1、I 4862573 Ob78732 957 m INTERNATIONAL TELECOMMUNICATION UNION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE Optical fibres for Telecommunications Geneva 1984 ISBN 92-61 -01 841 -6 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information
2、Handling ServicesE 4862591 Oh76733 695 I INTERNATIONAL TELECOMMUNICATION UNION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE Optical fibres for Telecommunications Geneva 1984 , ISBN 92-61-01841-6 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed
3、 by Information Handling Serviceso I.T.U. COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling Services1 . II . 111 . IV . V . VI . v11 . VIII . IX . X . XI . XI1 . XII1 . Optical fibres for Telecommunications CONTENTS Introduction Fundamental chara
4、cteristics of optical fibres Optical fibre fabrication techniques Optical fibre cables Splices and connectors for optical fibre communications Test methods . Sources and detectors for optical fibre communications . Transmission systems using optical fibres . The application of optical fibres in the
5、local and rural networks . The application of optical fibres in the junction network . The application of optical fibres in the trunk network . The application of optical fibres in submarine cable systems Conclusion . Page 5 7 13 19 27 37 47 59 69 19 83 93 101 3 L COPYRIGHT International Telecommuni
6、cations Union/ITU TelecommunicationsLicensed by Information Handling ServicesYBb2591 Db7873b ST4 I. Introduciion 1. General ELECDMMUNICATIONS have had a continuous development in T recent years and the actual trend shows that the evolution is becoming still more rapid, thus constituting a real chall
7、enge for the people involved in this field with the possibilities offered by the installation of new services. the introduction of new switching and transmission techniques and the appearance of new transmission media. In fact, on one side new services arc becoming a reality. with the consequent inc
8、reased utilization of the available bandwitdh: on the other, the network structure is evolving gradually to a di- gital form with the aim of establishing. in the long term, an integrated services digital network (SDN). Both these aspects will channel studies towards the possible utilization of new t
9、ransmission media, such as optical fibre cables, for telecom- munications. Experience in the past decade has proved that studies have not always finally resulted in the adoption of new facilities. Also it should be noted that, in some cases, proposed new services have appeared too early to be comple
10、tely understood by potential customers examining the possibilities offered and the relative cost involved. However, these studies have always had a useful outcome since they have found applications in other fields. For optical fibres, according to the experience gained in labora- tory and to the res
11、ults obtained in the field by many adminis- trations, their future appears to be more than promising. The amount of studies and research undertaken by various organiz- ations in this field indicates that the few remaining problems will shortly be overcome. thus optical fibre cables with reduced cost
12、 due to a wider utilization will in the near future become a very competitive transmission medium for telecommunication purposes. t. Historical developments of optical communications The idea of using light to cornmunicati is not a new one, but thc first proposal to use it for the transmission of in
13、formation in the modern mcaning of this term originated in the second half of the 19th century only. At that time the theory of Maxwell and Faraday on electromagnetic waves disclosed the possibility of using the entire spectrum of these waves for the purposes of communication. Since then the history
14、.of information transmis- sion has bccn a continuous sequence of progress towards the utilization of shorter wavelengths in order to provide still larger bandwidths. However, it is only aller the invention of the laser that research has been directed towards the realization of an optical transmis- s
15、ion system which, due to the high frequency of the bearer used (IO14 Hz), would allow the transmission of an enormous amount of information. Therefore the studies have mainly been devoted to examining in parallel the three fundamental parts of an optical transmission system: - the transmission mediu
16、m itsell; - the optical sources (in the visible or near infra-red range) modulated by thc signal carrying the information; - the optical receiver extracting from the modulated optical carrier a baseband signal practically equal to the signal present at the input. The first experiment concerning tran
17、smission media to be used for an optical system was carried out in the atmosphere. However, the results immediately proved the non-suitability of this transmission medium, due to the high values of attenuation introduced mainly by meteorological conditions (rain. fog. tur- bulence, etc.,). Also the
18、trials using tubes having an inside focal- izing lens or filled with gas have proved to be rather discourag- ing for technical and economic reason. In fact, at an early stage of the studies glass fibres. although be- ing potentially very attractive, were not considered a suitable transmission medium
