Normalized frequency

In telecommunication, the term normalized frequency ( V ) has several meanings; it may refer to the ratio between an actual frequency and a reference value, or to the ratio between an actual frequency and its nominal value.

In an optical fiber, normalized frequency is a dimensionless quantity, V , given by the following equation, where a is the core radius, λ is the wavelength in vacuum, n₁ is the maximum refractive index of the core, and n₂ is the refractive index of the homogeneous cladding:

$V={2\pi a \over \lambda }{\sqrt {{n_{1}}^{2}-{n_{2}}^{2}}}$

In multimode operation of an optical fiber having a power-law refractive index profile, the approximate number of bound modes (i.e. the mode volume), is given by the following equation, where V is the normalized frequency greater than 5 and g is the profile parameter:

${V^{2} \over 2}\left({g \over g+2}\right)$

For a step index fiber, the mode volume is given by V²/2. For single-mode operation, V < 2.405. Synonym: V number.

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