1. In an optical fiber , a dimensionless quantity, V , given by
where a is the core radius, 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. ( 188 )