19、 for optical systems duc to the high values of attenuation (several thousand dB/km). Only in 1966 was it proved that attenuation was not related to the material used and that it was possible to reduce it by eliminating impurities from the glass fibre. Further research culminated, in 1970, in the pro
20、duction of several hundred metres of single mode fibre having an attenuation of less than 20 dB/km and, finally, in 1972 it was possible to obtain a multimode fibre having an at- tenuation of less than 4 dB/km. Since then further steps have been taken in order to reduce the attenuation by improving
21、the manufacturing techniques of the fibres and by using wave- lengths in the regions around 1.3 and 1.5 pm greater in the part of the spectrum initially experienced (region 0.8 + 0.9 pm). To- gether with these studies progress has also been made towards the realization of multimode fibres with layer
22、 bandwidth, thus allowing the realization of high capacity transmission systems. Concerning optical sources. it can be said that the first cxperi- mental check of laser action in semiconductor devices was ob- tained in 1962. The first results confirmed that these devices could, in practice, be emplo
23、yed as optical sources. although only in 1970 was it possible to achieve a continuous wave (CW) Previous page is blank. COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling Services6 4862593 Ob76737 430 m working at room temperature made with altern
24、ate layers of GaAs and AlGaAs (hetero-structure laser). The initial life of these devices was only a few hours, whereas for practical ap- plications in telecommunications a mean time between failures (MTBF) in the range of 106 hours was necessary. For this reason a great deal of subsequent research
25、has been un- dertaken in order to understand the factors limiting the lifetime of laser devices and to extend it. These studies have reached the present state of the art which allows a lifetime long enough to appear compatible with the needs of telecommunication sys- tems, at least for laser devices
26、 operating in the wavelength range 0.8 + 0.9 Pm. Another type of optical source, the light emitting diode (LED), has been developed for utilization in conjunction with optical fibres since 1972 when the Burrus type LED was first produced, and in this field also progress has been rather impressive. A
27、l- though LEDs have not the same performances as lasers from the point of view of speed of modulation and of emitted optical power, they have a longer life and a lower price in comparison, thus making them also attractive for some particular applica- tions of optical systems. The results obtained in
28、 the field of optical sources and of trans- mission media have also stimulated studies for the development of corresponding optical detectors. These devices may be classi- fied in.two major types: - p-i-n diodes, giving an electron for almost any incident pho- - avalanche photodiodes producing I O-
29、1 O0 electrons for any , , ton, incident photon. Both types are used for different applications and their reliabil- ity is at present satisfactory for optical systems operating in the wavelength region 0.8 + 0.9 Pm. For optical detectors as well as for optical sources, studies are at present directe
30、d towards the realization of devices operating in the longer wavlength region around 1.3 and 1.5 Fm. The availability of the fundamental optical components (sources, optical fibres and receivers) and of the corresponding optical accessories (joints, connectors, etc.) has allowed the realization of t
31、he first generation of optical systems, not only for laboratory purposes but also for application in the field as a valid alternative to the traditional transmission systems. 3. CCITT studies in the field of optical fibres The potential interest for the application of optical fibres in telecommunica
32、tion networks was immediately recognized by the International Telegraph and Telephone Consultative Com- mittee (CCITT), which initiated studies in this field in the 1973-1976 study period. Subsequently, the Vlth Plenary Assembly of the CCITT (Gene- va, 1976) decided to divide the studies on optical
33、fibres between Study Group XV (Transmission systems) with its Question 38/XV (Physical characteristics of optical fibre cables) and Study Group XVlIl (Digital networks) with its Question 13/XVIII (Characteristics for digital line sections on optical fibre cables). The main achievement of the study p
34、eriod 1977- I980 has been Recommendation G.651 (Characteristics of 50/125 pn graded index optical fibre cables), which now appean in Vghme 111 of the Yellow Book. For the purpose of this introduction it should 6. be mentioned that the fibre described in the Recommendation has been chosen because mos
35、t administrations are considering this type of fibre for initial use in public networks. The recom- mended multimode graded-index optical fibre has a core dia- meter of 50 pm and a reference surface (generally the cladding) diameter of 125 pm and can be used for both analog and digital transmission.
