Bandwidth is the difference between the upper and lower frequencies in a continuous set of frequencies. It is typically measured in hertz.
In optics it is the width of an individual spectral line or the entire spectral range. A key characteristic of bandwidth is that any band of a given width can carry the same amount of information, regardless of where that band is located in the frequency spectrum.
Bandwidth is one of the key advantages of optical fiber sensors. The bandwidth of optical current sensors is limited intrinsically by material relaxation time and by transient time effect in the sensing coil.