It is a dimensionless parameter that determines the number of modes a fiber can support. It is given by:

$V= \frac{2π}λ a\sqrt{n_1^2-n_2^2} \\ \; \\ V = \frac{2πa}λ(N.A) \\ \; \\ V = \frac{2πan_1}λ(\sqrt{2∆}) \\ \; \\ $

where,

a = radius of the core

λ = wavelength of ray …