4. Recommendation G.653 CHARACTERISTICS OF A DISPERSION-SHIFTED SINGLE-MODE OPTICAL FIBRE CABLE The CCITT, considering (a) that dispersion-shifted optical fibre cables are going to be used widely in telecommunication networks; (b) that the foreseen potential applications may require several kinds of single-mode fibres differing in operation wavelength geometrical and optical characteristics, and attenuation dispersion and other transmission characteristics, recommends a dispersion-shifted single-mode fibre which has the zero-dispersion wavelength in the 1550 nm wavelength region and which is optimized for use at wavelengths around 1550 nm. This fibre may also be used at around 1300 nm subject to the constraints which are outlined in this Recommendation. Its geometrical, optical and transmission parameters are described below. The meaning of the terms used in this Recommendation are given in Annex A to Recommendation G.652 and the guidelines to be followed in the measurements to verify the various characteristics are indicated in the Annex B to Recommendation G.652. The characteristics of this fibre and the relevant values will be refined as studies and experience progress. 1. Fibre characteristics Only those characteristics of the fibre providing a minimum essential design framework for fibre manufacture are recommended in 1. Of these, the cabled fibre cut-off wavelength may be significantly affected by cable manufacture or installation. Otherwise, the recommended characteristics will apply equally to individual fibres, fibres incorporated into a cable wound on a drum, and fibres in an installed cable. This Recommendation applies to fibres having a nominally circular mode field. 1.1 Mode field diameter The nominal value of the mode field diameter at 1550 nm shall lie within the range of 7.0 to 8.3 m. The mode field diameter deviation should not exceed the limits of 10% of the nominal value. Note 1 - The choice of a specific value within the above range is not necessarily associated with a specific fibre design. Note 2 - It should be noted that the fibre performance required for any given application is a function of essential fibre and systems parameters, i.e., mode field diameters, cut-off wavelength, chromatic dispersion, system operating wavelength, and bit rate/frequency of operation, and not primarily of the fibre design. 2.2 Chromatic dispersion coefficient Under study. Note 1 - The maximum chromatic dispersion coefficient of single-mode fibres covered in this Recommendation shall be: UA 3Wavelength 3 Maxmimum chromatic 3 3 (nm) 3 dispersion coefficient 3 3 3 (ps/(nm.km)) 3 A' 31525-1575 3 3.5 3 3 3 3 31300 nm 3 Under study 3 3region 3 3 AAU Note 2 - The value of 3.5 ps/(nm.km) allows for attenuation limited section lengths at 560 Mbit/s, using suitable multi-longitudinal mode lasers and adequate line coding. Note 3 - For higher capacity (larger than 560 Mbit/s) or longer length systems, operation closer to the zero-dispersion wavelength is required (unless single- longitudinal mode laser diodes are used). Additional fibre parameters may then have to be specified (such as zero-dispersion wavelength, dispersion-slope, etc.). Further studies are needed to identify these parameters. Note 4 - It is not necessary to measure the chromatic dispersion coefficient on a routine basis. ANNEX B (to Recommendation G.653) Test methods for dispersion-shifted single-mode fibres The present experience on dispersion-shifted single-mode fibres is rather limited; therefore further study is needed on some reference and alternative test methods for this type of fibre. Nevertheless, most of the test methods described in Annex B to Recommendation G.652 are in principle applicable also to dispersion-shifted fibres. Therefore, for this annex, reference is made to the corresponding test methods of Annex B in Recommendation G.652; the specifics of each test procedure need further study. It should be noted that the working wavelength for G.653 fibres is in the 1550 nm region. In the following, some exceptions are listed pointing out where the test methods in Annex B to Recommendation G.652 need to be amended in order to be applicable to fibres covered in this Recommendation.