= Step-index fiber normalized frequency
{title2=$V=2\pi a\sqrt{n_1^2-n_2^2}/\lambda_0$}
The dimensionless <waveguide> parameter $V$ combines radius, vacuum <wavelength> and the <numerical aperture> factor. In the weak-guidance scalar model the first additional spatial family appears at $V=j_{0,1}=2.404825\ldots$, the first positive zero of a <Bessel function of the first kind>. The fundamental family has no positive cutoff. Its two <polarizations> are not two distinct spatial profiles.
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