The nonlinear coefficient (nLc) is the ratio of the Kerr nonlinear refractive index, n2, and the effective area, Aeff (see FOTP-132), as:
The nonlinear coefficient is related to the following nonlinear optical distortion effects as a combined parameter:
Self-phase modulation (SPM)
Cross-phase modulation (XPM)
Four-wave mixing (FWM)
Other fiber attributes, such as chromatic 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 fiber, measurement of this power (absolute), and measurement of the output spectrum – which is modified by nonlinear effects. Both methods use calculations that combine these measured results with those derived from other measurements such as attenuation (FOTP-61 or FOTP-78) and chromatic dispersion (FOTP- 168, FOTP-169, or FOTP-175). Both methods have limitations on the length of fiber that can be measured – in a relationship with the chromatic dispersion at the wavelength being measured.
