended. When choosing the optical fibre maintenance wavelength, it is better to consider the filter specification in preference to LDs and transmission system specification for total system cost. Therefore, the 1650 nm wavelength should be c
33、hosen for cases C and E. II.2.3 Fibre identification A fibre is identified by bending. Fibre identification tools detect leaked maintenance light without interfering with the transmission. Therefore, the wavelength difference between the transmission light and the maintenance wavelength is necessary
34、. In cases A, D and E, the insertion loss specification of the tool is less than 0.5 dB at 1310 nm and less than 2.5 dB at 1550 nm when the tool bends a fibre. In cases B and C, the loss specification is less than 0.5 dB at 1550 nm. 4 ITU-T L.41 (05/2000) II.3 Direction for the future II.3.1 LD mark
35、et Optical fibre maintenance support systems cannot represent a big market for LD so LDs, of wavelengths other than 1310 nm or 1550 nm, will remain in the minority in the future. II.3.2 Filter Fibre grating technique is under development. The fibre grating characteristics are shown in Figure II.2. I
36、f we get these characteristics, we do not need 100 nm-wavelength difference any longer. T0604680-995030151310 1550 1650InsertionlossWavelengthFigure II.2/L.41 Characteristics of grating II.3.3 Fibre identification and handling If fibre gratings can be used, the wavelength differences between transmi
37、ssion light and maintenance light for fibre identification will be needed. Therefore, long wavelength should be used as much as possible. An optical fibre loss wavelength trace is shown in Figure II.3. According to this figure, 1650 nm wavelength is the longest wavelength. T0604690-991200 1300 1400
38、1500 1600 1700Loss (dB/km)Wavelength (nm)0.60.40.2Figure II.3/L.41 Loss wavelength trace ITU-T L.41 (05/2000) 5 II.4 Result Considering the filter specification and fibre identification, the longer the wavelength, the better. Considering the fibre characteristics, it would be preferable to use from
39、1310 nm to 1650 nm. So therefore, the 1650 nm wavelength would be used. APPENDIX III Information of bending loss for considering the wavelength assigned This ITU-T Recommendation shows optical fibre bending characteristics, which is an important element for assigning wavelength, based on Japanese ex
40、perience. Optical fibre maintenance functions, especially fibre handling and fibre identification, are essential for maintaining fibres in the field. Operators have to handle fibres in central offices and manholes. They need to identify fibres with a clip-on power meter. The clip-on power meter has
41、to bend a fibre in order to detect leaking identification light. The insertion loss specification of an existing tool for single mode fibres is less than 0.5 dB at 1310 nm and less than 2.5 dB at 1550 nm, when the tool bends a fibre. The loss specification of an existing tool for dispersion shifted
42、fibres is less than 0.5 dB at 1550 nm. The handling loss is usually bigger than bending loss for identification. Figure III.1 shows the fibre general characteristics for bending. It shows that the longer the wavelength, the bigger the loss. So when long wavelength light is used for transmission, it
43、is easy to change loss of fibre. Transmission systems have to be designed taking into consideration loss change. It is difficult to determine the value of loss change. At least 5 dB or more would be necessary for 1550 nm in the case of single mode fibre. T0604700-991310 1310 1550 1310 1550 165016501
44、550 1650Wavelength (nm) Wavelength (nm)Wavelength (nm)Bending radius:9.5 mmBending radius:12.5 mmBending radius:16 mmBending loss(dB)Bendingloss(dB)Bending loss(dB)Cut off: 1.27 m MFD: 9.72 mCut off: 1.17 m MFD: 9.43 m0.9 dB29.8 dB0.3dB5.6 dB0.03 dB0.05.010.015.020.025.030.00.05.010.015.020.025.030.
45、00.05.010.015.020.025.030.01.27 dB0.25 dB1.9 dB7.0 dBFigure III.1/L.41 Bending characteristics Geneva, 2001 SERIES OF ITU-T RECOMMENDATIONS Series A Organization of the work of ITU-T Series B Means of expression: definitions, symbols, classification Series C General telecommunication statistics Seri
46、es D General tariff principles Series E Overall network operation, telephone service, service operation and human factors Series F Non-telephone telecommunication services Series G Transmission systems and media, digital systems and networks Series H Audiovisual and multimedia systems Series I Integ
47、rated services digital network Series J Transmission of television, sound programme and other multimedia signals Series K Protection against interference Series L Construction, installation and protection of cables and other elements of outside plant Series M TMN and network maintenance: internation
48、al transmission systems, telephone circuits, telegraphy, facsimile and leased circuits Series N Maintenance: international sound programme and television transmission circuits Series O Specifications of measuring equipment Series P Telephone transmission quality, telephone installations, local line
49、networks Series Q Switching and signalling Series R Telegraph transmission Series S Telegraph services terminal equipment Series T Terminals for telematic services Series U Telegraph switching Series V Data communication over the telephone network Series X Data networks and open system communications Series Y Global information infrastructure and Internet protocol aspects Series Z Languages and general software aspects for telecommunication systems
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