36、 The main transmission characteristics are for the time being defined for the wavelength region around 850 nm, while definition of other wavelengths is left in the framework of the Recommendation for further study. For the digital line systems on optical fibres it was only poss- ible, during ttie st
37、udy period 1977-1980. to agree on a list of parameters to be considered ill a possible Recommendation. However, it was recognized that these systems should be in agreement with Recommendations G.91 I to (3.918 giving the general characteristics for the digital line sections operating at various hier
38、archical bit rates in order to ensure their interna- tional interconnection. Finally the Vllth Plenary Assembly (Geneva, 1980) assigned for the study period I98 I - I984 five Questions to Study Group XV and has also involved Study Group VI (Protection and specifi- cations of cable sheaths and poles)
39、 in these studies. The Questions assigned to Study Group XV deal with the char- acteristics of optical fibre cables, their related test methods, as well as the characteristics of digital line systems on optical fibre cables (previously studied by Study Group XVIII). Some particular aspects of optica
40、l fibre cables, such as methods of making joints and mechanical aspects, will be studied by Study Group VI. 4. CCITT booklet on optical fibres In addition, the VIIth Plenary Assembly, at the request of its Committee D (CCITT technical assistance) assigned to Study Group XV the study of Question 15/X
41、V (Collection and updat- ing of information relating to optical fibre communications). The information collected is to be used for publishing in the “Telecommunication Journal” a series of articles which will later be issued in a booklet. Subsequent studies will be used to update the text of the boo
42、klet. In order to initiate the study of Question 1 WXV it was decided to proceed in two stages. As a first step it was agreed, in consul- tation with the Editorial Committee of the “Telecommunica- tion Journal”, to have two special issues (November 1981 and February 1982) devoted respectively to “op
43、tical components” and to “systems and applications”. In general, criteria adopted for the various articles are in line with the studies undertaken by the CCITT, Le. avoiding as far as possible the theoretical aspects of the problems and dealing mainly with the practical aspects of optical fibre plan
44、ts. As a second step, Study Group XV has further agreed to prepare a revised text of the various articles in order to publish a CCITT booklet on optical fibres. The text of this booklet has been agreed by administrations, recognized private operating agencies, scienti- fic or industrial organization
45、s and international organizations, in the framework of the studies undertaken by Study Group XV. Study Group XV has drafted the text of this booklet at the time of rapid evolution of optical fibre technology. The material reported in the booklet relates on the experience gained by the various con- t
46、ributors at the middle of the study period 1981-1984, therefore, consideration has been mainly given to the multimode graded index optical fibres of the present Recommendation 13.651. COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesII.
47、Fundamental characteristics of optical fibres 1. Introduction I N the decade since the first optical fibres having low enough loss for telecommunications applications were reported, I rapid progress has occurred in both loss reduction and band- width improvement. In addition to low loss and high ban
48、d- width, fibres arc space eflicient, resistant to crosstalk and elec- tromagnetic interference, and manufacturable from abundant raw materials. This chapter summarizes the basic structural and transmission properties of optical fibres. 2. Fibre structure and propagation Multimode optical fibres are
49、 dielectric waveguides which can have many propagation modes. The modes are periodic field distributions, which, when taken together, can be used to con- struct any allowed field distribution in the fibre. Light in these modes follows paths that can be represented by rays as shown in figure I. Regions I, 2 and 3 are the core, cladding and coat- ing, respectively. The cladding glass has a refractive index, a parameter related to the dielectric constant, which is slightly lower than the refractive index of the core glass. The fibre in figure I al is called “step-index“ because the refractive
