# Optical fiber V parameter and cutoff calculator

## About this calculator

This calculator computes the V parameter/number (also known as normalized frequency) of a step-index optical fiber. The V parameter is defined as

where is the wavelength of the signal, is the core radius of the fiber and is the numerical aperture of its core.

This calculator also computes the cutoff wavelength, which determines when the fiber becomes single-mode. At shorter wavelengths, at least two LP modes can propagate; at longer wavelengths the fiber guides only a single transverse mode. V parameter value at the cutoff wavelength is so the cutoff wavelength can be calculated from the V parameter as follows: