normalized frequency (V)
1. In an optical fiber, a dimensionless quantity, V, given by 
where a is the core radius, 
is the wavelength in vacuum, n1 is the maximum refractive index of the core, and n2 is the refractive index of the homogeneous cladding.
Note 1: 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 
where V is the normalized frequency greater than 5 and g is the profile parameter.
Note 2: For a step index fiber, the mode volume is given by V 2/
2. For single-mode operation, V <
2. 40
5. Synonym V number.
2. The ratio between an actual frequency and a reference value.
3. The ratio between an actual frequency and its nominal value.