Equivalent-step-index-fibre determination from wavelength dependence of far field

We compare two simple techniques for determination of equivalent-step-index parameters in single-mode fibres from measurement of the wavelength dependence of the far-field intensity profile. In one case the data is fitted directly by the step-index formula to yield the core radius and the v-value. In the other, wavelength dependence of the half-intensity angle is fitted to an empirical expression recently reported to give the core radius and the cutoff wavelength.