Normalized frequency

1. In an optical fiber, a dimensionless quantity, V , given by where a is the core radius, λ is the wavelength in vacuum, n ₁ is the maximum refractive index of the core, and n ₂ 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 < 2.405. 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.

Source: from Federal Standard 1037C and from MIL-STD-188