IEC TR 62285-2005 pdf – Application guide for non-linear coefficient measuring methods.
The non-linear coefficient is related to the following non-linear optical distortion effects as a combined parameter: − self-phase modulation (SPM); − cross-phase modulation (XPM); − four-wave mixing (FWM). Other fibre attributes, such as chromatic dispersion and polarisation mode dispersion, also influence the transmission. Two methods are given, with details specific to each in normative annexes. They are: − Method A Continuous-wave dual-frequency; − Method B Pulsed single-frequency. Both methods require injecting very high powers (5 dBm or more) into the fibre, measurement of this power (absolute) and measurement of the output spectrum (which is modified by non- linear effects). Both methods use calculations that combine these measured results with those derived from other measurements such as attenuation (see IEC 60793-1 -40) and chromatic dispersion (see IEC 60793-1 -42). Both methods have limitations on the length of fibre that can be measured – in relationship with the chromatic dispersion at the wavelength being measured. Method A [1 ] 1) requires injecting the light of two wavelengths into the fibre. The light of both wavelengths is constant at various power levels. At higher power, the lights beat due to the non-linear effect and produce an output spectrum that is spread. The relationship of the power level to a particular metric of spectrum spreading is used to calculate the non-linear coefficient. Method B ,  requires injecting pulsed light at a single wavelength. The pulses should be of duration substantially less than 1 ns and the input peak power of these pulses should be measured and related to the non-linear spreading of the output spectrum.
2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60793-1 -1 , Optical fibres – Part 1-1: Measurement methods and test procedures – General and guidance IEC 60793-1 -40, Optical fibres – Part 1-40: Measurement methods and test procedures – Attenuation IEC 60793-1 -42, Optical fibres – Part 1-42: Measurement methods and test procedures – Chromatic dispersion IEC 60793-2-50, Optical fibres – Part 2-50: Product specifications – Sectional specification for class B single-mode fibres IEC 61 31 5, Calibration of fibre optic power meters 3 Apparatus The following apparatus is common to both measurement methods. Annexes A and B include layout drawings and other equipment requirements for each of the methods, respectively. 3.1 Light source See Annexes A and B for detailed characteristics of the light sources. 3.2 Input optics The input optics include one or more lasers, amplifiers, variable attenuators, couplers and power meters. Bandpass filters and oscilloscopes may be needed for Method B. See Annexes A and B for specific details. 3.3 Input positioner Provide means of positioning the input end of the specimen to the light source. Typically, this connection is with a fusion splice to a short (1 m) pigtail of type B1 .1 fibre. 3.4 Cladding mode stripper Use a device that extracts cladding modes. Under some circumstances, the fibre coating will perform this function.
3.5 Output positioner Provide a suitable means for aligning the fibre to the output optics. Typically, this connection is with a fusion splice to a pigtail of type B1 .1 fibre. 3.6 Output optics The output optics include a power meter and optical spectrum analyser. An oscilloscope may be required for Method B. See Annexes A and B for details. 3.7 Computer Use a computer to perform operations such as controlling the apparatus, taking intensity measurements and processing the data to obtain the final results. 4 Samples and specimens A specimen is a known length of single-mode optical fibre (see IEC 60793-2-50). The sample and pigtails should be fixed in position at a nominally constant temperature throughout the measurement. Standard ambient conditions (see IEC 60793-1 -1 should be employed, unless otherwise specified. End faces for the input and output ends of the test sample should be prepared as appropriate to obtain low loss fusion splices.