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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 :

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 :

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

References

• Federal Standard 1037C
• MIL-STD-188