ÿWPCL ûÿ2BJ|xÐ ` ÐÐÌÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿH øÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÌÐÐ °°°è ÐÑ Âx„|ü@Ž ÑÐ Å°6Ø'°6Ø'Å ÐÕVÏ Ð ` Ð Áà@Á© ©ƒ Áà<ÁAP IX©60©Eƒ ÁàAÁƒVÕÕVÏ Ð ` Ð Áà@Á© ©ƒ Áà<ÁAP IX©60©Eƒ ÁàAÁƒVÕÕI (3201) ÕÕI (3201) ÕÐ °è  Ð7.ÁHÁÓÓÃÃRecommendation G.652ÄÄ Áà'ÁCHARACTERISTICS OF A SINGLE©MODE OPTICAL FIBRE CABLEƒ ÁHÁThe CCITT, ÃÃconsidering thatÄÄ ÁHÁ(a)Á   Ásingle©mode optical fibre cables are widely used in telecommunication networks; Ð H ÐÁHÁ(b)Á   Áthe foreseen potential applications may require several kinds of single©mode fibres differing in: ÁHÁ©Á  Ágeometrical characteristics, ÁHÁ©Á  Áoperating wavelengths, ÁHÁ©Âà  Âattenuation dispersion, cut©off wavelength, and other optical characteristics, ÆÆ ÁHÁ©Á  Ámechanical and environmental aspects; ÁHÁ(c)Á   ÁRecommendations on different kinds of single©mode fibres can be prepared when practical use studies have sufficiently progressed; ÃÃrecommendsÄÄ ÁHÁA single©mode fibre which has the zero©dispersion wavelength around 1300 nm and which is optimized for use in the 1300 nm wavelength region, and which can also be used in the 1550 nm wavelength region (where this fibre is not optimized). ÁHÁThis fibre can be used for analogue and for digital transmission. ÁHÁThe geometrical, optical, and transmission characteristics of this fibre are described below, together with applicable Test Methods. ÁHÁThe meaning of the terms used in this Recommendation is given in Annex A, and the guidelines to be followed in the measurements to verify the various characteristics are indicated in Annex B. Annexes A and B may become separate Recommendations as additional single©mode fibre Recommendations are agreed upon. 1.ÁHÁFibre characteristics ÁHÁOnly those characteristics of the fibre providing a minimum essential design framework for fibre manufacture are recommended in ÀÀ 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 installed cable. ÁHÁThis Recommendation applies to fibres having a nominally circular mode field. Ô _(ÔŒ ÃÃNoteÄÄ © A sufficient wavelength margin should be assured between the lowest©permissible system operating wavelength À/ÀÃÃsÄÄ of 1270 nm, and the Ð h Ðhighest©permissible cable cut©off wavelength À/ÀÃÃccÄÄ. Several Administrations favour a maximum À/ÀÃÃccÄÄ of 1260 nm to allow for fibre sampling variations and source wavelength variations due to tolerance, temperature, and ageing effects. ÁHÁThese two specifications need not both be invoked; users may choose to specify À/ÀÃÃcÄÄ or À/ÀÃÃccÄÄ according to their specific needs and the particular envisaged applications. In the latter case, it should be understood that À/ÀÃÃcÄÄ may exceed 1280 nm. ÁHÁIn the case where the user chooses to specify À/ÀÃÃcÄÄ as in I, then À/ÀÃÃccÄÄ need not be measured. ÁHÁIn the case where the user chooses to specify À/ÀÃÃccÄÄ, it may be permitted that À/ÀÃÃcÄÄ be higher than the minimum system operating wavelength, relying on the effects of cable fabrication and installation to yield À/ÀÃÃccÄÄ values below the minimum system operating wavelength for the shortest length of cable between two joints. ÁHÁIn the case where the user chooses to specify À/ÀÃÃccÄÄ, a qualification test may be sufficient to verify that the À/ÀÃÃccÄÄ requirement is being met. 1.9 Examples of fibre design guidelines Supplement No. 33 gives an example of fibre design guidelines for matched© cladding fibres used by two organizations. 2.1 Attenuation coefficient Optical fibre cables covered by this Recommendation generally have attenuation coefficients below 1.0 dB/km in the 1300 nm wavelength region, and below 0.5 dB/km in the 1500 nm wavelength region. 2.2 Chromatic dispersion coefficient The maximum chromatic dispersion coefficient shall be specified by: © the allowed range of the zero©dispersion wavelength between ÁHÁ À/ÀÃÃominÄÄ = 1295 nm and À/ÀÃÃomaxÄÄ = 1322 nm; Ð À ÐÂHH© the maximum value SÃÃomaxÄÄ © 0.095 ps/(nmÃÃ2ÄÄkm) of the zero©dispersion slope. ÆÆ Ð ` Ð Ô k+ÔŒ 3.2 Chromatic dispersion Ð ° Ð The chromatic dispersion in ps can be calculated from the chromatic dispersion coefficients of the factory lengths, assuming a linear dependence on length, and with due regard for the signs of the coefficients and system source characteristics (see ÀÀ 2.2). ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ The mode field diameter 2w is found by applying one of the following definitions. The integration limits are shown to be 0 to ÀÀ, but it is understood that this notation implies that the integrals be truncated in the limit of increasing argument. While the maximum physical value of the argument q is 1/À/À, the integrands rapidly approach zero before this value is reached. i) FAR©FIELD DOMAIN: In this domain three different measurement ÁH8"IÁ  implementations are possible: ÁHÁ  a) FAR FIELD SCAN: The far field intensity distribution FÃÃ2ÄÄ(q) is ÁK #LÁ      measured as a function of the far©field angle ÀÀ, and the mode Á>ˆ?