1 Scope

This document applies to single-mode optical fibres. Its object is to document the methods for measuring the effective area (A_eff) of these fibres.

It defines three methods of measuring A_eff. Information common to all the methods is found in the body of this document. Information specific to each method is found in the annexes. The three methods are:

1. direct far-field (DFF);

2. variable aperture in the far-field (VAMFF);

3. near-field (NF).

The reference method, used to resolve disputes, is method A, direct far-field.

Effective area is an optical attribute that is specified for single-mode fibres and used in system designs probably affected by the non-linear refractive index coefficient, n₂. There is agreement in both national and international standards bodies concerning the definition used in this document. Methods A, B, and C have been recognised as providing equivalent results, provided that good engineering is used in implementation.

The direct far-field is the reference method because it is the most direct method and is named as the reference method for mode field diameter in IEC 60793‑1‑45 and ITU-T Recommendation G.650.1.

A mapping function is a formula by which the measured results of one attribute are used to predict the value of another attribute on a given fibre. For a given fibre type and design, the mode field diameter (MFD) (IEC 60793‑1‑45) can be used to predict the effective area with a mapping function. A mapping function is specific to a particular fibre type and design. Mapping functions are generated by doing an experiment in which a sample of fibre is chosen to represent the spectrum of values of MFD and in which the fibres in the sample are measured for both MFD and A_eff. Linear regression can be used to determine the fitting coefficient, k, as defined by the following: