Normalized frequency (fiber optics) explained

In an optical fiber, the normalized frequency, V (also called the V number), is given by

V={2\pia\overλ}

	2
\sqrt{{n
	1}

	2}
{n
	2}

={2\pia\overλ}NA,

where a is the core radius, λ is the wavelength in vacuum, n₁ is the maximum refractive index of the core, n₂ is the refractive index of the homogeneous cladding, and applying the usual definition of the numerical aperture NA.

In multimode operation of an optical fiber having a power-law refractive index profile, the approximate number of bound modes (the mode volume), is given by

{V²\over2}\left({g\overg+2}\right) ,

where g is the profile parameter, and V is the normalized frequency, which must be greater than 5 for the approximation to be valid.

For a step-index fiber, the mode volume is given by V²/2. For single-mode operation, it is required that V < 2.4048, the first root of the Bessel function J₀.

Normalized frequency (fiber optics) explained

See also