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Group velocity dispersion is the phenomenon that the group velocity of light in a transparent medium depends on the optical frequency or wavelength. [quoted from wiki]. I have tried to do my research, but a lot of the answers are not helpful. There must be some physical mechanism behind this frequency dependence right? Or is this just a general term for describing all kinds of dispersion such as chromatic disperion, modal dispersion?

el psy Congroo
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    Possible duplicate of Why do prisms work (why is refraction frequency dependent)? – John Rennie Jul 05 '17 at 11:30
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    Also: Why does the refractive index depend on wavelength? – John Rennie Jul 05 '17 at 11:31
  • @JohnRennie I understand chromatic dispersion, I dun understand whether group velocity dispersion and chromatic dispersion share the same origin. it seems group velocity dispersion is a more general term. – el psy Congroo Jul 05 '17 at 11:45
  • My example would be from QM, where a Fourier Transformation allows us to express a particles position in terms of its momentum. A wave packet. Dispersion is in physical terms inevitable, as the momentum components are travelling at different speeds. I would consider this as an analogy to your question. –  Jul 05 '17 at 12:43
  • There is no such thing as "group velocity dispersion", but there is "phase velocity dispersion". So the question is do you understand why or how "phase velocity" could be frequency dependent, and that question as John Rennie pointed out is answered in https://physics.stackexchange.com/questions/65812/why-do-prisms-work-why-is-refraction-frequency-dependent. What happens after that is just summing up the Fourier components to describe what happens to a group of such wavelets. – hyportnex Jul 05 '17 at 13:15
  • @hyportnex There very much is such a thing as group velocity dispersion (GVD) in optics, so much so that it is effectively inescapable in a wide range of optical physics and engineering research fields. It is given as the derivative of the inverse of the group velocity with respect to angular frequency, but in my opinion it is easier to think of it as as the group delay dispersion per unit propagation distance. –  Jul 14 '17 at 10:56
  • @elpsyCongroo Chromatic dispersion (CD) and group velocity dispersion (GVD) are linked and share similar origins. CD is the wavelength-dependence of the phase and group velocity of light propagating in a material, and is defined using a Taylor expansion for wavenumber k as a function of frequency, with each term in the series containing a derivative of k with respect to angular frequency about the central angular frequency of the optical signal. Group delay dispersion is given by the third Taylor expansion term (second derivative of k, dk/dw), and GVD is group delay dispersion per unit length. –  Jul 14 '17 at 11:04

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