Á      field diameter (MFD) at the wavelength À/À is Ô k+ÔŒ Ð Ð Ð iii) NEAR©FIELD DOMAIN: The near field intensity distribution fÃÃ2ÄÄ(r) is ÁHÁ   measured as a function of the radial coordinate r and ÃÃNoteÄÄ © The mathematical equivalence of these definitions results from transform relations between measurement results obtained by different implementations. These are summarized in Figure A©1/G.652. ÁàHGÁFIGURE A©1/G.652ƒ ÁàHOÁƒ ÁàH2ÁÃÃMathematical relations between measurement implementationsÄă ÁàHOÁƒ The difference between the maximum cladding surface diameter DÃÃmaxÄÄ and minimum cladding surface diameter DÃÃminÄÄ (with respect to the common cladding surface centre) divided by the nominal cladding diameter, D, i.e., A.6 Mode field The mode field is the single©mode field distribution giving rise to a spatial intensity distribution in the fibre. A.7 Mode field centre The mode field centre is the position of the centroid of the spatial intensity distribution in the fibre. ÃÃNote 1ÄÄ © The centroid is located at rÃÃcÄÄ and is the normalized intensity©weighted integral of the position vector r: rÃÃcÄÄ = ÀÀÀÀ r I(r) dA / ÀÀÀÀ I(r) dA ÀÀÀÀ AREA ÀÀÀÀ AREA ÃÃNote 2ÄÄ © For fibres considered in this Recommendation, the correspondence between the position of the centroid as defined and the position of the maximum of the spatial intensity distribution requires further study. This ensures that each individual cable section is sufficiently single mode. Any joint that is not perfect will create some higher order (LPÃÃ11ÄÄ) mode power and single mode fibres typically support this mode for a short distance (of the order of metres, depending on the deployment conditions). A minimum distance must therefore be specified between joints in order to give the fibre sufficient distance to attenuate the LPÃÃ11ÄÄ mode before it reaches the next joint. If inequality (1) is satisfied in the shortest cable section, it will be satisfied ÃÃa fortioriÄÄ in all longer cable sections, and single mode system operation will occur regardless of the elementary cable section length. Specifying À/ÀÃÃccÄÄ < À/ÀÃÃsÄÄ for the shortest cable length (including loops in the splice enclosure) ensures single mode operation. It is frequently more convenient, however, to measure À/ÀÃÃcÄÄ, which requires only a two metre length of uncabled fibre. À/ÀÃÃcÄÄ depends on the fibre type, length, and bend radius, and À/ÀÃÃccÄÄ, in addition, depends on the structure of a particular cable. The relationship between À/ÀÃÃcÄÄ and À/ÀÃÃccÄÄ, therefore, is dependent on both the fibre and cable designs. In general À/ÀÃÃcÄÄ is several tens of nm larger than À/ÀÃÃccÄÄ: À/ÀÃÃcÄÄ can even be larger than the system wavelength, without violating inequality (1). Higher values of À/ÀÃÃcÄÄ produce tighter confinement of the LPÃÃ01ÄÄ mode and, therefore, help to reduce potential bending losses in the 1550 nm wavelength region. Short fibre lengths (<20m) are frequently attached to sources and detectors, and are also used as jumpers for interconnections. The cut©off wavelength of these fibres, as deployed, should also be less than À/ÀÃÃsÄÄ. Among the means of avoiding modal noise in this case are: a)Á  Áselecting only fibres with sufficiently low À/ÀÃÃcÄÄ for such uses; ÂHHÂÁ€Á b)Á  Ádeployment of such fibres with small radius bends.ÆÆ A.11 Chromatic dispersion The spreading of a light pulse per unit source spectrum width in an optical fibre caused by the different group velocities of the different wavelengths composing the source spectrum. ÃÃNoteÄÄ © The chromatic dispersion may be due to the following contributions: material dispersion, waveguide dispersion, profile dispersion. Polarization dispersion does not give appreciable effects in circularly©symmetric fibres. A.12 Chromatic dispersion coefficient Ð h Ð The chromatic dispersion per unit source spectrum width and unit length of fibre. It is usually expressed in ps/(nm . km). A.13 Zero©dispersion slope The slope of the chromatic dispersion coefficient versus wavelength curve at the zero©dispersion wavelength. A.14 Zero©dispersion wavelength That wavelength at which the chromatic dispersion vanishes. A suitable cladding mode stripper shall be used to remove the optical power propagating in the cladding. When measuring the geometrical characteristics of the cladding only, the cladding mode stripper shall not be present.