In an
optical fiber, the normalized frequency, (also called the V number), is given by
where is the
core radius, is the
wavelength in vacuum, is the maximum
refractive index of the core, is the refractive index of the homogeneous cladding, and applying the usual definition of the
numerical aperture .
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
where is the profile parameter, and 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 . For single-mode operation, it is required that , the first root of the
Bessel function .
See also
*
Abbe number
References
*{{FS1037C MS188
Fiber optics