1、- - - STD-ITU-T RECMN L.33-ENGL 399b E 4862593 Ob35232 T7T INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU L.31 (I 0196) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT Optical fibre attenuators ITU-T Recom
2、mendation L.31 (Previously CCIlT Recommendation) STD-ITU-T RECMN L.3L-ENGL L79b = 4Bb2571 Ob35233 70b ITU-T L-SERIES RECOMMENDATIONS CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT For further details, please refer to ITU-T List of Recommendations. FOREWORD Th
3、e IT-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (IT). The IT-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwid
4、e basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the IT-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the
5、 procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation L.31 was prepared by IT-T Study Group 6 (1993-1996) and was approved by the WTSC (Geneva, 9- 18 October 1996). NOTES 1. telecommunication administration and a recognized operating agency. In this Recomme
6、ndation, the expression “Administration” is used for conciseness to indicate both a 2. follows: The status of annexes and appendices attached to the Series L Recommendations should be interpreted as - - an annex to a Recommendation forms an integral part of the Recommendation; an appendix to a Recom
7、mendation does not form part of the Recommendation and only provides some complementary explanation or information specific to that Recommendation. O IT 1997 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, includin
8、g photocopying and microfilm, without permission in writing from the IT. Recommendation L.31 (10/96) 1 STD-ITU-T RECMN L-31-ENGL 177b LiBb2571 Ob35235 789 CONTENTS Page 1 Scope 1 2 Abbreviations . 1 3 General information 1 4 Configurations 2 5 Parameters and performance specifications 2 6 Test metho
9、ds 3 . . 11 Recommendation L.31 (10/96) SUMMARY This Recommendation describes the main features of optical attenuators, in terms of types, field of application and configurations. Moreover, this Recommendation examines the optical, mechanical and environmental characteristics of optical fibre attenu
10、ators, advising on general requirements and testing methods. Recommendation L.31 (10196) iii _ STD-ITU-T RECMN L-3L-ENGL L99b = 48b2591 b35237 551 m Recommendation L.31 OPTICAL FIBRE ATTENUATORS (Geneva, 1996) 1 Scope This Recommendation: - gives general information on fundamental types of optical f
11、ibre attenuator, their field of application and the main requirements about their Characteristics in terms of optical, mechanical and environmental behaviour; makes a classification of these components in terms of the configurations used in optical fibre plants; reports all the important optical par
12、ameters and gives general specifications on the optical, mechanical and environmental performances of optical fibre attenuators; reports the main testing methods of optical fibre attenuators. - - - This Recommendation refers to single-mode optical fibre attenuators only because this fibre is mostly
13、used in present telecommunication systems. 2 Abbreviations This Recommendation uses the following abbreviations: PON Passive Optical Network BER Bit Error Rate IEC International Electrotechnical Commission 3 General information Optical fibre attenuators are passive optical components that are often
14、required in an optical fibre transmission link to reduce the optical power incident on the photodetector. They can introduce a fixed level of attenuation vied attenuators) or they may have a tuning control to set the level of attenuation into a range of selectable values (variable attenuators). Typi
15、cal applications for optical fibre attenuators are: a) b) c) to assure the linear behaviour of optical fibre receivers avoiding optical power overloading; to balance the optical power into Passive Optical Network (PON) branches; to make measurements on an optical telecommunication system. Regarding
16、the first application, the optical power emitted by the source in a transmission system usually exceeds the needed power budget: the aim is to guarantee the operating condition of the system even if some degradation phenomena occur in the link. The direct control of the optical emission of the sourc
17、es can be made only for a limited dynamic range and may produce undesired modification of the characteristics of the emitted optical beam, like modal distribution or change of central wavelength. Therefore, attenuators are used in optical telecommunication systems to limit the optical power level at
18、 the receiver. The second application of these components is justified by the non-uniformity of the link losses in a real point-to-multipoint network. In fact, due to the topology of the network, different optical paths may suffer different losses so that specific optical attenuators may be needed i
19、n some branches of the network to assure the same linear operating range at each optical receiver. Recommendation L.31 (10196) 1 STD-ITU-T RECMN L-3L-ENGL L99b = 48b259L 0b3.5238 498 Finally, the third application mainly concerns variable optical attenuators. In fact, these kinds of components can b
20、e very important for making several measurements in an optical telecommunication system, for example, each time the performance (BER) as a function of the received optical power has to be characterized. Every type of optical attenuator is normally inserted at the receiving end of the link: in fact,
21、light intensity regulation at the transmitting end would require remote power monitoring of the received level of the optical signal. Since optical fibre attenuators may be used in central offices or in every type of outside closure, they should be able to operate in both controlled and uncontrolled
22、 environments. In particular, the ideal attenuator should have a stable attenuation over a wide temperature range and under mechanical stresses; it should be independent of wavelength and state of polarization and should not cause reflection or interference of the optical signal. In addition, other
23、desired characteristics for an ideal variable attenuator are low insertion loss, wide attenuation range and accurate mechanical or non-mechanical control of attenuation. The most common types of attenuator that are permanently installed in optical fibre plant are fixed. Therefore, technological effo
