TR61282-7IEC:2003(E) - 5 - ITU-T Recommendation G.671: Transmission characteristics of optical components and subsystems ITU-TRecommendationG.691:Opticalinterfacesfor single-channelSTM-64,STM-256and otherSDHsystemswithopticalamplifiers 3 Characterisation of chromatic dispersion coefficient versuswavelength This clause outlines the characterisation of dispersion as a function of wavelength - for a givenwavelengthrange. parameters that can vary from fibre to fibre for a given fibre design. Characterisations of these formulas should give an indication of the wavelength range over which the formula applies. Extrapolation beyond these ranges can result in error. HOFENSERTAMESENI THISLOEANINBNYASORELIED YBOOK SPLY UREAU. For optical fibre,chromatic dispersion coefficient, D,canvary with wavelength,a, according to a variety of formula types that are found in IEC 60793-1-42. The simplest is the linear dispersion slope,So,as: D(a)= So(a-2o) (ps/nm-km) (1) Ll nite Measurements are based either on fitting differential group delays (DGD) or by fitting the integral to the measured group delay. Other forms defined in 60793-1-42 are the three-term Sellmeier (Equation (2)), and the five D(a)= So (2) D(a)= 2C1 -2C2-3 + 4C3 3 - 4C4-5 (3) For components, similar types of expressions can be used to characterise the chromatic dispersion value, d, as a function of wavelength.For components, however, the units are most often given as ps/nm (unadjusted for length). [The use of the term "coefficient," for fibre indicates a length normalisation.j TR 61282-7@IEC:2003(E) -6 Even for the products for which the linear representation of Equation (1) is appropriate for each individual fibre, the combination of the distributions of the zero-dispersion wavelength and slope will normally not lead to a very clear understanding of the distribution of chromatic dispersion.Figure1shows such acombineddistributionthat illustrates acorrelationbetween the dispersion parameters. 0,100 0,095 0,090 0,085 HOFENSERTAMUSENI HISLOCANIONBANYASORELED Y DOK SPLY BUREAU. 0,080 0,075 0,070 0,065 0,060 0,055 0,050 1560 1562 1564 1566 1568 1570 1 572 1574 1576 1578 Lambda-0 nm NCHI IEC 3207/02 Figure1-Distributionof dispersionparameters Characterisation of the chromatic dispersion coefficient 4 statisticsversuswavelength This clause outlines the technique used to characterise the distribution of a single population of fibres. Similar approaches can be applied to components. The fibre distribution shown in Figure 1 was intended for use in the wavelength range of 1530 nm to 1560nm-aB4 type fibre(ITU-TG.655),see IEC 60793-2-50.The chromatic dispersion values for the lower end of this range are affected more by the variation of slope values for high zero-dispersion wavelength than for low zero dispersion wavelength.The combined contributions are therefore difficult to evaluate without some other means. The characterisation methodology suitable for use in concatenation statistics for this distribution alone,or for combination with other distributionsisto calculate the dispersion coefficient for each of the wavelengths in the range of the application -for each individual fibre. This creates a distribution of dispersion coefficient values for each wavelength. Figures2 and 3 show these distributions at two selected wavelengths for the distribution shown in Figure 1. TR 61282-7 @IEC:2003(E) - 7 - 180 160 140 120 100 Frequen 80 60 40 20 SE 5 5 8. 5. 5. 2 5 D(1 560) ps/nm × km IEC3208/02 Figure2-Histogramofvaluesat1560nm 180 LO 160 140 120 Frequency 100 80 60 40 20 D(1 530) ps/nm ×km IEC3209/02 Figure3-Histogramofvaluesat1530nm The distribution for each wavelength is characterised with an average and a standard the relationships.