Group Delay Dispersion | <<< | >>> | Feedback |
Acronym: GDD
Definition: the frequency dependency of the group delay, or (quantitatively) the corresponding derivative with respect to angular frequency
The group delay dispersion (also sometimes called second-order dispersion) of an optical element is the derivative of the group delay with respect to the angular frequency, or the second derivative of the change in spectral phase:
It is usually specified in fs2 or ps2. Positive (negative) values correspond to normal (anomalous) chromatic dispersion. For example, the group delay dispersion of a 1-mm thick silica plate is +35 fs2 at 800 nm (normal dispersion) or −26 fs2 at 1500 nm (anomalous dispersion). Another example is given in Figure 1.
Figure 1: Wavelength-dependent group delay dispersion of a Gires–Tournois interferometer made of a 5-μm thick silica layer on a high reflector.
Note that the group delay dispersion (GDD) always refers to some optical element or to some given length of a medium (e.g. an optical fiber). The GDD per unit length (in units of s2/m) is the group velocity dispersion (GVD).
See also: dispersion, group velocity dispersion, group delay