24、rts are mainly aimed to optimize the reliability and to minimize the dimensions of fixed attenuators. 4 Configurations A classification of optical fibre attenuators can be made considering whether they have attached optical fibre pigtails or not. If the attenuator has fibre pigtails, it is an attenu
25、ating patch-cord. It can have one or two permanently attached fibre pigtails, which may or may not be connectorized. Then, this kind of attenuator may also be directly spliced into the optical fibre link. Attenuators without fibre pigtails may be defined as attenuating adapters and they are used for
26、 insertion in connectorized optical fibre cables. They can be made in a female-female configuration (connector receptacle) or male-female configuration (optical pad). Optical attenuators without pigtails are preferred in most applications because of their compactness. in particular, the most widely
27、used configuration is the male-female; this is due to its intrinsic versatility. In fact, it is the only configuration that permits the connection or disconnection into the optical link, avoiding any other modification of the plant. Previously described configurations apply to both fixed and variabl
28、e attenuators even if most used variable attenuators are patch-cord connectors. A variable attenuator can be calibrated or uncalibrated. It may be continuously variable or adjustable in discrete steps. Most variable attenuators have a mechanical control, for example, a screw or a knob for tuning, bu
29、t there are also either electrically, magnetically, acoustically or optically controlled variable attenuators. However, while the field of application of non-mechanically controlled variable attenuators is essentially R available nominal value of attenuation; - attenuation tolerances; - polarization
30、 sensitivity; - optical power linearity; 2 Recommendation L.31 (10/96) - modal noise amplitude; - return loss. The minimum mandatory specifications that are required to describe the environmental and mechanical performances of optical attenuators should be: - mechanical endurance; - vibration; - col
31、d; - dry heat; - dampheat; - climatic sequence. Values of nominal attenuation, attenuation tolerance, operating wavelength ranges, polarization sensitivity and return loss, are given in Table 6.3/G.671. A linear response of the attenuator, without permanent damage of the attenuating zone, should be
32、assured at least for input power up to + 15 dBm and up to + 20 dBm will be allowed in some cases. For some advanced applications, an estimate of the modal noise introduced by the attenuator should be done. This can be made by calculating the amplitude of oscillations in the spectral response and the
33、n, to determine both the operating wavelength ranges and modal noise, a measurement of the spectral attenuation is recommended. For most applications, if the above-mentioned attenuation tolerances are met over the whole previously reported operating wavelength ranges, the modal noise effect introduc
34、ed by the attenuator is negligible. Conversely, a modal noise estimate is fundamental whenever a wavelength operating range smaller than the half period of the spectral attenuation oscillations is accepted. Finally, during the mechanical and environmental tests, a maximum variation of 10% on the act
35、ual value of attenuation in both operating wavelength ranges should be tolerated. After the test the measured attenuation values should meet the above-mentioned tolerances. High temperature Low temperature Duration of extreme temperature 6 Test methods The reference document for all the procedures t
36、hat should be considered in testing optical fibre attenuators: - IEC 869-1 (2nd ed.) Generic specijcation for opticalfibre attenuators. For measurement of polarization sensitivity, the only reference is the IEC Publication 1300-3-2. Moreover, the following details should be considered for mechanical
37、 and environmental tests: - Mechunical endurance: a cycle of 1000 repeated matings. The value of the attenuation should be measured during the test, after every 25 matings and at the end of the test. Vibration: the frequency of sinusoidal vibrations should be continuously variable in the range 10 to
38、 55 to 10 Hz with a cycle duration of 60 s; the amplitude should be 0.75 mm and the duration of the test should be 0.5 h per axis. Cold the test should be carried out at a temperature of-25 “C for 16 h. Dry heat: temperature of testing + 70 “C for 16 h. Damp heat: temperature of testing + 40 “C for
39、16 h at a relative humidity of 93 k 3%. Climate sequence: the sequence should be: - - - - - Internal External +70 OC +40 OC -40 “C + 10 “C 1 hour 1 hour Number of cycles 12 12 f 1 OCImin I Rate of temeerature change I Il “C/min I Recommendation L.31 (10196) 3 Series A Series B Series C Series D Seri
40、es E Series F Series G Series H Series I Series J Series K Series L Series M Series N Series O Series P Series Q Series R Series S Series T Series U Series V Series X Series Z ITU-T RECOMMENDATIONS SERIES Organization of the work of the ITU-T Means of expression: definitions, symbols, classification
41、 General telecommunication statistics General tariff principles Overall network operation, telephone service, service operation and human factors Non-telephone telecommunication services Transmission systems and media, digital systems and networks Audiovisual and multimedia systems Integrated servic
42、es digital network Transmission of television, sound programme and other multimedia signals Protection against interference Construction, installation and protection of cables and other elements of outside plant Maintenance: international transmission systems, telephone circuits, telegraphy, facsimi
43、le and leased circuits Maintenance: international sound programme and television transmission circuits Specifications of measuring equipment Telephone transmission quality, telephone installations, local line networks Switching and signalling Telegraph transmission Telegraph services terminal equipment Terminals for telematic services Telegraph switching Data communication over the telephone network Data networks and open system communication Programming languages
