Editing Spectral width (section)

{{Short description|Measurement in communication theory}}
{{Refimprove|date=January 2009}}

In [[telecommunications]], '''spectral width''' is the width of a [[spectral band]], i.e., the range of wavelengths or frequencies over which the magnitude of all [[spectral component]]s is significant, i.e., equal to or greater than a specified fraction of the largest magnitude.

In [[fiber-optic communication]] applications, the usual method of specifying spectral width is the ''[[full width at half maximum]]'' (FWHM). This is the same convention used in [[Bandwidth (signal processing)|bandwidth]], defined as the frequency range where power drops by less than half (at most &minus;3 [[Decibel|dB]]).

The FWHM method may be difficult to apply when the spectrum has a complex shape. Another method of specifying spectral width is a special case of [[Root mean square|root-mean-square deviation]] where the independent variable is wavelength, λ, and ''f'' (λ) is a suitable radiometric quantity.

The ''relative spectral width'', Δλ/λ, is frequently used where Δλ is obtained according to note 1, and λ is the center wavelength.